multiband engineering guideline

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Multiband Engineering Guideline v2.5 M Motorola Confidential Proprietary This document and the information contained in it is CONFIDENTIAL INFORMATION of Motorola, and shall not be Multiband Engineering Guideline Author: Tubagus Rizal ([email protected] ) Systems Support – Network Quality of Service Motorola GSM System Division - GTSS Date: 29th December 2003 Document ID: TR-1203-037-01 Document version: 2.5 Status: Released Intranet Download: http://compass.mot.com/go/dualband Abstract: This is a revised version describing basic guidelines to deploy Motorola multiband solution, which allows the operator to expand their network coverage and capacity by using more than one frequency band. This document covers planning, deployment, optimisation and configuration issues as well as recommending implementation best practices to meet network operator requirements. used, published, disclosed, or disseminated outside Motorola in whole or in part without Motorola´s consent. This document contains trade secrets of Motorola. Reverse engineering of any or all of the information in this document is prohibited. The copyright notice does not imply publication of the document

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Page 1: Multiband Engineering Guideline

Multiband Engineering Guideline v2.5

M

Motorola Confidential Proprietary

This document and the information contained in it is CONFIDENTIAL INFORMATION of Motorola, and shall not be

Multiband Engineering Guideline

Author: Tubagus Rizal ([email protected]) Systems Support – Network Quality of Service Motorola GSM System Division - GTSS Date: 29th December 2003 Document ID: TR-1203-037-01 Document version: 2.5 Status: Released Intranet Download: http://compass.mot.com/go/dualband

Abstract:

This is a revised version describing basic guidelines to deploy Motorola multiband solution, which allows the operator to expand their network coverage and capacity by using more than one frequency band. This document covers

planning, deployment, optimisation and configuration issues as well as recommending implementation best practices to meet network operator

requirements.

used, published, disclosed, or disseminated outside Motorola in whole or in part without Motorola´s consent. This document contains trade secrets of Motorola. Reverse engineering of any or all of the information in this document is

prohibited. The copyright notice does not imply publication of the document

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M

SIGN-OFF FORM

Author T Rizal Signature Digitally signed Date

Reviewed G Simpson Signature Date

Revised Signature Date

HISTORY OF REVISIONS

Revision Date Author Reviewed by Changes Description 0.1 1 Feb 99 T Rizal Draft

0.2 15 Feb 99 T Rizal P Nowak Internal review

1.1 23 Apr 99 T Rizal P Nowak Released

1.2 29 Jun 99 T Rizal, G Nagy

P Nowak Revised info on coincident handover and adding comparison graph of using MHA

1.3 12 Nov 99 T Rizal P Nowak More info on C1&C2 parameter, HorizonMacro description specifically on dualband, settings of coincident handover parameter.

2.0 07Jan 03 T Rizal K Wagentristl M Tomison

Fully revised to include many new BSS features. Available for internal review

2.1 31 Jan 03 T Rizal Updated per review. Released version

2.5 Jan 04 T Rizal Single BCCH enhancements

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M TABLE OF CONTENT

1. Introduction ............................................................................................... 6 1.1. Document Overview........................................................................................ 6 1.2. Quick Guide to Content................................................................................... 7

2. Basic Multiband Network.......................................................................... 8 2.1. The Needs for Multiband Network .................................................................. 8 2.2. General ETSI Specification of a Multiband Network ....................................... 9

2.2.1. Frequency Band.................................................................................. 9 2.2.1.1. GSM900..................................................................................... 10 2.2.1.2. GSM1800................................................................................... 10 2.2.1.3. EGSM ........................................................................................ 10

2.2.2. MSC Requirement............................................................................. 10 2.2.3. Multiband Mobile ............................................................................... 11 2.2.4. Idle Mode .......................................................................................... 12 2.2.5. Call Establishment ............................................................................ 14 2.2.6. Dedicated Mode ................................................................................ 14 2.2.7. Multiband Handover .......................................................................... 15 2.2.8. Backward Compatibility ..................................................................... 15

2.3. Motorola Multiband Network Solution ........................................................... 15

3. Planning and Design............................................................................... 17 3.1. System Design.............................................................................................. 18 3.2. Radio Wave Propagation .............................................................................. 20 3.3. Site Configuration ......................................................................................... 23

3.3.1. Mast Head Amplifier .......................................................................... 23 3.3.2. Antenna............................................................................................. 25 3.3.3. Antenna Feeder ................................................................................ 28 3.3.4. Horizon Platform ............................................................................... 28 3.3.5. Horizon 2............................................. Error! Bookmark not defined.

4. Multiband Mobile’s Idle Mode Behaviour .............................................. 32 4.1. Controlling the behaviour .............................................................................. 32 4.2. C1 and C2 parameters.................................................................................. 32 4.3. Example of implementation........................................................................... 34 4.4. Idle Mode Neighbour List .............................................................................. 35 4.5. Summary of Database Parameters............................................................... 36

5. Advanced Load Management................................................................. 37 5.1. Network and BSC level settings.................................................................... 37

5.1.1. MSC Settings .................................................................................... 37 5.1.2. Feature license verification ............................................................... 38 5.1.3. Handling mobile’s classmark information.......................................... 38 5.1.4. Allowed frequency band.................................................................... 39

5.2. Cell level parameters settings....................................................................... 39 5.2.1. Frequency type in a cell .................................................................... 39 5.2.2. Handover between frequency band .................................................. 39 5.2.3. Frequency band reported in the measurement report....................... 40 5.2.4. Frequency band preference .............................................................. 41 5.2.5. Band preference mode...................................................................... 42

5.2.5.1. Band_preference_mode=0 ........................................................ 42 5.2.5.2. Band_preference_mode=1 ........................................................ 42

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M 5.2.5.3. Band_preference_mode=2 ........................................................ 42 5.2.5.4. Band_preference_mode=3 ........................................................ 43 5.2.5.5. Band_preference_mode=4 ........................................................ 43 5.2.5.6. Band_preference_mode=5 ........................................................ 43 5.2.5.7. Band_preference_mode=6 ........................................................ 43

5.2.6. Multiband related statistics................................................................ 44 5.2.6.1. INTERBAND_ACTIVITY ............................................................ 44 5.2.6.2. MS_TCH_USAGE_BY_TYPE ................................................... 44 5.2.6.3. MS_ACCESS_BY_TYPE........................................................... 45

5.3. Advanced load management in the network................................................. 45 5.3.1.1. Microcell handover..................................................................... 46 5.3.1.2. Example of implementation........................................................ 47

5.4. Summary of BSS database parameters........................................................ 50

6. Multiband Feature Enhancement........................................................... 51 6.1. Support for BCCH and SDCCH in EGSM frequency band ........................... 51 6.2. Advanced Load Management with EGSM Carriers ...................................... 51 6.3. Multiband congestion relief enhancement .................................................... 52

7. Single BCCH (Dualband Cell) ................................................................. 53 7.1. Benefits of single BCCH feature ................................................................... 54 7.2. Dualband cell requirements .......................................................................... 56 7.3. Zone definition .............................................................................................. 56 7.4. Dualband Offset ............................................................................................ 57 7.5. Criteria for inner-zone usage ........................................................................ 58 7.6. Advanced load management in dualband cell .............................................. 61

7.6.1. Band_preference_mode=0................................................................ 61 7.6.2. Band_preference_mode=1................................................................ 61 7.6.3. Band_preference_mode=2................................................................ 62 7.6.4. Band_preference_mode=3................................................................ 62 7.6.5. Band_preference_mode=4................................................................ 62 7.6.6. Band_preference_mode=5................................................................ 62 7.6.7. Band_preference_mode=6................................................................ 63

7.7. Optional criteria for entering inner-zone........................................................ 63 7.8. TCH assignment delay.................................................................................. 63 7.9. Power budget calculation.............................................................................. 64 7.10. Single BCCH related statistics ...................................................................... 69

7.10.1. TCH_USAGE_INNER _ZONE .......................................................... 69 7.10.2. TCH_CONG_INNER_ZONE ............................................................. 69 7.10.3. ZONE_CHANGE_ATMPT................................................................. 69 7.10.4. ZONE_CHANGE_SUC ..................................................................... 69 7.10.5. ALLOC_TCH_INNER_Z.................................................................... 70 7.10.6. ALLOC_TCH_FAIL_INNER_Z .......................................................... 70 7.10.7. TCH_Q_REMOVED.......................................................................... 70

7.11. Impact of Single BCCH to Key Performance Metric...................................... 71 7.11.1. Cell level drop call rate...................................................................... 71 7.11.2. TCH RF Loss Rate............................................................................ 72 7.11.3. TCH Blocking Rate............................................................................ 73

7.11.3.1. TCH Blocking Rate Combined ................................................... 73 7.11.3.2. TCH Blocking Rate for inner-zone only...................................... 73 7.11.3.3. TCH Blocking Rate for outer-zone only ..................................... 73

7.12. Single BCCH interaction with other feature and limitation ............................ 74 7.13. Dualband cell conversion procedure............................................................. 76 7.14. Example of implementation........................................................................... 77

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M 7.15. Summary BSS database parameter ............................................................. 79

8. Coincident Multiband Handover ............................................................ 81 8.1. Definition of coincident cells and handover execution .................................. 81

8.1.1. Better cell detection........................................................................... 83 8.1.2. Coincident cell redirection ................................................................. 84

8.2. Coincident multiband handover settings ....................................................... 84 8.3. Example of implementation........................................................................... 85

8.3.1. Scenario 1 ......................................................................................... 86 8.3.2. Scenario 2 ......................................................................................... 88

8.4. Summary of BSS database parameters........................................................ 90

9. Optimisation in Multiband Network ....................................................... 91 9.1. Optimising Advanced Load Management ..................................................... 91 9.2. Optimising Single BCCH............................................................................... 93 9.3. Optimising coincident multiband handover ................................................... 98

10. Interaction with Other Features ........................................................... 101 10.1. Frequency hopping ..................................................................................... 101 10.2. General Packet Radio System (GPRS) ...................................................... 104 10.3. Microcellular................................................................................................ 104

11. Multivendor Implementation ................................................................ 105 11.1. Considerations ............................................................................................ 105 11.2. Idle mode .................................................................................................... 107 11.3. Dedicated Mode.......................................................................................... 108

Appendix A. .................................................................................................... 111

References ..................................................................................................... 112

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M 1. Introduction

Version 2.0 of this document is a fully revised from the previous version initially released on 1999. Motorola GSM product portfolio evolves together with more advance requirements, which means many new hardware and software features are available in the recent GSM software releases. These enhancements are improving Motorola Multiband Solution directly or indirectly. Along with this progress, the intention of publishing version 2 of this document is to record the recent updates and records as much as possible the knowledge based on latest field experiences. This document will cover the Motorola multiband solution up to GSR6.

Major content improvement in Version 3 of this document focused on Single BCCH feature. This version is documenting hardware, software additions, optimisation techniques, and interaction with other BSS features since Single BCCH initially introduced in GSR5.

For latest update and revision, this document also available only on Motorola intranet at http://compass.mot.com/go/dualband. It is possible to enable Compass auto-notify to receive latest news by email automatically when the new revision of this document is available. Refer to Compass help page for enabling auto-notify feature.

1.1. Document Overview The document’s objective is to provide Motorola GSM engineering community and customer to perform planning, deployment, and optimisation of Motorola dualband solution. It outlines the very basic set of engineering guidelines required to design a high quality multiband network. Reader with basic knowledge and experience in GSM cellular engineering may find this document useful to provide introduction to Motorola dualband solution.

In most cases, the document will assume that this guideline will provide assistance in upgrading an existing singleband network to a multiband network or assisting engineering activities on a multiband network. However, it is also applicable to assist in designing brand new multiband network.

This document will cover major aspects of multiband engineering. The topic covered in this document varies according activities in the GSM network life cycle, which ranging from planning consideration, site configuration, radio frequency planning, controlling traffic behaviour either in idle or dedicated mode, optimisation and multivendor environment. Major aspects of radio frequency planning consideration discussed in this document are both 900MHz and as well as in 1800MHz frequency band and the propagation differences between the two frequency bands.

Some examples of implementations are also included in this document, but these examples are not meant as a fixed rule, as each cellular network have specific characteristics, which differ from one to another. Therefore, the recommendation for engineers and readers to identify and use the multiband network parameter based on proper optimisation process.

Although the document covers many aspects of multiband engineering, in general the focus is only on the Base Station Subsystem part using Motorola

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M software and hardware features. Other subsystem, such as MSC, also discussed only when it is required and plays major impact to the successful implementation.

Some of the chapters in this document are relatively independent from one to each other, which is useful for referring to specific details in multiband feature. The subsection below provides an outlook of this document and purpose of each chapter.

1.2. Quick Guide to Content Chapter 1. Introduction.

Chapter 2. Basic Multiband Network. This chapter describes the generic multiband network as defined by ETSI (or 3GPP) and subsequently enhanced by Motorola.

Chapter 3. Planning and Design. This chapter describes many aspects of various field implementations with regard to designing and planning the multiband network.

Chapter 4. Multiband Mobile’s Idle Mode Behaviour. This chapter describes the idle mode behaviour of a multiband mobile and alternatives to control its behaviour.

Chapter 5. Advanced Load Management. This chapter describes Motorola solution to manage traffic between bands.

Chapter 6. Multiband Feature Enhancement. This chapter talks about further enhancement of multiband features.

Chapter 7. Single BCCH (Dualband Cell). This section describes in detail about GSR5 single BCCH feature

Chapter 8. Coincident Multiband Handover. Talks about the implementation of coincident multiband feature

Chapter 9. Optimisation in Multiband Network. This chapter talks about recommended optimisation procedure in multiband network.

Chapter 10. Dualband Interaction with Other Features. This chapter describes how the multiband feature working together with another feature

Chapter 11. Multivendor Implementation. This is a part of Motorola success story in providing solution, which benefit the customer who partner with multiple equipment manufacturers.

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M 2. Basic Multiband Network

Global System for Mobile communication (GSM) today is a global standard for digital cellular communication available worldwide. GSM is the name of a common European mobile telephone standard that would formulate specifications for a pan-European mobile cellular radio system operating at 900 MHz. GSM1800 frequency band introduced later as part of the GSM standard. The GSM Association, the representative body for the global wireless industry, from its recent claim in September 2002 confirmed that GSM global growth was continuing and that some 95 per cent of world’s countries have now adopted GSM mobile technology and providing wireless services to more than 747 millions customers.

From today’s GSM networks, many of them already have dualband solution implemented in their network, which is designed based on ETSI specification and further enhanced independently by network manufacturer. ETSI (the European Telecommunications Standards Institute) is a not for profit organization whose mission is to produce the telecommunications standards that will be used for decades to come, throughout Europe and beyond.

This section describes the basic concept of a multiband network, where requirements and technical realisation of a multiband network defined by ETSI. The document will assume that multiband system is commonly GSM900 combined with GSM1800, as this is the most popular combination of frequency band enabled in a multiband network. Other possible frequency band combination will also follow ETSI standard, which described later on the document.

2.1. The Needs for Multiband Network Multiband solution allows a single network operator with licences for both GSM900 and GSM1800 to support the use of multiband mobiles over both bands. By supporting transparent handover between GSM900 and GSM1800, multiband enables major benefits that can increase network capacity and flexibility.

For example, the GSM1800 band offers a single-band network operator the potential of three times the spectrum of the original GSM900 band, providing a capacity solution for a mature GSM900 network. With the availability of Multiband mobiles in 1997 and the regulatory bodies starting to allocate GSM1800 frequency band, the way is clear for network operators to plan and implement a major increase in network capacity, coverage or flexibility.

Many GSM network operators have now allocated their GSM900 frequencies as well as GSM1800. While other are still active in the process of licensing GSM1800 frequencies for use in Personal Communication Systems. GSM1800 frequency band consists of 75MHz of spectrum. This spectrum is available to both new operators and existing GSM900 operators. The need for Multiband networks is primarily to support the existing GSM900 operators who also have access to GSM1800 frequency band.

There are maybe a handful of GSM1800 operators who may be getting GSM900 spectrum or a portion of the EGSM spectrum of additional spectrum adjacent to

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M the original GSM900 frequencies. They also will benefit from a multiband network solution.

There are several ways that these additional channels can be used, often depend on both the regulatory and competitive environment within the country. For each of these scenarios, the network operator must implement a different type of traffic management model. This is to ensure the maximum benefit from the multiband implementation.

The additional spectrum available in the GSM1800 frequency band offers an existing operator the potential to significantly increase the capacity of their existing network. In many countries, mature GSM900 network operators have experiencing huge growth in the level of their macrocellular capacity by having multiband solution in place.

A multiband network (together with the availability of multiband mobile) offers the potential of providing a “capacity overlay” to an existing network using the same PLMN. This would allow traffic on the existing GSM900 network to transfer transparently to the GSM1800 frequency band. The network operator has to determine how the additional frequency band is to be deployed. The operator may choose to provide coverage for hotspots, or ubiquitous coverage in a limited area.

A network operator may decide to obtain a license for a portion of the GSM 1800 band in order to provide a completely separate network. Some country regulators are offering larger allocation of frequencies to network operators who are prepared to establish a differentiated second network.

The majority of revenue from a current network is still due to circuit switch calls. Now that SMS services and data / Fax capability is available on most GSM networks, the percentage of revenue due to non-speech calls is also increasing tremendously. The availability of data services provided by conventional circuit switch or General Packet Radio Services (GPRS) increase the diversity of overall wireless services offered to customer, which would require capacity in term of frequency band.

The multiband network on the later stage is available as a mean of providing contiguous coverage to all subscribers whilst offering a differentiated service to all subscribers in all geographic areas.

2.2. General ETSI Specification of a Multiband Network ETSI produced GSM 03.26 specifications, Multiband Operation of GSM/DCS 1800 by a Single Operator, which describes the functionality of a multiband network operated by a single operator and the multiband mobile stations. Motorola has designed a set of features, which comply with the GSM 03.26 specifications and adds the capability for the operator to have more flexibility controlling traffic behaviour on each frequency band.

2.2.1. Frequency Band For a multiband operator, the network that operate in GSM900 and GSM1800 frequency band, considered as one network with a single PLMN. Therefore, call initiation, dualband handover and other transaction between two frequency bands occurred in one PLMN.

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M It is common practice to nominate of the frequency band supported as the primary frequency band. There is no limitation introduced by ETSI in selecting the primary frequency band. Network operator requirements are the main consideration when selecting primary frequency band. For example, a singleband operator who already have GSM900 license may consider GSM900 as their primary band and GSM1800 as the secondary band to maintain the backward capability with earlier mobile generation. GSM1800 frequency band will act as capacity extension when there is a requirement to do so.

Absolute Radio Frequency Channel Number (ARFCN) identifies each pair of uplink and downlink physical frequency allocation. Following are the ARFCN allocation numbering for each frequency band and formula to determine the physical frequency.

2.2.1.1. GSM900 GSM900 provides 25MHz of frequency bandwidth and numbered with ARFCN 1 to 124:

• Uplink: 890 - 915 MHz

• Downlink: 935 – 960 MHz

ARFCN to frequency band function

• Freq uplink = 890 MHz + (ARFCN x 0.2) MHz

• Freq downlink = Freq uplink + 45 MHz

2.2.1.2. GSM1800 GSM1800 provides 75MHz of frequency bandwidth and numbered with ARFCN 512 to 885:

• Uplink: 1710 – 1785 MHz

• Downlink: 1805 – 1880 MHz

ARFCN to frequency band function

• Freq uplink = 1710.2 MHz + (ARFCN – 512) x 0,2 MHz

• Freq downlink = Freq uplink + 95 MHz

2.2.1.3. EGSM EGSM is an extension to GSM900 and provides 10MHz frequency bandwidth numbered with ARFCN 975 to 1023 and 0:

• Uplink: 880 - 915 MHz

• Downlink: 925 - 960 MHz

ARFCN to frequency band function

• Freq uplink = 890 MHz + (ARFCN - 1024) x 0.2 MHz

• Freq downlink = Freq uplink + 45 MHz

2.2.2. MSC Requirement As the MSC to BSS connection is standardised by ETSI, this means that BSS equipment from different manufacturers can connect to any MSC manufacturer.

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M This would also mean open up the possibility that each frequency band provided from different BSS manufacturer. For a multivendor environment in a multiband solution, more detailed description is available in chapter 11.

In order to have a working multiband capability in the network, some MSC feature requirements should not be restricted or disabled. The main feature that MSC should have is the capability to handle Classmark 3 (CM3) information element. CM3 sent by multiband mobile to MSC contains info of multiband capabilities and the mobile power classes in GSM900/GSM1800 frequency band. The CM3 info then is stored in the MSC for the duration of the call. Each MSC manufacturer will identify such feature with different names and different configuration procedure.

In case the mobile is required to perform an inter BSS multiband handover, the CM3 info must be transmitted to the target BSS with the help of MSC, informing the new BSS about the multiband capabilities of the mobile.

If such capability does not exist in the MSC, then in most cases the mobile is able to perform dualband handover, but after the dualband handover performed the mobile will be stuck in current frequency band used. This is because the MSC does not forward the CM3 information element to target BSC and the new BSC will assume that the mobile is a single band mobile.

2.2.3. Multiband Mobile

A mobile may operate in one of the following ways in a Multiband network:

Power Class

GSM900 Max. Power Output

GSM1800 Max. Power Output

Tolerance (dB)

Watt dBm Watt dBm Normal Extreme

1 1 30 2 ± 5.2 ± 2 8 39 0.25 24 2 ± 5.2 ± 3 5 37 4 36 2 ± 5.2 ± 4 2 33 2 ± 5.2 ± 5 0.8 29 2 ± 5.2 ±

Table 2-1. Power classmark supported by multiband mobile. Note the latest addition in the list, which is power class 3 in GSM1800

• The mobile supports only one band or the mobile supports more than one band, but can only function in one band at a time, which is known as "knife switch" mobiles. Knife switch mobiles are not on production anymore.

• Today, the multiband mobiles manufactured fall into the last category described as follows: mobile supports two frequency bands and can function seamlessly within each supported band at a time. This referred to as "band aware" mobiles. This document will assume that the population of the mobile falls into band aware category.

ETSI has defines the mobile classmark that needs to be supported regardless the mobile multiband capability, as presented in Table 2-1. The BSS is expecting the mobile to transmit this mobile classmark information very early in the location update process to advise the network that the mobile is able to utilise more than one band. Recent revision to the table above by ETSI is to include the new

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M GSM1800 mobile power class 3. A band aware mobile is able to listen on both frequency bands and to report to the BSS the signal strength received on either or both bands during dedicated mode. The BSS then can use this information together with the classmark information to select an appropriate handover candidate cell for the mobile.

The multiband mobile has the functionality to perform handover, channel assignment, cell selection and cell re-selection between all its frequency bands of operation within one PLMN, i.e. when one PLMN code is used in all frequency bands. In addition, it has the functionality to make PLMN selection, in manual or automatic mode, in all its supported frequency bands of operation. The multiband mobiles shall meet all requirements specified for each individual band supported for example the transmitted power allowed. Backwards compatibility by the multiband mobiles also an important factor for the mobile to support, which will be able to, functionally, work as single band mobiles in a single band network.

Figure 2-1. Some of recent Motorola mobiles with multiband capability as a standard feature

In the early days of dualband solution was introduced, a major consideration for any network operator considering the implementation of a multiband system is the availability of multiband mobile and the strategy for ensuring that a significant percentage of the subscriber traffic can easily and quickly be migrated to the new frequency band.

Today, all newly mobiles released into the market by various manufacturers are dualband mobiles. Motorola also offer triband mobile, which support up to three frequency bands.

2.2.4. Idle Mode The basic mobile operation in idle mode will remain the same in idle mode regardless on which frequency band it remains, but there are considerations relating to the frequency band selection on how the mobile should perform in idle state.

Each frequency band may have its own BCCH transmitted. In such case, GSM1800 cell have its own BCCH as well as GSM900. There is also single BCCH implementation where the BCCH provisioned only in one of the frequency band. Further information about implementation of Single BCCH is available in Chapter 7.

There is no modification in initial selection of a PLMN and first “camp-on” to the multiband network by the mobile with the introduction of additional frequency band in the network. The mobile will follow the normal cell re-selection procedures with the addition that they monitor all channels within the neighbour cell list, which are within the mobile’s frequency bands of operation. This would

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M allows the multiband mobile to scan all available frequencies in the area not only those in the frequency band the mobile is currently camped on.

Although the ETSI specifications do not specifically provide a means of directing a mobile to a particular band, it is possible to bias the idle mode behaviour of a dualband mobile, which predominantly by adjusting C1, C2, and related parameters. Another possibility is possible to have a separate list of neighbour cells for mobile in idle mode then the dedicated mode. Further discussion on idle mode behaviour can be found in chapter 4.

The multiband network broadcasts neighbour cell lists, which may contain a mixture of ARFCN from different frequency bands done by broadcasting SYSTEM INFORMATION TYPE 2 or SYSTEM INFORMATION TYPE 2TER in the BCCH. In idle mode, the mobile will receive SYSTEM INFORMATION TYPE 3, which contains ‘2ter’ indicator bit enabled (equal to 1) in “SI 3 Rest Octet”. This indicates that Layer 3 SYSTEM INFORMATION TYPE 2TER is broadcasted as well in BCCH and multiband mobile should decode the SYSTEM INFORMATION TYPE 2TER to decode the neighbour cells list.

The practical implementation of SYSTEM INFORMATION TYPE 2TER is to broadcast neighbour list on the other frequency band. Figure 2-2 displays the relation of each system information message and the type of info carried. A comprehensive description of System Information message content is available in GSM 04.08 ETSI Specification.

BCCH on GSM900

BCCH on GSM1800

System Information 2 GSM900 neighbours

GSM1800 neighbours

System Information 2ter GSM1800 neighbours

GSM900 neighbours

Figure 2-2. Layer 3 message types and the neighbour information included when transmitted in different band

Another system information used to transmit neighbour information in idle mode is SYSTEM INFORMATION TYPE 2BIS. This is an extension to System Information Type 2, but mainly will benefit most for GSM1800 operator allocated with huge frequency allocation.

The following description on SYSTEM INFORMATION TYPE 2 will help to understand the role of SYSTEM INFORMATION TYPE 2BIS. SYSTEM INFORMATION TYPE 2 in maximum can only able to carry 124 neighbour frequency definitions. This is more than enough for GSM900 network operator to use it without the help of SYSTEM INFORMATION TYPE 2TER.

For GSM1800 network operator, as the GSM1800 frequency allocation relatively bigger than GSM900, there is a theoretical possibility, that one GSM1800 network operator has more than 124 frequencies. To cope with such theoretical situation, SYSTEM INFORMATION TYPE 2 will carry the first 124 neighbour frequency definitions. The next group of neighbour frequencies carried by SYSTEM INFORMATION TYPE 2TER.

Another task performed during idle mode in a multiband network is location update procedure. This procedure should not be different compared with the location update procedure done in a single band network.

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M 2.2.5. Call Establishment

In order to inform the network of the frequency capability and power classmark associated in the multiband mobile, the mobile need to send a classmark change message with CM3 information as soon as possible. This procedure is can be done by enabling ECSC bit in Layer 3 SYSTEM INFORMATION TYPE 3 broadcasted in the BCCH. ECSC (Early Classmark Sending Control) bit placed in “SI 3 Rest Octet”. It is also possible to disables or delays the mobile to use ECSC. More discussion on ECSC setting is available in Advanced Load Management chapter.

In a call establishment process, the multiband mobile will send Layer 3 CM SERVICE REQUEST message to the network. The multiband information included in this message is CM3 bit indicator (set to enabled), which informs the network that Classmark 3 is used. Subsequently, the mobile sending CM3 info in CLASSMARK CHANGE message and received by BSS. Based on ECSC setting, the BSS can forward the CM3 info as soon as possible or delay it to MSC. As soon as the BSS acknowledge the mobile multiband capability, the serving cell starts to send SYSTEM INFORMATION 5TER in dedicated mode.

Figure 2-3. Layer 3 messaging example of mobile originated call in a multiband network

The same like SYSTEM INFORMATION 2TER, SYSTEM INFORMATION 5TER carries the neighbour information in the opposite band. When the mobile is in dedicated mode GSM900, then SYSTEM INFORMATION 5TER will contain neighbour information of GSM1800 and vice versa. Then the remaining procedure of call establishment for multiband mobile is the same like the normal call establishment.

Figure 2-3 gives an example of call establishment from the mobile side. Note that SYSTEM INFORMATION 5TER appeared after the network received the CM3 info via CLASSMARK CHANGE message.

2.2.6. Dedicated Mode In dedicated mode, the mobile will send Layer 3 MEASUREMENT REPORT to the network of the six strongest and identified neighbours. Those six neighbours may come from different frequency band. However there is a possibility that all those six strongest neighbours are in the same frequency band. To ensure that a mix

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M frequency band is reported to the BSS, it is possible to specify the minimum number of neighbour on each frequency band as indicated by multiband reporting parameter. Further discussion on multiband reporting configuration and implementation is available in chapter 5.

The neighbour list send to the mobile in dedicated mode is by using SYSTEM INFORMATION TYPE 5 or SYSTEM INFORMATION TYPE 5TER. Message format of SYSTEM INFORMATION TYPE 5 or SYSTEM INFORMATION TYPE 5TER is identical with SYSTEM INFORMATION 2 or SYSTEM INFORMATION TYPE 2TER subsequently. SYSTEM INFORMATION TYPE 5BIS also can be used to transport the additional neighbour list, which also identical with SYSTEM INFORMATION TYPE 2BIS.

2.2.7. Multiband Handover When a handover is required, to assign a TCH on the other frequency band, Layer 3 HANDOVER COMMAND message is used. The general procedure to do a multiband handover is the same like normal handover.

In case of inter-BSS handover, MSC is responsible to forward CM3 information to target BSS. This mechanism is also applicable to inter MSC handover where the source MSC should inform target MSC on the CM3 information therefore it is essential that both MSC are able to handle CM3 messages.

Figure 2-4. An example of Layer 3 messaging when multiband mobile performed multiband handover, which has no difference with the handover within the same frequency

2.2.8. Backward Compatibility A multiband network will normally support the singleband mobile in each band of operation. In some cases, it is not possible when using single BCCH feature (single BCCH in the primary band for all frequency of operation). This situation will only support singleband mobile, which is in the primary band.

For Phase 1 GSM mobile in a multiband network, the mobile will ignore SYSTEM INFORMATION 2TER and SYSTEM INFORMATION 5TER. For singleband Phase2 mobile, it will only ignore the channel number outside its supported frequency band. This specification specified to make sure that the network would work unaffected while the multiband feature introduced in the network, and the phase1 and phase2 mobile can work normally in the multiband network.

2.3. Motorola Multiband Network Solution Motorola has designed a complete multiband solution. This solution is compliance with ETSI specifications at the same time provides control, flexibility, and easier operability for the operator. The solution offering is ranging from the multiband mobile, BSS hardware, and sophisticated BSS software that allow the

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M operator to implement a high quality multiband network and able to control the traffic behaviour on multiple frequency bands.

Motorola multiband software designed to adapt the number of multiband capable traffic in the network. For example, a GSM900 operator planning to extend the capacity using GSM1800 band, on the initial deployment, the operator may need to encourage all multiband capable traffic to the new GSM1800 band and keep it as long as possible. As it progresses to a mature network, where multiband capable traffic is increasing, the operator may want to have a less aggressive setting in moving the traffic to the GSM1800 band. By implementing the Advanced Load Management (ALM), such scenario described above is achievable.

The ALM consists of three key elements, which are:

1. Band Preference, where the network is specified which one is the preferred band for a multiband handover,

2. Band Preference Mode, which controls how the multiband handover to the preferred band will take place.

3. Handover on Congestion, where a multiband handover to preferred band triggered when the serving cell is congested.

On the BSS hardware side, Motorola developed a flexible solution for the operator to deploy the multiband network. The infrastructure sharing between GSM900 and GSM1800 provides an efficient solution. A more detailed discussion about infrastructure sharing is available in the following section.

Further enhancement to the Motorola Multiband Solution is by introducing coincident multiband handover and single BCCH.

Motorola has gained many experiences on deploying the network in a multivendor environment. Such experiences enable Motorola multiband solution is adaptable for implementation with other vendor infrastructure equipment.

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M 3. Planning and Design

Planning andImplementation

Coverage planningand site selectionPropagationmeasurement andcoverage predictionand optimisationTraffic analysis,allowed blocking andBSS feature designInterference analysisBSS Featureparameter planningHandover strategyOther radio resourcemanagementparameter planning

2Definitions

NetworkconfigurationdimensioningRequirements andstrategy forcoverage, qualityand capacity

1 Operation andMaintenance

Network optimisationStatisticalperformance analysisQuality, efficiency, andavailability

3

This section discusses some major aspects of practical consideration to introduce the multiband feature. This is under assumption that the existing network will implement multiband feature, although it is also applicable to plan and design dualband network implementation from day one.

Figure 3-1. Radio network planning cycle

Figure 3-1 illustrates the basic planning cycle for any cellular network, which categorised into three main basic steps. The first step defines the initial dimensioning and design goals, which is to count the number of network entities required based on the design goals. This will provides a quick evaluation and estimation of the network entity requirements and all cost associated to it. The most common method to perform the basic dimensioning is by defining radio link budget, which outlined in more detail later on this section. In many 2G planning activity the common metric to use to represent network capacity is Erlang/km2. In addition to that, the amount of traffic will be produced in the network is determined by the number of mobile population, its distribution, and the amount of traffic generated for each mobile measured by Erlang. In planning the dualband network, the amount of mobile population in the network with multiband capable will be the main factor influencing the traffic generated in the supported frequency band.

The second step is the main activity where it is repeatable once the planned network is operating and has received feedback from the O&M activity. This second step relies heavily on computer assisted RF planning tool such as Netplan (intranet: http://www.sesd.cig.mot.com/). Such tool will provide all procedures required to elaborate in more details the initial system design and translate it into propagation model. Initially, identification of the most appropriate

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initial system design and translate it into propagation model. Initially, identification of the most appropriate
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all cost associated
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M propagation model is required and the later stage is to perform a procedure to simulate and verify planned coverage on a certain geographic area.

The third step is also acting as a feedback in the planning cycle to monitor the network growth and its performance during the entire life of the network. All data coming from O&M will be again in the planning step to ensure high performance and required capacity over the time.

3.1. System Design Initial system design usually presented in a RF Link Budget Calculation, which provides a first and fast evaluation on the network element required, capacity of those elements, and the associated cost attached to it.

In general, RF Link Budget Calculation is to define:

• Quantity of loss and gain along the path between transmitter and receiver as presented in Figure 3-2

• Maximum allowable path loss

• Assumptions to use in designing the network

• BTS antenna gain• Mast Head Amplifier• Feeder loss• Connector loss• BTS TX power• BTS RX Sensitivity

• Fading margin• Interference margin• RF Path Loss• Noise• Body/building/vehicle Loss

• Mobile TX Power• Mobile RX Sensitivity• Mobile Feeder Loss• Mobile Antenna Gain

BTS Side Mobile SideAir Interface

After identifying and quantifying all losses and gains that affect the link budget calculation for uplink and downlink connection, then the next step is to determine maximum allowable path loss for both uplink and downlink.

Figure 3-2. Most of the parameters identified to quantify loss and gain between transmitter and receiver

In uplink path, maximum allowable path loss is the sum of all losses and gain from the mobile to BTS direction. The limiting factor of uplink maximum allowable path loss is the receive sensitivity of the base station.

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M For downlink path, maximum allowable path loss is the sum of all losses and gains from the BTS to the mobile. The limiting factor of downlink maximum allowable path loss is the base station transmits power.

The equilibrium of quantity between maximum allowable uplink and downlink path loss is familiar in RF planning activity as link balance. By achieving link balance for each cell in the network, in general will use all available BTS resource with optimum efficiency absorbing all the traffic generated. At the end, this will lead to high quality of network mobility performance in term of handover and call setup performance.

It is important to achieve link balance during RF network planning activity. In short, the link balance will ensure that downlink and uplink have equal coverage footprint within the cell and enabling mobiles within the cell to communicate properly with the base station.

To translate the maximum allowable path loss into the number of network element required, a propagation model is used. There are two most widely used propagation models, namely Okumura-Hata and Walfisch-Ikegami. As the Okumura-Hata have a limitation in the frequency range to produce a valid

modelling then European Cooperation in the Field of Scientific and Technical Research (COST) sub group 231 modified the model and today COST231-Hata propagation model can support frequency range for both GSM900 as well as GSM1800. COST-231 also modified the Walfisch-Ikegami model, which based on the assumption that the transmitted wave propagates over the rooftops by multiple diffractions process. Further discussion on the propagation model is available on the appropriate references.

Network Element Reduction per 100 Km2

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

9 8 7 6 5 4 3 2 1

Improvement (dB) on link budget calculation

Figure 3-3. Percentage of network elements (cells) reduced by improving link budget calculation

Figure 3-3 illustrates the percentage of cells quantity requirement reduced by improving the link budget calculation. Figure shown above assumes that the propagation model used is COST231 urban environment for GSM900 frequency band with the same antenna heights. For example, if the link budget is improving

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M by 5 dB then the number of network elements (cell sites) required for providing such coverage reduced almost by 50%.

Table 3-1 provides an example of the actual link budget calculation. Link balance in uplink and downlink achieved after identifying all factors considered on each path. In this table, BSS equipment allows an almost balanced link budget with one stage of hybrid combining. The introduction of one stage of hybrid combiner would make the up-link 0.5 dB better than the downlink. The assumption here that the cavity combiner not considered in the table calculation and enabling synthesiser frequency hopping.

Another consideration in planning is capacity requirement. Ideally, the requirement of traffic capacity should come from network operator. This will include expected busy hour in Erlang, grade of service, and other traffic requirements then the total number of traffic channel derived from Erlang B table. In general, the method to determine the traffic for GSM1800 coverage within specified area, the same as determining the traffic for GSM900. The traffic calculation should also take into account the multiband mobile growth in near future.

Downlink, from BTS to MS Uplink, from MS to BTS BTS TX Power 42 dBm MS TX Power 30 dBm Combining Loss 3 dB MS Antenna gain 0 dB Duplexer Loss 0 dB Total EIRP 30 dBm Top of cabinet TX power 39 dBm Feeder Loss 2 dB Feeder Loss 2 dB BTS antenna gain 18 dBi BTS antenna gain 18 dBi Total EIRP 55 dBm MS RX sensitivity -100 dBm BTS RX sensitivity -104 dBm MS antenna gain 0 dB Diversity gain 5 dB Fading margin 6 dBm Fading margin 6 dBm Interference margin 3 dBm Interference margin 3 dBm Antenna body loss 3 dBm Antenna body loss 3 dBm Max. allowable path loss 143 dB Max. allowable path loss 143 dB

Link Balance (Downlink - Uplink) = 0

Table 3-1. Link Budget Calculation example

3.2. Radio Wave Propagation In the situation where the dualband feature introduced into the existing network, the operator will most likely try to maximise infrastructure utilisation where it is possible. Sharing such as cell site, cell ID, transmission link, and other things will be the common practice.

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M GSM900Microcells

GSM900Macrocells

GSM1800Macrocells

Figure 3-4 illustrates many possibilities for implementing the dualband solution in combination with Motorola multilayer solution. GSM900 macrocell can be overlayed with GSM900 microcell as well as GSM1800 microcell. The same configuration also applies for GSM1800 macrocell, which possible overlayed with microcell GSM900 and/or GSM1800. Adapted from multilayer solution, GSM1800 also may provide continuous coverage area or as a hotspot where there is a big demand for capacity in a certain area. In the figure above, GSM1800 coverage may act as an addition into existing GSM900 coverage. In this case, the network operator will select the GSM900 as their primary frequency band and will share the existing resources as much as possible. There is also a case when the network operator will start to deploy a multiband coverage from day one.

Figure 3-4. Some possibilities to deploy a Motorola dualband solution

The result of cell coverage planning is to deliver a good coverage within a logically defined service area. The network operator is usually interested in both extensive frequency reuse and good coverage. Therefore the selection of the best cell sites is essential whenever possible. The planning and design objective should be to cover the intended service area without any serious discontinuities as economically as possible. In practice, the boundary field strength that defines cell coverage for acceptable service is a function of terrain and radio propagation profile.

A number of studies performed in the industry which to recognise the radio propagation profiles on GSM900 as well as on GSM1800. ETSI specification also defined the radio planning aspect on GSM900 as well as GSM1800 in GSM03.30. The main radio frequency propagation properties in a cellular network are:

• Reflections, where the radio propagation wave hit and bounce on objects that are large in proportion to the wavelength. The object referred to in this discussion is for example building, thick wall, etc. The very basic behaviour of radio wave reflection is the angle of incoming wave is equal to the angle of reflected wave and independent to the wavelength. When a number of reflections occurred then the receiver will receive the radio wave from different direction and the total received power is the aggregate of all received radio waves, which reduced or amplified at a short time. This property called multipath fading.

• Radio Wave Penetration, where part of the incoming radio wave penetrates into object. The difference of radio wave power before and after penetration defined as penetration loss, which

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M dependant to the wavelength. Higher frequency radio wave will suffers more penetration loss.

• Diffraction, where propagation path of radio wave between transmitter and receiver is obstructed by sharp edges such as roofs, or waves are bending around multiple obstacles when the line of sight is shadowed in a wide range. Diffraction is slowly developed in the higher frequency compared to lower frequency.

• Scattering, where the radio wave hits on objects smaller than the wavelength of the propagating wave or within the size of a wavelength such as street signs or foliage.

Theoretically, based on the Frii’s free space propagation formula in an ideal environment, the radio wave propagation difference between GSM1800 and GSM900 frequency band is 6dB. In a real GSM network implementation, the radio wave propagation difference will be higher than the theoretical value because the line of sight from transmitter to the receiver is not guaranteed as well as the terrain difference.

Rec

eive

leve

l (dB

)

LOS dominates Non-LOS dominates

~ 150m - 300m

GSM 900

GSM 1800

>8 dB

6 - 8 dB

• same ERP on both bands• equal antenna pattern

near zone far zone

Rec

eive

leve

l (dB

)

LOS dominates Non-LOS dominates

~ 150m - 300m

GSM 900

GSM 1800

>8 dB

6 - 8 dB

• same ERP on both bands• equal antenna pattern

near zone far zone

A

typical GSM cell covering such area as illustrated in Figure 3-5, which separated into two zones:

Figure 3-5. Near and far zone urban cell coverage in a typical GSM network

1. Near zone, where it is at the close distance of about 150 – 300 meters. In this zone, the line of sight is predominantly exists.

2. Far zone, where the distance is higher than 300 meters. In this zone, the non line of sight is predominantly exists.

Although far and near zone difference can be commonly identified by the distance between transmitter and receiver, but the main factor influencing transition for near to far zone is determined by antenna height, building height, and other terrain properties.

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M 3.3. Site Configuration

3.3.1. Mast Head Amplifier When upgrading a GSM900 site to a multiband site due the propagation limitations at 1800 MHz the co-located GSM1800 cells will have in principle less coverage than the GSM900 ones. From the Link Budgets Calculation, one possibility to achieve link balance is to utilise masthead amplifier on uplink direction. As an example, the use of masthead amplifier will enable to increase the receiver sensitivity at 1800 MHz to 110.4 dBm.

The benefit of using masthead amplifier immediately after the receive path of the BTS antenna is better overall system noise figure, and hence, uplink sensitivity can be improved. Improved uplink receive sensitivity may result in a cell providing improved quality of service i.e. more successful assignments and fewer dropped calls. The improved link balance will also allow mobiles in a good coverage area to transmit at lower power, saving battery life and reducing uplink interference. The uplink RxQual for a call in a given area may also be improved. For the downlink path, it is possible to utilise the full power of 32Watt TCU, which extended the GSM1800 cell coverage.

Power Supply UnitDC and Alarm

Circuits

TXFilter

RXFilter

RXFilter

InternalBias Tee

Bypass Sw

itch

To Antenna

To BTS

ExternalBias Tee

Figure 3-6. Mast Head Amplifier block diagram

The decision to utilise MHA in the network also requires assessment on the impact upon overall system capacity. This impact is dependent to whether the capacity is downlink or uplink limited. If it is uplink limited then there will be no change in the system capacity, except the benefits of improved quality of service as described earlier. However, looking at the power budget calculation, the network capacity is moving closer to become downlink capacity limited. If the capacity is downlink limited then the use of MHA will decrease the system capacity. The reason behind this is that MHA introduce insertion loss of typically 0.5 dB in the downlink direction, which reducing the available EIRP. In addition, the fact that MHA has improved coverage means that user now supported in the locations that require greater BTS transmit power.

The MHA is a low noise amplifier, which mounted on the antenna mast as close to the BTS antenna as possible. The MHA is available to improve the system noise figure and thus the sensitivity of the base station receiver by reducing the effects of feeder loss between the base station and the antenna. The MHA receives power of a DC supply fed onto the RX coaxial cable from the BTS.

A dedicated power distribution unit (PDU) supplies a nominal 12 Volts dc onto the RF feeder by means of a bias tee Current Injector. This also provides the interface for the alarm system. Alarms from the MHA alerted to the PDU by a pre-set variation in current drawn by the MHA. Alarms processed by the PDU and interfaced into the BTS alarm system for reporting purpose to OMC-R.

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M

Figure 3-7. BTS receive sensitivity comparison from using MHA, when BTS receive sensitivity is -105dBm and receive noise figure is 5dB

-110-108

-106-104-102-100

-98-96-94

-92-90

0 1 2 3 4 5 6 7Feeder Loss (dB)

Sys

tem

Rec

eive

Sen

sitiv

ity (d

Bm)

8

System Sensitivity without MHA

System Sensitivity with MHA

Tower mounted amplifier (TMA) also known as a masthead amplifier, which is used to optimise the BTS receive uplink performance. One MHA is required per uplink path. Figure 3-6 shows the basic connection of the masthead amplifier.

The power distribution unit of the masthead amplifier mounted indoors in a weather-protected environment. The PDU constructed with a mounting bracket in order to meet 19-inch equipment practice. This unit provides dc power routed via the Bias Tee to the MHA. The PDU also monitors MHA performance and alarms forwarded to the OMC via the PIX system within the BTS.

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Figure 3-8. BTS receive sensitivity comparison from using MHA, when BTS receive sensitivity is -110dBm and receive noise figure is 2dB

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M

-111-110-109-108-107-106-105-104-103-102-101-100

0 1 2 3 4 5 6 7 8Feeder Loss (dB)

Syst

em R

ecei

ve S

ensi

tivity

(dB

m System Sensitivity without MHA

System Sensitivity with MHA

The last part of mastheads amplifier is the bias tee, which installed in line of the BTS-antenna feed, located at the BTS. The unit screws directly in line of the receive input to the BTS. The bias tee is fitted with 7/16 type connectors.

Figure 3-7 and Figure 3-8 are the theoretical comparison of BTS sensitivity with and without MHA installed. The graphs derived using the simple cascaded amplifier formula. In these two graphs, the assumption is that the system using GSM1800 MHA, where the noise figure is 1.4dB and receive-gain of this MHA is 12 dB.

The practical consideration applicable to use MHA includes the space availability in the mast as well as the requirement to have power source provided at the remote end of the antenna feeder. The weight and wind loading have to be included to the antenna. Also need to be considered that for each cross-polar antenna two MHAs. To calculate the benefit of MHA in Motorola BSS, link budget sheet in Excel Format is included in Appendix. Table 3-2 represents the typical parameter set for MHA.

Network Element Uplink Gain Downlink

Loss Noise Figure

MHA 2 -12 dB 0.5 dB 2 dB

Feeder -2 dB 2 dB 2 dB

Diplexor -0.3 dB 0.3 dB 0.3 dB

Bias-Tee -0.3 dB 0.3 dB 0.3 dB

Table 3-2. Typical parameter set for MHA. Note that the actual feeder loss is dependent on the site configuration and associated feeder length and quality

3.3.2. Antenna Today, a number of antenna manufacturers produced single band antenna as well as dualband antenna which flexible enough to suit the network operator’s installation requirements. Antenna configuration can be used in a multiband cell categorised into two different types:

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M • Single band antenna. This utilises the conventional antenna,

where each frequency band has its own antenna.

• Dualband antenna. Commonly as a combination of both GSM900 and GSM1800 frequency band. This means that the antenna shared for both frequency bands. Dualband antenna has approximately the same physical volume as the single band antenna.

The decision to use single band antenna or dualband antenna usually based on network operator preference as well as based on the advantages or disadvantages on each category. While single antenna deployment will provide a high degree of flexibility to fine-tune antenna properties such as tilt, bearing, and heights, which may introduce additional cost to maintain and optimise the antenna parameters. In the countries where the government requires network operator to limit the number of antenna in the network, dualband antenna maybe an attractive solution. On the other hand, dualband antenna will not provide high degree of flexibility of parameter tuning.

Other criteria that may have to be included in the process of selecting antenna type are:

• Land usage of the area required for coverage, whether the antenna is to provide coverage in rural or in urban area.

• Type of combiner, whether to use air combiner, diplexer, mast head amplifier

• Feeder plumbing or any other installation restrictions

Further details in the dualband antenna that described here is the different gains applied to each frequency band in the dualband antenna. The antenna vendors offer some alternatives to reduce the impact of propagation difference. From one of the antenna manufacturer here as an example, dualband antenna is offered with two different properties:

• Dualband antenna (GSM900/GSM1800) manufactured to provide maximum gain for each supported frequency band. This is to achieve the highest possible gain in the GSM1800 frequencies.

• Dualband antenna manufactured to provide the same gain for each frequency band supported.

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Figure 3-9. Allgon antenna radiation pattern on horizontal plane. On the left, the maximum gain antenna, the beam width for GSM900 is 14° and GSM1800 is 7° with the gain for GSM900 and GSM1800 is 16dB and 17.6dB respectively. As on the right side, the equal gain antenna, both band

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Shown on Figure 3-9 is the example of antenna radiation pattern, the maximum gain dualband antenna is possible for utilisation in the suburban area where the limiting factor is the GSM1800 coverage. For the equal gain dualband antenna, it is more suitable for the urban applications. The highlight is that the goal in selecting the dualband is to achieve maximum possibilities where the coverage of a dualband site is the same for GSM900 and GSM1800.

Following are some examples of how dualband antenna connected together within a BTS.

In Figure 3-10 left, this scenario of dualband antenna usage is assuming that antenna have 4 input ports, dual polarised with no air combining. TRX combining stage would depend on how many radios will be included in a sector. In more advanced dualband antenna, variable electrical downtilt is possible for consideration. Masthead amplifier is available as an option in this configuration. As most combining section focused on top of the cabinet, then the number of radios combined may be limited. Therefore, this combination is suitable for cell with relatively low traffic carried with small coverage footprint.

In Figure 3-10 right, this scenario of dualband antenna usage is assuming that the antenna have two input ports, dual polarised with air combining. As combining also done in the antenna, this provides advantage to combine more radio within a sector, which make it suitable for large traffic cell with large coverage footprint. To enhance the coverage specifically in the border area, masthead amplifier should be highly considered in this scenario.

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Figure 3-10. Dualband antenna deployment scenario

TX RX RX

GSM900

Dua

lban

d A

nten

na

D u p l e x e r

TX RX

TX RX RX

GSM1800

D u p l e x e r

TX RX

TRX Com bining Stage

Dua

lban

d A

nten

na

-45GSM900

GSM1800

+45GSM900

GSM1800

Duplexer

TX RX

Duplexer

TX RX

TX RX RX

GSM900

TX RX RX

GSM1800

TRX Combining Stage

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M 3.3.3. Antenna Feeder

There are several alternatives for consideration when selecting the media for delivering the RF signal from the base station to the antenna, and visa-versa. Ideally, the distribution media should be: low loss, flexible, durable, light weight, fire resistant, low cost and take up the smallest amount of space possible. One media that can meet these requirements is coaxial cable. Each version of cable has its own advantages. However, there are trade-offs involved in selecting a cable type. As a common rule, larger diameter cables have less loss but are less flexible and are difficult to handle in indoor environments. Other factors such as cost and fire resistance are should be considered as well.

3.3.4. Horizon Platform Horizon Platform is the new BSS hardware family introduced since February 1999. It supports backward compatibility to the previous MCell hardware and its height is half of the previous MCell cabinet with the same footprint like MCell6. The highlights on this new HorizonMacro hardware is that it is now support a highly flexible configuration to support dualband feature. Additionally, all transmit modules includes duplexing function as standard. This would avoid any additional duplexer losses on the antenna side of the RF interface, particularly critical where maximum power/sensitivity is required.

The planning rule still the same like the previous MCell cabinet, which is can support up to 12 carriers per cell, up to 24 carriers per site and up to 4 cabinets per site. Within a single cabinet, it is now possible to install mixed radio configuration of GSM900 and GSM1800, which also suitable for supporting the single BCCH feature due in GSR5 software release.

The GSM900 HorizonMacro cabinets can support up to 3x GSM900 cells plus 1x GSM1800 cell and by February 2000, the GSM1800 HorizonMacro cabinet can support up to 3x GSM1800 cells plus 1x GSM900 cell in one cabinet.

Figure 3-11. HorizonMacro

As it is has backward compatibility with the MCell product, then it is possible to expand the existing MCell site using HorizonMacro as one of the example configuration pictured here.

The modification of single band HorizonMacro cabinet into a dualband cabinet will only require a change on the field replaceable unit (FRU), which consist of radio carrier and transmit and combining blocks.

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Figure 3-12. Expanding capacity of existing MCell cabinet with HorizonMacro

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M 3.3.5. Horizon-II

Horizon-II hardware platform is the latest introduction to the Horizon platform. It is intended to replace old Horizon platform and at the same time supporting extra radio capacity within the same footprint. The major hardware improvement in Horizon-II platform is the transceiver unit, CTU2, which is configurable to run in single density or double density mode. In one fully populated Horizon-II cabinet, assuming all CTU2 transceivers are configured double density, then this single cabinet is providing up to 12 carriers.

Figure 13. Horizon-II Macro Indoor cabinet volume and footprint is equal to previous Horizon platform. Horizon-II is also stackable.

Following table represent the top-of-cabinet output power comparison between Horizon Macro and Horizon-II Macro

Horizon Macro (Watts ±2dB)

Horizon II Macro (Watts ±2dB)

Transceiver Type

Combining

EGSM900 DCS1800 EGSM900 DCS1800

None 40 32 N/A N/A CTU

External 20 16 N/A N/A

None 40 32 63 50 CTU2 Single Density

Mode External 20 16 28 22

Internal 10 10 20 16 CTU2 Double

Density Mode Internal & External 4.5 4.5 9 7

Table 3. Output power comparison between Horizon macro and Horizon-II Macro

Following table represents the receive sensitivity performance on Horizon-II CTU2

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EGSM900 GSM1800

Typical Guaranteed Typical Guaranteed

-108.5 dBm -107.5 dBm 109.5 dBm 108.5 dBm

Table 4. Receive sensitivity performance on faded channel conditions

More information on Horizon-II hardware configuration examples can be found on Motorola intranet http://compass.mot.com/go/107493020 or Motorola Customer Documentation.

Currently Horizon-II can only support uniform frequency band within one Horizon-II cabinet:

• all GSM900 only transceivers in a cabinet or

• all GSM1800 only transceivers in a cabinet

This means Horizon-II doesn’t support mixed GSM1800 and GSM900 transceiver within the same cabinet. When there is a requirement from the network operator to support mixed GSM900 and GSM1800 within Horizon-II cabinet, such requirement should be discussed with Motorola marketing representatives.

3.3.6. Horizon-II Interoperability with Existing Horizonmacro and MCell Platform

Horizon-II transceiver, CTU2, has backward compatibility with the previous Horizon platform. This means that CTU2 can be installed on earlier Horizon cabinet, but only with single density mode. Also it is possible to expand the existing Horizon cabinet with the new Horizon-II cabinet to configure multiband site.

The Horizon-II macro BTS platform can be used as a controlling and extension cabinet within sites with a mixture of M-Cell and Horizonmacro equipment. There are no restrictions on the mixture of cabinets allowed in a site. However the maximum number of carriers supported within a BTS site is still limited at 24 carriers. Therefore, a 24-carrier site can be implemented with two Horizon-II macro cabinets containing 12 double density CTU2’s, or four cabinets containing 24 CTU’s or CTU2’s in single density mode.

Following figures below provide examples on how to expand existing configurations with Horizon-II platform.

Horizon-II macro(6 x CTU2)

HorizonMacro(6 x CTU)

Horizon-II macro(6 x CTU2)

XMUX FMUX

E1 li

nk

Figure 14. Horizon-II macro, expanded with a Horizon-II macro and a Horizonmacro

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Horizon-II macro(6 x CTU2)

HorizonMacro(6 x CTU)

XMUX FMUX FMUX

HorizonMacro(6 x CTU)

FMUX

E1 li

nk

Figure 15. Horizonmacro controlling a Horizon-II macro and another Horizonmacro

Horizon-II macro(6 x CTU2)

MCell Macro(6 x CTU)

XMUX FMUX FMUX

HorizonMacro(6 x CTU)

FMUXE1

link

Figure 16. M-Cell 6 controlling a Horizon-II macro and a Horizonmacro

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M 4. Multiband Mobile’s Idle Mode Behaviour

In a multiband network where the BCCH is available in both GSM900 and GSM1800 frequency band, the recommendation is to ensure efficient usage of signalling resource in both bands i.e. paging channels and SDCCH. In order to achieve that, it is best to take a closer look on how the mobiles behave in the idle mode. By gaining understanding on MS idle mode behaviour and applicable BSS parameters, it is possible to influence the MS on how to utilise the BSS resources, specifically in idle mode. This section will explain the criterion used for MS to select and reselect cells and later on describes an example of implementation.

4.1. Controlling the behaviour By having the BCCH both in the GSM900 and GSM1800 band the operator may want to optimise the usage of SDCCH signalling, for example, by forcing the multiband mobile to camp on one certain frequency band whenever possible. As this can be achieve, assuming the MS required to stay in GSM900 frequency, operator may reduce the number of SDCCH sub-channels in the GSM1800 frequency and use available timeslots to handle traffic as much as possible to expand the network capacity.

The GSM recommendation introduced C1 and C2 parameter as the criteria for cell selection and reselection process. The MS will select the biggest C1 value for cell selection. Only Phase2 and Phase2+ mobiles can support C2 parameter. The Phase1 MS will ignore C2 parameter and will only use C1 for cell reselection.

4.2. C1 and C2 parameters In idle mode, the mobile will perform cell selection and reselection, which ensures the mobile ability to decode downlink information and have a good uplink connection. In order to do cell selection, the mobile will use C1 parameter, which use as the first criteria. C2 parameter used together with C1 parameter as the criteria for cell reselection.

Figure 4-1. System information Type 4 content indicates C2 parameters

In a situation where C2 parameter is not used, cell reselection will use C1 as the only criteria. The mobile only selects positive C1 and if the cell is within the same location area, the best C1 is chosen. These two parameters defined in ETSI recommendation 05.08.

Indication of C2 availability and the details of C2 parameter settings listed in the SYSTEM INFORMATION TYPE 4. The path loss criterion parameter C1 used for cell selection and reselection defined by (all values are expressed in dBm):

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C1 = (A - Max(B,0))

C1 = (RxlevelAverage - RxLevelAccessMin) – Max (Ms_TxPwr_Max_CCCH – P,0)

Where:

RxLevelAverage Received level measured by mobile.

RxLevelAccessMin The minimum received level in the MS required to access the network defined by rxlev_access_min parameter in BSS database.

Ms_TxPwr_Max_CCCH Maximum TX power level an MS may use when accessing the system. The power range divided based on its frequency as listed.

P Maximum RF output power of the MS. Refer to Table 2-1.

In above equation, (RxlevelAverage - RxLevelAccessMin), or also known as factor A, determines the quality of downlink path and (Ms_TxPwr_Max_CCCH – P) or also known as factor B, determines quality of the uplink path. As mobile choose only cell with highest positive C1 value then A must be greater than B factor, where the actual received downlink power is better than required minimum. When the B value becomes negative, the formula will determine that the mobile is in the condition where it more than capable to achieve requirement of access power.

If the mobile support GSM1800 power class 3 (maximum 4 watt of transmit power), then B factor should be adjusted into (Ms_TxPwr_Max_CCCH + power_offset – P) where power_offset is the power offset to be used in conjunction with the Ms_TxPwr_max_CCCH parameter by the class 3 GSM1800 mobile

The reselection criterion C2 used for cell reselection only and it is an optional parameter, which enabled on a per cell basis. C2 calculation result depends on the penalty_time settings, which is defined as:

If penalty_time <> 31

C2 = C1 + cell_reselect_offset – temporary_offset x H(penalty_time - T)

If penalty_time = 31

C2 = C1 – cell_reselect_offset

Where:

For non serving cells: For serving cells:

H(x) = 0 for x < 0 H(x) = 0

= 1 for x >= 0

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M T is a timer implemented for each cell in the list of strongest carriers. T should start from zero at the time the cell placed by the MS on the list of strongest carriers, except when the previous serving cell placed on the list of strongest carriers at cell reselection. In this, case, T will change to the value of penalty_time (i.e. expired).

When the cell_reselect_offset and penalty_time used together then it is possible to apply an offset after a time is expired. This is applicable where the fast mobile is not allowed to camp on the cell with better C2 value. Only the MS that already exceeded the penalty_time allowed to camp on it, assuming that penalty_time is not set to maximum (31). Figure 4-2 illustrates the description above.

Figure 4-2. The effect of penalty offset applied after the penalty_time has expired

C2 value will increase according to the value of penalty_offset after the penalty_time has expired. This would ensure that the mobile stays long enough to measure the C2 before making any cell reselection.

The purpose of cell_reselect_offset is to prioritise one cell to another. This means that adding cell_reselect_offset to the C2 parameter, it will virtually create the cell size bigger in the idle mode and making it as a better candidate for MS to camp on than it actually is. In the case where C2 parameter enabled only in the GSM1800 cells, then it will make GSM1800 cells more attractive compared to the GSM900 cells.

4.3. Example of implementation The example presented here was a field implementation trial. The objective of this test procedure is gain more detailed information about MS idle mode behaviour in a dualband environment. The following figure displays the amount of time spent on each band for the database parameter settings displayed next to it. For this result, distribution of GSM900 and GSM1800 derived at the ratio of 60:40.

In Figure 4-3 the database parameter settings, the cell_reselect_offset and temporary_offset for GSM1800 cell is slightly bigger than the GSM900 cell. This would mean that GSM1800 cell is more attractive for the mobile to camp-on. Penalty_time for all cells was set to have equal value.

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M Database Parameters: cell_reselect_offset=6 (1800 cells)

cell_reselect_offset=0 (900 cells)

temporary_offset=0 (1800 cells)

temporary_offset=3 (900 cells)

penalty_time=3 (for all 1800 and 900 cells)

Figure 4-3. Example of database parameters for C1/C2, and the field results

On the opposite, Figure 4-4 represents a more aggressive setting to force a mobile to camp in GSM1800. The database settings for this graph are set in a way that the GSM1800 cell is highly attractive for the MS rather than GSM900. By changing the cell_reselect_offset to a very high value in GSM1800 cells, it will force the MS to stay in GSM1800 cell as long as possible. The ratio achieved in this scenario was 80:20 for GSM1800 cells.

Database Parameters: cell_reselect_offset=35 (1800 cells)

cell_reselect_offset=0 (900 cells)

temporary_offset=0 (1800 cells)

temporary_offset=3 (900 cells)

penalty_time=3 (for all 1800 and 900 cells)

Figure 4-4. Example of an aggressive parameters setting for C1/C2 parameters, and field results

4.4. Idle Mode Neighbour List Idle mode neighbour list can also be used as an alternative in the scenario to limit mobile movement and reselection within the network. This may only apply where the mobile already have a neighbour list. In case where the mobile switched on, then the mobile will search possibly the entire frequency band supported to search the best server, which may not be in the frequency band it has to be. As soon as it synchronised and fully acquired the BCCH information of the best server then mobile will start to calculate the cell reselection criteria.

Following illustration will described an example of using the idle mode neighbour list. Due to network operator preference, the mobile should spend as long as possible in the GSM900. The multiband mobile will not allowed in idle state in the GSM1800.

This situation achieved by utilising the idle neighbour list for both GSM900 and GSM1800, which should only contain cells in GSM900 frequency band. In the event of mobile registering to the network (switch on), then the mobile may camp on the GSM1800. By enabling C2 parameter in the GSM1800 cells to make

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M neighbouring GSM900 cell more attractive, then the mobile will perform cell reselection to the best GSM900 cell. All of these are under assumption that the network will not supporting the single band GSM1800 mobile.

4.5. Summary of Database Parameters This section listing all database parameters to control idle mode behaviour using C1 and C2 parameters. Further detailed information on each parameter is available to Motorola Customer Documentation.

• Cell_reselect_param_ind. This is to enable the C2 information broadcasting in the BCCH.

• Cell_reselect_offset. This parameter specify the offset will be applied to C2

• Temporary_offset. This parameter used to apply a negative offset to C2 for the duration defined by penalty_time parameter.

• Penalty_time. The duration for which the negative temporary offset considered and compared with time T in the algorithm.

• Cell_bar_qualify. This is to identify whether a cell considered normal or low priority in the idle mode. The MS will always select cells with normal priority providing their C1 calculation is greater than zero. Only if a normal priority cell is not available and then reselection will go to lower priority cell. The common setting is to disable this parameter (cell_bar_qualify=0), and make all the cells in the network have normal priority.

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M 5. Advanced Load Management

The foundation of a multiband network is the ability to select appropriate frequency band for a particular mobile. This ability plays instrumental roles for the multiband network operator to direct traffic into the preferred frequency band and achieve higher network usage efficiency.

Motorola has extensive experience of managing multilayer as well as multivendor networks consisting of macrocellular and microcellular layers operating within the same band. Motorola has built on this experience, and has added specific Multiband parameters that allow the network operator to simply and easily control the management of traffic within the multiband network. This traffic management capability allows the network operator to customise the behaviour of the multiband network at a high level, taking into account factors such as network service goals and expected multiband mobile availability.

Figure 5-1 illustrates the basic procedure to enable the advanced load management feature in the BSS, which will the base of content in this section. Each bullet point represent BSS parameter, a set of parameter or BSS command that should be considered in procedure enabling advanced load management. Example of implementation on this procedure is decsribed later in this section.

Network & BSC levelsettings

MSC settingsFeature license verificationMobile's classmark handling

Network & BSC levelsettings

MSC settingsFeature license verificationMobile's classmark handling

Cell Level Settings

frequency_typeband_preference_modeinterband_ho_allowedmultiband_reportingEnabling statistics

Cell Level Settings

frequency_typeband_preference_modeinterband_ho_allowedmultiband_reportingEnabling statistics

Neighbour RelationsSettings

Assigning handovercandidates

Neighbour RelationsSettings

Assigning handovercandidates

1 2 3

Figure 5-1. Basic procedure to enable Advanced Load Management

5.1. Network and BSC level settings This involves some preliminary verification in order to ensure the required features are available and feature dependencies are met.

5.1.1. MSC Settings Discussed earlier in 2.2.2 MSC Requirement, that the MSC is required to support multiband operation by providing the ability to forward mobile classmark info to any BSC in the event of handover. As it is beyond the scope of this document and each MSC vendor has its own procedure on how to enable such feature then this requirement should be in discussion with network operator as well as the MSC technical support.

This requirement is based on ETSI recommendation, which applicable to any MSC vendor regardless the combination possibilities with BSS.

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M 5.1.2. Enabling Dualband Feature

A parameter is provided in BSC level to indicate whether dualband feature is enabled or not. This parameter is mb_preference.

5.1.3. Feature license verification This verification is done in BSS by running disp_options command. The required BSS software options required with unrestricted status for multiband operation is:

• Infrastructure sharing Homogeneous Cabinet

• Infrastructure Sharing Heterogeneous Cabinet

• Multiband Inter–Cell Handover

• Microcell Handover

The last required feature option, Microcell Handover (also known as Advanced Handover Algorithm) will provides essential ability to assigns and configures neighbour candidates on each frequency band on handover scenarios, specifically power budget and imperative handover. This is available later on this section.

5.1.4. Handling mobile’s classmark information

Mobile BSS MSC

Channel Request

Immediate Assignment

CM Service Request

Classmark Change

Chipering Mode Command

Chipering Mode Complete

Setup

Identity Request

Identity Respond

Call Proceeding

Classmark Update

A number of BSS parameters are available on how the BSS should handle the multiband mobile’s classmark information. This classmark handling is important so that BSS as well as MSC is able to define and distinguish the mobile ability operating in multiband network and assign appropriate supported frequency band.

Figure 5-2. Multiband mobile originated call signalling

In order to understand mobile’s classmark information handling by BSS and MSC. Figure 5-2 illustrates the initial message flow between mobile, BSS and MSC in a mobile originated call. In the figure above, BSS received CLASSMARK CHANGE message from the mobile, which inform the network about its multiband capabilities. Then the BSS will forward this information to the MSC using CLASSMARK UPDATE message and maintain the classmark record during the entire life of the call. If the MSC meets the requirements specified earlier in this

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M section, then MSC is able to forward the classmark information to any target BSC in the event of handover.

In order to perform such messaging and how the messaging should move between network entities, following parameters are available in the BSS software.

The first parameter is early_classmark_sending. This parameter defines on how to send the classmark info during call initiation process for mobile terminated call as well as mobile originated call. During channel assignment procedure, early_classmark_sending determine whether classmark information forwarding should be enabled on air interface, A-interface, or both. The typical setting is early_classmark_sending=3, which means that the classmark information will be send in both air interface and A-interface as displayed in Figure 5-2.

The second parameter is early_classmark_delay. This parameter specifies how long the BSS should delay sending the classmark update to MSC after receiving the CLASSMARK CHANGE message from the mobile. With the latest MSC processing speed capability, this parameter is recommended to set it to the lowest possible, which may potentially reduce the delay in call setup time.

The third parameter is phase2_classmark_enabled parameter. When BSC informs MSC about the mobile class using classmark update message, it should follow phase-2 message format according to ETSI recommendation. Phase2_classmark_enabled is the command to define info formatting. This is required for BSS to handle classmark info properly sent by multiband mobile, which already in phase-2. The typical setting is phase2_classmark_enabled=2, which enable to format the information sent to MSC in phase 2 along with the multiband information.

5.1.5. Allowed frequency band Freq_types_allowed defines the allowed frequency band to work in a BSS. There are 4 frequency types supported by BSS software and 15 permutations available to allow frequency bands to work in a BSS.

5.2. Cell level parameters settings Following are the list of parameters required for consideration on each cell enabled with multiband capability in the network.

5.2.1. Frequency type in a cell Frequency_type parameter defines the frequency type of a cell. This parameter has dependency with freq_types_allowed defined in a BSS as well as the feature option availability.

5.2.2. Handover between frequency band Interband_handover_allowed is the parameter to enable or allow the handover between frequency bands enabled in the BSS.

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M 5.2.3. Frequency band reported in the measurement report

Multiband_reporting is the BSS parameter to define how each frequency band reported to the BSS during dedicated mode within measurement report. The availability of this parameter based on the ETSI recommendation, which defines the multiband reporting information element should be sent to the mobile using SYSTEM INFORMATION TYPE 2TER or SYSTEM INFORMATION TYPE 5TER.

According to ETSI recommendation 05.08, there are 4 settings of multiband_reporting available:

• multiband_reporting=0, means that the mobile should sent the measurement report that consist of the normal 6 strongest neighbour cells with known BSIC irrespective the frequency band of the neighbour cells.

• multiband_reporting=1, means that through the measurement report, the mobile should report one strongest neighbour cell with known BSIC, excluding the frequency band of the serving cell. The remaining five positions available in the measurement report should be use for reporting the neighbour cells in the frequency band used in the serving cell. If there are remaining positions available, then these will be use to report the neighbouring cells irrespective to the frequency band.

• Multiband_reporting=2, means that through the measurement report, the mobile should report two strongest neighbour cells with known BSIC, excluing the frequency band of the serving cell. The remaining 4 position available in the measurement reportshould be use for reporting the neighbour cells in the frequency band used in the frequency band used in the serving cell. If there are still remaining positions avaialable, then these will be use to report the neighbouring cells irrespective to the frequency band.

• Multiband_reporting=3, means that through the measurement report, the mobile should report three strongest neighbour cells with known BSIC, excluing the frequency band of the serving cell. The remaining 3 position available in the measurement reportshould be use for reporting the neighbour cells in the frequency band used in the frequency band used in the serving cell. If there are still remaining positions avaialable, then these will be use to report the neighbouring cells irrespective to the frequency band.

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Figure 5-3. Multiband reporting sent to the mobile through System Information Type 5ter

By defining this parameter, it is possible for the BSS to always include all supported frequency bands to be included in the measurement report processing. Then the next process will be to assign the mobile to the preferred frequency band.

Figure 5-3 is the example on how the multiband reporting sent to the mobile through System Information Type 5ter during dedicated mode.

As example, using multiband_reporting=2 where the mobile is working in the multiband network supporting GSM900 and GSM1800, means that when the mobile is served by GSM900 cell, two positions of neighbour report available in the measurement report are reserved for GSM1800 neighbour measurements and the rest is GSM900 neighbour cells. When GSM1800 cell serves the mobile then two positions of neighbour report reserved for GSM900 neighbour measurements and the rest is GSM1800 neighbour cells.

5.2.4. TCH Assignment Delay The dualband feature provides an option where the SDCCH to TCH assignment can be delayed up to 2 seconds. The purpose of this option is to enable the BSS calculate the proper receive level reported by the mobile and decides whether the mobile is good enough to enter GSM1800 frequency. This option is configurable by sdcch_tch_band_reassign_delay parameter. This is the same parameter used in Single BCCH feature. More information on this option is available in section Single BCCH.

5.2.5. Frequency band preference Each cell in the multiband network should identify the preferred frequency band. This frequency band will be the target frequency band and has higher priority over other frequency band supported in the multiband network. Setting the preference is possible by using band_preference parameter.

Although there is no restriction in the BSS software to nominate the preferred frequency band, in most cases of multiband network implementation, band_preference=2, which means that the preferred frequency band is GSM1800. This is in combination with the network operator who has initially use GSM900 frequency band.

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M 5.2.6. Band preference mode

This parameter specifically identified the behaviour to move the call into the preferred frequency band. This parameter is the significant part of the advanced load management feature. Each setting on band_preference_mode will discussed here in detail. It is good to keep in mode that in this section that band preference mode settings would only affect the multiband mobiles in the network.

5.2.6.1. Band_preference_mode=0 This setting means that the frequency band preference set in the network will not taken into account. The call will assume normal handover, which will perform a handover to the strongest neighbouring cell irrespective frequency band of the target cell.

5.2.6.2. Band_preference_mode=1 In this setting, the BSS attempts to assign mobile to strongest cell of preferred band at the time of SDCCH to TCH assignment. In other word, after accessing the SDCCH channel, the BSS will try to assign the mobile directly into a TCH in the preferred band.

If attempt is unsuccessful, the BSS will not attempt to direct this mobile to the preferred band again for the life of the current call connection. In the event, where the call required performing handover then this is due to normal radio resource reasons.

This means that the BSS will only perform one attempt to move the call to the preferred band during the SDCCH to TCH assignment in the entire life of a call. If during the call the mobile performed handover to the preferred frequency band, it is because normal radio resource reason handover such as power budget or interference and not because this band preference mode settings. The handover cause value (ho_cause) caused by this setting is band reassignment.

5.2.6.3. Band_preference_mode=2 In this settings, the BSS attempts to assign mobile to the preferred frequency band when a handover is required for normal radio resource reasons or congestion relief reasons. The BSS places preferred band neighbours ahead of non-preferred band neighbours.

This means that when the call is already in the dedicated mode and up to a point, the mobile is required to perform handover then the neighbour cells from the preferred frequency band will be on top of the handover candidate list. Subsequently the handover will take place to the preferred band.

Once the call already in the preferred band then if the mobile required to perform another handover then the neighbouring cells from the preferred frequency band, again, will be on top of the handover candidate list. The handover cause value (ho_cause) caused by this setting is better cell.

The benefit on this setting is the ability to move the call to target cell in the preferred band, which have lower receive signal strength compared to the current serving cell in the non-preferred frequency band. In order to prevent the call coming back to the original serving cell (ping-pong effect), then the handover margin and other criteria should be modified.

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M 5.2.6.4. Band_preference_mode=3

In short, this setting is the combination of band_preference_mode=1 and band_preference_mode=2.

This means that the BSS will attempt to move the call to the preferred frequency band during the SDCCH to TCH assignment as well as when the call is required to perform the handover. In the event of SDCCH to TCH assignment, band_preference_mode=1 as described in 5.2.6.2 is applicable. In the event of the call required to perform handover then band_preference_mode=2 as described in 5.2.6.3 is applicable.

It is easy to conclude that the benefit of this setting is to have the benefit of band_preference_mode=1 and 2.

5.2.6.5. Band_preference_mode=4 In this setting, the BSS will enter to monitor mode of attempting to move the call into the preferred frequency band immediately after the call have been assigned to a TCH. No attempt will be performed during the SDCCH to TCH assignment. The BSS will enter to monitor mode, which continually monitoring the qualified neighbour cells in the preferred frequency band in order to handover the call to the preferred band. The BSS will stop performing in this mode when it successfully moved the call into the preferred band. Handover for normal radio resource reasons may occur during the monitor mode period and in the handover candidate list, the neighbour cells from preferred band will on top of the list.

5.2.6.6. Band_preference_mode=5 In short, this is the combination of band_preference_mode=1, 2, and 4.

5.2.6.7. Band_preference_mode=6 In short, this setting will perform band_preference_mode=5, but only when the cell is congested. For summary, the band_preference_mode settings illustrated in the following table

band_preference_modeSDCCH to

TCH assignment

On demandhandover

Monitor mode

On Congestion

0

1

2

3

4

5

6

Figure 5-4. Summary of band_preference_mode settings

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M 5.2.7. Multiband related statistics

In order to monitor the performance of advanced load management settings, following are the statistics available in the BSS. The availability of these statistics will depend on advanced load management feature options in the BSS. Other BSS statistics descriptions are available in Motorola Customer Documentation.

5.2.7.1. INTERBAND_ACTIVITY This statistics will count the handover attempts between frequency band based on the target frequency band. This statistic consists of several bins, which is used to count the number of handovers to each of the supported bands.

Additionally, it is possible to count the number of assignment failures due to incorrect or unsupported frequency information. Finally, it can be used to count the number of handover failures due to incorrect or unsupported frequency band information. This statistic is activated per cell basis. Description of each bin listed below:

Bin Name Descriptions 0 PGSM_HO_ATMPT Records handover attempt to GSM900

1 EGSM_HO_ATMPT Records handover attempt to EGSM

2 DCS1800_HO_ATMPT Records handover attempt to GSM1800

3 PCS1900_HO_ATMPT Records handover attempt to PCS1900

4 PGSM_HO_FAIL Records handover failure to GSM900

5 EGSM_HO_FAIL Records handover failure to EGSM

6 DCS1800_HO_FAIL Records handover failure to GSM1800

7 PCS1900_HO_FAIL Records handover failure to PCS1900

8 INVALID_FREQ_ASGN Frequency not implemented for assignment request.

9 INVALID_FREQ_HO Frequency not implemented for handover.

5.2.7.2. MS_TCH_USAGE_BY_TYPE This counter array statistics tracks the duration of a certain mobile type spent in the TCH. The exact duration is derived by multiplying the stats value with 6 seconds. Following are the description for each bin.

Bin Name Descriptions 0 MS_PGSM_ONLY Records duration of mobile supports

GSM900 only

1 MS_DCS1800_ONLY Records duration of mobile supports GSM1800 only

2 MS_PCS1900_ONLY Records duration of mobile supports PCS1900 mobile only

3 MS_PGSM_EGSM Records duration of mobile support GSM900 and EGSM

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M 4 MS_PGSM_DCS1800 Records duration of mobile support

GSM900 and GSM1800

5 MS_PGSM_EGSM_DCS1800 Records duration of mobile support GSM900, EGSM, and GSM1800

6 MS_PGSM_PCS1900 Records duration of mobile support GSM900 and PCS1900

7 MS_PGSM_EGSM_PCS1900 Records duration of mobile support GSM900, EGSM, and PCS1900

5.2.7.3. MS_ACCESS_BY_TYPE This counter array statistics tracks the number of system accesses by various types of mobile. A bin pegged when the corresponding mobile type accesses the network at the beginning of the call. The counter array description are the same as in statistics described above, MS_TCH_USAGE_BY_TYPE.

Bin Name Descriptions 0 MS_PGSM_ONLY Records duration of mobile supports

GSM900 only

1 MS_DCS1800_ONLY Records duration of mobile supports GSM1800 only

2 MS_PCS1900_ONLY Records duration of mobile supports PCS1900 mobile only

3 MS_PGSM_EGSM Records duration of mobile support GSM900 and EGSM

4 MS_PGSM_DCS1800 Records duration of mobile support GSM900 and GSM1800

5 MS_PGSM_EGSM_DCS1800 Records duration of mobile support GSM900, EGSM, and GSM1800

6 MS_PGSM_PCS1900 Records duration of mobile support GSM900 and PCS1900

7 MS_PGSM_EGSM_PCS1900 Records duration of mobile support GSM900, EGSM, and PCS1900

5.3. Advanced load management in the network This section outlines examples of multiband handover settings, which is possible for deployment in the network. As mentioned earlier, in order to maximise the ability of advanced load management to handle the traffic, it needs to work together with microcell algorithm (also known as Advanced Handover Algorithm). This combination will enable the network operator to optimise each neighbour to a particular role at the time a call needs a handover. Usually the neighbour cell role to a call divided into two groups, which power budget neighbours and imperative neighbours. Power budget neighbour is the neighbouring cell that available when the call required performing power budget handover. This type of handover is the preferred type when handover event took place as it represent the normal handover. If the call experiences degradation in uplink or downlink receives quality then the call should be handed-over to imperative neighbours to

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M save the call from further degradation. The quantity of imperative handover in a cell is available to indicate the interference level. The higher number of imperative handover, the higher of interference level and it should be address with higher priority.

Before moving forward to examples following is a short description on microcell algorithm. Further details on microcell handover are available in Motorola Customer Documentation.

5.3.1.1. Microcell handover Microcell handover algorithm is Motorola enhancement to power budget handover, which able to recognise the needs of the system and direct the traffic according to the resources and conditions of the network. There are 7 types of microcell algorithms which take into account the radio frequency parameters in the surrounding cells while a call take place. The concept introduced here is where the network consists of cellular layers, microcell and macrocell. Microcells are the cells with a small coverage footprint. Microcells antenna typically installed not higher than the rooftop. Macrocells are the conventional cell with large coverage footprint. These handover types are:

• Microcell handover type 1. This is the normal power budget handover as defined by ETSI. This type of handover typically assigned for handover from a macrocell to a macro cell.

• Microcell handover type 2. This type of handover also known as imperative handover. This imperative handover are available to uplink and downlink caused by receive quality, interference, receive level, and mobile distance.

• Microcell handover type 3. Also known as “around the corner handover”. This type of handover monitors the serving cell receive level and prevent a handover to neighbouring cells unless the serving cell receive level has dropped below threshold.

• Microcell handover type 4. This handover type incorporate the time delay to limit the handover rate between two cells. The handover will take place if the time delay has expired and the call still able to meet the criteria. This type of handover typically assigned for handover from a microcell to a microcell that involves line of sight factor.

• Microcell handover type 5. This type of handover will monitor the receive level of neighbouring cells and allow a handover to neighbouring cell when its receive level has exceeded a certain period of time. This type of handover typically used for handover from macrocell into microcell.

• Microcell handover type 6. This type of handover will change dynamically the handover by applying penalty value to handover margin after a certain period. It also effectively limits the number of handover rate.

• Microcell handover type 7. This type of handover will enable the possibility to assign adjacent frequency as a BCCH of a neighbouring cell. This type of handover will maximise the utilisation of frequency spectrum available.

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M 5.3.1.2. Example of implementation

GSM1800MACROCELL

BPM 2

GSM1800MACROCELL

BPM 2

GSM900MACROCELL

BPM 3

GSM900MACROCELL

BPM 3

GSM900MicrocellBPM 3

GSM900MicrocellBPM 3

Type 1

Type 1

Type 4

Type 5Type 5

Type 3

Type 5Type 2

Type 5

This example as illustrated in Figure 5-5 derived from a working life multiband network, which utilise advanced load management in combination with microcell algorithm.

The GSM1800 cells deployed into a part of the existing GSM900 network with the majority of current subscriber base being single band GSM900 subscribers, while the network is evolving into a multi-band subscriber network. All GSM900 and GSM1800 sites are co-located. The goal of maximising capacity is achieved through the reassignment of mobiles from the congested GSM900 band to the non-congested GSM1800 band, then keeping the multi-band capable mobiles on the GSM1800 layer by intelligent channel allocation algorithms. Microcellular algorithms are used to maintain a good quality of service by moving the call over to GSM900 layer when RF conditions (low signal level) on the GSM1800 layer deteriorate due to lack of coverage.

Figure 5-5. Example of advanced load management settings combined with microcell algorithm

Table 5-1. Microcell handover algorithm settings

The objective of the setting shown above is to bias multi-band subscribers to the GSM1800 layer such, that

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Band Preferred Band

Band Preference

Mode

Handover GSM1800

macro

Handover GSM900 macro

Handover GSM900

micro

GSM1800 Macro

DCS 2 HO Type 1 HO margin=6

HO Type 3 HO margin=-10

threshold=15

-

GSM900 Macro

DCS 3 HO Type 5 HO margin=-63

threshold=25 timer=1

HO Type 1 HO margin=6

HO Type 5 HO margin=-50

threshold=34 timer=4

GSM900 Micro

DCS 3 HO Type 5 HO margin=-63

threshold=25 timer=1

HO Type 2 HO margin=6

HO Type 4 HO margin=6

Figure 5-6. Handover settings in GSM1800 layer. Number in arrows denotes the handover priority

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traffic from GSM900 layer is relieved and the revenue from single band mobiles is not lost. The degree of bias is set to aggressive values in accordance with the number of multi-band subscribers, which is low. The priority associated with the cell layers is defined such that GSM1800 macro cells take priority over GSM 900 macro as well as micro cells and GSM900 micro cells over GSM900 macro cells.

Each GSM1800 cell has all the logical adjacent neighbour cells within the same frequency band equipped. In addition, neighbour cells of the co-located GSM900 cell are also added as multi-band handover candidates.

This is also a requirement for the coincident multi-band handover feature, which allows the operator to have only one network to optimise by maintaining the original handover boundaries between GSM900 cells on the GSM1800 layer. On the other hand, only the 3 GSM1800 co-located cells are defined as multi-band handover candidates on each GSM900 cell, to make sure that a specific GSM1800 cell will only offload traffic from its co-located GSM900 site.

Type 1 handover and handover margins between cells of the same band (GSM900–GSM900, GSM1800-GSM1800) are set as in a single band network to avoid ping-pong handovers and ensure reliable, interference free handover performance.

Type 3 handover from GSM1800 to GSM900 will ensure that a dual-band mobile, which is assigned to the GSM1800 layer remains there until it gets out of GSM1800 layer coverage (defined by the downlink and uplink signal threshold of type 3 handovers, which is –95 dBm). Afterwards the mobile will be forced to hand over (due to low level of received signal from serving DCS1800 cell) to a suitable GSM900 macro cell, working as an umbrella cell and providing wider area coverage.

Poor receive quality (interference) or congestion on the GSM1800 layer will trigger an imperative based on quality handover. This will however only result in an inter-band (from GSM1800 to GSM900) handover, if no suitable alternative GSM1800 neighbour candidates are available (due to reordering of handover candidate list with the preferred band (GSM1800) candidate on top of list – BPM 2).

There are no handovers configured on GSM1800 macrocells towards GSM900 micro cells to keep multi-band mobiles on the GSM1800 layer.

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Figure 5-7. Handover settings in GSM900 layer. Number in arrows denotes the handover priority System Support – Quality Of Service

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M Type 5 handovers from GSM900 macrocells towards GSM1800 macrocells and GSM900 microcells encourage mobiles to handover onto the GSM1800 or GSM900 micro layer respectively as soon as suitable RF conditions exist. The call will be handed over if reported Rxlev of the neighbour candidate exceeds handover type 5 Rxlev threshold (-85 dBm for GSM1800 macro cell neighbours).

BPM3 on the GSM900 layer (preferred band set to GSM1800) will ensure that mobiles are handed over first to the GSM1800 layer whenever possible (type 5 handover RxLev threshold criteria).

The ALM preferred band mechanism implies that the first choice of handover target is the GSM1800 cell (if qualified i.e. RxLev (N) stronger than rxlev_min_ncell and the GSM1800 neighbour is stronger than the server cell) in case an imperative (e.g. quality) handover is triggered. The handover candidate reordering mechanism due to the applied handover types (handover type 1 takes priority over handover type 5) allows non-power budget handovers to GSM900 microcells only if no other suitable candidates are available (GSM1800 as first choice, GSM900 macro cell as second choice).

Type 5 handovers from GSM900 microcells towards GSM1800 macro cells encourage mobiles to handover onto the GSM1800 layer as soon as suitable RF conditions exists; i.e. reported RxLev of the neighbour candidate exceeds RxLev threshold (-85 dBm for GSM1800 macro cell neighbours). Band_preference_mode=3 on the GSM900 layer (preferred band set to GSM1800) will ensure that mobiles are handed first to the GSM1800 layer whenever possible (type 5 handover RxLev threshold criteria).

Power budget handovers will not be triggered from GSM900 microcells to GSM900 macro cells (handover type 2) to keep the mobiles on the micro layer as long as the RF conditions allow to maintain the call with good quality on the GSM900 micro layer, where no suitable GSM1800 candidates are.

The ALM preferred band (GSM1800) mechanism implies that the first choice of handover target is the GSM1800 cell (if qualified i.e. RxLev (N) > rxlev_min_ncell and the GSM1800 neighbour is stronger than the server cell) in case an imperative (e.g. quality) handover is triggered. The handover candidate reordering mechanism due to the applied handover types (handover type 2 takes priority over handover type 4) allows non-PBGT handovers to

Figure 5-8. Handover settings in microcell GSM900 layer. Number in arrows denotes the handover priority

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M GSM900 micro cells only if no other suitable candidates are available (GSM1800 as first choice, GSM900 macrocell as second choice).

5.4. Summary of BSS database parameters Following are the list of associated advanced load management BSS database parameters. For more details with regard to setting valid range and default setting can be found in Motorola Customer Documentation.

• Mb_preference. This parameter to control whether dualband option is enabled or not for the given BSC.

• Early_classmark_sending. This specifies how to send the classmark information for the given BSC.

• Early_classmark_delay. This specifies how long BSS should delay the sending of classmark information to MSC.

• Phase2_classmark_enabled. This specifies how the classmark information formatting.

• Sdcch_tch_band_reassign_delay. This parameter is to delay the TCH assignment from SDCCH.

• Frequency_types_allowed. This specifies the list of frequency band will be supported in the network

• Frequency_type. Identify the frequency band used in a cell.

• Interband_handover_allowed. This to allow handover between frequency band

• Multiband_reporting. This specifies how is the preferred neighbour cell in the measurement report should be created

• Band_preference. This specifies the preferred frequency band

• Band_preference_mode. This specifies how the preferred band should be used.

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Following are enhancements to Motorola multiband solution included up to the recent software release.

6.1. Support for BCCH and SDCCH in EGSM frequency band Starting GSR4, Motorola introduce the support to put the BCCH in the EGSM frequency band. This feature will allow the operator to configure in their database the BCCH and SDCCH placement in the EGSM frequency band. This feature will also enable the operator to have dualband implementation where EGSM is one of the supported bands, for example GSM1800 and EGSM.

In the multiband system, where EGSM is one of the supported bands, frequency hopping is only supported within the band but not between frequency bands. For example, the operator has GSM900 as their primary band, and has EGSM and GSM1800 as secondary band. The operator also can configure that EGSM is the preferred band. Then the frequency-hopping feature will be limited to each frequency band.

The feature also has the capability to support standalone extension band, where EGSM frequencies are the extension band system from the primary GSM. In this case, it is possible to configure frequency hopping where some of the frequencies in the hopping list are in the EGSM Band. In addition to that, the SDCCH placement in the EGSM frequency band is also possible.

This impact should be considered when implementing BCCH and SDCCH in the EGSM band. As some of the mobiles do not support EGSM, these mobiles will not be able to access the system, as they are unable to camp on the BCCH.

Egsm_bcch_sd is the BSS database parameter to enable this feature

6.2. Advanced Load Management with EGSM Carriers As more multiband network operator enjoy the availability of GSM1800 frequency band as the capacity extension, in some case this extension is still considered not enough. This is due to high growth of multiband mobiles in the network and offered in the market. In addition to that, a number of multiband mobile manufacturers add more frequency band support into the mobile, especially EGSM frequency band.

When the advanced load management software feature is enabled in the network, regardless EGSM availability, the first candidate of handover will be the preferred band. This would lead to the situation where EGSM carriers configured in the network not efficiently utilised, as there is no certain method to direct traffic into EGSM frequency band.

To alleviate such situation, in GSR6, advanced load management has been modified to consider EGSM frequency band. This modification is available as a feature option with the BSS parameter named bss_egsm_alm_allowed. By enabling this feature, it is possible to direct a handover of a mobile on a EGSM frequency band to another available EGSM frequency band regardless the settings of band_preference parameter. This manipulates the handover list for

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M a mobile which support EGSM frequency band to use EGSM traffic channel (TCH) as the preference over the non EGSM TCHs.

There are a number of assumptions behind this feature, which are:

• The cell is not configured with co-incident multiband handover

• External handovers assume cell with GSM900 BCCH is GSM900 only cell

• No EGSM frequencies band configured as BCCH

• No frequency hopping trough EGSM frequencies within GSM900 or GSM1800 cell

6.3. Multiband congestion relief enhancement

Figure 6-1. Enhancement on congestion relief

An enhancement has been added to Congestion relief feature in GSR4 with regard to multiband feature. As seen on Figure 6-1 above, additional multiband congestion threshold is applicable only to dualband mobiles. When a cell traffic increasing, by the time it hit the multiband congestion threshold, then only the existing dualband capable traffic will be move to the preferred band. If the traffic still increasing then hit the congestion threshold, then congestion relief feature will work for both multiband and singleband mobile. These thresholds are stated in percentage.

For BSS database parameter, the multiband congestion threshold is mb_tch_congest_thres, and the congestion threshold is tch_congest_prevent_thres.

The benefit for operator is that the additional multiband congestion threshold will give a more efficient congestion control in the preferred band in the multiband network.

There are several dependencies should be followed in order to enable the multiband congestion threshold,

1. The band_preference_mode parameter should set to 6.

2. Congestion relief feature is enabled (ho_exist_congest)

3. mb_tch_congest_thres should be set less than tch_congest_prevent_thres.

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Cell A

Cell B

Cell C

Cell D

Inner Zone

Outer Zone

ConcentricCell

Dualbandcell

7. Single BCCH (Dualband Cell) Referring to ETSI Specification 03.26 about multiband operation by a single operator, it doesn’t require a mandatory availability of BCCH on every single frequency band; in fact, it is possible for the network operator to maximise TCH allocation by sharing the BCCH for all frequency bands enabled in the network. This configuration will enable the network operator to select the BCCH allocated in just one frequency band and other frequency band it support will use the same BCCH.

In practise, a cell may be specified in which the BCCH carrier (and any optional non–BCCH carriers) is allocated from one frequency band and the remaining non–BCCH carriers within the same cell are allocated from another frequency band. With this new feature, it is possible for carriers within a single cell to be configured with frequencies from different frequency bands. The frequency band used in a dualband cell for the BCCH carrier and any optional non–BCCH carriers of the same band is considered the primary band for the cell. The frequency band used in a dual band cell for the remaining non–BCCH carriers are considered the secondary band.

Starting GSR5, Motorola supports the single BCCH or dualband cell feature. Dualband cell is actually an adaptation from the existing feature named Concentric Cell, which allow traffic channel partitioning within a cell that allow tighter frequency reuse pattern and increase frequency band efficiency.

In concentric cells as illustrated in Figure 7-1, the traffic channels are divided into two partitions that translated into coverage area of a cell. The first part is the outer-zone, where it is the normal cell coverage footprint. The second part is the inner-zone, where it is only covers a subset of the outer-zone. The handover criteria between zones are regulated by receive level or interference level.

Figure 7-1. Dualband cell (below) as an adaptation from Concenctric Cell concept (above)

Adopting the concentric cell concept, in dualband cell, it also partitions the traffic channel resources into outer-zone and inner-zone. Outer-zone is where the primary frequency band will be allocated and inner-zone is where the secondary frequency band will be allocated. Unlike concentric cell, in dualband cell both zones can be configured to provide coverage footprint independently. This provides flexibility to tailor the coverage on each zone. In dualband cell, the handover criteria between zones are regulated only by receive level.

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M Handover between frequency band or inter-zone handover in a dualband cell is performed by a mean of intra-cell handover. In practice, the inter-zone handover command is send to the mobile via Layer 3 Assignment Command message.

There are essential information included in Assignment Command for multiband mobile to complete inter-zone handover. These are

• New ARFCN of the target zone, which is not in frequency band used in serving zone.

• New transmit power for the mobile to use. When assigning the new transmit power for mobile to use the BSS is automatically choose the relevant transmit power range allowed in a frequency band.

The handover between zones can occur during the SDCCH to TCH assignment as well as during the call. When the call is initiated, after finishing the SDCCH access in the outer-zone, the mobile will be assigned directly to the TCH in the inner-zone, assuming that it fulfilled the criteria to enter inner-zone. Likewise, during the entire life of the call, it may handover between zones assuming the criteria are met.

It is also possible for handover from inner-zone directly to inner-zone of another dualband cell once the criteria are met and it can only happen within the same BSC. This is because the BSC need to have access to both target and source dualband cell in order to determine inner-zone availability in target zone as well as calculating criteria to enter inner-zone in the new cell.

In the event of inter-BSC handover, in the target cell the, TCH from outer-zone will be assigned regardless the zone in the source cell. Further movement to any zone in the target cell will be evaluated by receive level criteria. The criteria for inter-zone handover will be discussed in detail in later subsection.

7.1. Benefits of Single BCCH Feature The availability of Single BCCH feature in GSR5 highly correlates to the benefits delivered, which improve the network operability and efficiency.

Following are some advantages enabling single BCCH feature in the network:

• Improved neighbour relationship management. This is a direct benefit from Single BCCH feature. In a conventional dualband network, where BCCH is available in both frequency bands, the handover between frequency bands have to be defined explicitly as part of the cell database parameter. Such requirements may increase the number of operational task to maintain and manage neighbour relationship in the network as well as the possibility to reach the maximum number of neighbour relations (32) prematurely.

• No requirement to broadcast System information Type 2ter/5ter. This is also a direct benefit from Single BCCH feature. In the conventional dualband network as described on earlier chapter, the network is required to broadcast System information type 2ter/5ter in order to inform the mobile the availability of other frequency band outside the current frequency band used in the serving cell. When Single BCCH feature is implemented then there is no more requirement for the mobile to process System Information Type 2ter/5ter. This automatically will increase the mobile internal processing ability to fully acquire network information in shorter period.

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M • Less inter-cell handover. As the handover between frequency bands is

considered as intra-cell handover in a dualband cell, then there is less inter cell handover occurred in the network when compared with the conventional dualband network.

• Increase network capacity. The requirement to allocated dedicated timeslot as BCCH in each frequency band means that the BCCH timeslot will not be able to carry any traffic. By enabling Single BCCH feature in the network, the timeslot used as BCCH in the secondary band is configured as TCH that can serves call. This means increase in cell capacity offered in the network.

• No hardware reconfiguration required. When transforming a conventional a site that supports multiband frequency, the conversion procedure is mainly performed in the software side. There is no hardware related configuration is required.

• Single BCCH feature is working as feature to provide efficient signalling resources as well as to provide capacity and coverage.

To illustrate the benefit of capacity increase (trunking efficiency) in the network when enabling Single BCCH, the following figure and table below is used. Figure 7-2 is a graphical representation of how much the traffic offered (measured in Erlang/Km2) in relation with the number of carriers in a site and its coverage area footprint. An example is a conventional co-located site that able to support GSM900 and GSM1800. Each frequency band on that site is configured with 2x2x2 carriers and designed to cover 0.5 Km2. Meaning that this site is able to offer traffic as much as 2x31 Erlang/Km2. When this site is converted into a dualband site, it can be considered as a site with 4x4x4 carriers configuration with the ability to offer traffic as high as 77 Erlang/ Km2. This represents increase of 24.19% capacity traffic on that site without additional hardware requirement.

Figure 7-2. Cell capacity offered in relation with the carrier configuration and coverage area

Another example derived from Figure 7-2 with the same analogy is on the site where GSM900 frequency band configured with 2x2x2 carriers, while the GSM1800 configured with 1x1x1 carriers. In a conventional site that supports multiband capability, this means that the site is able to provide offered traffic as much as (31+11 Erlang/Km2). When this site is configured with Single BCCH, then it is considered as a site with 3x3x3 carriers providing 54 Erlang/ Km2 offered traffic. This is an increase of 28.57% by enabling the Single BCCH feature on the site.

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The most important requirement to enable dualband cell in the network is that the cells are co-located and synchronised.

Co-located requirement means that the outer-zone and inner-zone within the same cell have to be serving the same coverage area.

Synchronised requirement means that outer-zone and inner-zone has to be configured within the same cell. From the hardware provisioning point of view this means that any carriers (DRI and RTF definition) has to be configured within the same cell by utilising the to mix a certain cabinet type as well as mixing frequency band carrier within the same cabinet.

Another requirement is that the SDCCH provisioning can only be done in the outer-zone. The number of SDCCH required in a dualband cell would follow the same BSS planning guide.

7.3. Zone Definition In order to clearly define the partition between inner-zone and outer-zone as illustrated in Figure 7-3, a number of BSS parameters are available.

Parameter Rxlevel_ul_zone and Rxlevel_dl_zone are receive level threshold reported by the mobile that need to be met to perform inter-zone handover. Those parameters are for uplink and downlink respectively.

Another parameter is zone_ho_hyst, which is to sphandover to inner-zone will takeproperly covered in the inner-zinner and outer-zone.

Fpm

Although there is no restrictionzone, the most common impleGSM900 frequency band and band. The requirement to pucoming from the design point ozone only. Therefore, single compatibility with GSM900 singstill able to be get BCCH inform

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RxLevel

Distance

RxLevel_xx_zone

Zone_ho_hyst

Inner zone

Outer Zone

ecify the margin that needs to be met before the place. This parameter is to ensure that mobile is

one and preventing ping-pong handover between

igure 7-3. Outer and inner-zone definition using BSS arameters. Red line represent receive level reported by the obile against distance

on the frequency type should be used for each mentation is that the outer-zone is assigned with inner-zone is assigned with GSM1800 frequency t GSM1900 frequency band in the outer-zone f view where BCCH is broadcasting in the outer-BCCH feature is able to maintain backward

le band mobile that can not access inner-zone but ation.

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M 7.4. Dualband Offset

In Motorola implementation of Single BCCH feature, a new factor, which has major role for the successful implementation is dualband offset. In BSS database parameter, it is defined as dual_band_offset.

Dualband offset is simply the delta of power level measured by mobile when comparing signal strength between outer-zone with inner-zone in the same cell. As described in 3.2 Radio Wave Propagation that each frequency band has its own propagation characteristic ranging from the actual frequency used, up to penetration loss, fading, and antenna heights. In order to summarise all different characteristics between frequency bands, then dualband offset will be used by the BSS software as the single source to identify all RF propagation property differences.

As a mathematical formula, the dualband offset is defined as:

Dual_band_offset = ∆power + ∆propagation

Where:

∆power Difference of loss of transmit power loss between radio unit and on top of cabinet.

= outerzone power loss – innerzone power loss

∆Propagation Difference of propagation loss over the air

As mentioned earlier that dualband offset is playing major role for successful of single BCCH feature implementation in the network. This means it is very important that dualband offset is set to the right value based on the current RF propagation profile where the cell is providing coverage.

Ideally, the dualband offset should be calculated for each cell prior the single BCCH implementation, but due to network and database optimisation management this may not suitable. One alternative is the cluster the cells into groups profiles. The group profile is defined based on the cell geographic coverage, for example, cells covering rural area and cells covering urban area. By taking measurement report sample from each group profile, the dualband offset can be derived for each group profile. The measurement report sample should come from the cell that represents the mean population on that particular group profile.

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Figure 7-4. CTP Screenshot which represent the receive level of GSM900 and GSM1800 colocated cell. The difference of this receive level is effectively dualband offset

Dualband offset can be considered as the cost for a cell to go to inner-zone. The higher the dualband offset the higher the cost for that cell. As it is derived from the inner-zone criteria, dualband offset will increase the threshold for a call to go to inner-zone or make it harder for a call to get into inner-zone. From the cell coverage point of view, this would mean the inner-zone coverage becomes virtually smaller.

In the case of where the dualband offset is set for each specific cell coverage profile, then the cost for a cell on that particular cell within a profile is still the same. For example the dualband offset for a specific cell coverage profile is derived from average of all cell within that profile, the more actual dualband offset deviates from the average dualband offset in that profile the higher probability for the mobile experiencing ping-pong handover between zones.

In a typical implementation where inner-zone is configured to use GSM1800 frequency band and outer-zone is configured to use GSM900 frequency band, then value of dualband offset should be negative.

Further optimisation procedure to identify dualband offset will be discussed later in later section.

7.5. Criteria for Inner-zone Usage A set of criteria is required to identify when the mobile in dedicated mode is required change the serving zone or stay in the same zone within a dualband cell. This set of criteria is based on both uplink and downlink receive level.

Before taking any decision according to the criteria to perform inter zone handover, for each call, the BSS will perform a simple calculation based on the received level while on outer-zone in order to estimate the receive level once the call is inner-zone. This is done with the help of dualband offset. Once this value is calculated then it will be compared with the criteria to enter inner-zone.

The mathematical representation to estimate the receive level in the inner-zone based on outer-zone receive level is:

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M RxLevelinner_zone = RxLeveloutter_zone + dualband_offset

Where

RxLevelinner_zone Estimated receive level in the inner-zone

RxLeveloutter_zone Measured received level in the outer-zone

In order to enter inner-zone, the RxLevelinner_zone should passed both uplink and downlink criteria, which are:

RxLevel_DLinner_zone > RXLEV_DL_ZONE + ZONE_HO_HYST + (BS_TXPWR –

BTS_TXPWR_MAX_INNER)

AND

RxLevel_ULinner_zone > RXLEV_UL_ZONE + ZONE_HO_HYST + (MS_TXPWR – MIN(MS_TXPWR_MAX_INNER, P))

Where

RxLevel_DLinner_zone RxLevelinner_zone on the downlink direction

RxLevel_ULinner_zone RxLevelinner_zone on the uplink direction

RXLEV_UL_ZONE As described in 7.3 Zone Definition

RXLEV_DL_ZONE As described in 7.3 Zone Definition

ZONE_HO_HYST As described in 7.3 Zone Definition

BS_TXPWR Base station transmit power

BTS_TXPWR_MAX_INNER Maximum base station transmit allowed in the inner-zone

MS_TXPWR Mobile transmit power

MS_TXPWR_MAX_INNER Maximum mobile transmit power allowed in the inner-zone

P Maximum transmit power capability of the MS in the inner-zone frequency band as described in Table 2-1

From the criteria definition above, as the transmit power in the BTS defined separately for each frequency band, then there is a requirement to have separate maximum transmit power allowed in the BTS on each zone. Bts_txpwr_max_inner and ms_txpwr_max_inner are BSS database parameters to configure maximum allowed transmit power for base station and mobile respectively. To configure the maximum transmit power for mobile as well as base station in the outer-zone, the existing BSS database parameters are used. Another transmit power related BSS database parameter is tx_pwer_cap, which specifies all cells within a site to be either low transmitting power capable or high transmitting power capable. In a dualband cell, this parameter should be set to 1.

Once the call is in inner-zone, then BSS continuously monitor the reported receive level. If the receive level is below the criteria then the call should be moved out from inner-zone. In contrast with criteria to enter inner-zone, to exit to outer-zone it only need to qualify one of the criteria, either downlink or uplink.

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M The criteria for moving call out from inner-zone depend on the availability of power control on uplink or downlink direction. Following are criteria matrix based on uplink and downlink direction as well as the power control availability. Note that the grey area in the matrix means it’s not applicable.

Downlink Uplink

ON RXLEV_DL < RXLEV_DL_ZONE

AND

BS_TXPWR = BS_TXPWR_MAX_INNER)

BTS power control

OFF RXLEV_DL < RXLEV_DL_ZONE

Not available

ON RXLEV_UL < RXLEV_UL_ZONE

AND

MS_TXPWR = MIN(MS_TXPWR_MAX_INNER,P))

MS power control

OFF

Not available

RXLEV_UL < RXLEV_UL_ZONE

Where

RXLEV_DL Reported downlink receive level while in the inner-zone

RXLEV_UL Reported uplink receive level while in the inner-zone

RXLEV_UL_ZONE As described in 7.3 Zone Definition

RXLEV_DL_ZONE As described in 7.3 Zone Definition

ZONE_HO_HYST As described in 7.3 Zone Definition

BS_TXPWR Base station transmit power

BTS_TXPWR_MAX_INNER Maximum base station transmit allowed in the inner-zone

MS_TXPWR Mobile transmit power

MS_TXPWR_MAX_INNER Maximum mobile transmit power allowed in the inner-zone

P Maximum transmit power capability of the MS in the inner-zone frequency band as described in Table 2-1

When one of the criteria to exit inner-zone has been met, for either uplink or downlink then BSS will evaluate the power budget value for each reported

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M neighbour. If the power budget value is higher than the handover margin for that particular neighbour then the mobile will be instructed performing inter cell handover to the qualified neighbour. Otherwise, move BSS will move the call to the outer-zone.

The reason with this arrangement is to increase the probability of keeping the call in the preferred band by an attempt to perform handover from inner-zone directly to inner-zone of a qualified neighbour once the inner-zone criteria are met. When all these arrangements are not possible then the only way to exit inner-zone is the outer-zone of the serving cell.

7.6. Advanced Load Management in Dualband Cell Advanced load management behaviour will be slightly different when it is implemented in a dualband cell, but the main objective of advanced load management is still the same, which is trying move and to keep the call as long as possible in the preferred band. This change of behaviour is mainly presented in band_preference_mode BSS database parameter.

7.6.1. Band_preference_mode=0 As described in 5.2.6.1, when band_preference_mode=0 the BSS will perform a handover to the strongest neighbouring cell irrespective frequency band of the target cell. This effectively will not take into account band preference settings.

In dualband cell after accessing SDCCH, the call will be assigned to the outer-zone and band_preference setting is ignored. If the criteria are met, then the call can enter to inner-zone. In the event of inter-cell handover is required for normal radio reasons, then BSS will try to handover the call to best neighbour candidate regardless the frequency band used by neighbour candidate.

7.6.2. Band_preference_mode=1 As described in 5.2.6.2, when band_preference_mode=1 the BSS will be assigned the call to the strongest neighbour cell in the preferred band during the SDCCH to TCH assignment.

In dualband cell, at the time of SDCCH assignment, the BSS will attempt to assign TCH according this order of priority to:

1. Inner-zone of the serving cell, once the inner-zone criteria are met.

2. The strongest neighbouring cell where the BCCH is in the preferred band

3. Neighbouring dualband cell with the available TCH is in the preferred band

4. Outer-zone of the serving cell

This priority arrangement will benefit the implementation where single BCCH is not deployed throughout the network; instead, it is deployed into a certain area, during trial for example. Again, this will enable to met the main objective advanced load management, which to move and keep the mobile in the preferred band as long as possible.

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M 7.6.3. Band_preference_mode=2

As described in 5.2.6.3, band_preference_mode=2 means that the BSS attempts to assign mobile to the preferred frequency band when a handover is required for normal radio resource reasons or congestion relief reasons. The BSS places preferred band neighbours ahead of non-preferred band neighbours.

In dualband cell, this setting will not affect during SDCCH to TCH assignment, so the TCH assignment will go to outer-zone. After the assignment, if the criteria to enter inner-zone are met, then the call will be moved to inner-zone.

When inter cell handover is required cased by normal radio resource or traffic control the BSS will attempt to assign TCH according this order of priority to:

1. The strongest neighbouring cell where the BCCH is in the preferred band

2. Neighbouring dualband cell with the TCH is in the preferred band

When a Single BCCH cell configured with band_preference_mode=2, there is a possibility that a call successfully assigned directly to inner-zone, although according to band_preference_mode=2 definition, direct TCH assignment to inner-zone is not allowed. This is due to fact that the time BSS will assign a TCH for a mobile, the outer zone was momentarily congested and there is a free TCH in the outer zone. Rather than dropping the TCH assignment request because there was no resource available in outer-zone, it is better to save this TCH assignment request with a resource from inner-zone. This direct TCH assignment in inner zone will happen as long as inner-zone resource is available and inner-zone entry criteria are met to ensure the call is in good RF condition.

7.6.4. Band_preference_mode=3 As described in 5.2.6.4, band_preference_mode=3 means it is a combination of band_preference_mode=1 and 2.

In dualband cell, this means also combination of band_preference_mode=1 and 2 working in dualband cell.

7.6.5. Band_preference_mode=4 As described in 5.2.6.5, band_preference_mode=4 means that the BSS will enter to monitor mode of attempting to move the call into the preferred frequency band immediately after the call have been assigned to a TCH.

In the dualband cell, this setting will not affect during the SDCCH to TCH assignment and the TCH assignment will go to outer-zone. After that, the BSS will enter to a mode trying to handover a call to a cell where the BCCH is in the preferred band or preferred resource in the non-preferred band BCCH. This mode will stop if the mobile met the inner-zone criteria and moved to inner-zone.

7.6.6. Band_preference_mode=5 As described in 5.2.6.6, band_preference_mode=5 means it is a combination of band_preference_mode=1 and 2 and 4.

In dualband cell, this means also combination of band_preference_mode=1 and 2 and 4 working in dualband cell.

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M 7.6.7. Band_preference_mode=6

As described in 5.2.6.6, band_preference_mode=6 means that band reasignment is trigerred by congestion.

In dualband cell, this means the usage of inner-zone will follow the behaviour described in band_preference_mode=1, 2, and 4 but trigerred only by congestion in the serving cell.

7.7. Optional Criteria for Entering Inner-zone There is also another criteria which can be configured optionally in order for a call to qualify to enter inner-zone. The BSS database parameter to configure this optional criteria is outer_zone_usage_level. This parameter will regulate the handover to inner-zone to occur only when the timeslot usage level in the outer-zone already pass the threshold defined by outer_zone_usage_level. If the TCH usage level is below this threshold, no handover to inner-zone will be performed although the call met the criteria to enter inner-zone.

The usage level of timeslot in inner-zone is ranging from 0 to 100%. When set to 0 (default), means that the handover to inner-zone will always be performed regardless the outer-zone usage level and the inner-zone criteria are met.

7.8. TCH Assignment Delay During SDCCH access the mobile also sending measurement report to the BSS, which enable the direct TCH assignment to the inner-zone. Due to various implementation and internal processing within the mobile, first couple of measurement report sent during SDCCH access is not valid. Means that the measrument report do not qualify to be use by BSS, because there are some missing information elements in the measurement report, such as neighbours frequency and its BSIC or the number of valid neighbour cell measurement. This would cause a high rate of unsuccessfull direct SDCCH to TCH assignment.

To cope with this issue, BSS provides an database parameter that will instruct the BSS to delay the direct TCH assignment, until BSS have enough number of valid measurements to define whether the call is qualified to enter inner-zone or not. This database parameter is called sdcch_tch_band_reassign_delay.

The maximum number of valid measurement report allowed for BSS to delay direct TCH assignment is 4. As the measurement report will reported to the BSS every 480msec, means that the maximum delay for the BSS to delay direct TCH assigment is 2 seconds.

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Figure 5. Dramatic volume increase direct TCH assignment to inner-zone for each sddch_tch_band_reassign_delay parameter setting within a Single BCCH trial area.

Figure 5 above ilustrates the performance of different TCH assignment delay for each possible setting of sdcch_tch_band_reassign_delay. There is a dramatic increase in the volume of direct TCH assignment in inner zone for each of setting value. When the parameter set to 0 direct TCH assignment volume to inner zone relative very low and can go up significantly high when the parameter set to 4 (2 seconds). Direct TCH assignment to inner zone volume is counted by ZONE_CHANGE_SUC[tch_assign_inner_zone] statistics

The impact of this parameter is the SDCCH holding time will increase maximum equivalent to the settings of this parameter, but the benefit of this settings is to guarantee a very high successful rate for direct TCH assigment and leaving the only reason for the mobile is not able to enter inner-zone because is not meeting the inner-zone criteria.

TCH assignment delay will only affect to the band_preference_mode settings where it involve direct SDCCH TCH assigment, which are band_preference_mode=1, 3, and 5.

7.9. Power Budget Calculation When power budget calculation is performed either when the call on outer-zone or inner-zone, it has to be calculated based on the received level of the outer-zone. This is due to the fact that power budget equation is essentially comparing the serving cell signal strength and the BCCH signal strength of the neighbouring cell, where the power level definition between serving cell and neighbouring cell are within the same frequency band.

When the call is in inner-zone, with different frequency band, then there should be a way that current receive level reported is based on the same power level definition as in neighbour BCCH cell and properly derive power budget value. With the help of dualband offset, a parameter called pbgt_mode is used to determined how the receive level should be considered in the power budget calculation while the call is inner-zone.

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M There are two settings available, which are:

• Pbgt_mode=0. When the call is in outer-zone, then there is nothing change in serving cell downlink receive level measurement report. When the call is in inner-zone, the serving cell receive level reported in the measurement report is actually the receive level of inner-zone that have been compensated with the dualband offset value. Or in other words, the serving cell downlink receive level is an estimation based on downlink receive level in inner-zone and dualband offset.

Mathematically this would be: RxLeveldownlink(estimated) = RxLevelinner_zone - dualband_offset

The value of RxLeveldownlink(estimated) then will be used in the power budget formula for each of the neighbour in the dualband cell, which is:

Figure 7-6. TEMS window snapshot, representing the measurement report using the pbgt_mode=0. The RxLevel reported by serving Cell-1300 is an estimation of RxLevel in outer-zone based on inner-zone RxLevel and dualband offset.

PBGT(n) = (Min(MS_TXPWR_MAX, P) – RxLeveldownlink(estimated) – PWR_CD) – (Min(MS_TXPWR_MAX(n), P) – RXLEV_NCELL(n))

Where:

PBGT(n) Power budget value for neighbour n

MS_TXPWR_MAX Maximum mobile transmit power allowed

MS_TXPWR_MAX(n) MS_TXPWR_MAX of neighbour n

RxLeveldownlink(estimated) RxLevel Inner-zone - dualband_offset

PWR_CD Maximum downlink power permitted in the outer-zone minus the BTS actual downlink power

RXLEV_NCELL(n) Receive level of neighbour n

P Maximum transmit power capability of the MS in the inner-zone frequency band as described in Table 2-1

• Pbgt_mode=1. When the call is in outer-zone, then there is nothing change in serving cell downlink receive level measurement report. When the call is in inner-zone, the serving cell downlink receive level reported in the measurement report is the actual downlink receive level in the inner-zone. The neighbour list will be added automatically with the its own serving cell,

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M which then BCCH signal strength will be reported in the neighbour list. This way the measurement report will report both inner-zone and outer-zone receive levels. This automatic addition of itself as a neighbour will reduce the number of neighbour can be configured in a cell to maximum 31.

The pbgt_mode parameter value also determines how the dualband offset value will be used by BSS software.

In pbgt_mode=0, once the call is in inner-zone, dualband offset will be used constantly to determine estimation of downlink receive level in the outer-zone.

While in pbgt_mode=1, the dualband offset will only be used once, that is when calculating the criteria to enter inner-zone as described in 7.5. Once the call is in inner-zone, the dualband offset will not be used anymore because the BSS already have both receive level of inner-zone and outer-zone within the same measurement report. This will provide better information for decision to exit inner-zone, because the inner-zone receive level is the actual measurement reported by the mobile.

Figure 7-7. TEMS window snapshot while pbgt_mode=1. Note that the reported receive level in the serving cell is the receive level of the inner zone. To identify the ARFCN of the inner-zone, it is available in other window in TEMS application

7.10. Ping-pong Handover Prevention between Zones Mobile Measured

Signal StrengthPeak: Mobile in GSM900

Bottom: Mobile in GSM1800

20-25dB

Very high offset

between GSM900 & GSM1800

time

Normally 6-10dB

Predicted GSM1800

signal level

Mobile Measured Signal Strength

Peak: Mobile in GSM900

Bottom: Mobile in GSM1800

20-25dB

Very high offset

between GSM900 & GSM1800

time

Normally 6-10dB

Predicted GSM1800

signal level

Figure 8. Illustration from real network measurement on a scenario where ping-pong handover between zones in a Single BCCH cell can occur

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The illustration above is derived from a real network experience. This scenario happened where the receive level in the outer zone (GSM900) is significantly high compared to inner-zone (GSM1800) within the same cell. When the call is in outer-zone, based on the single BCCH algorithm, this call is eligible to enter inner-zone based on the estimation of inner zone receive level provided in dual_band_offset parameter and inner zone entry criteria.

But unfortunately after the call moved to inner zone, the actual receive level is way below the estimation, therefore the call is moving back to outer zone. At the outer zone, the same process described in above paragraph is repeating. Such repetitive handover between inner and outer zone is also known as ping-pong handover in a Single BCCH cell. In the scenario above, the time spent in each zone during ping-pong is very short and significantly degrades the voice quality of that call. From BSS point of view, such ping-pong handover represents a very inefficient resource usage.

The root causes of such ping-pong handover in a Single BCCH cell are:

• Antenna parameter settings. Single BCCH feature is designed around the assumption where the outer zone and inner zone effective coverage footprint are more less the same and inner-zone radiated power level is uniformly less then the outer-zone radiated power level as defined in dualband offset. Antenna settings such antenna configuration, heights, alignment, bore angle, tilts, etc. can be optimised to achieve the assumptions above.

• RF propagation nature difference between GSM900 and GSM1800. This is especially applicable in fringe cell coverage or indoor coverage.

• In some networks, this is due to usage of wideband repeaters by the network operator or their competitor.

Even when those root causes have been properly addressed and the Single BCCH cell coverage has been properly optimised, there is still a possibility of high receive level difference between outer an inner zone. Such possibility will lead to as increase volume of ping-pong handover in the network. Therefore it is necessary to enhance Single BCCH feature to identify and prevent such ping-pong handover scenario.

Following are the list of BSS parameters to control the behaviour:

• zone_pingpong_count: how many times zone ping-pong handover is allowed during zone_pingpong_enable_win. Value range: 1-255, default value: 3

• zone_pingpong_enable_win: how long time zone ping-pong handover can be done continuously. Value range: 1-255 seconds, default value: 30

• zone_pingpong_disable_win: how long time zone ping-pong handover is not allowed after ping-pong handover has happened "zone_pingpong_count" times during "zone_pingpong_enable_win". Value range: 1-255 seconds, default value:30

• zone_pingpong_preferred_zone: which zone is preferred as a hop target zone. Value range: 0 (outer zone), 1 (inner zone), else (non-preferred zone). Default: 255

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M Note that the new commands introduced in this enhancement are BSC level commands.

Special Notes In the current GSR6 Horizon-II BSS software, these new commands are not supported yet by the Datagen or OMC GUI as this is still in its early stage of deployment. Therefore currently it is not possible to store the preferred value for these parameters to be saved in OMC or Datagen. When the BSS software version is modified or BSS reset, these parameters will return to the default values. So it is necessary to modify these values again via MMI commands. Further announcement will be made with regard to support for Datagen and OMC-GUI.

In order to use the new commands, they are still stored as global variable in BSS software with its native names (_bss_data[x]) as presented below:

• zone_pingpong_count _bss_data[5]

• zone_pingpong_enable_win _bss_data[6]

• zone_pingpong_disable_win _bss_data[7]

• zone_pingpong_preferred_zone _bss_data[8]

To modify the parameters above, the chg_ele and disp_ele commands can be used for example:

Disp_ele _bss_data,5 0

To display the zone_pingpong_count value at the given BSS

Chg_ele _bss_data,6 40 0

To change the zone_pingpong_enable_win value to 40 seconds at the given BSS

Starting BSS Software GSR6 Horizon 2 version, Single BCCH feature has been enhanced to prevent ping-pong handover scenario. Essentially the enhancement is defined as:

1. IF

The number of inter-zone handover (regardless the direction) exceeds the number set in zone_pingpong_count AND within the period of time set in zone_pingpong_enable_win

THEN

Start the zone_pingpong_disable_win timer; Cancel further zone handover by forcing to stay in the preferred zone set in the zone_pingpong_preferred_zone until Rule-2 below is satisfied.

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2. IF

The zone handover disable timer set in zone_pingpong_disable_win is expired

THEN

Further zone handover is allowed until Rule-1.

7.11. Single BCCH Related Statistics Following are the list of statistics used to monitor the single BCCH feature performance. As mentioned earlier that single BCCH is derived from concentric cell feature, therefore the statistics are actually reusing concentric cell statistics.

7.11.1. TCH_USAGE_INNER _ZONE This statistics tracks the usage of TCHs in inner-zone. TCH_USAGE statistics will be available to track the usage of TCH in outer-zone.

7.11.2. TCH_CONG_INNER_ZONE This statistics tracks the total length of time where all of the TCHs in the inner-zone are busy. TCH_CONG will be available to measure the total length of time where all of the TCHs in the outer-zone.

7.11.3. ZONE_CHANGE_ATMPT This bin array statistics records the number of zone change attempt. Pegging to each bin will depend to the zone change scenario as decribed below

Bin Name Descriptions 0 INNER_TO_OUTER_ZONE Number of handover attempt from

inner to outer-zone

1 OUTER_TO_INNER_ZONE Number of handover attempt from outer to inner-zone

2 INTRA_ZONE Number of handover attempt within the same zone

3 TCH_ASSIGN_TO_INNER_ZONE Number of handover attempt from SDCCH directly to inner-zone

4 IN_INTER_CELL_HO_TO_IN_ZONE Number of handover attempt of inter cell handover directly to inner-zone

7.11.4. ZONE_CHANGE_SUC This bin array statistics records the number of successfull zone change. Pegging to each bin will depend to the zone change scenario as decribed below, which exactly the same bin arrangement as above

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M Bin Name Descriptions

0 INNER_TO_OUTER_ZONE Number of handover attempt from inner to outer-zone

1 OUTER_TO_INNER_ZONE Number of handover attempt from outer to inner-zone

2 INTRA_ZONE Number of handover attempt within the same zone

3 TCH_ASSIGN_TO_INNER_ZONE Number of handover attempt from SDCCH directly to inner-zone

4 IN_INTER_CELL_HO_TO_IN_ZONE Number of handover attempt of inter cell handover directly to inner-zone

7.11.5. ALLOC_TCH_INNER_Z There are some new BSS statistics added into BS software, primarily added to BSS software GSR6 Horizon2. These new additions aimed to help network operator calculating the exact TCH blocking rate specifically for inner zone. The impact of these new statistics to Key Performance Metrics will be discussed in the next section

Starting with this one, ALLOC_TCH_INNER_Z, that counts the number of TCH allocation attempts only in inner-zone. The existing ALLOC_TCH statistics will continue to peg every TCH allocation attempts made in the cell regardless the zone definition. To calculate outer-zone TCH allocation attempts, subtract the ALLOC_TCH_INNER_Z from ALLOC_TCH.

7.11.6. ALLOC_TCH_FAIL_INNER_Z This new BSS statistics counts the number of TCH allocation failure only in inner-zone. The existing ALLOC_TCH_FAIL statistics will continue to peg every TCH allocation failure occurred in the cell regardless the zone definition. To calculate outer-zone TCH allocation failures, subtract the ALLOC_TCH_FAIL_INNER_Z from ALLOC_TCH_FAIL.

7.11.7. TCH_Q_REMOVED TCH_Q_REMOVED statistics has been enhanced by adding two bins. Following are the descriptions of all bins within this enhanced statistics

Bin Name Descriptions 0 ASSIGN_RES_REQ This existing statistic bin continues to

count the number of times an assignment request is successfully serviced after being initially queued due to lack of resources, regardless of the zone definition. To calculate the outer zone portion, subtract ASSIGN_RES_REQ_INNER_Z from ASSIGN_RES_REQ

1 HO_REQ This existing statistic bin continues to count the number of times an incoming handover request is successfully serviced after being initially queued due to lack of

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M resources, regardless of the zone definition. To calculate the outer zone portion, subtract HO_REQ_INNER_Z from HO_REQ

2 ASSIGN_RES_REQ_INNER_Z New statistics bin. This stats bin counts the number of times an assignment request is successfully serviced for the inner zone, after being initially queued due to lack of resources.

3 HO_REQ_INNER_Z New statistics bin. Number of handover attempt from SDCCH directly to inner-zone

7.12. Impact of Single BCCH to Key Performance Metric The impact, which will be described here, is most likely in the case where the current multiband network is upgraded to enable the single BCCH feature. It is unlikely the impact will be visible on the network where single BCH feature is deployed from day one together with the early implementation of the network. The description focused here is relevant to the conventional multiband network upgrading to network with Single BCCH. When upgrading the current conventional multiband network to a network with single BCCH enabled, Key Performance Metric will be the main indicator to evaluate and compare the performance before and after the single BCCH implementation.

Enabling single BCCH in the network means to combine co-located GSM900 and GSM1800 cells that provide the same coverage area into one cell. When combining cells to one, several key performance metrics should be revisited in order to maintain objective assessment to network performance before and after single BCCH implementation. This is due to limitation in the performance metric formula as described below.

7.12.1. Cell Level Drop Call Rate The formula below is used to determine cell level drop call rate:

The denominator of the formula counts the number of overall successful call in a cell, which consist of:

100

]BSS_HO_SUC[IN_INTRA_ ]BSS_HO_SUC[IN_INTER_

EARED]_BSS_HO_CL[OUT_INTER STMS]_BSS_HO_LO[OUT_INTRA

S]L_HO_LOSTM[INTRA_CEL

X

SS_HOIN_INTRA_BSS_HOIN_INTER_BSTOTAL_CALL

BSS_HOOUT_INTER_BSS_HOOUT_INTRA_

_HOINTRA_CELLTCHRF_LOSSES_

++

+

++

1. Call origination (TOTAL_CALLS)

2. Incoming handover from other BSC (IN_INTER_BSS_HO_SUC)

3. Incoming handover within the BSC (IN_INTRA_BSS_HO_SUC)

Before the co-located GSM900 and GSM1800 cells are combined by single BCCH, each of these cells has its own statistics to make the denominator of

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M formula above. This would also mean that the successful handover between collocated GSM900 and GSM1800 cell providing the same coverage area would be pegged in IN_INTRA_BSS_SUC. After Single BCCH implemented in that collocated GSM900 and GSM1800 cells, then the original handover between collocated cells turns into inter-zone handover within a dualband cell, which is pegged in ZONE_CHANGE_SUC.

Assume that during conversion there is no frequency change assigned to the collocated cells, then it is possible to assume the number of actual drop (counted in the numerator in the formula above) is more less the same. Looking at the denominator, it is decreasing considerably in quantity because the amount IN_INTRA_BSS_HO_SUC is decreasing due to the fact where some of the original inter cell successful handover is now pegged as successful inter zone handover.

To cope with this change after single BCCH is implemented, naturally, it is possible to alter the cell level drop call formula to cater this change by including successful inter-zone handover into the denominator, but there is disadvantage to modify such formula. This is because to differentiate cell level drop call formula for dualband cell and for conventional multiband cell will increase the management cost in optimisation as well as deriving performance metric from the network.

Moreover, cell level drop call rate is only suitable for one cell and not suitable to use it in a group of cells. From statistical point of view, single BCCH means to group two cells into one. For a group of cells, the correct formula should be used is the BSS level drop call rate, where it does not take into account the successful handovers occurred within the group. The disadvantage using BSS level drop call rate in a dualband cell is that the formula is to wide and to general for a group of only two cells.

The recommended alternative to assess and compare cell level performance after single BCCH implemented is to use Mean Time Between Drop, where the formula is written below:

Mean Time Between Drop Formula provides flexibility to provide performance metric independent to the number of cells grouped together, even for one cell only.

AREDBSS_HO_CLEOUT_INTER_ T_MSBSS_HO_LOSOUT_INTRA_ S_HO_LOST_MINTRA_CELL TCHRF_LOSSES_

_TCH_MEANBUSY

+

++

)length(sec_interval_StatisticsX

7.12.2. TCH RF Loss Rate TCH RF loss rate formula defined as:

]BSS_HO_SUC[IN_INTRA_SS_HOIN_INTRA_B

ON_REDIRECTIASSIGNMENTSTOTAL_CALLSTCH_RF_LOS

++

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M This formula also needs to be revisited when comparing the cell performance before and after single BCCH is implemented. This is due to the same fact where single BCCH is grouping two cells to one, which resulting that the quantity of IN_INTRA_BSS_HO_SUC reduced considerably as the original successful collocated inter cell handover is now pegged in ZONE_CHANGE_SUC statistics.

7.12.3. TCH Blocking Rate With the introduction of new BSS statistics as discussed in section 7.11, the TCH Blocking key statistics formulas have been adapted. Following are the new definition of TCH blocking rate formulas

7.12.3.1. TCH Blocking Rate Combined This key statistic formula is valid for both Single BCCH cell and non-SBCCH cell. Note that for SBCCH cells, the TCH blocking rate may appear to be inflated if there is traffic continuing (on timer expiry) to try access a congested inner zone. This is normal system operation to try to maximise the inner zone traffic where RF conditions are appropriate.

100%

]VED[ho_reqTCH_Q_REMO - rce_req]ment_resouVED[assignTCH_Q_REMO

- H_FAIL ALLOC_TC ALLOC_TCH]VED[ho_reqTCH_Q_REMO

- rce_req]ment_resouVED[assignTCH_Q_REMO - FAILALLOC_TCH_

RATE

NG_TCH_BLOCKI×

⎟⎟⎟

⎜⎜⎜

⎛ +

⎟⎟⎟

⎜⎜⎜

=

7.12.3.2. TCH Blocking Rate for Inner-zone Only

100%

_inner_z]VED[ho_reqTCH_Q_REMO- ner_z]rce_req_inment_resouVED[assignTCH_Q_REMO

- ER_ZH_FAIL_INN ALLOC_TC INNER_ZALLOC_TCH__inner_z]VED[ho_reqTCH_Q_REMO

- ner_z]rce_req_inment_resouVED[assignTCH_Q_REMO - _ZFAIL_INNERALLOC_TCH_

_ZRATE_INNERNGTCH_BLOCKI

×

⎟⎟⎟

⎜⎜⎜

⎛ +

⎟⎟⎟

⎜⎜⎜

=

7.12.3.3. TCH Blocking Rate for Outer-zone Only

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M

( )

( )

100%

_inner_z]VED[ho_reqTCH_Q_REMO - ]VED[ho_reqTCH_Q_REMO

- ner_z]rce_req_inment_resouVED[assugnTCH_Q_REMO

- rce_req]ment_resouVED[assignTCH_Q_REMO

- _ZFAIL_INNERALLOC_TCH_

- FAILALLOC_TCH_

INNER_ZALLOC_TCH_ - ALLOC_TCH

_inner_z]VED[ho_reqTCH_Q_REMO - ]VED[ho_reqTCH_Q_REMO

- ner_z]rce_req_inment_resouVED[assugnTCH_Q_REMO

- rce_req]ment_resouVED[assignTCH_Q_REMO

- _ZFAIL_INNERALLOC_TCH_

- FAILALLOC_TCH_

_ZRATE_OUTER

NG_TCH_BLOCKI×

⎟⎟⎟⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜⎜⎜⎜

⎟⎟⎠

⎞⎜⎜⎝

⎟⎟⎠

⎞⎜⎜⎝

⎛+⎟⎟

⎞⎜⎜⎝

⎟⎟⎟⎟⎟⎟⎟⎟

⎜⎜⎜⎜⎜⎜⎜⎜

⎟⎟⎠

⎞⎜⎜⎝

⎟⎟⎠

⎞⎜⎜⎝

=

7.13. Single BCCH Interaction with Other Features and Limitations

Following are the list of limitation and single BCCH interaction behaviour when combined with another feature

• It is not possible to combine Single BCCH with coincident multiband handover, which will be described in Chapter 8. This is due to the similar ability of single BCCH and coincident multiband handover to move traffic directly to the preferred band.

• It is not possible to perform frequency hopping between frequency bands. This is to comply with ETSI recommendation. However, it is possible to configure frequency hopping independently within one particular zone or enabling frequency hopping on both zones, as long as the frequency hopping definition does not include frequency hopping between frequency bands.

• SDCCH provisioning can only be done in the outer-zone. When SDCCH available across more than one carrier, then all of the SDCCH timeslots should be on outer-zone.

• GPRS timeslot provisioning can only be done in the outer-zone. When GPRS multi carriers enabled in the cell, then all the GPRS timeslot should be on outer-zone.

• Congestion relief algorithm will only triggered based on the outer-zone TCH usage level. Fully utilised TCH resources in the inner-zone will not trigger congestion relief algorithm.

• When extended range cell feature will only available in outer-zone only. If the mobile is on outer-zone and in extended range, although the criteria to enter inner-zone are met, the call will stay in outer-zone.

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M 7.13.1. Single BCCH and Derived Handover Power Level feature

Derived handover power level feature is introduced in GSR3 as unrestricted feature, when enabled, will command the mobile on inter-cell intra-BSS handover with optimal handover power level.

The optimal handover power level is derived from the path loss calculation with respect of the target cell. The calculation of handover power level is aimed at instructing the mobile to access the target cell at the middle of database defined uplink power control box. When this feature is enabled, the mobile will assume the handover power level as defined is the BSS database parameter.

The benefit of enabling this feature is to:

• promotes mobile’s battery conservation

• reduce uplink interference

• eliminated unnecessary mobile power control after a handover

In order to enable or disable this feature, a switch called use_derived_ho_power is available in the BSS database. Further description on enabling or disabling this feature using BSS database parameter can be found in Motorola Customer Documentation.

This feature is only applicable to inter cell intra BSS handovers. This is due to target cell needing the power level information on the initial downlink SACCH, which then transmitted in the HANDOVER COMMAND message. Another reason that this feature is only applicable to inter cell intra BSS handover is the GSM standard 08.08 does not provide any mean to convey power information to the target cell for an external handover. So for external handovers, the BSS instructs the mobile to use handover power level as defined in BSS database parameter (handover_power_level).

To workout mobile’s handover power level to arrive approximately at the middle of power control box on the target cell, the following formula will be used:

Handover power level = Min (C + (( A + gamma) – B), D, P)

Where:

A Max_tx_bts of the target cell

B RxLevel reported by the mobile for target cell

C Middle of power box, which is defined as

(u_rxlev_ul_p + l_rxlev_ul_p)/2

D Max_tx_ms on the target cell

P Maximum power capability allowed in the mobile

gamma Correction factor represents combined loss between top of cabinet and the actual radiated transmit power right after the antenna. This parameter is calculated internally by BSS software

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M When derived handover power level feature is enabled in Single BCCH cell and the target cell is in inner-zone then the above formula is slightly changes to:

Handover power level =

Min (C + (( A + gamma) – B + Dual_band_offset), D, P)

Where:

A Max_tx_bts of the target cell

B RxLevel reported by the mobile for target cell

C Middle of power box, which is defined as

(u_rxlev_ul_p + l_rxlev_ul_p)/2

D Max_tx_ms on the target cell

P Maximum power capability allowed in the mobile

gamma Correction factor represents combined loss between top of cabinet and the actual radiated transmit power right after the antenna. This parameter is calculated internally by BSS software

Dual_band_offset The dualband offset as discussed in section 7.4

7.14. Dualband Cell Conversion Procedure

Figure 7-9 represents a simplified procedure to convert conventional multiband cell into dualband cell. Some highlights in this conversion procedure is that enabling single BCCH does not require planned outage as well as site visit. This conversion procedure is entirely can be automated in OMC-R through script. This will maintain high availability of the network during single BCCH conversion. An example of conversion script is available in appendix.

Delete neighbourrelation of GSM1800 cell

Un-equip RTF ofGSM1800 cell

Un-equip GSM1800Cell and DRI

Enable dualbandCell feature and adjusthandover parameters

Recalculate SDCCHrequirement

Equip inner zoneDRI and RTF

Figure 7-9 Simplified procedure to convert conventional multiband cell into dualband cell

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M 7.15. Example of Implementation

The example provided here is based on single BCCH trial in one of the typical mature European multiband network, where the number of multiband mobile is very large compared with the number of single band mobile. The trial was performed in two different areas, which represent typical urban coverage and sub-urban coverage. The objective is to identify single BCCH behaviour on a certain land usage.

A number of scenarios were tested during the trial to evaluate traffic movement between zone, traffic movement in the surrounding cell along, as well as comparing cell performance before and after implementation of Single BCCH. Cell performance data were mainly coming from BSS statistics and CTP for detailed per-call analysis. For suburban trial, the scenario tested only to a small number of cells. This is to enable understanding Single BCCH behaviour within a cell, while in urban trial, the scenario tested to a large number of cells in order to understand single BCCH behaviour over a very large area and observe the traffic movement with the microcellular layer.

Table below represent sets of BSS database parameters tested on each scenario. Scenario numbering represents the time order when it was implemented. On scenario 1, all BSS database parameter values are written in the column, while on scenario 2 and scenario 3 written BSS database parameter only the one which have been modified from scenario 1.

PARAMETER NAME SCENARIO 1 - SUBURBAN

SCENARIO 2 - SUBURBAN

SCENARIO 3 - URBAN

band_preference GSM1800 band_preference_mode 4 bts_txpwr_max_inner 1 dual_band_offset -10 ho_pwr_level_inner 2 inner_zone_alg 3 ms_txpwr_max_inner 30 outer_zone_usage_level 0 pbgt_mode 1 rxlev_dl_zone 18 14 14 rxlev_ul_zone 18 10 10 secondary_freq_type 4 zone_ho_hyst 10 5 10

Figure 7-10 Scenarios tested on Single BCCH trial

Scenario 1 considered as moderate setting to move traffic to inner-zone, which is using GSM1800 frequency. In other words, such setting will virtually shrink the GSM1800 coverage footprint, because the criteria to enter inner-zone (using GSM1800) are set considerably high. This will lead to the case where the call that managed to enter inner-zone only the cell that relatively close enough with base station, which is not the optimal inner-zone utilisation.

Scenario 2 considered as aggressive setting to move traffic to inner-zone. This settings enhance the inner-zone coverage footprint, where from drive test results,

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M confirmed the similar footprint before single BCCH is implemented. Note that rxlevel_dl_zone and rxlevel_ul_zone using difference value. This is based on the CTP evaluation where uplink is the limiting factor for the mobile to enter inner-zone. Zone_ho_hyst also changed to make mobile entering inner-zone easier. This reduction has been evaluated through CTP as well as BSS statistics in order to ensure that ping-pong handover between zones will not occur.

Scenario 3 tested in urban area. The value presented here is based on the optimisation experiences gathered from the previous scenarios. Further details on single BCCH optimisation can be found in chapter 9.

Figure 7-11 Traffic carried in Erlang during implementation of Scenario 3 in urban area

In summary, from this trial, single BCCH clearly provides the benefit of reducing the number of neighbour relations in the network. Another one of benefit of single BCCH is increasing the offered traffic, it should be noted that to utilise increased of trunking efficiency, optimisation on single BCCH parameter is mandatory.

Figure 7-11 represent the overall TCH traffic carried in Erlang within a cell in one view before and after implementation. Single BCCH feature was enabled on that cell on 9 November. Cell 14878, 24878 and 34878 are GSM900 and 44878, 54878, and 64878 are GSM1800. As seen on the figure the GSM1800 cell performance data stopped at 9th November as it is combined into its collocated GSM900. This figure shows the increase of traffic in Erlang gained after single BCCH implementation.

Another statistic to represent the TCH blocking performance statistics in a site after enabled with single BCCH. Cell 1947, 2947, and 3947 are GSM900 cell and cell 4947, 5947, 6947 are GSM1800. The conversion took place on 9th November. As seen from the figure, before single BCCH implemented, two GSM1800 cells were suffering a very high TCH blocking. This is due to the situation where GSM1800 resources were fully occupied, and repetitive call

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M initiation as well incoming handover attempt in the cell during peak hours. After single BCCH implemented the overall TCH blocking for the area covered by this cell is reducing dramatically. This represents higher efficiency in resource usage within the cell covering that urban area.

Figure 7-12. TCH blocking reduction after single BCCH implemented

7.16. Summary BSS Database Parameter Following are the list of associated Single BCCH BSS database parameters. Detailed description with regard to setting valid range and default value can be found in Motorola Customer Documentation.

• Bts_txpwr_max_inner. This specifies BTS maximum transmit power for the inner-zone.

• Ms_txpwr_max_inner. This specifies mobile maximum transmit power for the inner-zone.

• Dual_band_offset. This estimates the effect effects of the power level differences that occur when comparing signal strengths from different zones.

• Ho_pwr_level_inner. This specifies the handover power level for the inner-zone

• Inner_zone_alg. This specifies to use single BCCH algorithm

• Outer_zone_usage_level. This specifies the percentage level of outer cell TCH usage before inner-zone TCHs are allocated.

• Pbgt_mode. This specifies the preferred method of compensating for a mismatch in frequency types between the serving channel and the neighbouring cell BCCH when calculating power budget.

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M • Rxlevel_dl_zone. This specifies the downlink receive level threshold that

must be crossed for an assignment to take place between the outer-zone and the inner-zone.

• Rxlevel_ul_zone. This specifies the uplink receive level threshold that must be crossed for an assignment to take place between the inner-zone and the outer-zone.

• Secondary_frequency_type. This specifies the frequency type of the inner-zone frequency band when a cell is configured as a dual band cell.

• Band_preference. This identifies frequency band selected in inner-zone.

• Band_preference_mode. This identifies how the preferred band should be used.

• Zone_ho_hyst. This specifies the margin for the inner-zone handover hysteresis.

• Tx_power_cap. This specifies the transmit power capability of the GSM1800 carriers in dualband cell.

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M 8. Coincident Multiband Handover

This feature is designed to complement the Multiband Inter-cell Handover feature (Advanced Load Management) available at GSR3, and the functionality described here is only available if that feature is enabled.

This feature enables operators to install new radios in a different frequency band and more easily configure multiple frequencies when implementing a new multiband network. One obstacle to this type of upgrade is the investment in time and money already made by the operator in optimising the existing infrastructure. With the addition of a secondary frequency band, with different propagation characteristics in the GSM900 and GSM1800 frequency band, this optimisation effort would have to be repeated.

To avoid this problem of optimising two networks, it is logical that the new secondary frequency band should complement the existing infrastructure. To achieve this, the software must be configurable enough to allow the new frequency band to use the same cell boundaries established by the original frequency band and to allow the new frequency band cells to use the handover measurement reports based on the cells in the original frequency band. This is done by using mobile-reported measurement reports of the primary frequency band, while a call is established on the secondary frequency band. This allows the mobile to be handled as if it were on the primary frequency band, using the primary's boundaries and minimising propagation characteristics differences, whilst not taking any primary frequency band resources. The software redirects the calls capable of operating in the secondary band to the secondary band so that the primary band does not get congested.

The main objectives of this feature are:

• To allow the multiband network operator to configure a cell as a secondary cell which only requires traffic from its coincident primary cell or neighbouring secondary cell?

• Maintain the quality of the primary cell frequency band and only require handover parameters to be configured for one frequency band.

• Simplify roll-out of multiband sites by allowing the operator to configure certain frequency band cells to have the same cell boundaries as a cell using different band.

8.1. Definition of coincident cells and handover execution There are several terms or definition used to defined cells properties in coincident multiband handover feature. Figure 8-1 illustrates these definitions:

• Coincident cell is a cell that has a co-located neighbour cell whose cell boundary follows that of the said cell, but has a different frequency type to that of the neighbour cell. The coincident cell has only one GSM1800 neighbour, which is collocated.

• Primary Cell is a cell (GSM900), which is already optimised in the network and has a co-located neighbour whose cell boundary follows that boundary of the said cell. The primary cell has a preferred band equal to the

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M frequency type of the coincident cell (GSM1800). If no coincident GSM1800 cell exists, then no GSM1800 neighbours are defined.

• Secondary Cell is A cell, which is not optimised and has a co-located neighbour whose cell boundary follows the boundary of the said cell. The secondary cell has a preferred band the same as that of its own frequency type (GSM1800). The co-located GSM1800 cell has all the same GSM900 neighbours, as does the GSM900 cell, in addition to the co-located GSM900 (coincident) cell itself. In addition to the GSM900 cells, the GSM1800 cell may have other GSM1800 neighbours.

GSM900 GSM900 GSM900

GSM1800

Secondary cell

Primary cell

Coincident cells

Cell D

Cell A

Cell B

Cell C

When enabling coincident multiband handover, the neighbour relation within coincident cell as well as neighbouring cells need to be modified. Cell A and Cell B is considered as coincident cell, where cell B is the primary cell and cell A is the primary cell. Cell A and cell B is a neighbour to each other. Cell B and Cell D is a neighbour of each other. Cell C also a neighbour to each other with cell B. Being collocated, cell A provides the same coverage as cell B. The neighbour relation defined in cell A would include cell B, cell C, and cell D.

Based on the objectives and description above, it is easy to identify similarity with single BCCH feature. Following table provides the comparison between two features. Note that the two features cannot be enabled in the network at the same time. When upgrading the conventional multiband network, one of these features should be selected.

Coincident Multiband Handover Single BCCH Requires 2 cells to make up coincident cell

Requires only 1 cell supporting multiband frequency in a cell

BCCH required to broadcast on primary and secondary cell

BCCH required to broadcast only on the primary frequency band

Full backward compatibility for the mobiles where each frequency

Single band mobiles that work only in the secondary frequency band

Figure 8-1. Definition of Coincident cells. The arrows represent the neighbour relation and its direction.

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M band can support single band mobile

cannot be supported.

Figure 8-2. Comparison table between Coincident handover and Single BCCH

Figure 8-3. Implementation of coincident multiband handover

8.1.1. Better cell detection Using Figure 8-3, there are two possible configurations in coincident multiband handover. The first one is called better cell detection.

In this case, Cell A and Cell B are co-located coincident neighbours of each other. Cell B is part of the GSM900 network, while Cell A has been added and is part of the, secondary, GSM1800 network. The figure 3 represents the neighbour relations that Cell A and Cell B have.

Assume that a mobile was using a traffic channel on cell A (GSM1800). The MS would be measuring the strength of Cell B and Cell D (GSM900 - because they are defined in the neighbour database). When Cell A receives the measurement report from the MS, in a coincident cell, the BSS uses the measurement level of Cell B as the downlink measurement, instead of using the downlink receive level of Cell A to make a decision as to whether a handover is needed. This is done because the propagation characteristics of the two cells can vary. The BSS uses the signal strength reports of Cell D from the mobile to determine whether there are any viable candidates for the needed handover (PBGT calculations).

If C (GSM1800) was also a neighbour of A, the downlink receive level of cell A will be used in the serving cell power budget calculations.

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M While comparing against the coincident neighbour E (GSM900) for power budget handover condition, the downlink receive level of cell F is used (GSM1800).

8.1.2. Coincident cell redirection The second possible configuration is called coincident cell redirection.

This is the enhanced functionality of handing over to an unreported neighbour. If the BSS decides that Cell D (GSM900) is a viable candidate for handover for a MS occupying a traffic channel on Cell A (GSM1800), the BSS will detect that Cell C (GSM1800) is a coincident cell of Cell D, and will redirect the handovers to Cell C.

The co-located coincident cells (GSM900 and GSM1800) must be synchronised in order to perform a handover to an unreported neighbour; therefore, the cells must be located at the same site.

For this type of coincident multiband handover, another requirement is that the coincident cells also have to use the same BSIC to have successful communication upon handover. This is not required when the coincident multiband handover is required to use better cell detection algorithm.

The cells must be synchronised because the Handover Command sent to the MS has the cell D (GSM900) cell description (the cell the MS was reporting on in the measurement reports), but the cell C (GSM1800) channel description. If the cells are not synchronised the handover will fail.

The Handover Access burst is encoded using the BSIC of the target cell – cell D (GSM900) and thus cell C must have the same value in order to successfully decode the message.

A BSS database parameter to select the type of coincident multiband handover is called coincident_mb, where coincident_mb=1 defines that better cell detection should be used, while coincident_mb=2 defines that coincident cell redirection should be used. coincident_mb=0 is to disable coincident multiband handover feature.

8.2. Coincident multiband handover settings Another settings that is required in configuring coincident multiband handover feature are:

• Coincident_offset. The BSS will use an additional offset to the power budget equation when the neighbour being used for downlink measurements (GSM900) is not reported. If the mobile is on a TCH on cell A (GSM1800) and downlink measurements for cell B (GSM900) were not being reported, then the serving cell’s measurements would be used in the power budget equation with addition of the offset.

• Low_sig_thres. When a handover condition is present to a neighbour with a coincident preferred band cell, the mobile supports multiple frequency bands and the mobile reported receive level of the target cell is above the threshold defined by this parameter; the BSS will attempt to hand the mobile directly to the coincident preferred band cell. This functionality is only used if coincident_mb is set to 2 and is set in both directions (both cells have to be coincident to each other).

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M The parameter low_sig_thres is equivalent to minimum receive level per neighbour in the redirected handover scenario. Because the BSC does not have access to this parameter of external neighbours, the low_sig_thres is not used for inter-BSC handovers.

Figure 8-4. Snapshot from TEMS showing Coincident MB HO functionality (HO redirection to an unreported neighbour)

8.3. Example of implementation Examples presented here based on a trial performed in a typical European network. This network is a mature network with large subscriber base that can support multi frequency bands. The trial performed on a group of sites covering suburban area, GSM1800 is selected to be the preferred band and band_preference_mode=3 is set on GSM900 cells and band_preference_mode=0 is set on GSM1800 cells

Prior to implementing the Coincident Multiband Handover feature, some preparation work needs to be done, namely setting-up the prerequisites for the feature testing, which are:

• For the second Coincident Multiband Handover functionality (handover to unreported neighbour in secondary band) to work, coincident cells must be synchronised (defined at the same site).

• Coincident cells must also use the same BSIC, to have successful communication upon handover. Due to this requirement, BSIC on the GSM1800 cells included in the test will be changed to that of the coincident GSM900 cells.

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M • Only the co-located coincident GSM1800 cell will be defined as neighbour of

the primary GSM900 cell (neighbour relationships in the same – GSM900 – band will not be modified).

• The secondary GSM1800 cell will have all the same GSM900 neighbours as the primary coincident GSM900 cell as well as the primary cell itself. The same handover parameters will be used as between any two GSM900 neighbour (see BSS parameter list below). No other GSM1800 neighbours with activated Coincident Multiband Handover will be defined for the coincident GSM1800 cell.

• GSM1800 neighbours of the coincident GSM1800 cells outside the test area will not be modified. This is necessary in order to keep MB MS outside the test area on the GSM1800 layer and to avoid unnecessary handovers to the GSM900 layer.

• Because the low_sig_thres is not applicable for inter-BSC handovers, the rxlev_min_ncell parameter will have to be raised to the value of 15 (initially set to 3) for handovers from GSM900 cells outside the test area towards GSM900 cell with coincident GSM1800 cells.

• The initial handover parameters between the coincident GSM900 – GSM1800 cells will stay as defined in the current database, however handover synchronisation will be activated.

Additional parameters considered in this trial are handover parameters. Following table below represent the handover parameter setting used.

Handover

(source- target)

Rxlev_m

in_ncell

Ho_m

argin

Pbgt_hreqave

Pbgt_alg

Cong_ho_m

argin

Ul_rxlev_serv_cell

Dl_rxlev_serv_cell

Qualify_tim

e_thres

Qualify_delay

Ncell_rxlev_thres

900 - 900 3 6 4 1 -3

900 - 1800 3 -63 8 5 0 1 25

1800 - 1800 3 6 8 1 0

1800 - 900 3 -5 6 3 -3 20 20

8.3.1. Scenario 1 The primary challenge in managing traffic in a dualband network is to account for the propagation differences between GSM900 and GSM1800 cells. The BSS must verify that reported neighbour cell signal strength is strong enough for an MS to be immediately redirected to the preferred band (GSM1800).

The trade-off is the following (especially if there is a significant difference in received signal strength between the GSM900 and GSM1800 cells):

If the threshold is chosen low, redirection will occur more easily and the GSM1800 cell will take a lot of traffic. However there is a danger that this will occur in a position, where there is low received signal level and/or high

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M interference and call quality will suffer or hand up to the co-located GSM900 cell will immediately take place.

If the threshold is chosen high, there will be high confidence that the call quality will be good on redirection, however it will happen less frequently and the GSM1800 cell will absorb less traffic.

The parameter low_signal_thres will be varied in an attempt to understand the effect of this parameter as a means to ensure that redirection occurs at a level for which good quality is guaranteed. The following settings were used:

GSM1800 coincident cell, Coincident_offset=0 and

• GSM900 coincident cell, low_signal_thres=35 (test set 1)

• GSM900 coincident cell, low_signal_thres=25 (test set 2)

• GSM900 coincident cell, low_signal_thres=20 (test set 3)

• GSM900 coincident cell, low_signal_thres=15 (test set 4)

• Coincident multiband handover is disabled (test set 5)

Network performance was gathered from CTP data as well as drive test and BSS statistics. In summary, there were no degradation in uplink and downlink receive quality when the multiband coincident handover was enabled in the network as long as the serving cell signal strength is strong enough. The receive quality may vary, but mostly due to day-to-day variance happened in the network, which is quite normal. As far as the measured Rxlev uplink & downlink is concerned, the results correspond to the actual thresholds set on the cells. The higher the threshold, the higher the received Rxlev, as the mobiles are redirected to the GSM1800 layer closer to the cell and are more into the centre of the coverage area.

In the case where low_signal_thres=15 the serving cell signal strength is not strong enough to maintain a good quality connection when the MS qualifies for redirection into the secondary GSM1800 band and there is an increased probability of encountering interference. In addition the assumption of similar received signal levels from different frequency bands (GSM900 & GSM1800) on specific coincident cells was not valid (up to 10 dB of average delta in favour of GSM900), which fact further aggravated the problem.

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M

Figure 8-5. Uplink and downlink performance on scenario 1

8.3.2. Scenario 2 The objective of this test scenario was to study the effect on system behaviour and performance of the parameter coincident_offset. This parameter provides the operator with an option to compensate for the mismatch of frequency types and different path loss, when calculating power budget. This mechanism is used when the MS being on the secondary GSM1800 band is using the serving cell (GSM1800) measurements, because the primary band coincident GSM900 cell is not available.

The parameter settings used for each data set are given below:

• Set 1 – coincident_offset=0 dB

• Set 2 – coincident_offset=6 dB

• Set 3 – coincident_offset=12 dB

• Set 4 – Coincident MB HO feature disabled

The parameter low_sig_thresh was set to 20 (-90 dBm) in all cases.

The effect of this parameter depends on the availability or non-availability of the coincident GSM900 cells largely and varies from cell to cell. The value of 12 dB corresponds also with measurements described earlier in the previous tests. The difference between GSM900 and GSM1800 coincident cells reaches its maximum at lower signal strength levels, where the probability of interference in the GSM900 band is also higher (i.e. the coincident GSM900 cell may not be detected) and here the coincident_offset plays a bigger role.

Although it is more difficult to quantify the impact of this parameter, in order to avoid moving the handover boundaries in case the primary frequency band is not detected. If signal strength measurements indicate after the initial RF planning, that there is a significant difference in level from different frequency bands, further fine tuning will be required to adjust the parameter on cells with higher than average difference.

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Figure 8-6. Uplink and downlink cumulative distribution on scenario 2

The most important aspect of implementation (confirmed by the trial results) is to ensure similar cell boundaries between the coincident cells. The RF planning of the coincident cells needs to be done so that this difference in receive level is minimised on the cell borders, where the hand-ins and hence the redirection to the secondary layer (GSM1800) occurs, rather than across the whole cell coverage area. Due to the different propagation characteristics and RF configuration in different frequency bands, the implications of different level of indoor coverage has to be assessed as well, while designing the parameter settings.

These potential differences in the actual level of coverage in the 900 and 1800 bands can be offset by proper definition of the low_sig_thres parameter. The final threshold can be adjusted to more conservative values (assuming stronger receive level on GSM900 cells), corresponding to the average delta in receive signal strength between the primary and secondary bands. This will lower the impact of different signal levels, thus the actual receive level in the secondary band (GSM1800) will be sufficient to maintain good radio conditions and high quality of service.

The same conclusions apply for the coincident_offset parameter. Trial results indicate that the best performance is reached when setting this parameter slightly higher than the average difference between the coincident cells. The potential difference between coincident cells reaches its maximum at lower signal strength levels (at bigger distance from the site or indoor), where the probability of interference in the GSM900 band is higher and the GSM900 cell's BCCH may not be detected.

It would be highly recommended to carry out a measurement campaign in order to establish the potential average receive signal level difference between coincident cells in various typical RF environments (e.g. inner city, outer districts etc.) before large-scale implementation of the feature. This information would

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M alleviate a great deal the task of finding the right parameter values and could be performed relatively simply by the use of CTP.

8.4. Summary of BSS database parameters Following are the list of associated Single BCCH BSS database parameters. Detailed description with regard to setting valid range and default value can be found in Motorola Customer Documentation.

• Coincident_mb. This to enable the coincident handover and the algorithm should be selected.

• Coincident_offset. This parameter enables and disables the configuration of an additional offset to the ho_margin value between a cell and its coincident cell.

• Low_sig_thres. This parameter specifies parameter specifies the minimum receive level for redirected handovers.

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9.1. Optimising Advanced Load Management Due to the flexibility of the Motorola multiband feature, many possible scenarios can be implemented according to the network requirement, which is hard to list them all in this guideline.

Figure 9-1. Basic handover scenario in a multiband and multilayer environment

What will be outlined in this section can be summarised with Figure 9-1. As the network now can be categorised to have two major layer based in it's frequency band used, the operator may want to have better control over traffic movement between these two layer. In the early day of multiband deployment, the operator may want to fully direct all multiband capable traffic to move to GSM1800 layer. This can be done using the Advance Load Management (ALM). As a way to ensure that the mobiles always have the most efficient uplink and downlink connection, imperative handover algorithm will be used for handover from GSM1800 to GSM900. When the mobile actually suffering a bad quality or low receive level, with this imperative algorithm will try to save this connection by move it to GSM900 layer. Bad quality can be sources from interference or the mobile is on the edge of GSM1800 coverage, where the power level is not sufficient.

Within the same frequency layer in GSM900 or GSM1800, the network may have the macro and a micro layer. Using the same existing algorithm that is already in place, the traffic can be directed to the lower layer (microcell) with the capturing algorithm. When the traffic can no longer survive the lower level because of certain RF conditions, the traffic gets moved to a higher layer, which provides a wider coverage. Again this setting is based on the philosophy that a call should be serviced under the most efficient RF environment and also recommended that the resource to serve it is coming from the layer acting as extra capacity (i.e. GSM1800 and microcell) whenever is possible.

The following paragraph will try to outline some of database parameter that need to be considered when implementing the dualband feature. In the case where band_preference_mode=0, the Advance Load Management capability is disabled. But the system is actually still can perform the multiband handover. All multiband handover occurred in the network will entirely rely on the radio

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M frequency environment within the area. So the operator will have no control or influence over the dualband capable traffic. The database parameter related to this radio frequency environment is:

• Neighbour handover margin. This is defining how attractive the target cell is to be the best candidate for a handover. The lower the value the more attractive the target cell. In a case where within the neighbour list where there is a GSM1800 cell as one of the candidate of handover, in order to make the GSM1800 target more attractive than the other; the neighbour handover margin should be lower. As there is no fixed value of this margin setting, so it is recommended to set the margin originally to 0. And then gradually can be lowered to desired value (possibly a minus value) through optimisation process.

• Neighbours receive level minimum. The parameter determines whether the handover candidate has enough receive level, which is acceptable for the mobile to establish a connection. A very high value in this parameter will result that handover will get harder to take place, and a very low value will make the handover easy, but giving a chance that receive level is to low and causing the call to drop. Recommended value to start up is neighbour receive level minimum set to 10. A suitable setting then can be reached through optimisation process.

When band_preference_mode=1 is chosen as the multiband setting in the network, it should be kept in mind that the setting will cause a delay in the assignment procedure as an inter-cell channel change will be attempted.

In the process to handover at the time of SDCCH to TCH assignment, the BSS expect the mobile to send L3 Measurement Report, and using at least one measurement report, the BSS will determine which is the strongest neighbour in the preferred band for a handover candidate.

Based on the field experience, parameter band_preference_mode=1 is may be dependent to the dualband mobile ability to have L3 Measurement Report sent to the BSS. When SDCCH to TCH assignment to preferred band, then it will be reverted back to the non-preferred band as the dualband band mobile works slightly slow to keep up sending the measurement report during this period.

This performance also has influence where

band_preference_mode=1 is part of combination in other band preference mode (3, 5, and 6).

Figure 9-2. Diagram flowchart of band_preference_mode=2

The simple flowchart displayed here outlines the basic property of how band_preference_mode=2 is working. It should be noted that the band preference mode is coming to action where ordering based on neighbour types is

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M already carried out. So reordering the candidate list based on each frequency band is done before performing the handover, with the preferred band on top of the list. It should also be noted that each candidate list subset is ordered by its power budget value.

The band_preference_mode=3 which is actually a combination of band_preference_mode=1 and 2. Where the network is using this parameter, all consideration about band preference in both types (1 and 2) also applies.

Band_preference_mode=4 is setting the BSS to work in a way that it will always constantly monitor the neighbour candidate. Once a qualified handover candidate in the preferred band, the BSS will try to handover the multiband mobile to the preferred band. The qualification for eligible candidate of handover is the neighbour candidate is on the preferred band and the power of receive level of candidate neighbour is better than neighbour receive level minimum.

As band_preference_mode=5 is a combination of band_preference_mode=1, 2, and 4. The requirements on those mode also applies for band_preference_mode=5.

Band_preference_mode=6 is effectively band_preference_mode=5 but only when the source/serving cell is congested. To set up the congestion threshold in a cell, the following major database parameter need to be considered:

• Congestion relief type. When the serving cell is congested, there are two options to offload the cell, attempt handover as many as possible which meets the congestion criteria or attempt a number of handover which equal to the amount of calls in the queue. The first attempt options will free more TCHs than the second option.

• Congestion relief handover margin. This parameter will determine how easy the handover will take place. For initial setup of the feature, it is recommended to set this parameter to -10. Further tuning suitable to the network requirement can be done through optimisation process

• Congestion relief trigger. In the GSR3 software release it is known as tch_congest_prevent_thres. This determines when the serving cell is considered as congested in term of percentage of busy TCH in the cell. Setting the threshold too high percentage may result preventing some TCH to serve incoming call through a handover.

9.2. Optimising Single BCCH Referring to chapter 7, dualband offset plays important role for successful implementation of Single BCCH feature in the network. Therefore, this section will discuss about optimising the dualband offset as well as other related BSS database parameter.

For BSS, dualband offset represent the summary of radio propagation properties between inner and outer zone. Dualband offset provides a tool for the BSS to estimate and/or assess the radio environment on both zones within a period of time and subsequently will determine whether a call is eligible to enter inner zone or stay in the outer zone or even move to other cell. When the dualband offset is not set properly then BSS will take the wrong assumption about the RF

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M environment difference between inner zone and outer zone. Known symptom of poorly optimise dualband offset is ping-pong handover between inner and outer zone, which result to excessive number of handover within a call.

Dualband Offset Profile

0

2

4

8

10

14

6

12

16

Urban cells Rural Cells

As presented in Figure 9-3, dualband offset for each cell may different, depend on the transmit power available to the antenna after a stage of combining as well as the propagation properties. Ideally, dualband offset should be optimised for each cell, the optimisation process will take a huge amount of time, which lead that an automated process is required. An alternative to optimise dualband offset is group the dualband cells in the network based on its usage placement geographically. As an example the dualband cells are group into two, which are cells serving urban area and cells serving suburban area. Then a dualband offset will be derived from each group by selecting a number of dualband cells that represent each group. As in the figure above, a number of dualband cells are selected to represent urban cell and dualband offset is derived for each cell. After a simple process of averaging, one dualband offset is available for this group and this is the optimum value. The same for the rural cells group, dualband offset was derived from the average of dualband offset from the sample cells representing this rural cell group.

Figure 9-3 Dualband offset profile for each cell in two different cell groups. Red bars are the nominated dual_band_offset will be implemented within each cell group.

The next optimisation step for dualband offset is to identify how far the real dualband offset deviate from the dualband offset set in the BSS database parameters. Taking example from the figure above, the last three cells on the right within the rural groups, the real dualband offsets are deviate 4 to 7dB than the dualband offset set in the BSS database parameter. After a site visit, then it was found that the antenna feeders were crossed between the two cells.

In summary, optimising dualband offset is a good exercise to verify and validate the RF front end of multiband site, although the single BCCH will be implemented or not as it has the ability the provide a single value summary of RF environment in the cell.

Deriving dualband offset is mainly done with the help of CTP. This will enable to perform dualband optimisation right before the single BCCH implemented in the network, although the normal step to optimise dualband offset after feature implementation also possible.

Following are the general step to derive dualband offset out of CTP, depends on when the feature is implemented.

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M To derive dualband offset before the feature is implemented:

1. Select the pair of co-located GSM900-GSM1800 cells, and start from GSM900 cell as the serving cell

2. Identify the measurement reports where the GSM900 serving cell is reporting co-located GSM1800 as the neighbouring cell. It should be noted that the co-located neighbour is not always reported as the strongest neighbour or reported in the same position in the measurement report neighbour list. This should be the subset of the whole measurement report captured for the serving cell.

3. Workout the dualband offset by deriving the delta of downlink RxLevel from the serving cell and the co-located neighbouring cell.

4. Dualband offset is the average of the delta over the subset of the measurement report.

5. Repeat the procedure for the GSM1800 co-located cell.

These steps assuming that that the measurement report data has been collected by CTP. On a co-located GSM900 and GSM1800 cells, each cell will report the other co-located cell as a neighbour. Therefore, it is recommended to take the measurement report where the serving cells are both GSM1800 and GSM900.

In the case to derive dualband offset after the feature is implemented:

1. pbgt_mode should be set to 1 As this will ensure that the BCCH RxLevel is included on the measurement report, then all measurement reports, while the call is on inner zone, from the single BCCH cell can be used in the calculation.

2. Dualband offset is the average of the delta between the RxLevel of the serving cell in the inner zone and the RxLevel of the BCCH.

The next point to optimise in Single BCCH feature is the zone definition as described in section 7.3, specifically rxlev_dl_zone and rxlev_ul_zone parameters. These parameters serve the function to limit the quantity of traffic served by the inner zone. Based on the availability of the traffic channel in the inner zone and the usage statistics, those parameters can be optimised so that blocking in the inner zone will be minimised or to increase the number of traffic channel is required.

The second function of rxlev_dl_zone and rxlev_ul_zone is to filter the call, which have a good uplink and downlink quality level. By filtering only the call with good receive quality this would increase the performance of inner zone and overall the performance of secondary frequency band.

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Figure 9-4 Optimising zone definition in single BCCH

Again, optimising rxlev_dl_zone and rxlev_ul_zone displays CTP as an essential tool to provide data measurement from the network. The measurement report collected in CTP for one particular dualband cell divided into 2-dimensional counter array, where first dimension is RXlevel while the serving frequency band is GSM1800 and second dimension is the RXQual. After simplifying the RXQual into just two groups, RxQual4-7 representing bad receive quality and RxQual0-3 representing good quality. The result is presented in Figure 9-4 where the ratio between good and bad receive quality displayed for each Rxlevel GSM1800 recorded in the CTP. As presented in the figure above, circle 1 identify the minimum receive level where the handover to inner zone should occur to maintain a good receive quality in the inner zone. Circle 2 represent the estimated receive level where the handover to inner zone will occur.

From the statistics point of view, Key performance metrics described in Motorola Customer Documentation can be used to assess singe BCCH performance. It should be noted cell level drop call and TCH RF loss require a different understanding as described in section 7.12 Impact of Single BCCH to Key Performance Metric. As an example, the following list of statistics can be use for analysing single BCCH performance. This set also valid for benchmarking performance before and after feature implementation during a trial

The statistics includes:

• System Access, which consist of SDCCH blocking rate, SDCCH access success rate, call setup success rate, TCH blocking rate, call setup TCH blocking rate, RF assignment success rate

• Handover Performance, which consist of outgoing intracell handover success rate, handovers per call, mean time between handover, handover cause distribution (plus bins), intra cell handover success rate, intra cell handover failure rate (lost ms), outgoing intra BSS handover success rate,

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M outgoing intra bss handover failure rate (lost ms), outgoing inter bss handover success rate, outgoing inter bss handover failure rate (lost ms), incoming inter cell handover success rate, zone_change_atmpt (plus bins), zone_change_suc (plus bins), interband_activity, per neighbour statistics (where required)

• Traffic, which consist of call volume, traffic carried, TCH usage, TCH usage inner zone, TCH mean hold time

• Key performance, which consist of mean time between drop, call success rate, SDCCH RF loss rate, TCH RF loss rate

Another parameter in Single BCCH needs attention in optimising the feature is zone_ho_hyst. As described in the earlier section, this parameter will ensure that the mobile is properly located in good coverage of the inner-zone. To understand more about zone_ho_hyst role in Single BCCH feature, it can be described by using the dualband offset profile for a given cell as illustrated below.

Figure 5. Dualband offset profile of a Single BCCH cell

In Figure 5, the blue bar graph represents the typical dualband offset distribution within a given cell and the red line represents its cumulative distribution. At this cell, the dualband offset has been identified and optimised at -9dB. The population on the left side of the dualband offset -9dB can be considered as the probability of a cell suffering ping-pong handover between zones. In order to suppress excessive ping-pong inter-zone handover volume, it is necessary to increase the threshold in addition to the existing dualband offset cut-off point. That is where the zone_ho_hyst come into play. The further left the threshold moving from the dualband offset point (increase of zone_ho_hyst) the more reduction in the volume of ping-pong handover.

But increasing the value of zone_ho_hyst will come at a cost, which is effectively reducing the ability of the cell to move traffic to the inner zone and leads to low

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M utilisation of GSM1800 resources. So there is a trade-off needs to be considered, increasing the threshold by increasing the value of zone_ho_hyst will effectively suppress the high volume of inter-zone handover, but at the same time will reduce the cell to absorb traffic into GSM1800 inner-zone.

With the Single BCCH enhancement which prevent the ping-pong handover as described in the previous section, will help a lot to reduce to effect of such trade-off in the optimisation. This enhancement will help network operator to maximise the inner zone GSM1800 utilisation and reducing significantly the volume of inter-zone handover caused by ping-pong handover.

9.3. Optimising coincident multiband handover Due to the different propagation characteristics in different frequency bands, power level differences, antenna characteristics and set-up, the received signal strength from the coincident cells can vary significantly. The low_sig_thresh is defined on the GSM900 cell and is used in the handover decisions as a reference point. However, if the receive signal strength levels on the coincident GSM900-GSM1800 cells differ, the result will be effectively moving the defined threshold to lower, more aggressive values (in case of the GSM900 cell being stronger) or to higher, more conservative values (GSM1800 is stronger). If an approach with less aggressive setting is taken, the impact of the high difference in receive level is reduced, because the actual level on the GSM1800 will be sufficient to prevent any degradation in quality. The disadvantage is naturally the loss of traffic on GSM1800, because the MS is not redirected to the secondary layer.

Figure 9-6 Average difference in receive signal strength on co-located coincident GSM900 and GSM1800 cells

Furthermore it is more important to achieve comparable signal strength on the cell borders, where the hand-ins and hence the redirection occurs, rather than across the whole cell coverage area. Based on the trial as described in chapter 8, Figure 9-6 shows the delta values in relation to the serving GSM1800 cell level, which gives an indication whether or not the MS is on the cell border. The figure above confirms, that for the two coincident cells with the smallest average delta

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M value -50971 and 52271- showing the best performance, the GSM1800 cell level is stronger or comparable to the GSM900 cell across the coverage area including the cell border, where during the trial set to -95 dBm.

The effect on the threshold, average differences in receive level in coincident cell and hence on the system performance of various signal strength levels on the coincident cells is illustrated on the following figures.

The diagrams show the probability of Rxqual values higher or equal to 4 depending on the serving cell signal strength. This gives an indication where the redirection should take place without compromising on quality. The red line marks the lowest threshold (-95 dBm) implemented during the trial. The dashed line represents the estimated receive level on the GSM1800 cell after redirection due to the difference in the signal strength levels on the coincident cells (see graphs above). The dotted line indicates the threshold point, that would have to be defined, if the desired –95 dBm signal level on the GSM1800 was to be maintained, when the signal strength criteria was met on the GSM900 cell.

Figure 9-7 Probability of bad Rxqual values on GSM1800 cell 50971

Figure 9-7 and Figure 9-8 present two cases with relatively small difference in the received signal strength of the coincident cells. Both GSM1800 cells (50971 and 52271) consistently performed well after the implementation of the feature (see BSS statistics below). The probability of bad Rxqual values (higher or equal to 4) remained the same through all settings (see Fig. 15) compared to the results with the feature disabled in the range of 1,63 % - 2,58% respectively 2,51% - 3,57%. The exception is the most aggressive setting, where an increase in bad quality can be noticed (probability of 4,40 %) on cell 50971. This can be attributed to the higher than average difference between the coincident cells (see Figure 9-6), when the serving cell level is close to –95 dBm.

Figure 9-8 Probability of bad Rxqual values on GSM1800 cell 52271

Figure 9-9 and Figure 9-10 typify two cells with big differences in signal strength between the coincident cells (50981 and 52281). The probability of bad Rxqual values (higher or equal to 4) keeps increasing in both cases from 5,08 to 8,47 and from 3,09 to 6,58 respectively. The increase is especially clear in case of the two lowest thresholds (-95 and –90 dBm). Due to the high delta values and thus the estimated signal strength level on the coincident GSM1800 cell being

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M different from the real value, the MS are redirected to the secondary band in areas with extremely high probability of interference.

The most important conclusion that can be drawn from experience gathered through the test is, that the difference in signal strength between the coincident GSM900 and GSM1800 cells is the key to the successful operation of the feature.

The RF planning of the coincident cells needs to be done so that this difference is minimised especially on the cell borders, where the redirection shall occur (depending on the low_sig_thresh parameter setting).

Figure 9-9 Probability of bad Rxqual values on GSM1800 cell 50981

delta needs to be taken into account. If this is not the case, knowledge of the average delta value is inevitable for the definition of the

low_sig_thresh parameter. In addition to selecting a suitable level, which ensures the MS will experience good radio conditions when being moved to the secondary band, this delta needs to be taken into account. The final threshold has to be moved to higher values (in case the GSM900 cell is stronger), with the adjustment corresponding to the average delta.

Figure 9-10 Probability of bad Rxqual values on cell 52281

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M 10. Dualband Interaction with Other

Features As more features or enhancements available each time the new GSM software release introduced, many of them is working together with dualband feature to enhance the network capacity as well as the quality. This section will describe some interaction between dualband feature and other capacity enhancement feature offered by Motorola.

10.1. Frequency hopping Frequency Hopping is Motorola’s solution to cope with Capacity and Quality problems arising in highly loaded GSM networks. The present document introduces this technique, describing its basic principles and the advantages that can be achieved by implementing it. There are two different ways to implement Frequency Hopping, known as Base Band Frequency Hopping (BBH) and Synthesiser Frequency Hopping (SFH), both available in all Motorola equipment without any hardware modification at all.

Synthesiser Frequency Hopping is the approach Motorola recommends as being the best solution considering the advantages it has with respect to BBH. This implementation is the only existing technique permitting to achieve simultaneously all the benefits previously described. SFH technique and Motorola’s experience in Frequency Hopping made up the most powerful weapon the system operators can fall back on to enhance the performance of a GSM network. GSM recommendation also defines that there will be no hopping system across the two frequency bands.

As a way to improve call quality in reducing the fading effect in GSM1800 band, frequency hopping also can be implemented in the network. Recent study shows a good result after the frequency hopping is enabled. This study was designed to test frequency-hopping performance to fight fading in 1800MHz band.

Hopping disabled

Hopping enabled (pseudorandom)

BCCH 683 683, non hopping TS0 TS1

Hopped over 2 adjacent frequencies (FHI0)

TS2 TS3 TS4

Hopped over 3 frequencies, with large intervals (FHI1)

TS5 TS6

Non-BCCH 680

TS7

Hopped over 6 adjacent frequencies (FHI2)

Figure 10-1Frequency assignments before and after hopping enabled in frequency hopping and multiband field testing

A good tool to measure frequency hopping is frame erasure rate, as it measures the number of percentage of frames that are actually discarded after the decoding and interleaving process.

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M In this study, A site has been chosen to test the frequency hopping. The site is located in city centre covering dense urban area. The carrier was configured 2/1/0. As synthesiser frequency hopping was used in this test, the study will be focused only on sector 1. Frequency assignments on each carrier presented in Figure 10-1.

Downlincoveragafter fretimeslofrequenused in

Within three frFER im

As the buildingfrequenmore thdistribu

As seedistribustarts tohoppinginside o

In comimplemhop bein the c

System SuppoMotorola Confi

90.00%

92.00%

94.00%

96.00%

98.00%

100.00%

Beforehopping

FHI0 FHI1 FHI2

inbuildingstreet

k Frame Erasure Rate analysis is presented in Figure 10-2. From street e analysis, a significant improvement of mean FER achieved up to 79% quency hopping is enabled. The best FER reduction can be seen on

t 2-4, which hopping trough 3 frequencies as they hop with a relatively big cy separation. With a common frequency hopping implementation as timeslot 5-7, 70% improvement of mean FER can be expected.

Figure 10-2. FER=<10% comparison for street and in-building coverage.

in-building coverage, mean FER improved by 84% where hopping using equencies with large frequency separation. On timeslots 5-7 the mean proved by 80%.

fading bandwidth outside the building is relatively smaller than inside the , big improvement can be gained immediately only with hopping over two cies (FHI0). In all frequency hopping schemes tested in location 1 (street) an 98% of the measurements have a FER less or equal 10%. The

tion graph with FER bigger than 10% is presented in the next graph.

n on Figure 10-3 that before hopping the FER measurements are widely ted which indicate the signals is suffering to fading. Moreover, the signal have much better resistance to fading when FHI1 or FHI2 is used. Both schemes can perform with a FER>10% less than 0.5%, whether it is r outside the building.

bination with the multiband feature, frequency hopping can be ented on each band separately, as the GSM recommendations don't allow tween the two frequencies bands. Separate lab studies showed also that ase of a multiband handover, while the target cell is actually hopping, the

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M multiband handover can be done successfully whether the target cell is either hopping or not.

In implementing frequency hopping in the network, multiband handover can be considered as a normal handover between cell, as the two features work independently but together can give enhancement to the network capacity.

To make the optimum reduction in Rayleigh fading, the frequencies in the hopping sequence should have highly de-correlated fading signatures. A study was carried out to determine minimum frequency de-correlation in order to have maximum benefit of frequency hopping against fading specifically in GSM1800 frequency band.

0.00%

0.50%

1.00%

1.50%

2.00%

2.50%

3.00%

3.50%

4.00%

Before hopping FHI0 FHI1 FHI2

inbuilding-FER10-20

inbuilding-FER20-30

inbuilding-FER30-40

inbuilding-FER40-100

street-FER10-20

street-FER20-30

street-FER30-40

street-FER40-100

When the test carried out, the maximum and minimum wanted frequency hopping bandwidths were identified as 20MHz and 0.6MHz. Bandwidth intervals between these two values were then identified such that the results of the tests could be used to produce a graph of bandwidth Vs fading correlation coefficient. The BCCH frequencies at the cell site were chosen to produce the required frequency bandwidths, and for each bandwidth, samples were taken at each of the thirteen test points on the test route. The sampling method was to move the antenna over a distance of 1m at a constant rate of approximately 1cm/second. This procedure then repeated in several different locations around the selected cell site. The result of the observation is displayed below.

Figure 10-3. Measurement report distribution for FER>10%

Figure 10-4. Average correlation of each bandwidth used in hopping list

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M From the average correlation coefficient it would appear from these results that a reasonable minimum bandwidth to apply between frequencies within a hopping sequence is 2.4MHz. Increasing the bandwidth above this figure appears to provide little additional de-correlation gain.

10.2. General Packet Radio System (GPRS) The consideration to put GPRS capability in a multiband network depends on the decision of how the GPRS timeslot should be available in a frequency band. From there, a number of scenarios of GPRS implementation are possible, which are

• Enabling GPRS timeslot across all frequency band enabled in the network. This provides total GPRS coverage in the network. This may costly solution as GPRS timeslot provisioning should be done in all cells regardless the frequency band.

• Enabling GPRS timeslot only on a certain frequency band. This will be applicable when the network is enabled with single BCCH feature, where in Motorola implementation GPRS timeslot will only available in the primary frequency band.

10.3. Microcellular The highlight of how the microcellular algorithm working together with advanced load management has been discussed with examples in 5.3.1.2 Example of implementation. One thing to note in here is that advanced load management take precedence over the microcellular algorithm. That is, when the band_preference is not set to 0 then BSS will try to create a separate neighbour candidate list based on the frequency band of the neighbour. Then for each list, it will be sorted based on the microcell algorithm. After that, all the lists will be combined again into one list, where the neighbours with preferred band are on top of the handover candidate list.

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M 11. Multivendor Implementation

As Motorola keeps creating sophisticated algorithms for the network, Motorola also try to ensure that the equipment is able to work together with other vendor equipment when it is necessary to create coverage within the same area.

Going further with field implementation, Motorola has proven ability to underlying networks created by other vendor such as Nokia, Ericsson, Alcatel or Siemens. Following table is an example where Motorola is part of multivendor deployment.

This section tries to describe some considerations, which might be needed for operating in multivendor environment.

Figure 11-1. Example of multivendor implementations where Motorola took part providing multiband solution for network operrator in regions

11.1. Considerations Considerations may range from technical preferences of the operator as well as policies within the operator. Another reason would be the operator feels more comfortable with specific features offered by certain equipment manufacturer, which not offered by other. The number of vendors involved in this environment also can be various, which also depend on operator decisions.

The benefit for an operator to have a multivendor environment, which will be outlined here, is that, by having the atmosphere of competition between vendors, the operator will gain a better array of service from each vendor.

Going along with the benefit of multivendor environment, there are also some disadvantages. The important thing that needs attention is to establish

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M communication between vendors via operator. This is needed where each vendor needs some technical information about site information and database parameter. When there is a need to have new sites in-service or network modification, it is necessary for operator to supply related info to each vendor in order to have smooth network operation.

With increased operation complexity when implementing multiband solution in multivendor environment, it is recommended that each involved party have a common reference of how the network should be operated. This common reference will provide a high level view of communication operation process, sub-processes and activities that is top down, customer centric, and end-to-end focused.

In the generic telecommunication industry, a model has been adopted to represent the common view of network management. This model is known as the Telecom Operation Process Model. It serves as a way to think logically about how the business of a service provider is operated. Figure 11-2 represent the generic model.

Customer

Customer Interface management Processes

Service Development & Operation Processes

ServiceConfiguration

Serviceplanning &

Development

ServiceProblem

management

Service QualityManagement

Rating andDiscounting

Customer Care Processes

OrderHandlingSales Problem

HandlingCustomerQOS& management

Invoicing &Collection

Network and Systems Management Processes

NetworkProvisioning

Networkplanning &

Developement

NetworkInventory

Management

NetworkMaintenance &

Restoration

Network DataManagement

Network Element Management Processes

Physical Network and Information Technology

InformationSystems

ManagementProcesses

Figure 11-2. Telecom Operation Map

In multivendor implementation will be discussed here is mainly on the lowest layer, which is Network and System management Processes. Within this layer, the most significant tasks in multiband multivendor implementation are:

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M • Network planning and deployment. This process encompass descriptions of

network configuration for operational use, definition of rules for network such as planning, installation as well as designing network capabilities to meet requirements.

• Network provisioning. This process encompasses the configuration of the network, to ensure that network capacity is ready for provisioning and maintenance of services. It carries out Network Provisioning, as required, to fulfil specific service requests, network and information technology additions, changes, deletions and configuration changes to address network problems.

• Network inventory management. This process encompasses anything to do with physical network and information technology equipment and the administration of this equipment.

• Network maintenance and restoration. This process encompasses maintaining the operational quality of the network, in accordance with required network performance goals. Network performance goals are or should be set to support the service levels of the services provided via the network infrastructure.

• Network data management. This process encompasses the collection of usage data and network and information technology events and data for the purpose of network performance and traffic analysis.

Focusing to inter-working of Motorola equipment with another vendor is handover from Motorola equipment into or from another vendor. While the call is on another vendor, it is very dependent at specific vendor about the handover algorithm. Once the call on Motorola side, then it is possible to exploit Motorola algorithm to maintain the traffic as long as possible and with the same time gives the most efficient connection.

11.2. Idle mode The first attempt in moving traffic to be served by Motorola equipment can be done as early as in the idle mode. The main idea is to make the cell, which using Motorola equipment, more attractive than others by adjusting the related C1 and C2 parameters. A detailed explanation of C1 and C2 parameters was discussed in an earlier section.

Suppose in the dualband network with Motorola equipment used as GSM1800 layer. In the cell selection process, the mobile will try to camp on the most strongest receive level, by providing better C1 value compared to the other the mobile will then select the highest C1. Refer to chapter 4 for formula relationship of C1 and C2 parameter. For practical implementation, by adjusting the RxLev_access_min to the lower value, this will result increasing the C1 value, which subsequently will make the cell more attractive to mobiles from the other. When this method is further

Figure 11-3. RXLev_access_min

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M implemented exclusively in the GSM1800 cells, this would results GSM1800 cells are more attractive than GSM900 cell. This is as described in the figure 9.1.

Some operators already set their RXLev_access_min to the "most attractive value" (RXLev_access_min=-110) in order to capture especially roamers as much as possible. A consideration should be noted when using RXLev_access_min=-110. While it is recommended to have this enabled in the area where there is a very good receive level within the area such as airport, or interstate railways stations. But there also recommended not to use this in the fringe area such as rural, where receive level in the mobile is very low. This will generate multiple failure attempts in the network as the mobile try to camp on the network.

With regard to C2 parameter to bias dualband mobiles to camp on GSM1800 layer, cell_bar_qualify can be used to prioritise cells for being normal or to have lower priority. In the cell selection process, after the mobile received a list of candidate cells to camp on based on strongest C1 and C2 parameter, the list will be resorted again based on cell_bar_qualify parameter (without changing the previous sorting scheme). The cell with cell_bar_qualify=0 will be on top of the list and cell with cell_bar_qualify=1 will be on the bottom. The mobile will only choose the cell with cell_bar_qualify=1 if the other cell is not qualified.

That cell_bar_qualify parameter also can be used to distinguish GSM1800 and GSM900 cell. To assign GSM1800 cells with normal priority (cell_bar_qualify=0) and GSM900 cells with lower priority, the GSM1800 cells will be listed before the GSM900 cells.

Another component in the C2 calculation is cell_reselect_offset. This parameter defines the offset value to C2. This parameter also can be used to prioritise a GSM1800 cell than GSM900 cell by applying a higher value of cell_reselect_offset in the GSM1800 cell.

When the C2 parameter is activated in the network, the higher cell_reselect_offset will virtually put that cell more attractive which will lead to be the cell for the mobile to camp on it. Also should be noted when using the parameter, If in the case where the cell is in the fringe area or at the border of the network, with a high value of cell_reselect_offset will inhibit the mobile to reselect another cell which actually have a better C1. The suitable cell_reselect_offset for each network can be determined via optimisation process.

Figure 11-4. Cell_reselect_offset

11.3. Dedicated Mode In dedicated mode, the issue is again how to manage traffic on the other equipment manufacturer and on Motorola equipment. Once the traffic is on Motorola, then it would be easy to make influence on these traffic using

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M advanced algorithms developed by Motorola, including Motorola's multiband algorithm, Advanced Load Management.

There are possibilities to implement multiband techniques in multivendor environment. The easy one would be where the network is actually multivendor but for a given region it is a single vendor. Then care should be taken in the border area between the two vendors. The other possibility would be where one band is one vendor, the other band is the second vendor, and the two are overlapping geographically. The following paragraph will try to describe an example where the existing band (GSM900) is certain vendor, and the other band served by Motorola.

In the multiband environment where, for example, Motorola equipment used as additional equipment to overlay existing network that using another vendor, possible scenario would be to create handover algorithm in favour to Motorola equipment.

Described in Figure 11-5 as an example scenario, each hexagon represents macrocell for both Motorola and other vendor. The arrows represent the handover directions. It is assumed that the MSC support multiband operation. To attract the traffic from other vendor, it is possible to use negative handover margin. This method allows the neighbours (using Motorola equipment) to pass the power budget handover criteria more easily, and put a higher priority in the neighbour list candidate.

Figure 11-5. Example of multiband scenario in multivendor environment

In order to have a smooth integration with the existing network, there is also possible to use multiband algorithm. In this example scenario, using band_preference_mode=2. Those mechanisms can be combined with microcell algorithm.

For the handover algorithm within Motorola equipment it possible now to fully utilise enhancements available. This to ensure that the mobile will get the most efficient uplink-downlink connection. In this example the congestion relief feature was enabled.

A more complex application of multivendor environment is in the case where microcells also deployed to capture hot spot traffic. A simple illustration is displayed in Figure 11-6. The bigger hexagon represents macrocell and the smaller one represent microcell. Motorola equipment used as capacity enhancement using multiband application in GSM1800 frequency band. And the existing network is using other vendor equipment.

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M In this example, the multilayer cell is also can be applied. The bigger coverage served by macrocell is used to serve fast moving traffic. And for the smaller coverage, which using microcell used to capture slow and high traffic within the area. The handover scenario for macrocell to macrocell still using the same as described above. For handover from macrocell to microcell can use type5 algorithm. Between microcells some options available, which depends on the RF environment within the area. In case of emergency where the call suffers a bad RxQual or low RxLev, then using type3 handover algorithm, the call can be moved to saver coverage either in GSM900 or GSM1800 macrocell.

Figure 11-6. Example of multiband scenario combined with microcell

For dualband enhancement within the same scenario, the handover from micro to micro can use band_preference_mode=2, which ensure the preferred band is on top of the handover candidate list. This is also applies for the handover candidate from microcell to macrocell within Motorola equipment.

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M Appendix A.

The following files are available for download on Motorola intranet only at http://compass.mot.com/go/dualband.

Erlang B Table Erlang B table in Microsoft Excel sheet format. Erlang_B.xls

Link budget sheet Motorola specific to perform link budget calculation for GSM900 and GSM1800 frequency band.

Link_budget.xls

Example of Single BCCH conversion Example text script to convert a conventional multiband site into a site with single BCCH enabled.

SingleBCCH_conversion_script.txt

Single BCCH introduction slides Details the major aspect on Motorola Single BCCH feature available in GSR5.

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M References

[1] ETSI Specification 03.26, Multiband Operation of GSM/DCS1800 By A Single Operator, ETSI

[2] ETSI Specification 03.30, Radio Network Planning Aspect, ETSI [3] ETSI Specification 04.08, Mobile radio interface layer 3 specification, ETSI [4] ETSI Specification 05.08, Radio subsystem link control, ETSI [5] GSR5 Motorola Customer Documentation, Motorola [6] Gabriel Nagy, Advance Traffic Management v03, Motorola, October 1999 [7] Gabriel Nagy, Tubagus Rizal, Marina Vilas, Enhanced Congestion Relief and

Coincident Multiband Handover Trial, Motorola, August 1999 [8] Tubagus Rizal, Single BCCH Introduction presentation slides, Motorola,

October 2002 [9] Kurt Wagentristl, Dualband RF Propagation, Motorola, August 1999 [10] Javier Escamilla, Microcell Engineering Book, Motorola, September 1998 [11] Joe Grant, GSM Indoor RF Distribution System Planning Guide, Motorola,

April 1998 [12] Michel Mouly, Marie-Bernadette Pautet, The GSM System for Mobile

Communication, Cell & Sys, 1992 [13] John Doble, Introduction To Radio Propagation For Fixed And Mobile

Communications, Artech House, 1996 [14] CDMA RF Planning Guideline v2.1, Motorola, December 1998 [15] GSR5 Motorola Customer Documentation, Motorola [16] Jaana Laiho, Achim Wacker, Tomas Novosad, Radio Network Planning and

Optimisation for UMTS, John Wiley & Sons, Ltd. 2001 [17] B Lindmark, M Ahlberg, E Lindquist, Measurement of Radio Coverage Using

Dualband Antenna, Allgon System AB, 1999 [18] GS910 Telecom Operation Map, Telemanagement Forum, March 2000 [19] GB923 Wireless Service Measurement Handbook, Telemanagemen Forum,

November 2002

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