gsm advanced cell planning

Copyright 2002 AIRCOM International Ltd All rights reserved AIRCOM Training is committed to providing our customers with quality instructor led Telecommunications Training. This documentation is protected by copyright. No part of the contents of this documentation may be reproduced in any form, or by any means, without the prior written consent of AIRCOM International. Document Number: P/TR/005/G103/2.0c This manual prepared by: AIRCOM International

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ADVANCED GSM

CELL PLANNING

Advanced GSM Cell Planning © AIRCOM International 2002 0-1

Table of Contents 1. Review of the GSM Air Interface

1.1 Introduction...................................................................................................... 1-1 1.2 Logical Channels.............................................................................................. 1-2 1.3 FDMA/TDMA Structures .............................................................................. 1-5 1.4 Timing Advance .............................................................................................. 1-7 1.5 Multiframes ...................................................................................................... 1-9 1.6 GSM Protocols................................................................................................ 1-12 Self Assessment Exercises............................................................................. 1-17

2. Traffic Theory and Channel Dimensioning 2.1 Introduction...................................................................................................... 2-1 2.2 Traffic measurement ....................................................................................... 2-2 2.3 Traffic Channel Dimensioning....................................................................... 2-5 2.4 Control Channel Dimensioning..................................................................... 2-6 2.5 Muli-Service Traffic Dimensioning............................................................. 2-16 2.6 Dimensioning Micro- and Picocells ............................................................ 2-27 Self-Assessment Exerecises .......................................................................... 2-31

3. Frequency Planning 3.1 Introduction ..................................................................................................... 3-1 3.2 Cellular Structures and Frequency Reuse Patterns. ................................... 3-2 3.3 Interference Calculations................................................................................ 3-5 3.4 Cell Splittuing Techniques ............................................................................. 3-6 3.5 Multiple Reuse Patterns (MRPs) ................................................................. 3-12 3.6 Frequency Hopping....................................................................................... 3-15 Self-Assessment Exerecises .......................................................................... 3-19

4. Base Station Positioning 4.1 Introduction...................................................................................................... 4-1 4.2 BTS Positioning for Different Environments............................................... 4-2 4.3 Microcell Positioning....................................................................................... 4-5 4.4 Picocell Arrangements .................................................................................... 4-6 4.5 Multilayer Cell Design.................................................................................... 4-7 4.6 Use of Repeaters............................................................................................. 4-12 Self-Assessment Exercises ............................................................................ 4-19

5. Base Station Engineering 5.1 Introduction...................................................................................................... 5-1 5.2 Site Suitability .................................................................................................. 5-2 5.3 Radio Property Testing ................................................................................... 5-3 5.4 Antenna Configurations ................................................................................. 5-8 5.5 Base Station Equipment ................................................................................ 5-15 5.6 Electrical Considerations .............................................................................. 5-21 5.7 Configuration Selection ................................................................................ 5-22 Self-Assessment Exercises ............................................................................ 5-29

0-2 Advanced GSM Cell Planning © AIRCOM International 2002

6. Network Operations

6.1 Introduction...................................................................................................... 6-1 6.2 Modes of MS Operation.................................................................................. 6-2 6.3 Operations in MS Idle Mode.......................................................................... 6-3 6.4 Operations in MS Dedicated Mode............................................................. 6-11 6.5 Handover Operations. .................................................................................. 6-13 6.6 Discontinuous Transmission (DTX)............................................................ 6-22 6.7 Extrending Cell Coverage. ........................................................................... 6-24 Self-Assessment Exercises ............................................................................ 6-27

7. System Optimisation 7.1 Introduction...................................................................................................... 7-1 7.2 The need for Optimisation ............................................................................. 7-2 7.3 The Optimisation Process............................................................................... 7-3 7.4 System Performance........................................................................................ 7-4 7.5 Test Mobile Survey Data ................................................................................ 7-6 7.6 Automated Analysis........................................................................................ 7-7 7.7 Remedial Action............................................................................................... 7-7

Appendix A - GSM Spectrum Allocation Appendix B - Solutions to Self Assessment Exercises Appendix C - Erlang B Tables


Course Objectives and Structure

Course ObjectivesCourse Objectives

• Calculate dimensioning requirements for traffic and control channels

• Understand the allocation of control channels on the multiframestructure

• Understand the principals of frequency re-use planning including multiple re-use patterns (MRP)

• Understand the principals of multi-layer cell design • Appreciate the considerations involved in positioning a base

station • Describe the characteristics of base station equipment • Understand a range of network operations including: cell

selection and re-selection, cell measurements, handover control • Appreciate the process of network optimisation

Course StructureCourse Structure

Day 1

• Review of the GSM Air

Interface

• Traffic Theory and

Channel Dimensioning

• Frequency Planning

Day 2

• Base Station Positioning

• Base Station Engineering

• Network Operations

• System Optimisation


Intentional Blank Page


1. Review of the GSM Air Interface

_____________________________________________________________________

1.1 Introduction

This section briefly reviews information relating to the GSM air interface. Areas covered include:

• Logical Channels • FDMA/TDMA structures • Physical Channels • Multiframes • GSM Protocols

Topics introduced for the first time in this section include:

• The structure of data bursts in the GSM physical channels • Timing advance • Protocols for speech and signalling


_____________________________________________________________________

1.2 Logical Channels

Logical ChannelsLogical Channels• GSM uses a set of logical channels to carry call traffic, signalling,

system information, synchronisation etc.• These logical channels use physical channels (timeslots) defined by

the FDMA/TDMA structure of the system

TCHTCH

TrafficTraffic

TCH/HTCH/H

TCH/FTCH/F

CCCHCCCH

ControlControl

BCHBCH DCCHDCCH

FCCHFCCH

SCHSCH

BCCHBCCH

PCHPCH

RACHRACH

AGCHAGCH

CBCHCBCH

NCHNCH

SDCCHSDCCH

SACCHSACCH

FACCHFACCH

Section 1 – Review of Air Interface

TCH Traffic Channels TCH/F Traffic Channel (full rate) (U/D) TCH/H Traffic Channel (half rate) (U/D) BCH Broadcast Channels FCCH Frequency Correction Channel (D) SCH Synchronisation Channel (D) BCCH Broadcast Control Channel (D) CCCH Common Control Channels PCH Paging Channel (D) RACH Random Access Channel (U) AGCH Access Grant Channel (D) CBCH Cell Broadcast Channel (D) NCH Notification Channel (D) DCCH Dedicated Control Channels SDCCH Stand alone Dedicated Control Channel (U/D) SACCH Slow Associated Control Channel (U/D) FACCH Fast Associated Control Channel (U/D)


Traffic Channels (TCH)Traffic Channels (TCH)• TCH carries payload data - speech, fax, data• Connection may be:

• Circuit Switched - voice or dataor• Packet Switched – data

• TCH may be:• Full Rate (TCH/F)

• one channel per user• 13 kb/s voice, 9.6 kb/s data

or• Half Rate (TCH/H)

• one channel shared between two users• 6.5 kb/s voice, 4.8 kb/s data


Broadcast Channels (BCH)Broadcast Channels (BCH)BCH channels are all downlink and are allocated to timeslot zero

Channels are:

• FCCH: Frequency control channel sends the mobile a burst of all ‘0’ bits which allows it to fine tune to the downlink frequency

• SCH: Synchronisation channel sends the absolute value of the frame number (FN), which is the internal clock of the BTS, together with the Base Station Identity Code (BSIC)

• BCCH: Broadcast Control Channel sends radio resource management and control messages, Location Area Code and so on. Some messages go to all mobiles, others just to those that are in the idle state


As the name suggests, the broadcast channels send information out to all mobiles in a cell. These channels are also important for mobiles in neighbouring cells which need to monitor power levels and identify the base stations.


Common Control Channels (CCCH) Common Control Channels (CCCH) CCCH contains all point to multi-point downlink channels (BTS toseveral MSs) and the uplink Random Access Channel:

• CBCH: Cell Broadcast Channel is an optional channel for general information such as road traffic reports sent in the form of SMS

• PCH: Paging Channel sends paging signal to inform mobile of a call• RACH: Random Access Channel is sent by the MS to request a

channel from the BTS or accept a handover to another BTS. A channel request is sent in response to a PCH message.

• AGCH: Access Grant Channel allocates a dedicated channel (SDCCH) to the mobile

• NCH: Notification Channel informs MS about incoming group or broadcast calls


The main use of common control channels is to carry the information needed to set up a dedicated channel. Once a dedicated channel (SDCCH) is established, there is a point to point link between the base station and mobile. Associated control channels carry additional signalling to support dedicated channels. SACCH is associated with either SDCCH or TCH. FACCH is only associated with TCH.

Dedicated Control Channels (DCCH)Dedicated Control Channels (DCCH)DCCH comprise the following bi-directional (uplink / downlink) point to point control channels:

• SDCCH: Standalone Dedicated Control Channel is used for call set up, location updating and also SMS

• SACCH: Slow Associated Control Channel is used for link measurements and signalling during a call

• FACCH: Fast Associated Control Channel is used (when needed) for signalling during a call, mainly for delivering handover messages and for acknowledgement when a TCH is assigned



_____________________________________________________________________ 1.3 FDMA / TDMA Structures

Multiple Access SchemesMultiple Access Schemes

• Frequency Division Multiple Access (FDMA):

• Time Division Multiple Access (TDMA):

User 1

User 2

User 3

User 4

User 5

Freq

uenc

y

Time

Freq

uenc

y

TimeFrame Timeslot


Use

r 1

Use

r 2

Use

r 3

Use

r 4

Use

r 5

Use

r 6

Use

r 7

Use

r 1

Use

r 2

Use

r 3

Use

r 4

Use

r 5

Use

r 6

Use

r 7

GSM systems use several spectrum allocations (P-GSM and E-GSM in the 900 MHz band and DCS and PCS in the 1800 MHz band). Details of these are given in Appendix A to these notes.

Frequency Division (FDMA)Frequency Division (FDMA)

Uplink Downlink

880 915 925 960 MHz

Duplex spacing = 45 MHzGuard Band

Channels (ARFCN)

200 kHz spacing

Range of ARFCN for E-GSM:

0 - 124

975 - 1023

For each GSM band:• Sub-bands are defined for uplink and downlink (Frequency Division Duplex)

• Channels (carriers) 200 kHz bandwidth

• ARFCN (Absolute Radio Frequency Carrier Number) identifies a channel (uplink / downlink pair)

Example:E-GSM 900 MHz band



Time Division (TDMA)Time Division (TDMA)• TDMA is used to provide a set of 8 physical channels (timeslots) on

each carrier:

0 1 2 3 4 5 6 7

4.615 ms

1 burst period (timeslot) = 0.577 ms

1 frame period

• One cycle of 8 timeslots forms the TDMA frame of 4.615 ms duration• Each timeslot lasts for 0.577 ms (156.25 bit periods) and can contain

one of several types of data burst• Uplink and downlink frames are offset by 3 timeslots to allow the MS to

switch between transmit and receive modes

Delay 3 timeslots

Downlink

Uplink


0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

A timeslot is the basic physical resource (channel) in GSM, which is used to carry all forms of logical channel information, both user speech/data and control signalling. Different structures of data burst are used in the timeslot for different purposes.

Types of Data BurstTypes of Data Burst• The 156.25 bit periods of a timeslot can hold different types of data burst:


8.2526 Training

Bits

142 fixed bits

8

Guard period

Normal Burst(Traffic and most control channels)

Frequency Correction Burst (FCCH)Data and tail bits are all 0

Synchronisation Burst (SCH)Data to synchronise MS with BTS

Dummy BurstTransmitted on BCCH carrier when there are no other bursts - allows power level measurements

Access Burst (RACH)Long guard period to avoid collisions

Tail bits

Stealing flag bits

57 Data Bits

41 Training Bits 36 Data Bits

1 3

3 8.253

3 8.2539 Data Bits

64 Training BitsSync Sequence

39 Data Bits 3

26 Training Bits 8.2533

157 Data Bits3

3 68.25


_____________________________________________________________________ 1.4 Timing Advance

Timing AdvanceTiming Advance• Signal from MS1 takes longer to arrive at BTS than that from MS2• Timeslots overlap - collision

MS1 - Timeslot 1

MS2 - Timeslot 2 time

• Timing Advance signal causes mobiles further from base station to transmit earlier - this compensates for extra propagation delay

time

time

MS1 - Timeslot 1

MS2 - Timeslot 2

1 2 3

time

time

time

Timing Advance


2 312 31

2 31

1 2 3

2 31

1 2 3

1 2 3

Timing Advance is needed to compensate for different time delays in the transmission of radio signals from different mobiles. The maximum value of Timing Advance sets a limit on the size of the cell. The TA value to use is found initially from the position of the received RACH burst in the guard period and is adjusted during the call in response to subsequent normal burst positions.


Timing AdvanceTiming Advance• Timing Advance is calculated from delay of data bits in the access burst

received by the base station - long guard period allows space for this delay

Guard PeriodAccess burst data

delay

Access burst data Guard Period

• TA signal is transmitted on SACCH as a number between 0 and 63 in units of bit periods

• TA value allows for ‘round trip’ from MS to BTS and back to MS• Each step in TA value corresponds to a MS to BTS distance of 550 metres• Maximum MS to BTS distance allowed by TA is 35 km


Timing AdvanceTiming Advance• Timing Advance value reduces the 3 timeslot offset between downlink and

uplink

0 1 2 3 4 5 6 7

Delay 3 timeslots

Downlink

Uplink

TimingAdvance

Actual delay

Uplink

• The Timing Advance technique is known as adaptive frame alignment


0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7


_____________________________________________________________________ 1.5 Multiframes

To provide all the logical channel operations with the physical resources (timeslots) available, an additional time frame structure is required in which the logical channels are multiplexed onto the timeslots. This is the concept of multiframes.

MultiframesMultiframes• Multiframes provide a way of mapping the logical channels on to the

physical channels (timeslots)• A multiframe is a series of consecutive instances of a particular timeslot

• GSM uses multiframes of 26 and 51 timeslots

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 70 1 2 3 4 5 6 7

1 1 1 1

Multiframe

FrameTime



T T

Traffic Channel MultiframeTraffic Channel Multiframe• The TCH multiframe consists of 26 timeslots.

• This multiframe maps the following logical channels:

• TCH Multiframe structure:

T T T T T T T T T T T T T T T T IT T T T T

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 24 2516 17 18 19 20 21 22 23

•TCH•SACCH•FACCH

T = TCH S = SACCH I = Idle

FACCH is not allocated slots in the multiframe. It steals TCH slots when required -indicated by the stealing flags in the normal burst.


TS

TCH is always allocated on the 26 frame multiframe structure shown above. Control channels may be allocated in several ways on the 51 frame structure. A basic BCCH multiframe is shown below. The main reason for other structures is the allocation of SDCCH/SACCH which is dealt with in Section 2.

Control Channel MultiframeControl Channel Multiframe• The control channel multiframe is formed of 51 timeslots• CCH multiframe maps the following logical channels:

0 1 42-45 46-49 5032-35 36-39 40 4122-25 26-29 30 3112-15 16-19 20 212-5 6-9 10 11

RACH

Uplink

Downlink

Downlink:•FCCH•SCH•BCCH•CCCH (combination of PCH and AGCH)

Uplink:•RACH

F = FCCH S = SCH I = Idle

• Other multiframe structures (for SDCCH and CCCH) are described in Section 2


S BCCHF CCCH S CCCHF CCCH S CCCHF CCCH S CCCHF CCCH S CCCHF CCCH I


Frame HierarchyFrame Hierarchy

0 1 2 3 4 5 6 7

1 timeslot = 0.577 ms

1 frame = 8 timeslots = 4.615 ms

= 26 TCH Frames (= 120 ms)or51 BCCH Frames (= 235 ms)

= 26 BCCH Multiframes (= 6.12s)or 51 TCH Multiframes (= 6.12s)

= 2048 Superframes(= 3 hr 28 min 53.76 s)


Multiframe:

Superframe:

Hyperframe:

The superframe provides a basic repeat period for both traffic and control multiframes. It is used as a reference period for reporting bit error rates. The timing of the hyperframe relates to the cycle of frame numbers transmitted on the synchronisation channel (SCH). After 26 x 51 x 2048 = 2715648 frames, the frame number (which consists of 22 bits) resets to zero.


_____________________________________________________________________

1.6 GSM Protocols

GSM Protocol ArchitectureGSM Protocol Architecture

• In the OSI Reference Model, the logical channels of the air interface are at the Service Access Point (SAP) of the Physical Layer (Layer 1)

• ISDN Reference Model divides the protocol plane into a Control Plane and a User Plane

• corresponds to the control and traffic channels of the logical channels

• Some user data (notably SMS text messages) is carried by the control plane

Control Plane User Plane

BC

HC

CH

DC

CH

TCH

Physical Layer


User Plane User Plane -- Speech TransmissionSpeech Transmission

GSC

FEC FEC MPX MPX

GSC A-law

Voice

TRAU ISDN format

ITU-T A-law

• Transport of speech across the Um and Abis interfaces:

Um A


MS BSS MSC(BTS - Abis - BSC)


Speech Transmission The diagram above outlines a possible transport path for speech in GSM. The physical layer (FDMA / TDMA on the air interface) has been omitted for clarity. Speech is encoded at the MS by the GSM Speech Codec (GSC) using hybrid encoders to give a data rate of 13 kbps. Forward Error Correction (FEC) is applied using a concatenated combination of half rate convolutional coding and block coding. At the BSS the forward error correction and any encryption is decoded by the TRX and the data is converted to the ISDN format (ITU-T A-law) by a Transcoding and Rate Adaption Unit (TRAU). The A-law format carries data at 64 kbps across the fixed network. The TRAU may be part of the BTS or part of the BSC. If the TRAU is located at the BSC, then up to 4 speech channels may be multiplexed at the BTS (MPX in the diagram) onto an ISDN B channel which reduces the bandwidth required across the Abis interface. Locating the TRAU at the BSC allows the TRAU operation for all the BTSs to be combined in one unit.

This however requires signalling on the Abis interface to control the TRAU function. One channel of 16 kbps is reserved on this link to allow in-band signalling (3 kbps) together with a speech channel (13 kbps).


GSM Signalling ProtocolsGSM Signalling Protocols

CM CM

MM MM

RR RR

RR

MAP

ISDNUP

DTA

P

DTA

P

BSS

MAP

BSS

MAP

BTSM SCCPBTSM SCCP SCCP

LAPDLAPDLAPDmLAPDm

MTPMTP’MTP’

TDMA/FDMA

TDMA/FDMA

G.703G.705G.732

G.703G.705G.732

MS BTS BSC MSC

Layer 1

Layer 2

Layer 3

Um Abis A

GSM specific protocols SS7 based protocols


Terminology of GSM Protocol Architecture CM Connection Management MM Mobility Management RR Radio Resources Management LAPD Link Access Procedure D LAPDm Link protocol adapted for air interface (Um) BTSM Base Transceiver Station Management BSSMAP Base Station System Management Application Part DTAP Direct Transfer Application Part SCCP Signalling Connection Control Part TCAP Transaction Capabilities Application Part MTP Message Transfer Part MAP Mobile Application Part UP User Part ITU-T G.703, G705, G.732: Protocols for digital transfer of signalling messages on the Abis and A interfaces at 2048 kb/s or 64 kb/s


AIR INTERFACE PROTOCOLS Layer 1 – Physical Layer On the air interface, the physical layer uses FDMA/TDMA, multiframe structure, channel coding etc. to implement the logical control channels. Services provided by layer 1 are:

• Access capabilities – multiplexing logical onto physical channels • Error protection – error detection / correction coding mechanisms • Encryption

Layer 2 – LAPDm – Link Access Procedure on Dm channels Data link protocol responsible for protected transfer of signalling messages between MS and BTS. LAPDm supports the transport of messages between protocol entities on Layer 3, in particular: BCCH, PCH, AGCH and SDCCH signalling. Layer 3 - Network Sub-layers:

• Radio Resource Management (RR) • Mobility Management (MM) • Connection Management – 3 entities: • Call Control (CC) • Supplementary Services (SS) • Short Message Service (SMS)

RR is responsible for:

• Monitoring BCCH and PCH • Administering RACH • Requests for and assignments of data and signalling channels • Measurements of channel quality • MS power control and synchronisation • Handover • Synchronisation of data channel encryption and decryption

MM is responsible for:

• TMSI assignment • Location updating • Identification of MS (IMSI, IMEI) • Authentication of MS • IMSI attach and detach • Confidentiality of subscriber identity


Within Connection Management, Call Control (CC) is responsible for:

• Set up of normal calls (MS originated, MS terminated) • Set up of emergency calls (MS originated only) • Terminating calls • DTMF signalling • Call related supplementary services • Service modification during a call (e.g. speech/data, speech/fax)

SummarySummary

• Logical Channels: TCH, BCH, CCCH, DCCH

• FDMA / TDMA structure: multiple access schemes, spectrum allocations, timeslots

• Physical Channels: Data bursts, timing advance

• Multiframes: traffic and control multiframe structures, hierarchy

• Protocols: speech channel, TRAU, signalling protocols, RR, MM, CC



Section 1 Self-Assessment Exercises

Exercise 1.1 - Logical Channel Usage The following tables list the operations involved in:

a) Location Updating b) Mobile Terminated Call

In each case, state the logical channels used for the operation Location Updating

Operation Channel Used Channel request Channel assignment Request for location updating Authentication challenge and response Cipher mode request and acknowledgement Confirmation and acknowledgement of update Channel release

Mobile Terminated Call

Operation Channel Used

Paging of mobile

Mobile requests a channel

Channel assigned

Mobile answers paging from network

Authentication challenge and response

Cipher mode request and acknowledgement

Set up message and confirmation by mobile

Traffic channel assigned

Traffic channel acknowledged

Alerting (phone rings)

Connect and acceptance (user answers)

Exchange of user data (speech)


Exercise 1.2 - Timing Advance Two mobiles, A and B, are operating in cell. Mobile A is allocated TS2 and a TA of 50. Mobile B is in TS4 and has TA of 30. a) Find the distance of each mobile from the base station. b) Draw a timing diagram indicating the actual start times of the up and downlink bursts

of each mobile. Mark time values in bit periods from the start of the frame, remembering that 1 timeslot (1 burst) = 156.25 bit periods.


Exsercise 1.3 - Multiframe Timings 1. SACCH is used to report cell measurements made by the mobile back to the serving

base station. It takes 4 bursts of SACCH to send one report. How often is a complete SACCH report received by the base station?

2. When a mobile has measured the power level from a neighbouring base station, it also identifies the BTS by synchronising with its FCCH and SCH channels. This is done in the idle frame of the TCH multiframe.

At a certain point in time, the start of the TCH and control channel multiframes are aligned: After various cycles of the TCH multiframe, the idle frame in TCH will align with the FCCH in the CCH multiframe. Find the first and second time this will occur (in terms of cycles of the TCH multiframe).

TCH

CCH


2. Traffic Theory and Channel Dimensioning

____________________________________________________________________ 2.1 Introduction

In this section the following topics will be covered:

• The theory of traffic measurement • Traffic channel dimensioning calculations • SDCCH dimensioning • CCCH configuration and dimensioning • Multi-service traffic dimensioning


____________________________________________________________________ 2.2 Traffic Measurement

• Unit of traffic measurement: erlang (E)

• Traffic in erlangs is the number of call-hours per hour:

A = C T / 3600

A = Traffic in ErlangC = number of calls during the hourT = mean holding time per call in seconds

• One channel in continuous use is carrying a traffic of 1 erlang

• Typical traffic per subscriber during the busy hour is 25 mE which corresponds to a mean call holding time of 90 s

Traffic MeasurementTraffic MeasurementSection 2 – Traffic & Dimensioning

Another traffic unit, used mostly in the USA, is the Call Centum Second (CCS):

1 CCS = 100 call seconds per hour 1 Erlang = 3600 call seconds per hour 1 Erlang = 36 CCS


BlockingBlocking

Offered Traffic : Total traffic offered to channel by all users

Carried Traffic : Traffic successfully carried by the channel

Blocked Traffic: Traffic which is blocked at call setup

Call Setup

ProcessOffered Traffic

Blocked Traffic

Carried Traffic

Offered Traffic = Carried Traffic + Blocked Traffic

Section 2 – Traffic & Dimensioning

Grade of Service (Grade of Service (GoSGoS))

• Typical Grade of Service is 0.02 (2%)

• Grade of Service is also called blocking probability or loss probability

• Grade of Service is the fraction of incoming calls (offered traffic) allowed to beblocked due to congestion in the channel


Offered Traffic

Blocked Traffic

Carried Traffic

A

A x GoS

A x (1 - GoS)Call Setup

Process

A good grade of service is a low value. This implies low channel utilization. If a poorer grade of service is accepted, more traffic can be offered to the same number of traffic channels.


Erlang Models of TrafficErlang Models of Traffic• Two commonly used models are Erlang B and Erlang C• Erlang B - blocked calls are lost or cleared• Erlang C - calls that cannot be handled are put in a queue until a channel

becomes available

A A(1-GoS)

A (GoS)

QueueErlang B

Erlang C

• GSM uses the Erlang B model not Erlang C


For GSM we are concerned with circuit switched voice traffic which must be handled in real time. Thus the Erlang B model with no queuing is appropriate.

Erlang B CalculationsErlang B Calculations• Tables based on the Erlang B model allow calculations to be made

relating:• Offered traffic• Grade of Service• Number of channels

• Structure of Erlang B table:

• Example: at 2% blocking (0.02 GoS), 2 traffic channels can carry 0.22347 erlangs of traffic

0.01 0.02 0.03

123

.01010 .02041 .03093

.15259 .22347 .28155

.45549 .60221 .71513

Grade of Service

n

Offered trafficNumber of channels



____________________________________________________________________ 2.3 Traffic Channel Dimensioning

Channel Dimensioning Channel Dimensioning -- ExampleExample

• In GSM channel dimensioning, the number of channels must be related to the number of carriers (frequencies) available:

• 8 channels (timeslots) per carrier• Some channels will be required for signalling

• Example - in a particular cell:Mean call holding time = 90 secondsGrade of Service = 1 %Total number of available carriers = 43 timeslots allocated for signaling

How many subscribers can this cell support ?


This type of traffic calculation, using Erlang B tables, is fundamental to all dimensioning problems whether for user traffic (TCH) or control signalling (SDCCH).

Channel Dimensioning Channel Dimensioning -- SolutionSolution

• Mean call holding time of 90 s implies the average traffic per subscriber is 25 mE

• Number of channels available is given by:(carriers x 8) - signalling channels

= 4 x 8 - 3 = 29 channels

• Using Erlang B tables for GoS = 0.01 and n = 29 channels, gives traffic that can be offered as 19.487 E = 19487 mE

• Number of subscribers that can be supported is: 19487 / 25 = 779



Trunking EfficiencyTrunking Efficiency

• Trunking efficiency or channel utilisation is given by:

carried traffic / number of channels

Trunking Efficiency = A (1- GoS) / n

• In the Erlang B model:

• Using the previous example:A = 19.487 E, GoS = 0.01, n = 29

• Trunking Efficiency = 19.487 (1 - 0.01) / 29 = 0.665 = 66.5 %


Grade of service measures how well the network is performing from the user’s perspective. They are just concerned with being able to make their call. Trunking efficiency looks at the situation from the network operator’s point of view and asks how well are we using the network resources?

____________________________________________________________________ 2.4 Control Channel Dimensioning

So far we have considered the channels required for user traffic and taken a given figure for those needed for signalling. There are several signalling channel requirements, which we must allow for. The most demanding of these is SDCCH. This is the only other type of dedicated channel (apart from TCH) that may be allocated to a mobile. It is used for call set up as well as several other purposes. This means it is a ‘gateway’ to TCH and if it is incorrectly dimensioned, we could have calls blocked due to insufficient SDCCH when there is capacity available on TCH to carry them.


• A Standalone Dedicated Control Channel (SDCCH) is allocated to a user by the access grant channel (AGCH) in response to a random access (RACH) request for a channel

• SDCCH carries signalling between the MS and BTS while no traffic channel (TCH) is active

• The main activities on SDCCH and the mean holding times for these are shown here

SDCCH DimensioningSDCCH Dimensioning

SDCCH Activity Mean Holding Time (s)

Call Set-up 2.5Location Updating (Automatic) 3.5Location Updating (Periodic) 3.5IMSI Attach 3.5IMSI Detach 3.0SMS Message 6.5Supplementary Services 2.5


SDCCH Grade of ServiceSDCCH Grade of Service• The main function of SDCCH is to carry call setup signaling

• Since access to a TCH is via SDCCH, the grade of service for SDCCH must be significantly better than for TCH - typically 2 to 4 times better - e.g. if TCH GoS = 2%, SDCCH GoS = 0.5% to 1%

SDCCHrequests

TCHrequests

Services using only SDCCHe.g. SMS

Blocking

Carried traffic on TCH

Blocking

Voice calls require SDCCH then TCH



SDCCH Grade of ServiceSDCCH Grade of Service

SDCCHGoS1

TCHGoS2

Offered voice traffic = A (1 - GoS1) A (1 - GoS2)(1 - GoS1)A

• The carried traffic can be calculated by considering a two stage process -Erlang B blocking at SDCCH, then at TCH:

(GoS1) A+

(GoS1) A’

GoS2 (1 - GoS1) A

Offered SDCCH only traffic = A’

(1 - GoS1) A’

• The effective grade of service for the overall process is:GoS1 + (1 - GoS1)GoS2


5mE per subscriber is a good ‘rule of thumb’ for SDCCH traffic, just as we took 25mE per subscriber for TCH dimensioning.

SDCCH ExampleSDCCH Example• Question:

A cell is required is serve 500 subscribersSDDCH grade of service is set at 0.5%Typical SDCCH traffic in the busy hour is 5 mE

How many SDCCH channels are required?

• Solution:Total SDCCH traffic = 500 x 5 = 2500 mE = 2.5 EFrom Erlang B tables, using GoS = 0.005, this requires 8

channels

• How are the required SDCCH channels to be allocated?



We must now be aware that an SDCCH channel is not simply allocated to a timeslot as is TCH, but to a set of instances of a timeslot within the multiframe structure. There are different ways of allocating SDCCH using combined or non-combined multiframes.

SDCCH AllocationSDCCH Allocation• SDCCH is allocated on the control channel multiframe structure in

blocks of 4 channels (SDCCH/4) or 8 channels (SDCCH/8)• SDCCH/4 is combined with other control channels on timeslot 0:

SACCH 2 and 3 are on the next multiframe

SDCCH/4 allocation

Combined multiframe structure

• One SDCCH channel may be replaced by CBCH if required


Downlink

S BCCHF CCCH S CCCHF CCCH S SDCCH0F SF SF ISDCCH

1SDCCH

2SDCCH

3SACCH

0SACCH

1

Uplink

RR RACH SDCCH0

SDCCH1

SDCCH3

SACCH0

SACCH1

SDCCH2RR

The combined multiframe (SDCCH/4) is only ever implemented on timeslot 0 of the BCCH carrier.

NonNon-- Combined Multiframe SDCCHCombined Multiframe SDCCH

SDCCH/8 may be allocated on a non-combined multiframe:

Other SACCH channels are on the next multiframe

SDCCH/8 allocation

Non -combined multiframe structure


Downlink

ISACCH0

SACCH1

SDCCH0

SDCCH1

SDCCH2

SDCCH3

SDCCH4

SDCCH5

SDCCH6

SDCCH7

SACCH2

SACCH3 I I

ISACCH1

SACCH2

SACCH3 I I SACCH

0SDCCH

0SDCCH

1SDCCH

2SDCCH

3SDCCH

4SDCCH

5SDCCH

6SDCCH

7

Uplink


SDCCH Allocation Depending on the SDCCH capacity required, SDCCH channels can be allocated in blocks of 4 or 8, as follows:

4 Channels SDCCH/4 8 Channels SDCCH/8 12 Channels SDCCH/4 + SDCCH/8 16 Channels SDCCH/8 + SDCCH/8 20 Channels SDCCH/4 + SDCCH/8 + SDCCH/8

Only one block of 4 channels is ever allocated since the combined multiframe used by SDCCH/4 is on the BCCH carrier. Cell broadcast (CBCH) will reduce the number of SDCCH channels by 1 if it is in use. The total amount of SDCCH traffic that must be accommodated will actually depend on the location of the cell, since other SDCCH activities such as location updating will only occur at certain cells.

Practical SDCCH Dimensioning Practical SDCCH Dimensioning • Certain locations make greater use of SDCCH and will require particular

allocation, e.g.

• Cells at the border between location areas where location updating occurs frequently

• Airport:

Passengers disembark in large numbers and switch on their mobiles imposing a lot of pressure on SDCCH for location updating

Location updating may be prolonged for international roaming subscribers

Location area boundary cells


In addition to SDCCH, the multiframe structure also carries the common control channel (CCCH) which handles paging and access grant messages. We will now consider how CCCH is configured to provide PCH and AGCH and how to dimension this requirement.


CCCH Configuration CCCH Configuration • On the downlink, CCCH consists of paging (PCH) and access grant (AGCH)

messages

• A combined multiframe has only 3 CCCH blocks to allow for SDCCH and SACCH:

• A non-combined multiframe has 9 CCCH blocks on timeslot 0:

• A complete paging or access grant message takes four bursts (timeslots),i.e. one CCCH block.



1SDCCH

2SDCCH

3SACCH

0SACCH

1


CCCH PriorityCCCH Priority• CCCH blocks are allocated to either PCH or AGCH according to the

following priority:

Immediate Assignment Reject Message (AGCH)

Priority

High

Low

PCH

Immediate Assignment Message (AGCH)

• During periods of heavy paging, PCH could dominate, leaving no blocks for access grant messages

• To avoid this, some blocks can be reserved for AGCH


Paging will make more use of CCCH than the access grant messages, since paging is done across a location area. All cells in the location area are paged, whether the required mobile is in that cell or not. AGCH only takes place in the specific cell containing the mobile.


• In a non combined multiframe, up to 7 of the 9 blocks may be reserved for AGCH:

Reserving AGCH Blocks on CCCHReserving AGCH Blocks on CCCH

• In a combined multiframe, up to 2 of the 3 blocks may be reserved for AGCH:

• Additional CCCH capacity can be provided on other timeslots (2,4 or 6) of the BCCH carrier if required

• The number of AGCH blocks reserved is specified in the system information messages which the mobile reads on the BCCH




1SDCCH

2SDCCH

3SACCH

0SACCH

1

CCCH Configuration Parameter - CCCH_CONF BCCH contains a number of system information messages, BCCH/SYS_INFO n. BCCH/SYS_INFO 3 carries a parameter, CCCH_CONF, which informs the mobile of the CCCH configuration to be used, including number of timeslots, combined or non-combined multiframes, reservation of AGCH blocks.

CCCH_CONF Number of Timeslots for CCCH

Configuration

0 1 TS0 non-combined 1 1 TS0 combined 2 2 TS0, TS2 non-combined 3 3 TS0, TS2, TS4 non-combined 4 4 TS0, TS2, TS4, TS6 non-combined


Paging CapacityPaging Capacity• Paging capacity is the number of mobiles that

can be paged per second

• This depends on:• CCCH configuration

• AGCH blocks reservation

• Type of paging message used

• Paging message takes 4 bursts (1 CCCH block)

• This can page up to 4 mobiles depending on the message type used


Paging Message Types: Type 1: can address up to 2 mobiles using either IMSI or TMSI. Type 2: can address up to 3 mobiles, one by IMSI and the other 2 by TMSI. Type 3: can address up to 4 mobiles using the TMSI only. If the network does not use TMSI, only Type 1 can be used. Paging message for individual mobiles are sent to BSS which stores them temporarily until there are enough to make up a full type 1,2 or 3 message or until a configurable timer (set by the operator) expires. The message is then broadcast.


Calculating Paging CapacityCalculating Paging Capacity

X = number of mobiles paged per paging message (1 to 4)

Y = number of possible paging messages per multiframe

Duration of channel multiframe = 0.235 seconds (235 ms)

• X depends on paging message type

• Y depends on CCCH configuration in the multiframe (e.g. 3 or 9) and the number of AGCH blocks reserved

235.0XYCapacity Paging = mobiles / second


PCH DimensioningPCH Dimensioning

Paging channel requirement in blocks per multiframe is given by:

4.25 x 3600 x PMFM x PF x MT x Calls

Calls = Number of calls predicted for the location area during busy hourMT = Fraction of calls which are mobile terminatedPF = Paging Factor = number of pages required per callM = safety marginPMF = Paging Message Factor = number of pages per messageNumber of control channel multiframes per second = 4.25 (1 / 0.235)



This gives the following data:Calls = 50 000MT = 0.3PF = 2PMF = 4A typical safety margin for peak variations in number of calls is 1.2

PCH Dimensioning PCH Dimensioning -- ExampleExample

• PCH requirement =

• A particular location area contains 50 000 subscribers. It is predicted that 30% of these will receive a call during the busy hour. On average 2 pages are needed per call and only type 3 paging messages (TMSI) are used.

4.25 x 3600 x 41.2 x 2 x 0.3 x 50000

= 0.6

• 1 PCH block per multiframe will be adequate


PCH Requirement = Calls x MT x PF x MPMF x 3600 x 4.25

AGCH DimensioningAGCH Dimensioning

• AGCH requirement is found by adding up the activities which need an AGCH message during the busy hour

• The following equation gives the number of AGCH blocks per multiframe:

4.25 x 2 x 3600M x SS) ID IA SMS LU (Calls +++++AGCH required =

The terms in brackets are the predicted numbers during the busy hour for:Calls, Location Updates (LU), SMS, IMSI attaches (IA), IMSI detaches (ID), Supplementary Services (SS) M = safety margin (e.g. 1.2) The factor of 2 is because each AGCH block can carry 2 immediate assignment

messages



AGCH Dimensioning AGCH Dimensioning -- ExampleExample• A cell has 1000 calls during the busy hour• Other AGCH activities are modelled as multiples of the calls figure.

A possible model is:

Activity Multiplier Total

LU 2 2000

SMS 0.1 100

SS 0.2 200

IMSI attach 0.2 200

IMSI detach 0.1 100

• This gives the total activity (including Calls) as 3600

AGCH required =4.25 x 2 x 3600

1.2 x 3600= 0.14 AGCH blocks per

multiframe


The main conclusion to draw from these examples is that CCCH dimensioning is not such a serious issue as that for SDCCH. The additional allocation allowed by the CCCH_CONF settings is seldom required.

____________________________________________________________________ 2.5 Multi-service Traffic Dimensioning

GSM was originally a voice only system. Developments will include an increasing proportion of the traffic offered being in the form of High Speed Circuit Switched Data (HSCSD). Initially the HSCSD service will entail a user seizing two or three timeslots on a carrier. The network will have to accommodate both voice and HSCSD services. Unfortunately, the Erlang B formula is not appropriate for calculating the required number of timeslots when the resource is shared amongst services of different amplitude (“amplitude” is the name given to the unit of resource required by different services: for example, an HSCSD connection requiring two timeslots would have an amplitude of 2.).


Accommodating a multiAccommodating a multi--service systemservice system

• The Erlang B formula relies on the variance of the demand equalling the mean (a Poisson distribution).

• If a particular service requires more than one “trunk” per connection, the demand is effectively linearly scaled and the variance no longer equals the mean.

• Methods to investigate:• Equivalent Erlangs• Post Erlang-B• Campbell’s Theorem


Equivalent ErlangsEquivalent Erlangs

+

Low Bandwidth Equivalent

High Bandwidth Equivalent

• Combine the two traffic sources together by converting one to the bandwidth of the other

• The trunking efficiency will VARY with the bandwidth of equivalent Erlang that you choose!

• Not suitable for use due to this property

2 Erlangs of Low

Bandwidth

1 Erlang of High

Bandwidth

Difference in capacity required for same GoS



Equivalent Erlangs ExampleEquivalent Erlangs Example

• Consider 2 services sharing the same resource:• Service 1: uses 1 trunk per connection. 12 Erlangs of traffic.• Service 2, uses 3 trunks per connection. 6 Erlangs of traffic.

• We could regard the above as equivalent to 30 Erlangs of service 1:• 30 Erlangs require 39 trunks for a 2% Blocking Probability

• Alternatively, we could regard the above as equivalent to 10 Erlangs of service 2.

• 10 Erlangs require 17 trunks, (equivalent to 51 “service 1 trunks”) for a 2% blocking probability

• Prediction varies depending on what approach you choose.


• Consider 2 services sharing the same resource:• Service 1: uses 1 trunk per connection. 12 Erlangs of traffic.• Service 2: uses 3 trunks per connection. 6 Erlangs of traffic.

• We could calculate the requirement separately• Service 1: 12 Erlangs require 19 trunks for a 2% Blocking Probability• Service 2: 6 Erlangs require 12 trunks (equivalent to 36 “service 1

trunks”).

• Adding these together gives 55 trunks.• This method is known to over-estimate the number of trunks required

as can be demonstrated by considering services requiring an equal number of trunks.

Post ErlangPost Erlang--BBSection 2 – Traffic & Dimensioning


• Consider 2 services requiring equal resource:• Service 1: uses 1 trunk per connection. 12 Erlangs of traffic.• Service 2: uses 1 trunk per connection. 6 Erlangs of traffic.

• We could calculate the requirement separately• Service 1: 12 Erlangs require 19 trunks for a 2% Blocking Probability• Service 2: 6 Erlangs require 12 trunks.

• Adding these together gives 31 trunks.• The accepted method of treating the above would be to regard it as a

total of 18 Erlangs that would require 26 trunks.• Post Erlang-B overestimates the requirement.

Post ErlangPost Erlang--BBSection 2 – Traffic & Dimensioning

Post ErlangPost Erlang--BB

• Combine the two traffic sources together after calculating required capacity

• The trunking efficiency variation with magnitude is not considered - pessimistic about offered traffic supported to the same GoS

• Not suitable for use due to this property

1 Erlang of Service A

1 Erlang of Service B

+

1 Erlang and 1 Erlang of of Service B

Illustration using 2 services of same bandwidth

Difference in

capacity required for same

GoS

Accepted correct method



Campbell’s TheoremCampbell’s Theorem• Campbell’s theorem creates a composite distribution where:

• c is known as the capacity factor• The amplitude used in the capacity is the amplitude of the target service• Once the offered traffic and Capacity are derived, GoS can be derived with

Erlang-B -> similarly Required Capacity can be calculated if Offered Traffic and GoS target is known

( )caCCapacity ii −= c

fficOfferedTra α=

∑∑

==

iiii

iiii

ba

bac

γ

γ

αν

2

α = meanυ = varianceγi = arrival rateai = amplitude of service bi = mean holding timeiibγ=Traffic Offered Service


Campbell’s Theorem is seen as an appropriate way to establish the required resource for a certain amount of mixed traffic is offered. It is best understood as a procedure. Suppose we needed to establish the required resource to accommodate 12 Erlangs of voice and 6 Erlangs of HSCSD traffic of amplitude 3. The first step is to calculate the mean:

3036112mean =×+×= Next we calculate the variance:

6636112variance 22 =×+×= From these two parameters a capacity factor is derived.

2.2mean

variance factor,capacity ==c


The equivalent offered traffic is calculated by dividing the mean by the capacity factor:

Erlangs 6.132.230 trafficoffered ==

From the Erlang B table, 21 trunks would be required. To convert this into equivalent voice trunks, this figure must be multiplied by the capacity factor.

46.22.221trunksvoiceEquivalent =×= A minor adjustment must be made depending on which service is defined as the target service. This is to reflect the fact that, if two services share the same resource, the one that demands the higher unit resource will experience a worse grade of service. So, if the HSCSD service is deemed to be the target service, a total of 46+3 = 49 timeslots should be available.

Campbell’s Theorem Example(1)Campbell’s Theorem Example(1)

• Consider the same 2 services sharing the same resource:• Service 1: uses 1 trunk per connection. 12 Erlangs of traffic.• Service 2, uses 3 trunks per connection. 6 Erlangs of traffic.

• In this case the mean is:

• The variance is:

∑ ∑ =×+×=×== 3063121Erlangs iiii aabγα

∑ ∑ =×+×=×== 6636112Erlangs 2222iiii aabγν




• Capacity Factor c is:

• Offered Traffic for filtered distribution:

• Required Capacity for filtered distribution at 2% GoS is 21

2.23066

===ανc

63.132.2

30 Traffic Offered ===cα



• Required Capacity is different depending upon target service for GoS(in service 1 Erlangs):

• Target is Service 1 C1=(2.2 x 21) + 1 = 47

• Target is Service 2, C2=(2.2 x 21) + 3 = 49

• Different services will require a different capacity for the same GoS. In other words: for a given capacity, the different services will experience a slightly different GoS.



Traffic Analysis Methods ComparedTraffic Analysis Methods Compared

• Equivalent Erlangs• Optimistic if you use the smallest amplitude of trunk (39)• Pessimistic if you use the largest amplitude of trunk (51)

• Post Erlang-B• Pessimistic (55)• Trunking efficiency improvement with magnitude ignored

• Campbell’s theorem• Middle band (47 - 49)• Different capacities required for different services - realistic• Preferred solution for dimensioning, but not ideal...


Capacity-Based Dimensioning with Campbell’s Theorem. Suppose a particular area was forecast to offer 250 Erlangs of voice traffic and 63 Erlangs of HSCSD traffic with an amplitude of 2. The calculation detailed below suggests that, if each cell is capable of providing 15 timeslots, 56 cells will be required to service that demand with each cell then capturing 4.46 Erlangs of voice traffic and 1.13 Erlangs of HSCSD.


Capacity Dimensioning with Campbell’s Capacity Dimensioning with Campbell’s TheoremTheorem

• Consider the following service definition and traffic forecast.


• Based on a theoretical availability of 15 voice trunks per cell and using voice as the ‘benchmark’ service, determine the number of cells required to serve the above traffic levels and the traffic offered per cell for each service

Service Amplitude ForecastVoice 1 250E

HSCSD 2 60E


• Assuming we have n cells, we can determine the loading per cell.

nnc

c

nnn

nnn

282335.1376mean trafficoffered

335.1376502

meanvariance

502263250variance

376263250mean

2

=×

==

===

=×

+=

=×

+=




• Unfortunately, we cannot now look up “282/n” in the Erlang B tables. • We need to introduce a notional capacity per cell in terms of “voice”

trunks.• We will assume that each cell has a capacity of 15 such trunks.

nnc282

335.1376mean trafficoffered =

×==



• Considering the equation

• Ci is predefined as 15. ai depends on the service we use as our “benchmark”. Choosing the voice service as the “benchmark” service make ai equal to 1.

• 10.5 (or, rather, 10) trunks will service 5.08 Erlangs.

caC ii −

= Capacity

( ) 5.10335.1

115=

−=iC




• 10 trunks will service 5.08 Erlangs.• Therefore,

• Cell requirement is established at 56 cells.• Each of the cells will service: 4.46 Erlangs of voice; 1.13 Erlangs

of HSCSD.

5.55

08.5282

=

=

n

n


Assessing Cell Loading using Campbell’s Theorem Campbell’s Theorem can be used to indicate the number of carriers that should be provided following a “traffic capture” exercise. An example is given below.

Assessing Cell Loading using Assessing Cell Loading using Campbell’s TheoremCampbell’s Theorem

• After placing sites on the coverage map and spreading the traffic, the next stage is to assess the cell loading.

• If mixed services are used, it is necessary to use Campbell’s Theorem to assess the required number of timeslots to satisfy the likely demand.

• Consider the case where a particular cell captures 7 Erlangs of voice and 2 Erlangs of HSCSD traffic that requires 2 timeslots per connection.



Assessing Cell Loading using Assessing Cell Loading using Campbell’s TheoremCampbell’s Theorem

• Using Campbell’s Theorem:

• Hence 20 timeslots required.

( ) 20136.114 :benchmark as voiceTakingrequired. trunks14 B, Erlang From

09.836.1

11 trafficoffered

36.11115

15227variance11227mean

2

=+×

==

==

=×+=

=×+=

c


____________________________________________________________________ 2.6 Dimensioning Micro- and Pico-cells

Dimensioning Micro and PicoDimensioning Micro and Pico--CellsCells• Erlang B assumes that demand doesn’t vary as connections are allocated.• E.g. 800 subscribers producing 20 Erlangs would require 28 connections.• Statistics of demand would reduce slightly as connections were allocated.• Reduction from 800 to 772 would produce only a tiny reduction in demand.

A1

Demand when no connections

allocated produced by 800 subscribers


A2

Demand when 28 connections



In predicting the provision that should be made for a given level of demand, the Erlang B formulas make certain assumptions. One assumption made is that the level of demand does not change as connections are allocated. For example consider the situation where a cell acts as the serving cell for 800 subscribers. These subscribers generate 20 Erlangs of demand. Consulting the Erlang B table would reveal that, for a 2% blocking ratio, provision should be made for 28 simultaneous connections to be possible. It is clear that the number of subscribers that could request a connection varies from 800, when no connections are allocated, to 772 when all 28 connections are allocated. This reduction in the number of subscribers who could request a connection would result in a very small change in the demand for connections. The Erlang B formula ignores this change.

The The EngsetEngset DistributionDistribution• Ignoring the reduction in demand is not justifiable if a cell covers a small

number of high-demand subscribers.• E.g. a cell covering just 6 subscribers who offer 3 Erlangs of traffic would

produce a required provision of 7 connections if Erlang B formula is used.• This is clearly wrong.• Engset distribution considers the reduction in demand as connections are

allocated.

Demand when no connections



Demand when 5 connections

allocated produced by 1 subscriber.

• Engset formula suggests 5 connections should be provided.

A1 A2

In the situation described above, ignoring the change would not result in a large error. This is because the cell covered a large number of subscribers whose average demand was very small. In certain circumstances, a cell may be required to cover a smaller number of high-demand subscribers.


Consider, for example, a micro-cell that covered only six subscribers that generated a busy hour demand of three Erlangs. The Erlang B table would suggest that provision should be made for seven simultaneous connections. However, this is obviously too many as the cell covers only six subscribers. In such circumstances, the Engset distribution should be used as it considers the reduction in demand that would occur as connections are allocated. In the situation described here, the Engset formula suggests that provision should be made for five simultaneous connections.

SummarySummary

• Theory of traffic measurement: The erlang (E), Blocking, Grade of Service, Erlang traffic models B and C

• Traffic channel dimensioning calculations: Erlang B tables, channel calculations, trunking efficiency

• SDCCH dimensioning: Grade of Service, channel calculations, SDCCH allocation- combined and non-combined multiframes, practical considerations

• CCCH configuration and dimensioning: CCCH configurations, PCH/AGCH priority, AGCH reservation, paging capacity, PCH dimensioning, AGCH dimensioning

• Multi-service traffic dimensioning using:Erlang C, post-Erlang B, Campbell’s Theorum

• Micro & Pico-Cell Dimensioning using Engset



Section 2 Self-Assessment Exercises Exercise 2.1 - TCH Dimensioning 1. In a cell the mean holding time for a call in the busy hour is 90 s. The Grade of Service

is 2%. 3 TRXs are provided, from which 2 timeslots are needed to handle signalling.

a) How many subscribers can this cell support?

b) What is the trunking efficiency of this cell? 2. A cell serves 1000 subscribers. At the busy hour, the mean traffic generated is found to

be 20 mE per subscriber. The cell should provide a Grade of Service of 2%. a) How many TRXs will be required in this cell, given that 3 channels will be needed for

signalling? b) What spare capacity (in terms of number of subscribers) does the cell have? c) Calculate the trunking efficiency for this cell


Exercise 2.2 - TCH and SDCCH Dimensioning 1. A cell has 2 carriers and is using SDCCH/8 with cell broadcast enabled on a non-

combined multiframe. An additional control channel is used for BCCH. At busy hour, the traffic per subscriber is:

20mE TCH 5mE SDCCH

The Grades of Service provided are: 3% TCH 1% SDCCH

a) Calculate the number of subscribers the cell can support for TCH and SDCCH. b) Is this cell properly dimensioned? c) Suppose only one signalling channel were in use, with an SDCCH/4 configuration and

no cell broadcast. Would this be a sensible dimensioning solution? 2. A cell is to serve 1200 subscribers each generating busy hour traffic of 25mE on TCH

and 5mE on SDCCH.

The Grades of Service are to be: 2% for TCH 0.5% for SDCCH

Find a suitable dimensioning solution.


Exercise 2.3 - Paging Capacity Calculate the paging capacity of cells with the following configurations: a) CCCH_CONF = 0

3 blocks reserved for AGCH Type 1 paging messages

b) CCCH_CONF = 1

1 block reserved for AGCH Type 3 paging messages


Exercise 2.4 - Paging Channel Dimensioning

1. A location area has 50 000 subscribers. It is estimated that 40% of these will receive a

call during the busy hour. Assume type 1 paging messages are used and that on average 2 pages are required per call. Also take a safety margin of 1.2 to allow for peak variations. Calculate the number of PCH blocks required per multiframe.

2. A location area provides a total traffic capacity of 500 E. In the busy hour, each

subscriber generates an average of 25mE. It is predicted that 25% of subscribers will receive a call during the busy hour, requiring 2 pages per call. Type 3 paging messages are used. Taking the usual safety margin of 1.2 for variations, find the number of PCH blocks required per multiframe.


Exercise 2.5 - AGCH Dimensioning

A cell has 1500 calls during the busy hour.

Other AGCH activities are modelled using the following multipliers from the number of calls:

Activity Multiplier

LU 2.5

SMS 0.2

SS 0.25

IMSI attach 0.1

IMSI detach 0.1 Taking a safety margin of 1.2, find the number of AGCH blocks required per multiframe.


Exercise 2.6 – Multi-Service Traffic Dimensioning A cell is seen to capture 6 Erlangs of voice traffic and 2 Erlangs of HSCSD traffic of amplitude 3. Determine the number of carriers that should be allocated to the cell in order to accommodate this offered traffic.


Exercise 2.7 – Dimensioning Micro and Pico Cells A picocell is to be configured to provide service within an office environment. The office has accommodation for twelve people. Each of these people are expected to offer 300 mE of traffic to the network. Determine the number of simultaneous connections that should be offered to accommodate this offered traffic and hence determine the number of carriers that should be provided. Compare solutions made using

1. The Erlang B formula 2. The Engset formula


3. Frequency Planning

____________________________________________________________________ 3.1 Introduction

In this section the following aspects of frequency planning will be covered:

• Cellular structures and frequency reuse patterns • Interference calculations • Cell splitting • Practical frequency planning • Multiple reuse patterns


____________________________________________________________________ 3.2 Cellular Structures and Frequency Reuse Patterns

Cellular StructureCellular Structure

• Cellular radio systems divided into small cells• Each cell surrounds a fixed radio site (BTS)• Hexagon shape used for convenience - tessellates to cover

large area• Real pattern rather different - use planning tools

Hexagons for planning Ideal Coverage Reality

Section 3 – Frequency Planning

Frequency ReFrequency Re--use use

• Cellular structure allows carrier frequencies to be re-used

• High frequency re-use:

• Short distance between same carriers

• High traffic capacity

• Low C/I ratio (i.e. worse interference)

• Frequency planning involves a compromise between requirements for capacity and interference

• Digital systems like GSM can cope with lower values of C/I than analog systems



Simple frequency plans assume a homogeneous distribution of carriers and equal sized cells. We can use this to give an estimate of the interference that is likely.

7 Cell Cluster7 Cell Cluster• Simple pattern - interlock 7 cell cluster to cover area• Same number of carriers in each cell• Re-use same carriers in corresponding cells, A, B etc.

AB

CD

E

FG

AB

CD

AF

G

AB

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

B

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

D

A

C

D

E

F

G

B

C FA

B G


E

Frequency ReFrequency Re--use Distanceuse Distance• Around each cell, there are 6 cells in adjacent clusters using the same

carriers• These cells will cause mutual co-channel interference

• The C/I due to these cells can be found from the re-use distance, D

• D can be calculated from the geometry of the clusters as:

R 73D =R = radius of cell to a corner

R


AB

CD

E

FG

AB

CD

AF

G

AB

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

B

CD

E

FG

AB

CD

E

FG

AB

CD

E

FG

D

A

C

D

E

F

G

B

C FA

B G


Finding the re-use distance is the first step towards estimating the interference in the plan.

General ReGeneral Re--use Patterns use Patterns • For a frequency re-use pattern based on clusters of N sites, each of cell

radius R, the re-use distance, D is:

N 3RD =

• Typical cluster sizes are:3, 4, 7, 12, 21

• Larger cluster sizes give better C/I ratios

• However, smaller cluster sizes give higher traffic capacity per cell - more carriers available in each cell



____________________________________________________________________ 3.3 Interference Calculations

Estimating C/I for ReEstimating C/I for Re--use Patternsuse Patterns• To estimate C/I we assume:

• Each base station radiating the same power• Homogeneous propagation throughout the service area• Propagation follows a 1/Rx law (x is the propagation co-efficient)• Re-use distance, D, is large compared with cell radius, R

• On the edge of the serving cell:

xR1C =

= xD

16I

=

x

RD

61 log 10 I/C

( )

=

63N log 10 I/C

x3N R D =


Serving cell 6 nearest interfering cells

D

Note the assumption that D >> R. This is more appropriate for large clusters. The value of x will depend on the local radio propagation properties, but 3.5 is generally a good estimate.

C/I for Typical Cluster SizesC/I for Typical Cluster Sizes

• Analog systems require a minimum C/I of about 20 dB • Digital systems can cope with C/I as low as 9 dB

( )

=

63N log 10 I/C

x

• Estimates of C/I in dB, using the equation:


28.2123.7119.2110.212123.3419.4515.567.781220.8517.2713.686.53918.6615.3612.055.44713.811.18.413.01411.38.926.531.763C

luster Size N

43.532

Propagation Coefficient x


____________________________________________________________________ 3.4 Cell Splitting Techniques

Cell Splitting Cell Splitting • Initial network based on omni-directional antenna sites• To increase capacity, split each cell into 3 using sectored antennas


Original omni site

New tri-sectored

site

Our estimates of interference have assumed a simple pattern of omni sites. Realistic plans will have sites spilt into sectors. Different methods of achieving a split are shown here.

Further SplittingFurther Splitting• As the network grows, capacity can be further increased by

another 3 way split as shown


Rotate original antennas through 30o

Add new sites as shown

New siteOld site rotated

New cell


1:4 Cell Split1:4 Cell Split

• Alternative way of further splitting the cells• No re-alignment of antennas needed• Increases traffic capacity, frequency re-use and number

of sites by a factor of 4


By reducing mutual interference effects, sectoring cells reduces the overall interference in the network.

Effect of Cell Splitting on InterferenceEffect of Cell Splitting on Interference

• Directional pattern of sectored antennas reduces response to interference

• Increases C/I significantly• Allows greater frequency re-use, i.e.

smaller cells

• If cells A and B use the same carrier:• B will cause co-channel interference in A• A will cause very little co-channel

interference in B

• Interference is no longer mutual

A

B



Transition ZonesTransition Zones

• Problems may occur at the boundaries between high and low traffic areas

• Large cells in rural areas will use higher power - can cause interference with smaller urban cells nearby

• Requires careful frequency planning -possibly reserve carriers for use in such transition zones

• Alternatively, hierarchy of cells (e.g. overlay / underlay) may be used

Large rural cells

Small urban cells


Transition Zone

Simple frequency plans for sectored networks are the 3/9 and 4/12 patterns. Again these assume a regular distribution of carriers and equal sized cells.

GSM Frequency PatternsGSM Frequency Patterns• Two common re-use patterns in GSM

are 3/9 and 4/12• 3/9 consists of 3 sites, each of which

has been tri-sectored giving a cluster of 9 cells

Frequencies are assigned in sequence to the cells A1 - C3

3/9 Frequency Group in ASSET


A1

A2A3

B1

B2B3

C1

C2C3

A1

A2A3

B1

B2B3

C1

C2C3

A1

A2A3

B1

B2B3

C1

C2C3

272625242322212019

181716151413121110

987654321

C3B3A3C2B2A2C1B1A1


Interference in the 3/9 PatternInterference in the 3/9 Pattern

• 3/9 pattern allows frequencies to be allocated so no physically adjacent cells use the same frequency

• C/I is about 9 dB, which is the minimum specified for GSM with frequency hopping

• Cells A1 and C3 are physically adjacent and are allocated adjacent carriers

• On the boundary of A1 and C3:C/A = 0 dB

• GSM specifies a minimum C/A of -9 dB


A1

A2A3

B1

B2B3

C1

C2C3

A1

A2A3

B1

B2B3

C1

C2C3

A1

A2A3

B1

B2B3

C1

C2C3

4/12 Re4/12 Re--use Patternuse Pattern• 4 sites, each tri-sectored to give a 12

cell cluster• Numbering of D cells allows carriers to

be allocated so that no adjacent carriers are used in physically adjacent cells

Frequencies are assigned in sequence to the cells A1 - D3

4/12 Frequency Group in ASSET


A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

363534333231302928272625

242322212019181716151413

121110987654321

D3C3B3A3D2C2B2A2D1C1B1A1


Interference in the 4/12 PatternInterference in the 4/12 Pattern

• 4/12 pattern has no physically adjacent cells with co-channel or adjacent channel carriers

• C/I is about 12 dB

• This is adequate in GSM without frequency hopping

• C/A is higher than in 3/9 pattern

• Traffic capacity is lower than 3/9 as there are fewer carriers per cell


A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

Practical Frequency PlanningPractical Frequency Planning

• Practical factors which must be considered include:

• Base stations do not radiate same power

• Different cells may use different antennas

• Variations in propagation due to clutter and terrain

• Use planning tool (e.g. ILSA) to assign carriers

• Adjust frequency plan manually to optimise C/I

Worst interference

Average interference Total cost

Number of iterations



Adjustments for CapacityAdjustments for Capacity• Simple re-use patterns assign same

number of carriers to each cell• Practical traffic may not be evenly

distributed• Moving carriers to other cells to handle

traffic will introduce new interference problems

• This can be avoided by reducing base station power - e.g. introduce an overlay cell

Moving any carrier from B3 to C2 will decrease C/A (with C3) and C/I (with B3 in neighbouring cluster)

A1

A2A3

B1

B2B3

C1

C2C3

A1

A2A3

B1

B2B3

C1

C2C3

Under loaded cell

Heavily loaded cell


272625242322212019

181716151413121110

987654321

C3B3A3C2B2A2C1B1A1

If there are several possible under loaded cells from which a carrier can be moved, consider carefully the interference implications (for both C/I and C/A) of each possible move. Select the carrier which causes the least increase in interference.


____________________________________________________________________ 3.5 Multiple Reuse Patterns (MRP)

MRP is a popular technique used to increase capacity across a network by using different levels of frequency re-use.

Multiple Multiple ReRe--useuse PatternsPatterns

• MRP :• A technique to vary the reuse pattern for different channels and

different levels of quality of service (QoS)• Combines conservative control channel reuse with aggressive traffic

channel reuse to achieve a tighter average reuse• Frequency Hopping, Power Control and DTX are necessary

• Frequencies can be reserved for microcells and picocells

• Best used with lots of spectrum• Performance results with 15 MHz (75 GSM carriers) are better than for

5 MHz (25 GSM carriers) because there are more frequencies to hop across

• In ASSET, carrier layers are used to represent these subsets


Planning with Planning with MRPsMRPs• The subset with the greatest number of

carriers is used exclusively to plan the BCCH channels

• The subset with the second greatest number of of carriers is used exclusively to plan the first TCH (TCH1) channel on cells

• The third greatest subset is used exclusively to plan the second TCH (TCH2) channel on cells

• The next subset is used exclusively to plan the third TCH (TCH3) channel on cells and so on

BCCH

TCH1

TCH2

TCH3



MRP: Planning the BCCH LayerMRP: Planning the BCCH Layer

• 12 available carriers (GSM Carriers 1-12) available for the BCCH Layer

• Maximum allocatable carriers per cell for the BCCH is 1

• The 12 BCCH carriers are then spread throughout the network using a 4/12 Reuse pattern

A1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D31 2 3 4 5 6 7 8 9 10 11 12


A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

MRP Planning the TCH1 LayerMRP Planning the TCH1 Layer

• 9 carriers (GSM Carriers 13-21) available for the TCH1 Layer

• Maximum allocatable carriers per cell for the TCH1 is 1

• The 9 TCH1 carriers are then spread throughout the network using a 3/9 Reuse pattern

A1 B1 C1 A2 B2 C2 A3 B3 C313 14 15 16 17 18 19 20 21


A1

A2A3

B1

B2B3

C1

C2C3

A1

A2A3

B1

B2B3

C1

C2C3

A1

A2A3

B1

B2B3

C1

C2C3


MRP Planning the TCH2 LayerMRP Planning the TCH2 Layer

• 3 carriers (GSM Carriers 22-24) available for the TCH 2 Layer

• Maximum allocatable carriers per cell for the TCH2 is 1

• The 3 TCH2 carriers are then spread throughout the network using a 1/3 Reuse pattern

A1 A2 A3 22 23 24


A1

A2A3 A1

A2A3A1

A2A3

Example of MRPExample of MRP• MRP example with 5 MHz of Spectrum

• 24 GSM RF Carriers (excluding one for guard band)• 12/7/5 reuse • Average cluster size = (12 + 7 + 5) / 3 = 8

81 2 3 4 5 6 7 12 151413119 10 242322212019181716

12 BCCH Frequencies

7 TCH Group 1

5 TCH Group 2



Interference in Interference in MRPsMRPs

• MRP uses progressively fewer carriers on each layer:• Progressively tighter frequency reuse• Progressively worse interference on each carrier layer

• Ways of reducing interference:• not every cell will employ all carriers - increases the reuse distance • MRP is often used in conjunction with:

• frequency hopping• discontinuous transmission• downlink power control

• These techniques reduce the impact of interference on calls and allow close reuse distances to work more reliably


Frequency HoppingFrequency Hopping• When using frequency hopping, the actual carrier frequency used

by a TRX changes on each frame (8 timeslots)• The frequency follows either a sequential or pseudo-random

pattern:

4 2 6 5 1 3 4 21 3 4 2 6 5 1 3

Frames cycle through carriers 1 to 6 :

Hopping sequence

• One frame is 4.6 ms long• Rate of hopping = 1/ (4.6 x 10-3) = 217 hops / second• This is also known as Slow Frequency Hopping (SFH) to distinguish

it from Fast Frequency Hopping used in CDMA systems



Frequency Hopping at the BTSFrequency Hopping at the BTS• If the BTS has implemented SFH:

• TRXs used only for traffic channels will hop through set sequences• TRX used for the BCCH carrier will not hop - mobiles must be able to

access this for periodic signal level measurements

• 64 hopping sequences are available in GSM:• 1 sequence is cyclic - 1,2,3 …, 1,2 …• 63 others are pseudo random patterns

• Hop Sequence Number (HSN) defines the sequence in use• HSN = 0 indicates the cyclic sequence

• The set of carrier frequencies assigned to the sequence (Mobile Allocation) may be the same for each TRX provided the sequence starts at a different point (Mobile Allocation Index Offset, MAIO)


Frequency Hopping at the MobileFrequency Hopping at the Mobile

• Base stations need not implement frequency hopping• Mobile must be capable of SFH in case it enters a cell in which it is

implemented• In addition to hopping in step with the BTS, the mobile must also

make measurements on adjacent cells • This is why the rate of hopping is limited to SFH in GSM• The mobile needs to know:

• Frequencies used for hopping (Mobile Allocation) - coded as a subset of the Cell Allocation frequencies

• Hop Sequence Number (HSN)• Start frequency (Mobile Allocation Index Offset, MAIO)



Frequency Hopping and HandoverFrequency Hopping and Handover

• Scenario:• Mobile is frequency hopping in a cell• It is being handed over to a new cell in which it can continue

hopping• Requirement:

• Handover command message must contain information to start the hopping process in the new cell

• Channel Description in the message must include:• Hopping / Non-hopping flag• MAIO• HSN MS BSS 1

Handover Command


SummarySummary• Cellular structure: ideal hexagon shape,

allows frequency re-use• Frequency re-use patterns: 7 cell, re-use

distance, simple patterns 3,4,7,12• Interference calculations: C/I related to N

and x• Cell splitting: tri-sectored sites, 3/9, 4/12,

effect on C/I, C/A• Practical frequency planning: assumptions

, planning tools, capacity adjustments

• Multiple Reuse Patterns: principle of MRP, planning with MRP, interference effects




Exercise 3.1 - Frequency Re-use Cluster Sizes The number of hexagon cells in a cluster, which can be repeated to form a frequency re-use pattern can be found from the formula:

22 jiji ++ where i and j and integers. The table gives the numbers produced by this formula for small values of i and j.

0 1 2 3 4 5 0 0 1 4 9 16 25 1 1 3 7 13 21 31 2 4 7 12 19 28 39 3 9 13 19 27 37 49 4 16 21 28 37 48 61 5 25 31 39 49 61 75

a) Which cluster sizes are typically used in GSM group frequency planning? b) For:

i) an analog mobile system ii) a digital mobile system

Choose a suitable cluster size (giving a reasonable compromise between frequency re-use and interference) and calculate the corresponding re-use distance. Take the radius of a cell to be 10 km and the propagation coefficient as 3.5.

i / j


Exercise 3.2 - Frequency Planning Adjustments

In part of a network using a 4/12 frequency re-use pattern as shown below, one B1 cell is particularly heavily loaded with traffic. The cells adjacent to it, B2 and B3 are lightly loaded, each with a spare carrier.

A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3 A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3A1

A2A3

C1

C2C3

D3

D2D1

B1

B2B3

Carriers are assigned to the cells as follows: A1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D31 2 3 4 5 6 7 8 9 10 11 1213 14 15 16 17 18 19 20 21 22 23 2425 26 27 28 29 30 31 32 33 34 35 36

Make a case for or against moving a carrier from either the B2 cell or the B3 cell into the B1 cell. Note: assume the re-use pattern continues beyond the cells explicitly shown in the diagram.

Heavily loaded cell

Lightly loaded cells


Exercise 3.3 - MRP Planning There are many ways to plan the frequencies to be assigned to each layer in an MRP plan. This exercise will take you through one example We will use a ‘staggered’ method of assigning carriers to the following situation: Carriers available are: ARFCN 30 – 63 Maximum of 4 TRXs at each site, giving BCCH, TCH1, TCH2 and TCH3 layers MRP pattern to be used is: 12/8/8/6 1. How many carriers are to be assigned to:

a) BCCH b) TCH1 c) TCH2 d) TCH3 2. Planning the BCCH layer:

Starting with carrier 30, assign every other carrier (up to the total needed) to the BCCH layer:

3. Planning the TCH layers

For TCH1 start from the last carrier (63) and assign every other carrier up to the total required:

For TCH2 start from the last available carrier and assign every other one up to the total required: Assign the remaining frequencies to TCH3:

4. Average re-use

What is the average re-use factor of this plan?


4. Base Station Positioning ____________________________________________________________________ 4.1 Introduction

In this section the following topics are covered:

• BTS positioning for different environments • Microcell positioning • Picocell arrangements • Multi-layer cell design • Use of Repeaters


____________________________________________________________________ 4.2 BTS Positioning for Different Environments

• Initial grid of cells produced by planning process

• Actual base station positions used depend on many factors such as:

• planning permission• site availability• site surveys• power wayleaves

• Nominal plan should take into account:• traffic distribution• transport routes• topography

Nominal PlanNominal PlanSection 4 – Base Station Positioning

Base Stations in Rural AreasBase Stations in Rural Areas

• Low traffic capacity required

• Large cell radius

• Aim for complete coverage on 900 MHz (macrocells)

• Concentrate 1800 MHz coverage on areas of higher population and transport routes

• Macrocells may be omni or tri-sectored - standard frequency plans, such as 4/12

Section 4 – Base Station Positioning


BTS Positioning BTS Positioning -- Topographic EffectsTopographic Effects

• Hilly regions may have dead spots and shadow areas

• The effects of different site placement and antenna heights

• Low antenna on top of hill is generally preferable to a high one at the base

Antenna on top of hillAntenna at the base of the hill

25m height

50m height

100m height

10m height 25m height


BTS Positioning BTS Positioning -- Water Surface EffectsWater Surface Effects• Water surfaces act almost as plane

Earth reflectors with very low path loss

• This can result in interference between widely spaced cells across bays or river estuaries

• may require directional or down tilted antennas to reduce interference

• The extra coverage may be useful to serve ferry routes and shipping lanes

• Similar problems may occur over very flat land

Coverage from similar sites -extended coverage across sea



BTS Positioning BTS Positioning -- Traffic RoutesTraffic Routes• Require continuous coverage along main road and

rail routes• Dead spots in hilly areas can be filled in by

directional microcells Directional antennas to fill in coverage along road

• Cells boundaries and Location Area boundaries should avoid traffic routes

• This would cause unnecessary handovers and location updates as users travel along the route

Road along cell boundaries - frequent handovers

Road crosses edges of cells - not along boundaries


BTS Positioning BTS Positioning -- Urban SitesUrban Sites

• High traffic capacity - smaller cells• Propagation strongly affected by clutter detail -

height and type of buildings

• Cell hierarchy:• Macrocells (umbrella cells) above roof height to

cover wide areas• Microcells below roof height - localised cover for

traffic hot spots

900 MHzmacrocell

1800 MHzmicrocell

underlay

overlay


____________________________________________________________________


4.3 Microcell Positioning

MicrocellsMicrocells• Coverage over a small area - typical range of a few

hundred metres - power output ~ 250 mW = 24dBm• Mounted below roof top• Energy contained within streets by ‘canyon’ effect• Lower power - less interference - shorter re-use

distance

> 2m

> 5m

Directional antennas Omni antenna

Coverage patterns confined to streets by ‘canyon’ effect


Microcell PositioningMicrocell Positioning

• Important considerations when placing microcells:• location in street - effect of reflections in nearby streets• distance above street and below roof top • type of antenna - omni, sectored • antenna parameters - gain, beamwidth, polarisation• orientation and tilt of antenna

• Examples:• directional antennas for long road• directional antenna down tilted for in-building coverage• omni-directional antenna for open spaces and cross-roads



InIn--Building CoverageBuilding Coverage• Path losses for signal from outside building:

External path loss (not necessarily direct path)

Penetration loss at external wall

Reflections at walls, floors, ceilingsPenetration through walls etc.

BTS antenna

Losses depend on building materials and thickness, angles of incidence, number of floors, walls etc. Each loss term may be several dB


____________________________________________________________________ 4.4 Picocell Arrangements

PicocellsPicocells• Microcell base stations sited inside buildings• Antennas may be:

• omni directional - ceiling mounted• directional panel array - wall mounted

• Propagation within a building is very complex• To achieve a more consistent coverage,

distributed antennas may be used:• antennas in different parts of building connected

to same TRX via splitters / combiners• active repeater amplifiers may be used to

overcome feeder losses• leaky feeders (radiating coaxial cable) can give

very uniform coverageTRX

Splitters / combiners

Ceiling mounted omni antenna

Distributed antennas



____________________________________________________________________ 4.5 Multilayer Cell Design

MultiMulti--layer Cell Design layer Cell Design • Network design considerations:

• Microcell positioning• Radio resource management (channels/frequencies)• Call and handover admission

• Use test cells to determine suitable microcellpositions:

Macrocell BTS

Test microcell

Mobile measures power levels of neighbour cells including test microcell

Dummy BCCH


A hierarchical GSM network can have macrocells providing continuous coverage, with microcells to serve hot spots of high traffic density (e.g. near a railway station) and to fill in coverage for regions of shadow from the main macrocell (e.g. street ‘canyons’ in cities). Problems with microcell use include the complex radio propagation environment, which is difficult to model and dealing with frequent handovers for fast moving mobiles. Important considerations for network designers are:

• Detecting hot spots and determining the best size and position for a microcell.

• Resource management between the network layers – channel allocation and frequency planning.

• Call admission and handover strategies between the layers.


1. Positioning Microcells

Positions for microcells may be determined by setting up test microcells which transmit a dummy BCCH channel so that mobiles in neighbouring cells will make signal level measurements. Access is barred to the microcell so that actual handover is not attempted. Reports can then be analysed to determine how often mobiles would have accessed the dummy microcell.

MultiMulti--layer Spectrum Allocationlayer Spectrum AllocationMethods are:

• Orthogonal sharing - generally used• Spectrum sharing - isolated microcells• Dynamic Channel Allocation - picocells

Orthogonal sharing

Spectrum sharing for an isolated microcellusing carrier 1 inside a macrocell using carrier 4


F1

F2

2. Resource Sharing

Methods of allocating spectrum to the layers are: • Orthogonal sharing – each layer uses its own frequencies. This may

lead to poor trunking efficiency • Spectrum sharing – same frequencies are used by macrocells and

microcells, relying on base station power control to reduce interference

• Dynamic Channel Allocation (DCA) – use same frequencies but not at the same time. The system intelligently allocates frequencies in order to minimise interference based on current activity.


Comparison of Orthogonal and Spectrum Sharing Simulations show that the cross layer interference caused by spectrum sharing leads to reduced overall capacity. The conclusion is that the simpler strategy of orthogonal sharing is the better one. Spectrum sharing may be suitable for isolated microcells. The interference from co-channel macrocells is small as a mobile using the microcell will generally be in line of sight of the microcell base station but not of the distant macrocells. Frequency must be selected to avoid co- and adjacent channel interference: In the example, carriers 2, 6, 7, 10, 11 and 12 are used in physically adjacent cells, carriers 3 and 5 are adjacent channels to 4 (used in the macrocell). Of the remaining carriers (1, 8 and 9), carrier 1 gives the greatest re-use distance.

Dynamic Channel Allocation DCA may be suitable for indoor picocells. Channels from a fixed set of available frequencies can be allocated dynamically based on current interference levels from surrounding cells. DCA allows a microcell / picocell layer to be introduced without reorganising the existing macrocell frequency plan.


3. Cell and Handover Admission Strategies

Two mobile behaviours should be distinguished:

• Slow moving or static (pedestrians) • Fast moving (motorists)

Fast moving mobiles are better handled by macrocells. Slow moving mobiles may be handled by microcells with overflow to macrocell if required.

Call and Handover AdmissionCall and Handover Admission

• Generally allocate:• slow moving handsets to microcells• fast moving handsets to macrocells

• In-car mobiles would move rapidly through microcells - causing many unnecessary handovers

• Pedestrians are generally at street level, in LOS with microcell base station - do not change cell often


Reversible and Non-reversible Systems In a non-reversible system, once a mobile has been handed over from a microcell to a macrocell, no handover is allowed back to the microcell layer. In reversible systems, handover and hand back between macro and micro cell layers are allowed as required. Simulations of the two systems have shown that reversible systems lead to more handovers causing extra signalling traffic without substantial benefit to the overall system performance.


Reversible or NonReversible or Non--ReversibleReversible• Reversible system:

Macrocell layer

Microcell layer

Macrocell layer

Microcell layer

• Non-reversible system:

Mobile can be handed back and forth between layers

Once in macrocell layer, mobile cannot be handed back


Estimation of Mobile’s Speed The speed of the mobile can be estimated by measuring the dwell time, i.e. the time the mobile spends in a particular cell. Various strategies are possible for handing over to the same layer or up/down to a different layer by comparing the dwell time with one or more threshold values. Speed estimation can be used to alter the handover margin algorithm used to determine the power level at which a handover is required. This can reduce unnecessary handovers for fast moving mobiles.

Speed Sensitive HandoverSpeed Sensitive Handover• One possible handover strategy based on dwell time

measurement (three layer system)

Macrocell layer

Microcell layers

Dw

ell t

ime

t2

t1High speed (short dwell time) - hand to higher layer

High speed - hand upMedium speed (dwell time between thresholds) - hand over on same layer

Low speed (long dwell time) - hand to lower layer

Low speed - hand down

Medium speed - hand over

• Simulations show this strategy has fewer handovers than one based on a single dwell time threshold value



Cell Selection Algorithm In GSM Phase 2, the cell selection algorithm uses a parameter C2, which includes a temporary offset value if the speed of the mobile (measured by a timer) is greater than a certain threshold value as it enters the cell. This is covered in Section 6: Network Operations. This ensures that a fast moving mobile will not select the microcell but will stay on in the macrocell. Further reading: Multitier Cell Design, Xavier Lagrange, IEEE Communications Magazine, August 1997. (calab.kaist.ac.kr/research/sig_network/old/papers/MultitierCellDesign.pdf)

____________________________________________________________________ 4.6 Use of Repeaters

Establishing a new site can be very expensive. Providing coverage where there is currently a “hole” can be more economically achieved by using a repeater. This is particularly true where the level of offered traffic is low. A repeater operates by using a high gain antenna (usually a Yagi or a parabolic dish) to receive the signal radiated by the BTS, amplifying it and re-radiating it. In this way, the power density in the region of the repeater is increased and coverage can be maintained. The repeater acts in both directions, amplifying uplink signals before transmitting them towards the BTS.


Cell RepeatersCell Repeaters• Repeaters allow coverage to be extended into

‘blackspots’ such as tunnels or cuttings or inside office buildings

• A repeater consists of two antennas back to back with amplifiers in each direction:

Repeaters by Allgon

Typical gain: 50 - 90 dBDirectional antenna towards base station

Directional or omni antenna as appropriate towards users

• Repeater passes on same frequency it receives• Response may be: • band selective

• channel selective

Band pass filter

Amplifier


As an example, consider the situation where coverage from the BTS can be maintained within a region where the path loss is less than 153 dB. Suppose that, due to obstructing terrain features, the loss at a particular point (at mobile height) is 163 dB. Placing a repeater can provide gain in three distinct ways:

• The repeater antenna is elevated to have line of sight to the BTS • The repeater antenna has a higher gain than the mobile antenna • The signal received will be amplified before it is retransmitted.

Using RepeatersUsing Repeaters• Coverage from a BTS can be achieved only if the pathloss is below a certain maximum

level.• A repeater may provide a more economic method of providing coverage in areas where

the pathloss to the BTS is above this maximum.


•Repeater can provide coverage in area of high pathloss to BTS.


Repeater ConstructionRepeater Construction

• A repeater consists of:• A Yagi or parabolic antenna• A high gain antenna• A sectored antenna similar to that used on the BTS.


Repeater AnalysisRepeater Analysis• Gain is provided in three ways:

• Repeater antenna is elevated above the height of a typical mobile• Repeater antenna has higher gain than a mobile antenna• The repeater is “active”, that is it contains an amplifier.


• Typical values• Elevation gives a 15 dB gain.• Yagi will have a 20 dBi gain.• Amplifier will have a 65 dB gain.

• Total Gain: 100 dB• Thus if pathloss was 10 dB bigger than maximum tolerated, coverage

will be provided in areas where pathloss to repeater antenna is less than 90 dB.


Typical values would be:

• The elevation of the repeater antenna would increase the signal strength by 15 dB.

• The antenna gain would be 20 dBi, • The gain of the repeater amplifier would be 65 dB.

This gives a total gain of 100 dB. This means that mobiles within a region such that the path loss to the repeater was less than 90 dB would receive a service. The coverage provided by repeaters is often very small and they are generally used to fill in gaps that would otherwise be very expensive to fill. The gain of the amplifier is limited by the need to avoid a positive feedback loop developing. The repeater is receiving, amplifying and retransmitting at the same frequency. The coupling loss between the two antennas must be greater than the gain of the amplifier by a suitable margin (typically 20 dB).

Repeater Design ConsiderationsRepeater Design Considerations• The gain of the amplifier is limited by the need to avoid positive

feedback (“singing”).• If the amplifier has a gain of 70 dB, the antennas would need to be

provided with typically 90 dB of isolation.


•Positive feedback


Adding a Repeater Adding a Repeater Asset screens showing the effect of adding a repeater:

Coverage restricted to a valley

Coverage needed at this end of valley

BTS site

Repeater added here

Extended coverage produced by repeater

A repeater is suitable here as the traffic loading on the cell is low in this country area.


Some Considerations with Repeaters: A repeater extends coverage range but does not add capacity. They should not be added to carriers, which are heavily loaded. Repeaters amplify and pass on everything they receive – noise as well as wanted signals. Feedback can cause a repeater to oscillate. If several repeaters are in a chain, they will all then oscillate, which makes troubleshooting difficult.


SummarySummary

• BTS positioning problems in specific types of location: rural areas, topographical effects, water surfaces, traffic routes

• Microcell positioning: urban areas, location and type of microcell antennas

• Picocell arrangements: in-building coverage, losses, types of antenna, distributed antennas

• Multi-layer cell design: determining best positions for microcells, resource sharing methods, call admission and handover strategies

• Repeaters


.




The following activities involve some general considerations of base station positioning in various situations and an exercise in selecting a suitable microcell carrier for spectrum sharing

Exercise 4.1 - Base Station Positioning Describe some of the considerations a planner should take into account when placing a base station in the following locations: 1. On the bank of a wide river 2. In a hilly countryside region 3. To provide coverage for a road through hilly countryside 4. In a long straight road in town 5. At a cross roads in town 6. To provide coverage for an office block


Exercise 4.2 - Spectrum Sharing in a Microcell

A network uses a standard 4/12 frequency plan as shown. Carriers are allocated to the groups in the usual way. The planner needs to place a microcell in the B1 cell marked. Suggest a carrier that could be used in this microcell

Microcell needed here


Exercise:4.3 – Repeater Positioning

The path loss from a particular region to the best serving BTS is 161 dB, 8 dB above the maximum level. It is decided to use a repeater to provide coverage for this region. A 22 dBi antenna is used to transmit and receive to and from the BTS. The signal strength at the repeater antenna is 15 dB above what it would be at the height of a typical mobile receiver. The maximum isolation that can be obtained between the two antennas is 78 dB and an isolation margin of 14 dB is to be provided. Deduce the maximum gain amplifier that can be used and hence determine the maximum path loss from the repeater that can be tolerated by mobile terminals assuming that the same antenna is used at both the BTS and the repeater. Solution. If the maximum isolation between antennas is 78 dB and a margin of 14 dB is to be provided, the maximum gain amplifier will be 64 dB. Thus the total gain is 15 + 22 + 64 = 101 dB. As the path loss was originally 8 dB too high, a maximum path loss from the repeater of 93 dB can be tolerated.


5. Base Station Engineering

____________________________________________________________________ 5.1 Introduction

The following topics are covered in this section:

• Site suitability • Radio property testing • Antenna configurations • Base station equipment • Electrical Considerations • Choice of Configuration


____________________________________________________________________ 5.2 Site Suitability

Site SuitabilitySite Suitability

• Nominal plan gives ideal pattern of cells• Actual cell sites must meet various requirements as seen

previously• Engineering requirements include:

• suitable radio properties (propagation, interference etc.)

• clearance of nearby obstacles for radio signal• space for equipment• power supplies - main and back up• transmission links

Section 5 – Base Station Engineering

Site FacilitiesSite Facilities• The site must have space for the antenna mast/tower

and the cabinets or building required to house the BTS equipment

• The ground should be structurally suitable for a tower or mast to be built

• Mains power supply should be available or able to be provided

• Back up power must be made available, such as:• batteries• diesel generator - space, fuel supply and noise

problems may be an issue• fuel cells - being considered - efficient, environmentally

friendly



TransmissionTransmission• The base station must be connected to the rest of the

network• Connection is via E1 (European) or T1 (American)

hierarchy PCM system• Physical link may be:

• copper (symmetrical pair or co-axial) cable• optical fibre• microwave• satellite link (rare)

• Link planning may be required, including:• network topologies• link budgets• surveys


____________________________________________________________________ 5.3 Radio Property Testing

Radio MeasurementsRadio Measurements

• Measurement of the radio properties of the site include:

• Propagation - this would have already been done in drive testing the area to tune the propagation model -further measurements for verification may be needed

• Time dispersion tests - to check the effect of multipath propagation on C/R values

• Interference - particularly from sources outside the network - frequency planning should already have given acceptable C/I and C/A values within the network



The C/R value is the ratio of the power in the direct path (Pd) compared to the power in the reflected path (Pr) and is expressed as: Carrier to Reflection ratio ( C/R ) = 10 log (Pd / Pr)

GSM recommends C/R should be 9 dB or greater.

Time Dispersion TestsTime Dispersion Tests• Transmitter sends pulse at appropriate frequency (e.g. 900 MHz)• Receiver picks up pulse and any echoes• Display shows the strength and time delay of the echoes• Problem results would contain strong echoes with long time delays -

equalisation can be used to deal with short delays

Main pulse

Echoes

Time delays Time (µs)

Rx

Leve

l (dB

m)


Interference TestsInterference Tests• Use spectrum analyser in ‘off - air’ monitoring mode• Check for radio activity from other operators in the area,

especially when sites are co-located with those of other operators

• Tests should check for:• direct interference• intermodulation products - particularly third order products

Frequency900 Mhz band 1800 Mhz bandf1 f2

f1 + f22f1 - f2 2f2 - f1

f1 + f2 - f2= f1

f1 + f2 - f1= f2

2f1 2f2

3rd order products are equalto or close to the carriers in use

Carriers

2nd order products

3rd order products



Intermodulation Interference Intermodulation products arise from mixing of frequencies in a non-linear system. The order of a product is the total number of frequencies involved in its production. Two frequencies f1 and f2 can produce second order products: 2f1, 2f2, f1 + f2, f1 – f2 and third order products: 3f1, 2f1 + f2, 2f1 – f2, 2f2 + f1, 2f2 – f1, 3f2, f1 +f2 – f1 (= f2), f2 + f1 – f2 (= f1). If f1 and f2 are in the 900 MHz band, most of the second order products will be in the 1800 MHz band, but many of the third order products are also in the 900 MHz band and cause interference problems. Calculating Intermodulation Power Levels In the case of signals radiated by a particular base station, the strength of these intermodulation frequencies can be estimated using data for the amplifiers causing the non-linear distortion. The important values are the gain, G dB, of the amplifier and a parameter known as the third order intercept point (IP3) measured in dBm. The power (PIMD) of the third order intermodulation products of two frequencies each input to the amplifier with power Pin is given by:

3inIMD IP 2P 3G 3P −+= Example: For a particular amplifier, G = 51 dB, IP3 = 47 dBm and two frequencies are input with powers of -8 dBm. Calculate the power of the third order intermodulation products produced by this amplifier.

PIMD = 3 x 51 + 3 x (-8) – 2 x 47 = 26 dBm The power levels of the intermodulation frequencies at any point can then be estimated using the same propagation models and power budgets that are used for the main carriers. If carriers are in use at the frequencies of these intermodulation products, the resulting C/I ratio can be found. This must be sufficiently large to allow the carriers to be used.


Reducing Intermodulation Distortion The non-linear amplification, which generates the products, should be minimised in the design and manufacture of the equipment. The non-linear effects can be reduced by running the system with lower than normal input power, or equivalently using a higher gain amplifier to produce the same output power. Frequency Hopping Frequency hopping can reduce the interference effects caused by intermodulation frequencies. Non-linear effects produced by poor connectors or equipment operated out of specification should be checked and corrected.

Fresnel Zone ClearanceFresnel Zone Clearance• The site of the base station and antenna height should allow

complete clearance of at least the first 100 metres of the firstFresnel zone

• At 100 m from the base station, the first Fresnel zone radius isabout 5.7 m for a distant receiver

• Using this figure, the required height of the antenna can be estimated

BTS

100 m

5.7 m

• The antenna height should not affect the coverage and interference predictions already made

• Some compromise may be necessary in the clearance allowed



Estimation of Fresnel Zone Radius: The first Fresnel zone is an ellipsoid with foci at the transmitter and receiver. The distances a and b to the surface of the ellipsoid are such that:

2dba λ

+=+

The distance d from a macrocell base station to the mobile receivers will typically be several kilometres, which is large compared to the distance d1 = 100 m.

Thus 2d d ≈ and the equation for the radius becomes: λ=λ

≈ 11

1 d ddd F

For the 900 MHz band m 0.33 ≈λ , m 5.7 33 0.33 100 F1 ==×≈ ____________________________________________________________________

Tx Rx

d1 d2

d

F1a b

ddd F 1

1λ

= 2

F1

The radius of the first Fresnel zone, F1 is given by:


5.4 Antenna Configurations

AntennasAntennas• Isotropic Radiator:

• Theoretical form of antenna• Equal radiation in all directions• Used as the basis against which practical antenna gains are

measured

• Half Wave Dipole:• Physically half the radiated wavelength• Radiation pattern is confined to ‘doughnut’ shape• Gain is 2.14 dBi

• Antenna manufacturers often quote gains relative to dipole in dBd

• Antenna gains used in power budget calculations must be in dBi

Gain in dBi = Gain in dBd + 2.14


Radiation PatternsRadiation Patterns• Antenna radiation pattern (polar diagram) shows antenna gain

against angular direction• Pattern is actually 3 dimensional - generally show horizontal (azimuth

or H plane) and vertical (elevation or E plane) plots

H plane E plane



Antenna GainAntenna Gain• Gain varies with angle as shown by the radiation pattern• Manufacturers’ quoted gain is the maximum value in the main lobe

(boresight) direction

Isotropic

Dipole

Practical antenna

Gain dBi

Gain dBd

2.14 dBi

Boresight

E plane (vertical) patterns for different antennas


BeamwidthBeamwidth• Antenna beamwidth is defined by the points on the radiation

pattern at which the radiated power falls to half the maximum value (- 3dB from boresight)

Gain = max

Gain = max - 3dB

Gain = max - 3dB

Beam width is quoted for vertical and horizontal pattern



Transmission and ReceptionTransmission and Reception• Theorem of Reciprocity states that the gain of an antenna is the same

whether it being used to transmit or receive a signal• Power received by an antenna depends on its effective aperture (Ae)

Pr = S x Ae

Pr = received power (W) S = power density (W/m2)

• Gain, G and effective aperture are related by the equation:

e2 Aλπ4 G =

• Differences between Tx and Rx antennas:• Tx uses higher power levels than Rx and requires higher rated components• Reflections of radio signals will have different effects on Rx and Tx antennas


OmniOmni--directional Antennasdirectional Antennas• Designed to give complete 360o coverage

around the base station• H plane pattern is circular• E plane pattern is generally narrow with some

side lobes• Typical gain: 6 - 12 dBi• Construction: collinear array of dipoles arranged

vertically - signal supplied to all dipoles in phase

Commercially availableomni antennas

3 m typical length for 900 MHz

TRX

dipoles

feeder cablecollinear array

housing



Sector AntennasSector Antennas• Designed to give give coverage within a

restricted angle• Horizontal beamwidth, typically 60o - 90o

• Used in sectored cells e.g. when an omni cell is tri-sectored

• Typical gain: 10 - 18 dBi• Construction: omni-directional collinear array

with corner reflector to direct the beam

corner reflector

collinear array

Commercially available sector antennas


Antenna TiltAntenna Tilt• Down tilt of antennas often used to:

• reduce interference• adjust cell size• direct coverage e.g. into a building

• Mechanical tilt:• set by operator• distorts azimuth (H plane) radiation

pattern

• Electrical tilt:• set by manufacturer• reduces radiation H plane pattern equally

in all directions, without distortion

Omni-directional antenna with electrical down tilt



Examples of Antenna TiltExamples of Antenna Tilt

-35

-30

-25

-20

-15

-10

-5

0

-35

-30

-25

-20

-15

-10

-5

0

-35

-30

-25

-20

-15

-10

-5

0

-35

-30

-25

-20

-15

-10

-5

0

No Tilt Mechanical Downtilt

Electrical Downtilt

Electrical Downtilt +

Mechanical Uptilt


Distributed Antenna SystemsDistributed Antenna Systems• In buildings, more uniform coverage may be achieved by having several

picocell antennas fed by the same TRX• Extreme form of distributed antenna is the leaky feeder:

• Coaxial cable with slots in outer conductor to allow r.f. energy to ‘leak out’• Arrangement of slots depends on operating frequency

TRX

Possible layout of leaky feeders in a building

construction

radiation pattern

• Applications : • underground railways• mines• tunnels

• Disadvantages : • high cost• no antenna gain



Antenna SeparationAntenna Separation• Physical separation isolates antennas, reducing:

• interference• intermodulation products

• Typical separation provides 30 -40 dB isolation• Vertical separation is more effective than horizontal• Physical separation required depends on:

• wavelength - longer λ, greater separation• antenna gain• beamwidth

• Typical separation used:• vertical ~ 0.2 metres or more• horizontal ~ several metres


Diversity ReceptionDiversity Reception• To overcome effects of multipath fading - receive signal with

two independent antennas• Two forms of diversity reception:

polarisation diversity

10 λ

Two collinear array antennas separated by 10λ (3 m in GSM 900)

Single antenna with dipoles at 450

Dual polarised PCS-1900 base station array by ERA Technologies


space diversity


Diversity Reception Diversity reception uses a second receiving antenna, which receives a signal that is independent of the first antenna. This independence is achieved either by separating the signals in space (space diversity) or by receiving two independent polarisation components of the signal (polarisation diversity). As the signals are independent, it is unlikely they will both experience fading at the same time. The signals can be combined to produce a diversity gain of about 3 – 5 dB. Space Diversity

Polarisation Diversity The polarisation of the radio signal changes due to multiple scattering and atmospheric effects. The many signals incident at the antenna have a wide range of planes of polarisation. Diversity gain can be achieved by mounting antennas in pairs at 45o either side of the vertical so that two independent polarisation components are received. The antennas are placed at 45o rather than horizontal and vertical, as the purely horizontal polarisation component is very small close to the ground. Advantages of polarisation diversity:

• Similar gain to space diversity (3 – 5 dB) • Smaller antenna arrangement – mount on mast rather than tower • Less environmental impact – easier planning permission

Most systems make widespread use of space diversity, but polarisation diversity is increasing in popularity.

Two antennas are mounted sufficiently far apart that they receive independent signals. The separation should be at least 10 wavelengths, which for the 900 MHz GSM band is about 3 metres.

10λ


____________________________________________________________________ 5.5 Base Station Equipment

Antenna CombinersAntenna Combiners

• Combiners allow several TRXs to share one transmit antenna

• Main considerations when using combiners are:

• power levels to be handled• minimising losses• isolation between carriers• linearity to avoid intermodulation distortion

• Two main types of combiner in use:• hybrid combiner• cavity filter combiner

TRX 1

TRX 2

TRX 3

TRX 4

Combiner


Hybrid CombinerHybrid Combiner• Passive device with two inputs, two outputs• Can combine two input signals• One output must be terminated by a matched

impedance - typically 50Ω load with heatsink for cooling

• Half total input power is lost to the load -combiner loss is at least 3dB

• Typical loss is about 3.3 dB

Load

Output to antennaInput from TRX 1

Input from TRX 2

Commercial hybrid combiner (Microlab/FXR)

90 mm

HybridCombiner

Terminating loads



Hybrid Combiner StacksHybrid Combiner Stacks• To combine more than two inputs, several combiners must be stacked• Each level introduces a 3 dB loss - gives inadequate output when

many signals to be combined

Hybrid

Combiner

Load

Output to antenna

Input from TRX 1

Input from TRX 2

Hybrid

Combiner

Hybrid

CombinerInput from TRX 3

Input from TRX 4Load

Load 3 dB loss

3 dB loss

3 dB loss

Combined loss is 6 dB for each TRX

• Hybrid combiners are cost effective for cells with few TRXs• They have a wide bandwidth - used in frequency hopping


Cavity FiltersCavity Filters• Tuned cavity acts as band pass filter• Centre frequency of pass band depends on the dimensions

of the cavity• Tuned by adjusting a plunger on the cavity - may be servo

motor operated to automatically follow the tuning of the TRX• Generally supplied as a block of several cavities

Block of 5 cavity filters by RFS Ltd.

Tunable band pass cavity filter by K&L

Cavity filters by Aerial Facilities Ltd.



Cavity Filter CombinerCavity Filter Combiner• Cavity filters can be used to combine several frequencies:

• Outputs of filters are directly connected together• band pass filters isolate the different frequency outputs• connection harness and stub must be correctly matched to the

wavelength to reduce losses

Input from TRX 1

Input from TRX 2

Input from TRX 3

Connectionharness

Matching stub

• Losses:• Typically 2 - 5 dB per cavity• No addition of losses when

more signals are combined

• More expensive than hybrid combiners but give low loss when many frequencies are combined

f1

f2

f3


Combiners for Frequency HoppingCombiners for Frequency Hopping• Frequency hopping provides a particular example of the use of combiners• There are two methods of frequency hopping:

• Baseband hopping

BasebandData Signal TRX

Tuning controller

Antenna• Synthesiser hopping

TRX

TRX

TRX

CombinerAntenna

Switch controller

Switch between several TRXsin hopping sequence

One TRX which is re-tunableto a set of frequencies


BasebandData Signal


Combiners for Combiners for BasebandBaseband HoppingHopping• The baseband signal is fed to one of several TRXs in turn by a

switch • The TRX outputs must be combined to be fed to the antenna• The combiner must be able to handle a wide bandwidth of signals• This can be achieved using either:

• hybrid combiners - several stages causing large loss • cavity filters - one associated with each TRX - maximum loss ~ 5 dB

TRX

TRXBasebandData Signal

TRX

Antenna

Switch controller

Cavity filter method is preferred as it gives lower loss


Combiners for Synthesiser HoppingCombiners for Synthesiser Hopping

• A single channel using synthesiser hopping has only one TRX output and would not require a combiner

• If several channels are to be combined and fed to one antenna, the combiner must have a wide bandwidth to deal with the range of frequencies from the synthesiser

• Hybrid combiners must be used in this case

Tuning controller

BasebandData Signal 1 TRX 1

BasebandData Signal 2 TRX 2

HybridCombiner

Load

Antenna



Antenna MulticouplerAntenna Multicoupler• Required to couple the receiving antennas - main (A) and

diversity (B) to the TRXs• Power from each antenna is split and amplified• Identical pairs of outputs are available for each TRX• Multicoupler produces no overall gain or loss - neutral

Multicoupler

Rx A Rx B

Rx A outputs

Rx B outputs

TRX 1

TRX 2

Further TRXs

Commercial multicoupler


Antenna DuplexerAntenna Duplexer• With diversity reception, a cell would require 3

antennas - transmit (Tx), main receive (Rx A), diversity receive (Rx B)

• Duplexer (duplex filter) can reduce this to 2 antennas by combining Tx with one Rx

• Duplexer consists of two band pass filters - one tuned to the uplink frequency (Rx) and one tuned to the downlink (Tx)

• Isolation between Tx and Rx typically 50 - 80 dB• Power loss < 1 dB

Rx Tx

FuFd

Tx / RxAntenna

Duplexer

TRX

Duplex filter by AMP Ltd



Duplexer with Space DiversityDuplexer with Space DiversityUsing a duplexer on a tri-sectored site can reduce the number of separate antennas on the tower from 9 to 6

Tx

Tx

Tx

Rx

Rx

Rx

Rx

Rx

Rx

Rx

Rx

Rx

Tx/Rx

Tx/Rx

Tx/Rx

Without duplexer - separate Tx and Rx antennas

With duplexer - common Tx/Rx antennas


Duplexer with Polarisation DiversityDuplexer with Polarisation DiversityUsing a duplexer can reduce the number of separate antennas from 6 to 3 - a mast could be used rather than a tower

2 Rx

2 Rx

2 Rx

Tx

Tx

TxTx Rx A + Rx B

Separation of about 2λfor isolation

Without duplexer:

Tx/Rx

Tx/RxTx/Rx

With duplexer:

Tx + Rx A Rx B



Losses in Feeders and ConnectorsLosses in Feeders and Connectors• Long feeder cables from antenna to base station

equipment can cause considerable power loss• Typical loss in co-axial cable: 3 -10 dB per 100m • Loss increases with frequency:

• 1800 MHz can have 4 - 10 dB greater loss than 900 MHz

• Loss depends on quality of cable:• Cheap cable may give 20 dB per 100m• Very expensive cable can have:

• 1 dB / 100m for 900 MHz• 3 dB / 100m for 1800 MHz

• Connectors between duplexers, combiners, couplers and so on should produce no more than 0.2 dB loss


____________________________________________________________________ 5.6 Electrical Considerations

Base Station Grounding SystemsBase Station Grounding Systems• Efficient grounding required for

protection against lightning strikes:• strike energy must be dissipated across

wide area• local ground potential should not rise

and cause equipment damage

• Grounding also needed for efficient RF operation of antenna

• BTS equipment grounding:• A.C power - separate grounding for

each phase (3 phase systems)• D.C. power grounding - taken

separately to ground or possibly combined with lightning protection above ground

Feeder cable outer conductor bonded to tower at top and bottom - using feeder grounding kit

Earth bar bonded to feeder

Separate grounding for D.C. power, A.C. power etc.

Earth ringsElectrodes driven into ground

Enhanced soil conductivity

Conducting concrete

Underground connection of earthing systems to produce equipotential



Lightning Protection Lightning Protection • Lightning protection finial at top of

tower or building - rod or spiked sphere - provides 45o protection zone

• Connection to ground via flat copper strap - required on towers as well as buildings

• Conductor thickness should increase nearer ground if several routes are combined

• Path of conductor must always be downwards - never turn back up

45o protection zone provided by finial

Lightning protection finial

Conductor turns back -

lightning won’t !


____________________________________________________________________ 5.7 Configuration Selection

Selecting An Appropriate Configuration When deciding on the configuration of a site, the network planner can choose a site that falls in one of the following four categories:

• Omni-directional • Omni-directional with diversity • Sectored • Sectored with diversity


Selecting the Correct ConfigurationSelecting the Correct Configuration

There a four major categories of site:

Omni


Rx

Rx

Rx

Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx

Tx/RxTx/Rx

Tx/Rx

Tx/RxTx/Rx

Omni with diversity

Sectored

Sectored with diversity

The choice made will affect the coverage and capacity achievable from that site. As an example, consider a typical link budget for a GSM 1800 mobile channel;

Base Station Transmit Power 43 dBm Receiver Sensitivity -95 dBm Feeder Loss 5.0 dB Combiner Loss 6.0 dB Mobile Antenna Gain 0.0 dBi Allowable link loss 127 dB

Now, if the antenna is an omni-directional antenna, a gain of 13 dBi can be assumed, whereas 18 dBi is more likely if the antenna is sectored. That means that the maximum path loss for an omni-directional site is 140 dB whereas 145 dB can be tolerated on a sectored site.


Estimating the Affect on Cell RangeEstimating the Affect on Cell Range• The choice of configuration will affect capacity and

coverage.• A sectored antenna will have about 5 dB more gain than

an omni antenna (18 dBi compared with 13 dBi).


• Maximum Path Loss• Omni site: 140 dB• Sectored site: 145 dB (Link loss 127 dB in both cases)

• Maximum Range• Omni site: 1.22 km• Sectored site: 1.69 km

• (assuming path loss model L = 137 + 35 log [R] )

If an urban path loss model of L = 137 + 35 log(R) is taken to be appropriate then the path losses can be translated into a cell range.

Path Loss Cell Range 140 dB 1.22 km 145 dB 1.69 km

An omni-directional site would cover an area of 4.0 km2. The sectored site would cover an area of approximately 5.6 km2. However, the sectored site would consist of three cells, each cell covering 1.9 km2. Therefore the sectored configuration would not only cover a greater range but also be able to serve an area of greater user density. Omni-directional sites are cheaper to provision and would be used when they can meet the demands for coverage and anticipated traffic.


Calculating the Area of CoverageCalculating the Area of CoverageSection 5 – Base Station Engineering

• Maximum Range• Omni site: 1.22 km• Sectored site: 1.69 km

• (assuming path loss model L = 137 + 35 log [R] )

1.22 km

Area = 4.0 km2

1.69 km

Area = 5.6 km2

Estimating the Affect on CapacityEstimating the Affect on CapacitySection 5 – Base Station Engineering

• Sectored site will have approximately 3 times the capacity of an omni-directional site (assuming the same number of carriers).

• Sectored site will accommodate a traffic density more than twice that of an omni-directional site.

1.22 km

Area = 4.0 km2

1.69 km

Area = 5.6 km2

1.69 km


Remember that link balance can be maintained when the base station transmit power is lower as the mobile power can be reduced using the power control system. The decision whether or not to provide uplink diversity is connected with the issue of link balancing.

Deciding whether to use DiversityDeciding whether to use DiversitySection 5 – Base Station Engineering

• Diversity is used when necessary to balance the system.• It helps the uplink but not the downlink.• Diversity allows the BTS to operate at higher power whilst

maintaining link balance.• Hence it allows greater coverage to be achieved.

Uplink limitDownlink limit

Unbalanced system

Uplink limitDownlink limit

Balanced system

In the above situation it may well be that the uplink would not be able to operate over the allowable link loss of 127 dB without diversity. Suppose that the maximum link loss that the uplink could tolerate was 125 dB without diversity. A diversity gain of 2 dB would restore link balance. If diversity was not employed, the base station transmit power would have to be reduced to 41 dBm and the allowable link loss would be 125 dB. A 2 dB reduction in path loss corresponds to the range altering by a factor of approximately 0.88. Therefore, the new ranges would be:

Cell Configuration Range without Diversity Omni-directional 1.07 km Sectored 1.49 km


Deciding whether to use diversity Deciding whether to use diversity -- ExampleExampleSection 5 – Base Station Engineering

• The need to maintain balance limits the transmit power of the BTS relative to that of the mobile.

• E.g. Mobile Tx power: 33 dBm.Without diversity: Maximum BTS power for link balance = 41 dBmWith diversity: Maximum BTS power for link balance = 43 dBm

• This 2 dB of extra power will provide greater coverage.• Diversity is only used when the need exists to extend

coverage.

Summarising, using diversity allows link balance to be maintained whilst increasing the base station transmit power. If coverage can be provided on the downlink using a low transmit power, then diversity is not required.

Selecting the Correct Configuration Selecting the Correct Configuration -- SummarySummary


Sectored site; diversityMaximum Coverage, high capacity requirements

Sectored site; no diversityLarger Coverage Region, high capacity requirements

Omni site; diversityLarge Coverage Region, low capacity requirements

Omni site; no diversitySmall Coverage Region, low capacity requirements.


SummarySummary

• Engineering requirements at a base station site: radio measurements, clearance, space, power supplies, transmission links

• Antennas: isotropic, dipole, radiation patterns, gain, beamwidth, tilt, leaky feeders, separation, diversity reception

• Base station equipment: combiners - hybrid, cavity filter - use with frequency hopping, multicouplers, duplexers, feeders

• Earthing and lightning protection: reasons for grounding, grounding systems, lightning protection equipment

• Configuration Selection




Exercise 5.1 - Intermodulation Products At a base station two GSM carriers are used, ARFCN 30 and 35. 1. What are the actual frequencies of these carriers? 2. Calculate the second order intermodulation frequencies.

Will any of these frequencies interfere with DCS 1800 carriers? 3. Calculate the third order intermodulation frequencies that overlap with the 900 MHz

band. 4. Non-linear distortion producing the intermodulation products is produced by

amplifying equipment of overall gain 20 dB and third order intercept point 35 dBm.

If the carriers are input to the system at a power level of 5 dBm, what will be the power of the third order intermodulation products?


Exercise 5.2 - Antenna Patterns The H plane patterns shown below are for antennas of beam width 16, 26, 60 and 86 degrees and gains of 11, 13, 15 and 18 dBd (not in that order). Suggest a possible beamwidth and gain for each antenna.


Exercise 5.3 - Base Station Equipment – Power Loss Calculation Calculate the power in dBm supplied to the antenna from one TRX in this system: TRX output power: 5 W Hybrid combiner loss: 3.2 dB Duplexer insertion loss: 1 dB Cable loss at 900 MHz: 6 dB per 100m Height of tower: 20m Length of feeder from equipment to tower base: 10m Allowance for bends and cable routing: 5m Loss per connector: 0.1 dB

TRX Hybrid Combiner TRX

TRX

TRX

Hybrid Combiner

Hybrid Combiner Duplexer Feeder cable


Exercise 5.4 – Choice of Cell Configuration 1. Coverage is to be provided over a small area such that the range from the proposed transmitter site is approximately 100 metres. Each cell can be allocated two carriers that can then serve 15 traffic channels (timeslots). Suggest appropriate cell configurations (including BTS Tx power) if the offered traffic is expected to be:

a) 4 Erlangs b) 12 Erlangs

Assume that the maximum path loss at the cell edge is 102 dB. Additional information:

Omni antenna gain 12 dBi Sectored antenna gain 17 dBi Feeder and Combiner Losses 8 dB Mobile Threshold -90 dBm

2. Link balance can be maintained on a particular cell if the BTS transmit power is no more than 8 dB higher than the mobile transmit power. If uplink diversity is used, the BTS power can be 10 dB higher than the mobile transmit power. Determine the maximum coverage range from the cell with and without diversity given the following information:


Exercise 5.5 – Effects of Diversity Link balance can be maintained on a particular cell if the BTS transmit power is no more than 8 dB higher than the mobile transmit power. If uplink diversity is used, the BTS power can be 10 dB higher than the mobile transmit power. Determine the maximum coverage range from the cell with and without diversity given the following information:

Mobile Transmit Power 33 dBm Path Loss Model L = 137 + 35 log (R)

R = 10(L-137)/35

Mobile Threshold -92 dBm Combiner and Feeder Losses 8 dB Antenna Gain 18 dBi

Advanced GSM Cell Planning © AIRCOM International 2002

6-1

6. Network Operations

____________________________________________________________________ 6.1 Introduction

In this section the following topics are covered:

• Modes of MS operation • Network operations in MS idle mode • Network operations in MS dedicated mode • Extending the coverage of cells


____________________________________________________________________ 6.2 Modes of MS Operation

Mobile Station ModesMobile Station Modes

• No service - MS can find no coverage

• Limited service - MS cannot find acceptable cell, may use any cell for emergency calls only

• Idle - MS is camped on to a cell, is receiving BCCH / CCCH data and making measurements on neighbouring cells - no communication channels in use

• Dedicated - MS has established a SDCCH or TCH channel - communication is taking place

112

!! !!

• GSM defines four possible operating modes for a mobile station:

Section 6 – Network Operations

No Service Mode The mobile is unable to find any cell providing GSM coverage in its area. Limited Service Mode This mode may occur if:

• The mobile’s IMSI is not known in the network • The SIM is missing from the mobile • The EIR reports illegal mobile equipment at registration • The cell with the best selection criteria is not part of a PLMN allowed

to the mobile Idle Mode The mobile has registered with its selected PLMN and is thus known to exist on the system. It will have carried out cell selection / re-selection and location updating procedures to camp on to its current cell. By receiving BCCH information, the mobile will know the BCCH carrier frequencies to measure in neighbouring cells.


6-3

CCCH will supply location information and allow the mobile to be paged in the event of an incoming call. Dedicated Mode For communication to take place via TCH or SDCCH, the mobile must be:

• Time synchronised with the base station • Under power control by the base station • Providing measurement reports to the base station for possible

handovers

____________________________________________________________________ 6.3 Operations in MS Idle Mode

Operations in Idle ModeOperations in Idle Mode• In idle mode the mobile does not have a communication

channel established• Activities of the mobile include:

• Monitoring system information on BCCH• Cell selection and re-selection• Location updating• Checking for paging messages (Discontinuous Reception)



The BCCH Carrier The BCCH Carrier • The operation of the mobile in idle mode depends on data it receives

from the BCCH carrier• BCCH data is generally organised as a 51 frame multiframe in

timeslot 0 of the BCCH carrier - giving 4 data bursts (one BCCH message) each multiframe

0 1 42-45 46-49 5032-35 36-39 40 4122-25 26-29 30 3112-15 16-19 20 212-5 6-9 10 11

F = FCCH S = SCH I = idle

• A mobile in idle mode, monitoring the cell follows the sequence:• tune to carrier frequency using FCCH• get BSIC and TDMA Frame Number from SCH - synchronise to frame• obtain system information from BCCH



BCCH System Information MessagesBCCH System Information Messages• BCCH messages contain data relating to:

• cell selection / re-selection• cell access

• System messages are divided into different types -transmitted with different periodicities so more important messages are sent more often

• Note:• Cell selection - the mobile monitors up and downlink quality

and power levels of cells • Re-selection - hysteresis value prevents rapid switching

between cells• Access to some cells may be barred for mobiles in idle

mode - e.g. underlaid cells are only used for handovers in established calls - re-selection must be to the overlaid (umbrella) cell



6-5

BCCH System Messages

Message Type

Messages Purpose

1 Cell Allocation List of frequencies used in the cell BCCH Allocation (BA) list Frequencies of neighbouring cells 2 RACH Control Number of re-transmissions

allowed Spread of re-transmissions Access classes * Cell barring / access

Control Channel Description

IMSI attach/ detach permitted CCCH configuration

Cell Options Is DTX in use Power control indicator set/not set Radio link timeout

3

RACH Control As message type 2 Location Area Identity MCC, MNC, LAC Cell Selection Parameters MS_TXPWR_MAX_CCH

RXLEV_ACCESS_MIN (see notes on selection/reselection below)

4

Cell Re-selection Parameters

Hysteresis value

User Access Classes

Class 0 – 9: Normal users Class 10: Emergency calls (on 112)

Classes 11 – 15: Security and emergency services

Normal users may be barred if a cell is required for emergency use due to an incident


Cell Selection Cell Selection -- Parameter C1Parameter C1• Mobile uses parameter C1 (the Path Loss Criterion) to select a cell to

camp on when it is first switched on (idle mode)• For a particular cell (n):

C1(n) = [ RXLEV(n) - RXLEV_ACCESS_MIN - max(0, (MS_TXPWR_MAX_CCH - P) ) ]

where:RXLEV(n) = average received BCCH power level from cell nRXLEV_ACCESS_MIN = minimum received power level needed by the mobile to access the systemMS_TXPWR_MAX_CCH = maximum transmit power mobile is allowed to use to access systemP = maximum possible transmit power of the mobile

max (0, x) = either x or 0 whichever is the greater

• Mobile compares cells which give a positive value of C1 and selects the highest value


Example C1 Calculation Factors set by network: RXLEV_ACCESS_MIN = -90 dBm MS_TXPWR_MAX_CCH = 37 dBm - (some mobiles may have higher output than the normal Class 4 maximum (33 dBm)) Factor dependent on mobile: P = 33 dBm – Class 4 GSM 900 mobile Measurement made by mobile: RXLEV (n) = -85 dBm Then: C1 = -85 – (-90) – max(0, 37 – 33) = 5 – max (0,4) = 5 – 4 = +1 The term, max(0, (MS_TXPWR_MAX_CCH – P)) in C1 gives some advantage to mobiles with a higher power than normal, but places a limit on that advantage (after 37dBm in this example).


6-7

Cell ReCell Re--selection selection -- Phase 1 Mobiles Phase 1 Mobiles • Once a mobile has camped on to a cell, it will continue to measure

neighbouring BCCH carriers, looking for a better cell• Phase 1 mobiles use the C1 calculation, modified as follows:

• Between cells within a location area, the criterion for selecting a new cell is:C1 (new) > C1 (old) for more than 5 seconds

• Between cells on a location area boundary, the criterion is:C1 (new) > C1 (old) + CELL_RESELECTION_HYSTERESIS for more than 5 seconds

• The hysteresis term prevents unnecessary re-selection on a location area boundary which would require extra signalling to perform the location update


The purpose of introducing the C2 parameter was to control access to microcells. The CELL_RESELECT_OFFSET can be set to make a microcell more attractive than a surrounding macrocell, while the TEMPORARY_OFFSET controls access depending on the speed of the mobile. There is an example of this in the activities at the end of this section.

Cell ReCell Re--selection selection -- C2 ParameterC2 Parameter• Phase 2 mobiles use a modified parameter, C2, for cell re-selection:

C2(n) = C1(n) + CELL_RESELECT_OFFSET - [TEMPORARY_OFFSET x H(PENALTY_TIME - T)]where the function H is defined as: H(x) = 0 for x<0, H(x) = 1 for x ≥ 0

CELL_RESELECT_OFFSET effectively moves the boundary of the cellTEMPORARY_OFFSET only applies while T < PENALTY_TIME,where T is the time since the mobile first detected the cell with C1>0

• This introduces a time hysteresis to prevent fast moving mobiles from selecting the cell for very short periods

• To select a new cell using C2, either:• C2 > 0 within a location areaor• C2 > CELL_RESELCT_HYSTERESIS on a location area boundary



MSC 2

Location UpdatingLocation Updating

• The PLMN is divided into a number of location areas

• Each location area consists of several cells controlled by the same MSC, but not necessarily the same BSC

• The main use of location areas is in paging a mobile

• Location area is stored in the VLR of the MSC• The HLR stores the current MSC the mobile is

registered with and is only updated if the mobile moves to new MSC

• LAI - Location Area Identity - is transmitted on BCCH

MSC 1

Location Areas

VLR


VLR

Structure of LAI The Location Area Identity is formed from three codes:

• Mobile Country Code (MCC) identifies the country • Mobile Network Code (MNC) identifies the network operator • Location Area Code (LAC) identifies the location area within the

network Example: 262 01 154 MCC and MNC codes can be searched at the following website: http://www.bryte.net/gsm-net.asp

Germany MCC D1-Telekom

MNC

Location area LAC


6-9

Automatic Location UpdatingAutomatic Location Updating• Mobile receives LAI from BCCH transmission• When it detects a new LAI it automatically requests an update• Within same MSC:

Location Update Request

Acknowledgement

New Location Area stored in VLR

• Change of MSC:

MSC2

VLR

HLR

Location Update Request/ Acknowledgement

New VLR Request/ Acknowledgement

Cancel old VLR Location/ Acknowledgement


MSC1

VLR

MSC2

VLR

Periodic Location Updating Network operator may require mobiles to update their locations periodically whether a change of location has been detected or not. The periodic time for this updating can be set in units of deci-hours (6 minutes). The period in use is broadcast on BCCH. One use for periodic updating is to check that the mobile is still attached to the network. It may for instance have lost power without doing a normal IMSI detach, e.g. if the battery were removed. Acknowledgements Either acceptance or rejection messages may be sent following a location update request. The reason for rejection is sent with the message. Possible reasons are:

• Network fail • Area not allowed • IMSI unknown • Illegal mobile (IMEI)

If no acknowledgement is received, the mobile repeats the request after 10 seconds.


Discontinuous Reception (DRX)Discontinuous Reception (DRX)• DRX is a network option to reduce mobile battery drain• The mobile is allowed to ‘sleep’ in idle mode and only listen periodically

for paging messages (PCH) and to monitor BCCH• The periods during which the mobile must be active depends on:

• CCCH configuration - set by the CCCH_CONF parameter• Reservation of CCCH blocks for AGCH (BS_AF_BLKS_RES)• Paging group allocated to mobile (BS_PA_MFRMS)

Paging group example: A mobile need only listen for PCH once every 2 multiframes


S BCCHF CCCHA S CCCH

BF CCCHC S CCCH

DF CCCHE S CCCH

FF CCCHG S CCCH

HF CCCHI I

S BCCHF CCCHJ S CCCH

KF CCCHL S CCCH

MF CCCHN S CCCH

OF CCCHP S CCCH

QF CCCHR I

S BCCHF CCCHA S CCCH

BF CCCHC S CCCH

DF CCCHE S CCCH

FF CCCHG S CCCH

HF CCCHI I

CCCH Configuration CCCH_CONF parameter in BBCH system messages determines the allocation of CCCH within the timeslots and whether TS0 uses a multiframe in which CCCH is combined with SDCCH or a non-combined multiframe.

CCCH_CONF Number of Timeslots for CCCH

Configuration

0 1 TS0 non-combined 1 1 TS0 combined 2 2 TS0, TS2 non-combined 3 3 TS0, TS2, TS4 non-combined 4 4 TS0, TS2, TS4, TS6 non-combined

Non-combined multiframe:

IS BCCHF CCCH S CCCHF CCCH S CCCHF CCCH S CCCHF CCCH S CCCHF CCCH

Combined multiframe:

IS BCCHF CCCH S CCCHF CCCH S SDCCH

0F SDCCH1 S SDCCH

2F SDCCH3 S SACCH

0F SACCH1

Some of the CCCH blocks may be reserved for AGCH use by the parameter BS_AF_BLKS_RES. The remaining blocks are used for PCH.


6-11

____________________________________________________________________ 6.4 Operations in MS Dedicated Mode

Dedicated Mode OperationDedicated Mode Operation• In dedicated mode the mobile has established a

communication channel, either TCH or SDCCH and is time aligned with the base station

• Activities of the mobile may include:• Measurements on neighbour cells• SACCH measurement reports• Handover• Power control• Frequency Hopping• Discontinuous Transmission


Cell MeasurementsCell Measurements• The current cell provides a list of all neighbouring BCCH carrier

frequencies - the BCCH Allocation (BA) list• Mobile measures RXLEV for these carriers in the times between its

uplink and downlink timeslots

01 2 3 4 5 6 7 0 1 2 3 4 5 6 70 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 70 1 2 3 4 5 6 7

Uplink

Downlink

1

Measurement periods



Cell MeasurementsCell Measurements• Up to 100 cell measurements are made over 480 ms period (104

frames)• In the SACCH frame of the TCH multiframe, the mobile sends a

measurement report to the BTS• In addition to BCCH carrier measurements, the mobile must also

identify the actual cell it has measured:• Mobile must synchronise with the neighbouring cell - search for the

FCCH and SCH channels and read the BSIC information• Search is done during the idle frame of the TCH multiframe• As TCH multiframe has 26 frames and BCCH has 51, the idle frame

moves relative to BCCH on each cycle of the multiframe

T T T T T T T T T T T T S T T T T IT T T T T T T T Mobile has found FCCH on this cycle of multiframe



We looked at this synchronisation process and the timing of SACCH messages in the multiframe timing activity in Section 1.

IIII

SACCH MessagesSACCH Messages

• SACCH is used to report measurements from neighbouring cells which have been identified

• Complete message requires 4 SACCH bursts• For TCH, this requires 4 multiframes or 480 ms

S 12 TCH12 TCH S 12 TCH12 TCH S 12 TCH12 TCH S 12 TCH12 TCH

4 TCH multiframes = 480 ms

1 SACCH message reporting measurements over the last 480 ms



6-13

Downlink SACCH Usage On the downlink, SACCH is used by the network to send:

• Power control commands • Timing Advance information • System Information messages (Type 5)

– BA list of neighbour cells • System Information messages (Type 6)

– Cell options (e.g. DTX), NCC permitted, radio link timeout values

____________________________________________________________________ 6.5 Handover Operations

HandoverHandoverHandover decisions are made by the network based on measurementsby the mobile and the BTS:

Downlink:Mobile reports

current RXLEV and RXQUAL; RXLEV for neighbour cells

Uplink:BTS measures current RXLEV and RXQUAL; distance; interference in

unoccupied timeslots

Measurement pre-processing

Threshold analysis

BSS handover decision algorithm

MSC destination selection algorithm Required if handover involves a change of BSC



Handover Priorities and ThresholdsHandover Priorities and Thresholds• Handover algorithm prioritises the reasons for making a handover:

RXQUAL

RXLEV

Distance

Power Budget

High priority

Low priority

L_RXQUAL_UL_H, L_RXQUAL_DL_H

Threshold Parameters

L_RXLEV_UL_H, L_RXLEV_DL_H

MS_RANGE_MAX

(PBGT calculation)

• Threshold parameters are defined by the operator• Handover may be triggered when a certain fraction of measurements

are outside the threshold limits


Average values of RXLEV are found at the pre-processing stage from the measurements sent to the BTS by the mobile. RXQUAL is found for uplink (by the BTS) and downlink (by the MS) from measurements of bit error rate (BER). Distance measurement is based on the Timing Advance value. MS_RANGE_MAX is typically set between 2 and 35 km in steps of 1 km. For handovers triggered by RXQUAL or RXLEV power control will attempt to restore the measurements to within the thresholds before the handover occurs.


6-15

Handover due to Power BudgetHandover due to Power Budget• Ideal GSM handover would be based on power budget - minimising

path loss and reducing transmit power levels and their interference• The power budget for a neighbour cell (n) is PBGT(n) calculated as

follows:

PBGT(n) = [min(MS_TXPWR_MAX, P) - RXLEV_DL - PWR_C_D] - [min(MS_TXPWR_MAX(n), P) - RXLEV_NCELL(n)]

Where:MS_TXPWR_MAX = maximum power that network allows mobile to use for access to a cell

P = maximum power that mobile can transmit

RXLEV_DL = average received downlink power level from serving cell

RXLEV_NCELL(n) = average power level from neighbour cell n

MS_TXPWR_MAX(n) = maximum access power allowed in neighbour cell n

PWR_C_D = maximum downlink power in cell - actual downlink power due to power control

• Handover may occur if: PBGT(n) > 0 and PBGT(n) > HO_MARGIN(n)


Handover MarginHandover Margin

Nom

inal

cel

l bou

ndar

y

BTS 1 BTS 2

Handover to BTS 2Handover to BTS 1

Mobile remains with BTS 1 or BTS 2

Hysteresis due to handover margin


Handover Margin Handover margin HO_MARGIN(n) for neighbour cell n may be set between 0 and 24 dB in steps of 1 dB. This parameter prevents rapid handovers back and forth of mobiles on the boundary between two cells. It creates a hysteresis effect which means that a mobile must move significantly towards the neighbour BTS to be handed over to it and then significantly back towards the original BTS to be handed back.


Example Calculation

Network settings: Mobile maximum power (P) = 33 dBm

MS_TXPWR_MAX = 38 dBm

MS_TXPWR_MAX(n) = 38 dBm Measurements:

Serving cell max power = 45 dBm RXLEV_DL = -90 dBm

Serving cell actual power = 36 dBm RXLEV_NCELL (n) = -80 dBm

HO_MARGIN(n) = 4 dBm

1. Calculate PBGT(n) and state whether a handover may occur. Solution PBGT(n) = [min(38, 33) – (-90) – (45-36)] - [min(38, 33) – (-80)] = [33 + 90 – 9] - [33 + 80] = 1 dB PBGT(n) > 0 but PBGT < HO_MARGIN Handover will not occur. 2. Assuming other factors remain unchanged, what value of RXLEV_NCELL(n) would result in a handover? Solution For a handover to occur, PBGT(n) must be at least 5 dB, i.e. an increase of 4 dB. RXLEV_NCELL(n) must therefore increase by 4 dB to (–80 + 4) = -76 dBm.

Serving cell

Neighbour cell n


6-17

Handover SignallingHandover Signalling

Signalling for a basic handover involving only one MSC (Intra - MSC):

MS MSCBSS 1 BSS 2Measurement report

Measurement report

Measurement report

Measurement report

Handover Required

Handover Request

Handover Command

Acknowledgement

Handover Command

Handover AccessHandover Detection

Physical Information

Handover CompleteHandover Complete

Clear Command

Clear Complete

Measurement report

Measurement report


This example shows the signalling involved when a mobile is handed over between base stations under the same MSC. Note that the handover is initiated by reports from the mobile but the actual decision to handover is made by the network. For a mobile moving from one MSC area to another, further signalling will be required between the MSCs and also to update the HLR. The originating MSC retains overall control of the call for billing purposes.

Handover Command MessageHandover Command Message

Structure of the message sent to mobile by original BSS:

Message Type

Cell Description

Handover Reference

Power Command

Channel Description

Frequency List

or

Mobile Allocation

Includes Frequency Hopping information if required

Non - Frequency Hopping

Frequency Hopping


MS BSS 1

Handover Command


The handover command message sends all the carrier and power control information needed to establish the call in the new cell. This may include frequency hopping information if this is in use. Interference Handover Interference may result in a handover within the same cell (intra-cell). The call is handed over to another timeslot. The need for this may be indicated if the RXLEV measurement is good and power does not need to be increased, but the RXQUAL value is poor. A BTS monitors the timeslots that are not currently in use and categorises them into 5 bands according to the interference they would experience. Two new threshold parameters are used to trigger intra-cell handover. These are L_RXLEV_UL_IH (uplink) and L_RXLEV_DL_IH (downlink). These values would be set above the threshold required to increase power.

Adaptive Power ControlAdaptive Power Control• GSM power control aims to use the minimum power needed to

maintain communication• Reasons for controlling power:

• reduces interference in system• conserves energy - prolonging battery power in mobiles

• Power control is applied to:

Uplink and Downlink

BTS instructs MS to change power

BTS adapts power in response to measurement reports



6-19

Power Classes of Mobiles GSM 900

Class Maximum Power Minimum Power Power levels

1 Deleted from specifications 2 39 dBm (8W) 5 dBm (3.2 mW) 18 3 37 dBm (5W) 5 dBm (3.2 mW) 17 4 33 dBm (2W) 5 dBm (3.2 mW) 15 5 29 dBm (0.8W) 5 dBm (3.2 mW) 13

DCS 1800

Class Maximum Power Minimum Power Power levels 1 30 dBm (1W) 0 dBm (1 mW) 16 2 24 dBm (0.25W) 0 dBm (1 mW) 13 3 36 dBm (4W) 0 dBm (1 mW) 19

Base Station Power Classes GSM 900

Class Maximum Power W dBm 1 320 55 2 160 52 3 80 49 4 40 46 5 20 43 6 10 40 7 5 37 8 2.5 34

M1 250 mW 24 M2 80 mW 19 M3 30 mW 14

Microcell base stations


DCS 1800

Class Maximum Power W dBm 1 20 43 2 10 40 3 5 37 4 2.5 34

M1 1.6 32 M2 0.5 27 M3 0.16 22

Power Control TriggersPower Control Triggers

• Decisions to increase or decrease power are triggered by:• RXLEV - average measurements of up or downlink power• RXQUAL - average bit error rates

• Average measurements are implemented by requiring a number P of measurements out of a total N to be outside the thresholds before a power control command is triggered

• Limits on power control:

Increase power in steps of 2, 4 or 6 dB

Decrease power in steps of 2 or 4 dB

Mobile may only make one change in 60 ms


These are recommended power classes for GSM base stations. Actual power levels are set according to local interference conditions. The actual power transmitted depends on the TRX output power (typically 40 – 60 W) and the combined losses in the base station equipment. Adaptive power control is not applied to the BCCH carrier from the base station. This is continually radiated at full power. Power control on other carriers is applied independently to each timeslot.

Microcell base stations


6-21

Power Control Parameters RXLEV thresholds: RXQUAL thresholds:

L_RXLEV_UL_P

U_RXLEV_UL_P

Power increase triggered

Power decrease triggered Uplink

Downlink

L_RXLEV_DL_P

U_RXLEV_DL_P


Power decrease triggered

Threshold values for RXLEV may be set as numbers from 0 to 63 corresponding to bands of power levels in the range: –110 dBm to –48 dBm

L_RXQUAL_UL_P

U_RXQUAL_UL_P


Power decrease triggered Uplink

Threshold values for RXQUAL may be set as numbers from 0 to 7 corresponding to bands of BER in the range: 0.2% to 12.8%

Downlink

L_RXQUAL_DL_P

U_RXQUAL_DL_P


Power decrease triggered


Other Power Control Parameters:

Parameter Purpose Range of Values N1 – N4, P1 – P4 Numbers of

measurements made for averaging

1 - 31

P_Con_Interval Minimum time interval between power control commands

0 – 30 seconds

Pow_Inc_Step_Size Step by which power may be increased

2,4 or 6 dB

Pow_Red_Step_Size Step by which power may be reduced

2 or 4 dB

____________________________________________________________________ 6.6 Discontinuous Transmission (DTX)

Discontinuous Transmission (DTX)Discontinuous Transmission (DTX)• In a conversation, a person generally only speaks for about

30% to 40% of the time• DTX makes use of this by stopping transmission when no

voice signal is detected• VAD - Voice Activity Detection unit

• Advantages:• Reduces interference• Prolongs battery life of mobile



6-23

Silence Descriptor (SID) Silence Descriptor (SID) • Silence Description Frames (SID) are sent at the end of a speech

frame - prevents sudden cut off of sound

• SID frames also sent periodically during periods of silence

• Receiver produces ‘comfort noise’ for the listener

• If speech frames are lost, they can be extrapolated from previous frame to fill the gap

Voice activity SID frames Signal transmitted by mobile


Speech Processing for DTXSpeech Processing for DTX

DTX processing functions in the mobile:

PCM voice signal

13 bit resolution

8000 samples / s

Voice Activity Detection

Speech Coder

SID Frame Generator

VAD

Voice Frame

SID Frame

DTX

Tra

nsm

issi

on

Bad Frame Replacement

BFI

Voice Frame

SID Frame

Voice Decoder

Comfort Noise Synthesiser

PCM voice signal

13 bit resolution

8000 samples / s


Transmitter Receiver

BFI (Bad Frame Indicator) allows a speech frame that has been lost or interrupted by FACCH to be replaced by extrapolation from the previous frame. If this occurs for several frames, audio output is muted.


____________________________________________________________________ 6.7 Extending Cell Coverage

Extending Coverage of CellsExtending Coverage of Cells

• Extending the range of a cell means overcoming two problems:• Relative timing of bursts due to path delay (Timing Advance)• Obtaining radio coverage at the extra distance

Extended range to provide coverage to offshore installations


Extended Range CellsExtended Range Cells

• The coverage limit of a cell is set by the Timing Advance maximum of 63, corresponding to a radius of 35 km

• Beyond this range, the bursts would arrive at the BTS in the next timeslot

• The limit can be extended by keeping every other timeslot free so that bursts from beyond 35 km can arrive without overlapping another transmission

• Capacity is half that of a normal cell• Coverage will also depend on having a

suitable power budget

0 1 2 3 4 5 6 7

Burst from within 35 km

Burst from beyond 35 km

Burst from about 120 km

Limit of extended range cell is about 120 km

User allocated to TS 2



6-25

SummarySummary• Modes of operation: No service, limited service, idle, dedicated• Network operations in idle mode: BCCH system information

messages, cell selection and re-selection (C1 and C2), location updating, DRX

• Network operations in dedicated mode: Measurements, SACCH reports, handover, power control, frequency hopping, DTX

• Extending the coverage of cells: extended range cells, repeaters



6-27

Section 6 Self-Assessment Exercises Of the following three activities, the first two relate to cell selection and reselection using parameters C1 and C2 and the third to a handover decision based on the power budget.

Exercise 6.1 - Cell Selection and Reselection When a Class 4 GSM 900 mobile is switched on, it measures the RXLEV for two cells (1 and 2) as: RXLEV(1) = -90 dBm RXLEV(2) = -93 dBm The network parameters are set as: RXLEV_ACCESS_MIN = -95 dBm MS_TXPWR_MAX_CCH = 35 dBm Calculate the C1 parameter for each cell and decide which one the mobile will camp on to.


Exercise 6.2 - Macrocell / Microcell Scenario – Cell Reselection A mobile is switched on within the coverage area of a microcell and a macrocell as shown. The set value of RXLEV_ACCESSA_MIN is –90 dBm The mobile measures the BCCH power levels for each cell as: RXLEV(macrocell) = -70 dBm RXLEV(microcell) = -80 dBm The network has set MS_TXPWR_MAX_CCH as 35 dBm. The mobile is a Class 4 GSM 900 handset with maximum power output of 33 dBm. 1. Compare C1 for the two cells and state which one the mobile will camp on to. 2. The network operator wants to attract slow moving mobiles in this location into the

microcell. Suggest a possible value for CELL_RESELECT_OFFSET in the C2 re-selection criterion of the microcell, which will achieve this. Note that values for CELL_RESELECT_OFFSET are from 0 to 126 dB in steps of 2 dB.

3. Mobiles should only re-select to the microcell if they remain in the area for more than 1

minute. Show how the rest of the C2 calculation could be used to achieve this. Note that TEMPORARY_OFFSET values range from 0 to 60 dB in steps of 10 dB and PENALTY_TIME ranges from 20 to 620 seconds in steps of 20 seconds.

Macrocell

Microcell


6-29

Exercise 6.3 - Handover Calculation The table shows parameter values relating to a mobile’s serving cell and a neighbouring cell, n. Find the value of RXLEV_NCELL (n) which would result in a handover to the neighbour cell due to power budget.

Network settings: Mobile maximum power (P) = 33 dBm MS_TXPWR_MAX = 35 dBm MS_TXPWR_MAX(n) = 35 dBm Measurements: Serving cell max power = 40 dBm RXLEV_DL = -95 dBm Serving cell actual power = 32 dBm RXLEV_NCELL (n) = ? HO_MARGIN(n) = 3 dBm


7-1

7. System Optimisation

____________________________________________________________________ 7.1 Introduction

In this section the following aspects of GSM network optimisation will be discussed:

• The need for optimisation • The optimisation process • System Performance • Test mobile survey data • Automated analysis • Remedial Action


____________________________________________________________________ 7.2 The Need for Optimisation

The Need for OptimisationThe Need for Optimisation• Optimisation tries to find the best performance parameters for the

network at any given stage of its lifecycle

• Changes in a network that can make optimisation necessary: • New sites introduced• Old sites enhanced or assigned new carriers• Omni-directional sites being sectorised

• Imperfections in original design:• accuracy of models• accuracy of digital map data• implementation issues

• Can lead to poor quality and dropped calls

X

Section 7 – System Optimisation


7-3

____________________________________________________________________ 7.3 The Optimisation Process

Optimisation ProcessOptimisation Process

Monitor network

Analyse data

QoS Targets

Met?

Yes Identify problems

Implement Changes

No

• Optimisation is an ongoing process of analysing network performance against Quality of Service targets:



____________________________________________________________________ 7.4 System Performance

Performance MeasurementsPerformance Measurements• Measurements of network performance cover:

• Traffic in erlangs• TCH and SDCCH Grade of Service (congestion)• Call success rate• Handover failure• Coverage area • Coverage quality• Subscriber base and growth

• Key Performance Indicators (KPI) are measurable dynamic parameters that help to target areas of concern


Defining KPIsDefining KPIs

• Appropriate KPIs to use depend on:• The nature of the network• Data sources available• Measurement tools available• Ability of engineering team• Cost of network infrastructure

• Sources of data include:• Surveyed data - from drive tests (Neptune)• Network statistics - from OMC (Optima)• Field engineer reports• Customer complaints



7-5

Surveyed Data Surveyed Data -- BenchmarkingBenchmarking

• Surveyed data from test-mobile measurements can be used to benchmark system performance against that of a competitor

• Problems that may be identified from surveyed data:• Poor coverage• Unexpected interference• Missing handover definitions• Installation problems at BTS

• Test-mobile measurements should include:• continuous calls to test coverage• repetitive short calls to test call-success


Possible ProblemsPossible Problems

• Test-mobile measurements may highlight problems such as:

• Coverage not as predicted• Vegetation absorption• Blockages• EIRP problems• BTS equipment installation problems

• Interference• Poor frequency plan• Unexpected coverage

• Handover problems• Missing handover definitions• ‘Islands’ of coverage with incorrect neighbour lists



____________________________________________________________________ 7.5 Test Mobile Survey Data

Advantages of a TestAdvantages of a Test--mobile mobile

• Test-mobile measurements have several advantages over network statistics from the BSC:

• BSCs provide counters with the number of dropped calls but do not indicate why or where

• BSCs do not collate information on poor downlink quality• BSCs cannot give information on areas without Network Access from

either poor signal or quality• BSCs do not store detailed information on calls

• Test-mobiles are the only way of diagnosing localised network performance issues


Using a TestUsing a Test--mobilemobile

• Laptop computer provides geo-referenced network information• Test-mobile provides:

• Signal strength and quality for serving cell and up to 6 neighbours• Layer 3 information in the form of instructions from the BTS• Frequency scan information



7-7

____________________________________________________________________ 7.6 Automated Analysis

Automated AnalysisAutomated Analysis

• Software such as Neptune allows analysis to be carried out in the field• Network configuration can be changed and re-tested immediately

• Performance data that can be analysed includes:• Call success - including RxLev, RxQual, set-up time, clear-down,

unexpected termination

• Attempted handovers -successful, unsuccessful, suggestions for better cells

• Neighbours - comparison of measured neighbours with list



____________________________________________________________________ 7.7 Remedial Action

Remedial ActionsRemedial Actions

• Possible ways of improving system performance:

• Adding sites or repeaters• Re-plan frequencies to reduce interference• Add or delete listed neighbours• Tune BSS parameters for handover, power

control etc.

Neptune analysis showing measured neighbours


SummarySummary

• The optimisation process: need for optimisation, on-going process

• System performance: measurements, KPIs, sources of data

• Test-mobile survey data: using survey data, benchmarking, possible problems shown by test-mobile, advantages of test-mobile data over network statistics, use of a test-mobile

• Automated analysis: Neptune, data that can be analysed, remedial action



A-1

Appendix A GSM Spectrum Allocation

PP--GSM Spectrum (Primary GSM)GSM Spectrum (Primary GSM)

Uplink Downlink

890 915 935 960 MHz

Duplex spacing = 45 MHz

Guard Band100 kHz wide

Channel Numbers (n) (ARFCN)200 kHz spacing

Range of ARFCN:1 - 124

1Guard Band100 kHz wide

Fu(n)

2 3 4 n

The initial allocation of spectrum for GSM provided 124 carriers with Frequency Division Duplex for uplink and downlink: Duplex sub bands of width 25 MHz - duplex spacing 45 MHz Uplink sub band: 890 MHz to 915 MHz Downlink sub band: 935 MHz to 960 MHz Frequency spacing between carriers is 200 kHz (0.2 MHz) One carrier is used for guard bands, giving: Total number of carriers (ARFCNs) = (25 – 0.2) / 0.2 = 124 (ARFCN = Absolute Radio Frequency Carrier Number) Uplink frequencies: Fu(n) = 890 + 0.2 n (1 <= n <= 124) Downlink frequencies: Fd(n) = Fu(n) + 45 (where n = ARFCN)

A-2 Advanced GSM Cell Planning © AIRCOM International 2002

EE--GSM Spectrum (Extended GSM)GSM Spectrum (Extended GSM)

Uplink Downlink

880 915 925 960 MHz




Range of ARFCN:1 – 124975 - 1023 1 n


Fu(n)

2 3 4

E-GSM allocated extra carriers at the low end of the spectrum. The ARFCN numbers of P-GSM were retained (with 0 now included) and new ARFCNs introduced for the lower end, numbered 975 – 1023. Duplex sub bands of width 35 MHz - duplex spacing 45 MHz (same as P-GSM) Uplink sub band: 880 MHz to 915 MHz Downlink sub band: 925 MHz to 960 MHz Frequency spacing of 200 kHz One carrier used to provide guard bands, giving: Total number of carriers (ARFCNs) = (35 – 0.2) / 0.2 = 174 Uplink frequencies: Fu(n) = 890 + 0.2 n (0 <= n <= 124) Fu(n) = 890 + 0.2 (n – 1024) (975 <= n <= 1023) Downlink frequencies: Fd(n) = Fu(n) + 45


A-3

DCSDCS--1800 Spectrum1800 Spectrum

Uplink Downlink

1710 1785 1805 1880 MHz






Fu(n)

2 3 4 n

Digital Communication System – 1800 MHz introduced a further spectrum range for GSM, typically used for smaller microcells overlaid over existing macrocells. Duplex sub bands of width 75 MHz - duplex spacing 95 MHz Uplink sub band: 1710 MHz to 1785 MHz Downlink sub band: 1805 MHz to 1880 MHz Frequency spacing of 200 kHz One carrier used to provide guard bands, giving: Total number of carriers (ARFCNs) = (75 – 0.2) / 0.2 = 374 Uplink frequencies: Fu(n) = 1710.2 + 0.2 (n – 512) (512 <= n <= 885) Downlink frequencies: Fd(n) = Fu(n) + 95

A-4 Advanced GSM Cell Planning © AIRCOM International 2002

PCSPCS--1900 Spectrum1900 Spectrum

Uplink Downlink

1850 1910 1930 1990 MHz






Fu(n)

2 3 4 n

Personal Communication System – 1900 MHz is used in USA and Central America to provide a service similar to GSM. Duplex sub bands of width 60 MHz - duplex spacing 80 MHz Uplink sub band: 1850 MHz to 1910 MHz Downlink sub band: 1930 MHz to 1990 MHz Frequency spacing of 200 kHz One carrier used to provide guard bands, giving: Total number of carriers (ARFCNs) = (60 – 0.2) / 0.2 = 299 Uplink frequencies: Fu(n) = 1850.2 + 0.2 (n – 512) (512 <= n <= 810) Downlink frequencies: Fd(n) = Fu(n) + 80


B-1

Appendix B Solutions to Self-Assessment Exercises SECTION 1 Exercise 1.1 - Logical Channel Usage Location Updating

Operation Channel Used Channel request RACH Channel assignment AGCH Request for location updating SDCCH Authentication challenge and response SDCCH Cipher mode request and acknowledgement SDCCH Confirmation and acknowledgement of update (possibly assignment of TMSI)

SDCCH

Channel release SDCCH Mobile Terminated Call

Operation Channel Used Paging of mobile PCH Mobile requests a channel RACH Channel assigned AGCH Mobile answers paging from network SDCCH Authentication challenge and response SDCCH Cipher mode request and acknowledgement SDCCH Set up message and confirmation by mobile SDCCH Traffic channel assigned SDCCH Traffic channel acknowledged FACCH Alerting (phone rings) FACCH Connect and acceptance (user answers) FACCH Exchange of user data (speech) TCH

B-2 Advanced GSM Cell Planning © AIRCOM International 2002

Exercise 1.2 - Timing Advance 1. Each bit in the timing advance corresponds to mobile – base station distance of 550 metres.

Mobile A distance = 550 x 50 = 27500 m = 27.5 km Mobile B distance = 550 x 30 = 16500 m = 16.5 km

2. Timings are:

A downlink 312.5 bp A uplink 731.25 bp B downlink 625 bp B uplink 1063.75 bp

Exercise 1.3 - Multiframe Timings A SACCH burst occurs once every TCH multiframe, i.e. once every 120 ms. To send a complete message using 4 bursts will take 4 x 120 = 480 ms. The alignment between the multiframes changes because the TCH contains 26 frames and CCH contains 51.

T T T T T T T T T T T T S T T T T IT T T T T T T T

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 24 2516 17 18 19 20 21 22 23

T = TCH S = SACCH I = Idle

I

0 1 42-45 46-49 5032-35 36-39 40 41

S BCCHF CCCH S CCCHF CCCH S CCCHF CCCH S CCCHF CCCH S CCCHF CCCH

22-25 26-29 30 3112-15 16-19 20 212-5 6-9 10 11

Downlink F = FCCH S = SCH I = Idle

0 1 2 3 4 5 6 7

0 312.5 625 781.25 1093.75

Bit periods

A DL

B DL

50 bp

731.25A UL

30 bp

1063.75 B UL


B-3

The table below shows which frame of CCH the idle slot of TCH will align with over several cycles:

TCH Cycle CCH Frame Number

CCH contents

1 25 CCCH 2 0 FCCH (first alignment) 3 26 CCCH 4 1 SCH (used to get BSIC) 5 27 CCCH 6 3 BCCH 7 28 CCCH 8 4 BCCH 9 29 CCCH 10 5 BCCH 11 30 FCCH (second

alignment) The first two times the alignment occurs are after 2 and 11 cycles of the TCH multiframe. This is actually 240 ms and 1320 ms.


SECTION 2 Exercise 2.1 - TCH Dimensioning 1. Number of traffic channels = 3 x 8 – 2 = 22 22 channels at 2% GoS can support 14.896 E (from table) 90 s holding time implies 25 mE per subscriber Number of subscribers = 14896 / 25 = 595 Trunking efficiency = Offered Traffic x (1 – GoS) / number of channels = 14.896 x 0.98 / 22 = 66% 2. Busy hour traffic = 20 x 1000 = 20 000 mE = 20 E From tables 20 E at 2% GoS requires 28 channels 3 signalling channels are needed, so the total required is 28 + 3 = 31 31 channels can be provided by 4 TRXs, giving 4 x 8 = 32 channels The actual number of TCH available is 29 (32 – 3) 29 channels at 2% GoS supports 21.039 E of traffic Number of subscribers = 21039 / 20 = 1051 51 subscribers spare capacity 3. Trunking efficiency = Offered Traffic x (1 – GoS) / number of channels Use the figures for full capacity of the cell: 20 x 0.98 / 29 = 67% Exercise 2.2 - TCH and SDCCH Dimensioning 1. TCH dimensioning:

Number of channels = 2 x 8 – 2 = 14 For GoS of 3%, this can support 8.8035 E Number of subscribers = 8803.5 / 20 = 440

SDCCH dimensioning:

Number of channels = 8 – 1 = 7 (SDCCH/8 less 1 for CBCH) For GoS of 1% this can support 2.5009 E Number of subscribers = 2500.9 / 5 = 500


B-5

This is sensible dimensioning as there is some spare capacity in SDCCH compared with TCH. Traffic will not be blocked by SDCCH when there are TCH channels free. TCH dimensioning:

There are now 15 traffic channels (2 x 8 –1) For GoS of 3% this can support 9.6500 E Number of subscribers = 482 SDCCH dimensioning Number of channels = 4 For GoS of 1% this can support 0.86942 E Number of subscribers = 869.42 / 5 = 173

This is a very poor configuration. Many traffic channels will not be used due to blocking at SDCCH. 2. TCH requirement:

Total traffic = 25 mE x 1200 = 30 E At GoS = 2%, this requires 39 channels

SDCCH requirement:

Total traffic = 5 mE x 1200 = 6 E At GoS = 0.5%, this requires 14 channels 14 SDCCH channels can be provided by 2 x SDCCH/8 1 BCH channel will also be needed Total signalling requirement = 3 channels Total channels required = 39 + 3 = 42

This can be provided by 6 carriers, giving 6 x 8 = 48 channels This solution in fact provides 45 TCH and 16 SDCCH channels 45 TCH at 2% GoS supports 35.607 E, or 35607 / 25 = 1424 subscribers 16 SDCCH at 0.5% GoS supports 8.0995 E, or 8099.5 / 5 = 1619 subscribers The balance between TCH and SDCCH is sensible, with spare capacity on SDCCH. It would also be possible to use CBCH, reducing the SDCCH channels to 15, which supports 7. 3755 E or 1475 subscribers.


Exercise 2.3 - Paging Capacity CCCH_CONF = 0 means TS0 is used in a non-combined multiframe, providing 9 CCCH blocks. 3 blocks reserved for AGCH, so 6 are available for PCH. Type 1 messages can page 2 mobiles per message. Paging capacity = 6 x 2 / 0.235 = 51 mobiles / second CCCH_CONF = 1 means TS0 is used in a combined multiframe, providing 3 CCCH blocks. 1 block reserved for AGCH, so 2 available for PCH. Type 3 messages can page up to 4 mobiles per message. Paging capacity = 2 x 4 / 0.235 = 34 mobiles / second Exercise 2.4 - Paging Channel Dimensioning PCH requirement = (50 000 x 0.4 x 2 x 1.2 ) / (2 x 3600 x 4.25) = 1.6 2 PCH blocks are required per multiframe. 2. To find the answer the number of subscribers from total traffic and mean traffic per subscriber must be found:

Number of subscribers = 500 / 0.025 = 20 000 PCH requirement = (20 000 x 0.25 x 2 x 1.2) / (4 x 3600 x 4.25) = 0.2 1 PCH block per multiframe will be sufficient.

4.25 x 3600 x PMFM x PF x MT x Calls t requiremen PCH =


B-7

Exercise 2.5 - AGCH Dimensioning (Suggested Solution)

Activity Multiplier Total

LU 2.5 3750

SMS 0.2 300

SS 0.25 375

IMSI attach 0.1 150

IMSI detach 0.1 150

Calls 1.0 1500

6225 The total activity including calls is 6225 AGCH requirement = (6225 x 1.2) / (3600 x 2 x 4.25) = 0.24 1 AGCH block per multiframe will be sufficient. Exercise 2.6 – Multi-Service Traffic Dimensioning Mean = 12 Variance = 6 + 18 = 24 Capacity factor = 2 Offered traffic = 6 Erlangs From Erlang B table, 12 trunks required. Number of timeslots required = 12 x 2 =24 If voice is target service then 26 timeslots should be allocated. If HSCSD traffic is target service then 27 timeslots should be allocated. Regardless of the target service chosen, four carriers should be sufficient. Exercise 2.7 – Dimensioning Micro and Pico Cells Using the Engset calculator to assess the trunking requirement for the traffic offered it is found that:

• Using the Engset formula, seven trunks should be provided. • Using the Erlang B formula, eight trunks should be provided.


SECTION 3 Exercise 3.1 - Frequency Re-use Cluster Sizes Typical GSM frequency re-use cluster sizes are: 3, 4, 7, 9, 12 e.g. 3/9, 4/12 patterns. i) analogue system requires a minimum C/I of about 20 dB. From the table in the notes, when x = 3.5, a cluster size of 12 gives C/I of 19.45dB. Re-use distance, km606x1012x310N3RD ==== ii) digital systems can cope with C/I of about 9 dB. From table, cluster size of 3 gives C/I of 8.9 dB. Re-use distance, km303x103x310N3RD ==== Exercise 3.2 - Frequency Planning Adjustments Consider the change in C/A and C/I caused by moving either carrier. B2 carriers are adjacent to A2 and C2 carriers – both of which border on the B1 cell. B3 carriers are adjacent to A3 and C3 carriers – only C3 borders on the B1 cell. Thus from the decrease in C/A, B3 is a better prospect. Both moves will place a carrier (either B2 or B3) closer to another of the same group – either the B2 to the north west (west of A1) or B3 to the north east (east of D3). (These are not shown explicitly on the diagram.) These will cause similar decreases in C/I. On balance the B3 move is better although it will cause increased interference.


B-9

Exercise 3.3 - MRP Planning How many carriers are to be assigned to: a) BCCH 12 b) TCH1 8 c) TCH2 8 d) TCH3 6 Planning the BCCH layer: Starting with carrier 30, assign every other carrier (up to the total needed) to the BCCH layer: 12 carriers assigned: 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52 Planning the TCH layers For TCH1 start from the last carrier (63) and assign every other carrier up to the total required: 8 carriers assigned: 63, 61, 59, 57, 55, 53, 51, 49 For TCH2 start from the last available carrier and assign every other one up to the total required: 8 carriers assigned: 62, 60, 58, 56, 54, 47, 45, 43 Assign the remaining frequencies to TCH3: 6 carriers remain: 31, 33, 35, 37, 39, 41 Average re-use What is the average re-use factor of this plan? Average re-use = (12 + 8 + 8 +6) / 4 = 8.5

52 is assigned to BCCH next available is 47


SECTION 4 Exercise 4.1 - Base Station Positioning 1. On the bank of a wide river Path loss across water much lower than land. Directional or down tilted antenna may be needed to confine coverage to one bank Effect could be used to provide coverage for ferry passengers 2. In a hilly countryside region Dead spots and shadow regions BTS on top of hill generally better Reflections from hills may cause time dispersion problems 3. To provide coverage for a road through hilly countryside Need to fill in gaps caused by shadow areas Directional antennas (microcells) ‘back to back’ along road 4. In a long straight road in town Microcells below building height Directional antennas Use canyon effect Possible reflections into side streets Adjust power to avoid overlapping coverage at junctions causing handovers Macro/micro cell handover strategies for vehicular and pedestrian users 5. At a cross roads in town Omni antenna near centre of cross roads Do not use overlapping directional antennas - handovers 6. To provide coverage for an office block Down tilt outdoor antennas for in-building coverage Extra path losses in building Use picocells inside building – distributed antenna, leaky feeder


B-11

Exercise 4.2 - Spectrum Sharing in a Microcell Consider the available carrier groups: A1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D3 Look at the possible interference effects that would be caused by using each of these in the B1 cell: B1 is used in the cell in question – C/I poor in cell A2 B2 B3 C2 C3 D1 are used in physically adjacent cells – C/I poor on cell borders A1 and C1 are adjacent carriers to B1 – C/A poor in cells This leaves D2 A3 D3 to compare D3 is physically closer to the B1 cell than the other two D2 and A3 are equally spaced from B1 Either D2 or A3 could be used. Exercise 4.3 - Repeater Positioning If the maximum isolation between antennas is 78 dB and a margin of 14 dB is to be provided, the maximum gain amplifier will be 64 dB. Thus the total gain is 15 + 22 + 64 = 101 dB. As the path loss was originally 8 dB too high, a maximum path loss from the repeater of 93 dB can be tolerated.


SECTION 5 Exercise 5.1 - Intermodulation Products F (30) = 890 + 30 x 0.2 = 896 MHz F (35) = 890 + 35 x 0.2 = 897 MHz Second order products: 2 x 896 = 1792 MHz 2 x 897 = 1794 MHz 896 + 897 = 1793 MHz These frequencies are in the duplex spacing region of the spectrum between the uplink and downlink bands. They should not cause interference. Third order products in the 900 MHz band are: 2 x 896 – 897 = 895 MHz 2 x 897 – 896 = 898 MHz 897 + 896 – 897 = 896 MHz 896 + 897 – 896 = 897 MHz PIMD = 3 x 20 + 3 x 5 – 2 x 35 = 5 dBm Exercise 5.2 - Antenna Patterns The beam widths can be estimated directly from the pattern by judging the -3 dB points. The gain is generally higher for antennas with smaller beamwidth – more concentrated signal. In practice, remember that the patterns are three dimensional and we are only looking at the H Plane here.

86o

11 dBd


B-13

Exercise 5.3 - BS Equipment – Power Loss Calculation TRX output power = 5 W = 10 log (5 / 0.001) = 37 dBm Feeder loss: Total length = 20 + 10 + 5 = 35m Loss = 35 x 6 / 100 = 2.1 dB Connector Loss: For one TRX there are a total of 8 connectors from TRX to antenna Total connector loss = 8 x 0.1 = 0.8 dB Total system loss:

= 2 x combiner loss + duplexer insertion loss + feeder loss + connector loss = 2 x 3.2 + 1 + 2.1 + 0.8 = 10.3 dB

Power supplied to antenna = 37 – 10.3 = 26.7 dBm

16o

18 dBd

26o

15 dBd

60o 13 dBd


Exercise 5.4 – Choice of Cell Configuration If the cell uses an omni-directional antenna, then a transmit power of 8 dBm would be required (this is easily achieved). If a sectored antenna was used then a transmit power of 3 dBm would be sufficient. As the required transmit power is very low, there is no need for uplink diversity.

a) If 4 Erlangs was to be served then 9 traffic channels would be needed. This can be provided using two carriers and hence the omni-directional configuration with a transmit power of 8 dBm would be most suitable.

b) If, however, 12 Erlangs of traffic was offered, 19 traffic channels would be required

and two carriers would be insufficient. In this case it would be necessary to use the sectored configuration with each cell (sector) serving 4 Erlangs of traffic. In this case the transmit power would be 3 dBm.

Exercise 5.5 – Effects of Diversity Without diversity, the maximum BTS power is 41 dBm. Then the maximum path loss will be (41+92+18-8) = 143 dB. The range is 10(6/35) = 1.48 km. With diversity the maximum BTS power is 43 dBm and the maximum path loss will be 145 dB. The range is then 1.69 km.


B-15

SECTION 6 Exercise 6.1 - Cell Selection and Re-selection C1(n) = [RXLEV(n) – RXLEV_ACCESS_MIN – max(0, (MS_TXPWR_MAX_CCH – P))] C1(1) = -90 – (-95) – max(0,2) = 5 – 2 = 3 C1(2) = -93 – (-95) – 2 = 0 The mobile will camp on to cell 1. Exercise 6.2 - Macrocell / Microcell Scenario 1. C1(macrocell) = -70 – (-90) – max(0, (35-33)) = 20 – 2 = 18 C1(microcell) = -80 – (-90) – max(0, (35-33)) = 10 – 2 = 8 The macrocell will be selected. 2. Set CELL_RESELECT_OFFSET as 12 dB for the microcell and 0dB for the macrocell. Then: C2 (macrocell) = 18 C2 (microcell) = 8 + 12 = 20 The mobile will re-select the microcell. 3. C2 (macrocell) should remain higher than C2 (microcell) for the first 60 seconds. Use: TEMPORARY_OFFSET = 10 dB PENALTY_TIME = 60 seconds Then: C2 (microcell) = 20 – 10 x H(60 – T)


While T ≤ 60 seconds, C2 (microcell) = 20 – 10 = 10 When T > 60 seconds, C2 (microcell) = 20 – 0 = 20 After 60 seconds, C2 will be higher in the microcell than the macrocell and the mobile will re-select to the microcell. Exercise 6.3 - Handover Calculation PBGT(n) = [ min (35,33) – (-95) – (40 – 32)] – [ min(35, 33) – RXLEV_NCELL(n)] PBGT(n) = 33 +95 – 6 – 33 + RXLEV_NCELL(n) PBGT(n) = 89 + RXLEV_NCELL(n) For handover, PBGT(n) >0 AND PBGT(n) >HO_MARGIN i.e. 89 + RXLEV_NCELL(n) > 3 RXLEV_NCELL(n) > 3 – 89 RXLEV_NCELL(n) > - 86 dBm Handover will occur if the measured level RXLEV_NCELL(n) becomes –85 dBm or higher.


C-1

ANNEX C – ERLANG B TABLES

n Grade of Service n

0.00001 0.00005 0.0001 0.0005 0.001 0.002 0.003 0.004 0.005 0.006 1 .00001 .00005 .00010 .00050 .00100 .00200 .00301 .00402 .00503 .00604 1 2 .00448 .01005 .01425 .03213 .04576 .06534 .08064 .09373 .10540 .11608 2 3 .03980 .06849 .08683 .15170 .19384 .24872 .28851 .32099 .34900 .37395 3 4 .12855 .19554 .23471 .36236 .43927 .53503 .60209 .65568 .70120 .74124 4 5 .27584 .38851 .45195 .64857 .76212 .89986 .99446 1.0692 1.1320 1.1870 5 6 .47596 .63923 .72826 .99567 1.1459 1.3252 1.4468 1.5421 1.6218 1.6912 6 7 .72378 .93919 1.0541 1.3922 1.5786 1.7984 1.9463 2.0614 2.1575 2.2408 7 8 1.0133 1.2816 1.4219 1.8298 2.0513 2.3106 2.4837 2.6181 2.7299 2.8266 8 9 1.3391 1.6595 1.8256 2.3016 2.5575 2.8549 3.0526 3.2057 3.3326 3.4422 9 10 1.6970 2.0689 2.2601 2.8028 3.0920 3.4265 3.6480 3.8190 3.9607 4.0829 1011 2.0849 2.5059 2.7216 3.3294 3.6511 4.0215 4.2661 4.4545 4.6104 4.7447 1112 2.4958 2.9671 3.2072 3.8781 4.2314 4.6368 4.9038 5.1092 5.2789 5.4250 1213 2.9294 3.4500 3.7136 4.4465 4.8306 5.2700 5.5588 5.7807 5.9638 6.1214 1314 3.3834 3.9523 4.2388 5.0324 5.4464 5.9190 6.2291 6.4670 6.6632 6.8320 1415 3.8559 4.4721 4.7812 5.6339 6.0772 6.5822 6.9130 7.1665 7.3755 7.5552 1516 4.3453 5.0079 5.3390 6.2496 6.7215 7.2582 7.6091 7.8780 8.0995 8.2898 1617 4.8502 5.5583 5.9110 6.8782 7.3781 7.9457 8.3164 8.6003 8.8340 9.0347 1718 5.3693 6.1220 6.4959 7.5186 8.0459 8.6437 9.0339 9.3324 9.5780 9.7889 1819 5.9016 6.6980 7.0927 8.1698 8.7239 9.3515 9.7606 10.073 10.331 10.552 1920 6.4460 7.2854 7.7005 8.8310 9.4115 10.068 10.496 10.823 11.092 11.322 2021 7.0017 7.8834 8.3186 9.5014 10.108 10.793 11.239 11.580 11.860 12.100 2122 7.5680 8.4926 8.9462 10.180 10.812 11.525 11.989 12.344 12.635 12.885 2223 8.1443 9.1095 9.5826 10.868 11.524 12.265 12.746 13.114 13.416 13.676 2324 8.7298 9.7351 10.227 11.562 12.243 13.011 13.510 13.891 14.204 14.472 2425 9.3240 10.369 10.880 12.264 12.969 13.763 14.279 14.673 14.997 15.274 2526 9.9265 11.010 11.540 12.972 13.701 14.522 15.054 15.461 15.795 16.081 2627 10.537 11.659 12.207 13.686 14.439 15.285 15.835 16.254 16.598 16.893 2728 11.154 12.314 12.880 14.406 15.182 16.054 16.620 17.051 17.406 17.709 2829 11.779 12.976 13.560 15.132 15.930 16.828 17.410 17.853 18.218 18.530 2930 12.417 13.644 14.246 15.863 16.684 17.606 18.204 18.660 19.034 19.355 3031 13.054 14.318 14.937 16.599 17.442 18.389 19.002 19.470 19.854 20.183 3132 13.697 14.998 15.633 17.340 18.205 19.176 19.805 20.284 20.678 21.015 3233 14.346 15.682 16.335 18.085 18.972 19.966 20.611 21.102 21.505 21.850 3334 15.001 16.372 17.041 18.835 19.743 20.761 21.421 21.923 22.336 22.689 3435 15.660 17.067 17.752 19.589 20.517 21.559 22.234 22.748 23.169 23.531 3536 16.325 17.766 18.468 20.347 21.296 22.361 23.050 23.575 24.006 24.376 3637 16.995 18.470 19.188 21.108 22.078 23.166 23.870 24.406 24.846 25.223 3738 17.669 19.178 19.911 21.873 22.864 23.974 24.692 25.240 25.689 26.074 3839 18.348 19.890 20.640 22.642 23.652 24.785 25.518 26.076 26.534 26.926 3940 19.031 20.606 21.372 23.414 24.444 25.599 26.346 26.915 27.382 27.782 4041 19.718 21.326 22.107 24.189 25.239 26.416 27.177 27.756 28.232 28.640 4142 20.409 22.049 22.846 24.967 26.037 27.235 28.010 28.600 29.085 29.500 4243 21.104 22.776 23.587 25.748 26.837 28.057 28.846 29.447 29.940 30.362 4344 21.803 23.507 24.333 26.532 27.641 28.882 29.684 30.295 30.797 31.227 4445 22.505 24.240 25.081 27.319 28.447 29.708 30.525 31.146 31.656 32.093 4546 23.211 24.977 25.833 28.109 29.255 30.538 31.367 31.999 32.517 32.962 4647 23.921 25.717 26.587 28.901 30.066 31.369 32.212 32.854 33.381 33.832 4748 24.633 26.460 27.344 29.696 30.879 32.203 33.059 33.711 34.246 34.704 4849 25.349 27.206 28.104 30.493 31.694 33.039 33.908 34.570 35.113 35.578 4950 26.067 27.954 28.867 31.292 32.512 33.876 34.759 35.431 35.982 36.454 5051 26.789 28.706 29.632 32.094 33.332 34.716 35.611 36.293 36.852 37.331 51

0.00001 0.00005 0.0001 0.0005 0.001 0.002 0.003 0.004 0.005 0.006

C-2 Advanced GSM Cell Planning © AIRCOM International 2002


0.007 0.008 0.009 0.01 0.02 0.03 0.05 0.1 0.2 0.4 1 .00705 .00806 .00908 .01010 .02041 .03093 .05263 .11111 .25000 .66667 1 2 .12600 .13532 .14416 .15259 .22347 .28155 .38132 .59543 1.0000 2.0000 2 3 .39664 .41757 .43711 .45549 .60221 .71513 .89940 1.2708 1.9299 3.4798 3 4 .77729 .81029 .84085 .86942 1.0923 1.2589 1.5246 2.0454 2.9452 5.0210 4 5 1.2362 1.2810 1.3223 1.3608 1.6571 1.8752 2.2185 2.8811 4.0104 6.5955 5 6 1.7531 1.8093 1.8610 1.9090 2.2759 2.5431 2.9603 3.7584 5.1086 8.1907 6 7 2.3149 2.3820 2.4437 2.5009 2.9354 3.2497 3.7378 4.6662 6.2302 9.7998 7 8 2.9125 2.9902 3.0615 3.1276 3.6271 3.9865 4.5430 5.5971 7.3692 11.419 8 9 3.5395 3.6274 3.7080 3.7825 4.3447 4.7479 5.3702 6.5464 8.5217 13.045 9 10 4.1911 4.2889 4.3784 4.4612 5.0840 5.5294 6.2157 7.5106 9.6850 14.677 1011 4.8637 4.9709 5.0691 5.1599 5.8415 6.3280 7.0764 8.4871 10.857 16.314 1112 5.5543 5.6708 5.7774 5.8760 6.6147 7.1410 7.9501 9.4740 12.036 17.954 1213 6.2607 6.3863 6.5011 6.6072 7.4015 7.9667 8.8349 10.470 13.222 19.598 1314 6.9811 7.1155 7.2382 7.3517 8.2003 8.8035 9.7295 11.473 14.413 21.243 1415 7.7139 7.8568 7.9874 8.1080 9.0096 9.6500 10.633 12.484 15.608 22.891 1516 8.4579 8.6092 8.7474 8.8750 9.8284 10.505 11.544 13.500 16.807 24.541 1617 9.2119 9.3714 9.5171 9.6516 10.656 11.368 12.461 14.522 18.010 26.192 1718 9.9751 10.143 10.296 10.437 11.491 12.238 13.385 15.548 19.216 27.844 1819 10.747 10.922 11.082 11.230 12.333 13.115 14.315 16.579 20.424 29.498 1920 11.526 11.709 11.876 12.031 13.182 13.997 15.249 17.613 21.635 31.152 2021 12.312 12.503 12.677 12.838 14.036 14.885 16.189 18.651 22.848 32.808 2122 13.105 13.303 13.484 13.651 14.896 15.778 17.132 19.692 24.064 34.464 2223 13.904 14.110 14.297 14.470 15.761 16.675 18.080 20.737 25.281 36.121 2324 14.709 14.922 15.116 15.295 16.631 17.577 19.031 21.784 26.499 37.779 2425 15.519 15.739 15.939 16.125 17.505 18.483 19.985 22.833 27.720 39.437 2526 16.334 16.561 16.768 16.959 18.383 19.392 20.943 23.885 28.941 41.096 2627 17.153 17.387 17.601 17.797 19.265 20.305 21.904 24.939 30.164 42.755 2728 17.977 18.218 18.438 18.640 20.150 21.221 22.867 25.995 31.388 44.414 2829 18.805 19.053 19.279 19.487 21.039 22.140 23.833 27.053 32.614 46.074 2930 19.637 19.891 20.123 20.337 21.932 23.062 24.802 28.113 33.840 47.735 3031 20.473 20.734 20.972 21.191 22.827 23.987 25.773 29.174 35.067 49.395 3132 21.312 21.580 21.823 22.048 23.725 24.914 26.746 30.237 36.295 51.056 3233 22.155 22.429 22.678 22.909 24.626 25.844 27.721 31.301 37.524 52.718 3334 23.001 23.281 23.536 23.772 25.529 26.776 28.698 32.367 38.754 54.379 3435 23.849 24.136 24.397 24.638 26.435 27.711 29.677 33.434 39.985 56.041 3536 24.701 24.994 25.261 25.507 27.343 28.647 30.657 34.503 41.216 57.703 3637 25.556 25.854 26.127 26.378 28.254 29.585 31.640 35.572 42.448 59.365 3738 26.413 26.718 26.996 27.252 29.166 30.526 32.624 36.643 43.680 61.028 3839 27.272 27.583 27.867 28.129 30.081 31.468 33.609 37.715 44.913 62.690 3940 28.134 28.451 28.741 29.007 30.997 32.412 34.596 38.787 46.147 64.353 4041 28.999 29.322 29.616 29.888 31.916 33.357 35.584 39.861 47.381 66.016 4142 29.866 30.194 30.494 30.771 32.836 34.305 36.574 40.936 48.616 67.679 4243 30.734 31.069 31.374 31.656 33.758 35.253 37.565 42.011 49.851 69.342 4344 31.605 31.946 32.256 32.543 34.682 36.203 38.557 43.088 51.086 71.006 4445 32.478 32.824 33.140 33.432 35.607 37.155 39.550 44.165 52.322 72.669 4546 33.353 33.705 34.026 34.322 36.534 38.108 40.545 45.243 53.559 74.333 4647 34.230 34.587 34.913 35.215 37.462 39.062 41.540 46.322 54.796 75.997 4748 35.108 35.471 35.803 36.109 38.392 40.018 42.537 47.401 56.033 77.660 4849 35.988 36.357 36.694 37.004 39.323 40.975 43.534 48.481 57.270 79.324 4950 36.870 37.245 37.586 37.901 40.255 41.933 44.533 49.562 58.508 80.988 5051 37.754 38.134 38.480 38.800 41.189 42.892 45.533 50.644 59.746 82.652 51

0.007 0.008 0.009 0.01 0.02 0.03 0.05 0.1 0.2 0.4


C-3


0.00001 0.00005 0.0001 0.0005 0.001 0.002 0.003 0.004 0.005 0.006 51 26.789 28.706 29.632 32.094 33.332 34.716 35.611 36.293 36.852 37.331 51 52 27.513 29.459 30.400 32.898 34.153 35.558 36.466 37.157 37.724 38.211 52 53 28.241 30.216 31.170 33.704 34.977 36.401 37.322 38.023 38.598 39.091 53 54 28.971 30.975 31.942 34.512 35.803 37.247 38.180 38.891 39.474 39.973 54 55 29.703 31.736 32.717 35.322 36.631 38.094 39.040 39.760 40.351 40.857 55 56 30.438 32.500 33.494 36.134 37.460 38.942 39.901 40.630 41.229 41.742 56 57 31.176 33.266 34.273 36.948 38.291 39.793 40.763 41.502 42.109 42.629 57 58 31.916 34.034 35.055 37.764 39.124 40.645 41.628 42.376 42.990 43.516 58 59 32.659 34.804 35.838 38.581 39.959 41.498 42.493 43.251 43.873 44.406 59 60 33.404 35.577 36.623 39.401 40.795 42.353 43.360 44.127 44.757 45.296 60 61 34.151 36.351 37.411 40.222 41.633 43.210 44.229 45.005 45.642 46.188 61 62 34.900 37.127 38.200 41.045 42.472 44.068 45.099 45.884 46.528 47.081 62 63 35.651 37.906 38.991 41.869 43.313 44.927 45.970 46.764 47.416 47.975 63 64 36.405 38.686 39.784 42.695 44.156 45.788 46.843 47.646 48.305 48.870 64 65 37.160 39.468 40.579 43.523 45.000 46.650 47.716 48.528 49.195 49.766 65 66 37.918 40.252 41.375 44.352 45.845 47.513 48.591 49.412 50.086 50.664 66 67 38.677 41.038 42.173 45.183 46.692 48.378 49.467 50.297 50.978 51.562 67 68 39.439 41.825 42.973 46.015 47.540 49.243 50.345 51.183 51.872 52.462 68 69 40.202 42.615 43.775 46.848 48.389 50.110 51.223 52.071 52.766 53.362 69 70 40.967 43.405 44.578 47.683 49.239 50.979 52.103 52.959 53.662 54.264 70 71 41.734 44.198 45.382 48.519 50.091 51.848 52.984 53.848 54.558 55.166 71 72 42.502 44.992 46.188 49.357 50.944 52.718 53.865 54.739 55.455 56.070 72 73 43.273 45.787 46.996 50.195 51.799 53.590 54.748 55.630 56.354 56.974 73 74 44.045 46.585 47.805 51.035 52.654 54.463 55.632 56.522 57.253 57.880 74 75 44.818 47.383 48.615 51.877 53.511 55.337 56.517 57.415 58.153 58.786 75 76 45.593 48.183 49.427 52.719 54.369 56.211 57.402 58.310 59.054 59.693 76 77 46.370 48.985 50.240 53.563 55.227 57.087 58.289 59.205 59.956 60.601 77 78 47.149 49.787 51.054 54.408 56.087 57.964 59.177 60.101 60.859 61.510 78 79 47.928 50.592 51.870 55.254 56.948 58.842 60.065 60.998 61.763 62.419 79 80 48.710 51.397 52.687 56.101 57.810 59.720 60.955 61.895 62.668 63.330 80 81 49.492 52.204 53.506 56.949 58.673 60.600 61.845 62.794 63.573 64.241 81 82 50.277 53.012 54.325 57.798 59.537 61.480 62.737 63.693 64.479 65.153 82 83 51.062 53.822 55.146 58.649 60.403 62.362 63.629 64.594 65.386 66.065 83 84 51.849 54.633 55.968 59.500 61.269 63.244 64.522 65.495 66.294 66.979 84 85 52.637 55.445 56.791 60.352 62.135 64.127 65.415 66.396 67.202 67.893 85 86 53.427 56.258 57.615 61.206 63.003 65.011 66.310 67.299 68.111 68.808 86 87 54.218 57.072 58.441 62.060 63.872 65.897 67.205 68.202 69.021 69.724 87 88 55.010 57.887 59.267 62.915 64.742 66.782 68.101 69.106 69.932 70.640 88 89 55.804 58.704 60.095 63.772 65.612 67.669 68.998 70.011 70.843 71.557 89 90 56.598 59.526 60.923 64.629 66.484 68.556 69.896 70.917 71.755 72.474 90 91 57.394 60.344 61.753 65.487 67.356 69.444 70.794 71.823 72.668 73.393 91 92 58.192 61.164 62.584 66.346 68.229 70.333 71.693 72.730 73.581 74.311 92 93 58.990 61.985 63.416 67.206 69.103 71.222 72.593 73.637 74.495 75.231 93 94 59.789 62.807 64.248 68.067 69.978 72.113 73.493 74.545 75.410 76.151 94 95 60.590 63.630 65.082 68.928 70.853 73.004 74.394 75.454 76.325 77.072 95 96 61.392 64.454 65.917 69.791 71.729 73.896 75.296 76.364 77.241 77.993 96 97 62.194 65.279 66.752 70.654 72.606 74.788 76.199 77.274 78.157 78.915 97 98 62.998 66.105 67.589 71.518 73.484 75.681 77.102 78.185 79.074 79.837 98 99 63.803 66.932 68.426 72.383 74.363 76.575 78.006 79.096 79.992 80.760 99 100 64.609 67.760 69.265 73.248 75.242 77.469 78.910 80.008 80.910 81.684 100101 65.416 68.589 70.104 74.115 76.122 78.364 79.815 80.920 81.829 82.608 101

0.00001 0.00005 0.0001 0.0005 0.001 0.002 0.003 0.004 0.005 0.006

C-4 Advanced GSM Cell Planning © AIRCOM International 2002

n Grade of Service n 0.007 0.008 0.009 0.01 0.02 0.03 0.05 0.1 0.2 0.4

51 37.754 38.134 38.480 38.800 41.189 42.892 45.533 50.644 59.746 82.652 51 52 38.639 39.024 39.376 39.700 42.124 43.852 46.533 51.726 60.985 84.317 52 53 39.526 39.916 40.273 40.602 43.060 44.813 47.534 52.808 62.224 85.981 53 54 40.414 40.810 41.171 41.505 43.997 45.776 48.536 53.891 63.463 87.645 54 55 41.303 41.705 42.071 42.409 44.936 46.739 49.539 54.975 64.702 89.310 55 56 42.194 42.601 42.972 43.315 45.875 47.703 50.543 56.059 65.942 90.974 56 57 43.087 43.499 43.875 44.222 46.816 48.669 51.548 57.144 67.181 92.639 57 58 43.980 44.398 44.778 45.130 47.758 49.635 52.553 58.229 68.421 94.303 58 59 44.875 45.298 45.683 46.039 48.700 50.602 53.559 59.315 69.662 95.968 59 60 45.771 46.199 46.589 46.950 49.644 51.570 54.566 60.401 70.902 97.633 60 61 46.669 47.102 47.497 47.861 50.589 52.539 55.573 61.488 72.143 99.297 61 62 47.567 48.005 48.405 48.774 51.534 53.508 56.581 62.575 73.384 100.96 62 63 48.467 48.910 49.314 49.688 52.481 54.478 57.590 63.663 74.625 102.63 63 64 49.368 49.816 50.225 50.603 53.428 55.450 58.599 64.750 75.866 104.29 64 65 50.270 50.723 51.137 51.518 54.376 56.421 59.609 65.839 77.108 105.96 65 66 51.173 51.631 52.049 52.435 55.325 57.394 60.619 66.927 78.350 107.62 66 67 52.077 52.540 52.963 53.353 56.275 58.367 61.630 68.016 79.592 109.29 67 68 52.982 53.450 53.877 54.272 57.226 59.341 62.642 69.106 80.834 110.95 68 69 53.888 54.361 54.793 55.191 58.177 60.316 63.654 70.196 82.076 112.62 69 70 54.795 55.273 55.709 56.112 59.129 61.291 64.667 71.286 83.318 114.28 70 71 55.703 56.186 56.626 57.033 60.082 62.267 65.680 72.376 84.561 115.95 71 72 56.612 57.099 57.545 57.956 61.036 63.244 66.694 73.467 85.803 117.61 72 73 57.522 58.014 58.464 58.879 61.990 64.221 67.708 74.558 87.046 119.28 73 74 58.432 58.930 59.384 59.803 62.945 65.199 68.723 75.649 88.289 120.94 74 75 59.344 59.846 60.304 60.728 63.900 66.177 69.738 76.741 89.532 122.61 75 76 60.256 60.763 61.226 61.653 64.857 67.156 70.753 77.833 90.776 124.27 76 77 61.169 61.681 62.148 62.579 65.814 68.136 71.769 78.925 92.019 125.94 77 78 62.083 62.600 63.071 63.506 66.771 69.116 72.786 80.018 93.262 127.61 78 79 62.998 63.519 63.995 64.434 67.729 70.096 73.803 81.110 94.506 129.27 79 80 63.914 64.439 64.919 65.363 68.688 71.077 74.820 82.203 95.750 130.94 80 81 64.830 65.360 65.845 66.292 69.647 72.059 75.838 83.297 96.993 132.60 81 82 65.747 66.282 66.771 67.222 70.607 73.041 76.856 84.390 98.237 134.27 82 83 66.665 67.204 67.697 68.152 71.568 74.024 77.874 85.484 99.481 135.93 83 84 67.583 68.128 68.625 69.084 72.529 75.007 78.893 86.578 100.73 137.60 84 85 68.503 69.051 69.553 70.016 73.490 75.990 79.912 87.672 101.97 139.26 85 86 69.423 69.976 70.481 70.948 74.452 76.974 80.932 88.767 103.21 140.93 86 87 70.343 70.901 71.410 71.881 75.415 77.959 81.952 89.861 104.46 142.60 87 88 71.264 71.827 72.340 72.815 76.378 78.944 82.972 90.956 105.70 144.26 88 89 72.186 72.753 73.271 73.749 77.342 79.929 83.993 92.051 106.95 145.93 89 90 73.109 73.680 74.202 74.684 78.306 80.915 85.014 93.146 108.19 147.59 90 91 74.032 74.608 75.134 75.620 79.271 81.901 86.035 94.242 109.44 149.26 91 92 74.956 75.536 76.066 76.556 80.236 82.888 87.057 95.338 110.68 150.92 92 93 75.880 76.465 76.999 77.493 81.201 83.875 88.079 96.434 111.93 152.59 93 94 76.805 77.394 77.932 78.430 82.167 84.862 89.101 97.530 113.17 154.26 94 95 77.731 78.324 78.866 79.368 83.134 85.850 90.123 98.626 114.42 155.92 95 96 78.657 79.255 79.801 80.306 84.100 86.838 91.146 99.722 115.66 157.59 96 97 79.584 80.186 80.736 81.245 85.068 87.826 92.169 100.82 116.91 159.25 97 98 80.511 81.117 81.672 82.184 86.035 88.815 93.193 101.92 118.15 160.92 98 99 81.439 82.050 82.608 83.124 87.003 89.804 94.216 103.01 119.40 162.59 99

100 82.367 82.982 83.545 84.064 87.972 90.794 95.240 104.11 120.64 164.25 100101 83.296 83.916 84.482 85.005 88.941 91.784 96.265 105.21 121.89 165.92 101

0.007 0.008 0.009 0.01 0.02 0.03 0.05 0.1 0.2 0.4

gsm advanced cell planning

Technology

traffic channel dimensioning

assessment exerecises

self assessment exercises

control channel dimensioning

traffic theory

traffic measurement

advancedgsm cell planning

frequency reuse patterns