2g huawei refarming.ppt

1 © Nokia Siemens Networks Presentation / Author / DateFor internal use

HUAWEI 2G REFARMING


Contents

1.Overview2.2G Refarming3.Tight Frequency Reuse


Document Information

Document Version: 1.0

Issue Date: November 12, 2010

Document Owner: Ville Salomaa

SOFTWARE RELEASE: GBSS9.0

SCOPE: 2G Refarming Tight frequency reuse

CONVENTION: Raw counters are marked in BLUE Formulas are marked in GRAY Parameters are marked in RED MML commands are marked in GREEN


Contents



Overview

A UMTS network can be constructed in the 900 MHz frequency band at a lower cost with better coverage than a UMTS2100 network. At the same time demands for mobile broadband services are ever increasing.

According to radio wave propagation features, radio signals are transmitted farther at a lower carrier frequency and allow one site to cover a wider area. This makes the UMTS900 an excellent wide coverage solution. Therefore, investment for mobile networks goes down as wider coverage per site means fewer sites.

Second, the UMTS900 network is better for indoor coverage and has better network coverage performance.

Low-frequency carrier signals suffer less loss when penetrating building walls. Thus, with a UMTS900 network, Quality of Service is improved and better user experience enabled.

However, due to limited spectrum resources on the GSM900 band, most operators cannot provide a complete 5MHz frequency band to build the UMTS network. This is why the GSM/UMTS 900MHz refarming solution was proposed in order to allocate part of the existing GSM900/1800 spectrum to 3G services.


Contents



2G Refarming

Since 2G networks still carry large amounts of voice and data traffic, releasing 2G spectrum for 3G servicesraises various issues for operators:

• Which part of the 900/1800 MHz band to refarm for 3G service • How to carry the remaining 2G traffic over the reduced frequency band more efficiently.• How to migrate the 2G traffic onto new 3G 900 network (handset replacement, etc.)• How to minimise the cost of migration (number of replacement sites required, number of sites needinghardware upgrades, labour costs, etc.)• How to minimize the interference between GSM and UMTS networks.

The present document focuses on the first 2 points above.


Main Refarming Challenges

Operators will face a number of challenges in clearing the 2G spectrum:

- Reconfigure the 900 MHz band for 3G service: Decide which part of 2G spectrum will be given to 3G services. Some GSM spectrum allocations are interleaved between operators; to avoid fragmentation,

reconfiguration between operators may be required. This requires co-ordination and co-operation, and management of interference between operators and

networks.

- Avoid disruption to existing 2G users and encourage migration to 3G network: Strategies to accelerate 3G handset adoption. Ways to carry 2G traffic more efficiently in the interim. Planning the most effective means of migration; methods to avoid substantial frequency/site

replanning.

- Reduce the cost of reconfiguring the spectrum: Decide whether frequency reconfiguration is necessary. What extend of site optimisation is required (e.g. repeat of drive testing, site location and geographical

analysis, new algorithms introduced, etc.)? This study should be done both for the “new” 3G sites and the remaining 2G ones.

Depending on the age/type of existing equipment across the network, what proportion needs to be upgraded or replaced?


Adjacent Frequency Guard Band Solution

Huawei refarming solution supports two types of frequency allocation: edge-type and sandwich-type allocation.

1. Edge type GSM/UMTS frequency allocation:

2. Sandwich type GSM/UMTS frequency allocation:

For frequency gap f1, minimum bandwidth is 2.4 MHz in urban and 2.2 MHz in rural.For frequency gap f2, minimum bandwidth should be 2.6 MHz, unless the adjacent frequency is idle, then 2.5 MHz can be used.

f1 and f2 are equal.For frequency gaps f1 and f2, minimum bandwidth is 2.4 MHz in urban and 2.2 MHz in rural.


GSM Frequency Bands

The main frequency bands, currently allocated to GSM system are:

According to sandwich-type allocation that was described in the previous slide, the UMTS carrier spectrums can be placed anywhere within the spectrum of the operator (not necessarily in the center of the spectrum). This can be determined based on the operator’s strategy, e.g. plans for future 2nd carrier in the 900 or 1800 MHz bands.

SystemFrequency (MHz)

ARFCNUL DL

P-GSM 890 ~ 915 935 ~ 960 1 ~ 124

E-GSM 880 ~ 915 925 ~ 960 975 ~ 1023, 0 ~ 124

DCS 1710 ~ 1785 1805 ~ 1880 512 ~ 885


Checking 2G Spectrum Efficiency (1)

One of the main factors that will decide which part of 2G spectrum will be given to 3G service, is the utilization of the 2G spectrum.

Nastar tool can be used for this purpose as it has the relative function embedded:

- In Nastar client, choose Frequency Analysis > Spectrum Utilization:

- The Spectrum Utilization dialog box is displayed:


Checking 2G Spectrum Efficiency (2)

- Set the ARFCN range.- Select the ARFCN type: BCCH or TCH.- Click OK to check the BCCH or TCH spectrum efficiency.- The ARFCN Utilization dialog box is displayed:

- Select an ARFCN in the ARFCN Utilization dialog box, and right-click the selected ARFCNto save the check result in .txt format.


Contents



Tight Frequency Reuse

After the re-farming is applied the spectrum available for GSM service will be less. In order to better utilize the remaining frequency band, Huawei system provides a number of features that help to reuse the available frequencies in a more tight scheme in order to partly compensate for the loss of available channels.

These features are:1. BCCH Dense Frequency Multiplexing2. Interference Based Channel Allocation (IBCA)3. Flex MAIO


BCCH Dense Frequency Multiplexing (1)

1. Introduction

When frequency resources are limited, relatively few frequencies at the FH layer are a capacity bottleneck. Increasing the number of frequencies at the FH layer improves the system capacity.

In general, the frequencies planned for a network include BCCH frequencies and TCH frequencies. BCCH frequencies and TCH frequencies adopt different multiplexing modes. For example, the BCCH frequencies are multiplexed in 4x3 mode, while the TCH frequencies are multiplexed in 1x3 mode. In a network with limited available frequencies, if the BCCH uses more frequencies, fewer frequencies are available for the TCHs, thus limiting the system capacity.

BCCH dense frequency multiplexing enables the BCCHs to reuse frequencies more tightly to free more frequencies for non-BCCH TRXs, thus increasing the system capacity.

2. Technical description

When BCCH dense frequency multiplexing is adopted, a cell is classified into two logical layers: TCH layer on the BCCH TRX and FH layer:- The FH layer serves and covers the entire network, including cell edges.- The TCH layer on the BCCH frequency, however, covers only the MSs near the BTS to guarantee call

access and to reduce interference near the BTS.



A denser frequency multiplexing pattern tends to increase the interference on the BCCH, therefore, proper channel allocation and handover algorithms are required to allocate the TCHs on the BCCH TRX to the MSs near the BTS. In this way, the restriction of multiplexing density on the BCCH TRX is reduced. The BCCH dense frequency multiplexing consists of:- Tight BCCH common channel assignment- Tight BCCH handover algorithm- Channel assignment for tight BCCH handover

Call moved to hopping layer if the quality

degrades too much

Limit to move to hopping layer

Limit to move to BCCH

BCCH Frequency

coverage area



3. Parameters

TIGHTBCCHSWITCH: The switch to enable the BCCH aggressive frequency reuse algorithm.

4. Impact on Other Features

The impact of BCCH dense frequency multiplexing on other features is as follows: - Concentric cells do not support dense BCCH frequency multiplexing. - Multiband networks do not support dense BCCH frequency multiplexing.

5. Impact on System Performance

The number of handovers in the network may increase.


Interference Based Channel Allocation (1)

1. Introduction

On a network where the frequency resources are insufficient, the same frequency is repeatedly used in neighboring cells. In this case, severe co-channel interference and adjacent-channel interference exist on the network, and such interference cannot be eliminated even if the frequency hopping (FH) technology is applied. When the number of calls on such a network exceeds a certain limit, the mutual interference between calls will decrease the speech quality to such a level that the C/I ratio required by a call is not guaranteed. In this case, even if there is an idle channel on this network, the idle channel cannot be assigned to a call because of the severe interference. As a result, the utilization of the frequency resources is restricted, and the network capacity is thus decreased.

To alleviate the interference on the network, the Interference Based Channel Allocation (IBCA) algorithm is introduced. The IBCA algorithm requires the BSC to estimate the C/I ratio of the new call in every

channel assignment procedure; it also requires the BSC to estimate the interference caused to the established calls on the network when an idle channel is assigned to a new call. In this way, the optimal channel, that is, the one that meets the C/I ratio requirement of the new call and causes the least interference to the established calls after being occupied, is assigned to the new call to alleviate the interference and ensure the full use of the frequency resources.




The IBCA algorithm needs to estimate the interference between calls on channels in the IBCA cell group in every channel assignment procedure. Therefore, the IBCA algorithm can be enabled only on a

synchronous network with cyclic FH enabled (HSN = 0).

The main procedures involved in the IBCA algorithm are: • Calculation of the interference probability: the interference probability between every two MAIOs for each MA table is calculated.• Collection of call information: The IBCA algorithm requires the BSC to estimate the interference caused to a new call from all the established calls in the IBCA cell group. The calls in a cell under the BSC may be processed by different central processing units (CPUs). Each CPU, therefore, needs to report the information on calls in the same IBCA cell group to the XPUa/XPUb board.• Dynamic measurement of the neighboring cells: The BSC obtains the downlink level of the IBCA neighboring cell from the measurement report sent from the MS in order to calculate the path loss between the IBCA neighboring cell and the MS. The IBCA algorithm can enable the MS to report more than 6 cells that belong to IBCA cell group.• Estimation of the C/I ratio of the new call: The BSC calculates the uplink and downlink C/I ratios of the new call.• Estimation of the interference of the new call to the established calls: To estimate the interference of

the new call to the established calls (on channels of the same timeslot), the BSC considers the new call as the interference source and calculates the C/I ratio of the established call after the new call is established.



• Selection of the optimal MAIO group: After evaluating all timeslots that have idle channels in the cell, the

BSC evaluates the C/I ratio of the new call by using the optimal MAIO and the interference of the new call to

the established calls on channels of the same timeslot. Then, the BSC selects the optimum MAIO/TS group.

• Selection of the TSC: After selecting the optimal MAIO, the BSC selects the TSC that is the least relevant to the TSCs used for the established calls on this timeslot.

3. Parameters

IBCAALLOWED: The switch to enable the IBCA algorithm.

4. Prerequisites

- To enable the IBCA algorithm, two XPUa/XPUb boards should be added to the BSC. The two boards are used to estimate the interference experienced by each idle channel in every channel assignment procedure and estimate the interference of this new call to established calls on the same timeslot in the IBCA neighboring cells.

- To enable the inter-BSC IBCA algorithm (i.e. the situation that an IBCA cell group has external neighbours), the FG2a/FG2c board should be added to the BSC. This board is used to carry the inter-BSC communication links that transfer the information related to the IBCA algorithm.


Flex MAIO (1)

1. Introduction

BSC dynamically adjusts the MAIO according to the current interference level of a channel when assigning an MAIO to the channel (note that the BSC assigns an MAIO to only a channel under activation). In this

way, the BSC assigns the MAIO with the minimum interference to the channel, and the channel experiences the minimum interference in the BTS.


Flex MAIO feature works as follows:- The BSC estimates the interference between FH channels based on the MAIOs of FH channels and

updates the record of the interference of the current channel to other channels after assigning or releasing the channel.

- During channel assignment, the BSC selects a timeslot, assigns the MAIO with the minimum interference to the timeslot, and then preferentially assigns the channel with the minimum interference. To prevent continuous adjacent-channel interference, the BSC dynamically changes the hopping sequence number (HSN) of the current channel to randomly distribute the interference of the channel to other channels.

3. Parameters

- FLEXMAIO: The switch that enables the function of Flex Mobile Allocation Index Offset.


Flex MAIO (2)

4. Limitations

- A baseband FH network does not support Flex MAIO. It only supports the function of assigning a channel with the minimum interference.

- Only CS services support Flex MAIO. PS services do not support Flex MAIO.


Enhanced Dual Band Network

After refarming it is likely to have cut a part of 900 band but still have 1800 untouched. Advanced handover algorithms are necessary in order to provide seamless mobility and, especially, traffic sharing between the two bands. Traffic on 900 band will need to be offloaded to 1800 band. Huawei system provides specific handover algorithm for load balancing between the 2 bands. It is called “Enhanced Dual Band Network Handover”.

The enhanced dualband network is an improvement on the existing dualband network. It is implemented as follows: physically, two single-band cells are located at the same layer and have the same priority but different coverage areas; logically, the two cells serve as neighboring cells of each other and form a cell group, namely, one overlaid cell and one underlaid cell. The enhanced dualband network algorithm enables channel sharing and load balancing between the two cells in the cell group.

The underlaid cell works in 900 band and the overlaid in 1800 band.

Distance

Overlaid cell A

Cell group

Underlaid cell B

Cell group

Overlaid cell A

Underlaid cell B


Enhanced Dual Band Network Handover

Enhanced dual-band network handover is performed based on the traffic volume of the overlaid and underlaid cells and based on the receive level. This handover is classified into the following types:• Handover due to high load in the underlaid cell• Handover due to low load in the underlaid cell• Handover due to MS movement to the border of the overlaid cell

Triggering Conditions of Handover Due to High Load in the Underlaid CellThe triggering conditions of the handover due to high load in the underlaid cell are as follows:- The two cells are in the enhanced dual-band network and Load HO Allowed is set to Yes.- The MS supports the frequency band on which the overlaid cell operates.- The handover due to high load in the underlaid cell is performed only on TCHs.- The load in the underlaid cell is higher than or equal to UL Subcell General Overload Threshold.- The load in the overlaid cell is lower than Inner Cell Serious OverLoad Thred.- The system traffic volume is lower than or equal to Subcell HO Allowed Flow Control Level.- The current call is within the handover margin and the receive level is greater than or equal to Incoming OL Subcell HO Level TH.When all the preceding conditions are met, the handover due to high load in the underlaid cell is triggered.

Triggering Conditions of Handover Due to Low Load in the Underlaid CellThe triggering conditions of the handover due to low load in the underlaid cell are as follows:- The load in the underlaid cell is lower than UL Subcell Lower Load Threshold.- The system traffic volume is lower than or equal to Subcell HO Allowed Flow Control Level.- The current call is within the handover margin and the receive level is greater than or equal to Outgoing OL Subcell HO Level TH.When all the preceding conditions are met, the handover due to low load in the underlaid cell is triggered.


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2g huawei refarming.ppt

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