COBCCH

7/30/2019 COBCCH

1/36

Application of the Co-BCCHFunction

R2.0

7/30/2019 COBCCH

2/36

Application of the Co-BCCH Function Internal Use Only

LEGAL INFORMATION

By accepting this certain document of ZTE CORPORATION you agree to the following

terms. If you do not agree to the following terms, please notice that you are not allowed

to use this document.

Copyright 2013 ZTE CORPORATION. Any rights not expressly granted herein are

reserved. This document contains proprietary information of ZTE CORPORATION. Any

reproduction, transfer, distribution, use or disclosure of this document or any portion of

this document, in any form by any means, without the prior written consent of ZTE

CORPORATION is prohibited.

and are registered trademarks of ZTE CORPORATION. ZTEs company

name, logo and product names referenced herein are either trademarks or registered

trademarks of ZTE CORPORATION. Other product and company names mentioned

herein may be trademarks or trade names of their respective owners. Without the prior

written consent of ZTE CORPORATION or the third party owner thereof, anyones access

to this document should not be construed as granting, by implication, estopped or

otherwise, any license or right to use any marks appearing in the document.

The design of this product complies with requirements of environmental protection and

personal security. This product shall be stored, used or discarded in accordance with

product manual, relevant contract or laws and regulations in relevant country(countries).

This document is provided as is and as available. Information contained in this

document is subject to continuous update without further notice due to improvement

and update of ZTE CORPORATIONs products and technologies.

ZTE CORPORATION

Address:

NO. 55

Hi-tech Road South

ShenZhen

P.R.China

518057Website:

http://dms.zte.com.cn (Technical Support)

Email: [email protected]

ZTE Confidential Proprietary 2013 ZTE CORPORATION. All rights reserved. I

7/30/2019 COBCCH

3/36


Revision History

Product Version Document Version Serial Number Reason for Revision

V1.0 First published

iBSC V6.20.200f R2.0

The information ofhandover/resource allocationalgorithm and CA coding hasbeen updated in the version ofiBSC V6.20.200f.

Author

Date Document Version Prepared by Reviewed by Approved by

2009-07-04 V1.0 Chen Chun Zheng Hao Zheng Hao

2010-07-13 R2.0 Hou Shuai Zheng Hao Zheng Hao

ZTE Confidential Proprietary 2013 ZTE CORPORATION. All rights reserved. II

7/30/2019 COBCCH

4/36


Applicable to: GSM after-sales staff

Proposal:Before reading this document, you had better have the followingknowledge and skills.

SEQ Knowledge and skills Reference material

1 Radio parametersZXG10 iBSC (V6.20.61) Base StationController Radio Parameter Reference

2 Performance countersZXG10 iBSC (V6.20.21) Base StationController Performance Counter Reference

3

Follow-up document: After reading this document, you may need thefollowing information.

SEQ Reference material Information

1 Null Null

2

3

ZTE Confidential Proprietary 2013 ZTE CORPORATION. All rights reserved. III

7/30/2019 COBCCH

5/36


About This Document

Summary

Chapter Description

1 Overview Overview

2 Handover and Channel AllocationAlgorithms

Handover and channel allocation algorithms

3 Requirements for the LengthLimitations of the Frequencies in theDual Band Co-BCCH Cell

Requirements for the length limitations of the frequencies inthe dual band Co-BCCH cell

4 Subcell Performance Analysis Subcell performance analysis

5 Cases on Configuration of Co-BCCH Parameters

Cases on configuration of Co-BCCH parameters

6 Indicator Performance in Large-Scale Use of Co-BCCH

Indicator performance in large-scale use of Co-BCCH

AppA Radio Parameters Relevantto Co-BCCH

Radio parameters relevant to Co-BCCH

AppB Judgment Standard Relatedto the Co-BCCH Threshold

Judgment standard related to the Co-BCCH threshold

ZTE Confidential Proprietary 2013 ZTE CORPORATION. All rights reserved. IV

7/30/2019 COBCCH

6/36


TABLE OF CONTENTS

1 Overview 11.1 Introduction to the Concept of Co-BCCH.....................................................................11.2 Application Scenarios................................................................................................... 11.2.1 Dual Band Co-BCCH Cell.....................................................................................11.2.2 Requirements for the Wide Coverage..................................................................21.2.3 How to Increase the Capacity of the System........................................................2

2 Handover and Channel Allocation Algorithms............................................................32.1 Handover Algorithms.................................................................................................... 3

2.1.1 Handover Algorithm Based on Path Loss/TA.......................................................32.1.2 Handover Algorithm Based on C/I........................................................................42.1.3 PBGT Algorithm Update.......................................................................................52.2 TCH Allocation Algorithm............................................................................................. 52.2.1 Channel Allocation of the Subcells in the Case of Assignment.............................52.2.2 Channel Allocation of the Subcells in the Case of Handover................................62.3 PDTCH Allocation Algorithm........................................................................................ 72.3.1 Subcell Channel Allocation in the Case of the Initial Allocation............................72.3.2 Subcell Channel Allocation in the Case of the TS Reallocation............................8

3 Requirements for the Length Limitations of the Frequencies in the Dual Band Co-BCCH Cell9

3.1 Overview of the Principles............................................................................................93.1.1 Versions Earlier than iBSC V6.20.200f.................................................................93.1.2 iBSC V6.20.200e and Latter Versions................................................................103.2 Case 11

4 Subcell Performance Analysis.................................................................................... 114.1 Congestion Counters.................................................................................................124.2 Traffic Counters......................................................................................................... 12

5 Cases on Configuration of Co-BCCH Parameters.....................................................135.1 Scenario 1: Most TA = 0............................................................................................. 135.2 Scenario 2: TA = 0 Accounts for About 50%..............................................................15

5.3 Scenario 3: Proportion of TA 1 Equals to Proportion of TA > 1...............................16

6 Indicator Performance in Large-Scale Use of Co-BCCH...........................................176.1 Information of the Software Version...........................................................................176.2 Information of the Hardware Environment..................................................................186.3 Configurations of Co-BCCH Parameters....................................................................186.4 Clarification of Comparison between Indicators.........................................................186.5 Relevant KPI Formulas.............................................................................................. 196.6 Comparison Results of the Indicators......................................................................... 20

ZTE Confidential Proprietary 2013 ZTE CORPORATION. All rights reserved. V

7/30/2019 COBCCH

7/36


FIGURES

Figure 1-1 Dual-Band Network with Co-BCCH Adopted................................................1

Figure 2-2 Handover Model.............................................................................................. 4

Figure 5-3 TA Distribution of a Co-BCCH Cell..............................................................13





TABLES

Table 4-1 Counters for Congestion in the Inner Circle................................................12

Table 4-2 Counters for Traffic in the Inner Circle.........................................................12

Table 6-3 Value Range of the Frequency Band............................................................22

ZTE Confidential Proprietary 2013 ZTE CORPORATION. All rights reserved. VI

7/30/2019 COBCCH

8/36


1 Overview

1.1 Introduction to the Concept of Co-BCCH

One cell can be divided into two subcells with Co-BCCH function. The two subcells

share one BCCH. Subcell 1 is configured with BCCH; subcell 2 is newly added. This is

also referred as concentric circle; Subcell 1 is also referred as the outer circle, and

Subcell 2, the inner circle. See Figure 1 -1.

Figure 1-1 Dual-Band Network with Co-BCCH Adopted

1.2 Application Scenarios

1.2.1 Dual Band Co-BCCH Cell

Dual band Co-BCCH cell refers to the situation when two TRXs of different frequency

bands are configured in the same cell. Usually, the TRX with frequency band of better

transmission performance is configured in Subcell1 as well as BCCH and SDCCH; the

other TRX is configured in Subcell2. In this situation, the handover algorithm based on

path loss/TA is often adopted. (See Handover and Channel Allocation Algorithms for

details.)

For example, it can be applied to the Co-BCCH cells (where there are both 900M TRXs

and 1800M TRXs), and BCCH and SDCCH should be configured on the 900M

frequency band. The advantage of the Co-BCCH networking is that one BCCH can be

ZTE Confidential Proprietary 2013 ZTE CORPORATION. All rights reserved. 1

7/30/2019 COBCCH

9/36


saved. More importantly, this method makes it possible that the 1800M frequency band

can absorb the traffic of the 900M frequency band without the reselections and

handovers among the dual-band cells. Besides, when the capacity expansion is done for

the network where only GSM900M is used, it is possible to configure the 1800M TRXs in

the 900M cells directly without changing the original relations of the neighbor cells.

1.2.2 Requirements for the Wide Coverage

For the site with the multi-carrier configuration, the coverage radius will be reduced if the

combiners are connected in series. In this case, the technology of concentric circle

should be used. In this way, the outer circle can make the coverage stable. In this

situation, the handover algorithm based on path loss/TA is often adopted. (See

Handover and Channel Allocation Algorithms for details.)

1.2.3 How to Increase the Capacity of the System

Configure the TRXs of a cell in subcell 1 and subcell 2 respectively. Increase the TRXs

of subcell 2 and employ a tighter frequency reuse pattern so as to improve the capacity

of the system. The inner circle and the outer circle adopt a different reuse coefficient:

The inner circle adopts a tighter frequency reuse pattern, for example, 4X3, 3X3, or a

tighter frequency reuse pattern. Usually, the frequency reuse pattern adopted by the

outer circle is 4X3, 5X3, or a less tight frequency reuse pattern.

This scenario can be further divided into the following two categories:

The general concentric circle

Usually, the inner circle reduces the transmission power of TRXs. Compared with

the outer circle, its coverage range is small and it does not absorb the indoor traffic

easily. Therefore, the inner circle mainly provides service for the outdoor

subscribers who are near the base station. In this situation, the handover algorithm

based on path loss/TA is often adopted. (See Handover and Channel Allocation

Algorithms for details.)

The intelligent concentric circle

The inner circle and the outer circle have the same transmission power of TRXs.

The outer circle makes the continuous coverage possible, and it mainly provides

service for the subscribers at the boundaries of the cells. The inner circle can not

provide the continuous coverage (in terms of C/I or carrier-to-interference ratio). It

mainly provides service for those subscribers who are near the base station or in

the buildings and for those who can not enjoy the high quality telecommunications

service due to the fact that the environment they are in is affected by the

interferences or the fast attenuation. In this situation, the handover algorithm based

on C/I is recommended (See Handover and Channel Allocation Algorithms for

details.).


7/30/2019 COBCCH

10/36


2 Handover and Channel Allocation

Algorithms

2.1 Handover Algorithms

2.1.1 Handover Algorithm Based on Path Loss/TA

2.1.1.1 Calculation Method of PathLoss

Here is the formula of PahtLoss:

PahtLoss = BSTXPWR - Rxlev_dl

Here,

BSTXPWR is the actual transmission power of BTS;

Rxlev_dl is the current downlink Rxlev.

Here is the formula of BSTXPWR:

BSTXPWR = PowerClass - 2*PwrReduction - 2*BSPower

Here,

PowerClass indicates the maximum transmission power of TRX;

PwrReduction indicates the static power level.

BSPower indicates the dynamic power adjustment grade of TRX.

2.1.1.2 Introduction to the Algorithm

If MS is in subcell 1 and every SubCellP out of SubCellN satisfies both the

conditions of (PATHLOSS = PathLossMax) or the condition (TA > SubCellTAMax), it

is believed that a handover should be made from subcell 2 to subcell 1.

If SubCellTAMax = SubCellTAMin = TAMAX (the maximum TA), the prerequisite

for the handover mentioned above changes and the path loss becomes the only

criterion to be used. Similarly, if PathLossMax = PathLossMin = LMAX (the

maximum path loss), the prerequisite for the handover mentioned above also


7/30/2019 COBCCH

11/36


changes and TA becomes the only criterion to be used.

For example, here is a handover model of PahtLoss, as shown in Figure 2 -2.

Figure 2-2 Handover Model

The area which connects PathLossMax and PathLossMin is a protection area. Its

function is to avoid the oscillation which goes back and forth.

2.1.2 Handover Algorithm Based on C/I

2.1.2.1 Calculation Method of C/I

1. Define the interference cells in the neighbor cell relations:

Interference cells are a kind of neighbor cells, which are mainly used to calculate

C/I when there are handovers between the subcells. There is not a crystal clear

definition of this kind of cells. When the neighbor cells are configured, those

neighbor cells which may interfere with the current cells can be configured as the

interference cells. This configuration can be done according to the actual situation.

2. If the received measurement reports show that the current cells have some

interference cells, the Rxlev of the interference cells can be transformed into the

power (unit: W). Then, the power of several interference cells can be summed up.

Besides, the minimum Rxlev of the neighbor cells should be recorded.

3. If the summed magnitude of power of the interference cells is larger than zero, it

can be transformed into Rxlev.

4. If the summed magnitude of power of the interference cells is zero, it is believed

that the interference level of this time is zero.


7/30/2019 COBCCH

12/36


5. If no interference cells are defined among the neighbor cells and the reported

number of neighbor cells is smaller than the number of neighbor cells configured in

the database (Here is a typical situation: The number of neighbor cells which are

configured is larger than six while the reported number of neighbor cells is smaller

than six.), it is believed that the interference level of this time is zero. Otherwise, the

interference level is the minimum Rxlev of the neighbor cells, which is shown by the

measurement reports.

6. Finally, the C/I of this time is calculated according to the Rxlev_dl of the serving

cell.

2.1.2.2 Introdution to the Algorithm

For the C/I-based handover, it is necessary to judge whether the subscriber resides in

subcell 1 or subcell 2. If MS is in subcell 1, a handover towards subcell 2 can be made if

C/I is good enough. On the other hand, if MS is in subcell 2, a judgment should be made

to see whether the current C/I is really bad. If so, a handover towards subcell 1 can be

made. Here are the details:

If MS is in subcell 1 and every GoodCiP out of GoodCiN satisfies the condition of

(C/I> GoodCiThs), it is believed that a handover should be made from the outer

circle to the inner circle.

If MS is in subcell 2 and every BadCiP out of BadCiN satisfies the condition of (C/I

< BadCiThs), it is believed that a handover should be made from the inner circle to

the outer circle.

2.1.3 PBGT Algorithm Update

The parameter DuleBandOffset indicates the value to compensate power in second cell

in the dual band Co-BCCH cell. If there are subcells, the two subcells can adopt two

different PBGT handover criteria so as to control the PBGT handover better. If the

current service is in subcell 2, DuleBandOffset should be subtracted from the calculation

results of PBGT margin of the neighbor cells.

2.2 TCH Allocation Algorithm

2.2.1 Channel Allocation of the Subcells in the Case of Assignment

If it is confirmed that the cause for the application for resources is assignment, the

channel allocation of the subcells is completed in the following way:

If the handover algorithm of the subcells is based on path loss, the measurement

results of path loss on SDCCH should be considered: If the intra-cell handover

threshold is satisfied and the handset supports the frequency band of subcell 2, the


7/30/2019 COBCCH

13/36


channels of subcell 2 will be chosen first. If the threshold is not satisfied or the

handset does not support the frequency band of subcell 2, only the channels of

subcell 1 can be chosen.

If the handover algorithm of the subcells is based on C/I, the measurement resultsof path loss on SDCCH should be considered: If C/I satisfies the intra-cell handover

threshold and the handset supports the frequency band of subcell 2, the channels

of subcell 2 will be chosen first. If the threshold is not satisfied or the handset does

not support the frequency band of subcell 2, only the channels of subcell 1 can be

chosen.

2.2.2 Channel Allocation of the Subcells in the Case of Handover

If it is confirmed that the cause for the application for resources is handover (including

the directional retry), the channel allocation algorithm of the subcells is completed in thefollowing way:

For the intra-cell handover,

If the cause for the handover is C/I or path loss, the handover is between the

subcells within the cell. If the channel request message indicates that the

original cell is subcell 1, only the channels of subcell 2 can be chosen. If the

channel request message indicates that the original cell is subcell 2, only the

channels of subcell 1 can be chosen.

If the handover decision criteria for subcell 1 and subcell 2 are met but no

channels are available in the target subcell, it takes at least a period ofHoFailPenaltyTime before the handover attempt starts.

If the cause for the handover is the uplink/downlink interference, the handover

is between the subcells. If the channel request message indicates that the

original cell is subcell 1, only the channels of subcell 1 can be chosen. If the

channel request message indicates that the original cell is subcell 2, only the

channels of subcell 2 can be chosen.

For the inter-cell handover or the directional retry (versions earlier than iBSC

V6.20.200f),

The BTS parameter named inHoEnable does not exist.

If the original cell and the target cell are co-sited (with the same SITEID) and

the original cell is in subcell 1, the only choice is to make a handover to the

channels of subcell 1 of the target cell.

Suppose the original cell and the target cell are co-sited (with the same

SITEID), the original cell is in subcell 2, and the handset supports the

frequency band of subcell 2 of the target cell. Then, the first choice is to

make a handover to the channels of subcell 2 of the target cell.

If the original cell and the target cell are not co-sited (with different SITEIDs),

the handover can only be made to the channels of subcell 1 of the target cell


7/30/2019 COBCCH

14/36


no matter MS is in subcell 1 or subcell 2 of the original cell.

For the inter-cell handover or the directional retry (iBSC V6.20.200f and the later

versions),

If the original cell and the target cell are co-sited (with the same SITEID) and

the original cell is in subcell 1, the only choice is to make a handover to the

channels of subcell 1 of the target cell.


SITEID), the value of inHoEnable of the site is one, the original cell is in

subcell 2, and the handset supports the frequency band of subcell 2 of the

target cell. Then, the first choice is to make a handover to the channels of

subcell 2 of the target cell.


SITEID), the value of inHoEnable of the site is zero, and the original cell is insubcell 2. Then, the only choice is to make a handover to the channels of

subcell 1 of the target cell.

If the original cell and the target cell are not co-sited (with different SITEIDs),

the handover can only be made to the channels of subcell 1 of the target cell

no matter the original cell is in subcell 1 or subcell 2.

2.3 PDTCH Allocation Algorithm

2.3.1 Subcell Channel Allocation in the Case of the Initial Allocation

If it is the initial allocation, only the PDTCH of subcell 1 can be allocated to the

subscriber. From this perspective, the following aspects should be paid special attention

to when PDTCH is configured for the Co-BCCH cell.

Subcell 1 must be configured with PDTCH.

If the TS reallocation algorithm based on Rxlev and TA is not used (In other words,

the configuration of the parameter PSALLOCSC_0 is that only subcell 1 is

allowed.), subcell 2 should not be configured with PDTCH. Otherwise, there may be

a waste of resources.

Suppose the TS reallocation algorithm based on Rxlev and TA is used (In other

words, the configuration of the parameter PSALLOCSC_0 is not that only subcell 1

is allowed.). When the cell is initially configured as the Co-BCCH cell, it is

suggested that PDTCH should be mainly configured in subcell 1. Then, some minor

adjustments can be made later according to the TA distribution and the Rxlev

distribution.


7/30/2019 COBCCH

15/36


2.3.2 Subcell Channel Allocation in the Case of the TS Reallocation

The TS reallocation algorithm based on Rxlev and TA is enabled from the version iBSC

V6.20.200fp002. Here are the newly added parameters:

PSALLOCSC_0

PSALLOCSC_1

PSALLOCSC_2

Here are the borrowed radio parameter fields:

Wnd

PbcchBlks

PagBlkRes

PrachBlks

Here are some scenarios where the TS reallocation algorithm based on Rxlev and

TA is used or not used:

If the configuration of PSALLOCSC_0 is that only subcell 1 is allowed, only

PDTCH of subcell 1 can be allocated to the PS subscribers during the TS

reallocation.

If the configuration of PSALLOCSC_0 is that subcell 1 or subcell 2 enjoys thepriority, it means that the TS reallocation algorithm based on Rxlev and TA is

enabled. If neither the Rxlev-based judgment standards not the TA-based

judgment standards are met, whether TS is reallocated to subcell 1 or

subcell 2 depends on the value of PSALLOCSC_0.

If subcell 1 is configured with enough PDTCHs, the TS reallocation algorithm

based on Rxlev and TA is not recommended.

The TS reallocation algorithm based on Rxlev:

The original sample of Rxlev is obtained from C_Value of Packet Downlink

Ack/Nack.

The size of the window related to the judgment is defined on basis of Wnd.

The value of N related to the judgment (The value of P does not exist.) is

defined on basis of PbcchBlks. In order to ensure that PbcchBlks is valid, the

parameter Psi1RepPer must be configured as any value which is at least ten

(This is a constraint condition of the system, and it does not have any actual

meanings.).

Currently, the PDTCH occupied by the subscriber is in subcell 2, and the

value of Rxlev, which is calculated on basis of the window and the value of

N, is no larger than PSALLOCSC_1. Therefore, from the perspective of


7/30/2019 COBCCH

16/36


Rxlev-based TS reallocation algorithm, the requirements for the TS

reallocation to subcell 1 are satisfied.

Currently, the PDTCH occupied by the subscriber is in subcell 1, and the

value of Rxlev, which is calculated on basis of the window and the value ofN, is equal to or larger than PSALLOCSC_2. Therefore, from the perspective

of Rxlev-based TS reallocation algorithm, the requirements for the TS

reallocation to subcell 2 are satisfied.

The TS reallocation algorithm based on TA:

For TS reallocation algorithm based on Rxlev and TA, the judgment based on

Rxlev is made first. If the judgment based on Rxlev is approved, TA update

will be started via the polling. After the TA update, if it is found that TA also

satisfies the requirements, the TS reallocation will be carried out for the

subcells. If no Packet Control Ack responds to the polling after the Rxlev-

based judgment is approved, the TA which is updated most recently will be

borrowed to be involved in the judgment.

Whether the TA threshold of PS-based TS reallocation to subcell 1 is satisfied

or not is defined on basis of the borrowed PagBlkRes, and the sign of the

judgment is .

Whether the TA threshold of PS-based TS reallocation to subcell 2 is satisfied

or not is defined on basis of the borrowed PrachBlks, and the sign of the

judgment is .

3 Requirements for the Length

Limitations of the Frequencies in the

Dual Band Co-BCCH Cell

3.1 Overview of the Principles

3.1.1 Versions Earlier than iBSC V6.20.200f

The frequencies configured at OMCR are not distinguished according to their subcell. All

of them are put in the CA of the BTS table. Since the system message 1 clarifies the

limitations of the quantity of frequencies, there are some constraint conditions for the

configuration of frequencies of the Co-BCCH cell (subcell 1 + subcell 2):

For system with PGSM900 only:

CA list may at most contain 124 frequencies; and at most 64 frequencies for

each cell.


7/30/2019 COBCCH

17/36


For system with mixed frequency bands and system with EGSM or DCS1800 only:

If the difference between the maximum frequency ARFCN and the minimum

frequency ARFCN is smaller than 112, then the CA list may at most contain

112 frequencies, and each cell may at most contain 64 frequencies.

If the difference is smaller than 128, then the CA list my at most contain 29

frequencies.

If the difference is smaller than 256, then the CA list may at most contain 22

frequencies.


frequencies.

If the difference is NOT smaller than 512, and frequency 0 is included, then

the CA list may at most contain 17 frequencies; if frequency 0 is not

included, then the CA list may at most contain 16 frequencies.

3.1.2 iBSC V6.20.200e and Latter Versions

Changes to the versions:

System message 1 only broadcasts the frequency of Subcell1;

For CS service, CA in system message 1 cannot be used in the channel

assignment of Subcell2; while the frequency list carried by the assignment

message and handover message can be used.

For PS service, CA (Direct Cipher Mode1) in system message 1 and indirect cipher

mode (obtaining frequency list from system message 13) cannot be used in the

channel assignment of Subcell2; while Direct Cipher Mode 2(using the frequency

list carried by assignment and TS reallocation messages) can be used.

Based on the changes to the iBSC versions, the constraint conditions for Subcell1 and

Subcell2 are as follows:

For system with PGSM900 only:

CA list may at most contain 124 frequencies; and at most 64 frequencies for

each cell.

For system with mixed frequency bands and system with EGSM or DCS1800 only:

If the difference between the maximum frequency ARFCN and the minimum

frequency ARFCN is smaller than 112, then the CA list may at most contain

112 frequencies, and each cell may at most contain 64 frequencies.

If the difference is smaller than 128, then the CA list my at most contain 29

frequencies.


frequencies.


7/30/2019 COBCCH

18/36



frequencies.

If the difference is NOT smaller than 512, and frequency 0 is included, then

the CA list may at most contain 17 frequencies; if frequency 0 is not

included, then the CA list may at most contain 16 frequencies.

3.2 Case

Phenomenon Description

An overseas network adopts 900/1800M dual band Co-BCCH cell; BCCH is

configured on 900M; both the inner circle and the outer circle adopt FH. Large

number of block calls are detected in DT with cause value (47) Resources

unavailable, unspecified.

Cause Analysis

BSC V 6.10 series are used on site. Both 900M and 1800M adopt FH1X1; the

frequency sequence for 900M is 79-86 (8 frequencies); and that for 1800M is 586-

629 (44 frequencies). The difference between the max frequency ARFCN and the

minimum frequency ARFCN is larger than 512 with frequency 0 excluded,

therefore, the total length of FH sequence (No. of frequencies) of the dual-band

subcell shall be no larger than 16. The current frequency length in planning well

exceeds the FH sequence length specified in system, which leads to assignment

failure and block calls.

Solution

After the inspection and analysis, we should make adjustment to FH configuration

and FH sequence length. The adjustment principles are as follows:

900M maintains FH1X1, frequency number in FH sequence is 8;

1800M FH mode is changed to 1X6, frequency number in FH sequence is 8 7.

After the frequencies are adjusted according to the above principles, the problem is

solved.

4 Subcell Performance Analysis

Counters related to subcells are under Subcell Statistical Measurement. When

subcells are configured, the measurement task measures the channels in subcells

and handovers between the subcells, and focuses on the traffic sharing in Subcell2

(inner circle). For detailed introduction to the counters, please refer to the

corresponding users manual. This chapter mainly introduces the counters related

to traffic analysis. For Co-BCCH, what we shall concern about is whether the traffic


7/30/2019 COBCCH

19/36


sharing between the two subcells is reasonable.

Currently our system cannot directly output the situation of congestion and traffic in

the two cells. We may temporarily solve the problem by setting up Subcell

Statistical Measurement. From the measurement data, we may obtain the statistics

of congestion and traffic in the inner circle; from performance reports, we obtain the

statistics of congestion and traffic in the cell. We may obtain data about the outer

circle by making subtraction between the two sets of statistics.

4.1 Congestion Counters

The statistics for congestion in the inner circle may be obtained from the following

counters in Table 4 -1.

Table 4-1 Counters for Congestion in the Inner Circle

Counter No.Counter Name

V2 V3

C12033 C901130047No. of TCH/F seizure failures in Subcell2(assignment)

C12036 C901130050No. of TCH/F seizure failures in Subcell2(handover)

C12039 C901130053No. of TCH/H seizure failures in Subcell2(assignment)

C12042 C901130056No. of TCH/H seizure failures in Subcell2(handover)

4.2 Traffic Counters

The statistics for traffic in the inner circle may be obtained from the following counters in

Table 4 -2.

Table 4-2 Counters for Traffic in the Inner CircleCounter No.

Counter NameV2 V3

C12045 C901130059 Total TCH/F busy time in Subcell2

C12046 C901130060 Total TCH/H busy time in Subcell2


7/30/2019 COBCCH

20/36


5 Cases on Configuration of Co-BCCH

Parameters

TRX power in Subcell2 drops by 4 dB. Analysis (with RMA) of TA distribution statistics in

Abis interface signaling suggests that Co-BCCH cell falls into two scenarios:

If user TA is equally distributed within the cells service range, we may balance the

traffic in the inner circle through setting TA. With the assistance of handover

algorithm based on path loss, handover to the inner circle can be performed when

the signal is good, and handover to the outer circle can be performed in time when

the signal quality deteriorates.

When users are centered around the site (most TA=0), setting of TA is not useful in

balancing the traffic. In such case, we need to use path loss and limit the innercircles service range with the handover algorithms based on path loss, in order to

reach traffic balance.

5.1 Scenario 1: Most TA = 0

Case 1

Figure 5-3 TA Distribution of a Co-BCCH Cell

The SubCellTAmin/SubCellTAmax of the cell is changed from 3/5 to 1/3, and here is a

comparison of traffic before and after the adjustment.


7/30/2019 COBCCH

21/36


Inner CircleTraffic (Erl)

Outer CircleTraffic (Erl)

Percentage of InnerCircle Traffic

BeforeAdjustment

10.44 5.98 63.58%

After Adjustment 11.17 6.56 63.00%

It can be seen that the traffic migration is not obvious when the

SubCellTAmin/SubCellTAmax is adjusted at that moment. However, since the traffic

distribution of the cell is reasonable, no further adjustment is made on basis of Path

Loss-based handover algorithm.

Case 2


The SubCellTAmin/SubCellTAmax of the cell is changed from 3/5 to 1/3, and here is a

comparison of the traffic before and after the adjustment.

Inner Circle

Traffic (Erl)

Outer Circle

Traffic (Erl)

Percentage of Inner

Circle Traffic

Before Adjustment 1.96 0.35 84.85%


It can be seen that the traffic migration is not obvious when the

SubCellTAmin/SubCellTAmax is adjusted at that moment. Then, the

PathLossMax/PathLossMin is adjusted, and the effect is evident. Here is a comparison

of the data before and after the adjustment:

PLmin/ PLmaxInner CircleTraffic (Erl)



121/131 8.97 1.65 84.46%


7/30/2019 COBCCH

22/36


PLmin/ PLmaxInner CircleTraffic (Erl)



116/126 4.29 1.24 77.58%113/123 2.94 2.14 57.87%

5.2 Scenario 2: TA = 0 Accounts for About 50%

Case 3


Original configuration: SubCellTAmin = 3, SubCellTAmax = 4

Modified configuration: SubCellTAmin = 1, SubCellTAmax = 3

A comparison of traffic migration before and after the modification:




BeforeAdjustment

49.48 20.74 70.46%


Case 4


7/30/2019 COBCCH

23/36




Modified configuration: SubCellTamin = 1, SubCellTAmax = 3

A comparison of traffic migration before and after the modification:




BeforeAdjustment

15.81 28.3 35.84%


5.3 Scenario 3: Proportion of TA 1 Equals to

Proportion of TA > 1

Case 5


7/30/2019 COBCCH

24/36




Modified configuration: SubCellTAmin = 2, SubCellTAmax = 4

A comparison of traffic migration before and after the adjustment:




BeforeAdjustment

8.1 5.04 61.64%


6 Indicator Performance in Large-Scale

Use of Co-BCCH

6.1 Information of the Software VersionSoftware Environment Explanation

iOMCR iOMCR V6.20.200e

OMCB OMCB V4.00.200k p003

iBSC iBSC V6.20.200e p002

MINOS V4.10.430d p002

SDR SDR V4.00.210e p07


7/30/2019 COBCCH

25/36

7/30/2019 COBCCH

26/36


after the replacement is finished.

In this network, only 6% of the cells are Co-BCCH cells. In order to avoid the

influence from the worst cells as much as possible, eight cells of non Co-BCCH

part, which are the worst, are filtered, and two cells of Co-BCCH part are filteredbefore the indicators are compared.

The congestion rate indicators are involved in the traffic distribution, so it is not

necessary to make a reference to those indicators.

The replacement of the network is just finished, and the centralized KPI

optimization has not been done yet, so the results of the comparison is only for

your reference and they cannot be taken as a guidance on KPI Q & A.

6.5 Relevant KPI Formulas

KPI Formulas

UL Quality 67 Share

(C900060072+C900060073)/(C900060066+C900060067+C900060068+C900060069+C900060070+C900060071+C900060072+C900060073)

DL Quality 67 Share

(C900060080+C900060081)/(C900060074+C900060075+C900060076+C900060077+C900060078+C900060079+C900060080+C900060081)

UL Quality 01 Share

(C900060066+C900060067)/(C900060066+C900060067+C900060068+C900060069+C900060070+C900060071+C900060072+C900060073)

DL Quality 01 Share

(C900060074+C900060075)/(C900060074+C900060075+C900060076+C900060077+C900060078+C900060079+C900060080+C900060081)

SDCCH assignment SuccessRate

C900060242/C900060241

TCH Assignment SuccessRate

1-(C900060029+C900060037+C900060200+C900060211)/(C900060019+C900060030+C900060042+C900060046+C900060021+C900060032+C900060048+C900060044)

TCH Congestion Rate(Excluding Handover)

(C900060020+C900060031+C900060043+C900060047)/(C900060019+C900060030+C900060042+C900060046)


7/30/2019 COBCCH

27/36


KPI Formulas

Handover Success Rate

(C900060098+C900060102+C900060120+C900060094+C900060096)/(C900060097+C900060213+C900060214+C900060215+C900060099+C900060100+C900060101+C900060216+C900060119+C900060093+C900060095)

Inter-cell Handover SuccessRate

(C900060098+C900060102+C900060094+C900060096)/(C900060097+C900060213+C900060214+C900060215+C900060099+C900060100+C900060101+C900060216

+C900060093+C900060095)SDCCH Drop Rate C900060053/C900060004

TCH Call Drop Rate (ExcludingHandover)

(C900060054+C900060055)/(C900060028+C900060036+C900060199+C900060210)

DL TBF EstablishmentSuccess Rate

(C900040007+C900040015+C900040008+C900040016)/(C900040141+C900040142+C900040143+C900040144+C900040145+C900040146+C900040147+C900040148)

UL TBF EstablishmentSuccess Rate

(C900040025+C900040033+C900040026+C900040

034)/(C900040159+C900040160+C900040161+C900040168+C900040163+C900040164+C900040165+C900040166)

6.6 Comparison Results of the Indicators

KPI Co-BCCH non Co-BCCH

UL Quality 6 7 Share 0.42% 0.49%

DL Quality 6 7 Share 0.94% 1.02%

UL Quality 0 1 Share 98.46% 98.00%

DL Quality 0 1 Share 95.91% 95.53%

SDCCH assignment Success Rate 99.24% 97.60%

TCH Assignment Success Rate 99.80% 99.81%

TCH Congestion Rate (Excluding Handover) 0.00% 0.02%

Handover Success Rate 98.44% 96.91%

Inter-cell Handover Success Rate 97.86% 96.90%

SDCCH Drop Rate 0.01% 0.07%

TCH Call Drop Rate (Excluding Handover) 0.38% 0.59%

DL TBF Establishment Success Rate 96.06% 91.79%


7/30/2019 COBCCH

28/36


KPI Co-BCCH non Co-BCCH

UL TBF Establishment Success Rate 99.43% 96.43%

The comparison of the indicators shows that the average values of all the indicators ofthe cells where Co-BCCH is enabled are as satisfying as or more satisfying than those

of the cells where Co-BCCH is not enabled. However, it should be noticed that all the

Co-BCCH sites are those in the dense urban areas of the capital and they have a good

coverage. However, some of the non Co-BCCH sites are isolated sites or suburban

sites. Besides, the altitudes of different areas in the suburb vary greatly and the

continuity of the coverage is not good there. Therefore, it can not be concluded that the

performance indicators can be improved when the Co-BCCH function is enabled.

However, the indicators here show that at least they will not deteriorate when Co-BCCH

function is enabled. So Co-BCCH can be enabled for the commercial networks without

any risks.


7/30/2019 COBCCH

29/36


AppA Radio Parameters Relevant to Co-BCCH SubcellUsed It indicates whether the cell uses the subcell structure.

Description: It indicates whether the cell uses the subcell structure.

Value range: 0: No 1: Yes

FreqBand The frequency band of subcell 1

Description: The frequency band of subcell 1 refers to the frequency band where all

the frequencies used by subcell 1 are.

Value range: See Table 6 -3.

Table 6-3 Value Range of the Frequency Band

Value Range Explanation

0 P-GSM (ARFCN = 1 124)

1 E-GSM (ARFCN = 0 124, 975 1023)

2 DCS1800 (ARFCN = 512 885)

3 R-GSM (ARFCN = 0 124, 955 1023)

4 GSM1900 (ARFCN = 512 810)

7 GSM850 (ARFCN = 128251)

SubFreqBand The frequency band of subcell 2

Description: The frequency band of subcell 2

Value range: See Table 6 -3 .

DuleBandOffset Power compensation between frequencies

Description: It indicates the value to compensate power in second cell in the dual

band Co-BCCH cell. If there are subcells, the two subcells can adopt two different

PBGT handover criteria so as to control the PBGT handover better. If the currentservice is in subcell 2, DuleBandOffset should be subtracted from the calculation

results of PBGT margin of the neighbor cells.

Value range: 050 dB

Default value: 0

HoControl18 Subcell handover algorithm

Description: This parameter defines two handover modes of subcell handover

algorithm: Handover based on C/I, handover based on path loss and TA.


7/30/2019 COBCCH

30/36


Value range: 0: Handover based on C/I; 1: Handover based on path loss and TA

Default value: 0

Note: HoControl8 (The concentric handover is supported.) is used to

control whether the function of intelligent concentric circle is enabled (an

old concept). This parameter is invalid.

PathLossMax The MAX of path loss

Description: It is one of the subcell handover parameters, and it indicates the

maximum path loss.

Value range: 0150 dB

Default value: 126

Note: The judgment standard is .

PathLossMin The MIN of path loss


minimum path loss.

Value range: 0150 dB

Default value: 120


SubCellTAMax The MAX of time advance


maximum time advance.

Value range: 063

Default value: 1

Note: The judgment standard is >.

SubCellTAMin The MIN of time advance


minimum time advance.

Value range: 063

Default value: 0


7/30/2019 COBCCH

31/36



GoodCiN Value N (GoodCiN) of the special layer TRX frequency

Description: Please refer to GoodCiThs.

Value range: 131

Default value: 3

GoodCiP Value P (GoodCip) of the special layer TRX frequency

Description: Please refer to GoodCiThs.

Value range: 131


7/30/2019 COBCCH

32/36


Default value: 2

BadCiN Bad C/I threshold of the special layer TRX frequency when there is an

outgoing handover

Description: If the paging is on the special layer TRX frequency and P of the latest

N C/I values fall below the bad C/I threshold, then perform a handover from the

special layer TRX frequency to the common layer TRX frequency. The cause for

the handover is Bad C/I.

Value range: 0255

Default value: 130

Note: The judgment standard is

7/30/2019 COBCCH

33/36


Note: This parameter is a BTS parameter, and it becomes valid from the version

iBSC V6.20.200f.

PSALLOCSC_0 PS channel allocation subcell choice

Description: When the configuration of subcells is completed, the channel

reallocation strategy of the PS service of the subcells can be controlled via this

parameter. There are three options: Priority subcell 1, priority subcell 2, only subcell

1

Value range: 0: Priority subcell 1; 1: Priority subcell 2; 2: Only subcell 1

Default value: Priority subcell 1

Note: This parameter becomes valid from the version iBSC V6.20.200f

p002.

PSALLOCSC_1 The level threshold of subcell 1 allocated by PS channel

Description: When the configuration of subcells is completed, this parameter can

control the level threshold for choosing subcell 1 when the channel reallocation of

PS service starts. If the PS channel is at subcell 2 and the level is smaller than or

equal to PSALLOCSC_1 and TA value is larger than or equal to PagBlkRes (This

field is borrowed by the version of iBSC V6.20.200f.), it is necessary to transfer to

subcell 1.

Value range: 0 63

0: < -110 dBm;

1: -110 dBm -109 dBm;

2: -109 dBm -108 dBm;

...

62: -49 dBm -48 dBm;

63: > -48 dBm

Default value: 0


p002.

PSALLOCSC_2 The level threshold of subcell 2 allocated by PS channel

Description: When the configuration of subcells is completed, this parameter can

control the level threshold for choosing subcell 2 when the channel reallocation of

PS service starts. If the PS channel is at subcell 1 and the level is larger than or

equal to PSALLOCSC_2 and TA value is smaller than or equal to PagBlkRes (This

field is borrowed by the version of iBSC V6.20.200f.), it is necessary to transfer to


7/30/2019 COBCCH

34/36


subcell 2.

Value range: 0 63

0: < -110 dBm;

1: -110 dBm -109 dBm;

2: -109 dBm -108 dBm;

...

62: -49 dBm -48 dBm;

63: > -48 dBm

Default value: 63


p002.

Wnd The size of the sliding window where the measurement reports are kept

Description: When the subcells are configured, this field can be used to decide

whether C_value calculated on basis of PSALLOCSC_1 and PSALLOCSC_2

satisfies the requirements of the window size when the level threshold of the TS

reallocation is reached.

Value range: 18

Default value: 4

Note: The version iBSC V6.20.200f p002 borrows this field first.

PbcchBlks PBCCH reserved blocks

Description: When the subcells are configured, this field can be used to decide

whether C_value calculated on basis of PSALLOCSC_1 and PSALLOCSC_2

reaches the value of N when the level threshold of the TS reallocation is reached.

Value range: 03 (corresponding to the value of N = 4, 1, 2, 3 respectively)

Default value: 3


PagBlkRes PAGCH reserved blocks

Description: When the subcells are configured, this field is used to check whether

the TA threshold of the PS-based TS reallocation is reached so as to enter subcell

1. The judgment standard is .

Value range: 010


7/30/2019 COBCCH

35/36


Default value: 5


PrachBlks PRACH reserved blocks

Description: When the subcells are configured, this field is used to check whether

the TA threshold of the PS-based TS reallocation is reached so as to enter subcell

2. The judgment standard is .

Value range: 015

Default value: 2



7/30/2019 COBCCH

36/36


AppB Judgment Standard Related to the Co-

BCCH ThresholdParameter Code Range & Unit Default

JudgmentStandard

GoodCiThs0255; 0:-127 dB, 1:-126 dB,...,255:128 dB

133 >

BadCiThs0255; 0:-127 dB, 1:-126 dB,...,255:128 dB

130 =

PathLossMin 0150, dB 120

SubCellTAMin 063 0 -48 dBm

0 -48 dBm

63 >=

l PagBlkRes 010 5 >=

l PrachBlks 015 2

COBCCH

Documents

Transcript of COBCCH