GSM P&O TCH Call Drop & Solutions-Special Subject Guidebook

Internal Use Only ▲

GSM P&O TCH Call Drop & Solutions

Special Subject Guidebook

Version: V2.0

Released by:

GSM Network Planning & Optimiation !ept. "ngineering Ser#i$e !i#ision %" 'orporation

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements.


GSM Network Planning & Optimiation Dept! Special Subject Guidebook

"ersion introduction# Version

Date

Writer

Assessor

V.!

"!!#$"$

%a &unhua

%a &unhua

V".!

"!!'$($"

)u *ixiao

%a &unhua

Amendment records

Document format standardi+ation



$e% words TC) call drop

call drop due to ,- loss

、

call drop due to handoer failure

、

call drop

、

due to /A0D lin1 failure

bstract# This guideboo1 mainly describes types and causes of TC) call drop and the handling procedures.

bbr!#

'e(erences#


Contents 1

Statistical points & types of TCH call drop.......................................................................................1

.

Call drop due to ,- loss....................................................................................................................

."

Call drop due to handoer failure......................................................................................................"

.(

Call drop due to /A0D lin1 failure...................................................................................................2

2

Causes for different types of call drop...............................................................................................5

".

%ain causes for call drop due to ,- loss3.........................................................................................#

"."

%ain causes for call drop due to handoer failure............................................................................4

".(

%ain causes for call drop due to /A0D lin1 failure.........................................................................5

3

Flow of prole! "andlin#...................................................................................................................$

%

Typical cases......................................................................................................................................1'

2.

)igh call drop rate at Cell 6 ( of 7T8 A 9of a region:...................................................................!

2."

)igh call drop rate at Cell 7$( of a region......................................................................................

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. ;

Fi#ure contents -ig $ Call drop due to ,- loss........................................................................................................ ....... -ig $" T(!( expires（inter$cell handoer failure ）............................................................................( -ig $( T(!5 expires（intra$cell handoer failure ）............................................................................( -ig $2 T< expires（inter$78C handoer failure ）.................................................................................2 -ig ($ -low of handling call drops.........................................................................................................'

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. ;;


) Statistical points & t%pes o( TCH call drop ;n mobile communications6 call drop refers to the phenomenon that calls are lost or interrupted due to some reasons after TC) assignment. Call drop brings a lot inconenience to subscribers6 which is also the problem that subscribers complain about most. 8tatistical point of TC) call drop3 78C sends C/EA,=,E> message to %8C6 the channel currently occupied by %8 is TC). Call drop falls into the following t ypes3 

Call drop due to ,- loss 9i.e. radio lin1 fault:?

"

Call drop due to handoer failure?

(

Call drop due to /A0D lin1 failure.

)!) Call drop due to '* loss

-ig $ Call drop due to ,- loss

Call drop due to ,- loss consists of two parts3 A. D/ failure3 according to @8% regulations6 there is a timer 8 9T!!:6 which is gien an initial alue when the %8 starts tal1ing6 that is （ radio=lin1=time out ） . The alue is broadcasted on 7CC). Each time when %8 cant decode an 8ACC) message 92 This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 

Internal Use Only ▲ 8ACC) 7/BC:6 8 is deducted by . Each time when %8 decodes an 8ACC) message6 8 is increased by ". 7ut 8 wont exceed the initial alue defined by radio lin1=time out. When 8 is !6 %8 will Fuit connecting to networ1 and enter idle mode. )ence call drop happens once. 7. G/ failure3 the parameter for inspecting G/ failure is lin1 fail. When 7T8 cant decode an 8ACC) message6 a counter in )D0C 9whose max alue is defined by lin1 fail: is deducted by ? when 7T8 decodes an 8ACC) message correctly6 the counter increments by " 9the alue shall not exceed what defined by lin1 fail:. When the counter shows !6 7T8 stops sending D/ 8ACC) and starts timer rr=t(!' 9rr=t(!'HT!!:at the same time. When %8 T!! expires6 %8 returns to idle mode6 hence call drop occurs. 7T8 releases radio channel when timer rr=t(!'HT!! expires. 78C needs to send a message Clear$reFuest to %8C. Either of G/ and D/ fails6 7T8 and %8 will stop sending 8ACC) to each other6 thus force the counterpart to release TC). Each time lin1=failhappens on TC)6 ,-=/B88E8=TC) increments.

)!+ Call drop due to ,ando-er (ailure 0rinciple of call drop due to handoer failure3 After the original cell receied )andoer Command or Assignment 9corresponding handoer control timer is started by 78C:6 %8 hasnt accessed into the target cell6 nor has it returned to the original cell. i.e. %8 not only failed to occupy TC) in target cell and send )andoer Complete or Assignment Complete6 but also failed to return to TC) in original cell and send )andoer -ailure or Assignment -ailure6 thus it is disconnected with networ1. At the same time6 the 78C$controlled handoer control timer expires6 and %8C will be notified to clear the release6 and it will count this abnormal call as call drop due to handoer failure. )andoer control timer in 78C is classified into3 T< expires 9inter$78C handoer:6 T(!( expires 9inter$cell handoer under one 78C:6 T(!5 expires 9intra$cell handoer:. -ig $" illustrates call drop due to h andoer failure.

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. "

Internal Use Only ▲ %8

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This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. (

Internal Use Only ▲ -ig $2 T< expires（inter$78C handoer failure ）

)!. Call drop due to /PD link (ailure Explanation3 when /A0D lin1 brea1s6 calls on carriers will be interrupted. 78C counts after it receies message showing that /A0D lin1 is bro1en.

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 2


+ Causes (or di((erent t%pes o( call drop +!) Main causes (or call drop due to '* loss# 9: Wea1 coerage area6 poor signal? 9": ;nterference3 li1e internal interference caused by inappropriate freFuency planning and external interference? 9(: Gnreasonable radio parameters3 

%inimum receie leel is set too low6 which leads to %8 suffering from call drop in wea1 coerage area.



Gnreasonable setting of ICC 0ermitted3 in some networ1s6 the sering cell and adKacent cells may adopt different ICC6 which reFuires input of ICC adopted by adKacent cells in ICC 0ermitted. Bnce the setting is not reasonable6 adKacent cells of an ICC wont be detected by %86 which will result in handoer nonoccurance and call drop.



Value of radio lin1 timer is set too small 9radio lin1 will time out soon:6 which leads to call drop when it expires due to sudden deterioration in radio enironment? if its set too large6 use ratio of TC) will decrease.



Gnreasonable power control parameters3 such as unreasonable power control threshold for leel and Fuality6 which may cause %8 power to decrease when signal and Fuality are poor.



Gnreasonable -) parameters3 wrong setting of %aio leads to co$channel interference within a site.



Definition of adKacent cell data is set wrong or not complete6 which disables %8 to improe signal Fuality by handoer6 hence call drop due to signal deterioration.



Gnreasonable handoer parameters6 which disables %8 to improe radio Fuality through handoer when necessary6 hence call drop is resulted.

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. #

Internal Use Only ▲ 

Congestion in adKacent cells3 it causes call drops6 because %8 is unable to improe radio Fuality through handoer. the congestion problem shall be soled first.

92: )ardware fault3 such as too low output of power amplifier6 big difference between in transmission power of different carriers6 faults of carrier transmitter6 combiner and diider. 9#: Antenna system fault3 such as difference in down$tilt and a+imuth of two antennas? too large feeder V8W,? oerlarge coerage caused by unreasonable antenna height or down$tilt? all these will cause s1ip$+one coerage6 thus creates isolated$island effect and call drop is resulted. 94: %8 malfunction3 for example6 power$fail due to poor contact of battery6 etc..

+!+ Main causes (or call drop due to ,ando-er (ailure We need to ta1e into consideration optimi+ation of handoer success rate 9especially that of success rate of outgoing handoer: when trying to sole problem about call drop due to handoer failure. 9: ;nterference3 li1e internal interference caused by inappropriate freFuency planning and external interference. 95: )ardware fault3 cloc1 malfunction in target cell or sering cell6 too low output of power amplifier6 big difference between in transmission power of different carriers6 faults of carrier transmitter6 combiner and diider. 9<: Gnreasonable settings of radio parameters 

Co$7CC) and co$78;C in target cell6 high outgoing handoer failure rate is caused6 thus call drop is resulted?



;nappropriate adKacent cell relation or wrong adKacent cell data6 high outgoing handoer failure rate is caused6 thus call drop is resulted?



Gnreasonable settings of handoer parameters ， 0ingpong handoer will be caused6 thus call drop is resulted.



+!. Main causes (or call drop due to /PD link (ailure 9: 7T8 transmission problem3 li1e interruption in transmission and unstable transmission 9on and off:6 etc.? 9": 7T8 hardware problem3 li1e unreliable E6 problems about C%% board and bac1board connection lines? 9(: 78C hardware problem3 li1e problem about /A0D processing module.



. *low o( problem ,andling Chec1ing of radio parameters and hardware is adised for locating problems. -low of handling call$drop problem3 9: Analysis of performance report3 to confirm the cause of call drop in cell with high call drop rate? 9': -or call drops due to different reasons6 ma1e analysis accordingly? 9!: ;f there are more call drops due to ,- loss6 the following procedures are recommended3 

Chec1 radio parameters3 adKust the unreasonable settings of radio parameters?



Chec1 indicators li1e 7E, and leel of idle interference band6 reduce or eliminate radio interference?



Chec1 if coerage problem exists through DT. -or wea1 coerage6 focus on hardware problem chec1ing? for s1ip$+one coerage6 focus on chec1ing power parameters6 handoer parameters and antenna down$tilt6 etc.?



Chec1 and eliminate eFuipment fault? change panels with problems?



Chec1 antenna system6 especially the parts with problems.

9: ;f there are more call drops due to handoer failure6 the following procedures are recommended3 

Chec1 radio parameters3 adKust the unreasonable settings of radio parameters?



Chec1 indicators li1e 7E, and leel of idle interference band6 reduce or eliminate radio interference?



Chec1 and eliminate eFuipment fault? change panels with problems?

9": ;f there are more call drops due to /A0D lin1 failure6 the following procedures are recommended3 

;nestigate eFuipment problem at 78C?



;nestigate 7T8 transmission?



;nestigate hardware problem at 7T8.

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. <

Internal Use Only ▲ 7asic flow of handling call drops3

-ig ($# -low of handling call drops

This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. '


0 T%pical cases# 0!) Hig, call drop rate at Cell )1 . o( 2TS  3o( a region4 【0roblem description】 0erformance indicators at B%C, show high call drop rate at Cell A$6 A$(.

【0roblem analysis】 @et detailed performance statistics6 inestigate call drop cause6 its found that the main cause for call drop is ,- loss. Chec1 radio parameter settings6 its found that Cell A$6 A$( co$channel6 and its confirmed that co$channel interference exists6 thus call drop is resulted.

【0roblem solution】 AdKust freFuency6 eliminate interference. Iumber of call drop times is obiously reduced. o. of TCH TCH call o. of occupancy drop rate TCH call ti!es)inclu )includin# drops din# HOHO-)/-

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0!+ Hig, call drop rate at Cell 25. o( a region 【0roblem description】 0erformance indicators at B%C, show high call drop rate at Cell 7$(.

【0roblem analysis】 @et detailed performance statistics6 inestigate call drop cause6 its found that the main reason is handoer failure. Chec1 data of cell freFuency and adKacent cells6 no problem is found. Trace signaling6 its discoered that G/ leel is stronger6 but G/ Fuality is rather poor6 interference leel of idle TC) indicated in ,- resource is #6 as shown in the following figure. Therefore6 its confirmed that external interference exists in the cell.

【0roblem solution】 Try to apply out$of$band freFuency 9usable freFuency gien by operator according to the external interference at the region:. After freFuency adKustment6 number of call drops reduced greatly6 indicators display normal6 and the problem is soled. This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. 

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This document contains proprietary information of ZTE Corporation and is not to be disclosed or used except in accordance with applicable agreements. "

GSM P&O TCH Call Drop & Solutions-Special Subject Guidebook

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