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UMTS CS Call Drop Analysis

ZTE CORPORATIONZTE Plaza, Keji Road South,Hi-Tech Industrial Park,

Nanshan District, Shenzhen,P. R. China518057Tel: (86) 755 26771900 800-9830-9830Fax: (86) 755 26772236

URL: http://support.zte.com.cn E-mail: [email protected]

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Contents

Chapter 1.........................................................................1

Introduction ....................................................................1

Chapter 2.........................................................................3

Definition.........................................................................3

Definition of Call Drop from Drive Test Aspect .....................3

Definition of Call Drop at OMC Side ....................................3

Chapter 3.........................................................................5

Call Drop Analysis............................................................5

Call Drop Reasons............................................................ 5

Call Drops Caused by Poor Coverage.......................................5

Call Drop Caused by Neighbor Cells......................................... 6

Call Drop Caused by Interference ...........................................7

Call Failure Caused by Two Cells Using the Same PSC ................8

Call Drops Caused by Engineering Causes.............................. 10

Call Drops Caused by 2G/3G Interoperability.......................... 12

Call Drops Caused by the System......................................... 13

Analyzing Call Drops by DT ............................................. 13

Analyzing Call Drops by Traffic Statistics........................... 15

Procedure of KPI Analysis.................................................... 16

Basic Methods to Analyze KPIs ............................................. 17 KPI Analysis Tools.............................................................. 18

Radio Parameters Involved During Optimization ................20

Radio Parameters Related with CS Call Drops ......................... 20

Timer and Counter Related with Call Drop.............................. 22






Confidential and Proprietary Information of ZTE CORPORATION 1

C h a p t e r 1

Introduction

This document is compiled to guide the network optimization

engineers to solve the call drop problem, to reduce the call droprate, and to improve the quality of the network. It alsointroduces ways to evaluate, test, analyze and solve the calldrop problem. In addition, it also includes some typical cases. Inthe actual network optimization activities, handover and calldrop are strongly related. In most cases, handover failure wouldlead to call drops. For this kind of call drops, you may refer tothe guidebook for call drops caused by handover. This documentmainly focuses on call drops which are not caused by handoverfailures.





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C h a p t e r 2

Definition

Definition of Call Drop from

Drive Test AspectAir interface signaling at the UE side: Call drops refer to callreleases caused by Not Normal Clearing, Not Normal, orUnspecified when the message on the air interface satisfying anyof the following three conditions:

n The UE receives any BCH information (system information).

n The call is released for Not Normal and the UE receives theRRC Release information.

n The UE receives CC Disconnect, CC Release Complete, andCC

Release information.

Signaling recorded at the RNC side: Call drops refer to callreleases when the RNC has sent the Iu Release Request to theCN through the Iu interface, or when the RNC has sent the RABRelease Request information to the CN through the user panel.

Definition of Call Drop atOMC SideThe definition of call drop in a broad sense contains the call droprates at both the CN and UTRAN sides. Since the networkoptimization focuses on the call drop rate at the UTRAN side,this document only focuses on the KPI analysis at the UTRANside.

The KPIs at the UTRAN side refers to the number of releasedRABs of different services triggered by the RNC. Two aspects areinvolved: (1) After the RAB is established, the RNC sends theRAB RELEASE REQUEST information to the CN. (2) After the RABis established, the RNC sends the IU RELEASE REQUEST to theCN, and then it receives the IU RELEASE COMMAND from the CN.

The statistics can be collected based on specific services.








If the UL TX power before the call drop has reached themaximum value and the UL BLER is bad, or it is found outthrough the single user tracing record at the RNC that the NodeBhas reported RL failure, then the call drop is caused by bad UL

coverage. If the DL TX power before the call drop has reachedthe maximum value and the DL BLER is bad, then the call dropis caused by bad DL coverage.

For the coverage optimization method, see the WCDMA RadioNetwork Optimization Guide.

Call Drop Caused by Neighbor Cells

Missed neighbor cell

Neighbor cell optimization is an important link of radio networkoptimization. If certain cells should be included but excludedfrom the neighbor cell list of one cell, then call drop wouldhappen and the interference in the network would also increaseand system capacity would be impacted. Therefore, neighbor celloptimization is an important part of the engineeringoptimization.

It is easy to estimate whether the cell is configured with anyneighbor cell, and you can playback the call drop data, performNCOS analysis, and analyze the scanner data.

n Use ZTE CNA to playback the call drop data. If the blue pillar(representing the detected set) in the histogram of the pilot

signals is the longest, then the missed neighbor cell problemexists.

n Use the automatic analysis tool of ZTE NCOS, it would studythe handover data of the network, and automatically add themissed neighbor cell. For details, see the operation guide ofNCOS.

n During the drive test, the UE would acquire the neighbor celllist from the NodeB, and the scanner would scan the 512PSCs and record the Ec/Io. If one of the PSCS is not includedin the neighbor cell list, and its pilot strength is stronger thanthe threshold, and the phenomenon lasts for a few seconds,

then the missed neighbor cell problem exists.

Removal of key neighbor cells caused by combination of macrodiversity

Assign the priority of the neighbor cell when performing theinitial neighbor cell planning, then optimize the priority andnumber of neighbor cells periodically with NCOS as the trafficvolume increases.

Untimely update of the external cell information

Check the external cells of the RNC periodically, and ensure thecells in the list are correct.






Chapter 3 Call Drop Analysis


Call Drop Caused by Interference

Distinguish the UL and DL interferences.

The interferences from the UL and DL would both lead to calldrop. Generally, when the CPICH RSCP of the active set is largethan -85dBm, and the comprehensive Ec/Io is lower than -13dB,call drop occurs, then the call drop is caused by the DLinterference. Note that when the handover is not timely, theRSCP of the serving cell may be good, but the Ec/Io is bad.However, the RSCP and Ec/Io of the monitored set are bothexcellent under this condition. When the UL RTWP is 10dBhigher than the normal value, which is -107~-105, and theinterference duration is 2s or 3s longer, call drop may happenand the problem must be solved.

Two reasons may cause DL interferences, which are pilotpollution and missed neighbor cell. The missed neighbor cell hasalready been discussed in the above part and would not berepeated here. In the pilot pollution area, signals of multiplecells exist, the RSCP of these cells is good, while Ec/Io is bad,the UE would frequently reselect the neighbor cell or perform thehandover, and the incoming and outcoming of calls can hardlyreach the UE. Generally, three factors would lead to pilotpollution in the network.

n Overshooting of sites at a high location

n NodeBs in ring-shaped distribution

n Wave-guide effect, large reflectors, and some other effectsthat may cause the distortion of signals.

The typical feature of DL call drops is that the RNC sends theActive Set Update message, while the UE cannot receive it, thenthe call is dropped for RL Failure.

You can judge whether the UL interferences exist by the AverageRTWP and Max RTWP on the OMC-R. For an idle cell, theAverage RTWP is about -105dBm; for a cell carrying 50% of ULload, the Average RTWP is around -102dBm. If the AverageRTWP of an idle cell exceeds -100dBm, we can believe that ULinterferences exist. The UL interferences make the UL TX power

of the cell in connected mode increase, and then an excessivelyhigh BLER is generated. Then call drop happens. Duringhandover, the newly-added link is out of sync for ULinterferences, which further leads to failed handovers and calldrops. The UL interference may be intra-RAT or inter-RATinterferences. In most cases, the UL interferences are inter-RATinterferences.

When DL interference exists, the UL TX power is very small orthe UL BLER may converge, however, when the DL TX power ofthe UE reaches the maximum value, the DL BLER does notconverge. If UL interferences exist, the same problem would








insist. Thus, in actual analysis, this method can be used todistinguish whether interferences exist.

For methods to investigate the interferences, see the UMTSInterference Investigation Guidebook .

Call Failure Caused by Two CellsUsing the Same PSC

Scenario One

F I G URE 1 SCENARI O O NE T HAT M AY CAUSE T HE SAM E PSC P R O B L E M

Cell A and Cell B (source cell) are configured as neighbor cell foreach other, however, the geographical distance between Cell Aand Cell B is huge. Cell A and Cell C has the same PSC, and CellC and Cell B (source cell) is very close, however, Cell C and CellB are not configured as neighbor cells for each other.

Under this situation, the UE detects signals from Cell C andsends Event 1A request to be soft handed over to Cell C. ThePSC in the Event 1A request is 123. After receiving the Event 1Arequest, the RNC checks from the neighbor cell list of Cell B(source cell) for cells with PSC of 123, then it finds Cell A. Thenthe RNC tries to build the radio link on Cell A. The RNC instructsthe UE to add Cell A to its active set. Then, the update of theactive set times out for the cell measured by the UE is different

from the cell where the radio link is built.








Scenario Two

F I G URE 2 SCENARI O T WO T HAT M AY CAUSE T H E SAM E PSC P R O B L E M

In this scenario, the UE has established the radio link with two

cells, Cell B and Cell C. Cell A is the neighbor cell of Cell B, andCell D is the neighbor cell of Cell C, and these two cells have thesame PSC. When the UE is in soft handover state, the RNCwould combine the neighbor cell lists of Cell B and Cell C, thenthe same PSC problem would happen.

Scenario Three

F I G URE 3 SCENARI O T HR EE T HAT M AY CAUSE T HE SAM E PSC P R O B L E M

Cell B and Cell D are not configured as neighbor cell for eachother, however, these two cells are both included in the activeset owing to the third-party handover among Cell B, Cell C, andCell D. Cell A is the neighbor cell of Cell B, and Cell E is theneighbor cell of Cell D, and these two cells have the same PSC.The RNC would combine the neighbor cells of Cell B, Cell C, andCell D in the active set, then the same PSC problem may occur.








Call Drops Caused by EngineeringCauses

Reversely-connected antenna

You can check whether the diversity is reversely connected bythe PSC distribution figure of the drive test data. For theconnection of the diversity, the PMS can be used to measure thecell performance. The antenna would only generate power whenUEs try to access the network, and the measured value of thepower equals to the demodulation power. You can check theratio of two antennas, if the power of one antenna is lower thanthe other one in a long period of time, then the diversity mustbe reversely connected.

The balance level checking of two antennas in whole networkcan be implemented by OMCB measurement. However, youneed to manually process the acquired data.

An excessive VSWR

You can check the VSWR of the current site at the RNC SDR. Ifthe VSWR is large than or equals to 1.4, then it must beadjusted.

Multi-band antenna problem

In the network of some cities, multi-band antennas exist. Theoperator usually refuses to adjust the parameters of the

multi-band antenna for fearing of affecting the subscribers of theexisting 2G network. Then pilot pollution or overshooting mayoccur. To solve this problem, you should try to persuade theoperator to change the antenna, so that 2G and 3G networkscan have separate antennas. If these antennas cannot bechanged, then the specific environment must be carefullystudied before taking any actions. You can optimize the neighborcells to avoid call drops.

Leakage of signals from indoor distribution system

In most cities, call drops caused by signal leakage from indoordistribution system exist. You should persuade the operator toreconstruct the indoor distribution system. Or, the indoordistribution system can be merged to the whole network, whichcan be done by optimizing of the coverage of the ambientoutdoor cells and addition of neighbor cells.

Call drop caused by unsteady transmission

As the bottom level of transmission medium, E1 would reportthe loss of E1 electrical signals and reception failures at theremote end. Meanwhile, several E1s would be bound together asa group, and then E1 would report the fault of IMA group innon-operating mode.

The following table lists several E1 faults that must be handled

and the related handling suggestions.








T ABL E 2 CO M M O N E 1 F AUL T S AND HANDL I NG SUG G EST I O NS

Fault Causes Solutions

Lost of E1electricalsignals

The RX end detectsno line circuit pulseor cannot detectlogic 1 withincontinuous periods,then the LOS alarmis reported. Thisalarm is generallycaused by the RXfault of the E1/T1 orbroken lines, thenthe E1/T1 cannotdetect the signalsfrom the remote end.

1. Check whether the SAboard is secure, andwhether the E1 adapter isslack.

2. Check whether the pinsof the adapter aredamaged.

3. Check whether the jointconnector of the E1 cable isdamaged, and whether the

joint connector is securelyconnected with the E1cable.

4. Check whether the

cabling of the E1 cablesatisfies the engineeringspecification, whether theE1 cable bears any externalforce.

5. Use the E1 self-loopcable to recycle the line, ifthe alarm is cleared, thencheck the E1 cable at thepeer end.

Remotereceptionfailure of the

E1

It indicates theE1/T1 remote alarm.This alarm indicates

the abnormalreceptions at theremote end. Theremote end insertsthe RAI indicator bitto the signals andthen sends it to thelocal end, and thelocal end reports thealarm after detectingthe alarm. Theremote receptionerror is reported.

1. The TX line is faulty orbroken. Check whether theTX line is correctly

connected. For details, seethe Handling suggestionsfor the LOS Alarm.

2. Check whether the framestructures of the E1 frameat the local end and remotematch. The E1 frame atboth ends must both workat dual-frame ormulti-frame mode.

3. Check for error codes atthe TX line.

E1 frame outof sync

The first bit of slot 0of both E1 and T1carries thesynchronous clocksignals, which informthe RX end of thestart of one frame. Ifthe RX ends of theE1 and T1 are out ofsync, then dataframes would be lostand the LOF alarm isreported.

1. Whether E1 and T1 workat the same state.

2. Check whether E1 framesare of the same modes(dual-frame/multi-frame).

3. Check whether theimpedance modes of E1/T1matches.

4. Check for interferencesfrom digital devices aroundE1/T1.

5. Check whether the clocksignals are normal.








Fault Causes Solutions

SSCOP linkerror

This alarm is causedby that the SSCOPsignaling link is

unsuccessfullyestablished or theSSCOP signalingfrom the remote endis not received withina certain period.Then the SSCOP linkwould be broken off,and this alarm isreported.

See the handlingsuggestions for E1 faults.

IMA group innon-operatingmode

After the IMA groupis successfullyconfigured, if IMA

remains innon-operating modefor over 1s, then thisalarm is reported.

See the handlingsuggestions for E1 faults.

Currently, some sites are configured with IP transmission.Therefore, the alarm of "Lack Ethernet electrical signals" alsoshould be handled on site.

Call Drops Caused by 2G/3GInteroperability

Optimization of 2G neighbor cells configured for 3G cells

If the 2G cells are congested, or interfered, then the successrate of 3G -> 2G handovers is low. During the neighbor celloptimization, this kind of neighbor cells must be removed fromthe list.

Parameters must be refined based on different scenarios.

To improve 3G->2G handover success rate, the parametersmust be detailed planned based on different scenarios.

Compatibility of UEs

The 2G->3G handovers of some cells are slow. This is becausesome smuggled 3G handsets have some difficulties in supportingthe 2G network.

2G/3G data synchronization

To support 2G/3G handovers, the 2G/3G cells must beconfigured as the neighbor cells for each other firstly. If the cellinformation is updated timely, then the handover would fail andcell reselection cannot be performed. Therefore, the data of2G/3G network should be synchronized timely.








Call Drops Caused by the System

If the alarm is not caused by the causes listed in the above

section, then it may be caused by the system. You need tocheck the alarm information of the equipment and system logsto further analyze reasons that cause call drops. For example,an abnormal NodeB would lead to the synchronization failures,which would lead to frequent removal and addition of radio links,and then call drops may happen; call drops caused by poor DLsignals may be because of abnormal RF module, and call dropscaused by that the UE fails to report the measurement reportEvent 1A.

It should be noted that in many foreign countries, the TXenvironment is bad and unstable. Therefore, influences of calldrops caused by TX problem are huge.

Analyzing Call Drops by DTThe following figure describes the flow chart for using DT andCQT to test call drops.








n When the RSCP is normal, while the Ec/Io is bad, pilotpollution or DL interference exists.

n When RSCP and Ec/Io are both normal, if cells in the activeset of the UE are not the optimal cells (which can be checked

through playback of data), then the call drops may becaused by missed neighbor cell or untimely handovers; ifcells in the active set of the UE are the optimal cells, thencall drops may be caused by UL interferences or abnormalcall drops.

Reproducing of problems with DT

Since you cannot collect all necessary information by one DT,then multiple DTs shall be performed to collect sufficient data. Inaddition, multiple DTs can also help to ascertain whether the calldrop is random or always happens at the same spot. Generally,if call drops always happen at the same spot, this problem must

be solved, or if call drops happen randomly, multiple DTs mustbe performed to find inner reasons.

Analyzing Call Drops byTraffic StatisticsWhen analyzing the traffic statistics, check the call drops indexon the RNC firstly to learn the operating status of the wholenetwork. Meanwhile, a cell-by-cell analysis can be performed toacquire the detailed call drop indexes of each cell. During theanalysis, the traffic statistic analyzing tool can be used toanalyze the call drop situations of different services and thepossible causes.

Acquire data about cells with abnormal KPIs through the trafficstatistics. If KPIs of these cells used to be normal, then theabnormal KPIs may be brought by software version, hardware,transmission, antenna, or data, then you can check theseaspects based on the alarms. If no obvious abnormal cells exist,the statistics can be classified based on the carrier in each sector,then cells with poor KPIs can be screened out. Further analyze

the traffic statistics of these cells, such as analyzing morerelated KPIs, such as analyzing data at a shorter interval, oranalyzing KPIs that are more likely to cause call drops, such ashandover. Meanwhile, you can analyze the reasons for call dropsbased on system logs. During the analysis, you should considerthe effect of other KPIs when focusing on a certain KPI. It shouldbe specified that the result of traffic statistics is meaningful onlywhen the traffic volume reaches a certain amount. For example,a 50% of call drop rate does not mean that the network is bad.This value is meaningful only when the calling number, succeedcalling number, call drop times all make statistical significances.








Procedure of KPI Analysis

The commonly used KPI analysis method is the TOP cell method,

which means the top cells will be screened out according tocertain index, then these top cells are optimized and then thetop cells are selected again. After several repetitions, the relatedKPI can be speedily converged. At the initial stage of networkconstruction, there are few subscribers in the network. At thisstage, the KPIs of many cells might be unstable, such as calldrop rate. You can collect the data in seven days or longerperiods, then select the top cell and then perform theoptimization. For example, optimization of call drop rate of CSservices. When selecting top cells, you can select the cell withcall drop numbers exceeding the specified threshold, and thenarrange the priority based on the call drop rate.

The procedures of top cell selection are the same as theprocedures of handling input information from other team ofengineers (complains or single site acceptance), and are shownin the following figure.

F I G URE 5 FL O W CHART F O R T O P CEL L SEL ECT I O N








Basic Methods to Analyze KPIs

Speedily Collecting the Field Data

To locate the problem, you have collect data from manydifferent spots between the UE and the pdn server. While,speedy and accurate collection of the field data is essential tolocate and solve the problem and to improve the KPIs. Datacollection can be divided into multiple layers.

Collecting UE log, RNC signaling, KPI data, alarms, abnormalprobes, and packet captured at the Iub interface

NodeB and RNC debug log

Some common skills are required to collect data of the first layer,and the network optimization & maintenance personnel caneasily master these skills. At present, most field questions canbe located through the data analysis at this layer. Collection ofthe debug log of the second layer should be performed orremotely supported by the relative R&D engineers. Data at thislayer can help to solve some deep layer problems.

The following chapter focuses on the data collection tool andmethod for the first layer data, and only gives a briefintroduction to that of the second layer.

Health Check of Sites

For sites where alarms are reported, you should first performthe health check for the site, which mainly covers the followingaspects:

n Alarms

n Frequently added or removed common transport channels

n UL & DL power

n Radio link restore

n Balance level between two antennas

n Statistics of service failures

The RL restore rate is shown by the NodeB cell measurementrecorded by PMC as shown in the following figure, and isaccumulated since the establishment of cells. If the RL restorerate of a cell is lower than 80%, the cell is treated as abnormal,and the possible causes are as follows:

n UL interferences

n Insufficient cell radius or overshooting

n Reuse of the same PSC

n Abnormal UL RF channel








For these possible causes, you may check them combining othermeasurement results and data analysis.

KPI Analysis Tools

Signal Trace

This tool traces signaling of RNC, you can trace the signaling atthe Iu, Iur, Iub, and Uu interfaces, TNL signaling, and RNLsignaling through this tool. The most commonly used method tocheck the KPIs is to trace the RNL signaling. This tool is veryuseful, and can trace the signaling on the basis of cell (tracesignaling of multiple UEs) and IMSI (trace signaling of one UE).

It should be emphasized that signaling tracing by cells can onlytrace the UE that initiates the call from this cell. The UE can betraced as long as it remains in the same RNC, even if it ishanded over to other cells. However, if a UE initiates the callfrom other cells and then is handed over this call, and its calldrop happens in this cell, it cannot be traced. Therefore, whenyou trace the signaling of a cell with high call-drop rate, thesignaling of cells in close handover relation with this cell shouldalso be traced, then the result would be more comprehensive.

The RNC R&D engineers also develop a RNC signaling tracingtool, WinSigAn, which can mark the call drop spots more clearly.

RNC Association Log

This tool helps to record the context of the abnormal systemflow, and then the context would be counted and analyzed tolocate the network problem.

It is usually used when the system is abnormal and no RNCsignaling is traced. It can help to locate the problem by the timewhen the system exception happens. The exception can bequeried on the basis of IMSI and CELL ID.

NodeB LMT

Besides all functions of OMCB, NodeB Local MaintenanceTerminal (LMT) can also provide detailed cell and UEinformation.

The NodeB LMT consists of EOMS, EFMS, DMS, and PMS.








NodeB Exception Probe

In the field of the WCDMA commercial network, this tool caneffectively help to monitor the operating status of the NodeB.Different modules of the NodeB would record the informationwhen exceptions happen, thus facilitating the location ofproblems. However, specialized knowledge is required. You haveto understand the functions and interfaces of different boards. Ifthe field engineers cannot analyze the report, they can simplysend these data to the R&D engineers.

The exception probe reported by different NodeBs can be savedon different OMCB servers based on the RNC they belong to.Then, this tool would download the file from different OMCB FTP,and then analyze them.

CTS

CTS is the tool for the CN, and it can be used to perform deepsignaling by IMSI. Unlike SignalTrace, which is applicable to thesignaling tracing within one RNC, CTS can perform the signalingtracing across the RNC border, Therefore, it is applicable to thesignaling tracing of VIPs.

CTS can trace the interactive signaling among different NEswithin the CN, and can trace the signaling at the Iu and Uuinterfaces, and this is called deep tracing. The working principlesof CTS is as follows: First establish an IMSI task on CTS server,and then sent this IMSI task to the CN, which is further sent todifferent modules through the arranged interfaces, then eachmodule collects the signaling related to IMSI, and then thecollected signaling is transmitted back to the CTS server throughthe CN. The above interfaces are all private interfaces, thus thistool only work on ZTE CN and RNC.

UE Log

DT is an important means to analyze KPIs. Many problems,

signaling tracing at the network side and tracing of problemswhich are hard to be located, can be finally located aftercombining the UE logs. The commonly used DT software isQXDM/APEX(QCAT), CNT/CNA, and TEMS.








Radio Parameters InvolvedDuring Optimization

Radio Parameters Related with CSCall Drops

Time To Trigger

Time To Trigger is the interval between the moment that theevents (1A, 1B, 1C, and 1D) are monitored and the moment thatthe events are reported. The setting of TTT would influence

timely handover.The adjustment of handover parameters should first ensure thatthis cell is overlapped by other cells, then you can adjust therelated radio parameters to ensure that the time that the UEpasses the handover area is longer than the handover delay ofthe whole system, thus ensuring the continuity of the services.The other is to ensure that the handover area ascertained by thesignals and radio parameters cannot be too large to avoid theincrease of handover overhead and reduction of resourceutilization ratio.

For areas where the signals may change greatly, the trigger timeof Event 1A must be reduced, and that of Event 1B must beincreased. Meanwhile, the CIO of the corresponding neighborcells should be adjusted so that Event 1A can happen earlier andEvent 1B would happen later, thus ensuring successfulhandovers.

For highways, the cells are sparsely distributed. If the vehiclesdrive too quickly and cannot access the new cell in time, calldrops would happen. The optimization is the same as that forthe optimization for street corners in dense urban, which is tomake cells with good signals join the active set speedily toensure continuity of services.

For the adjustment of the related parameters, a whole new set

of parameters must be assigned to the target cell.

Cell Individual Offset

The sum of the value of Cell Individual Offset (CIO) and theactually measured value is used in the evaluation of the eventsof the UE. The UE would use the original measurement value ofthis cell plus the CIO as the measurement result for theintra-frequency handover judgment. CIO can help to ascertainthe cell edge.








The larger this parameter is set, the easier the soft handover willbe, and more UEs will be in soft handover state. However, moreresources are consumed. This smaller is parameter is set, themore difficult the soft handover is.

CIO is valid only for the neighbor cell. For Event 1A, the CIO canbe set in the neighbor cell; for Event 1B, the CIO can be set inthe cell to be removed. The formula is as follows:

Formula of Event 1A triggering:

),2/(10)1(1010 11

1

aa Best

N

i

i New New H R LogM W M Log W CIO LogM A

−−⋅⋅−+

⋅⋅≥+⋅ ∑

=

MNew is the measurement of the to-be-evaluated cells that hasentered the report range.

Mi is the mean measurement result of cells (exclude the best cell)

in an active set.NA is the current cell number (exclude the best cell) in the activeset.

MBest is the measurement result of the optimal cell in the activeset.

W is the weight proportion of the best cell to the rest cells in theactive set.

R1a is the reporting range of Event 1A.

H1a is the reporting hysteresis of Event 1A.

Formula of Event 1B triggering:

Mnew is the measurement of the to-be-evaluated cells that hasentered the report range.

Mi is the mean measurement result of cells (exclude the best cell)in an active set.

NA is the current cell number (exclude the best cell) in the activeset.

MBest is the measurement result of the optimal cell in the active

set.

W is the weight proportion of the best cell to the rest cells in theactive set.

R1bis the reporting range of Event 1B.

H1b is the reporting hysteresis of Event 1B.

Start/Stop Threshold for Compressed Mode

Compressed mode is frequently used during inter-frequency and

inter-RAT handovers. The compressed mode is started before

1 1

1

10 10 (1 ) 10 ( / 2), A N

Old Old i Best b b

i

LogM CIO W Log M W LogM R H =

⋅ + ≤ ⋅ ⋅ + − ⋅ ⋅ − +

∑








the handover, and the system can use the time slot brought bycompressed mode to perform the signal quality test on theinter-frequency or inter-RAT neighbor cells. In the currentsystem, the compressed mode is started through Event 2D, and

stopped through Event 2F. The measurement value of RSCP orEc/Io can be selected. Currently, the default value is RSCP.

Generally, the quality and other related information of the targetcell (inter-frequency or inter-RAT) must be acquired for thecompressed mode. Meanwhile, the moving of the UE would leadto the deteriorate of the quality of the cell, therefore, the startthreshold of the compressed mode should satisfy the conditionthat the UE can finish the measurement of the target cell andreport for handover before call drops happens. For the stopthreshold, it should help to avoid the frequent start or stop ofcompressed mode.

In dense urban, the continuous coverage of the 3G should beensured, thus avoiding unnecessary inter-RAT handovers andincrease of system load. For edges of the 3G network andhighways, the UEs should be handed over to the 2G networkbefore the heavy fading. Under this condition, the triggerthreshold of Event 2D should be raised so that the UE caninitiate the compressed mode as early as possible.

Maximum DL TX power of the Radio Link

If large amounts of call drops happen due to coverage causes,

then the maximum DL TX power of the services can be increasedappropriately. However, this is at the risk that the UEs at celledges may consume too much power, and then affect the otherUEs, and reduce the DL capacity of the system. For cells with agreat deal of access failures caused by excessive load, thisparameter can be set to a small value.

Inter-Frequency/Inter-RAT Handover Threshold

The UE can be handed over to the inter-RAT/frequency neighborcells when the measured value of the signals from these cells is

higher than the threshold. This parameter can be set combiningthe start threshold of the compressed mode. If this parameter isconfigured with a little value, then the handover can betriggered early. If this parameter is configured with a large value,then the handover will be prolonged.

Timer and Counter Related with CallDrop

The following table lists the timer and counter related to the UE.







T ABL E 3 T I M ER AND CO UNT ER REL AT ED T O T HE UE

Name DescriptionValueRange

DefaultValue

T312

Connected T312 in connected mode,and indicates the time thatUE waits from thesynchronization indicatorfrom L1 when it starts toestablish the DPCCH.

(1..15)s 1s

N312

Connected T312 in connected mode,and indicates the number ofsynchronization indicatorthat the UE received from L1before the DPCCH isestablished.

(1, 2, 4, 10,20, 50, 100,200, 400,600, 800,1000)

1

T313 Indicates the waiting time of

the UE in CELL_DCH stateafter the DPCCH channel isestablished.

(0..15)s 3s

N313 Indicates the number ofmaximum number of out ofsync indicators that the UEreceives from L1.

(1, 2, 4, 10,20, 50, 100,200)

20

T314 Start: When the criteria forradio link failure are fulfilled.The timer is started if radiobearer(s) that areassociated with T314 exist

or if only RRC connectionexists only to the CSdomain.

(0, 2, 4, 6, 8,12, 16, 20)s

4s

T315 Start: When the criteria forradio link failure are fulfilled.The timer is started if radiobearer(s) that areassociated with T314 existor if only RRC connectionexists only to the CSdomain.

(0,10, 30,60, 180, 600,1200, 1800)s

30s

N315 Indicates the maximumnumber of synchronization

indicators that the UEreceived from L1 after T313is activated.

(1, 2, 4, 10,20, 50, 100,

200, 400,600, 800,1000)

1

T309 Indicates the waiting time ofthe UE after sends theinter-RAT handoverrequests.

(1..8)s 3s

umts cs call drop analysis guide_book.pdf

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