Drop Analysis in Huawei

Contents 1. CALL DROP DEFINITION and MEASUREMENT POINTS ............................................................................................................ 2

2. CALL DROP COUNTERS ................................................................................................................................................................ 3

2.1 CALL DROP COUNTERS RELATIONS ....................................................................................................................................... 3

2.2 CALL DROP COUNTERS DEFINITIONS .................................................................................................................................... 4

2.3 CALL DROP COUNTERS INCREMENT LOGIC .......................................................................................................................... 4

3. CALL DROP TROUBLESHOOTING ................................................................................................................................................. 5

3.1 CALL DROP CAUSE ANALYSIS ................................................................................................................................................ 5

3.2 CALL DROP REASONS for GENERAL CALL DROP TYPES ......................................................................................................... 6

3.3 TROUBLESHOOT STEPS FOR CALL DROP ............................................................................................................................... 6

3.3.1 PARAMETER PROBLEMS ................................................................................................................................................ 6

3.3.2 PATH BALANCE PROBLEMS ............................................................................................................................................ 7

3.3.3 COVERAGE GAPS PROBLEMS ......................................................................................................................................... 8

3.3.4 QUALITY and INTERFERENCE PROBLEMS .................................................................................................................... 11

3.3.5 MISSING NEIGHBOR PROBLEMS .................................................................................................................................. 15

1. CALL DROP DEFINITION and MEASUREMENT POINTS

Generally TCH Drop Formula is like below;

TCH call drop rate=TCH call drops / Successful TCH seizures (all)

Measurement points of TCH Drop are showed in below sketch.

TCH serves as traffic channel, BSC receives ERROR INDICATION message from BTS.

TCH is seized as traffic channel, BSC receives CONNECT FAILURE INDICATION message from BTS.

In assignment procedure and handover procedure, failure of decoding HANDOVER DETECTION and HANDOVER COMPLETE message.

TCH serves as traffic channel, incoming BSC handover initiated and the timer for the target cell to wait for HANDOVER COMPLETE message expires.

TCH serves as traffic channel, outgoing BSC handover initiated and the timer for the source cell to wait for CLEAR COMMAND message from MSC expires (T8 expires).

In intra-BSC handover procedure, the target cell sends Inter Clear Request to the source cell when the timer for the target cell to wait for HANDOVER COMPLETE from MS expires, in this case this item is measured in the source cell.

In Intra-BSC handover procedure, the source cell, excluding the source cell for directed retry, measures the item when the timer for the source cell to wait for Inter Clear Request with cause value HANDOVER COMPLETE from the target cell expires.

In Intra-BSC handover procedure, when the target cell AM/CM net-drive fails (due to timeout or negative acknowledgement), the target cell sends Inter Clear Request to source cell, in this case, this item is measured in the source cell.

In the case that MS reverses to the original channel after intra BSC handover fails, the source cell first releases the terrestrial connection but the AM/CM re-net-drive fails (due to timeout or negative acknowledgement). In this case this item is measured in the source cell.

The resource of the lower_priority call will be preempted by the higher_priority call if MSC and BSC both support preemption, which will cause call drop.

This item is measured when the RSL link of the TRX that the call is using disconnects, which will cause call drop.

2. CALL DROP COUNTERS

2.1 CALL DROP COUNTERS RELATIONS

Call Drop has a set of counters which related to each other like below schema

CM332 CM333 CM334 CM335

H3027Ca

H3028Ca

H3127Ca

M3100A M3101A M3102 H3128Ca

M3100B M3101B M3202 H3327Ca

M3100C M3101C H3328Ca

M3200A M3101D

M3200B M3101E

M3200C M3201A

M3201B

M3201C

M3201D

M3201E

CM330 CM331

CM33C

CM33

CM3300 CM3301 CM3302

2.2 CALL DROP COUNTERS DEFINITIONS

These Call Drop counters meaning are below.

2.3 CALL DROP COUNTERS INCREMENT LOGIC

Radio Link Timeout increasing and decreasing in below sequence.

As seen, when uudecoded SACCH occurs, RLT

decreased by one, decoded SACCH occurs

increased by two. If RLT becomes zero than

Radio Link will be released. It is calculated

continuously for both uplink and downlink.

Also if ERROR INDICATION message sent to BSC,

reasons like;

T200 expired : If BTS could not receive any

acknowledge message to send I Frame till T200

expired, it repeats sending I Frame for N200+1

times. At the end if BTS still could not get

acknowledge for I Frame, it sends ERROR

INDICATION with cause of timer T200 expired

(N200+1) times (0x01) to BSC. M3100A or M3200A are incremented according to suitable channel type (TCHF or TCHH).

Unsolicited DM Response : If BTS gets unexpected DM Frame, it sends ERROR INDICATION with cause unsolicited DM

response (0x05) to BSC. M3100B or M3200B are incremented according to suitable channel type (TCHF or TCHH).

Sequence Error : If BTS gets I and S Frames not in correct order, it sends ERROR INDICATION with cause sequence error

(0x07). M3100C or M3200C are incremented according to suitable channel type (TCHF or TCHH).

If CONECTION FAILURE message sent to BSC;

M3100A Call Drops due to ERR IND Received on TCHF (Traffic Channel) in Stable State (T200 Expired)

M3100B Call Drops due to ERR IND Received on TCHF (Traffic Channel) in Stable State (Unsolicited DM Response)

M3100C Call Drops due to ERR IND Received on TCHF (Traffic Channel) in Stable State (Sequence Error)

M3200A Call Drops due to ERR IND Received on TCHH (Traffic Channel) in Stable State (T200 Expired)

M3200B Call Drops due to ERR IND Received on TCHH (Traffic Channel) in Stable State (Unsolicited DM Response)

M3200C Call Drops due to ERR IND Received on TCHH (Traffic Channel) in Stable State (Sequence Error)

M3101A Call Drops due to CONN FAIL Received on TCHF (Traffic Channel) in Stable State (Radio Link Failure)

M3101B Call Drops due to CONN FAIL Received on TCHF (Traffic Channel) in Stable State (HO Access Failure)

M3101C Call Drops due to CONN FAIL Received on TCHF (Traffic Channel) in Stable State (OM Intervention)

M3101D Call Drops due to CONN FAIL Received on TCHF (Traffic Channel) in Stable State (Radio Resource Unavailable)

M3101E Call Drops due to CONN FAIL Received on TCHF (Traffic Channel) in Stable State (Other Causes)

M3201A Call Drops due to CONN FAIL Received on TCHH (Traffic Channel) in Stable State (Radio Link Failure)

M3201B Call Drops due to CONN FAIL Received on TCHH (Traffic Channel) in Stable State (HO Access Failure)

M3201C Call Drops due to CONN FAIL Received on TCHH (Traffic Channel) in Stable State (OM Intervention)

M3201D Call Drops due to CONN FAIL Received on TCHH (Traffic Channel) in Stable State (Radio Resource Unavailable)

M3201E Call Drops due to CONN FAIL Received on TCHH (Traffic Channel) in Stable State (Other Causes)

M3102 Call Drops due to REL IND Received on TCHF (Traffic Channel)

M3202 Call Drops due to REL IND Received on TCHH (Traffic Channel)

H3027CaFailed Internal Intra-Cell Handovers

(TimerExpired) (TCHF) (TrafficChannel)

H3028CaFailed Internal Intra-Cell Handovers

(TimerExpired) (TCHH) (TrafficChannel)

H3127CaNumber of Unsuccessful Outgoing Internal

Inter-CellHandovers (Timer Expired)(TCHF)

H3128CaNumber of Unsuccessful Outgoing Internal

Inter-CellHandovers (Timer Expired)(TCHH)

H3327CaFailed Outgoing External Inter-Cell

Handovers (T8 Expiry)(TCHF) (Traffic

H3328CaFailed Outgoing External Inter-Cell

Handovers (T8 Expiry)(TCHH) (Traffic

CM332Call Drops Due to No MR from MS

for a Long Time (Traffic Channel)

CM333Call Drops due to Abis Terrestrial

Link Failure (Traffic Channel)

CM334Call Drops due to Equipment Failure

(Traffic Channel)

CM335Call Drops due to Forced Handover

(Traffic Channel)

Call Drops on Traffic Channel in Stable

State (Connection Failure)


State (Release Indication)

CM33Call Drops on

Traffic Channel

CM33CCall Drops on Radio Interface

(Traffic Channel)

CM330

CM331

Call Drops on Radio

Interface in Stable

State (Traffic

Channel)

Call Drops on Radio

Interface in Handover

State (Traffic

Channel)

CM3300

CM3301

CM3302


State (Error Indication)

In Uplink, if BTS could not decode SACCH then it sends to BSC CONNECTION FAILURE message with reasons Radio Link

Failure, HO Access Failure, OM Intervention, Radio Resource Unavailable and Other Causes. According to reason and suitable

channel type, one of the M3101A, M3101B, M3101C, M3101D, M3101E, M3201A, M3201B, M3201C, M3201D and M3201E

are incremented.

If Multi Frame link established and BTS gets DICS Frame from MS, than BTS sends RELEASE INDICATION to BSC according to

suitable channel type.

3. CALL DROP TROUBLESHOOTING

3.1 CALL DROP CAUSE ANALYSIS

For troubleshooting, first thing to do search about what kind of drops occurs generally.

Get stats for all call drop counters for a period.

As seen in one day total drop numbers;

% 99,7 of drops occurs in Radio Interface,

% 90,2 of Radio Interface Drops occurs in Stable State,

% 34,1 of Stable Drops occurs in Error Indication and % 65,9 in Connection Failure,

All of Error Indication drops occurs in T200 expired,

All of Connection Failure drops occurs in Radio Link Failure,

So generally, we should focus on T200 expired drops, Radio Link Failure drops. Also Failed Outgoing Internal Inter-Cell

Handovers (Timer Expired) drops are should be touched.

Drop counters Values Level 1 Level 2 Level 3 Level 4Sum of CM33:Call Drops on Traffic Channel(times) 16135 100,0

Sum of CM33C:Call Drops on Radio Interface (Traffic Channel)(times) 16081 100,0 99,7

Sum of CM330:Call Drops on Radio Interface in Stable State (Traffic Channel)(times) 14505 100,0 90,2

Sum of CM3300:Call Drops on Traffic Channel in Stable State (Error Indication)(times) 4947 100,0 34,1Sum of M3100A:Cal l Drops due to ERR IND Received on TCHF (Traffic Channel ) in Stable State (T200 Expired)(times) 4554 92,1

Sum of M3100B:Cal l Drops due to ERR IND Received on TCHF (Traffic Channel ) in Stable State (Unsol ici ted DM Response)(times) 0 0,0

Sum of M3100C:Cal l Drops due to ERR IND Received on TCHF (Traffic Channel ) in Stable State (Sequence Error)(times) 1 0,0

Sum of M3200A:Cal l Drops due to ERR IND Received on TCHH (Traffic Channel ) in Stable State (T200 Expired)(times) 392 7,9

Sum of M3200B:Cal l Drops due to ERR IND Received on TCHH (Traffic Channel ) in Stable State (Unsol ici ted DM Response)(times) 0 0,0

Sum of M3200C:Cal l Drops due to ERR IND Received on TCHH (Traffic Channel ) in Stable State (Sequence Error)(times) 0 0,0

Sum of CM3301:Call Drops on Traffic Channel in Stable State (Connection Failure)(times) 9553 100,0 65,9Sum of M3101A:Cal l Drops due to CONN FAIL Received on TCHF (Traffic Channel ) in Stable State (Radio Link Fa i lure)(times) 9079 95,0

Sum of M3101B:Cal l Drops due to CONN FAIL Received on TCHF (Traffic Channel ) in Stable State (HO Access Fa i lure)(times) 6 0,1

Sum of M3101C:Cal l Drops due to CONN FAIL Received on TCHF (Traffic Channel ) in Stable State (OM Intervention)(times) 0 0,0

Sum of M3101D:Cal l Drops due to CONN FAIL Received on TCHF (Traffic Channel ) in Stable State (Radio Resource Unavai lable)(times) 0 0,0

Sum of M3101E:Cal l Drops due to CONN FAIL Received on TCHF (Traffic Channel ) in Stable State (Other Causes)(times) 0 0,0

Sum of M3201A:Cal l Drops due to CONN FAIL Received on TCHH (Traffic Channel ) in Stable State (Radio Link Fa i lure)(times) 468 4,9

Sum of M3201B:Cal l Drops due to CONN FAIL Received on TCHH (Traffic Channel ) in Stable State (HO Access Fa i lure)(times) 0 0,0

Sum of M3201C:Cal l Drops due to CONN FAIL Received on TCHH (Traffic Channel ) in Stable State (OM Intervention)(times) 0 0,0

Sum of M3201D:Cal l Drops due to CONN FAIL Received on TCHH (Traffic Channel ) in Stable State (Radio Resource Unavai lable)(times) 0 0,0

Sum of M3201E:Cal l Drops due to CONN FAIL Received on TCHH (Traffic Channel ) in Stable State (Other Causes)(times) 0 0,0

Sum of CM3302:Call Drops on Traffic Channel in Stable State (Release Indication)(times) 5 100,0 0,0Sum of M3102:Cal l Drops due to REL IND Received on TCHF (Traffic Channel )(times) 5 100,0

Sum of M3202:Cal l Drops due to REL IND Received on TCHH (Traffic Channel )(times) 0 0,0

Sum of CM331:Call Drops on Radio Interface in Handover State (Traffic Channel)(times) 1576 100,0 9,8Sum of H3027Ca:Fai led Internal Intra-Cel l Handovers (Timer Expired) (TCHF) (Traffic Channel )(times) 1 0,1

Sum of H3028Ca:Fai led Internal Intra-Cel l Handovers (Timer Expired) (TCHH) (Traffic Channel )(times) 4 0,3

Sum of H3127Ca:Fai led Outgoing Internal Inter-Cel l Handovers (Timer Expired) (TCHF) (Traffic Channel )(times) 1472 93,4

Sum of H3128Ca:Fai led Outgoing Internal Inter-Cel l Handovers (Timer Expired) (TCHH) (Traffic Channel )(times) 97 6,2

Sum of H3327Ca:Fai led Outgoing External Inter-Cel l Handovers (T8 Expired) (TCHF) (Traffic Channel )(times) 2 0,1

Sum of H3328Ca:Fai led Outgoing External Inter-Cel l Handovers (T8 Expired) (TCHH) (Traffic Channel )(times) 0 0,0

Sum of CM332:Call Drops due to No MRs from MS for a Long Time (Traffic Channel)(times) 2 0,0

Sum of CM333:Call Drops due to Abis Terrestrial Link Failure (Traffic Channel)(times) 0 0,0

Sum of CM334:Call Drops due to Equipment Failure (Traffic Channel)(times) 45 0,3

Sum of CM335:Call Drops due to Forced Handover (Traffic Channel)(times) 7 0,0

3.2 CALL DROP REASONS for GENERAL CALL DROP TYPES

Other drops like Abis Terrestrial Link Failure drop caused by Transmission Link broken, Equipment Failure drops caused by

HW problems and Forced Handover drops caused by OM Intervention. These drops should be handled by separately.

For these two general drop cause Radio Link Timeout and T200 Expired, the reasons are;

Coverage gaps,

Quality or Interference problems,

Unbalanced Path Losses,

HW Fault or Installation faults,

Parameter definition and OSS problems,

Missing Neighbor Relations.

Also for other big percent of drop cause Failed Outgoing Internal Inter-Cell Handovers (Timer Expired), the reasons are;

Wrong or missing neighbor definitions,

Wrong cell to cell neighbor parameters or timers,

Coverage gaps,

Quality or Interference problems,

HW Faults or Installation faults.

3.3 TROUBLESHOOT STEPS FOR CALL DROP

3.3.1 PARAMETER PROBLEMS

First of all for a problematic cell, we should check general parameters of this cell and also this cell’s neighbor cells.

Cells general parameters like;

In Basic Attributes Parameter set;

LAC, Layer of Cell, Cell Priority, Cell Extension Type, Cell IUO Type, MAX TA, RXLEV_ACCESS_MIN, TCH/F Uplink DTX, TCH/H

Uplink DTX, Encryption Algorithm, UL PC Allowed, DL PC Allowed, Direct Retry, TCH/F Use Downlink DTX, TCH/H Downlink

DTX should be checked. These would affect general quality of serving cell.

If cell is a border cell or have external definitions in other BSCs or RNCs. All external definitions should be checked also.

In Idle Mode Parameter set;

BS-PA-MFRAMS, T3212, CRH, PI, CRO, TO, PT, NCC Permitted should be checked. These would affect service area of cell.

In Other Attributes Parameter set;

MS_TXPWR_MAX_CCH, STIRC Allowed, T3101, T3103A, T3103C, T7, T3107, T3121, T8, T3109, T3111, T3122 should be

checked. These would affect general quality of serving cell.

In Call Control Parameter set;

Paging Times, MS MAX Retrans, SACCH Multi-Frames, AFR SACCH Multi-Frames, AHR SACCH Multi-Frames, AFR Radio Link

Timeout, AHR Radio Link Timeout, Radio Link Timeout, T200 SDCCH, T200 FACCH/F, T200 FACCH/H, T200 SACCH TCH SAPI0,

T200 SACCH TCH SAPI3, T200 SACCH SDCCH, T200 SDCCH SAPI3, Use LAPDm N200, N200 of Establish, N200 of Release, N200

COUNTER NUMBER COUNTER NAME

S462A Number of MRs (Uplink-and-Downlink Balance Level = 1)(times)

S462B Number of MRs (Uplink-and-Downlink Balance Level = 2)(times)

S462C Number of MRs (Uplink-and-Downlink Balance Level = 3)(times)

S462D Number of MRs (Uplink-and-Downlink Balance Level = 4)(times)

S462E Number of MRs (Uplink-and-Downlink Balance Level = 5)(times)

S462F Number of MRs (Uplink-and-Downlink Balance Level = 6)(times)

S462G Number of MRs (Uplink-and-Downlink Balance Level = 7)(times)

S462H Number of MRs (Uplink-and-Downlink Balance Level = 8)(times)

S462I Number of MRs (Uplink-and-Downlink Balance Level = 9)(times)

S462J Number of MRs (Uplink-and-Downlink Balance Level = 10)(times)

S462K Number of MRs (Uplink-and-Downlink Balance Level = 11)(times)

of SACCH, N200 of SDCCH, N200 of FACH/Half rate, N200 of FACCH/Full rate should be checked. These would affect deciding

time of drop events.

In Handover Data Parameter set;

Pathloss Ho. Enable, Co-BSC/MSC Adj, Intracell HO Allowed, Intracell F-H HO Allowed, Load HO Allowed, MS Fast Moving HO

Allowed, Rx_Level_Drop HO Allowed, PBGT HO Allowed, Level HO Allowed, Fringe HO Allowed, BQ HO Allowed, TA HO

Allowed, Concentric Circles HO Allowed, Interference HO Allowed, Quick Handover Enable, UtoO Traffic HO Allowed, Penalty

Allowed, MR.Preprocessing, No Dl Mr.HO Allowed should be checked. These would affect HO performance and decision of

serving cell.

Also the parameters related with Watch Time/Valid Time should be checked. These would affect deciding faster or slower of

HO.

Also Cell to Cell neighbor definitions should be checked. Timer, hysteresis and thresholds between cells would affect HO

performance between these cells.

3.3.2 PATH BALANCE PROBLEMS

Path Balance is a statistic

considering Uplink Path Loss and

Downlink Path Loss. It is TRX based,

so we could see unbalanced TRX or

have an opinion about feeder

connections. On left these counters

are shown.

Formula is UL Path Loss- DL Path Loss. By counter meaning, “6” means difference is zero. So it is expected to be all samples in

“6” ideally. More samples less than “3” means there is a DL Path Loss problem more samples greater than “8” means there is

a UL Path Loss problem.

These differences generally points out;

HW Problems,

TRX Power parameters differences,

Cross-connections of feeder between sectors,

RXU definitions, Send mode and Receive mode definitions problems.

You should keep in mind that, if there is a TMA installation in sector path balance would shift to “1” or in use of PBT (Power

Boost Technology) path balance would shift to “11” because of power changes.

Also if there is a Power difference between TRXs of cells, it would affect path balance. In TRX definitions;

Power Level,

Power Fine Tune,

Power Type parameters would decide maximum TRX output power.


S4400A Number of MRs (TA = 0)(times)






























S4430A Number of MRs (TA = 30 or 31)(times)





S4440A Number of MRs (TA = 40 to 44)(times)




S4463A Number of MRs (TA greater than 63)(times)

There are sample stats of TRX based path balance statistic.

As seen on the left for TRX-

1343 there is a Uplink path loss

problem. HW Check should be

done.

3.3.3 COVERAGE GAPS PROBLEMS

For finding coverage gaps;

”Numbers of MRs based on TA per TRX”,

“Radio Link Failure Measurement based on TA per TRX”,

“TCHF Receive Level Measurement per TRX”,

“TCHH Receive Level Measurement per TRX” measurement sets should be used.

“Numbers of MRs based on TA per TRX” counters are shown below;

These counters are MR samples in each TA based on TRX.


S4400B Radio Link Fa i lures (TA = 0)(times)






























S4430B Radio Link Fa i lures (TA = 30 or 31)(times)





S4440B Radio Link Fa i lures (TA = 40 to 44)(times)




S4463B Radio Link Fa i lures (TA greater than 63)(times)

As seen in below graph, cells have some overshooting and coverage gaps.

“Radio Link Failure Measurement based on TA per TRX” counters are

shown on the left;

From “Radio Link Failure Measurement based on TA per TRX” counters, you would have an idea of where cells drop generally

occurs. If it is gathered to one TA, it could be said that in that TA area there is a coverage problem.

“TCHF Receive Level Measurement per TRX ” counters are shown below. There are 128 counter for each RxLevel between 0-

7 (-110 dBm—47 dBm), RxQuality between 0-7.

COUNTER NUMBER COUNTER NAME COUNTER NUMBER COUNTER NAME

S4100B Number of MRs on Downlink TCHF (Receive Level Rank 0 and Receive Quality Rank 0)(times) S4100A Number of MRs on Uplink TCHF (Receive Level Rank 0 and Receive Quality Rank 0)(times)
































































As seen above, in that TRX there is some Uplink signal level problem. Cross connection, VSWR may be problem.

As a result, according to TA distribution, RLT over TA distribution and TCH Receive Level measurements;

If cell’s TA distribution shows cell covers a big area with overshoots, coverage gap related call drop may occur.

If cell’s RLT over TA and TA distribution shows together, cell cover a big area and drop gathers in one TA (or some of

TA), coverage gap related call drop may occur.

If cell’s TCH Receive Level measurements shows cells have unbalanced uplink and downlink RxLevels, it means cell is

a dragon cells with overshoot service areas or have HW problem.

For solutions of coverage gaps and overshoot problems, cells antenna direction, height, mechanic and electric tilt degree may

be changed or cell addition may be done. For HW problems, HW check should be done detailed.

3.3.4 QUALITY and INTERFERENCE PROBLEMS

For finding quality and interference problems;

“Interference Band Measurement per Cell”,

“Neighbor Cell Level Measurement per Cell”,

“TCHF Receive Level Measurement per TRX”,

“TCHH Receive Level Measurement per TRX” measurement sets should be used.

“Interference Band Measurement per Cell” counters are shown below;

With these counters, BTS measure uplink interference according to below signal level table. If there is interference, it means

that Band5 counters should be incremented.

As seen above, generally this TRX has less interference

If Band5 numbers is high, it means cell have uplink interference and frequency change should be considered. (Keep in mind

that BB Hopping will affect this result, for test hopping should be closed)


AS4200A Mean Number of SDCCHs in Interference Band 1(number)

AS4200B Mean Number of SDCCHs in Interference Band 2(number)

AS4200C Mean Number of SDCCHs in Interference Band 3(number)

AS4200D Mean Number of SDCCHs in Interference Band 4(number)

AS4200E Mean Number of SDCCHs in Interference Band 5(number)

AS4207A Mean Number of TCHFs in Interference Band 1(number)

AS4207B Mean Number of TCHFs in Interference Band 2(number)

AS4207C Mean Number of TCHFs in Interference Band 3(number)

AS4207D Mean Number of TCHFs in Interference Band 4(number)

AS4207E Mean Number of TCHFs in Interference Band 5(number)

AS4208A Mean Number of TCHHs in Interference Band 1(number)

AS4208B Mean Number of TCHHs in Interference Band 2(number)

AS4208C Mean Number of TCHHs in Interference Band 3(number)

AS4208D Mean Number of TCHHs in Interference Band 4(number)

AS4208E Mean Number of TCHHs in Interference Band 5(number)

Interference Band Level Threshold of the Interference Band

Interference band 1 -105 dBm to -98 dBm





INNER PARAMETER Name Value

Neighbour Cell Interference Level Threshold 0 0








“Neighbor Cell Level Measurement per Cell” counters are shown below.

According to inner BSC parameter settings, these counters

incremented when measured Neighbor Cell signal level and serving

cell signal level difference greater than related threshold. These

thresholds are shown on the left.

As seen below, serving cell measures all BCCH in its active Ba List

and decodes BSIC (not needed to be neighbor, but BCCH frequency

should be in active Ba List). According to thresholds, co-channel and adjacent channel interferer of serving cells could be

found.


S363Number of MRs in Which the Signal Strength Difference Between the Serving Cell and the

Neighbor Cell is Smaller Than the Neighbor Cell Interference Level Threshold 1(number)


Neighbor Cell is Greater Than the Neighbor Cell Interference Level Threshold 1(number)













“TCHF Receive Level Measurement per TRX” counter may be used for detecting interference problem also. Quality problems

like high Rxquality may be caused by low signal level. But interference means quality is bad in good signal level also. As seen

below with these counters, quality in good and bad signal levels for uplink and downlink could be detected.

As seen upper graph shows uplink RxLevel-RxQual

distribution, lower graph shows downlink RxLevel-RxQual

distribution. From the graphs, it could be said that, there is

an uplink signal level problem but no interference

problem.

As a result, if quality problems exist in a cell, with help of

above stats we should define is there an adjacent or

cochannel frequency or is it related with signal level.

If it is frequency, with help of neighbor cell level

measurement we could find the best frequency for cell.

If it is a signal level problem we should analysis for

coverage gap and HW problems.

3.3.5 MISSING NEIGHBOR PROBLEMS

Another cause of high drop rate is missing neighbor. Missing neighbor may be a real closer cell to serving cell or because of

serving cell overshoot there is a far away cell that should be neighbor.

Best way to find missing neighbor is analysis with help of “Neighbor Cell Level Measurement per Cell” counters.

These counters collects all BCCH-BSIC reported by MS in MRs for serving cell. By thresholds in BSC Parameters, related

counter is incremented according to signal level difference between serving cell and measured BCCH-BSIC.

For finding missing neighbor, we should collect “Neighbor Cell Level Measurement per Cell” for a period (keep in mind that

active ba list of serving cell should be modified as contain all BCCHs). Than with help of MRs on TCHs counter, you could find

which BCCH-BSICs are measured above a certain threshold. Than in these measured BCCH-BSICs, which ones are defined as

neighbor which ones are not, you could find. (Keep in mind that same BCCH-BSIC in an area may affect reliability of result. So

try to give same BCCH-BSIC to cells that distance between them are as far as you can).

For example from analysis this cell should be defined as neighbor with serving cell.

Drop Analysis in Huawei

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