CCSI_2G RNO BASIC TRAINING

Prepare By: Peter Wylson Marpaung.

Call Phases

establishTCH

connection

establishTCH

connection

getservice

getSDCCH

establishSDCCH

connection

getTCH

callphase

releasephase

Call Completion RateCall Setup Success Rate

SDCCHBlocking(system)

and

SDCCH call

Blocking

TCHBlocking(system)

and

TCH CallBlocking

SDCCHSuccess Rate

Overall Call Success Rate

Mobile Originated Call - Speech (1)MS BTS BSC MSC VLR

CH. REQUEST (RACH)

CH.ACTIVATION

ACK.

IMMEDIATE ASSIGN(AGCH)

SERVICE REQUEST (SDCCH)

AUTHENTICATION REQUEST (SDCCH)

AUTHENTICATION RESP. (SDCCH)

CIPHERING MODE COMM. (SDCCH)

ACK.

TMSI REALLOCATION COMMAND (SDCCH)

ACK

ACK.

SETUP (SDCCH)

Sdcch_Assign

Sdcch_Seiz_Orig or Succ_Seiz_Termor Succ_Emerg_Callor Sdcch_Call_Re_Estor Sdcch_Loc_Updor Imsi Detach (S7)

Check Restrict.

Sdcch_Seiz_Att(and) Sdcch_Busy_Attor Ghost_Ccch_Res

PHYS. CONTEXT REQUEST

PHYS. CONTEXT CONFIRM

ASSIGNMENT COMMAND (SDCCH)

Mobile Originated Call - Speech (2)

SETUP (SDCCH)

CALL PROCEEDING (SDCCH)

ASSIGNMENT REQUEST

CH.ACTIVATION

ACK.

SERVICE REQUEST (FACCH)

ASSIGNMENT COMPLETE (FACCH)

CH.RELEASE

ACK.

CONNECT (FACCH)

CONNECT ACK. (FACCH)

ALERTING (FACCH)

+ Start of BSC trafficMeasurement

+ Start of MSC trafficMeasurement

MS BTS BSC MSC VLR

SETUP (SDCCH)

Tch_RequestTch_Norm_Seiz

or Tch_Req_Rej_Lack

RELEASE (FACCH)

MEAS. REPORT (SACCH)

DISCONNECT (FACCH)

RELEASE COMPL. (FACCH)

CH. RELEASE (FACCH)

SACCH RELEASE

RF.CH. RELEASE

ACK. & CLEAR COMPLETE

Mobile Originated Call - Speech (3)

CONNECT ACK. (FACCH)

DISC. (FACCH)

ACK.

SCCP RELEASE

ACK.

+ End of MSC trafficMeasurement

+ End of BSC trafficMeasurement

MS BTS BSC MSC VLR

Dropped Calls

Dropped calls show the number of abnormal disconnections during call setup or during conversation. From a subscriber point of view, the most serious dropped calls are those that interrupts an ongoing conversation, i.e. a call dropped on the TCH.

1.Radio Link Failure•Every time a SACCH message can not be decoded the radio link time-out counter is decreased by 1. If the message can be decoded the counter is incremented by 2. However, the value can not exceed the initial value.• The initial value is set by the parameter RLT for radio link time-out in the mobile station and by SACCH Multi Frame for time-out in the BSS. • If the mobile moves out of coverage and no measurement reports are received in the BSS, there will be a radio link time-out and the message Channel Release (cause: abnormal release) sent to the mobile station and the SACCH is deactivated in the BTS. A Clear Request message is sent to the MSC. • To be sure that the mobile has stopped transmitting, the BSS now waits RLT SACCH periods before the timeslot is released and a new call can be established on the channel.

Dropped Calls

Radio Link Timeout BSS ≥ Radio Link Timeout MS because MS Should release radio channel first

1. Radio Link Timeout BSS ≥ Radio Link Timeout MS 2. because MS Should release radio channel first3. Too High Radio Link Timeout BSS can cause congestion due to longer channel holding time.4. Too High Radio Link Timeout MS can cause costumer complain due to connect no voice.

Causes of Radio Link Failure• Radio Link Failure event are due to below problem:

– Interference • Internal interference• External interference• Equipment interference

– Poor coverage • Coverage hole• Island sites• Uplink/downlink imbalance

– Improper parameter setting• Radio link timeout, SACCH multi-frames• Handover parameters• Power control parameters

– Equipment problem (Antenna, feeder, combiner, TRX)– Clock problem– Transmission problem

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Radio Link Failure- Interference

Page 11

• Category– Co-channel interference– Adjacent-channel interference– Inter-modulation interference and other external interference

C/I : GSM Recommendation >9 dBPlanning Criteria >12 dB (Non Hopping)Planning Criteria >9 dB (Hopping)C/I is to measure Co channel Interference tolerance.

C/A :GSM Recommendation >-9 dBPlanning Criteria >3 dBC/A is to measure Adjacent channel Interference tolerance.

Radio Link Failure- Interference

Page 12

C/I : GSM Recommendation >9 dBPlanning Criteria >12 dB (Non Hopping)Planning Criteria >9 dB (Hopping)C/I is to measure Co channel Interference tolerance.

C/A :GSM Recommendation >-9 dBPlanning Criteria >3 dBC/A is to measure Adjacent channel Interference tolerance.

Radio Link Failure- Interference

Page 13

Action:– First check equipment problems for inter-modulation interference. Mostly is bad feeder

installation or bad hardware output signal.– Perform drive test to check interference area and distribution of Rx-Quality to find the

interferer frequency for internal interference. Then do Cell/Cluster MAL/MAIO/HSN retune.

– Further search for the interference source with the spectrum analyzer to search external interferer then escalate to proper part. Mostly repeater or illegal transmitter, then escalate to proper part.

– Activate Frequency hopping, DTX (Discontinuous Transmit) and power control functions to reduce internal interference of the system. This is parameter setting.

Analysis:1. If Scan-TRX of cell results in the interference band 3, 4, and 5, usually the interference problem

should be taken into consideration. 2. If there are too many times of good Rx-Level but low Rx-Quality, it means: co-frequency or adjacent

frequency interference or external interference.3. Handover measurement function from outgoing handover attempts distribution. If there are too

many times of handover caused by UL/DL Quality, it indicates possibly there is interference.4. See from Scan TRX for Rx-Quality level of TRX for reference.5. See from Scan TRX for Rx-Level and Rx-Quality upon call drop for reference.

Radio Link Failure- Interference

Page 14

Not Overshoot, but has ICM band 5 and Bad UL Signal Quality

15

Sample of Clear spectrum result Sample of external interference from CDMA which impact to Telkomsel cells performance

DL CDMA Band suspected has too high power that disturb TSEL UL GSM Band (900.2Mhz).

Radio Link Failure- Interference

16

Radio Link Failure- Interference

Consider as interference issue.

Radio Link Failure- Coverage

Page 17

1. Island Sites/Standalone sitesIsland sites is a site which work alone to cover wide traffic area.2. Coverage hole: uncovered area between cells—Blank Spot.3. Signal attenuation: serious fading occurs during signal propagation so that handover cannot be implemented in time and this causes a call drop. 4. The adjacent cell definition: incomplete neighbor relation definition, so that MS keeps conversation in the current cell until it goes beyond this cell coverage edge and as a result, call drop occurs.5. Imbalance UL/DL: If the uplink signal coverage is larger than the downlink signal coverage, the downlink signal of the cell edge will become weak and can easily be “submerged” by the intensive signals of other cells. While if the downlink signal coverage is larger than the uplink signal coverage, MS has to remain under this intensive signal. However, if the uplink signal is too weak or the voice quality is too bad, call drop will occur.

System Balance

Double UL receiver = Double UL Receive power (UL Coverage become wider))

Radio Link Failure- Coverage

Page 19

Uplink Loss is Large (Uplink Coverage is small)

Downlink Loss is Large (Downlink Coverage is small)

Radio Link Failure- Coverage

Page 20

Analysis:Drive test result is the best information to found the coverage problem.1.Idle Receiving level report show proportion of low receiving level times is too large.2.Inter-cell handover measurement function, the level when triggering a handover is too low and the average receiving level is too low.3.Receiving level during a call drop is too low and the TA value before a call drop is big (Check from Scan-TRX report).4.From scanning result, founded undefined adjacent cell receiving level is too high (over-shooting coverage).The average level of undefined adjacent cells is too high (isolated island phenomenon).5. In outgoing-cell handover measurement function, the handover success rate to a certain adjacent cell is low.

Solution for Coverage:– Adjust network parameters

1. Activate EDGE handover2. Faster Edge (ULEDGETHRES/DLEDGETHRES) and Interlayer handover

(HOTHRES)3. Adjust Cell Reselection Parameter (CRO/PT/CRH/RXMIN)

– Add new sites– Increase antenna gain (change antenna type)– Adjust antenna direction (Tilt / Azimuth)

2. Layer 2 Time-OutT200 is a timer of acknowledgement transmission from BTS to MS through LAPD. When BTS transmits a acknowledgement message to MS, T200 times is started in LAPD. If this acknowledgement message is not received by MS until T200 timer is expired then the transmission will be repeated (retransmission).The maximum retransmission is N200+1 times. T200 will be restarted in each retransmission. So, N200 is the maximum number of retransmission of LAPD (Layer-2). If until N200+1 times of retransmission the acknowledgement message, MS still doesn’t receive this message, then the connection will be dropped.

Longer T200 value, means longer BSS to wait. Longer T200 value, means longer channel will hold by an UE. This will cause congestion for sites which have hi Channel utilization.

Shorter T200 Value , means Faster BSS to trigger disconnection. This will cause low “SDSR”.Shorter T200 value , means easy for BSS to release channel which hold by UE previously. This will reduce congestion at cell channel due to shorter channel holding time.

3. Excessive Timing AdvanceThe TCH Drop counters due to Excessive Timing Advance will pegged during the time of disconnection, the last Timing Advance value recorded was higher than the Max TA Parameter. This drop reason is commonly apparent to isolated or island sites with a wide coverage area.Action: Check if the cell parameter Max TA is < 63. Check if the co-channel cells are overshooting.Solution: Set Max TA to a value close to 63. Activate TAHOEN.Faster handover trigger due to TA -> Adjust “TALIMIT” to proper TA value base on site to site distance.Tilt antenna/reduce antenna height/output power, etc. for co-channel cells.

4. Low Signal Strength on Downlink or Uplink or Both LinksNormally a call is dropped at the border of large rural cell with insufficient coverage. Bad tunnel coverage cause many dropped calls as well as so called coverage holes. Bad indoor coverage will result in dropped calls. Building shadowing could be another reason.Action: Check coverage plots. Check output power. Check power balance and link budget. Check if Omni site. Check antenna configuration & type. Check antenna installation.Perform drive tests & site survey.Check TRX with high Fail Number. Solution:Add a repeater to increase coverage in for example a tunnel.Change to a better antenna (with higher gain) for the base station.Add a new base station if there are large coverage holes.Block/unblock TRXAdjust Power control parameter (SET GCELLPWRBASIC/SET GCELLPWR2/SET GCELLPWR3)

On 7th Nov. the power control optimization, improved DL/UL quality to reduce drop calls due to handover.

On 16th Nov. the power control optimization, improved DL/UL quality to reduce drop calls due to handover.

Parameter type

DLAFSREXQUALHIGHT

HRED

DLAFSREXQUALLOWTH

RED

DLAHSREXQUALHIGH

THRED

DLAHSREXQUALLOWT

HREDDLMAXDO

WNSTEP

ULAFSREXQUALHIGHT

HRED

ULAFSREXQUALLOWTH

RED

ULAHSREXQUALHIGH

THRED

ULAHSREXQUALLOWT

HREDULMAXDO

WNSTEP

DLRXLEVPROTECTFA

CTOR

DLRXQUALPROTECTFA

CTOR

Before 16 16 18 18 8 16 16 18 18 8 10 60After 14 14 16 16 4 14 14 16 16 4 10 65

Parameter type

DLFSREXQUALHIGHTHR

ED

DLFSREXQUALLOWTHRE

D

DLHSREXQUALHIGHTHR

ED

DLHSREXQUALLOWTHRE

D

ULFSREXQUALHIGHTHR

ED

ULFSREXQUALLOWTHRE

D

ULHSREXQUALHIGHTHR

ED

ULHSREXQUALLOWTHRE

D

ULRXQUALPROTECTFAC

TOR

DLRXLEVPROTECTFACT

OR

DLRXQUALPROTECTFAC

TOR

Before 18 18 18 18 18 18 18 18 65 10 65

After 14 14 15 15 14 14 15 15 75 15 75

5. Poor Quality on Downlink or Uplink or Both LinksProblem on Bad Quality is usually associated with Co-channel Interference on BCCH or TCH. Faulty MAIO assignment can cause frequency collisions on co-sited cells especially on 1x1 Reuse. External interference is also one possible cause of problem on quality.Action: Check C/I and C/A plots. Check Frequency Plan (Co-BCCH or Co-BSIC Problem).Check MAIO, HOP, HSN parameters.Check FHOP if correctly configured (BB or SFH).Check for External Interference.Perform drive tests.Solution: Change BCCH frequency.Change BSIC.Change MAIO, HOP, HSN.Change MAL.

6. Sudden Loss of ConnectionThere are some common scenarios that could lead to Sudden Loss of connections such as very sudden and severe drops in signal strength, such as when subscribers enter into buildings, elevators, parking garages, etc., very sudden and severe occurrence of interference, MS runs out of battery during conversation, Handover Lost, BTS HW faults, Synchronization or A-bis link fault (transmission faults), and MS Faults.Action: Check BTS Error Logs, Alarms and Fault Codes.Check Fail number per TRX and TS.Check Transmission Link (A-bis).Check LAPD Congestion.Correlate Handover Lost to Drops due to Sudden LossSolution: Fix Hardware Faults and Alarms.Reset TRX with high Fail Number.Ensure that Synchronization and A-bis Link are stable.increase Transmission CapacityInvestigate HO Lost Problem

7. Improper feature activationFeature activation which activated not in proper cell will cause new problem.Incorrect use of radio features such as Dynamic Power Control, handover, Intra-Cell Handover, Frequency Hopping, etc.Action: Check Feature parameter setting.Solution: Correct strange and erroneous parameter setting. Below is the sample

Adjusted 119 cells INTRACELLHOEN YES->NO at 16 Nov, Observe the performance of the adjusted, Call Drops on Radio Interface in Handover State decreased, Call Drops on Radio Interface in Stable State did not significantly improve. Significantly improved the overall call drop number.

8. Bad Parameter ConfigurationSome idle and dedicated parameter which adjusted not in rule will cause KPI degradation.Action: Check parameter setting.Solution: Correct strange and erroneous parameter setting. Below is the sample

After the cell Handover parameters optimization, improved the handover performance to reduce drop calls due to handover.

Parameter type T3103A T3103C T7 T8 T3109 T3105 MAXRESEND

Before 15000 15000 10000 16000 27000 7 30

After 20000 20000 22000 22000 30000 15 60

SDCCH Drop Performance

Low Signal Strength on Down or Uplink The reason for poor coverage could be too few sites, wrong output power, shadowing, no indoor coverage or network equipment failure.Action: Check coverage plots. Check output power. Perform drive tests. Check BTS error logSolution: Add new sites. Increase output power. Repair faulty equipment.Adjust TRX POWER parameter (POWT/POWL)Adjust antenna direction & Tilt

Poor Quality on Down or UplinkAction: Check C/I and C/A plots. Check frequency plan. Perform drive tests.Solution: Change frequency.Adjust TRX POWER parameter (POWT/POWL)Move SDCCH to BCCH TRX

Too High Timing AdvanceAction: Check if the cell parameter Max TA is < 63. Check if the co-channel cells are over-heard.Solution: Set Max TA to a value close to 63. Tilt antenna/reduce antenna height/output power, etc. for co-channel cells.

Mobile ErrorSome old mobiles may cause dropped calls if certain radio network features are used. Another reason is that the MS is damaged and not working properly.Action: .Check MS type from Core team.Solution: Inform operator.

Probable Reasons of Drops on SDCCH

Subscriber BehaviorPoorly educated subscribers could use their handsets incorrectly by not raising antennas, choosing ill-advised locations to attempt calls, etc.Action: Check customer complaints and their MS.

Battery FlawWhen a subscriber runs out of battery during a conversation, the call will be registered as dropped call due to low signal strength or others.Action: Check if MS power regulation is used. Check if DTX uplink is used.

Congestion on TCHThe SDCCH is dropped when congestion on TCH.Action: Check TCH congestionSolution: Increase capacity on TCH or using features like Assignment to another cell (Direct retry), Cell Load Sharing, HCS, Half rate parameter(TCHAJFLAG,TCHBUSYTHRESH) etc.

Probable Reasons of Drops on SDCCH

Handover Performance

Handover Performance

Handover is a key function in a GSM network and a key technology of mobile communication system which make continued conversation become possible. If the handover performance is poor the subscriber will perceive the quality of the network as bad.

target

MSC 1

MSC 2

MSC controlled

BSC 1

out-going

intracell

inter BSC source

BSC 2 in-coming

intercell

MSC controlled

Bad handover Parameter SettingA bad setting of handover control parameters might result that the handover will seldom rank the cell as a candidate.Action: Check parameter setting.Solution: Correct bad parameter setting (GCELLHOBASIC/GCELLHOEMG/GCELLHOCTRL, etc)

Unnecessary Neighboring Cell RelationNone or very few handovers might indicate an unnecessary neighboring cell relation.Action: Check neighbor cell relationsSolution: Check if the relations really should be defined. Remove unnecessary cell relations. Maximum relation are 32 for inter2G and 32 for Inter System (2g to 3G). But recommended are 15 for each handover type. To reduce signaling load.

The Base Station is Defined But Not in Service.Action: Check reason for BTS not in service.Solution: Take action to set the base station in service.

HW faults.Action: Check BTS error log.

Wrong Output Power due to Faulty Transceiver Action: Check output power setting. Check BTS error log

Probable Reasons of Bad Handover Performance

Wrong External Cell ConfigurationThis will cause no handover decisions to the an external cell.Action: Check external cell data (BCCH/NCC/BCC/LAC/CI)Solution: Change it to correct Value.

Permitted Network Color Code problemIf NCCPERMIT doesn’t include neighboring cell’s NCC, there will be no handovers.Action: Check NCCPERMIT.Solution: Add NCC of neighbors to NCCPERMiT.

Wrong Use of LayerAction: Check Layer related parameters. Wrong layer will influence traffic share strategy. Then it will give impact to other KPI.Solution: Change to proper value. SET GCELLBASICPARA: LAYER= x;

Poor inter-MSC/BSC handover performanceIf the cell is at the border of inter-BSC or inter-MSC, poor inter-MSC/BSC handover performance will cause few or no handover attempts.Action: Check inter-MSC/BSC handover performance

The MS Measures Signal Strength of Another Co- or Adjacent. Action: Check frequency plan..Perform drive tests.Solution: Decrease interference. .

Bad Use of Radio Network FeaturesIncorrect use of radio features such as Dynamic Power Control, handover, Intra-Cell Handover, Frequency Hopping, etc.Action: Check Feature parameter setting.Solution: Correct strange and erroneous parameter setting.

Probable Reasons of Bad Handover Performance

CongestionA high congestion might lead to dragged calls (handover performed at a improper location) and a lot of unsuccessful handovers.Action: Check TCH congestion at both origin and destination cells.Solution: Add more TCH capacity. Activate Half rate feature (TCHAJFLAG), Adjust Share traffic parameter.

Timer Expire After MS is Lost (T3103A/C,T7,T8,etc)The MS never answers the base station.Action: Check coverage. Check interference. Longer the timer may improve it, but will make longer channel holding time.

Link Connection or HW FailureAction: Check BTS error log. Perform site visit. Perform link performance measurements.Solution: Repair faulty equipment.

Bad Antenna Installation Action: Perform site survey and check antenna installation. Check antenna cabling.Solution: Adjust antenna installation, antenna type or cabling.

Antennas Connected to Wrong Feeder Action: Perform site survey and check antenna installation. Check antenna cabling.Solution: Correct the antenna to the right sector.

Incorrect Down Tilt Action: Perform site survey and check antenna installation.Solution: Correct antenna tilting. To much down tilt value will cause blank coverage and dragging. Too Big tilt value will cause overshoot till N Layer, which neighbor not create at N layer area.

Probable Reasons of Bad Handover Performance

TRX346 & 223 Hardware problem of site 2131103_AntsnKecilTimur. After solved the problem, the incoming handover success number became normal.

Link Connection or HW Failure

SDCCH Congestion

Low AvailabilityAction: Check SDCCH Availability. Check if the channels are manual, control or automatic blocked.Solution: Change and repair faulty equipment. Review the O&M procedures.

Increasing Traffic Demand The high traffic could be related to an occasional event or due to a long term growth.Action: Check if short term traffic growth. Make trend comparisons. Check SDCCH dimensioning.Solution: Increase the number of SDCCH channels. Note, that an increase may lead to the need for new transceivers.

Long Mean Holding Time If the mean holding time is long, this generates a higher traffic load.Action: Check SDCCH Mean Holding Time.

Too Frequent Periodic RegistrationAction: Check Random Access Distribution. Check the timer T3212 in the BSC and the parametersBTDM and GTDM in the MSCSolution: Decrease the periodic registration (t3212) and Adjust CRH (Cell Reselection Hysteresis).

Probable Reasons of SDCCH Congestion

Location Area Border CellIf the cell is situated on a misplaced Location Area border, this means that unnecessary many normal LUs are performed.Action: Check site position and location area border. Check Location Update Performance. Check parameter CRH etc.Solution: If the site is located close to major road or railway, consider to move the Location Area border. Increase the hysteresis CRH. The CRH is the hysteresis value used when the MS in idle mode crosses a LA border. The default value for this parameter is 4. If a high number of Location Updating occurs in a Location Area border cell, a higher CRH can be set in order to reduce the number of LUs.

Extensive SMS UsageExtensive SMS usage increases the SDCCH traffic and could cause congestion if badly dimensioned SDCCH channels.Action: Check SMS activity.Solution: Re-dimension the SDCCH channels with consideration taken to SMS usage.

Cell Broadcast UsedAction: Check if Cell Broadcast is active. .If active, check if it is used by the operator.Solution: Remove Cell Broadcast if not used (SDCCH_CBCH).

IMSI Attach/Detach in Use. An introduction of IMSI attach/detach will increase the traffic on SDCCH. However, the benefits are that the paging success rate will increase. The recommendation is to use Attach/Detach.

BTS /Cell Software HangAction: Reset BTS . It will restart all hardware onsite.

.

Probable Reasons of SDCCH Congestion

Congestion on TCH Action: Check TCH Congestion Solution: Increase the TCH capacity.

Congestion on Signaling RoutesAction: Check signaling performance & transmission capacity.Solution: Add more transmission capacity or re-route traffic if possible.

False AccessesNo response from MS after Channel Request. The system waits about T200 seconds before performing a disconnection and the channel is available again.Action: Check frequency plan. Check interference.Solution: Improve frequency plan and reduce interference. Reduce T200 SDCCH value.

Faulty TransceiverAction: Check BTS error log.Solution: Change & repair faulty equipment

Probable Reasons of SDCCH Congestion due to Long Mean Holding Time

TCH Congestion

Increasing Traffic Demand The high traffic could be related to an occasional event or due to a long term growth.Action:. Check if short term traffic growth. Make trend comparisons..Check TCH dimensioning. Check the use of congestion relieving features such as Assignment to Worse cell, Cell Load Sharing and HCS.Solution: Increase the number of transceivers. But check for frequency availability.

Bad DimensioningBad allocation of TCH in a system may cause unnecessary congestion. Investigate if possible to move transceivers from non-congested areas to congested areas (Rebalancing). Of course, the base station type, current number of transceivers, floor space, combiner type, etc., should be considered before a recommendation to move transceiver could be made.Action: Check TCH traffic and dimensioning.Solution: Re-dimension the TCH.

Hardware Fault & Installation Fault Faulty equipment will lead to that all time slots could not be used for handling traffic causing congestion. Low availability can happen if the channels have been manually or automatically blocked and taken out of service.Action: Check TCH Availability. Check TCH blocking.Solution: Change and repair faulty equipment. Review the O&M procedures.

Probable Reasons of TCH Congestion

High Antenna Position A high antenna position could mean a too large service area. Also antennas placed on hilltops will cover large areas. A large coverage area might mean that the cell takes a lot of traffic.Action: Check antenna height. Check antenna type. Check antenna tiltSolution: Lower antenna if there is no risk for loss of coverage (no coverage at all). Tilting of the antenna or changing antenna type may also decrease the coverage area.

Wrong Use of LayerAction: Check Layer related parameters. Wrong layer will influence traffic share strategy. Then it will give impact to other KPI.Solution: Change to proper value. SET GCELLBASICPARA: LAYER= x;

Low Handover Activity A low handover activity may lead to congestion if the MS is forced to stay on a cell longer than necessary.Action: Check if congestion in neighboring cell. Check handover performance. Check neighboring cell definitions. Missing relationscould cause handover problems.Solution: Correct handover parameters such as too high or too low hysteresis/Thresholdvalues, missing neighbor relations, one-way handovers.

Low Congestion in Surrounding Cells Action: Check congestion in neighboring cells. Review neighbor cell list. New relation could relieve the congestion. Solution: Add new neighbor cells if appropriate. Then adjust CRO/GCELLHOBASIC/GCELLHOEMG parameter.

Probable Reasons of TCH Congestion

PS Access Success Rate

Radio Channel CongestionHigh PS traffic compare to available PS channel.Action:. Check if PS has higher traffic load but CS is not. Or PS and CS has same high load.Solution: Add more PS capacity (TCHFR or PDTCH)—SET GTRXCHAN and adjust PS channel conversion threshold.

TCHs are set to TCHHRWhile a TCH is on TCHHR status, then it can not become a PS channel.Action: Check PS traffic compare to TCHFR+PDTCH.Solution: Change TCHHR to TCHFR as initial channel state.

Fail Conversion from TCH to PDTCHWhile PDTCH capacity in a cell already full, then system will try to convert TCHFR to PDTCH. But it will fail if TCH in congestion stateAction: Check TCH Availability. Check TCH blocking.Solution: Change and repair faulty equipment. Review the O&M procedures. Do CS traffic share to improve PS capacity.

Imbalance/Overload PDTCH distribution at DSP board.DSP use in BSC to process PS service before forward to SGSN. When DSP load is more than 80% then some cells under this DSP will have low PS accessibility.Action: Check DSP load distribution for every slot number.Solution: If Imbalance load: try to make Cell-DSP mapping become automatic (SET PSCELLTODSP: IDXTYPE=BYBSC;)If Overload DSP: Add more DSP board.

Abis Congestion2G system using PCM30 technology. 1E1=2.048Mbps. 1 E1=32 Abis Timeslot. 1 Abis timeslot=4 Sub slot.Action: Check Abis Load between E1 if Site has more than 1 E1. Sometime, 1 Sites has 3 E1 (example), but load mostly at E1 number 2. This is not good for TR which connected to E1 number 2.Solution: Balance E1 Load with TRX-E1 mapping. Add E1 if existing E1 already has >80% utilization.

Probable Reasons of Low PS Access Success

E1 Description

1 E1 contain 32 timeslot (0-31)1 Timeslot in E1 contain 4 Sub slot.1 E1 =2.048 Mbps1 Timeslot in E1 = 2.048 Mbps/32 = 64 Kbps1 E1 Sub slot in E1 = 64 Kbps/4 = 16 Kbps

If user get 1 E1 sub slot and single/alone TBF in 1 PDTCH, then he has 16 Kbps throughput at maximum (Theoretical). Then we have coding scheme to compress the data become smaller. GPRS has CS1-CS4/EDGE has MCS1-9.

HI TBF number In Uplink and DownlinkHigh PS traffic compare to TBF capacity in 1 PDTCH.Action:. Check for maximum TBF in BH.Solution: Adjust UL/DL multiplexing. Too high will cause throughput degradation/Too Small will cause high throughput but small TBF capacity.

Probable Reasons of Low PS Access Success

Parameter LQCMODE T3168 UPDYNCHNTRANLEV DWNDYNCHNTRANLEV PDCHUPLEV PDCHDWNLEV

Before LA 500ms 40 40 70 80

After IR 1000ms 20 20 70 160

LQCMODE: Use IR can to obtain better effect when the UM transmission quality is poor.T3168:Decrease the number of times of MS no response .UPDYNCHNTRANLEV: Faster uplink switch PDCH request.DWDYNCHNTRANLEV: Faster downlink switch PDCH request.PDCHDWNLEV:TBF to increase the number of carrying PDCH.

GPRS AND EDGE

Both GPRS and EDGE using same 2G GSM technology. EDGE developed to improve 2G data Rate better than GPRS.EDGE is a method to increase the data rates on the radio link for GSM. Basically, EDGE only introduces a new modulation technique and new channel codingthat can be used to transmit both packet-switched and circuit-switched voice and data services.

Although GPRS and EDGE share the same symbol rate, the modulation bit rate differs. EDGE can transmit three times as many bits as GPRS during the same period of time. This is the main reason for the higher EDGE bit rates.

GPRS AND EDGE

EDGE using GMSK for MCS1-4 then 8PSK for MCS5-9.

GPRS using GMSK modulation technology.

Both GPRS CS1 to CS4 and EGPRS MCS1 to MCS4 use GMSK modulation with slightly different throughput performances. This is due to differences in header size (and payload size) of the EGPRS packets.

Frequency Hopping

There are 3 Types of Frequency Hopping:1. Baseband Hopping (BB)

Baseband Hopping concept, assign Frequency for every TRX in a cell.This Frequency planning method has less capacity, because limitation TRX count base on frequency availability. 1 TRX= 1 Frequency

Minimum MAL Frequency should provide/Sites= Count TRX Hopping

2. Synthesizer Frequency Hopping (SFH)• SFH 1*3• SFH 1*1

SFH Concept offer more TRX capacity with efficient frequency management. Result are:• increment capacity which improve CS and PS performance• Improved voice quality and prevention of dropped calls in GSM

Minimum MAL Frequency should provide= 2 * Count TRX Hopping * 3

3. Enhanced SFH

Frequency Hopping Parameter

• MAL (Mobile Allocation Set): MA is the set of available RF bands when hopping, containing at most 64 frequency

carriers. The frequency being used must be those of the available frequency

• MAIO (Mobile Allocation Index Offset) MAIO is used to define the initial frequency of the hopping.

Be careful to configure the MAIO of same timeslot in all channels, otherwise

interference occurs.

• HSN (hopping sequence number) HSN is used to define the hopping sequence from one frequency list.

HSN=0： cycle hopping.HSN≠0： random hopping. Every sequence number corresponds a pseudo random sequence.

Baseband Frequency Hopping Mapping

Every TRX have 1 Frequency result. If we have 4 TRX then we should have 4 clean frequency.

SFH 1*3 Frequency Hopping Mapping

MAL is drawn up from high to low

Every sector has “different” MAL.MAIO is depend on TRX HOPPING Count.

SFH 1*1 Frequency Hopping Mapping

Every sector has “Same“ MAL.MAIO is depend on TRX HOPPING Count.

MA LIST 1*10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

SECTOR1 F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 F13 F14 F15 F16 F17 F18 F19 F20 F21 F22 F23 F24 F25 F26 F27 F28 F29 F30 F31 F32 F33SECTOR2 F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 F13 F14 F15 F16 F17 F18 F19 F20 F21 F22 F23 F24 F25 F26 F27 F28 F29 F30 F31 F32 F33SECTOR3 F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 F13 F14 F15 F16 F17 F18 F19 F20 F21 F22 F23 F24 F25 F26 F27 F28 F29 F30 F31 F32 F33

Cell Selection / Reselection

Cell Selection and Reselection Parameter

C1 is a cell selection algorithm employed in GSM and GPRS. The algorithm uses the power received from cells plus additional parameters in order to assess the cell that will provide the best radio connection for the MS (Mobile Station).

C2 is the GSM cell reselection algorithm. Once the MS (Mobile Station) has camped onto a cell it will continue to assess the surrounding cells to ensure it is monitoring the cell that will offer the best radio connection. As the user moves the camped on cell may become unsuitable. This situation will generate a cell reselection.

C31 is a criteria based algorithm used as part of the GPRS cell reselection process. It is used to assess if prospective cells qualify as reselection candidates prior to applying the C32 GPRS cell reselection algorithm.

C32 is the GPRS cell reselection algorithm. Once the MS (Mobile Station) has camped onto a cell it will continue to assess the surrounding cells to ensure it is monitoring the cell that will offer the best radio connection. As the user moves the camped on cell may become unsuitable. This situation will generate a cell reselection.

Cell “Selection” ParameterC1 = (A−max(B,0))where •A = Average Received level from Cell − RX_ACCESS_MIN (in dBm) •B = MS_TXPWR_MAX_CCH − P (in dBm). •The Average received level (AV_RXLEV) is found by averaging RXLEV samples over a period. •RX_ACCESS_MIN is a cell parameter which set minimum allowed RXLEV for an MS to access that cell.•MS_TXPWR_MAX_CCH is the maximum TX power an MS may use when accessing the system (using RACH). •P is the maximum RF output power of the MS, usually 33dBm for a handheld GSM900 and 30dBm for a handheld GSM1800 MS. Often the latter term in C1 equals 0 and equation (1) can be simplified to;

C1 = AV_RXLEV − RX_ACCESS_MIN

For example, if the minimum allowed level to gain access to a cell is −100dBm and the received average level at the cell’s BCCH frequency is -80 dBm, MS calculates C1 as +20 for that particular cell. MS camps to the cell with the highest C1 value. There is an exception to the standard procedure described above. When MS evaluates C1 values for cells belonging to a different Location Area (LA), it subtracts a parameter called CELL_RESELECT_HYSTERESIS from the C1 value, which means that those cells are given a negative offset. The reason for this is that changing LA requires a Location Update (LU) procedure that consumes network signaling capacity. Thus, by assigning a negative offset to C1, unnecessary LUs caused by slow fading can be reduced. MS receives information of the cell dependent CELL_RESELECT_HYSTERESIS values through BCCH.

Cell “Re-Selection” ParameterCell reselection criterion C2 is defined as C2 = C1 + CELL_RESELECT_OFFSET − TEMPORARY_OFFSET*H

when timer T > PENALTY_TIME then H=0 >>>> C2 = C1 + CELL_RESELECT_OFFSET timer T PENALTY_TIME then H=1 >>>> C2=C1 + CELL_RESELECT_OFFSET − TEMPORARY_OFFSETPenalty Time=31 >>>> C2 = C1 - CELL_RESELECT_OFFSET

BCCH Re-selection in Border LAC

Higher CRH value will hold an UE in a cell longer. Then give decrement of Location update attempt.