Optimization Processes

Network Optimization process involves the following activities:

• FIRST SET THE CRITERION (GOAL) OF OPTIMIZATION PROCESS

o BASELINE & TARGET KPI’s.

o DELIVERABLES

• CONDUCTING A BASELINE PHYSICAL AUDIT

• REMOVING ALL SERVICE AFFECTING ALARMS

• IDENTIFYING POOR COVERAGE AREAS

• IDENTIFYING CAPACITY CONSTRAINTS & OVERUTILIZED CELLS

• VARIOUS KPIs with Root-Cause-Analysis of problems.

o Frequency Plan (BCCH & TCH)

o Neighbor plan

• CONDUCTING A GSM SYSTEM PARAMETERS AUDIT

• Deliverables of an Optimization activity:

o Baseline Drive test comparison with post implementation results.

o Statistical comparison of baseline & improved network.

o Parameter Audit report.

o Physical parameter inconsistencies.

o Frequency & neighbor plan inconsistencies

o Recommendations for

Coverage

Capacity

Physical Optimization

Location Area Optimization.

Troubleshooting KPI’s

This sections contains information to control & optimize the following w.r.t. Nokia Systems

1. SDCCH Drop

2. SDCCH Blocking (See SD Drop)

3. TCH Drop

4. Handover Failures

5. TCH Blocking (See Handover Failure)

6. Downlink Quality

7. Uplink Quality

Probable Reasons for SD Drop • A bis failure. • Path unbalance between DL/UL caused by difference in sensitivity between BTS & MS. • Co-BCCH Frequency and BSIC in the nearby BTS Cells in a Coverage area. • SDCCH defined on TRX having poor path loss. • High Interference level. • High SD congestion. • Greater Rx level access min. • Due to heavy location updates on the cell. • Hardware Issues.

SD Drop Check Points 1. A bis failure.

a. Check PCM Errors and carry out PCM Checks on regular Basis 2. Path unbalance between DL/UL caused by difference in sensitivity between BTS & MS.3. Co-BCCH Frequency and BSIC in the nearby BTS Cells in a Coverage area.

a. Clearing ZEAT on regular Basis. All Network Effecting Alarms to be monitored for Clearance.

4. SDCCH defined on TRX having poor path loss. a. ND Report 208 – Shift SDCCH from the TRX with Poor Path Loss/Get the Hardware

Checked. 5. High Interference level

a. ND Report 190 – Get it Checked for any Uplink Interference, SD requires better C/I. 6. SD congestion.

a. Allocate Dynamic SDCCH if needed or increase SD Allocation seeing the TCH Traffic. b. If SDCCH congestions occurs accompanied with High HO Failures, check the LAC of the

source cells & its neighbors. Try to avoid many HO to different LAC if cell is not at the boundary f the LAC. If the cell is at the boundary & neighbor definitions are all OK, then you must check if a LAC re-dimensioning of the problem area is required. In addition to LA, you should also be able to visualize your RA(Routing area) boundaries. If there’s significant movement of Data users across this LA/RA boundary then RA need to be dimensioned accordingly.

c. SD Congestion could also be caused by certain large quantity SMS user (Banks, stock brokers etc). This congestion would appear only at specific time intervals. Increase the SD in the cell to peak requirements of the cell.

7. Greater Rx level access min. a. Less than -102dBm. MS should Access the Network in good Coverage Area.

8. Due to heavy location updates on the cell. a. Increase Cell Reselect Hysterises up to -10db (Mostly on BSC Location Boundaries). b. Increase location area update timer from 4 to 6 Hrs.

9. BTS Hardware Issues, All Connector Checks to be done for BTS and Antenna Cable Path to be checked till Antenna Port. Any major Alarm on ZEOL to be monitored and Cleared.

Probable Reason for TCH Drop 1. Interference level. 2. Poor coverage. 3. Poor path loss between different TRX. 4. Poor adjacencies definition. 5. Transcoder failure. 6. Abis failure (PCM related faults). 7. BTS Hardware Issues. 8. High TA Value/Calls Originated by far of Areas (Big Coverage Area for respective

Cells).

TCH Drop Check Points

1. Interference level a. To reduce CI for the respective Network Cells. Frequency Plan Checks for

achieving better CI ratio in the network. 2. Good BSIC and HSN Planning. Parameters Checked on regular Basis from the

BSC Dump.a. ND Report 196 to be checked regularly for Interference recorded on TRX

basis. 3. Poor Coverage – Major call drops due to sudden loss of Signal Strength

a. Proper Coverage Mapping over defined Coverage Area Per Site. Physical Audit from Source to target and vice versa to be done keeping Clutter in View for proper Coverage Boundary definition.

b. High TA or High Coverage Area – ND Report 232 to be checked. c. Keep Rx level access min----(-102dBm or less, -100dbm good to attain

and sustain Calls ) so that only the MS in good coverage area will allowed to make a call.

d. Make RLT value high for Remote sites (Cells on the Rural Side can be looked Into, RLT = 20/24 proposed for City Cells and RLT = 28 for the Rural Cells in the Network).

4. Poor path loss between different TRX.a. Path unbalance between DL/UL caused by difference in sensitivity

between BTS(-110dBm) & MS(-102dBm). b. Check ND Report 208 for the same on regular basis.

5. Poor adjacencies definition (Related to HO Definition). 6. Transcoder failure. 7. Abis failure (PCM related faults). 8. Hardware Issues, All Network Effecting Alarms from ZEOL to be monitored for

Clearance. .

Probable Reason for Handover Failures

1. Neighbours Definition with Co BCCH and BSIC. 2. Wrong HO Synchronisation. 3. Non Symmetrical (One Way Neighbours). 4. Adjacencies Discrepancies. 5. High TCH Congestion. 6. Missing Potential Neighbours. 7. Missing Frequencies on Active State of BA List. 8. Creation of unwanted far of Neighbours with Low Signal Strength. 9. Abis failure (PCM related faults). 10.VSWR-DAC Values Issues. 11.BTS Hardware Issues.

Handover Failures Check Points 1. Neighbours Definition with Co BCCH and BSIC.

a. ND Report 62 – Neighbours with same BCCH. b. ND Report 76 – Neighbours with Co BSIC.

2. Excess or too-few neighbors for source cellsa. ND 070 for BTSs with maximum number of adjacencies b. ND 071 for Cells with minimum number of adjacencies

3. Wrong HO Synchronisation. a. ND Report 67 – Synchronous Neighbours (Same BCF) / Non

Synchronous (Different BCF).4. Non Symmetrical (One Way) Neighbours.

a. ND Report 61 –One way Neighbor Definitions5. Adjacencies Discrepancies.

a. ND Report 60 – Wrong Definitions of Source Parameter in Target Cell.6. High TCH Congestion.

a. Source Cell – Putting high HO Margins, Directed Retry & TRHO (BLT to be set accordingly).

b. Target Cell - Reducing Coverage area , Implementing TA Value or Implementing Half Rate.

7. Missing Potential Neighbours.a. ND Report 73 to be checked – Missing Neighbour Frequencies with High

SS should be defined. b. Double BA List should be Activated for Neighbour Audit.c. Missing Frequencies on Active State of BA List if Double BA list Option

Activated.8. Creation of unwanted far of Neighbours with Low Signal Strength.

a. Deletions of those neighbors with i. Poor ranking with TGT.ii. Poor Success History over last few days.iii. Far away neighbours (Distance formula in Excel – Easiest Way)

9. Abis failure (PCM related faults).10.BTS Hardware Issues

a. Alarmsb. VSWR checkc. Site DAC Values Issues - DAC Clock & ET Mapping check.

Probable reasons for poor Downlink Quality1. Poor Frequency plan (BCCH)2. Interference in DL3. Overshoot of neighboring cells.4. Poor Level on Downlink5. Fault in BCCH TRX6. External interferences – Restricted area/Electronics equipment

Factory/Jammers.

Downlink Quality Checkpoints

1. Check the BCCH & BSIC Plan - (ND 111) for frequency plana. Remove Co-BCCH and Co-BSIC frequencies from neighborhood

2. Interference in DLa. Check for Adjacent BCCH in neighboring sites & remove them. A good

design should have a difference of -9 dBm between serving and other cell’s frequency for reasonably good C/I.

b. See ND 154 for HO Cause distribution. Power Budget HO cause should constitute more than 60 % of HO decisions.

3. Check the Rx Level of Overshooting sites in the cell’s serving area. a. ND: 232 TA report of neighboring sites will show the extent of overshoot.

4. Poor Level on Downlinka. Possible coverage problem.b. Check ND 213 BTS Doctor or 211 Cell Doctor for Rx Level Versus Rx

Quality distribution per TRX on a cell.c. TMB’s can be used judiciously used to enhance DL Signal level.d. High Gain antennas can also be used where applicable.e. If the maximum users are in-door then an In-Building solution can be

proposed.f. If the maximum users are pedestrian traffic then a street level microcell

can be planned to improve coverage.

5. Faulty BCCH TRXa. If there’s an alarm on the BCCH TRX, take action accordingly. If there’s no

alarm shift the BCCH from one TRX to another & see if the DLQ problem persists. If the problem persists it is a frequency plan issue.

b. Check ND 208 report for path balance issues on the BCCH TRX.

Probable reasons for poor Uplink Quality1. Poor Frequency plan (TCH)2. Interference in UL3. Overshoot of neighboring cells.4. Poor Level on the UL.5. Fault in TCH TRX6. Codec issues.7. Transmission related issues.8. Boosters/Repeater related issues.9. External interferences – Restricted area/Electronics equipment

Factory/Jammers.

Uplink Quality Checkpoints

1. Poor Frequency Plan - (ND 111) for frequency plana. Always resolve DL quality issues before attempting to correct the UL.

2. Interference in ULa. Avoid using Co & adjacent TCH frequencies in the same cell or site.b. Avoid using co TCH on neighboring cells.c. Wrong values of the HSN or MAIO/MAIO Offset.

i. Do not reuse HSN in nearby sites.ii. Review MAIO & MAIO Offsets as per the TCH plan(1x1, 1x3, adhoc

etc).d. In cases where intra-cell handovers are allowed, interference will cause a

lot of intra-cell handovers thus degrading the UL & DL quality (see ND 154 for HO Cause distribution)

3. Overshooting of neighboring cells.a. TCH reuse becomes tight is there’s a lot of overshooting of nearby cells.

Allow only 1 or up to 3 dominant servers only.b. Reduce the overshooting of neighboring cells.

4. Poor level on the uplinka. Possible coverage problem.b. Check ND 213 BTS Doctor or 211 Cell Doctor for Rx Level Versus Rx

Quality distribution per TRX on a cell.c. TMA’s can be used judiciously used to enhance UL level.

5. Fault in TCH TRXa. Check the alarm printouts.(ZEOL)b. ND 190 (BTS UL Quality history at 24 Hour/10 day resolution). Check if

the BTS is within defined interference boundary limits & for how long it has been out of limits of acceptable interference.

c. ND216: BTS Analyzer. Check if the BTS is within defined interference boundary limits.

d. ND:208: Path balance for TCH TRXs

6. Codec Issues

a. Run ND 244 & 245 report for AMR related quality issues.b. Run 53 to see AMR related parameter settings. Check if the Codec

(AMR/Non-AMR) settings are OK. c. Check if the BTS s/w version is OK & supports the codec. d. If the problem is with many sites in a BSC then that BSC’s parameter file

needs to be checked/updated.7. Transmission related issues.

a. Check the BSC ET availability & Quality profile report ND 522.b. Check the TCSM ET availability and quality, ND 523.c. Check the QOS

8. Boosters/Repeater related issues.a. Check for repeaters and/or booster installations. Check for spillage of the

repeater signals in areas not intended to be covered.b. If repeaters are a problem( you will know once you switch off the repeater

for a short duration), adjust the gain of repeaterc. Adjust the repeater antenna & orient it to closest serving cell. DO NOT

latch a repeater with a DISTANT dominant cell.9. External Interferences

a. If you suspect external interference on single TRX, lock the TRX & see if the problem persists. If the problem is resolved then the TRX or its implementation is at fault.

b. If you suspect external interference on the entire site, Lock the site & scan the area served by the site for potential interferers. Somebody may be transmitting the same frequencies in the serving area of affected site.

c. Workaround: If you indeed found an interferer over which you have no control, try allocating a different frequency (beyond 2 MHz). There’s a high probability that the frequency which is being severely interfered now will no longer be interfered after frequency change.

What to check?

1. QOS parameters

a. Dropped call rate

b. Dropped call rate due to radio

c. Cumulative UL/DL quality statistics

d. TCH BH blocking rate

e. SDCCH BH blocking rate

f. (Call setup success rate)

g. (Handover success rate)

ND 270 report for checking the QOS & ND 800 for QOS Survey.

2. RF planning parameters

a. Number of calls

b. TCH RF loss rate

c. SDCCH RF loss rate

d. TCH mean holding time

e. Handovers per call

f. Cumulative UL/DL level statistics

g. Idle channel UL interference

h. Power balance

3. Capacity planning parameters

a. TCH BH traffic (e.g. weekly and average of daily BH traffics)

b. BH activity per subscriber (segment)

c. Total TCH time (per subscriber)

d. SDCCH weekly BH traffic

e. BH paging load

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MISCELLANEOUS CHECKS

FREQUECNY PLAN LAC CHECK – PAGING SUCCESS & FAILURE RATES IN MSCs/BSCs/LACsCORE NETWORK ISSUES

Additional Checks

• Finding the same LAC & CI cells in network• Comparison neighbors of cells in system with reference data base • Showing Number of neighbors for each cell

GSM Parameter check/ Parameter Audit

Comparison of main parameter of cells/BTS/BSC currently in the system with reference data base (recommended parameter set).

Tools used

OEMs : Nokia Siemens, Ericsson, ZTE, Huawei, Alcatel-Lucent, Motorola.

RF Network Planning Tools: Nokia NetAct Planning Tool, Aircom Asset, Atol, EDX, Planet Ev, TEMS CellPlanner & TCP-Universal.

Optimization Tools: Schema’s Ultima Forte.

Drive test tools : Ericssion TEMS, Nemo TOM, Agilent E74xx, Comarco, Xtel and Grayson & Cal Lucent.

Post processing Tools: Actix, Quality of Asset, MapInfo .

Performance tools: Nokia Report builder, Nokia DX200 MML, Ericsson BO .