GSM - Paging Success Rate (PSR) Analysis

Paging success rate can be degraded due to increase in MOC/MTC attempts, low TCH availability of source and neighboring cells, high LAC/BSC utilization. Following steps should be taken to analyze the root cause:

• Check for MOC/MTC trend - increase may cause high PPS (Paging Per Second) causing paging discards, indicating paging capacity limitation. LAC splitting could be done to resolve the issue
• Examine TCH Availbility of sites in the affected BSC
• Inspect cell level paging stats from the core network to zero in on the problematic LACs
• Parameter discrepancy between BSC and MSC can cause degradation - check parameters such as Location Update Timer, paging retransmissions by MSC, paging times etc.
• Interference, low coverage due to large distance or dense areas, path balance issues contribute to PSR degradation

UMTS Drive Test Basic Analysis

A basic overview of UMTS drive test analysis comprises of two key KPIs which are RSCP and EcIo corresponding to coverage and quality. The common cases and their remedies are presented below:

1. Bad RSCP and bad EcIo (Coverage): This means weak coverage of the serving cell which should be improved to better the EcIo
2. Good RSCP and bad EcIo (Pilot Pollution/High Cell Load): If the issue is due to multiple servers (pilot pollution) having RSCP within 3dB, dominance of one cell should be formed. For high cell load problem, carrier expansion or traffic balancing are some ways of improving the EcIo.
3. Bad RSCP and good EcIo: Low cell load or no handover in the area represents this condition. 

An example of pilot pollution issue is shown below:

UMTS Paging Success Rate

Paging success rate is a KPI that can be checked if there are complaints involving user not responding messages or missed call notifications. If paging success rate is degraded, it is mainly due to poor coverage. In such case, below actions may be taken:

• increase minimum required received level (QRxLevmin) (eg:-111 to -105) and minimum required quality level (qqualmin) (eg: -18 to -15) of worst cells
• increase PICH power by a few dB (eg: -7 to -5) and increase downlink DCH AC threshold (eg: 85 to 95)
• reduce detected preamble threshold (dB) (eg: -21 to -24)
• increase PRACH initiation Tx power constant value (dB) (eg: -21 to -18)
• Reduce Location update timer both at the core and RNC (say from 3 hour to 1 hour)

Paging flow chart is given below for understanding.

Note:
Paging type 1 = Idle mode
Paging Type 2 = Dedicated mode

BS PA MFRMS - PSR Alcatel-Lucent

Improvement in PSR (Paging Success Rate) can be achieved by tuning of BS_PA_MFRMS and reducing Paging discards. Paging discards are mostly due to congestion in the BSC, on the Abis link and/or on the PCH (Paging Channel) ie Air interface.

Parameter:

• BS_PA_MFRMS

Target Cells: Cells with higher number of paging discards

Theory: 

• This parameter defines the the number of 51 multiframes between two consecutive occurrences of Paging group (a number of pagings)
• Higher value means less number of pagings will be transmitted in a given interval thereby conserving lesser power of the MS
• Reducing this parameter increases number of pagings per paging group (for a given value of MSC paging timer T3113) and therefore probability of no paging response decreases

High SDCCH Blocking Statistical Analysis

SDCCH Blocking is a critical KPI that depicts the quality of optimization in a network as this KPI is mostlty controlled via soft optimization. The considerations for maintaining this KPI are as follows:

1. SDCCH/TCH Availability %
1. Many times, the SDCCH traffic is enough to be carried in defined channels, but still the blocking is high. This could be mostly due to momentary surge in traffic or site fluctutation causing blocks for a small portion of an hour, thereby averaging the traffic/availability in the hour.
2. SDCCH Drops
1. TA Analysis
2. Interference (Co/Adjacent)
3. TCH Congestion
4. Equipment Failure
5. Low output power
3. SDCCH Channels/Traffic/Blocking (Erlang Table)
1. SDCCH Addition (Static/Dynamic)
2. SDCCH/TCH Conversion Timer
3. Maximum SDCCH Channels Threshold
4. Penalty Timer (Set PT = 31 of cell)
5. Increase CRH (Cell Reselect Hysteresis) if cell is on LAC Boundary
6. Directed Retry (Forced)

KPIs Thresholds

What should be the values of network KPIs to be considered as degraded? Different operators have their own targets and it varies greatly depending upon vendor SLA (Service Level Agreement), Terrain (Plain/ Hilly/), Urban/Rural Area etc. However general idea is presented below:

• DCR % (Dropped Call Rate) < 1-2%
• HOSR % (Handover Success Rate) > 95-98%
• TCH Blocking % < 2% (GoS Standard)
• SDCCH Blocking % < 0.1%
• TRX Efficiency % (TCH Seizures/TCH Call Attempts X 100) > 90-99%
• IBI % (Band 4+5) < 1%

Major KPIs

The major KPIs that need to be monitored on daily basis on BSC/Cell/TRX level in a network are:

1. DCR  % (Dropped Call Rate)
2. HOSR % (Handover Success Rate)
3. TCH Blocking %
4. SDCCH Blocking %
5. TRX Efficiency % (TCH Seizures/TCH Call Attempts X 100)
6. IBI % (Band 4+5)