GSM - TCH Availablility

TCH Availability is the ratio available TCH (Full Rate, Half Rate, dynamic radio channels) to the total available and unavailable TCH (Full Rate, Half Rate, dynamic radio channels). Generally, TCHA follows the pattern of available TCH/F and dynamic radio channel.

TCHA is one of the first KPI that should be checked in environments where power outages are common. It degrades blocking, DCR, HOSR and other KPIs to a large extent. More often than not, low TCHA of neighboring cell causing severe KPI degradation in a particular cell. It is always safe to revive TCHA of the network before implementation of parametric or design changes for KPI improvement.

Major alarms causing low TCHA are STP link association broken (transmission), and GENSET on (power outage).

UMTS Low CS/PS IRAT Handover Success Rate Analysis

Analysis of low CS/PS IRAT HOSR can be done using the below mentioned procedure:

1. Neighbor Audit - removal of illogical neighbors is equally important as adding Tier 1 cells
2. External neighbors configuration check - Often times, BCCH/NCC/BCC is modified and should be updated in external cells on the UMTS end
3. Parameter check
4. GSM State mode - can be modified in case of severe handover failures on one relation 

Apart from these steps, it should be checked whether the IRAT HOSR is low for both CS and PS or just one of these. If it is low for only one of the services, compressed mode parameters can be tuned to trigger early handover when the signal strength is high. Analysis should be followed from cluster to cell to relation level to pinpoint the issue.

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

UMTS - Analysis for Second Carrier Expansion

Second Carrier expansion can be proposed if there is low user throughput due to high number of users. One way of finding Node B/Cells that requires such an expansion is presented below. Extract the cell hourly level performance statistics of last 10 days and check for below criteria:

• RoT (Rise Over Thermal) >= 6dB and Cell DCH users >= 16
• HS User Throughout is less than 500 kbps and Average HSDPA users are larger than 16
• Non HSDPA TCP Utilization avg >=55% or max>=90%  and Cell DCH users >=16 

If these conditions are fulfilled by cells in at least 10 hours, the cell should be recommended for second carrier expansion. 

Note that second carrier expansion will not increase the peak user throughput, but the average user throughput is enhanced and so is the user QoS. The peak throughput is 21 Mbps for UMTS, however with Dual Carrier technology, the theoretical throughput limit is increased to as high as 42 Mbps.

GSM - Low Paging Sucess Rate Issue

Paging discards can be a source low PSR or users complaining about getting "user not responding" messages as they call party B in GSM. The steps that can be taken to reduce or eliminate discards are as follows:

1- LAC Splitting
2- Cell paging capacity
      - can be increased of worst offenders
      - Shifting of SD/PD timeslots to non-BCCH TRXs
3- Audit of Periodic Location Update BSC Timer Value (t3212)
      - Can be set to 6 hours
      - This timer value at the MSC should be greater than the BSC value
4- Activation of Precise Paging Feature
      - Paging is done only on cells where there is high probability of finding subscribers according to the location record saved in the BSC

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)