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

Mobile Originating Call Flow

Here is the detailed Mobile Originating Call Flow divided into 4 functional modules depicting the network nodes for easy comprehension:

Sector Swap (Cross-sector) Issue

Sector-Swap Issue means that sector of a site is serving the area in a direction different to its azimuth. For instance, sector 1 is serving the area of sector 2 and sector 2 is serving the area of sector 1. This is known as complete Sector Swap. Another type is Partial Swap in which the logical area of say sector 1 is served partially by sector 2 and partially by sector 1 itself.

This problem arises due to jumbled cables at the BTS which could be caused due to human mistake during site maintenance activities. Issue can be diagonosed through Drive Test results as well as observing the number of Handover requests in Handover statistics of the site.



The issue can cause increase in CDR, RxQual degradation, increased DL interference,

Resolution can be done by closely following the cables from the antenna to the respective TRX of each sector of the BTS and correcting the cross-connections.

Candidate Cell Priority (HO Priority) - CDR Alcatel-Lucent

Improvement in Quality and reduction in Call Drops can be achieved in Alcatel-Lucent (B11, B10) by proper adjustment of Candidate Cell Priority (HO Priority Level).

Parameter:

• Candidate_Cell_Priority

Target Cells: Radio Drops, HO Drops, Bad UL/DL Quality

Theory: 

• This parameter decides the priority of target cells for each source cell during Handover
• One standard approach is use highest priority for DCS neighbors (0), 2nd highest (1) for less interfered and 3rd highest (2) for others

Concentric Cell (Co-BCCH) Technology

Concentric cell (also known as Common BCCH) are those that operate with both GSM and DCS TCH frequencies but with a single BCCH (of GSM), thereby having below advantages compared with dual-BCCH:

• DCS BCCH resource is saved per cell
• Reduced BA List
• Reduced DCS BCCH interference
• Reduced number of neighbours
• Potential for Reduction in number of Handovers

An important physical parameter consideration for Concentric Cells is the tilt difference between the DCS and GSM antennas. Generally, in an interfered GSM network, the DCS antenna has lower downtilt than the GSM antenna to equalize the coverage area.

Repeated SACCH/FACCH - CDR Alcatel-Lucent

Call Drops can be reduced to a great extent in the equipment of Alcatel-Lucent (B11, B10) by using the feature of repeated SACCH/FACCH frames.

Parameter:

• EN_REP_DL_FACCH
• EN_REP_SACCH

Target Cells: Radio Drops, HO Drops

Theory: 

• Each DLFACCH frame is sent twice by enabling this parameter thereby improving handover reliability in AMR Calls reducing call drop rate
• If a SACCH is not decoded correctly by MS, the BTS will resend it that enhances coverage and decreases drops (SACCH is used for transmission of radio measurement data such as TA, Power Control Info, SMS during call etc)

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)

High TCH Blocking Cell Statistical Analysis

Below mentioned procedure should be adopted in general to resolve the TCH blocking issue:

1. Check TCH Availability % (Cell/Neighbours)
2. HRU % (Half Rate Utilization)
1. If HRU = 0; Enable HR
2. If HRU > 0; Tune HR Thresholds
3. TA Analysis (TA Distribution)
4. Traffic Balancing
1. CRO (Cell Reselect Offset) Adjustment (reduce in Cell/Increase in Neighbours)
2. Penalty Timer
3. Traffic Handover
4. Downtilt
5. Neighbour Audit
6. Propose TRX/Sector/Site Addition

Low HSR Cell Statistical Analysis

Following statistics should be checked for low HOSR Cell Analysis:

1. IHSR %
2. HOSR %
3. IBI % (Band 4+5)
4. TRX Efficiency
5. Hardware Alarms (Clock Reference, PCM/SUMA Issue)
6. Neighbour Definitions
7. Handover Stats per adjacency (Attempts, Success, Fails)
8. Handover Parameters (Margins, Priority)
9. Handover distribution
10. TA distribution

High DCR Cell Statistical Analysis

Following statistics trend (say 2 weeks) should be checked for high DCR Cell:

1. TRX Efficiency %
2. Equipment Failure Drops (RTC/BSS/Abis/Equipment Failure etc)
3. Incoming Handover Success Rate (IHSR)
4. Handover Failures
5. IBI % (Band 4+5)
6. Handover Drops
7. Radio Drops
8. UL/DL Level Drops
9. UL/DL Quality Drops
10. TA (Timing Advance) Drops
11. TA Distribution
12. Handover Distribution
13. RxQual Rank/Index (Mean Quality of UL/DL Signals)
14. Delta Path Loss (Path Imbalance)

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)