Description for “GPRS LINK ADAPTATION” feature

Description:-

• GPRS Link Adaptation feature is used for dynamic selection of most optimal coding scheme from CS-1 to CS-4 for data transmission over radio interface.

• GPRS Link Adaptation feature is implemented in Packet Control Unit.

• The selection of coding scheme with optimal performance depends on the quality of radio link.

• CS-1 coding scheme provides highest throughput under poor radio conditions.

• CS-4 coding scheme provides optimal performance under good radio conditions.

Objective:-

There are two objectives of GPRS Link Adaptation feature as mentioned below:-

• To maximize data throughput.

• To keep low latency.

Reasons for GPRS Link Adaptation feature usage:-

• Enhancement in system capacity.

• Lower transfer delays.

• High bit rate.

Dynamic selection of higher coding scheme from lower coding scheme is performed as per below mentioned criteria:-

• Selection Coding scheme CS-2 from CS-1

• Criteria:- Required BLER is less than 4%

• Selection Coding scheme CS-3 from CS-2

• Criteria:- Required BLER is less than 6%

• Selection Coding scheme CS-4 from CS-3

• Criteria:- Required BLER is less than 2%

• Lower coding scheme is dynamically selected from higher coding scheme when BLER > 10%.

Important Parameters for GPRS Link Adaptation feature :-

• Parameter Name:- LA

• Used to on/off GPRS Link Adaptation feature.

• Parameter Name:- CHCODING

• Parameter CHCODING controls the uplink coding scheme. It is a BSC level parameter.

• Parameter Name:- CHCSDL • Parameter CHCSDL controls the downlink coding scheme. It is a cell level

parameter.

• Parameter Name:- EITHIGHCS• Parameter EITHIGHCS define the highest coding scheme which can be

selected through GPRS Link Adaptation feature. It is a BSC level parameter.

GPRS coding schemes with their respective RLC data block size and RLC data bit rate

• Coding scheme:- CS-1• RLC data block size :- 20 Bytes• RLC data bit rate :- 8.0 kbps

• Coding scheme:- CS-2

• RLC data block size :- 30 Bytes

• RLC data bit rate :- 12.0 kbps

• Coding scheme:- CS-3

• RLC data block size :- 36 Bytes

• RLC data bit rate :- 14.4 kbps

• Coding scheme:-CS-4

• RLC data block size :- 50 Bytes

• RLC data bit rate :- 20.0 kbps