Explain the different coding schemes used in GPRS and their importance.
Multiple Access Coding Scheme:- Multiple access scheme is used in GPRS based on the FDD and TDMA.
- One pair of up-link and down-link frequency channels are assigned to a user during a session.
- The Multiple Access Coding Scheme is combined with statistical multiplexing [packet mode communication], that allows several uses to share the same frequency channel.
- Downlink uses first-come first-served packet scheduling and uplink uses a scheme that is similar to reservation ALOHA.
- Slotted ALOHA is utilized for reservation inquiries in a contention phase, followed by transferring data by utilizing dynamic TDMA with first-come, first-served scheduling.
Channel Encoding Scheme- Channel Encoding Scheme is based on a convolution code at various code rates and GMSK modulation
- The table below summarizes the options:
| Multislot Class | Speed |
| CS-1 | 8.0 |
| CS-2 | 12.0 |
| CS-3 | 14.4 |
| CS-4 | 20.0 |
- The least robust and fasted coding scheme is CS-4 and is available near a Base Transceiver Station.
- The most robust coding scheme is CS-1 and is used in case of mobile station is further away from a BTS.
- A speed of 20.0 Kbit/s/time slots can be achieved with CS-4 and has 25% normal cell coverage.
- A speed of 8.0 Kbit/s/time slots can be achieved with CS-1 and has 98% of normal coverage.
Multislot Class- Speed of data transfer available in the Uplink and Downlink directions is determined by Multislot Class.
- The speed varies between 1 and 45 for allocating by the network to allocate radio channels in the uplink and downlink channels.
- The representation of multi slot class is 5+2, for example, where the first number is the number of down link time slots and the second number is the number of up link time slots that are allocated to use by a mobile station.
Multislot Classes for GPRS/EGPRS| Multislot Class | Downlink TS | Uplink TS | Active TS |
| 1 | 1 | 1 | 2 |
| 2 | 2 | 1 | 3 |
| 3 | 2 | 2 | 3 |
| 4 | 3 | 1 | 4 |
| 5 | 2 | 2 | 4 |
| 6 | 3 | 2 | 4 |
| 7 | 3 | 3 | 4 |
| 8 | 4 | 1 | 5 |
| 9 | 3 | 2 | 5 |
| 10 | 4 | 2 | 5 |
| 11 | 4 | 3 | 5 |
| 12 | 4 | 4 | 5 |
| 30 | 5 | 1 | 6 |
| 31 | 5 | 2 | 6 |
| 32 | 5 | 3 | 6 |
| 33 | 5 | 4 | 6 |
| 34 | 5 | 5 | 6 |
