|
GPRS classes and coding schemes
In
a GPRS network there are four coding schemes:-
| Channel
Coding Scheme |
CS-1 |
CS-2 |
CS-3 |
CS-4 |
| Pre-cod.
USF |
3 |
6 |
6 |
12 |
| Infobits
without USF |
181 |
268 |
312 |
428 |
| Parity
bits BC |
40 |
16 |
16 |
16 |
| Tail
bits |
4 |
4 |
4 |
- |
| Output
conv encoder |
456 |
588 |
676 |
456 |
| Punctured
bits |
0 |
132 |
220 |
- |
| Code
rate |
1/2 |
~2/3 |
~3/4 |
1 |
| Data
rate kbit/s |
9.05 |
13.4 |
15.6 |
21.4 |
| Maximum
data speed with 8 time-slots |
72.4
kb/s |
107.2
kb/s |
124.8
kb/s |
171.2
kb/s |
The choice of coding scheme
depends on the condition of the channel provided by the cellular
network (quality of the radio link between cell phone and base station). If
the channel is very noisy, the network may use CS-1 to ensure higher
reliability; in this case the data transfer rate is only 9.05 kbit/s per GSM
time slot used. If the channel is providing a good condition, the network could use
CS-3 or CS-4 to obtain optimum speed, and would then have up to 21.4 kbit/s
per GSM time slot.
The multislot classes are as
follows:-
| Class |
Download |
Upload |
Max.
slots
|
| 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 |
5 |
| 8 |
4 |
1 |
5 |
| 9 |
3 |
2 |
5 |
| 10 |
4 |
2 |
5 |
| 11 |
4 |
3 |
5 |
| 12 |
4 |
4 |
5 |
| 13 |
3 |
3 |
unlimited |
| 14 |
4 |
4 |
unlimited |
| 15 |
5 |
5 |
unlimited |
| 16 |
6 |
6 |
unlimited |
| 17 |
7 |
7 |
unlimited |
| 18 |
8 |
8 |
unlimited |
| 19 |
6 |
2 |
unlimited |
| 20 |
6 |
3 |
unlimited |
| 21 |
6 |
4 |
unlimited |
| 22 |
6 |
4 |
unlimited |
| 23 |
6 |
6 |
unlimited |
| 24 |
8 |
2 |
unlimited |
| 25 |
8 |
3 |
unlimited |
| 26 |
8 |
4 |
unlimited |
| 27 |
8 |
4 |
unlimited |
| 28 |
8 |
6 |
unlimited |
| 29 |
8 |
8 |
unlimited |
| 
