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Page 26

Interfaces, Protocols, Procedures   Siemens

TM2110EU01TM_0003
25

Channel Bundling, Sharing of Channels

e.g. BTS with 2 RFCs => 2 TRX = 16 channels

RFC 1

RFC 2

UL

RFC 1

RFC 2

DL sharing of physical
channels

=> packet switching
on UmTDMA frame = 8 time slots

multislot classes
•29 classes defined
•assignment of 
channels by PCU
according to
capabilities of MS

• identifying “high
end“ and “low cost“
MS

e.g. 6 GSM
CS users

e.g. 4 GPRS
PS users

Signaling:
BCCH,
SDCCHs,...

time
slot

Fig. 12 Channel Bundling, sharing of channels, multislot classes

Page 27

Siemens Interfaces, Protocols, Procedures

TM2110EU01TM_0003
26

2.3 Channel Coding

Channel coding was modified substantially for GPRS purposes (GSM Rec. 03.64).

Channel coding starts with the division of digital information into transferable blocks.
These radio blocks, i.e. the data to be transferred (prior to encoding) comprise:

 a header for the Medium Access Control MAC (MAC Header)

 signaling information (RLC/MAC Signaling Block) or user information (RLC Data
Block) and

 a Block Check Sequence BCS.

The functional blocks (radio blocks) are protected in the framework of convolutional
coding against loss of data. Usually, this means inserting redundancy.

Furthermore, channel coding includes a process of interleaving, i.e. different ar-
rangement in time. The convolutional radio blocks are interleaved to a specific num-
ber of bursts/burst blocks. In the case of GPRS, interleaving is carried out across four 
normal bursts NB in consecutive TDMA frames and, respectively, to 8 burst blocks

 with 57 bit each.

Four new coding schemes were introduced for GPRS (Rec. 03.64): CS-1 to CS-4.
These can be used alternatively depending on the information to be transferred and
on the radio interface’s quality.

Page 52

Interfaces, Protocols, Procedures   Siemens

TM2110EU01TM_0003
51

MS Network

Start Packet data transfer 

1

2

Packet Channel Request

Packet Immediate Assignment (TA, PC)

3

4

Packet Resource Request

Packet Resource Assignment

One Phase
Packet Access

Two Phase
Packet Access

(optional)

RLC Data Transfer 

4
RLC block

RLC block







PRACH or RACH

PAGCH or AGCH

PACCH

PACCH

PDTCH

Fig. 25 Start of packet data transfer

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