6.5.4 Radio Block Structure

03.643GPPGeneral Packet Radio Service (GPRS)Overall description of the GPRS radio interfaceStage 2TS

Different Radio Block structures for data transfer and control message transfer purposes are defined. The Radio Block structure for data transfer is different for GPRS and EGPRS, whereas the same Radio Block structure is used for control messages. For detailed definition of radio block structure, see GSM 04.60 [7].

For GPRS, a Radio Block for data transfer consists of one MAC Header, one RLC header and one RLC Data Block. It is always carried by four normal bursts.

Radio Block

MAC header

RLC header

RLC data

BCS

Figure 4: Radio Block structure for data transfer for GPRS

The MAC header contains control fields which are different for uplink and downlink directions. The MAC header has constant length, 8 bits.

The RLC header contains control fields which are different for uplink and downlink directions. The RLC header has variable length.

The RLC data field contains octets from one or more LLC PDUs.

The Block Check Sequence (BCS) is used for error detection.

For EGPRS, a Radio Block for data transfer consists of one RLC/MAC header and one or two RLC Data Blocks. It is always carried by four normal bursts. The interleaving depends on the MCS used.

Radio Block

RLC/MAC header

HCS

RLC data

BCS

Figure 5: Radio Block structure for data transfer for EGPRS

The RLC/MAC header contains control fields which are different for uplink and downlink directions. The RLC/MAC header has variable length.

The RLC data field contains octets from one or more LLC PDUs.

The Block Check Sequence (BCS) is used for error detection of the data part.

The Header Check Sequence (HCS) is used for error detection of the header part.

The header part is independently coded from the data part and has its own check sequence. Tail biting (i.e. no explicit tail bits are appended before encoding. The encoder is initialised with the last information bits enabling tail biting decoding in the receiver) is used to reduce the size of the header.

For GPRS and EGPRS, a Radio Block for control message transfer consists of one MAC header and one RLC/MAC Control Block. It is always carried by four normal bursts.

Radio Block

MAC header

RLC/MAC Control Message

BCS

Figure 6: Radio Block structure for control message for GPRS and EGPRS

The MAC header contains control fields which are different for uplink and downlink directions. The MAC header has constant length, 8 bits.

The Block Check Sequence (BCS) is used for error detection.

The RLC/MAC Control message field contains one RLC/MAC control message.