4.2 General coding/multiplexing of TrCHs

25.2223GPPMultiplexing and channel coding (TDD)Release 17TS

This section only applies to the transport channels: DCH, RACH, DSCH, USCH, BCH, FACH and PCH. Other transport channels which do not use the general method are described separately below.

Figure 1 illustrates the overall concept of transport-channel coding and multiplexing. Data arrives to the coding/multiplexing unit in form of transport block sets, once every transmission time interval. The transmission time interval is transport-channel specific from the set {5 ms^(*1), 10 ms, 20 ms, 40 ms, 80 ms}.

Note: ^(*1) may be applied for PRACH for 1.28 Mcps TDD

The following coding/multiplexing steps can be identified:

– add CRC to each transport block (see subclause 4.2.1);

– TrBk concatenation / Code block segmentation (see subclause 4.2.2);

– channel coding (see subclause 4.2.3) ;

– radio frame size equalization (see subclause 4.2.4);

– interleaving (two steps, see subclauses 4.2.5 and 4.2.11 );

– radio frame segmentation (see subclause 4.2.6);

– rate matching (see subclause 4.2.7);

– multiplexing of transport channels (see subclause 4.2.8);

– bit scrambling (see subclause 4.2.9);

– physical channel segmentation (see subclause 4.2.10);

– sub-frame segmentation(see subclause 4.2.11A only for 1.28Mcps TDD)

– mapping to physical channels (see subclause 4.2.12).

The coding/multiplexing steps for uplink and downlink are shown in figures 1 and 1A.

Figure 1: Transport channel multiplexing structure for uplink and downlink for 3.84Mcps and 7.68 Mcps TDD

Figure 1A: Transport channel multiplexing structure for uplink and downlink of 1.28Mcps TDD

Primarily, transport channels are multiplexed as described above, i.e. into one data stream mapped on one or several physical channels. However, an alternative way of multiplexing services is to use multiple CCTrCHs (Coded Composite Transport Channels), which corresponds to having several parallel multiplexing chains as in figures 1 and 1A, resulting in several data streams, each mapped to one or several physical channels.