4.2 General coding/multiplexing of TrCHs

25.2123GPPMultiplexing and channel coding (FDD)Release 17TS

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

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 {10 ms, 20 ms, 40 ms, 80 ms}, where 80 ms TTI for DCH shall not be used unless SF=512.

The following coding/multiplexing steps can be identified:

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

– transport block concatenation and code block segmentation (see subclause 4.2.2);

– channel coding (see subclause 4.2.3);

– radio frame equalisation (see subclause 4.2.4);

– rate matching (see subclause 4.2.7);

– insertion of discontinuous transmission (DTX) indication bits (see subclause 4.2.9);

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

– radio frame segmentation (see subclause 4.2.6);

– multiplexing of transport channels (see subclause 4.2.8);

– physical channel segmentation (see subclause 4.2.10);

– mapping to physical channels (see subclause 4.2.12).

The coding/multiplexing steps for uplink and downlink are shown in figure 1 and figure 2 respectively.

Figure 1: Transport channel multiplexing structure for uplink

Figure 2: Downlink transport channel multiplexing structure for transport channels that are not concatenated.

Figure 2A: Downlink transport channel processing for transport channels that are concatenated. The concatenated transport channel inherits the parameters of the transport channel i₁.

The single output data stream from the TrCH multiplexing, including DTX indication bits in downlink, is denoted Coded Composite Transport Channel (CCTrCH). A CCTrCH can be mapped to one or several physical channels.