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.