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Channel Multiplexing Structure
This is a short overview how data stream is modified during processing in layer 2 and 1 in downlink direction. Uplink coding is done in a similar way.
Ciphering happens in RCL or MAC-d part of the layer 2. f8 algorithm gets five inputs to generate a keystream block that is ciphered by binary addition to a data stream. Channel coding separates different down link connection to users within a cell. In the uplink direction Channel coding is used for separation of physical data and control channels. Half-rate and 1/3-rate convolutional coding is used for low data rates, turbo coding is used for higher bit rates. Channel coding includes the spreading. Rate matching is dynamic frame-by-frame operation and done either by puncturing or by repetition of the data stream. Interleaving is done in two stages. It is first done by inter-frame and then by intra-frame.
Transport channel multiplexing structure for downlink
Further reading: 3GPP TS 25.212
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