Physical Downlink Shared Channel (PDSCH)

Physical Downlink Shared Channel (PDSCH) - 5G NR Simulation

It carries user data and SIB messages in DL.
User bit stream (Transport block or Payload) received from MAC sublayer over transport channels are sent to the L1 PDSCH physical channels and output generated as IQ data (Quadrature signals).
There are multiple steps performed while processing TBs –
• CRC – Cyclic redundancy check – error detection
• Segmentation of TBs – two TBs are used in spatial multiplexing
• LDPC Encoder – error correction (after CRC and parity check)
• Rate Matching – match radio frame size with TB size (number of code bits to schedule)
• Scrambler – use of different scrambling codes reduces interference
• Modulation mapper – transforms block of scrambled bits into modulation symbols
• Layer Mapper – distribute modulation symbols across different transmission layers
• RE Mapper – symbols are transmitted on antenna ports and map to available REs
Downlink Reference Signals –
• Demodulation Reference Signal (DMRS) for channel estimation
• Phase Tracking Reference Signal (PTRS) for phase noise compensation (occurs with DMRS) and mostly used for FR2 frequency range.
• Channel State Information Reference Signal (CSI-RS) for interference estimation and provide support for beam management and mobility.
Considerations – PDSCH Mapping Type-A (1 codeword), BWP-1, PDSCH format-0
Note – Partial PDSCH slot allocation is used for low latency services. Mapping type-B is preferred for partial slot allocation.

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