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PDSCH/PUSCH Mapping Type (Type A, Type B)

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In the context of 4G LTE (Long-Term Evolution) and 5G NR (New Radio) wireless communication standards, PDSCH (Physical Downlink Shared Channel) and PUSCH (Physical Uplink Shared Channel) are key channels used for transmitting downlink and uplink data, respectively. The mapping types, Type A and Type B, refer to the different methods of mapping symbols and resource elements between the physical layer and the transport layer. Let's delve into the technical details of each mapping type:

  1. PDSCH Mapping Type A:
    • Resource Element Mapping:
      • In Type A mapping, resource elements are mapped in a localized manner. This means that a block of resource elements is mapped to a consecutive set of symbols in the time domain.
    • Symbol Mapping:
      • The symbols are mapped to consecutive OFDM (Orthogonal Frequency Division Multiplexing) symbols within a slot.
    • Frequency Domain Mapping:
      • In the frequency domain, the resource elements are mapped to consecutive subcarriers within the available bandwidth.
    • Reference Signals:
      • Reference signals, such as cell-specific and UE-specific reference signals, are also transmitted in the same localized manner.
    • Advantages:
      • Type A mapping simplifies the receiver processing as symbols are mapped consecutively in both time and frequency domains.
  2. PDSCH Mapping Type B:
    • Resource Element Mapping:
      • Type B mapping employs a distributed resource element mapping, where resource elements are distributed across multiple symbols within a slot.
    • Symbol Mapping:
      • Symbols are not necessarily consecutive; they are distributed across various OFDM symbols within a slot.
    • Frequency Domain Mapping:
      • The resource elements are distributed across different subcarriers in the frequency domain.
    • Reference Signals:
      • Reference signals are also distributed in a similar fashion to the data symbols.
    • Advantages:
      • Type B mapping provides greater flexibility in terms of resource element allocation and may offer improved performance under certain channel conditions.
    • Considerations:
      • The receiver needs to perform more complex processing to demodulate and decode the symbols due to their distributed nature.

The choice between Type A and Type B mapping depends on the specific requirements and characteristics of the wireless channel. Type A simplifies receiver processing but may not be as flexible, while Type B offers more flexibility but requires more complex receiver processing. The selection is typically based on factors such as channel conditions, interference, and overall system performance goals. The mapping types are defined in the 3GPP (3rd Generation Partnership Project) specifications, which standardize the design and operation of cellular networks.