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5G NR PDSCH Mapping Types

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The Physical Downlink Shared Channel (PDSCH) is a key component in the 5G New Radio (NR) air interface, responsible for delivering downlink user data to the user equipment (UE). The PDSCH mapping types describe how the physical resource elements (REs) are allocated and mapped to transmit downlink data.

  1. Type A PDSCH Mapping:
    • Resource Element Mapping:
      • In Type A mapping, resource elements (REs) are mapped to the same location in both time and frequency domains for each slot within a subframe.
      • It uses frequency-domain orthogonal cover codes to spread symbols across different resource blocks (RBs).
      • Time-domain spreading is achieved using a cyclic shift.
    • Processing Steps:
      • The transmitter performs the modulation and layer mapping.
      • Precoding may be applied for multiple antenna transmission.
      • Mapping to the resource grid is done with orthogonal cover codes and cyclic shift.
    • Advantages:
      • Simplifies receiver processing as the same REs are used across different slots.
      • Well-suited for Frequency Division Duplex (FDD) deployments.
  2. Type B PDSCH Mapping:
    • Resource Element Mapping:
      • In Type B mapping, REs are distributed across different locations in both time and frequency domains for each slot within a subframe.
      • Frequency-domain mapping uses interleaved resource blocks.
      • Time-domain mapping involves a cyclic shift.
    • Processing Steps:
      • Modulation and layer mapping are performed.
      • Precoding is applied if needed.
      • The data is mapped onto the resource grid using interleaved resource blocks and cyclic shift.
    • Advantages:
      • Provides more flexibility in resource element allocation compared to Type A.
      • Suitable for both FDD and Time Division Duplex (TDD) deployments.
  3. Type C PDSCH Mapping:
    • Resource Element Mapping:
      • In Type C mapping, REs are assigned to different locations in the frequency domain for each slot within a subframe.
      • Time-domain mapping involves cyclic shifts, and frequency-domain mapping uses scattered resource blocks.
    • Processing Steps:
      • Modulation and layer mapping are carried out.
      • Precoding may be applied.
      • The data is mapped onto the resource grid using scattered resource blocks and cyclic shifts.
    • Advantages:
      • Offers additional flexibility compared to both Type A and Type B.
      • Suitable for TDD deployments with asymmetric uplink/downlink configurations.