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UL Transmission Scheme / PUSCH Precoding / Transmission Mode (Codebook vs Non-Codebook based)

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The UL (Uplink) Transmission Scheme, PUSCH (Physical Uplink Shared Channel) Precoding, and Transmission Modes, particularly focusing on Codebook-based versus Non-Codebook-based methods in the context of LTE (Long-Term Evolution) and 5G NR (New Radio) standards.

1. UL Transmission Scheme:

The Uplink Transmission Scheme refers to how data is transmitted from the User Equipment (UE) or mobile device to the Base Station (BS) or eNodeB in LTE and gNodeB in 5G NR.

  • Scheduling: Uplink transmissions are scheduled by the base station. The scheduler decides when and how a UE should transmit data.
  • Multiple Access Methods: LTE uses SC-FDMA (Single Carrier Frequency Division Multiple Access) for uplink transmission, while 5G NR introduces a flexible waveform called CP-OFDM (Cyclic Prefix Orthogonal Frequency Division Multiplexing) and DFT-spread OFDM for uplink.

2. PUSCH Precoding:

PUSCH Precoding involves shaping the transmitted signals from the UE to improve the received signal quality at the BS.

  • Purpose: The main goal is to mitigate interference, enhance the signal-to-noise ratio (SNR), and ensure that the transmitted signal is optimally aligned with the reception capabilities of the BS.
  • Mathematical Operation: Precoding involves matrix multiplication operations on the transmitted signal vector. Different precoding matrices or vectors can be used based on the transmission mode and channel conditions.

3. Transmission Mode:

Transmission Modes dictate how the UE transmits data based on its channel state and the requirements of the system.

a) Codebook-based Transmission:

  • Pre-defined Codebooks: A set of pre-defined precoding matrices or vectors (codebook) is available. The UE selects the most suitable precoding matrix from this codebook based on the channel state information (CSI) feedback from the BS.
  • Feedback Mechanism: The BS periodically sends feedback to the UE about the current channel conditions. Based on this feedback, the UE selects an appropriate precoding matrix from the codebook.
  • Advantages:
    • Simplified UE design as the UE only needs to select from a pre-defined set.
    • Efficient in scenarios where channel conditions change slowly.

b) Non-Codebook-based Transmission:

  • Adaptive Precoding: In this mode, the UE dynamically adjusts its precoding strategy without strictly adhering to a pre-defined codebook.
  • Channel State Information: The UE estimates the channel state and directly computes the precoding matrix or vector based on this information.
  • Advantages:
    • More flexibility and adaptability to rapidly changing channel conditions.
    • Potentially higher spectral efficiency in dynamic environments.