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PUSCH Channel Coding and Transmssion Process

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The Physical Uplink Shared Channel (PUSCH) is an essential component of the Long Term Evolution (LTE) and 5G New Radio (NR) wireless communication systems. The PUSCH is responsible for carrying user data from the User Equipment (UE) to the Base Station (eNodeB in LTE or gNodeB in 5G NR). Here's a technical breakdown of the PUSCH channel coding and transmission process:

1. Channel Coding:

a. Source Data Input:

  • The data to be transmitted is first prepared at the higher layers of the protocol stack, such as the Radio Link Control (RLC) and Medium Access Control (MAC) layers.

b. Segmentation and Concatenation:

  • If the data is too large to fit into a single transport block, it is segmented into smaller pieces.
  • These segments can then be concatenated with redundancy bits to form code blocks. The size of these code blocks depends on the coding rate and other system parameters.

c. Channel Encoding (Turbo or LDPC Coding):

  • The code blocks are then channel encoded using advanced forward error correction (FEC) schemes like Turbo codes in LTE or Low-Density Parity-Check (LDPC) codes in 5G NR.
  • Turbo codes and LDPC codes provide a robust mechanism to correct errors that may occur during transmission by adding redundant bits.

2. Modulation and Mapping:

a. Symbol Mapping:

  • After encoding, the coded bits are mapped to modulation symbols. In LTE, the modulation schemes used for PUSCH include Quadrature Phase Shift Keying (QPSK), 16-QAM, and 64-QAM.

b. Resource Mapping:

  • The modulation symbols are mapped onto specific resource elements (REs) in the frequency-time grid of the PUSCH. This mapping takes into account the channel state information (CSI) and other system parameters to optimize the transmission.

3. Layer Mapping and Precoding:

a. Layer Mapping:

  • In technologies like LTE and 5G NR, multiple antennas (MIMO) are employed for enhancing the data rate and reliability. The mapped symbols may be distributed across multiple layers (transmit antennas) based on the number of available antennas and the transmission scheme.

b. Precoding:

  • Before transmission, precoding is applied to the symbol streams intended for different antennas. Precoding helps in optimizing the signal quality by taking into account the channel conditions between the UE and the gNodeB/eNodeB. Different precoding matrices are used to shape the transmitted signals to maximize the Signal-to-Interference-plus-Noise Ratio (SINR).

4. Scrambling and Modulation:

a. Scrambling:

  • The precoded symbols are scrambled using a cell-specific scrambling sequence to avoid any systematic interference and to differentiate transmissions from different cells.

b. Final Modulation:

  • After scrambling, the symbols are modulated using the assigned modulation scheme (e.g., QPSK, 16-QAM, 64-QAM) to prepare them for transmission over the air interface.

5. Transmission:

  • Once the symbols are modulated, the UE transmits them over the PUSCH to the gNodeB/eNodeB using the allocated resources. The gNodeB/eNodeB receives these signals, processes them, and decodes the transmitted data based on the established protocols and procedures.