How do polar codes and LDPC codes affect the complexity and latency of LTE transceivers?

1 What are polar codes and LDPC codes?

Polar codes and LDPC codes are both based on the idea of splitting a message into multiple subchannels with different reliability levels. The sender then assigns more bits to the more reliable subchannels and less bits to the less reliable ones, so that the overall error rate is minimized. However, the way they achieve this is different. Polar codes use a recursive transformation to polarize the subchannels into either very reliable or very unreliable ones, and then encode only the reliable ones. LDPC codes use a sparse matrix to map the message bits to the subchannel bits, and then apply an iterative decoding algorithm to recover the message.

2 How do they compare in complexity and latency?

The complexity and latency of error correction codes depend on several factors, such as the code length, the code rate, the modulation scheme, and the channel conditions. Generally speaking, polar codes have lower encoding complexity than LDPC codes, but higher decoding complexity. This is because polar codes use a simple XOR operation to encode the message, but require a complex successive cancellation decoding algorithm to decode it. LDPC codes, on the other hand, use a more complicated encoding process, but a simpler decoding process based on belief propagation. The latency of polar codes and LDPC codes also varies depending on the implementation and the hardware. Polar codes can achieve low latency by using a list decoding algorithm that reduces the number of decoding iterations, but this increases the memory and power consumption. LDPC codes can achieve low latency by using a layered decoding algorithm that decodes the subchannels in parallel, but this increases the complexity and the error floor.

3 How do they affect the performance of LTE transceivers?

The performance of LTE transceivers depends on the trade-off between the error correction capability, the spectral efficiency, and the power consumption of the error correction codes. Polar codes and LDPC codes have different advantages and disadvantages in this regard. Polar codes can achieve near-optimal error correction capability for short code lengths, which is suitable for low-latency applications such as control signaling and machine-type communication. However, they have lower spectral efficiency than LDPC codes for longer code lengths, which is suitable for high-throughput applications such as data transmission and multimedia streaming. Moreover, polar codes have higher power consumption than LDPC codes due to their higher decoding complexity and memory requirements. Therefore, polar codes and LDPC codes have different impacts on the complexity and latency of LTE transceivers, depending on the application scenario and the design constraints.

4 How to choose between polar codes and LDPC codes for LTE?

There is no definitive answer to which error correction code is better for LTE, as it depends on the specific requirements and preferences of the system designer and the user. However, some general guidelines can be followed to make an informed decision. First, consider the code length and the code rate of the error correction code, as they determine the error correction capability and the spectral efficiency of the system. Second, consider the modulation scheme and the channel conditions of the system, as they affect the error probability and the decoding performance of the error correction code. Third, consider the hardware and software resources available for the system, as they limit the complexity and latency of the error correction code. Finally, consider the application scenario and the quality of service expected from the system, as they define the trade-off between the reliability, the throughput, and the power consumption of the system.