Channel Coding in NR

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Channel Coding in NR

Channel coding is a fundamental technique used in wireless communications to improve the reliability of data transmission over noisy channels. In the New Radio (NR) standard, channel coding is used to provide robustness against various types of errors that can occur during wireless transmission. In this article, we will discuss channel coding in NR in more technical detail.

Overview of Channel Coding in NR

Channel coding in NR involves adding redundant information to the transmitted data, which enables the receiver to detect and correct errors. The NR standard uses two main types of channel coding: forward error correction (FEC) and hybrid automatic repeat request (HARQ).

Forward error correction (FEC)

FEC is a form of channel coding where redundant information is added to the transmitted data in a systematic way, so that the receiver can detect and correct errors without the need for retransmission. In the NR standard, FEC is implemented using two main coding schemes: Polar coding and low-density parity-check (LDPC) coding.

Hybrid automatic repeat request (HARQ)

HARQ is a form of channel coding where the receiver sends feedback to the transmitter, indicating whether the transmitted data was received correctly or not. If errors are detected, the transmitter can retransmit the data with additional redundancy to improve the chances of correct reception. The NR standard uses two main HARQ modes: Chase Combining (CC) and Incremental Redundancy (IR).

Polar Coding

Polar coding is a type of FEC used in NR for control and data channels. It was selected as the main channel coding scheme for NR due to its excellent error correction performance and low decoding complexity. Polar coding uses a mathematical technique called channel polarization to construct an optimal code for a given channel.

The process of polar coding involves splitting the data into several smaller sub-blocks and encoding each sub-block using a binary polar code. The encoding process involves combining the sub-blocks in a systematic way, so that the receiver can decode the original data using a process called successive cancellation decoding. This process involves iteratively canceling out the effects of the noisy channel until the original data is obtained.

Low-Density Parity-Check (LDPC) Coding

LDPC coding is another type of FEC used in NR for data channels. It is a linear block code that is based on a sparse parity-check matrix. The matrix is designed to have a low density of ones, which enables efficient encoding and decoding. LDPC codes are used in NR for high data rate channels, where they provide excellent error correction performance.

The process of LDPC encoding involves multiplying the data vector with the sparse parity-check matrix to obtain the parity-check bits. The encoded data is then transmitted over the wireless channel. At the receiver, the data is decoded using an iterative algorithm, which involves estimating the data vector and the parity-check matrix iteratively until the original data is obtained.

Chase Combining (CC)

CC is a HARQ mode used in NR that involves combining the original and retransmitted data using an XOR operation. The combined data is then decoded using the channel decoding algorithm. If the decoded data is still incorrect, the process is repeated with additional retransmissions until the maximum number of retransmissions is reached.

Incremental Redundancy (IR)

IR is another HARQ mode used in NR that involves transmitting the original data and additional parity bits in each retransmission. The additional parity bits are computed using the previous transmissions and the channel state information. The receiver combines the original and additional parity bits and decodes the data using the channel decoding algorithm.

Conclusion

Channel coding is a critical technique used in the NR standard to provide robustness against errors in wireless transmission. The NR standard uses two main types of channel coding: FEC and HARQ. The FEC schemes used in NR include Polar coding and LDPC coding, which provide excellent error correction performance and low decoding complexity.