Channel Coding in 5G-NR

Introduction:

In the fifth-generation (5G) wireless communication system, the design of the physical layer has undergone significant changes compared to its predecessors. One of the critical aspects of the physical layer design is channel coding. The channel coding scheme used in 5G New Radio (NR) is polar coding, which is a type of error-correcting code that can achieve the capacity of a binary input discrete memoryless channel (B-DMC). This article will explain channel coding in 5G-NR in detail, including its technical aspects.

Channel Coding:

Channel coding is a technique used to add redundancy to the transmitted data to make it more resilient to errors caused by the communication channel. Channel coding is essential in wireless communication systems as the transmitted signal may experience noise, fading, and other channel impairments. Without channel coding, even a small amount of error can make the received signal unusable. Channel coding techniques aim to reduce the error rate of the received signal by adding redundancy to the data. This redundancy allows the receiver to correct errors and recover the original data.

Polar Coding:

Polar coding is a channel coding scheme that has gained significant attention in the 5G wireless communication system. It is a type of linear block code that can achieve the capacity of a binary input discrete memoryless channel (B-DMC). Polar coding was first introduced by Arikan in 2009 and has been adopted as the channel coding scheme for 5G-NR. Polar coding has some advantages over other channel coding schemes, including low complexity, high coding gain, and provable optimality for the B-DMC.

Polar coding works by splitting the original data into two parts: information bits and frozen bits. The frozen bits are known to both the transmitter and receiver and are used to protect the information bits. The information bits are encoded using a polar transformation, which maps the input bits to a set of output bits, where some bits are more reliable than others. The more reliable bits are used to protect the less reliable bits, and this protects the information bits from errors.

Polar coding achieves its high coding gain by selecting the most reliable bits and protecting them with the less reliable bits. This is done by using a process called channel polarization, which splits the channel into two parts: good and bad. The good channels are protected by the less reliable bits, and the bad channels are protected by the more reliable bits. This process results in a set of output bits that have different reliabilities, with the most reliable bits being used to protect the information bits.

Polar coding also has low complexity, which makes it attractive for implementation in 5G-NR. The encoding and decoding process in polar coding can be implemented using simple operations, such as XOR and bit-reversal. This makes it possible to implement polar coding using hardware or software-based solutions. Polar coding also has provable optimality for the B-DMC, which makes it an attractive channel coding scheme for 5G-NR.

Polar Coding in 5G-NR:

In 5G-NR, polar coding is used for both control and data channels. The control channels in 5G-NR are used for signaling between the base station and the user equipment. The data channels are used for transmitting user data. Polar coding is used in both channels to ensure that the transmitted data is protected from channel impairments.

The control channels in 5G-NR use a specific polar code called the CRC-Aided Polar (CA-Polar) code. This code is used to protect the control signaling from errors, ensuring that the base station and user equipment can communicate reliably. The CA-Polar code is constructed by concatenating a cyclic redundancy check (CRC) code with a polar code. The CRC code is used to detect errors, and the polar code is used to correct errors. The CA-Polar code is designed to provide a coding gain of 0.5 dB, which improves the reliability of the control signaling.

The data channels in 5G-NR use a different polar code than the control channels. The polar code used for data channels is called the Rate Matching Pattern (RMP) Polar code. The RMP Polar code is used to protect user data from channel impairments. The RMP Polar code is constructed by rate-matching a polar code with the user data. The rate-matching process involves selecting a subset of bits from the polar code that matches the size of the user data. The selected bits are then XORed with the user data to form the encoded data.

The RMP Polar code is designed to provide a coding gain of 1.5 dB, which improves the reliability of the user data transmission. The RMP Polar code is also designed to support different code rates, which allows for efficient use of the available bandwidth. The code rate determines the amount of redundancy added to the user data, and a higher code rate results in higher reliability but lower data rate.

Polar coding in 5G-NR also supports different modulation schemes, including quadrature amplitude modulation (QAM) and phase shift keying (PSK). The modulation scheme determines the number of bits transmitted per symbol, and higher-order modulation schemes result in higher data rates but lower reliability.

Conclusion:

Channel coding is an essential aspect of the physical layer design in the 5G wireless communication system. The channel coding scheme used in 5G-NR is polar coding, which is a type of error-correcting code that can achieve the capacity of a binary input discrete memoryless channel (B-DMC). Polar coding has several advantages over other channel coding schemes, including low complexity, high coding gain, and provable optimality for the B-DMC.

Polar coding is used for both control and data channels in 5G-NR, with different polar codes used for each channel. The control channels use the CRC-Aided Polar (CA-Polar) code, which is designed to provide a coding gain of 0.5 dB. The data channels use the Rate Matching Pattern (RMP) Polar code, which is designed to provide a coding gain of 1.5 dB and support different code rates and modulation schemes.

Overall, the use of polar coding in 5G-NR ensures that the transmitted data is protected from channel impairments, resulting in a more reliable wireless communication system.