CRC Interleaver in 5G NR

Introduction

Cyclic redundancy check (CRC) is a type of error detection code used in digital communication systems to detect errors in the transmitted data. Interleaving is a technique used to rearrange the transmitted data in such a way that if some part of the data is lost or corrupted during transmission, it can be reconstructed using the remaining parts of the data. In this article, we will discuss the use of CRC interleaver in 5G New Radio (NR) communication systems.

Overview of 5G NR Communication System

5G NR is the latest cellular communication standard that promises to deliver higher data rates, lower latency, and better reliability compared to the previous generation systems. The 5G NR system is based on a new air interface that uses orthogonal frequency-division multiplexing (OFDM) as the modulation scheme. The 5G NR system also uses advanced error correction techniques, such as low-density parity-check (LDPC) codes and polar codes, to improve the reliability of the transmitted data.

In the 5G NR system, the data to be transmitted is first encoded using a channel coding scheme, such as LDPC or polar codes. The encoded data is then divided into a number of transport blocks (TBs) of equal size. Each TB is further divided into a number of code blocks (CBs) of equal size. Each CB is then processed separately and transmitted over the air interface.

CRC Interleaver in 5G NR

In the 5G NR system, a CRC interleaver is used to interleave the CBs before they are transmitted over the air interface. The CRC interleaver is used to protect the transmitted data from errors that may occur during the transmission. The CRC interleaver is a two-stage interleaving process, where the CBs are first interleaved within a TB, and then the TBs are interleaved within a transport block set (TBS).

The first stage of the CRC interleaver is the intra-TB interleaving, which interleaves the CBs within a TB. The intra-TB interleaving is done to prevent the errors that occur due to the channel characteristics, such as fading or noise. The intra-TB interleaver is a systematic interleaver that maps the input CBs to the output CBs in a predetermined way. The mapping is done using a permutation function, which is defined by the standard. The permutation function ensures that the CBs are rearranged in such a way that any error introduced by the channel is spread out over multiple CBs.

The second stage of the CRC interleaver is the inter-TB interleaving, which interleaves the TBs within a TBS. The inter-TB interleaving is done to protect the data from the burst errors that occur due to the channel fading. The inter-TB interleaver is a random interleaver that shuffles the TBs in a random order. The random interleaving ensures that the burst errors are spread out over multiple TBs.

The input data is first divided into TBs. Each TB is further divided into CBs. The CBs are then interleaved using the intra-TB interleaver. The interleaved CBs are then grouped into TBs again. The TBs are then interleaved using the inter-TB interleaver. The interleaved TBs are then transmitted over the air interface.

Advantages of CRC Interleaver

The CRC interleaver provides several advantages in the 5G NR system. Some of the advantages are:

1. Error Detection: The CRC interleaver provides error detection capability for the transmitted data. The CRC code is added to each TB before interleaving, and it is checked at the receiver end to detect any errors in the received data. If an error is detected, the receiver requests the retransmission of the TB.
2. Error Correction: The CRC interleaver also provides error correction capability for the transmitted data. The CRC code is used to correct any errors that may have occurred during the transmission. The receiver can use the CRC code to identify the bit position where the error occurred and correct it.
3. Interference Resilience: The CRC interleaver provides interference resilience to the transmitted data. The interleaving process spreads out any errors introduced by the channel over multiple CBs and TBs, reducing the impact of the errors on the received data.
4. Reduced Latency: The CRC interleaver reduces the overall latency of the system by enabling faster retransmission of the TBs that have errors. The receiver can detect the errors in the TBs quickly using the CRC code and request the retransmission of the TB.
5. Improved Throughput: The CRC interleaver improves the overall throughput of the system by reducing the number of retransmissions required due to errors. The interleaving process reduces the impact of errors on the received data, reducing the need for retransmission.

Conclusion

In conclusion, the CRC interleaver is an essential component of the 5G NR communication system that provides error detection and correction capability for the transmitted data. The interleaving process spreads out any errors introduced by the channel over multiple CBs and TBs, reducing the impact of the errors on the received data. The CRC interleaver improves the overall throughput of the system by reducing the number of retransmissions required due to errors, reducing the latency of the system, and providing interference resilience to the transmitted data. The CRC interleaver is a crucial tool in ensuring reliable and efficient communication in the 5G NR system.