An Efficient Low-Latency Algorithm and Implementation for Rate-Matching and Bit-Interleaving in 5G NR

Abstract

5G New Radio (NR) is primarily characterized by multi-Gbps throughput and up to 10X lower latency than LTE. 5G adopts Low-Density Parity Check (LDPC) code as the channel coding candidate for data channels. Rate-Matching and BitInterleaving functions are performed after LDPC encoding in the transmit signal chain. The purpose of Rate Matching is to select a specific set of encoded bits for transmission by the process of puncturing and/or repetition to support HARQ operation. The output of the Rate-Matching butter goes through row-column permutation function in Bit-Interleaving process. The rate-matched bits from the circular butter are written in row-first order into another butter and read in column-first order. While copying the bits from the rate-matching circular butter, the filler bits are skipped and does not enter the row-column butter. The ratematching butter to row-column butter copy operation accounts for the overall latency in the transmit chain. This paper addresses the latency aspects while processing the large Transport Blocks corresponding to the maximum downlink (DL) throughput. An efficient M-parallel look-ahead pointers generation algorithm is proposed to read M-interleaved bits directly from rate-matching butter, avoiding row-column permutation operation, and thus the need of a separate butter, where M is programmed for a target latency.