Turbo Decoder Design based on an LUT-Normalized Log-MAP Algorithm.

Jun Li,Liang Shan,Jinlong He,Xiumin Wang,Chen Su

doi:10.3390/e21080814

Abstract

Turbo codes have been widely used in wireless communication systems due to their good error correction performance. Under time division long term evolution (TD-LTE) of the 3rd generation partnership project (3GPP) wireless communication standard, a Log maximum a posteriori (Log-MAP) decoding algorithm with high complexity is usually approximated as a lookup-table Log-MAP (LUT-Log-MAP) algorithm and Max-Log-MAP algorithm, but these two algorithms have high complexity and high bit error rate, respectively. In this paper, we propose a normalized Log-MAP (Nor-Log-MAP) decoding algorithm in which the function max* is approximated by using a fixed normalized factor multiplied by the max function. Combining a Nor-Log-MAP algorithm with a LUT-Log-MAP algorithm creates a new kind of LUT-Nor-Log-MAP algorithm. Compared with the LUT-Log-MAP algorithm, the decoding performance of the LUT-Nor-Log-MAP algorithm is close to that of the LUT-Log-MAP algorithm. Based on the decoding method of the Nor-Log-MAP algorithm, we also put forward a normalization functional unit (NFU) for a soft-input soft-output (SISO) decoder computing unit. The simulation results show that the LUT-Nor-Log-MAP algorithm can save about 2.1% of logic resources compared with the LUT-Log-MAP algorithm. Compared with the Max-Log-MAP algorithm, the LUT-Nor-Log-MAP algorithm shows a gain of 0.25~0.5 dB in decoding performance. Using the Cyclone IV platform, the designed Turbo decoder can achieve a throughput of 36 Mbit/s under a maximum clock frequency of 44 MHz.

Highlights

Turbo codes were proposed in 1993, and have been widely used in 3G and 4G wireless communication systems due to their good error correction [1]
The simulation results show that the LUT-Nor-Log maximum a posteriori (Log-MAP) algorithm can save about 2.1% of logic resources compared with the LUT-Log-MAP algorithm
The idea of normalized approximation mainly comes from the low-density parity check (LDPC) decoder based on the normalized min-sum (NMS) algorithm, as proposed by Wu et al in 2010 [7], and we use this method to approximate the function max*

Summary

Introduction

Turbo codes were proposed in 1993, and have been widely used in 3G and 4G wireless communication systems due to their good error correction [1]. Yang et al proposed new, partially information-coupled (PIC) turbo codes in 2018 [2], which can improve decoding performance without changing the decoder. In order to reduce logic resource consumption with the Log-MAP algorithm, Martina et al proposed a turbo decoder with low complexity based on an approximated Log-MAP algorithm in 2014 [3]. Of logic resources by linear approximation of the function max*. In 2018, Liu et al proposed an improved turbo decoder that approximates the function max* with a Taylor series [6]. The idea of normalized approximation mainly comes from the low-density parity check (LDPC) decoder based on the normalized min-sum (NMS) algorithm, as proposed by Wu et al in 2010 [7], and we use this method to approximate the function max*. In 2011, Sun et al proposed a dynamic interleaving structure based on a quadratic permutation polynomial (QPP) interleaver that performs real-time

Methods

Results

Conclusion