一种适用于短码长LT码的改进编码算法

An Improved Encoding Scheme for Short Length LT Codes

LT码是第一种实用的无速率码,但短码长LT码在加性高斯白噪声(AWGN)信道中的性能不佳,原因是度数为1的校验节点的数量过少以及小度数值信息节点的存在。为了提高短码长LT码的误比特率(BER)性能,提出了一种改进编码算法。改进算法引入了权重因子和小度数分布函数用以间接地提高度数为1的校验节点的比例,从而提高了译码成功概率。算法按度数值从小到大的顺序将信息节点分类成若干个集合,并通过改变校验节点选择信息节点的方式,使得靠前集合中的信息节点始终能被优先选取,从而消除了小度数值的信息节点。仿真结果表明,改进算法在给定信噪比和码率值条件下均能实现BER性能的提升,且最多可获得近4. 6 d B的性能增益。

As the first practical realization of rateless codes, short length LT codes perform poorly in additive white Gaussian noise channel. The reason for this lies in the lack of degree 1 check nodes (CNs) and small degree information nodes (INs). In order to improve the bit error rate (BER) performance of short length LT codes, an improved encoding scheme is proposed. A new degree distribution and two weighting factors are presented, which are used to improve the proportion of degree 1 CNs and increase the probability of decoding successfully. INs are sorted into several sets according to their degrees, and then CNs will preferentially select INs as their neighbors from small degree sets. Thus small degree INs were eliminated. Simulation results show that the proposed scheme can improve the BER performance across a given range of SNR and overhead values, and the proposed LT code can achieve performance improvement up to about 4.6 dB.