面向不等差错保护的低误码平台LT编码算法

Low error floor LT coding algorithm for unequal error protection

为了解决传统不等差错保护(UEP)LT码算法在加性白高斯噪声信道中存在的高误码平台、慢收敛速度等问题,设计一种系统UEP-LT编码方案。该方案将校验节点分成两段传输以实现对重要数据的保护。固定段校验节点只连接到重要数据以使其最接近译码成功状态。无速率段的节点会按照权重系数选取邻居消息节点,从而使重要数据始终优先译码,并且简化了编码结构。此外,基于外信息传递(EXIT)图法分析了不同等级数据的译码收敛性,旨在为重要数据提供足够宽的译码通道,为次要数据提供开放且不太窄的译码通道。之后,以此为约束条件构建了度分布设计模型,为固定段和无速率段设计了独立的校验度分布。仿真结果表明,所提方案的误比特率性能优于现有的UEP-LT编码方案,且编码开销可节省至码长的18%。

To solve the problems that high error floor and poor convergence of the conventional unequal error protection(UEP)LT code algorithm in additive white Gaussian noise(AWGN)channel,a systematic UEP-LT coding scheme was proposed.In the proposed scheme,the check node was divided into two segments for transmission to protect the important data.The check nodes in the fixed segment were only connected to important data to make it nearest to decoding success.Check nodes in the rateless segment would select neighbor message nodes according to weight coefficients,so that important data was always preferentially decoded,and the coding structure was simplified.Moreover,the decoding convergence behavior of different levels of data was analyzed based on the extrinsic information transfer(EXIT)chart method,and it was expected to provide a wide enough decoding tunnel for important data and an open but not too narrow decoding tunnel for secondary data.Then,a degree distribution design model was proposed based on this constraint,and independent check degree distributions were designed for the fixed segment and the rateless segment.Simulation results show that the bit error rate performance of the proposed scheme outperforms the existing UEP-LT coding schemes,and the coding overhead can be saved up to 18%of the code length.