栅格终止方案对Turbo码性能的影响

Effect of Trellis Terminating Scheme on Turbo Code Performance the Trellis by Different Schemes

针对码速率为 1/3、编码存储级数为 m的 Turbo码 ,研究了 3种栅格终止方案 :传统的单归零栅格终止方案 ,作者提出的前 m尾交织双归零栅格终止方案和第三代移动通信系统 (3GPP)推荐采用的无尾交织双归零栅格终止方案 . Turbo码的译码采用软输出维特比算法 (SOVA) .从译码原理出发 ,对 3种栅格终止方案的设计、译码性能及编码效率进行了分析和比较 ,并通过仿真给出了分别采用 3种栅格终止方案的 Turbo码的误码率曲线 .仿真结果表明 ,前 m尾交织双归零栅格终止方案具有最低的误码率底限 .

Based on 1/3 rate Turbo codes whose memory order is m , three trellis termination schemes are studied: the conventional trellis termination scheme, which only makes one sub encoder have all zero state at the end of encoding; the trellis termination scheme proposed in this paper, which makes two sub encoders have all zero state at the end of encoding and makes the first m tail bits be interleaved and encoded; the trellis termination scheme recommended by 3GPP, which makes two sub encoders have all zero state at the end of encoding and doesn't make any tail bits be interleaved and encoded. Soft output Viterbi algorithm (SOVA) is applied to decoding Turbo codes. On the basis of the decoding principle, the scheme design, decoding performance and encoding efficiency of the three trellis termination schemes are analyzed and compared. The computer simulation results show that the proposed trellis termination scheme has the optimum 'error floor' performance.