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交织器的引入使Turbo码对不同信息位具有明显的不等保护特性,从而对其性能产生影响。为了提高Turbo码译码性能,在给定的S距离伪随机交织器下,首先通过对多组随机输入信息序列的位误比特率仿真分析,找到对Turbo码性能影响较大的关键比特位置,然后在对Turbo码不等保护特性和已知比特Turbo码进行理论分析和研究的基础上,提出了关键比特不等保护和结合已知比特的Turbo码不等保护两种方案。最后,对提出的方案进行了仿真验证,结果表明在交织长度分别为200和400两种条件下,两种保护方案在高信噪比时与未保护相比均有0.2 dB以上增益,且结合已知比特的Turbo码不等保护方案比关键比特保护方案性能更优。
The introduction of the interleaver makes Turbo codes have obvious unequal protection for different information bits and thus affect its performance. In order to improve the decoding performance of Turbo codes, we first find out the key bit positions which have a great influence on the performance of Turbo codes by simulating the bit error rate of multiple random input information sequences for a given S-distance pseudo-random interleaver. Then based on the theoretical analysis and research on the unequal protection features of Turbo codes and the known bit Turbo codes, two schemes of unequal protection of key bits and unequal protection of Turbo codes combining with known bits are proposed. Finally, the proposed scheme is verified by simulation. The results show that both schemes have a gain of more than 0.2 dB at high signal-to-noise ratio (SNR) and unprotected at both interleaving lengths of 200 and 400 respectively. Known bit Turbo Code Unequal Protection Scheme performs better than Key Bit Protection scheme.