摘要： LT码的BP译码算法复杂度较高，在译码时由于Tanner图短环的出现易产生震荡效应。为此，提出一种软比特域迭代译码算法。将双曲正切函数进行变换和量化处理，得到( 1,1)区间的软比特域，并将变量节点信息更新算法变换到软比特域中进行计算。为解决LT码中短环的存在导致某些变量节点的外信息出现震荡效应的问题，给出一种新的震荡判断准则，只有当变量节点在连续2次迭代时符号发生反转，且软比特域值均高于阈值时判定为出现震荡。仿真结果表明，简化软比特域震荡迭代译码算法约比传统BP算法降低75%的运算量，并在误码率性能上逼近BP算法。
关键词:
LT码,
BP算法,
软比特域,
双曲正切函数,
震荡效应,
符号翻转规则
Abstract: The Belief Propagation(BP) algorithm of LT codes not only has high complexity but also has oscillation effect due to present of short loop in the tanner graph. To solve the two problems, a new oscillating iteration algorithm based on soft-bit domain is proposed. The hyperbolic tangent function is transformed and quantified to soft-bit domain( 1,1). The information update algorithm of variable nodes is transferred to soft-bit domain. In LT codes, some outer information of variable nodes exists oscillating effect due to short loops, and the decoding performance is affected badly. A new criterion is presented to judge the oscillate effect. When the sign of variable node flips between two adjacent iterations and the soft-bit values are higher than a given threshold, the oscillate effect exists. The simulation results show that the proposed algorithm gets 75% lower than the BP algorithm in the amount of computation and the bit error rate performance of soft-bit domain decoding algorithm is very close to the traditional BP algorithm.
Key words:
LT codes,
Belief Propagation(BP) algorithm,
soft-bit domain,
hyperbolic tangent function,
oscillating effect,
symbol flip criterion
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