This paper compares the accuracy and complexity of Raghavan and Baum’s Reliability Output Viterbi Algorithm (ROVA), Polyanskiy’s accumulated information density (AID), and Fricke and Hoeher’s lower complexity approximation of ROVA. It turns out that AID is far less accurate than ROVA in practice. This paper proposes codeword information density (CID), which modifies AID to improve its accuracy and leads to a lower-complexity implementation of ROVA. The paper includes an analytical expression for the random variable describing the correct decoding probability computed by ROVA and uses this expression to characterize how the probabilities of correct decoding, undetected error, and negative acknowledgement behave as a function of the selected threshold for reliable decoding. This paper examines both the complexity and the simulation time of ROVA, CID, AID, and the Fricke and Hoeher approximation to ROVA. This paper also derives an expression for the union bound on the frame error rate for zero-terminated trellis codes with punctured symbols and uses it to optimize the order of symbol transmission in an incremental retransmission scheme. This paper concludes by comparing the performance of an incremental retransmission scheme using ROVA as a stopping condition to one that uses a CRC as a stopping condition.

中文翻译：

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维特比解码器可靠性的有效计算与可变长度编码的应用

本文比较了 Raghavan 和 Baum 的 Reliability Output Viterbi Algorithm (ROVA)、Polyanskiy 的累积信息密度 (AID) 以及 Fricke 和 Hoeher 的 ROVA 的较低复杂度近似的准确性和复杂性。事实证明，AID 在实践中远不如 ROVA 准确。本文提出了码字信息密度（CID），它修改了 AID 以提高其准确性，并导致 ROVA 的实现复杂度更低。本文包括一个描述由 ROVA 计算的正确解码概率的随机变量的解析表达式，并使用该表达式来表征正确解码、未检测到的错误和否定确认的概率如何作为可靠解码所选阈值的函数。本文研究了 ROVA、CID、AID，以及 ROVA 的 Fricke 和 Hoeher 近似。本文还推导了带有穿孔符号的零终止格子码的帧错误率联合界的表达式，并使用它来优化增量重传方案中的符号传输顺序。本文通过比较使用 ROVA 作为停止条件的增量重传方案与使用 CRC 作为停止条件的方案的性能来得出结论。