According to the Consultative Committee for Space Data Systems (CCSDS) recommendation for TeleCommand (TC) synchronization and coding, the Communications Link Transmission Unit (CLTU) consists of a start sequence, followed by coded data, and a tail sequence, which might be optional depending on the employed coding scheme. With regard to the latter, these transmissions traditionally use a modified Bose-Chaudhuri-Hocquenghem (BCH) code, to which two state-of-the-art Low-Density Parity-Check (LDPC) codes were later added. As a lightweight technique to detect the presence of the tail sequence, an approach based on decoding failure has traditionally been used, choosing a non-correctable string as the tail sequence. This works very well with the BCH code, for which bounded-distance decoders are employed. When the same approach is employed with LDPC codes, it is necessary to design the tail sequence as a non-correctable string for the case of iterative decoders based on belief propagation. Moreover, the tail sequence might be corrupted by noise, potentially converting it into a correctable pattern. It is therefore important that the tail sequence is chosen to be as much distant as possible, according to some metric, from any legitimate codeword. In this paper we study such problem, and analyze the TC rejection probability both theoretically and through simulations. Such a performance figure, being the rate at which the CLTU is discarded, should clearly be minimized. Our analysis is performed considering many different choices of the system parameters (e.g., length of the CLTU, decoding algorithm, maximum number of decoding iterations).

翻译：根据空间数据系统咨询委员会（CCSDS）关于遥控指令同步与编码的建议，通信链路传输单元由起始序列、编码数据及尾序列组成，其中尾序列根据所采用的编码方案可能为可选部分。在编码方案方面，此类传输传统上采用改进的Bose-Chaudhuri-Hocquenghem码，后续又引入了两种先进的低密度奇偶校验码。作为一种轻量级的尾序列存在性检测技术，传统方法基于解码失败机制，选择不可纠正字符串作为尾序列。该方法在采用限距解码器的BCH码中表现优异。当将相同方法应用于LDPC码时，需针对基于置信传播的迭代解码器设计不可纠正的尾序列字符串。此外，尾序列可能受噪声干扰而转变为可纠正模式。因此必须依据特定度量标准，使尾序列与所有合法码字保持最大距离。本文研究该问题，并通过理论与仿真分析遥控指令拒绝概率。该性能指标表征通信链路传输单元的丢弃率，显然应当最小化。我们的分析考虑了多种系统参数选择（如通信链路传输单元长度、解码算法、最大解码迭代次数）。