[论文解读] On the Optimality of Successive Decoding in Compress-and-Forward Relay Schemes

Xiugang Wu, Liang‐Liang Xie|arXiv (Cornell University)|Sep 29, 2010

Cooperative Communication and Network Coding被引用 9

一句话总结

本文证明，在压缩-转发中继网络中，连续解码始终能实现原始消息的最优速率，即使存在多个中继或联合解码的情况。它证明了不支持连续解码的压缩方式会导致严格更低的速率，且联合解码无法提升速率——这表明，延迟的逐块反向解码，而非重复编码，才是近期框架中速率增益的真正来源。

ABSTRACT

..... joint decoding provides more freedom in choosing the compression at the relay. However, the question remains whether this freedom of selecting the compression necessarily improves the achievable rate of the original message. It has been shown in (El Gamal and Kim, 2010) that the answer is negative in the single-relay case. In this paper, it is further demonstrated that in the case of multiple relays, there is no improvement on the achievable rate by joint decoding either. More interestingly, it is discovered that any compressions not supporting successive decoding will actually lead to strictly lower achievable rates for the original message. Therefore, to maximize the achievable rate for the original message, the compressions should always be chosen to support successive decoding. Furthermore, it is shown that any compressions not completely decodable even with joint decoding will not provide any contribution to the decoding of the original message. The above phenomenon is also shown to exist under the repetitive encoding framework recently proposed by (Lim, Kim, El Gamal, and Chung, 2010), which improved the achievable rate in the case of multiple relays. Here, another interesting discovery is that the improvement is not a result of repetitive encoding, but the benefit of delayed decoding after all the blocks have been finished. The same rate is shown to be achievable with the simpler classical encoding process of (Cover and El Gamal, 1979) with a block-by-block backward decoding process.

研究动机与目标

• 确定在具有多个中继的压缩-转发中继方案中，联合解码是否能提高可实现速率。
• 研究不支持连续解码的压缩方式是否能提升原始消息的速率。
• 澄清近期多中继网络中速率提升框架里，重复编码与延迟解码各自的作用。
• 确定压缩选择对原始消息解码无效的条件。

提出的方法

• 在压缩-转发中继网络中，对连续解码与联合解码下的可实现速率进行分析比较。
• 推导考虑不同压缩策略的多中继压缩-转发方案的速率界。
• 通过评估Lim等人（2010）提出的重复编码框架，将延迟解码的贡献与重复编码的贡献分离开来。
• 在经典编码中使用逐块反向解码，以复现重复方案中观察到的速率增益。
• 识别即使在联合解码下也无法解码的压缩方式，以及它们对原始消息解码的无关性。

实验结果

研究问题

• RQ1 在多中继压缩-转发网络中，联合解码是否能提供高于连续解码的可实现速率？
• RQ2 不支持连续解码的压缩方式是否能提升原始消息的速率？
• RQ3 Lim等人（2010）提出的重复编码框架中的速率提升，是由于重复还是延迟解码？
• RQ4 是否存在即使在联合解码下也无法对原始消息解码产生任何贡献的压缩方式？

主要发现

• 在多中继压缩-转发方案中，联合解码无法提升可实现速率，相较于连续解码。
• 不支持连续解码的压缩方式会导致原始消息的可实现速率严格降低。
• 任何即使在联合解码下也无法解码的压缩方式，对原始消息的解码均无贡献。
• Lim等人（2010）提出的重复编码框架中的速率提升，源于延迟解码，而非重复。
• 通过使用经典编码与逐块反向解码，可获得与重复框架相同的可实现速率。