[论文解读] The Multi-way Relay Channel

Denız Gündüz, Aylin Yener+2 more|arXiv (Cornell University)|Apr 14, 2010

Cooperative Communication and Network Coding参考文献 28被引用 7

一句话总结

本文引入了多路中继信道（mRC），一种多个用户簇通过公共中继交换信息的模型，每个簇需实现簇内全通信。提出压缩转发（CF）与放大转发（AF）协议，证明CF在任意功率约束下均能实现与容量相差恒定比特数的交换速率，且在对称高斯网络中优于AF，差距有限。

ABSTRACT

The multiuser communication channel, in which multiple users exchange information with the help of a relay terminal, termed the multi-way relay channel (mRC), is introduced. In this model, multiple interfering clusters of users communicate simultaneously, where the users within the same cluster wish to exchange messages among themselves. It is assumed that the users cannot receive each other's signals directly, and hence the relay terminal in this model is the enabler of communication. In particular, restricted encoders, which ignore the received channel output and use only the corresponding messages for generating the channel input, are considered. Achievable rate regions and an outer bound are characterized for the Gaussian mRC, and their comparison is presented in terms of exchange rates in a symmetric Gaussian network scenario. It is shown that the compress-and-forward (CF) protocol achieves exchange rates within a constant bit offset of the exchange capacity independent of the power constraints of the terminals in the network. A finite bit gap between the exchange rates achieved by the CF and the amplify-and-forward (AF) protocols is also shown. The two special cases of the mRC, the full data exchange model, in which every user wants to receive messages of all other users, and the pairwise data exchange model which consists of multiple two-way relay channels, are investigated in detail. In particular for the pairwise data exchange model, in addition to the proposed random coding based achievable schemes, a nested lattice coding based scheme is also presented and is shown to achieve exchange rates within a constant bit gap of the exchange capacity.

研究动机与目标

• 建立并分析一种新型协作通信框架，其中多个用户簇通过共享中继交换信息。
• 刻画高斯多路中继信道（mRC）的可实现速率区域与外 bounds。
• 在编码器受限约束下，评估基本中继协议（解码转发、放大转发、压缩转发）的性能。
• 在对称网络场景下，建立CF与AF协议的性能界限，特别是与容量的差距。

提出的方法

• 采用块马尔可夫编码结构，包含B个消息块与B+1个信道块，中继在下一信道块中转发量化信号。
• 使用随机编码生成码书：用户基于输入分布生成独立同分布的码字，中继基于条件分布生成量化与中继码字。
• 在接收端采用联合典型性译码，每个用户利用传输与接收信号的联合典型序列，译码来自其他用户及中继的信息。
• 在中继引入量化策略：中继观测到信道输出后，从码书中选择一个量化版本，并向所有用户转发。
• 利用典型集论证推导误码概率界限，证明在满足适当速率约束下，当块长n → ∞时，误码项趋于零。
• 通过互信息不等式建立速率约束，尤其针对CF，涉及项如 I(X(S); ˆYr|X(Sc))、I(Xr; Yi) − I(Yr; ˆYr|XK) 与 I(Yr; ˆYr)。

实验结果

研究问题

• RQ1 压缩转发协议是否能在多路中继信道中实现与交换容量相差恒定比特数的交换速率，且与发射功率约束无关？
• RQ2 在可实现交换速率方面，压缩转发与放大转发相比表现如何？
• RQ3 在对称高斯多路中继网络中，决定信息交换的根本速率约束是什么？
• RQ4 在成对数据交换场景中，格编码是否能提升性能？若能，提升幅度如何？
• RQ5 受限编码器（忽略接收信号，仅使用本地消息）对可实现速率区域有何影响？

主要发现

• 压缩转发协议在任意发射功率约束下，均能实现与交换容量相差恒定比特数的交换速率。
• 压缩转发与放大转发协议之间存在有限比特差距，且CF严格优于AF。
• 在成对数据交换模型中，嵌套格编码方案可实现与交换容量相差恒定比特数的交换速率。
• 在对称高斯网络中，CF下的可实现对称交换速率与容量之间存在与信噪比无关的恒定偏差。
• 对高斯mRC的外边界与可实现区域进行了刻画，表明CF在恒定差距内最优。
• 误码概率分析表明，只要速率满足推导出的互信息约束，所有译码错误在块长n → ∞时均趋于零。