[论文解读] Transmission Schemes for Four-Way Relaying in Wireless Cellular Systems

Huaping Liu, Petar Popovski+4 more|arXiv (Cornell University)|Sep 26, 2012

Cooperative Communication and Network Coding参考文献 17被引用 4

一句话总结

本文提出了一种用于蜂窝网络中四路中继的两阶段传输方案，其中两个移动站（MS）通过相对中继站（RS）与基站（BS）双向通信。通过利用上行链路/下行链路的并发传输以及网络编码，该方案显著提升了频谱效率——尤其在解码与转发（DF）中继下表现突出——实现了比传统时分复用或无干扰方案更优的空间复用增益和更大的可译码速率区域。

ABSTRACT

Two-way relaying in wireless systems has initiated a large research effort during the past few years. While one-way relay with a single data flow introduces loss in spectral efficiency due to its half-duplex operation, two-way relaying based on wireless network coding regains part of this loss by simultaneously processing the two data flows. In a broader perspective, the two-way traffic pattern is rather limited and it is of interest to investigate other traffic patterns where such a simultaneous processing of information flows can bring performance advantage. In this paper we consider a scenario beyond the usual two-way relaying: a four-way relaying, where each of the two Mobile Stations (MSs) has a two-way connection to the same Base Station (BS), while each connection is through a dedicated Relay Station (RS). While both RSs are in the range of the same BS, they are assumed to have antipodal positions within the cell, such that they do not interfere with each other. We introduce and analyze a two-phase transmission scheme to serve the four-way traffic pattern defined in this scenario. Each phase consists of combined broadcast and multiple access. We analyze the achievable rate region of the new schemes for two different operational models for the RS, Decode-and-Forward (DF) and Amplify-and-Forward (AF), respectively. We compare the performance with a state-of-the-art reference scheme, time sharing is used between the two MSs, while each MS is served through a two-way relaying scheme. The results indicate that, when the RS operates in a DF mode, the achievable rate regions are significantly enlarged. On the other hand, for AF relaying, the gains are rather modest. The practical implication of the presented work is a novel insight on how to improve the spatial reuse in wireless cellular networks by coordinating the transmissions of the antipodal relays.

研究动机与目标

• 为解决传统半双工单向或双向中继在蜂窝网络中频谱效率受限的问题，探索新型业务模式。
• 研究通过协调中继联合处理四个数据流（两个双向链路）所带来的性能增益。
• 设计一种两阶段传输方案，结合广播与多址阶段，以在四路中继场景下最大化频谱效率。
• 将所提方案与传统时分复用及无干扰方案进行比较，重点分析不同中继协议下的可译码速率区域。
• 通过相对中继部署，为蜂窝网络中的空间复用与干扰协调提供理论洞见。

提出的方法

• 设计两阶段传输方案：第一阶段为BS向两个RS广播下行链路，同时MS向RS进行上行多址接入；第二阶段角色反转，RS向MS和BS发送信号。
• 在第一阶段，BS采用叠加编码以支持同时向两个RS传输，实现速率分割与干扰管理。
• 在RS处应用网络编码原理，联合解码并重新编码上行链路信号后转发，利用信道状态信息。
• 基于信息论的高斯码本，分析在两种中继模型下的可译码速率区域：解码与转发（DF）和放大与转发（AF）。
• 通过BS处多址（MA）区域角点之间的时分复用，实现第二阶段的完整MA容量区域。
• 推导并证明通过逐次检测与干扰消除技术，第二阶段速率的上界可实现。

实验结果

研究问题

• RQ1 在通过相对中继实现的四路中继场景中——即两个双向MS-BS链路——是否能实现比传统时分复用或无干扰方案更高的频谱效率？
• RQ2 在两阶段传输方案中，网络编码的使用如何改善可译码速率区域，相较于传统中继协议？
• RQ3 在此四路中继设置中，解码与转发（DF）中继与放大与转发（AF）中继相比，性能增益如何？
• RQ4 通过在最优码字之间进行时分复用，是否能实现第二阶段BS处的完整多址容量区域？
• RQ5 该方案在多大程度上通过协调相对中继的传输，提升了蜂窝网络中的空间复用能力？

主要发现

• 在解码与转发（DF）中继下，所提方案相比传统时分复用方案，显著扩大了可译码速率区域。
• 在放大与转发（AF）中继下，与传统方案相比性能增益有限，表明在此设置中DF更为有效。
• 通过在实现MA区域角点的码字之间进行时分复用，第二阶段BS处的完整多址（MA）容量区域可实现。
• MS处的下行链路速率 $ R_i^d $ 达到了其对应信道 $ h_{i1} $ 的单用户容量，证实了单个链路的最优性能。
• 上行链路速率 $ R_i^u $ 通过联合解码与干扰消除进行优化，其速率取决于BS处的有效信干噪比。
• 第二阶段速率的理论上限被证明可实现，验证了在给定假设下所提传输策略的最优性。