无线多用户多跳中继网络可达自由度研究

Due to the ability of providing wireless systems with diversity gain and communication range extension in a cost-effective and flexible fashion, relay techniques have attracted much interest in both academia and industry in the past few years. Recent research has discovered that, in multi-user multi-hop relay networks, relay terminals also have the potential to further provide degrees of freedom (DoF) gain and enhance spectral efficiency. However, to realize such an advantage, an ideal environment where neither relay’s self-interference nor inter-relay interference exists is normally required. When such interference cannot be avoided, directly applying half-duplex operation to eliminate interference would lead to DoF gain loss. This project aims to combine spectrally efficient half-duplex relaying transmission protocol with network-level interference management technique to handle this issue. Specifically, we alternatively activate half-duplex relays to emulate full-duplex relay operation, and apply interference alignment to minimize the impact of interference, in order to improve channel usage. We consider three situations commonly appeared in practical wireless systems: each relay layer may not contain the same number of relays, terminals attain imperfect channel state information, and wireless links experience time-invariant and frequency-flat fading. We study multi-user multi-hop relay networks’ achievable DoF, to investigate the DoF gain offered by relays. The results of this project will provide new achievable lower bounds for the networks’ optimal DoF, as well as theoretic supports and potential technical solutions for using relays to enhance spectral efficiency in future wireless systems.

以经济、灵活的方式为无线系统提供分集增益和拓展通信范围的中继技术近年来受到了学术界和企业界的高度重视。近来的研究发现，在多用户多跳中继网络，中继还具有进一步带来自由度增益、提高频谱效率的潜力。但是，这通常需要不存在中继自干扰和中继间干扰的理想环境。当这些干扰难以避免时，直接运用半双工机制消除干扰将丢失自由度增益。针对这个问题，本课题将高效半双工中继协议与网络级干扰管理技术相结合，令半双工中继交替工作以模拟全双工机制，并利用干扰对齐技术最小化干扰影响，达到提高信道利用率的目的。针对实际系统中各层中继数目可能不等、节点具有的信道状态信息不准确、无线链路呈现平坦衰落特性等三种情况，通过对多用户多跳中继网络的可达自由度进行深入研究，探索中继带来的自由度增益。研究成果将为多用户多跳中继网络的最优自由度提供新的可达下界，也将为在未来无线系统中运用中继技术提高频谱效率提供理论支持和潜在的技术方案。

近十年来，无线通信技术高速发展，带动了移动互联网和移动物联网业务的日新月异。新设备、新服务、新产业的不断涌现，也给无线网络设计和信息传输技术革新提出了新的挑战。部署中继，以经济、灵活的方式增强无线系统性能的技术在近年来受到学术界和业界的广泛关注。本课题从网络信息论的角度出发，针对无线多用户中继网络的理论极限通信性能分析和高效信息传输方案设计展开了深入研究。课题首先将高频谱利用率的中继转发协议与干扰对齐技术相结合，研究了一系列多用户多跳半双工中继网络和多天线中继网络的可达自由度，探索了中继节点为无线网络带来的自由度增益。通过分析达到最优自由度的理论极限条件，展示了该条件下多用户多跳中继网络的容量随信噪比变化的特征。进一步，基于多用户网络潜在的自由度和频谱效率增益，课题研究了信噪比受限、发射端信道状态信息不准确、平坦慢速衰落等条件对信息传输性能影响的机理，提出了数种利用网络级干扰管理、跨层优化、网络编码等技术实现高效传输的方法。课题的研究成果将为发掘中继技术的潜力、在未来无线网络中提高通信性能和资源利用效率提供理论支持和潜在的技术方案。

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