【作者】 王宁；

【导师】 戴旭初；

【作者基本信息】 中国科学技术大学 ， 通信与信息系统， 2012， 博士

【摘要】 无线通信系统中,频谱资源的相对匮乏严重制约着无线通信的发展。因此,人们希望可以在同一频率资源上服务更多的用户,以提高频谱资源的利用率。无线通信中的多天线技术,不仅可以获得传输分集增益,提高通信质量,还可以大幅提高系统的容量。协作中继技术,可以增加系统的覆盖范围,更重要的是提高了通信链路的传输速率及传输可靠性。无线中继系统中的网络编码技术基于干扰利用的观点来处理干扰问题,可以实现信号的双向传输,与传统的单向中继协议相比,提高了系统的吞吐量及频谱效率。无线协作通信系统中的单中继双向信道,将以上几种技术紧密结合,大幅提高了系统的频谱利用率和信道容量,因此得到了广泛的关注。本文在分析和总结已有研究工作的基础上,首先将服务两个用户的单中继双向信道拓展到服务多个用户的单中继多向信道,然后对单中继的多向中继信道展开分析和研究。重点解决该信道中的用户间干扰问题,在此基础上对“对称信道”和“非对称信道”场景中所存在的几个问题展开讨论,并提出了相应的解决方法,改善信道的传输性能。主要研究内容和贡献如下：1)对单中继多向信道系统进行建模,提出了消除多向信道中多个用户之间干扰的方法。在已知精确信道状态信息的条件下,通过用户节点和中继节点的联合预编码设计实现信号空间对齐,并结合网络编码技术,实现用户间无干扰的信息传输。给出了预编码设计的详细步骤,以及每个用户和中继节点的信号处理方法；同时,对该信道模型的误码率性能进行了分析,并得出分集增益。当存在预编码选择自由度时,通过一种简单的预编码选择算法,获得了更好的分集增益性能。理论分析和仿真结果验证了预编码设计和选择方法的有效性、以及信道的误码率性能。2)针对用户与中继节点之间的信道为“对称信道”的场景,提出降低中继节点运算复杂度的方法。在中继节点接收到的信息,是多个用户发送信息的叠加混合,若中继节点直接进行解调和解码,其运算复杂度非常高。在对称信道的情况下,若用户未采用信道编码,提出一种简单的星座图映射方法,降低中继节点接收星座图中的信号点数量；若用户采用了信道编码,在采用星座图映射方法的同时,还利用简化网格图的方法,化简中继节点解码时所使用网格图的结构；同时,提出省略解码-重新编码过程的方法,直接由接收信号解码出在下个时隙所要广播的信号。通过以上几种方法,实现中继节点运算复杂度的降低。对中继节点的运算复杂度做了分析,并进行了仿真验证。3)针对用户与中继节点之间的信道为“非对称信道”的场景,提出了一种自适应传输方案及实现技术。当两个用户与中继节点间的信道状态相差较大时,如果采用固定的调制方式来进行信息传输,整条链路的性能是由较差的信道所决定的。为了充分利用信道的传输能力,提出了一种自适应传输方案,重点解决非对称信道条件下不对称的信息传输问题。用户节点根据各自的信道状态自适应地选择调制方式,在中继节点采用缓存技术来存储传输信道中的不匹配信息；同时,中继节点采用了改进的网络编码和分层调制技术,实现了用户之间不对称的信息传输。对中继节点的缓存大小和信道吞吐量进行了理论分析,并且通过仿真实验验证了该传输方案的性能。更多还原

【Abstract】 With the rapid development of wireless communication, the spectrum resource is becoming scare. The lack of spectrum resources restricts the rapid development of the wireless communication. It is hoped that the same spectrum resource can serve more than one users to improve the spectrum efficiency. The multi-antenna technique can not only get more diversity gain, i.e., more reliability, but also improve the system capacity. Cooperative relaying technique increases the coverage of the system, the data rate and reliability of the transmission links. Network coding technique deals with interference by making use of the interference instead of cancelling it. When the network coding is applied in the cooperative relaying channel, the signals can be transmitted in two-way relaying channel. Compared with the traditional one-way relaying channel, two-way relaying channel can improve the throughput and the spectrum efficiency of the system. The two-way relaying channel with network coding and MIMO technique has recently drawn great attention.This dissertation is an extension of the existing researches. First of all, the two-way relaying channel with two users is generalized to the multi-way relaying channel with multiple users, then the multi-way relaying channel is fully studied. The elimination of the interferences between different users is mainly focused on. And then some problems of the scenario with symmetric channels or asymmetric channels are investigated, and the corresponding solutions are proposed to improve the system performance. The main works and contributions of the dissertation are listed as following:1) The multi-way relaying channel system model is established, and the method for eliminating of the interferences between different users is proposed. Under the assumption that the perfect channel state informations can be known by each node, the precoding of the users and the relay can be designed jointly to align the signal space. With the assistance of network coding, the interference between different users is eliminated. The system symbol-error-rate performance is analyzed, and the diversity gain is obtained consequently. When the dimension of the signal space has redundancy, the selection of the precoding is discussed to obtain higher diversity gain. The theoretical analysis and the simulation results demonstrate the method of the precoding design and selection as well as the system performance.2) Some methods for reducing the computational complexity of signal processing at the relay are proposed, which is fit for the scenario with symmetric relaying channels. The signal received at the single relay is a mixture of the signals from multiple different users, the complexity of decoding and demodulation will be huge. Considering the scenario with symmetric channels, some methods are presented to reduce the computational complexity of signal processing at the relay. If the users do not use channel coding, a simple constellation mapping method is applied to reduce the signal points in the demodulation constellation at the relay. While the users use channel coding, the reduced trellis method is jointly applied with the constellation mapping to further decrease the computational complexity. A modified decoding scheme is proposed by omitting the decoding and re-encoding process, and the signals which will be broadcasted in next phase are decoded directly from the received signals. The complexity at the relay node is reduced by applying the above methods. Finally, the complexity of signal processing at the relay is analyzed, and simulation results demonstrate the system performance.3) An adaptive transmission scheme is proposed for the scenario with asymmetric relaying channels. The channels between users and the relay are different, and the capacity will be determined by the worse channel if the fixed modulation is applied. In order to make full use of the channels, an adaptive modulation scheme is proposed to realize the asymmetric transmission in the scenario with asymmetric channels. Each user can adaptively select the modulation according to their own channel. And at the relay, the buffer technique is applied to save the unmatched bit messages in the channels, meanwhile, a modified network coding and hierarchical modulation are used. The buffer size at the relay and the end-to-end through of the scheme are analyzed, and the simulation is provided to illustrate the performance of the proposed transmission scheme.更多还原