无线异步双向中继通信系统中的协作分布式编码技术研究

It is well known that the multiple relay nodes can assist to transmit the information signals between two communication terminals in wireless two-way relay networks, which are important wireless communication technique for the future fourth-generation (4G) age and have wide application prospects. However, it was found that the data asynchronous transmission is inevitably occuring in the cooperative system because the different relay nodes at in dirrerent locations and have their own oscillators. Therefore, in this project we will build the transmission model of wireless relay network. To combat the time errors and frequency offsets at the relay nodes, orthogonal frequency-division multiplexing (OFDM)-based cooperative transmission technique is exploited. Besides, carrier frequency offset (CFO) may destroby the orthogonality of the subcarriers and result in inter carrier interference (ICI) in asynchronous cooperative OFDM transmissions, which will have to be overcomed. In addition, it is important to analytically find the relay power allocation that minimizes an upper bound on the pairwise error probability (PEP), which can improve performance of cooperative system. In order to achieve full diversity and maximum coding gain in cooperative system, we will propose novel distributed space-time block codes. In fact, they have the best performance of all known codes in their class. Beyond this, the decoding complexity of this codes will be reduced greatly. Our work will not only provide an efficient way of distrubuted coding but also promote the development of the wireless relay networks, showing important theoretical and practical significance.

无线双向协作网络能够利用多个中继节点在两个通信节点之间相互传输信息,是未来4G时代重要的无线通信技术,有重要的应用前景。本项目拟研究其三个关键点，首先，由于不同的中继节点有着不同的位置和振荡器，协作系统不可避免的产生信号异步传输等问题，本项目拟建立双向中继传输网络模型，利用OFDM协作技术解决多个中继节点之间的时间误差和频率偏移问题，并克服载波间频率偏移引起的载波干扰问题；其次，中继节点的能量分配方案直接影响到协作系统的性能，研究节点能量分配方案、提高系统能源效率，使其在有限的能量消耗下获得最优性能为项目第二个内容；最后，为了获取协作系统的最大分集和编码增益，本项目将提出一种全新的协作分布式空时编码，其性能在同类主流编码中达到最优，同时又能大幅降低解码复杂度。本项目的研究内容，不仅为分布式编码方法的研究提供一条有效途径，同时也会推动无线中继网络理论及应用技术研究的发展。

课题组在无线异步通信协作的几个关键论题上进行了探索和研究。一是在无线异步通信协作分布式编码技术和协作策略上，进行了全新的编码和协作策略设计，获得了更高的协作分集增益、编码增益和带宽利用效率，从而使得无线中继网络通信获得更高的通信速率和质量，在中继网络模型理论研究中，设计了两种新的双向中继网络模型及相应协作传输方案：半双工异步双向中继网络模型和全双工异步双向中继网络模型及相应传输方案。二是对无线多中继协作通信系统中频偏/时偏问题进行了研究，解决由多个中继节点组成的无线中继通信系统在同步环境下具有满分集增益问题，提出并证明了定理：在无线中继通信系统中，如果中继节点与目的节点之间的等效信道矩阵具有正交性，那么简化的迫零译码等效于最大似然译码，将已有的正交空时分组码改进设计成了一类对应的正交空频码，将此类正交空频码应用于无线中继通信系统中时，系统的码率、误比特率、译码复杂度三个性能得到了全面提升。三是对MIMO-中继信道建立了数学模型，对格基规约在MIMO信道预编码中创新性的提出利用格基规约进行发送端、中继端的联合预编码，提出了一种基于取模的优化转发方案，大大提高了中继节点的功率效率，又提出了一种平移策略，用来降低预编码后畸变的发送符号星座的平均能量，进而进一步提高了发送端的效率。这些研究内容是无线中继网络通信研究的重要组成部分，在理论推导和实验数据方面给出了非常有意义的参考。发表的研究成果获得了国际权威期刊认可和好评。 课题组在项目完成过程中遵守财务规则，计划与实际科目数字基本一致，决算符合要求。