【作者】 董波；

【导师】 仇佩亮；

【作者基本信息】 浙江大学 ， 信息与通信工程， 2006， 硕士

【摘要】 在无线通信系统中,分集是一种对抗多径衰落以及信道干扰的有效技术。相比时间分集与频率分集,空间分集可以在不增加传输时间和带宽的条件下,提高系统的传输可靠性。在分布式通信系统中,学者们提出了一种新型的单用户空间分集技术,即合作分集技术。该技术将分布在无线网络中的节点集合起来,构成虚拟多天线阵列,利用多个节点的合作来达到空间分集的效果。目前常用的合作协议包括有固定中继协议、选择中继协议以及增量中继协议。在这些协议中,中继可以工作在放大前向或者译码前向等模式下。不同中继合作系统具有不同的分集系数。基于空时编码的合作分集技术在理论上可以实现完全的空间分集增益,分集系数等于参与合作的节点数量。 论文首先介绍了分布式通信系统中常用的中继模式以及合作分集协议。然后通过对传统的单中继和双中继分布式空时编码合作系统的研究,我们提出了带反馈信息的双中继分布式空时合作系统,并在放大前向模式和译码前向模式下给出了具体的反馈机制和实现方法。该系统能够更充分地利用通信网络中的节点,提高系统的分集增益,改善系统的误比特率性能,但是中继节点在网络中的位置会对系统的性能产生很大影响。 空间分集技术还可以与优秀的纠错码进行结合来进一步提高系统性能。低密度奇偶校验(LDPC)码是一种分组码,它的性能能够逼近香农限,而且译码算法复杂度低,与码长呈线性关系,容易实现。论文在介绍了LDPC码后,对LDPC码与空时分组编码的级联方案(LDPC-STBC)进行了分析。鉴于LDPC-STBC在传统多天线系统中所体现的优越性,我们将LDPC-STBC扩展到了分布式通信系统中,提出了LDPC编码的分布式空时合作系统(LDPC-DSTC)。在放大前向模式下,系统采用固定中继协议来实现,论文给出了多个信号处理方案;而在译码前向模式下,系统采用选择中继协议,并通过凿孔LDPC码以及更换LDPC码组的方式来实现。研究结果表明,LDPC-DSTC系统既能够实现分集增益,又能提供编码增益,有效地提高了系统性能。最后,论文探讨了LDPC码在分布式合作通信系统中的优化问题。更多还原

【Abstract】 Diversity is an effective technique to combat multi-path fading and co-channel interference in the wireless communication system. Compare with the time and frequency diversity, Space diversity gives dramatic performance gains without the additional expenditure of transmission time or bandwidth. A new form of single-user space diversity for the distributed communication system has been proposed, which is called "cooperative diversity". Distributed nodes in the wireless network are collected so that the nodes form a virtual antenna array. Then, the cooperation of the nodes is utilized to achieve the space diversity. The most common cooperative diversity protocols are fixed relaying, selection relaying and incremental relaying. The relay in the system can employ different types of processing, such as amplify-and-forward (AF), decode-and-forward (DF). It is found that different protocols have distinct diversity orders. Space-time based cooperative diversity can achieve full spatial diversity in the number of cooperating terminals.In this dissertation, we first introduce the common cooperative diversity protocols. And then, by studying the conventional one-relay and two-relay distributed space-time cooperative (DSTC) systems, we propose the two relay DSTC system with feedback information. The specific implementations of the proposed system are discussed in both the AF mode and DF mode.The proposed system utilizes the nodes in network more efficiently, so it can reduce the transmission error and offer higher diversity order, but the location of the relays has profound impact on the system performance.Space diversity can be combined with good error correcting codes to obtain more excellent performance. The low-denstiy parity-check (LDPC) code is a linear block code. The performance of the LDPC codes can get close to the Shannon limit, and the complexity of the decoding algorithm is linear with the code length. The concatenation scheme of LDPC codes and space-time block coding (LDPC-STBC) are analyzed. Due to the advantage of the LDPC-STBC in the conventional multi-antena system, this scheme is extended to the distributed communication system, and the LDPC coded distributed space-time cooperative system (LDPC-DSTC) is proposed. In the AF mode, the fixed relaying protocol is employed, and severl signal processing schemes are proposed;in the DF mode, the selection relaying protocols is employed, and the puctured LDPC and the change of LDPC sets are utilized to implement the proposed system. The LDPC-DSTC system can offer both the diversity gain and coding gain. Finally, the optimization of the LDPC codes in the DSTC systems is discussed.更多还原