LDPC Coded Distributed Space-Time Cooperative Communication System

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.