Study On Coding And Cooperative Transmission In Wireless Relay Systems

How to achieve higher transmission rate and provide wider bandwidth is be-coming more and more important with the rapid development of wireless commu-nications. The key issue of these problems is how to increase the channel capacity.The emergence of relay and cooperative transmission can expand the network cov-erage and increase the network capacity. This technology can solve the problem oftransmission distance, which is becoming one of the focuses in recent years. Basedon the existing theoretical results, the traditional coding techniques are appliedto the relay channel in order to achieve the better performance, and cooperativetransmissions are researched in this dissertation.We consider the time variant property in (1,1,1) relay channel with one sourcenode, one relay node and one destination node at frst. A new system scheme is de-signed based on the system error probability. According to the encoding function,the error correct code with optimal Hamming distance is chosen for the transmittedsignal on diferent channel in order to minimize the system error probability. More-over, the time variant power allocation algorithm is used to optimize the transmitpower between the source node and relay node. When the channel is (1, MR,1)(MR>1) relay channel consists of multiple relay nodes, a selective relay schemeby using high efcient q-ary Low-Density Parity-Check (LDPC) codes is proposed.The parity check matrices have the dual-diagonal structure. The relay nodes aresorted according to the channel state information, and maximum likelihood decod-ing (MLD) is performed based on the best NRnodes (NR≤MR). This scheme canlower the complexity and error probability of the system on quasi-static Rayleighfading channels.Then, a superposition modulation algorithm is proposed, which can mitigatethe inference between users in (MS, NR,1)(MS>1, NR>1) relay channel withMSsource nodes, NRrelay nodes and one destination node. Each user transmitsits own signal while relays other users’ signals, and the superposition modulationfunctions are designed jointly to form the reconstructed signals. The destinationcancels the inference by the use of these functions. The reconstructed signal powerof each user is adjusted to maximize the system capacity. When the channel is(MS, NR, KD)(MS>1, NR>1, KD>1) relay channel consists of multiple des-tination nodes, a new multi-user cooperative communication scheme is presentedbased on the opportunistic communication and network coding. On the basis of outage probability, each user decides whether to help forward its partner’s infor-mation as a relay or not. The relay node processes its own information and thepartner’s information by the use of network coding, and transmits it to the receiver.The receiver can obtain several transmitters’ information and handle them with co-herent detection. This method can select the relay node reasonably and increasethe network throughput evidently in the quasi-static Rayleigh fading channel.