Reseach On High Spectral Efficiency Transmission Techniques Based On Broad-Sense Cooperative Communication

Distributed wireless network (DWN), such as wireless ad hoc network and wireless sensor network, is one of the hot research directions in wireless communication. On one hand, the reliability, spectral efficiency and energy efficiency of the DWN is low, influenced by wireless fading, distributed control and node capability. So the development and application of DWN are limited. On the other hand, broad-sense cooperative communications, based on multi-hop relaying, fit well the basic characteristic of DWN. This technology can increase the cooperation grade and performance of the whole network and drive the research, development and application of DWN.This dissertation focuses on the multi-hop wireless network and its self characteristic and design demand are considered. On the basis of analyzing the characteristics and advantages of broad-sense cooperative communication, including cooperative diversity, cooperative multiplexing, network coding and opportunistic communication, a research on the broad-sense cooperative communication is presented to improve the performance of DWN. Precisely, the work can be divided into the following four parts.1. In 2x1 MIMO, Alamouti scheme's diversity gain is 2 at most over time-selective fading channels. To achieve more diversity gain, a full-rate space-time codes for time-selective fading (STC-TS) is proposed. The parameter constraint of achieving the diversity gain 2N is discussed. When N=2 and BPSK and QPSK are assumed, the parameters are optimized aiming to maximizing the diversity gain. Simulating results show that the diversity order is almost 4 when N=2 and channels fade fast enough. In middle and high SNR regimes, the transmission scheme based on the proposed code has the better spectral efficiency performance.2. It is well known that opportunistic relaying combats wireless fading and network coding in multicast reduces retransmission times. A network coded multicast retransmission scheme based on opportunistic relaying (NCMR-OR) is proposed, which combines the two above techniques to further improve the efficiency of wireless multi-hop multicast. The outage probability and transmission bandwidth are deduced when two destinations are involved. The two relay selecting strategies, reactive and proactive, are involved. The numerical results show that NCMR-OR is more efficient than the schemes that employs either opportunistic relaying or network coding in multicast.3. Complex field network coded cooperation based on non-orthogonal transmission (CFNCO-NOT) is proposed. Complex field network coding and simultaneous transmission is used to combat wireless fading and improve efficiency of multi-hop multi-user transmission. A simplified detection at destination has the optimal performance. The spectral efficiency is analyzed in two-hop multiple access channels. The results show that at high SNR regimes, the CFNCO-NOT has the higher spectral efficiency compared with the traditional and Alamouti-based strategies. In order to further improve spectral efficiency in middle and low SNR regimes, Cooperative Relaying based on Compressed Packet (CRCP) is proposed. The relay nodes encode and retransmit the received packet cooperatively. The number of transmitting slot is decreased and diversity gain combats wireless fading effectively. The spectral efficiency is analyzed in two-hop multiple access channels. The results show that at high SNR regimes, CRCP has the higher spectral efficiency compared with the traditional strategies. At low and medium SNR regimes, CRCP has the much better spectral efficiency in contrast with complex field network coded cooperation based on non-orthogonal transmission (CFNCO-NOT) strategies. Signal design of multi-access channel is analyzed to decode several signals based on one receiving equation. Signal designing in transmitting node is proposed4. Cooperative multiplexing based transmission in N-way relay networks is proposed. Multiple relaying nodes equipped with single antenna amplify their received signals, which are spatial multiplexing. Receiving nodes can decode with enough observations and the efficiency is improved. The spectral efficiency is analyzed when three nodes communicate with one another via two relaying nodes. Simulation results show that at high SNR regimes, the cooperative multiplexing based transmission has the higher spectral efficiency compared with the traditional and cooperative diversity strategies.