Research On Some Key Technologies Of Broad-Sense Cooperative Communication

Multi-hop wireless network (MHWN), such as wireless ad hoc network and wireless sensor network (WSN) is one of the hot research directions in wireless communication. On the one hand, the reliability, spectral efficiency and energy efficiency of the MHWN is low, influenced by wireless fading, distributed control and node capability. So the development and application of MHWN are limited. On the other hand, broad-sense cooperative communications, based on multi-hop relaying, fit well the basic characteristic of MHWN. This technology can increase the cooperation grade and performance of the whole network and drive the research, development and application of MHWN.In this dissertation, we focus 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 MHWN. Precisely, the work can be divided into the following four parts.1. The application circumstance of physical-layer network coding (PNC) is expanded from two-way relaying model to general network. The general model for PNC is defined and the estimating-and-encoding mapping algorithm based on maximum posterior probability (MAP) is presented. The influences of channel type, number of the participant nodes and channel state information on the performance of PNC are analyzed. And then the optimal energy partition problem is discussed on the condition that the same transmitting energy is maintained. To improve the reliability of PNC for wireless fading channel, the idea of opportunistic relaying is applied into PNC scheme and an opportunistic relaying scheme based on physical-layer network coding (PNC-OR) for two-way wireless relaying channel is proposed. The sum capacity of the destination nodes in PNC-OR for the quasi-static fading environment is developed.2. In order to improve the bandwidth efficiency of half-duplex relays in multi-hop communication, a novel successive relaying scheme based on physical-layer network coding (PNC-SRS) is proposed. And the PNC-SRS achieves the same spectral efficiency in half-duplex multi-hop relaying communication as point-to-point transmission does. Focusing on the 3-hop chain network, the spectral efficiency of three relaying schemes, traditional hop-by-hop relaying scheme, PNC scheme and PNC-SRS, are analyzed. The achievable rate for the PNC-SRS is characterized and results show that PNC-SRS outperforms traditional two-path relaying (TPR) schemes when the links involved in PNC are symmetrical. And then the general PNC-SRS packet-forwarding mechanism for any-hop relay network is presented.3. To improve the transmission efficiency of cooperative diversity and increase the reliability of wireless network coding, cooperative diversity is integrated into network coding scheme. A network coded cooperation technique based on space-time coding is proposed, which combats wireless fading and improves resource efficiency and network throughput. A close form expression for theoretical Bit Error Rate (BER) performance of the information exchange in two-hop chain network is derived and its diversity gain and network coding gain is analyzed. To avoid information exchange error, the ST-NCC scheme is ameliorated and the opportunistic network coded cooperation (ONCC) is proposed. Focusing on the bi-directional traffic flows in wireless cooperative relaying network, we group the ONCC schemes, termed as 3-step and 2-step schemes respectively, and we develop and analyze their bit error probabilities and network-coding gain. The numerical results show that in contrast to traditional scheme full diversity is achieved by both ONCC schemes and asymptotical 4/3 and 2 times of network-coding gain are obtained by 3-step and 2-step ONCC schemes respectively. In addition, because of opportunistic relaying of multiple nodes, the network-coding gain of ONCC is more considerable in the medium SNR range.4. To improve the reliability of cooperative multiplexing technique in low SNR range, network path selection technique is combined with distributed spatial multiplexing technique and the cooperative multiplexing based on network path selection (NPS-CM) is proposed, which can achieves both spatial multiplexing gain and multi-user diversity gain. Focusing on the two-hop model in which two source nodes communicate with a destination node through several relay nodes, the BER and the spectral efficiency of NPS-CM are analyzed. To improve spectral efficiency farther, the idea of opportunistic decoding is applied into distributed spatial multiplexing and the cooperative multiplexing based on opportunistic decoding-and-forwarding is proposed, which utilizes the advantageous opportunities to improve the network throughput.