Relay Selection And Transmission Mechanism In Cooperative Communications

In wireless communications, the performance of data transmission would be significantly affected by fading path. Due to the dramatic diversity gain, many researchers pay attentions on the hot technique, named Multiple Input Multiple Output(MIMO), to improve data transmission rate and system performance. However, MIMO requires equipped multiple antennas, which is an obstacle for implementation in wireless networks considering the constraints of size, energy consumption and cost in mobile users. In order to solve this issue, cooperative communications have been adopted in recent years.In cooperative communications, the antenna of idle users can be used to forward data, and thus obtain MIMO gain based on Virtual Antenna Array(VAA) without multiple antennas. The selected idle node, called relay, receives data from source node and forwards it to destination node, and thus the system performance can be effectively improved due to the declined fading effect with cooperation. Meanwhile, because of relay, the data transmission procedure in cooperative communications is more complicated comparing with that in conventional direct communications. As a result, collision probability could be increased and interference range could be extended, and these consequences would decline the system performance. Therefore, how to effectively schedule the resource and select the suitable relay is a very important issue in cooperative communications, and this is the reason that relay selection and transmission mechanism should be designed. In this dissertation, according to the characteristic of cooperative communications and construction of relay wireless networks, this dissertation discusses the issues of data transmission scheduling, relay selection and transmission strategy, propose a cooperative new Media Access Control(MAC) mechanism with relay selection, an auction based scheme for relays assignment, cooperative transmission strategies using game theory, and a retransmission mechanism with network coding, respectively.The contributions of this dissertation are listed as follows.This dissertation first analyzes the impact of data packet loss on the system performance caused by transmission error, chooses the suitable relay to forward data to decline the transmission error probability, and further exploits the advantage of cooperative communications. Then, considering the transmission rate improvement and error declination, this dissertation proposes a cooperative MAC mechanism with optimal relay selection(ORS-MAC) to select the most suitable relay and schedule data transmission in cooperative communications. Moreover, this dissertation revises the classic saturation network throughput performance analysis model for cooperation. Finally, the experimental results have validated the rightness and effectiveness of ORS-MAC.Second, on the one hand, cooperative communications could effectively solve the fading effect to improve system performance. On the other hand, relay forwarding would be the interference at other nodes and decline the system performance in multi-hop wireless networks. In order to effectively allocate the resource for cooperation considering both the cooperation advantage and adverse effect of interference, this dissertation proposes an auction model for relay assignment. In auction model, the cooperation advantage and adverse effect of interference is defined as value and cost respectively, to guarantee the benefit of cooperative communications, relay would be assigned for cooperation when value>cost. Specifically, this dissertation proposes a Single round double Auction Scheme(SAS) for centralized wireless network and a Multiple rounds sequential Auction Scheme(MAS) for decentralized wireless network for relay assignment. This dissertation conducts extensive simulation experiments to validate the effectiveness of SAS and MAS.Besides interference, relay might cause the additional competition in MAC layer, which does not exist in direct transmission. As a result, transmission delay would be greater due to the longer back-off duration time, and thus the system throughput would be degraded even data transmission rate in cooperative communications is higher than that in direct transmission. Therefore, this dissertation investigates the impact of transmission strategies on the system throughput using game theory. And then, based on our thorough investigation, Nash Equilibrium Cooperative Transmission Strategies(NECTS) are proposed to guarantee the maximum throughput of individual users and decline the unnecessary competition. The numerical results validate the effectiveness of NECTS strategy and the system performance improvement.In wireless networks, the retransmission should be performed when the transmitted data packet is received incorrectly. Conventional Automatic Repeat Request(ARQ) protocol is inefficient because it retransmits the loss data packet separately. However, due to the broadcasting characteristic of wireless channel, the loss data packet might be obtain by other nodes, which can retransmit data packet to destination node instead of source node. Moreover, Network Coding(NC) can combine multiple data packets as one, which can be adopted at the suitable relay to improve retransmission efficiency. Therefore, this dissertation proposes a probabilistic NC retransmission mechanism, and use Stackelberg game to select relay and motivate it for NC. The experimental results validate the advantage of proposed retransmission mechanism.