Cooperative Transmission Techniques In Cross-Layer Design

Cooperative communication is one of the most vibrant research areas in the communication field today, which is considered as the next big step after multiple-input multiple-output (MIMO), and is very likely to be a key technique in future wireless communication systems. Conventional cooperative transmission techniques are severely limited by the layered architecture of wireless communication systems, which can not fully exploit the diversity gain brought by node cooperation. Therefore, cross-layer design is especially important for cooperative transmission techniques. On the other hand, by introducing the relay nodes, the structure of the networks becomes more complex, and the number of wireless links increases dramatically, which brings a lot challenges to the design of the cooperative system. This thesis explores the node cooperation techniques in a cross-layer design framework, and discusses the design principles of combining cross-layer design with node cooperation. Several cooperative transmission schemes with low complexity are proposed for multimedia unicast and multicast in future wireless communication systems. The effectiveness and feasibility of the proposed schemes are validated through theoretical analysis and simulation.First, the problem of energy-efficient transmission in two-way relay cellular networks is investigated. We study the impact of asymmetric traffic, energy constraint and mobility of user terminals and relays on the energy-efficiency of cooperative transmission techniques. Convex optimization tools are used to derive the optimal transmission rate and relay location which maximizes the energy-efficiency. And, a joint uplink and downlink relay selection scheme is proposed to incorporate the above results in practical systems. The proposed scheme considers the traffic condition in application layer and the energy consumption in hardware layer, which outperforms the relay selection schemes introduced in previous works in terms of energy efficiency, and can be easily implemented in future wireless networks.Then, the problem of relay selection and link adaptation is studied. Traditional methods can not exploit the temporal and spatial diversity gain brought by channel variation and multiple relays effectively. To deal with this problem, we propose a joint relay selection and link adaptation scheme and the corresponding feedback mechanism, which enables the link adaptation to exploit the good channel condition created by relay selection. Simulation results and theoretical analysises suggest that the proposed scheme can enhance the throughput effectively compared with pure relay selection and link adaptation, which proves the benefit of cross-layer design in cooperative networks. Moreover, the overhead of relay selection and link adaptation is reduced dramatically.Afterwards, we consider the scenario where cooperating nodes trying to jointly decode the multicast packets from the base station (BS). To improve the throughput of multicast transmission, a sophisticated relaying protocol which combines the hybrid automatic retransmission request (HARQ) with application layer network coding is proposed. The proposed Leader in Charge (LiC) architecture exploits the short range communication between the users, which reduces the load of the BS, and improves the throughput of the multicast session. In order to make the proposed LiC architecture work in practical systems, some practical issues are also studied, such as the delay-throughput tradeoff, the opportunity of network coding and retransmission scheduling.Finally, we investigate the relay selection problem in a multicast scenario, which has hardly been addressed in the relay selection literature. The biggest challenge in a multicast relay selection is how to select the optimal relay in a timely fashion using limited feedback. As the solution to this problem, two relay selection schemes are proposed for Max-Min selection and Best Harmonic Mean selection criteria respectively. Instead of obtaining the CSI of each specific channel, the relays compute the harmonic mean function of the channel information via the multiple access channels from the destinations to each relay. By doing so, the overhead is limited to O(L), while achieving a diversity of L-ε, where L is the number of relays andεis a positive number that can be arbitrarily small. From the thesis, it can be found that, cooperative transmission techniques based on cross-layer design exploits the characteristics of different protocol layers, and utilizes the diversity generated from the antenna and channel of different nodes effectively, which can significantly improve the performance and increase the energy-efficiency and throughput of the systems.