Research On Power Allocation And Energy Efficiency For Relay Cooperative Communication System

Relay cooperative communication technology can effectively expand the coverage area and improve the system performance of wireless network. In relay cooperative system, the power allocation for each node will change the link performance so as to cause the change in overall system performance. Adopting different power allocation strategies can improve the system performance with fixed power consumption, or it can save energy consumption under the constraint of performance. In the network with energy-constrained nodes, energy efficiency is related to the entire lifetime of network. In order to draw up cooperation strategies suitable for different application scenarios, it is necessary to analyse and compare the energy efficiencies of different cooperative relay networks. The major work and contribution of this paper are as follows:(1) One-way relay transmission(OWRT) system is studied. Considering the trade-off of the multihop channel and the multihop diversity channel, an improved multihop OWRT system based on decode-and-forward protocol is proposed. The improved system can improve the system performance without extra computational costs and hardware complexity at the receiver of each relay node. Outage probability of the proposed system is derived, power allocation optimization problem are formulated and evaluated by minimizing the outage probability with the use of Lagrange multiplier method. Numerical results show that optimal power allocation can enhance system performance, especially if the number of relays is large.(2) Two-way relay transmission(TWRT) system is studied. For the two hop two-way relay transmission(TWRT) system, the outage probabilities(OPs) of amplify-and-forward(AF) and decode-and-forward(DF) strategies are derived, respectively. Optimal power allocation(OPA) problem are formulated and evaluated by minimizing the outage probability with the constraint of total power. Simulation results show that, the outage performance of AF-TWRT is inferior to that of DF-TWRT when the relay is close to one end. Compared with DF-TWRT, AF-TWRT is more suitable for the scenes with asymmetric two-way data rates. Moreover, OPA scheme can enhance system performance under the constraint of total power, especially when the difference of the two hop channel state is large.(3) AF-TWRT system with multi relays is studied. The signal-to-noise ratio(SNR) of two hop AF-TWRT system is analyzed, and the joint optimization problem of relay selection and power allocation based on instantaneous SNR is investigated under the predefined data rate requirements. It is proved that the proposed relay selection scheme can achieve the same DMT performance as obtained by the popular outage-optimal opportunistic relaying scheme. Simulation results demonstrate that the proposed scheme can significantly decrease the power consumption compared with random relay selection and other schemes.(4) AF-TWRT system with asymmetric rates is studied, the problems of relay selection and power allocation based on statistical channel state information are investigated for this system. First, by converting the Geometric Programming to convex optimization problem, the closed-form solution of the power allocation aiming at minimizing total transmit power under the outage probability constraints are obtained. Further, an optimal relay selection criterion based on minimum total power is proposed. As a result, the strategy and steps of joint relay selection and power allocation are given. Simulation results demonstrate that the proposed scheme can significantly decrease the outage probability under the predefined power consumption constraints.(5) Considering of both the transmit power and circuit power, the energy efficiencies(EEs) of OWRT and TWRT systems based on decode-and-forward protocol are studied. The EEs are maximized by jointly optimizing the transmission time and the transmit powers. In the simulations, the optimum EE and optimum transmit time of OWRT is compared with that of TWRT, and the impacts of circuit power, packet size, time deadline and the channel gain to EE are revealed.