Energy Efficiency In Cooperative Communication

Higher link data rates will be required because more demanding services are expected in future wireless networks. This requirement cannot easily be achieved by the traditional infrastructure networks currently used, but it is believed that relaying based networks hold great potential in this respect. Relay networks achieve high throughput by utilizing cooperation between nodes and they can be broadly classified as multi-hop networks and virtual antenna arrays (cooperative Multiple-Input Multiple-Output relaying networks).Cooperative diversity is an important technique in wireless communication, it exploit the potential of spatially dispersed user antennas to improve communication reliability. However, in such network, an optimum power allocation method would be useful for the resource management. With energy-constrained networks, such as wireless sensor networks, have nodes typically powered by batteries, for which replacement or recharging is very difficult, if not impossible. Minimizing the energy consumption per unit information transmission becomes one of the most important design considerations for such networks. For that, the relay selection scheme and the relaying techniques used to transmit the information should be written in order to achieve energy efficiency. The power given to both relay and source must be optimized to achieve better performances.This thesis presents a power allocation method called Decode-and-Forward under optimum power allocation. By making a BPSK demodulation and equalization plus hard-decision-decoding at the receiver, we analyze the BER performances when MRC and EGC are used at the receiver as the combining technique. From the simulation results, the average SNR improvement of MRC is typically about 1 dB better than with EGC. The power allocation problem is to find the power of the source and the relay node that maximize the SNR under a total power constraint. We discuss at which position the node should cooperate and how much power should be allocated for cooperation, from the source power and the total power ratio,? the relay position is chosen in order to minimize the BER. Two power allocation methods are deducted, the OPA method and the EPA methods; each one performs better than the other according to the total power and the relay position.