Cooperative OFDM for energy-efficient wireless sensor networks

This paper presents a new energy-efficient cooperative sensor network scheme. Cooperative nodes shift the carrier frequency of the source node, and the destination node receives the signal from the source node and the cooperative nodes as a standard orthogonal frequency division multiplexing (OFDM) receiver. The maximal ratio combining (MRC) approach is applied to achieve full diversity with low complexity. The proposed scheme is scalable with respect to the number of nodes and is robust to time synchronization. A clustered network topology and cooperation protocol are proposed to realize multi-hop long haul signal transmission. The effect of the cluster scale is studied thoroughly to obtain the optimal size of clusters subject to the cooperation overhead. Simulation results show that the proposed cooperation scheme can consistently reduce the transmission power with the increase of cooperation scale. However, there is an optimal cluster scale where a good tradeoff between the diversity gain and cooperation cost can be established to minimize the total power consumption of the whole network.