Sequential Random Selection Relaying for Energy Efficient Wireless Sensor Networks

In a wireless sensor network with relaying capability, intermediate relay nodes are with limited energy budget. To maximize lifetime of relay nodes, selective relay strategies, requiring full channel state information (CSI), are used to utilizes the best relaying channel. Pilot overhead on relay nodes lifetime is reduced by assuming pilot transmission from destination instead of relay nodes. This is only valid if channel reciprocity is assumed. It is evident that channel reciprocity is not valid for low cost simple transceivers, such as sensor node transceivers. In this paper a novel sequential random (SR) selective cooperative relay strategy is proposed in amplify and forward (AF) relay networks for applications with non reciprocal links. The outage probability of SR strategy is derived and its average lifetime, average number of pilot signals per transmitted message, and average transmit energy per message are simulated. SR strategy uses less number of pilots than selective cooperative relay strategies (S-CRSs). A dynamic transmit power threshold is adopted for the proposed SR strategy to improve its performances. In contrast to S-CRSs, in which each relay knows its CSI to the destination before every transmission, SR acquires CSI on the need- to-know basis and significantly outperforms the lifetime of S-CRSs for large number of relays and relatively good channel conditions. The proposed SR selects relay nodes in a distributed manner which makes it suitable for heterogeneous ad-hoc sensor networks in which some relays have processing capabilities and less restricted energy supply, i.e. these relays can act as the intermediate destinations.