Use of relays in extending network lifetime

We describe a simple physical-layer relay scheme for wireless communication in which a set of low-noise linear amplify-and-forward relays are placed between transmitter and receiver to assist radio communication. By exploiting the geometric gain resulting from the location of properly deployed relays, part of the radio transmission power of the information source can be off-loaded to these relays. We argue that such a simple relay scheme can thus provide a transparent and management-free alleviation to the problem of limited battery time in application scenarios like sensor networks, where radio transmission can consume a significant portion of the battery-provided energy. We use simulation to quantify the bit error rate (BER) performance of the relay scheme in a low signal-to-noise ratio (SNR) regime when used in conjunction with the maximal ratio combining (MRC) scheme and Alamouti space-time codes. We show that, under a reasonably precise indoor radio propagation model derived from measurements, the proposed relay scheme is capable of reaping the geometric gain attained from a set of relays deployed midway between the transmitter and the receiver to extend effectively the battery lifetime of the network.