Relay Selection Schemes for Uniformly Distributed Wireless Sensor Networks

The relay selection problem in a large wireless sensor network (WSN) with uniformly distributed identical nodes is investigated for a two-phase cooperative protocol where the signal transmitted from a single source is overheard by the network and is then relayed by multiple selected nodes subject to a total average transmission power. First, a relay selection technique is considered that maximizes the average signal-to-noise ratio (SNR) at the access point (AC) while is applicable to a distributed WSN where only a limited information is available to the nodes. As this technique is shown to be energy inefficient, two other alternative relay selection techniques are also presented that substantially reduce the energy consumption of the network. One of these alternative techniques takes advantage of the static nature of the network topology and, as verified by simulations, achieves near-optimal SNR performance, while the other one randomly selects the relays from a neighborhood around the source and further guarantees a fair power consumption among the nodes at the cost of possible SNR performance drop at AC. Accounting for the randomness of the nodes locations as well as the inter-terminal fading channel coefficients, the SNR performances of the energy efficient relay selection schemes are analyzed and a condition is derived under which the average SNR at AC is independent from the technique used to select the relaying nodes. This condition clarifies when the energy efficient and fair random relay selection scheme may be used without compromising the quality of the received signal at AC.