Threshold based distributed detection that achieves full diversity in wireless sensor networks

It is well known that decode and forward relaying protocols, in which the relays decode and re-encode the message, can achieve full diversity when combined with distributed space time coding or relay selection schemes. However, in wireless sensor networks, decoding and re-encoding the message at the relays can be costly due to severe energy limitations. A question arises: is it possible to achieve full diversity when the relays only detect (or demodulate) and forward the message? In this paper a distributed detection scheme is developed that achieves full diversity in wireless sensor network, with the relays only detecting and forwarding the message. It is seen that such a relaying scheme is SNR threshold-based, i.e., the relays will perform detection only if the receive SNR is above a certain threshold. The threshold that achieves full diversity is derived. Furthermore, a single bit feedback scheme is developed to make relaying more spectral efficient, such that the network can achieve the diversity-multiplexing tradeoff of a point-to-point multiple-input single-output (MISO) system in the high SNR regime.