Improving amplify-and-forward relay networks: optimal power allocation versus selection
IEEE Transactions on Wireless Communications
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Opportunistic spectrum access (widely known as cognitive radio) enables the use of unoccupied licensed radio spectrum and thus assures efficient use of the spectrum. In this paper, we investigate the outage probability of a wireless amplify-and-forward cooperative two relay (diamond relay) network which consists of a source, a destination and two network clusters. Each cluster is defined by a number of cognitive nodes (unlicensed) and a primary node (licensed). The cognitive nodes relay the source information by employing opportunistic spectrum access using either repetition-based or best relay selection (i.e. selection cooperation) relaying protocol. Closed-form expressions of outage probability are obtained for non-identical independent Rayleigh fading channels. Selection cooperation exhibits lower outage probability than that of the repetition-based relaying protocol. However, the unavailability of the spectrum causes much increase in the outage probability of Selection cooperation. An improvement of the performance can be provided if the neighbouring nodes of the cognitive node within a cluster sense the spectrum cooperatively. The analytical outage probability expressions have been validated through the simulations.