Joint design of sensing and transmission in energyefficient cognitive radio systems over fading channels

In this study, the authors focus on energy efficiency of a cognitive radio (CR) system, in which a secondary user (SU) senses periodically and accesses opportunistically a specific band authorised to a primary user (PU). Based on a generalised expression of energy consumption, we jointly optimise sensing, transmission and frame durations to maximise the energy efficiency for a CR system and investigate the performance of the proposed design over Rayleigh fading channels. The problem of energy efficiency is formulated as a function of sensing and transmission durations with the constraints on the interference to the PU. To protect the PU, we limit the detection probability as well as restrict the interference caused by the SU because of the re-occupancy of the PU. In a generalised model, energy consumptions of sensing, transmission and idling state need to be considered for the SU. The optimal sensing and transmission durations are obtained by a sub-optimal iterative algorithm. The performance of energy efficiency and duration of the SU over a Rayleigh-faded channel is investigated. Numerical results show that the proposed reduced-complexity approach performs comparably with that of the exhaustive search algorithm.