Energy Efficiency of Cooperative Relay in a Spectrum Sharing Network

Abstract

As underutilization of spectrum causes wastage, sharing spectrum between primary and secondary users is a possible solution. On the other hand, as hostile jamming corrupts data reception, having the secondary user to relay primary data introduces diversity, increasing the likelihood of receiving uncorrupted data. This paper proposes such spectrum sharing model that deploys physical layer security measure against jamming. A primary transmitter (PT) sends data to a primary receiver (PR). A cognitive radio transmitter (CT) relays PT's data to PR in return for spectrum access, i.e. CT uses the channel unoccupied by PT to send its own data. CT is capable of sensing the channel occupancy. Relaying data benefits PT, but to what extent it benefits CT? The main concern is CT's energy efficiency. In this paper, we find that there are optimal CT's transmission power and sensing duration that will result in optimal energy efficiency of CT, µ*. This work is novel in formulating an optimization method that finds µ* of a friendly relay (CT) that is part of a spectrum sharing network. We contribute the formula of finding the optimums under various scenarios: strong cognitive radio, sensing, jamming, and forwarding channels, and a powerful jammer. We find that (1) strong cognitive radio and sensing channels contribute positively towards µ*. (2) Although strong jamming channel, powerful jamming, and weak forwarding channel do not affect the energy efficiency of CT, they nevertheless deteriorate the capacity of the CT -PR forwarding channel under jamming.