Outage performance for cognitive two-way relaying networks with underlay spectrum sharing

This paper presents an analytical study on the outage performance of cognitive decode-and-forward (DF) two-way relaying networks with underlay spectrum sharing. The bidirectional protocol, i.e., two time-slot multiple access broadcast (MABC) and three time-slot time division broadcast (TDBC), are considered. We propose a definition of outage probability by jointly considering outage events in the whole transmission process and the exact outage probability expressions are given. For both the protocols, the dependence among the received signal- to-noise ratios (SNRs) in the broadcast phase is introduced due to the interference power constraint. The joint probability of the received SNRs is derived. Based on that, the closed-form solutions to outage probability for the two protocols are obtained. The theoretical analysis is verified by Monte-Carlo simulations. Results demonstrate that MABC can achieve better outage performance through optimal interference power distribution between the two secondary users.