Outage capacity analysis of a secondary network in interference limited cognitive radio spectrum sharing system

In this paper, we investigate the outage capacity of a secondary network in a cognitive radio (CR) cooperative spectrum sharing system consisting of a primary transmitter (PTx)-receiver (PRx) pair as well as multiple secondary transmitter (STx)-receiver (SRx) pairs. We evaluate the outage capacity of the secondary network in slow fading channel by considering three different scenarios based on the primary user (PU) activity. The scenarios are: spectrum access by a secondary user (SU) when the data rate of the PTx to PRx over the direct link achieves primary request target rate R_PT, spectrum access by a SU when the data rate of the PTx to PRx falls below R_PT over the direct link but achieves R_PT on the relaying link (PTx-relay-PRx) and spectrum access by two SUs at the same time when PTx-PRx pair is idle or primary system is in outage. In this paper, a closed-form expression of the outage capacity is derived. Theoretical results show that outage capacity improves when the active secondary transmitter is located farther away from the PRx.