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In this paper, we propose a two-phase protocol based on cooperative relaying for a secondary system to achieve spectrum access along with a selective relaying primary system. The primary system comprises of a transmitter-receiver pair PT-PR and M relays. The secondary system is a multi-user system with N transmitters which intend to communicate with a common receiver SR. In the proposed protocol, Q out of N secondary transmitters are designated as possible candidates for assisting the primary system while the remaining secondary transmitters are chosen as possible candidates for secondary spectrum access, where 0 ≤ Q <; N. One relaying terminal Rp which achieves the request target rate for the primary system and has the best channel to PR, is first selected to serve as a decode-and-forward (DF) relay for the primary system. With the cooperation of Rp, the primary system is able to tolerate some interference lower than a certain threshold in the relaying phase, without degrading its outage performance. The secondary transmitter Rs which satisfies this interference constraint and optimizes the outage performance for the secondary system, is then selected to access the spectrum band simultaneously when Rp is relaying the primary signal. We show that both primary and secondary systems are able to achieve better outage performance with increasing N.
Date of Conference: 17-19 Nov. 2010