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This paper proposes to use a cognitive-relay technique to mitigate intercell interference (ICI) in cellular systems. In the proposed system, several relay stations (RSs) that are equipped with cognitive radio are deployed near the cell boundary. The base station (BS) and the RS in each cell operate in the same spectrum band as primary and secondary transmitters, respectively. Once an interference-limited mobile station (MS) requests an RS for assistance, the RS senses the spectrum band and accesses a spectrum hole to forward its received signal (and interference) to the MS. At the receiver of the MS, optimum combining is employed to combine the original signal that is received from the BS and the relayed signal to cancel the ICI. The system performance is analyzed in terms of the outage capacity and the average capacity considering the impact of the availability of cognitive-relay channels and the link quality between the RS and the MS. The location and the coverage radius of the RS are designed based on the requirement of the RS-MS link quality. Finally, simulation results are given to validate the theoretical analysis and to show the capacity improvement due to the ICI cancellation with the assistance of cognitive relay.
Date of Publication: May 2010