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This paper considers a spectrum sharing wireless environment, where an OFDM-based cognitive radio system is allowed to access the spectrum originally licensed to an OFDMA primary system. A new criterion referred to as the rate loss constraint, in the form of an upper bound on the maximum rate loss of the primary user due to the secondary transmission, is proposed for primary transmission protection. In addition, assuming that some PUs are protected by the rate loss constraint, and some PUs are protected by the interference power constraint, the optimal power allocation strategy to maximize the rate of the cognitive radio system under such a hybrid protection to PUs together with a transmit power constraint is derived. Then, the relationship between the rate loss constraint and the interference power constraint is investigated, and it is shown by simulation that the cognitive radio system can achieve a significant rate gain under the proposed constraint compared with that under the conventional interference power constraint.
Date of Conference: Nov. 30 2009-Dec. 4 2009