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This paper considers a sum-rate-maximizing power allocation for the Gaussian cognitive Multiple-Access Channel (MAC), where primary users and secondary users may communicate under mutual interference. Formulation of the problem as a standard nonconvex Quadratically Constrained Quadratic Problem (QCQP) provides a simple method to find a solution using Semi-Definite Relaxation (SDR). Numerical examples for the comparison illustrate a tradeoff between the maximum sum-rate and computational complexity. Investigation of spectrum utilization suggests that not all the spectrum is in use all the time. Cognitive radio technology offers the potential of efficient use of this unused spectrum, potentially allowing large amounts of spectrum to become available for future high bandwidth applications.
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