Optimal Bit and Power Allocation in Broadband Cognitive Radio System

In this paper, we study the problem of bit and power allocation in broadband cognitive radio system. In the broadband communication system, the primary transmitter employs Orthogonal Frequency Division Multiplexing (OFDM) technique on the whole bandwidth. A cognitive user, which has the ability of detecting the transmission of the primary link on each subcarrier, attempts to use the same bandwidth. The goal of this paper is to study how to optimally allocate bit and power on each subcarrier at the cognitive transmitter so that the sum-rate of the cognitive user is maximized under the condition that the primary transmission is not affected. Based on the framework presented by A. Jovicic and P. Viswanath, we first formulate the problem into an optimization problem with integer variables and then propose a greedy bit and power allocation algorithm. We also prove that the proposed algorithm is the optimal solution to the optimization problem.