A Two-Stage Power and Rate Allocation Strategy for Secondary Users in Cognitive Radio Networks

Abstract

In this paper, we attempt to evaluate the optimal power and rate distribution choices for secondary users in order to maintain their quality of service (QoS) in a multichannel cognitive radio network (CRN). We assume that multiple secondary users share a single channel and multiple channels are simultaneously used by a single secondary user (SU) to satisfy their rate requirements. Our measures for QoS include signal to interference plus noise ratio (SINR)/bit error rate (BER) and minimum rate requirement. We propose a two-stage optimization framework in order to solve for the optimal resource management strategy. In the first stage, we formulate a convex optimization problem to determine the minimum transmit power that SUs should employ in order to maintain a certain SINR. At first, the convex optimization problem is solved in a centralized manner and then we employ dual decomposition theory to derive three different distributed solutions. In the second stage, we formulate the rate distribution problem as a maximum flow problem in graph theory. We also develop a heuristic approach to determine the rate distribution. Simulation results demonstrate that optimal transmit power follows “reverse water filling” process and rate allocation follows SINR. We also observe that the distributed solution converges to the centralized solution and rate distribution based on our proposed heuristic is close to the graph theoretic optimal solution.