Optimal Channel and Power Allocation for Secondary Users in Cooperative Cognitive Radio Networks - (Invited Paper)

Cognitive radios are a natural evolution of Software Defined Radios (SDRs) that are supposed to be equipped with the ability to learn their RF environment and reconfigurability. A cognitive radio can communicate over a primary user’s channel as long as the introduced interference does not degrade the primary Single-to-Interference-plusNoise-Ratio (SINR) below its minimum Quality of Service (QoS) requirement. Previously, node cooperation has been applied to cognitive radios to achieve improved spectrum sensing performance. In this paper, on the other hand, we employ cooperation in data transmission in order to increase the secondary transmit power limit. Thus, the secondary user will achieve a higher SINR and the primary will gain additional spatial diversity, leading to increased sum-rate. We present, in this paper, an optimal power allocation scheme for secondary users in order to achieve maximum SINR. We show that the optimal channel assignment problem that maximizes the sum-rate can be solved via the so-called Hungarian algorithm at a cubic complexity order. Also, we develop a suboptimal algorithm that permits to solve the channel assignment problem with a quadratic complexity order and with only a slight performance degradation compared to that of the optimal solution.