Distributed Control of Multiple Cognitive Radio Overlay for Primary Queue Stability

In this paper, we investigate distributed control of multiple secondary users attempting to access the channel of a high priority primary user. Our aim is to maximize the sum cognitive (secondary) user throughput under the constraint of primary user´s queue stability. We consider the effect of primary user link adaptation that allows the primary transmitter (PTx) to adapt its transmission rate in response to the secondary interference-level at the primary receiver (PRx). To control the sum secondary interference to PRx beyond the traditional collision-avoidance paradigm, we propose a novel power-control algorithm for secondary nodes to function. To develop such a distributed algorithm and to improve secondary user adaptability, we allow secondary nodes to monitor primary´s radio link control information on the feedback channel. We present practical schemes that approximate the optimum solution without relying on global channel information at each secondary node.