Resource Management in Spectrum-Sharing Cognitive Radio Broadcast Channels: Adaptive Time and Power Allocation

In this paper, we consider a primary/secondary spectrum-sharing system, and study adaptive resource management in cognitive radio (CR) fading broadcast channels (BC). Specifically, we propose utilizing spectrum sensing information about the primary's activity at the secondary base station for an efficient allocation of the resources, namely, transmission time and power, to the secondary users. Spectrum sensing information about the primary user, and secondary channel side information, are assumed available at the base station and receivers of the secondary CR network. The sensing information is obtained using spectrum-aware sensors deployed in the secondary network coverage area. Based on this information, we present an optimal time-sharing and power allocation policy to maximize the achievable capacity of fading cognitive radio broadcast channels, where transmission is limited by appropriate constraints on the average received-interference at the primary receiver and peak transmit-power pertaining to the secondary transmitter. Furthermore, considering that availability of full soft-sensing information at the CR transmitter may result in a severe load of feedback data and high system complexity, we present a quantized spectrum sensing mechanism wherein only restricted levels of primary activity are considered for the sensing observations. Our theoretical results are sustained by numerical and simulation analyses, and insightful discussions are provided.