Hybrid power control scheme in hierarchical spectrum sharing network for cognitive radio

Abstract

Recently, Hierarchical Spectrum Sharing Network (HSSN) has been proposed to efficiently and flexibly unitize available spectrum resource in cognitive radio context. In the HSSN, available spectrum bands are classified into two types to support both centralized and distributed communications simultaneously. A stable and efficient power control scheme is required to fully make use of the potential of HSSN. An effective power control scheme in the HSSN faces several challenges, such as low power emission, high level of quality of service (QoS), and suitability for the hybrid architecture of the HSSN. To effectively meet these requirements, a novel hybrid power control scheme is proposed in this paper. The proposed scheme is composed of three parts: a centralized power control scheme, a distributed power control scheme, and a coordination policy to coordinate these two types of power control schemes when both of them are exploited in the same channels. In the centralized power control design, we propose a Two-Step Fair Allocation (TSFA) scheme. In its first step, resources, such as channels and powers, are allocated by cognitive radio base station (CRBS) based on fairness and QoS requirements to obtain the maximum available resources of cognitive radio users (CRUs). In the second step, to get the final resource and reduce algorithm complexity, the allocation task is accomplished by each CRU simultaneously. In the distributed power control design, we propose Utility based Power Control algorithm combined with Admission Control (UPCAC). We also provide a protocol to effectively implement UPCAC. We formulate a utility function, i.e., payoff function minus price function, to measure the requirements of primary users (PUs) and CRUs. The payoff function represents CRUs’ signal-to-interference-plus-noise ratio (SINR) objectives, and the price function specifies protection for PUs and CRUs’ power consumptions. By analyzing the geometric characteristics of the payoff and price functions, we properly set the parameters of the utility function. Further, we propose coordination policy to combine centralized power control scheme with distributed power control scheme when they are exploited in the same channels. Simulation results show that the proposed hybrid power control scheme can meet the requirements of low emission power as well as high QoS level.