Total spectral efficiency maximization in multi-users cognitive radio networks with energy-harvesting capability

Abstract

In this paper, the joint radio resource management issues in a cognitive radio network driven by radio frequency energy harvesting (CRN- RF-EH) functionalities are investigated. For the CRN-RF-EH, the cognitive radio (CR) node first harvests its required energy directly from  the transmitter of spectrum licensed user for its data communication and consequently transmits its data on the licensed frequency of  the legacy user using the underlay accessing technique. Thus, RF-EH is an exciting innovation for energizing low-powered next- generation wireless networks (NGWNs). Consequently, due to CRN-RFEH’d low power limitations, the resource allocation for CRN-RF-EH  has to be optimized considering the trade-off among spectral efficiency, energy efficiency, and RF energy supply. Equal allocation of  transmission time and/or transmission power may not be efficient for CRN-RF-EH with limited transmission time and power resources. A  joint optimal time and power allocation (OTPA) strategy for CRN-RF-EH is proposed to maximise the total spectral efficiency of the CRN- RF-EH. The coupled variables in the formulated joint resource allocation problems create a non-convex optimization problem formulation.  For analytical tractability, the non-convex optimization formulation is initially converted to its equivalent standard convex  optimization formulation using proper variables and next, it is then solved using the convex optimization technique. The CONOPT solver,  a powerful optimization-solving tool for solving convex optimization problems, is utilized to resolve the equivalent standard convex  optimization problem formulation. When compared with the baseline biased random time optimum power allocation (BRTOPA) scheme,  numerical simulation results show that the OTPA strategy dramatically improves the total spectral efficiency performance. In a severe  radio propagation environment with a path loss exponent (PLE) equal to 3.5 such as in urban areas and less severe radio propagation  environment with a path loss exponent (PLE) equal to 2.0, such as in rural areas, the OTPA outperformed the BROTPA with a mean  performance improvement of approximately 23. 96% and 42.94% , respectively.