Information and Energy Cooperation in Overlay Hierarchical Cognitive Radio Networks

In overlay hierarchical cognitive radio (HCR) networks, the primary system (PS) and the secondary system (SS) can cooperate to exploit the spectrum resource more efficiently. In this paper, we propose a new HCR, in which an energy harvesting (EH) device is additionally deployed at the primary receiver (PR) such that the PS can not only share the spectrum resources with the SS, but also harvest energy from the SS, achieving a new simultaneous wireless information and power transfer (SWIPT) paradigm. In the considered structure, the secondary base station (SB) can help relay the PS's signal via an amplify-and-forward (AF) protocol, and a power splitting EH device is adopted at the PR. A cooperative strategy is proposed for maximizing the efficiency of the information and power transfer. We optimize two precoders at the SB (for the PS and SS, respectively) and the power splitting factor for the PR. Since the optimization problem is non-convex, it is a real challenge. To facilitate the optimization process, a precoding structure is first proposed to reduce the number of parameters. The resultant optimization problem can then be equivalently solved using a semidefinite relaxation (SDR) approach. Numerical results show that the proposed strategy provides a promising improvement for information and energy cooperation, as compared with existing methods.