The fifth generation (5G) wireless networks are expected to achieve 1000 times higher capacity compared to the fourth generation (4G) wireless networks. Thus, improving the spectrum efficiency (SE) is a crucial problem, which must be considered. Cognitive radio (CR) is considered as an effective approach to alleviate the spectrum scarcity problem. In this paper, based on the location information of the primary transmitter (PT) and the CR network, we estimate the distance between the PT and the secondary transmitter (ST) and then propose a joint spectrum sensing and power allocation (JSS-PA) scheme to improve the SE of the CR network. In the JSS-PA scheme, we focus on jointly optimizing the sensing parameters and the transmit power of the secondary user (SU) such that the SE is maximized while the primary user (PU) outage constraint is satisfied.

When cooperative spectrum sensing is employed to detect the PU’s status, we analyze two cooperative strategies, i.e., soft information fusion (SIF) and hard information fusion (HIF). Under SIF strategy, the optimization of sensing and power (S-OSP, for short) algorithm is proposed to maximize the SE. Under HIF strategy, the optimization of thresholds (H-OT, for short) algorithm is proposed, and then the optimization of sensing and power (H-OSP, for short) algorithm is proposed to find the optimal duration of local sensing, the optimal transmit power of SU and the optimal final decision threshold. Finally, we present the simulation results to evaluate the performance of the proposed JSS-PA scheme and discuss the effects of the optimal parameters on different schemes under SIF and HIF strategies.