Optimizing the Coexistence Performance of Secondary-User Networks Under Primary-User Constraints for Dynamic Spectrum Access

In this paper, we address the following two types of coexistence between wireless networks: 1) coexistence among secondary user (SU) networks and 2) coexistence between primary user (PU) and SU networks. The former type addresses the sharing of a common spectrum opportunity among SU networks to achieve an efficient spectrum usage, whereas the latter type addresses the interference from SUs to PUs. Following the trend of spectrum regulations and industrial standardization, we postulate a potential deployment scenario and describe the management procedure of SU networks under the interference constraints to the PU receivers. For the quantitative evaluation of coexistence, we first propose a new parameter called the quality of coexistence (QoC). Then, we introduce a novel coexistence scheme called interference-constrained time slot splitting and allocation. In addition, we derive the distribution of the interference to the PU receiver caused by SU transmitters weighted by the time slot fraction assigned to each SU network. After optimizing individual SU transmission under the PU interference constraint, we use the analytical model as a basis to obtain the optimal time slot allocation ratios of multiple SU networks by maximizing the aforementioned QoC. This leads to an efficient spectrum usage by SUs without incurring harmful interference to the PUs. Finally, we compare the proposed scheme with other schemes that select a single SU network to operate based on simplistic criteria. It is shown that when the SU network employs adaptive transmit power control, the medium value of QoC is doubled using the optimal time slot allocation, resulting in significant improvement in coexistence.