On the Coexistence of Infrastructure-Based and Ad Hoc Connections for a Cognitive Radio System

Cognitive radio (CR) can sense the current spectrum usage of existing networks and make intelligent decisions on the opportunity of reusing the frequency spectrum. One fundamental issue for the CR system is how to rapidly establish a temporary communication link on the spectrum of the exiting users. In this paper, we investigate the feasibility issue of establishing both an infrastructure-based link and an ad hoc link using the same spectrum simultaneously in an overlapped area. We also present a cross-layer performance analysis from both the physical (PHY) layer and medium access control (MAC) layer perspectives. The analytical results show that the probability that both an infrastructure-based connection and an ad hoc link coexist in an overlapping area can be as high as 45%. In addition the normalized total throughput of the both links is more than 145% compared to the pure infrastructure-based link. However, considering the shadowing effects, the transmission reliability varies from 30% ~ 90% depending on the locations of mobile stations