Hierarchical spectrum sharing in cognitive radio communications

In this paper, according to the interference temperature model and channel conditions, we classify available bands, on which cognitive radios are capable of sharing with legacy systems, into two types — TYPE I used for direct communication between cognitive radio service access point (CR-SAP) and cognitive radio base station (CR-BS), and TYPE II used for direct communication between CR-SAP and its neighbor CR-SAPs. We name this classification as hierarchical spectrum sharing (HSS) and propose an identification process. Four kinds of communication scheme are designed based on HSS so that the cognitive radio can adapt to different transmission requirements. Numerical results show that HSS provides a considerable extension to available bands so that the spectral utility may be improved further.