Dynamic Spectrum Access in Cognitive Radio Networks

Spectrum inefficient utilization and growing in demand of wireless services is one of the challenges facing the wireless communication systems as the spectrum is a finite resource. There is a need of better and smarter exploitation of the limited spectrum which will enables the usage and to allowing sharing of temporally unused spectrum allocated to the television broadcast service in non interfering basis, to bring broadband access to hard –to-reach low population density areas. Cognitive radio is employed as a technique in the managements and sharing of the white space (unused spectrum). This research provides study techniques for sensing the white space and managements for multiple accesses. A dynamic spectrum access scheme for cognitive radio networks is proposed. The approach will allow secondary user to operate in the presence of a primary user. The cognitive capabilities of the system includes electromagnetic interference (EMI) awareness, ranging and transmit power to control the spectrum access among primary and secondary users. (The scheme is based on electromagnetic interference (EMI) control. Ranging and transmitter power are parameters that need to be calculated/controlled in order to control the EMI). OPNET (optimized Network Engineering Tool) have been used to model primary user with priority access and multiple secondary users. Two dynamic spectrum access architectures are considered, centralized and distributed spectrum access. Performance analysis of results shows that, the proposed schemes protects the primary user from harmful EMI from the secondary user and also achieves a low packets loss of about 0.001% which is three orders of magnitude lower than the basic CSMA/CA MAC protocol. Based on spectrum opportunities generated from primary user transmission, the proposed scheme provides an efficient way of exploiting the white spaces with 88.89% efficiency. In terms of delay, it was found that, packets arrival rates, data rates, distance and number of secondary users have significant effects on delay. The proposed MAC protocol achieves 99.91% spectrum utilization. In comparison with basic MAC protocol, it improves spectrum utilizations by about 27% while limiting the interference imposed on the primary receiver.