Higher order statistics for underlay cognitive radio system

Abstract

In last few decades, the wireless communication technology observes a rapid advancement because of its escalating demand and day-to-day importance. Subsequently, the field has attracted recent interest from researchers to find new approaches which can be more promising for throughput enhancement over the restrained spectrum. These new arising techniques must be able to utilize scarce spectrum resources efficiently and reliably. One of such emerging technologies is cognitive radio which can be seen as a potential solution to mitigate the problem of spectrum scarcity. In this thesis, we investigate the outage probability and second order statistics viz., level crossing rate (LCR) and average fade duration (AFD) of an underlay cognitive radio system in the presence of multiple primary receivers. We consider an underlay scenario where the communication between secondary source and secondary destination takes place over the same spectrum licensed to primary system. This cognitive radio communication is subject to the constraint that interference temperature at primary receiver should lie below a predefined level. With this setup, we investigate first order statistics such as outage probability of the considered system. The first order statistics alone are not sufficient to address wireless communication system design issues. Since the pragmatic wireless channel is slowly time-varying, various design issues can be addressed by combining first order statistics with the second order statistics of wireless communication systems. In the considered system, the receivers are assumed to be mobile and hence the fixed-to-mobile channels are adopted. To the best of our knowledge, little attention has been directed for such systems in terms of the temporal characteristics such as LCR and AFD without which overall system may not bedesigned and rigorously tested. In this thesis, we investigate second order statistics viz., LCR and AFD of the cognitive radio system in a Rayleigh fading environment. First, we obtain closed-form expressions of LCR and AFD by using appropriate mathematical tools. Then, we confirm our analysis through numerical and simulation investigation. Finally, the impact of system parameters on LCR and AFD are highlighted. Results demonstrated that by using efficient power and bandwidth allocation method, the throughput of the cognitive radio system can be increased. The results presented in the thesis can thus provide vital information for proper deployment of a cognitive radio system.