PERFORMANCE ENHANCEMENT OF RELAYING TECHNIQUES FOR UNDERLAY COGNITIVE RADIO NETWORKS

Abstract

In this thesis, we propose and investigate di erent relay selection algorithms in underlay cognitive radio networks. Firstly, we consider a multiple relay selection scheme. This scheme is an attempt to reduce the outage probability of the secondary cognitive network. For each channel realization, we allow for multiple relay selection in case the best relay, which provides the highest signal to noise ratio among those that satisfy the interference constraint, does not satisfy the desired signal to noise ratio. A cumulative density function for the signal to noise ratio for two relays is deduced. Secondly, we analyze the bit error rate performance of a secondary cognitive network with a source and multiple decode and forward relays using di erent modulation levels sharing the spectrum with a nearby primary user. We obtain a closed form expression for the bit error rate for two scenarios. Examiners: Prof. Essam Sourour (External examiner) Professor at the Faculty of Engineering, Alexandria University Prof. Magdi Fikri (Internal examiner) Prof. Mohamed M. Khairy (Thesis main advisor) Table