Performance Analysis Of Spectrum-sharing Cognitive Relay Networks

Cooperative relaying techniques have held tremendous interests due to itscapacity to combat wireless fading and improve channel capacity. Recently, cooperativerelaying techniques have been applied into cognitive networks to improve theperformance of the secondary user (SU), and become a new research topic. However, incontrast to conventional relay networks, an additional transmission power constraint,the interference constraint, exists in cognitive relay networks, making the conventionalcooperative relaying theory inappropriate. Therefore, in this thesis, we focus on theperformance of cognitive relay networks and our main contributions are below as:(1) In the presence of multiple users (PUs), the exact outage probability of partialamplify-and-forward (AF) relay selection in the spectrum-sharing relay networks isinvestigated. To gain more insight, a simple and accurate outage probabilityapproximation is also derived in the high signal-to-noise (SNR) region. It is shown that,at high SNR, the outage probability is affected only by the channel gain ratio betweenrelay-destination links to relay-PU links, regardless of the number of relays.(2) In the presence of imperfect channel state information (CSI), especially causedby channel estimation error, the closed-form expressions for interference probability ofopportunistic relaying (OR) and selection cooperation (SC) are derived. It is shown that,in terms of the interference proability, the SC is better than the OR. However, the limitinterference probability of the OR is identical to that of the SC. Moreover, withimperfect CSI, for both the SC and the OR, increasing the number of relays means ahigher interference level on the PU.(3) In the presence of CSI, especially caused by the outdated CSI, the exactclosed-form expression for inteferrence probability of the PU is derived. It is shown thatthe PU’s interference probability is always equal to0.75when the CSI of interferencelinks is imperfect, regardless of the channel coefficeint. In order to guarantee the PU’sinterference probability below an acceptable value, a back-off power control mechanismis adopted. Then, under the PU’s interference probability constraints, the exact outageprobability of partial AF relay selection scheme is derived.