Cognitive radio network has emerged as a prevailing technique and an exciting and promising technology which has the potential of dealing with the inflexible prerequisites and the inadequacy of the radio spectrum usage. In cognitive radios, in-band sensing is fundamental for the protection of the licensed spectrum users, enabling secondary users to vacate channels immediately upon detection of primary users. This channel sensing scheme directly affects the quality-of-service of cognitive radio user and licensed user especially with the undesirable delay induced into the system. In this thesis, a combination of different delay reduction schemes from different papers has been introduced, the first paper [47] argues about performing fine sensing for non-real time traffic, while real time traffic continues transmission in the channel. The second paper [46] argues about performing fine sensing after multiple alarms that have been triggered. Both schemes have combined with applying data rate reservation as well in order to reduce as much as possible this crucial factor of delay for IEEE 802.22 wireless regional area network and to improve the channel utilization. Data rate reservation for real time users has been applied in order to reduce the queuing delay for real time services [47]. The average packet delay for the proposed scheme combination has been analyzed, with both numerical and simulation results. The results show that the scheme combination considerably reduces the average packet delay for both real time and non-real time services and hence satisfies the performance of IEEE 802.22 wireless regional networks. Index terms–Channel sensing, Cognitive radio, energy and feature detection, IEEE 802.22, quiet period. / Kognitiv radio nätverk har vuxit fram som en rådande teknik och en spännande och lovande teknik som har potential att hantera de oflexibla förutsättningar och den bristfälliga Radiospektrumanvändningens. I kognitiv radio, är i-band Sensing grundläggande för skyddet av de licensierade spektrumanvändare, möjliggör sekundära användare att utrymma kanaler omedelbart vid detektering av primära användare. Denna kanal sensing system påverkar direkt kvaliteten på tjänsterna för kognitiv radio användare och licensierade användaren särskilt med oönskad fördröjning induceras i systemet.   I denna avhandling har en kombination av olika system delay minskning från olika tidningar införts, den första papper [47] argumenterar om att utföra fina avkänning för icke-realtid trafik, medan realtid trafiken fortsätter sändningen i kanalen. Den andra artikeln [46] argumenterar om att utföra fina avkänning efter flera larm som har utlösts. Båda systemen har i kombination med tillämpning datahastighet bokning samt för att minska så mycket som möjligt denna avgörande faktor för försening för IEEE 802,22 trådlös regionala nätverk och förbättra kanalutnyttjandet. Datahastighet reservation för realtidanvändare har tillämpats för att minska den queuing fördröjningen för realtidstjänster [47]. Den genomsnittliga paket fördröjning för det föreslagna systemet kombinationen har analyserats, med både numeriska och simulering resultat. Resultaten visar att systemet kombinationen avsevärt minskar den genomsnittliga paket fördröjning för både realtid och icke-verkliga tjänster tiden och därmed uppfyller prestanda IEEE 802,22 trådlösa regionala nätverk. / Kungsmarksvagen 71, karlskrona +4520939959

Wireless communication is facing an increasingly severe spectrum scarcity problem. Hybrid free space optical (FSO)/ millimetre wavelength (MMW) radio frequency (RF) systems and cognitive radios are two candidate solutions. Hybrid FSO/RF can achieve high data rate transmission for wireless back haul. Cognitive radio transceivers can opportunistically access the underutilized spectrum resource of existing systems for new wireless services. In this work we carry out accurate performance analysis on these two transmission techniques. In particular, we present and analyze a switching based transmission scheme for a hybrid FSO/RF system. Specifically, either the FSO or RF link will be active at a certain time instance, with the FSO link enjoying a higher priority. We consider both a single threshold case and a dual threshold case for FSO link operation. Analytical expressions are obtained for the outage probability, average bit error rate and ergodic capacity for the resulting system. We also investigate the delay performance of secondary cognitive transmission with interweave implementation. We first derive the exact statistics of the extended delivery time, that includes both transmission time and waiting time, for a fixed-size secondary packet. Both work-preserving strategy (i.e. interrupted packets will resume transmission from where interrupted) and non-work-preserving strategy (i.e. interrupted packets will be retransmitted) are considered with various sensing schemes. Finally, we consider a M/G/1 queue set-up at the secondary user and derive the closed-form expressions for the expected delay with Poisson traffic. The analytical results will greatly facilitate the design of the secondary system for particular target application. / Graduate

No description available.