Opportunistic Adaptive Relaying in Cognitive Radio Networks

Combining cognitive radio technology with user cooperation could be advantageous to both primary and secondary transmissions. In this paper, we propose a first relaying scheme for cognitive radio networks (called "Adaptive relaying scheme 1"), where one relay node can assist the primary or the secondary transmission with the objective of improving the outage probability of the secondary transmission with respect to a primary outage probability threshold. Upper bound expressions of the secondary outage probability using the proposed scheme are derived over Rayleigh fading channels. Numerical and simulation results show that the secondary outage probability using the proposed scheme is lower than that of other relaying schemes. Then, we extend the proposed scheme to the case where the relay node has the ability to decode both the primary and secondary signals and also can assist simultaneously both transmissions. Simulations show the performance improvement that can be obtained due to this extension in terms of secondary outage probability.Comment: 5 pages, 4 figures. Accepted for publication in Proc. IEEE International Communications Conference (ICC), Ottawa (ON), Canada, June 201

Techniques de coopération dans les réseaux à radio cognitive : conception et évaluation des performances

RÉSUMÉ La technologie de radio cognitive permet aux usagers sans licence (appelés usagers secondaires) de transmettre dans les bandes de fréquences avec licence, sans dégrader la qualité de service des transmissions des usagers avec licence (appelés usagers primaires). Afin d’éviter l’interférence indésirable aux récepteurs primaires, les émetteurs secondaires doivent réduire leurs puissances de transmission. Cette limitation de puissance génère généralement des performances secondaires dégradées. Combiner la technologie à radio cognitive à d’autres technologies de transmission émergentes comme la coopération et la technologie des antennes multiples pourrait bénéficier aux transmissions primaires et secondaires. Dans cette thèse, nous proposons et étudions différentes techniques de coopération pour le réseau à radio cognitive. Certaines techniques exploitent la sélection d’antennes ou bien le pré-codage à un seul relai à plusieurs antennes, alors que d’autres utilisent la sélection de relai(s) lorsque plusieurs relais à une seule antenne sont disponibles pour assister la transmission primaire, la transmission secondaire ou les deux simultanément. Le problème d’allocation de puissance ou de pré-codage associé est étudié, et les expressions exactes des probabilités de blocage primaire et/ou secondaire ou de capacité ergodique secondaire sont dérivées. Pour certaines des techniques proposées, la connaissance imparfaite des canaux de transmission est prise en compte, modifiant ainsi la résolution du problème d’allocation de puissance ou de pré-codage associé. Nous montrons par analyse et simulation que chacune des techniques de coopération proposée est capable d’améliorer considérablement la performance secondaire, tout en respectant la qualité de service primaire. Ces performances dépassent d’une manière significative celles des techniques de transmission conventionnelles (techniques coopératives ou non) utilisées dans le contexte du réseau à radio cognitive.---------- ABSTRACT Cognitive radio technology allows unlicensed users (called secondary users) to transmit on the licensed frequency bands, without degrading the quality-of-service of the licensed users’ transmissions (called primary users). In order to avoid undesirable interference at the primary receivers, the secondary transmitters have to limit their transmit power. This limitation may cause performance degradation for the secondary transmissions. Combining cognitive radio with other emerging technologies, such as user cooperation and multiple antennas may have many benefits on both the primary and secondary transmissions. In this dissertation, we propose and investigate different cooperation techniques for the cognitive radio network. Some of the proposed techniques exploit antenna selection or precoding at one multi-antenna relay node, while the other proposed techniques use relay(s) selection when several single-antenna relay nodes are available to assist either the primary, the secondary or both transmissions simultaneously. The associated power allocation problem or pre-coding problem is investigated and the exact expressions of the primary and secondary outage probabilities or the secondary ergodic capacity are derived. For some of the proposed techniques, the imperfect knowledge of the channel states at the secondary transmitters is taken into account, hence modifying the power allocation or pre-coding process. We show by analysis and simulation that each of the proposed cooperation technique is able to improve significantly the secondary performance with respect to the primary Quality-of-Service. The realized performances outperform those of conventional transmission techniques used in the context of cognitive radio networks