Cooperative Spectrum Sharing in Cognitive Radio Networking

Driven by the massive growth in communications data traffic as well as flourishing users' demands, we need to fully utilize the existing scarce spectrum resource. However, there have been several studies and reports over the years showing that a large portion of licensed spectrum is actually underutilized in both temporal and spatial domains. Moreover, aiming at facing the dilemma among the fixed spectrum allocation, the ever enormous increasing traffic demand and the limited spectrum resource, cognitive radio (CR) was proposed by Mitola to alleviate the under usage of spectrum. Thus, cognitive radio networking (CRN) has emerged as a promising paradigm to improve the spectrum efficiency and utilization by allowing secondary users (SUs) to utilize the spectrum hole of primary users (PUs). By using spectrum sensing, SUs can opportunistically access spectrum holes for secondary transmission without interfering the transmissions of the PUs and efficient spectrum utilization by multiple PUs and SUs requires reliable detection of PUs. Nevertheless, sensing errors such as false alarm and misdetection are inevitable in practical networks. Hence, the assumption that SUs always obtain the exact channel availability information is unreasonable. In addition, spectrum sensing must be carried out continuously and the SU must terminate its transmission as soon as it senses the re-occupancy by a PU. As a better alternative of spectrum sensing, cooperation has been leveraged in CRN, which is referred as cooperative cognitive radio networking (CCRN). In CCRN, in order to obtain the transmission opportunities, SUs negotiate with the PUs for accessing the spectrum by providing tangible service for PUs. In this thesis, we study cluster based spectrum sharing mechanism for CCRN and investigate on exploiting the cooperative technique in heterogeneous network. First, we develop cooperation protocols for CRN. Simultaneous transmission can be realized through quadrature signalling method in our proposed cooperation protocol. The optimal power allocation has been analyzed and closed-form solution has been derived for amplify and forward mode. Second, we study a cluster based spectrum sharing mechanism. The spectrum sharing is formulated as a combinatorial non-linear optimization problem which is NP-hard. Afterwards, we solve this problem by decomposing it into cluster allocation and time assignment, and we show that the result is close to the optimal solution. Third, we propose a macrocell-femtocell network cooperation scheme for heterogeneous networks under closed access mode. The cooperation between the femtocell network and macrocell network is investigated. By implementing the cooperation, not only the macrocell users' (MUEs') and femtocell users' (FUEs') utility can be improved compared with the non-cooperation case, but also the energy consumption as well as the interference from the femtocell network to the macrocell network can be reduced

Distributed space-time block coding in cooperative relay networks with application in cognitive radio

Spatial diversity is an effective technique to combat the effects of severe fading in wireless environments. Recently, cooperative communications has emerged as an attractive communications paradigm that can introduce a new form of spatial diversity which is known as cooperative diversity, that can enhance system reliability without sacrificing the scarce bandwidth resource or consuming more transmit power. It enables single-antenna terminals in a wireless relay network to share their antennas to form a virtual antenna array on the basis of their distributed locations. As such, the same diversity gains as in multi-input multi-output systems can be achieved without requiring multiple-antenna terminals. In this thesis, a new approach to cooperative communications via distributed extended orthogonal space-time block coding (D-EO-STBC) based on limited partial feedback is proposed for cooperative relay networks with three and four relay nodes and then generalized for an arbitrary number of relay nodes. This scheme can achieve full cooperative diversity and full transmission rate in addition to array gain, and it has certain properties that make it alluring for practical systems such as orthogonality, flexibility, low computational complexity and decoding delay, and high robustness to node failure. Versions of the closed-loop D-EO-STBC scheme based on cooperative orthogonal frequency division multiplexing type transmission are also proposed for both flat and frequency-selective fading channels which can overcome imperfect synchronization in the network. As such, this proposed technique can effectively cope with the effects of fading and timing errors. Moreover, to increase the end-to-end data rate, this scheme is extended for two-way relay networks through a three-time slot framework. On the other hand, to substantially reduce the feedback channel overhead, limited feedback approaches based on parameter quantization are proposed. In particular, an optimal one-bit partial feedback approach is proposed for the generalized D-O-STBC scheme to maximize the array gain. To further enhance the end-to-end bit error rate performance of the cooperative relay system, a relay selection scheme based on D-EO-STBC is then proposed. Finally, to highlight the utility of the proposed D-EO-STBC scheme, an application to cognitive radio is studied

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