Investigation On Cognitive Radio Facilitating The Deployment Of Femtocells

The requirements of access opportunities and higher service quality have been growing during the past thirty-five years in the wireless cellular network, which has always been forc-ing people to more efficiently utilize fundamental but scarce spectrum resources. Recently, cognitive radio (CR) and femtocells emerged as intelligent spectrum paradigm and hetero-geneous networking methodology has aroused wide concern. Cognitive radio technology to enable unlicensed devices seamless coexist with assigned spectrum license holders by exploit-ing wasted or underutilized frequency as far as possible in temporal and spatial units, has been recognized as an innovative software defined radio. Deploying femtocells on the originally designed macrocell infrastructure, contributing to shortening the distance between a transmit-ter and receivers, the radio link quality and spectrum reuse opportunities have been improved. The mutual infiltration and integration of the above two technology have become a trend. This dissertation is founded on cognitive radio technology to address a couple of critical techni-cal challenges born with femtocells overlaying an old-fashioned macrocell, mainly focusing on femto-users spectrum access, two-tier interference of heterogeneous femtocell networks, and reliable communication of cell-edge macro-users aided by femtocell. Specific contents including innovative results of the thesis are summarized below.Firstly, the purposes, the basic principles, the traditional methods and classification of spectrum sensing have been elaborated. Depending on carefully comparing the pros and cons of major well-known spectrum sensing methods, Spectrum-Cognizing Server (SCS) model has been proposed, which first definitely appoints the communication entity, who should be loaded with the cognitive ability within the wireless cellular network. Four distinguishing ap-plications of SCS according to sensing feasibility have been proposed. Spectrum-Cognizing Server can take the benefits of server equipment to enhance the accuracy of a single sens-ing, can employ a higher complexity sensing technique, and minimizes the interference to licensed primary users resulted from sensing, along with the total network sensing cost mini-mized. Furthermore, this model has been extended to the heterogeneous femtocell network, to regulate the acts of dynamic spectrum access for femto-users, which is in a fully compatible with existing network infrastructure and terminal design, facilitates current terminals seamless access to cognitive femtocell networks.Secondly, on the premise of profoundly pointing out three inherent issues of distributed spectrum sensing schemes, centralized cognitive spectrum overlay and underlay (spectrum two-lay) management effectively mitigating two-tier femtocell interference has been put for-ward. Note that it is an interference cancellation method appropriate for both uplink and downlink transmission. After reiterated the three essential tasks of cognitive cycle, based on the solutions to the first two tasks in SCS scheme, transmission-power control and dy-namic spectrum management, i.e., the third task has been targeted. For example, reliable downlink transmission employing current widespread modulation technology, i.e., orthogonal frequency division multiplexing (OFDM), under cross-layer interference constraints has been investigated. An optimal power control algorithm based on the subgradient method of adopt-ing cognitive radio spectrum two-lay models, together with a low-complexity suboptimal so-lution have been proposed. Theoretical analysis and extensive simulation results show that, regarding transmission rate, the proposed optimal algorithm is identical to other optimiza-tion algorithm, but with reduced complexity, and superior to several classic power allocation schemes and outperforms the traditional spectrum underlay or spectrum overlay, via maximiz-ing the utilization of multi-carrier transmission. Compared with optimal schemes, classical water-filling, equal power and the ladder proportional power allocation approaches, the pro-posed sub-optimal solution is more attractable, because it can achieve significant rate, feature moderate peak-to-average power ratio (PAPR) with lower complexity, and take the advantages of multi-carrier channel, attaining the best trade-off between complexity and performance.Thirdly, following a detailed explanation of three femtocells access modes, it is impos-sible for selfish femtocells to choose the open access mode has been pointed out. So a novel utility-driven relay framework to stimulate selfish femtocells choose hybrid access mode as-sisting macro base station to provide relay service to cell-edge macro-users, meanwhile avoid-ing two-tier interference, has been proposed, wherein interference is the main aspect hindering heterogeneous femtocell performance much better. Macro base station spectrum management scheme based on cognitive radio spectrum auction, is suggested. Then utility functions related to transmission rate, normalized bid, spectrum price, relay compensation, and femtocell ac-cess mode control parameters, have been modeled. In addition, the proposed model employs Cournot Game to describe the competition-ship between femtocells, also adopts Stackelberg Game to present the competition and cooperation between macrocell and femtocells. To the best of our knowledge, it is the first time to integrate Cournot Game and Stackelberg Game to regulate the actions and reactions among communicating entities. The existence and unique-ness of Cournot game Nash equilibrium plus existence of Stackelberg equilibrium have also been proved. Importantly, two algorithms of the macrocell determining the proper refund factor and spectrum price to achieve Stackelberg equilibrium have been proposed, whose convergence has also been demonstrated. A protocol to implement the details of the game framework is presented. In terms of relay channel quality, rental bandwidth relay transmis-sion proportion factor and price discount factor, extensive numerical simulations have been carried out to verify the effectiveness of the proposed schemes and algorithms. Simulation results show that the proposed femtocell hybrid access mechanism can match a win-win sit-uation, benefiting cell-edge macro users for better quality of service (QoS) and higher access opportunities for femto users.The goal of this dissertation is to motivate the deployments of femtocells employing centralized cognitive radio spectrum management, geared to the evolution needs of the upcoming fifth generation (5G) heterogeneous cellular infrastructure, featuring high-rate low-power intelligent spectrum access.