Cooperative Scheme And Resource Allocation In Cooperative Cognitive Radio Networks

Due to the rapid increasing demand of spectrum resources in wireless communica-tion, cognitive radio technology has been studied in the past decade. Cognitive radio is considered as an efficient way to improve the spectrum efficiency under the traditional fixed spectrum allocation. In convetional cognitive radio networks, there are two kinds of access schemes for the secondary users (SU), one is overlay technology in which the sec-ondary uesrs opportunistically access the spectrum holes that has not been occupied by the primary users, and the other is underlay technology in which the secondary uesrs access the spectrum being occupied by the primary users without causing harmful interference to the primary users (PU). However, these two kinds of access schemes cannot guarantee the consecutive transmission and the performances of the SUs.Cooperative communication is a promising technology that can exploit the space di-versity and bring extra gains to the wireless systems. We introduce cooperative relay technology into cognitive radio networks, which is called cooperative cognitive radio net-works (C-CRN). The cooperative relay technology can help improve the spectrum utiliza-tion and bring revenue to both the PUs and SUs. There are two kinds of C-CRNs, one is called intra-C-CRN in which the SUs cooperate among themselves, the other is named inter-C-CRN in which the SUs cooperate with the PUs and play as relays of the PUs. The thesis studies the resource allocation and spectrum leasing problems in C-CRN. The main research work is summarized as follows:1. Based on corresponding cooperative cognitive radio models, two cognitive cooper-ative decode-and-forward (DF) relaying schemes are proposed. The two cognitive cooperation schemess called Scheme A and Scheme B are the extensions of the con-ventional cooperative relaying schemes, which are based on the division of the time duration and spectrum bandwidth. The cognitive cooperation schemes, which are composed of the necessary cooperation conditions and the resource allocation al-gorithms, are given for each model, respectively. These schemes aim to maximize secondary uesr’s own transmission data rate while garanteeing the data rate of the PU. Numerical results show that under the same constraints, Scheme A can bring higher data rate of SU; Scheme B brings more energy saving of the PU; in the two schemes, the data rates of SU’s own transmission both reach the top when the secondary trans-mitter (ST) of the SU is located in the middle between the primary transmitter (PT) and the primary receiver (PR).2. Considering spectrum market, we propose a utility based cooperative spectrum leas-ing (CSL) scheme for cognitive radio networks, in which both the primary user (PU) and the secondary user target to maximize their individual utility. The PU leases a portion of its spectrum to the SU to obtain revenue when its quality of service (QoS) is guaranteed, and the SU rents the spectrum to achieve its target data rate. This cooperative spectrum leasing problem is formulated as a Stackelberg game. The op-timal strategy for the PU and SU on the pricing and spectrum renting is analyzed. Under this cooperative spectrum leasing scheme, both the PU and the SU improve their individual utility. This CSL scheme is a promising paradigm for both the PU and SU for its mutual benefit in cognitive radio systems. Furthermore, we extend this CSL to multiple primary and multiple secondary user cooperative cognitive ra-dio networks. We formulate the spectrum leasing problem as a nonlinear integer programming problem, and decouple it into two sub-problems, one is spctrum leas-ing which is solved as above descrption, the other is relay selection problem. We transform the relay selection problem as an assignment problem which is solved by the Hungarian method. Numerical results show that, under the proposed cooperative spectrum leasing-optimal-relay-selection scheme, both the primary and secondary network can achieve high utilities.3. In multiple SUs C-CRN, the PU and SUs cooperate with each other adopting space-time coding relay scheme. We formulate the network framwork and adress the utility functions of the PU and the SUs. The SUs access the channel of the PU in a TDMA way with consideration of fairness. Based on utility functions maximizing, this thesis studies the spectrum allocation and relay selection problem. A spectrum allocation algorithm is derived under given number of SUs, and a low complexity relay selec-tion strategy is proposed to maximize the utility of the licensed user while guaran-teeing the data rate of the licensed user and the fairness among the cognitive users. Numerical results show the feasibility and efficiency of the proposed relay selection strategy.4. Considering multiple users C-CRN, OFDM based C-CRN is a promising network framwork which can exploit the diversity gain in both frequency and space. Firstly, we investigate the subcarrier allocation and power adjustment to maximize the sum data rate of the SUs with limited interference to the PUs adopting two-way amplify- and-forward (AF) relay. As there are two kinds of subcarriers in subcarrier alloca-tion, we propose subcarrier allocation algorithms and power adjustment methods for coresponding cases where the subcarriesr are being occupied by primary users or not. Simulation results show that the proposed algorithms significantly increase the sum data rate of the SUs. Secondly, we propose a low complexity resource allocation algorithm for the orthogonal frequency division multiplexing cooperative cognitive radio networks, where multiple PUs and multiple SUs coexist; We introduce a new concept of’efficiency capacity’ to represent the channel conditions of SUs, by con-sidering both of the interference caused by the PUs and the channel gains of the SUs with the assist of the relays; And then, we allocate the relay, subcarrier and transmis-sion power jointly under the constraint of limiting interference caused to the PUs. Simulation results show that the proposed algorithm can achieve a high data rate with a relative low power level. Finally, the thesis considers an OFDMA-based co-operative cognitive radio network where the SUs act as the relay of the PUs while guaranteeing the QoS of the PUs. In return, the SUs access the spectrum licensed to PUs in both time and frequency. A joint resource allocation problem is formulated to maximize the data rate of the SUs. It is proved that the optimization problem can be decomposed into two coupled subproblems which are power allocation and relay selection. Simulation results show that the proposed algorithm can bring revenue to both the PUs and SUs.