Research On Key Technologies Of Cognitive Radio Ad Hoc Networks

With the rapid development of wireless communication technology, the contradictions between increasing wireless spectrum resource needs and limited spectrum resource supply are becoming increasingly acute. The data of research report shows that, the traditional licensed spectrum allocation policy decreases the efficiency of wireless spectrum resource utilization. The cognitive radio technology adopts dynamical spectrum access technology and dynamically discovers the spectrum opportunity which is impulsive for increasing the spectrum utilization efficiency. The Cognitive Radio Ad Hoc Networks (CRAHNs) extend the cognitive radio technology to the multi-hop wireless ad hoc networks scenario, which changes the centralized network structure of cognitive radio networks, and the large range of transmission and flexible network structure make the spectrum resource discovering on the time, space and frequency domain more sufficient.However, the CRAHNs face lots of challenges nowadays:firstly, the disordered competition for the wireless resources decrease the network capacity; secondly, due to the dynamical spectrum availability, the wireless link becomes unstable which decreases the end-to-end stability and quality of service by using the traditional network protocol; besides that, the break routes cause packet loss and congestion problem during the multi-hop routing and data transmission. To solve the problem described above, this dissertation investigates the architecture of CRAHNs which is the research basis for the dissertation. The dissertation studies the power allocation schemes, routing schemes and traffic assignment scheme on the link layer, network layer and transport layer, in order to increase the end-to-end transmission quality of service in CRAHNs. The dissertation content and contributions are summaried as follows:Considering the interference which exists among secondary users and between the primary users and secondary users on the physical and link layer in CRAHNs, which decreases the resource utilization efficiency, a distributed power allocation scheme, which is based on the interference temperature limit, is proposed in this dissertation to guarantee the transmission quality of primary users and maximize the capacity of secondary user networks. Firstly, the interference monitor nodes are set up in this scheme to ensure that the interference to the primary users is below the interference temperature limit. Secondly, based on the Stackelberg game, the secondary users allocate the power after the primary users and get the optimal power control schemes by iterative solution. Finally, the simulation verifies the convergence property of the proposed scheme. Furthermore, by comparing with the equally allocation and channel gain based ratio allocation, the proposed scheme outperforms other schemes in capacity.Considering the low stability and poor end-to-end quality of service on the network layer in multi-hop CRAHNs, this dissertation proposed a3-dimensional conflict graph based multi-path routing scheme. The multi-path routing scheme characterizes the interference and resource utilization conflicts among secondary users by3-dimensional conflict graph and performs the conflict-free routes selection to transmit data based on the maximum independent set. Considering the limited energy of nodes in CRAHNs, if the changes of channel gain and the availability are neglected in multi-path routing, the energy of node can not be efficient utilized in data transmission which incurs the waste of node energy and spectrum resource. In order to optimize the efficiency of multi-path routing in CRAHNs, an optimal routes selection scheme is proposed in this dissertation. The Markovian chain is used to model the state transformation of channel gain, channel availability and energy level of nodes. The problem is modeled based on the Restless Bandit theory, which is a stochastic process optimization problem, to jointly optimize the transmission delay and energy cost. The simulation results show that the scheme proposed in this dissertation outperforms the random selection scheme and greedy selection scheme in joint optimal utility function of transmission delay and energy cost, and increases the efficiency of routing in CRAHNs.Considering the dynamical factors of spectrum availability and service arrival rate in multi-path transmission CRAHNs, the end-to-end delay and packet loss ratio are enhanced due to the lack of adaptive traffic assignment. A dynamical traffic assignment scheme for multi-path transmission in CRAHNs is proposed in this dissertation. The scheme assigns the traffic to the paths according to the processing ability to attain optimized end-to-end delay. The queue theory is used to model the packet arrival rate, processing ability and spectrum availability of secondary users which affects the end-to-end delay of multi-path transmission. The problem is formulated as a min-max problem which minimizes the maximum delay in multi-path transmission, and gets the optimal traffic assignment proposal by iterative solution. The simulation verifies the convergence property of this scheme. Moreover, the proposed scheme is compared with the equal and ratio assignment scheme which outperforms other schemes in end-to-end delay.In the end, the research is summarized in this dissertation, and the related directions are pointed out in CRAHNs.