Research On Time-domain Opportunistic Spectrum Access Strategy In Cognitive Radio Network

With the rapid development of wireless communication service, the total wireless available spectrum resource has been almost allocated exhaustively while the allocated spectrum is largely under-utilization resulting from the current static spectrum management policy, which leads to spectrum shortage. Time-domain opportunistic spectrum access(OSA) based on cognitive radio can effectively improve the spectrum efficiency by allowing secondary users to exploit instantaneous spectrum opportunities with no harmful interference to primary users. However, how do secondary users get access to these rapidly varying spectrum opportunities dynamically poses many brand-new challenges for opportunistic spectrum access in cognitive radio networks. In order to intelligently tracking and rationally exploit temporal spectrum opportunities, we perform research on time-domain opportunistic spectrum access strategy in cognitive radio network. The main contributions and works are outlined as follows:1. Aiming at improving the gain of opportunistic spectrum access in the absence of prior knowledge of slotted primary users network, a channel selection scheme based Q-Learning was proposed. The present algorithm overcame the reliability of the traditional selection algorithm for the prior knowledge. So the agent can select the channel with the maximum cumulative reward by continuous interaction and learning between the agent and unknown environment. During the learning stage, we considered the influence of the reward-function caused by traffic load and signal-noise-ratio, and also a Boltzmann learning rule using simulated annealing ideas was employed to realize the tradeoff between channel exploration and exploitation. As the simulation results show, the proposed algorithm can raise the average selected capacity and throughput of the secondary user effectively.2. In order to optimize the spectrum access time and improve the throughput of the secondary user in the unslotted primary user network, opportunistic spectrum access under periodic sensing framework was analyzed. By constructing the secondary user channel sense and access model, we derivate the proposed the effective transmission throughput concept by the derivation of the secondary user idle time probabilistic expression. So we proposed an opportunistic spectrum access algorithm based on user request data packet length. According to the service data packet length allocated by each slot, the present algorithm could automatically modify the strategy of opportunistic spectrum access with abundant idle time. Experiment results show that the proposed algorithm can enhance the secondary users expect effective throughput under the condition of tight interference, and realize the tradeoff between effective throughput and collision probability, as well as possessing strong robustness if exotic environment changes.3. A novel energy efficient opportunistic spectrum access strategy was proposed to solve the energy constrain issue of one secondary user in non-slots cognitive radio network, in which a secondary user sensed the channels licensed to some primary users sequentially before it decided to transmit. To maximize energy efficiency, the algorithm can make the secondary user specify the optimal channel sensing time and transmission power to be used upon transmission by establishing sensing access joint optimization model. During the power control process, packet length to be transmitted of the secondary use was considered to regulate the transmission power adaptively. In order to solve above nonlinear fractional programming problem, we converted it into a linear programming problem and obtained the maximum energy efficiency by Binary Search algorithm. Simulation results indicate that the proposed strategy can achieve the tradeoff between the sensing performance and sensing overhead and also effectively improve the energy efficiency of the secondary user.4. The simulated test platform of opportunistic spectrum access strategy was designed and realized under the VS2010 platform. Based on hierarchical Modular Design Technology, different primary network environment was designed and built up. Finally, opportunistic spectrum access strategy proposed in previous chapters was evaluated and Test results show that the system simulation platform is provided with better reliability and practicability.