Research Of Carrier Aggregation Technologies In MAC Layer Based On Cognitive Radio

Cognitive Radio(CR) technology is a milestone in the history of the development of radio technology. CR is an intelligent technology of spectrum sharing, with the help of which, sec-ond users can detect multiple discontinuous spectrum opportunities by spectrum sensing, and utilize them together by spectrum access to satisfy the service requirement. Consequently, CR has become the key technology in solving the paradox between spectrum scarcity and spectrum underutilization. As the foundation of CR, the technology of Carrier Aggregation can aggregate scattered and narrow spectrum fragments into a complete spectrum with high capacity, as a result of which, the efficiency of the spectrum and the throughput of the system can be improve a lot. This paper is focused on the research of Carrier Aggregation technologies in MAC layer based on Cognitive Radio, and proposed some innovative solutions to solve the problems.First, a POMDP-based optimal spectrum sensing and access scheme is designed. The prac-tical hardware limitations bring technical challenges to cognitive radio, e.g. limited capability of spectrum sensing and certain frequency range of spectrum access. We develop an analytical framework for joint spectrum sensing and access scheme based on Partially Observable Markov Decision Process (POMDP). For obtaining the reward function of POMDP, the channel access and switching probabilities are estimated by theoretic deduction. With the help of linear pro-gramming, an optimal spectrum sensing and access scheme is proposed to minimize the channel switch times. Simulation results show that our proposed optimal scheme reduces the times of channel switches significantly.Next, a Rollout-based low complexity spectrum sensing and access scheme is studied. In order to achieve a balance between system performance and computation complexity, we propose a Rollout-based joint spectrum sensing and access scheme. Two heuristic policies are proposed to serve as base policies, based on which the developed Rollout-based policy approximates the value function and determines the appropriate spectrum sensing and access actions. We establish mathematically that the Rollout-based policy achieves better performance than the base policy. We also demonstrate that the low-complexity Rollout-based policy leads to only slight perfor-mance loss compared with the optimal policy.Finally, a CSMA protocol with the utilization of Carrier Aggregation technology is pro-posed. It is more difficult to design a medium access control protocol for CR network which utilizes Carrier Aggregation technology to improve performance. In our protocol, time is di-vided into frame intervals, and a small window called CN window is placed at the start of each frame interval, during which the second users that have packets to transmit will negotiate chan-nels with the destination users. This protocol can not only solve the problems of hidden terminal and exposed terminal in single-channel environment, but also avoid the multi-channel hidden terminal problem and the missing receiver problem. At last, the communication quality of the network is guaranteed and the system throughput is improved.