Researches On Key Techniques Of MAC Layer And Security Authentication Of Cognitive Radio Networks

The rapid growth of the ubiquitous wireless services has imposed great pressure on the fixed and limited radio spectrum. Given this fact, the research society has adopted the new concept of cognitive radio (CR) to change the traditional static spectrum allocating and to use spectrum dynamically. Cognitive radio has been proposed as a way to improve spectrum efficiency by detecting the unoccupied spectrum, changing the system operation parameters (e.g., symbol rate, power, bandwidth, latency) in real-time to use radio resources according to a certain learn and schedule algorithm. Therefore, in theory, it can achieve the multi-dimension spectrum utilization including frequency, time and space, which greatly reduces the limitation of spectrum and bandwidth to wireless communication technology. Thus, spectrum utilization is enhanced. However, there are lots of new challenges in order to realize dynamic spectrum sharing among cognitive users in cognitive radio networks. First of all, media access control (MAC) layer faces many difficulties that are not presented in the conventional wireless networks. Especially, how to design a cognitive users accessing mechanism and control signaling, how to schedule several channel access request and how to implement channel handoff in dynamical environment are all open research issues. Additionally, the security mechanism for cognitive radio also has lots of threats.This thesis mainly focuses on the MAC layer key technology of CR networks and performs the theory analysis and experiment research. During the process of access schedule, MAC layer control signaling and multi-channel handoff, how CR user adaptively utilizing spectrum and satisfying some quality of service (QoS) parameters are studied in detail. Several solutions are presented for CR ad hoc application environment. In addition, the authentication security for the spectrum sensing result and membership maintaining of CR networks are also explored. The main contents and contributions are as following:1. In order to fully utilize channel opportunity and efficiently transmit data in cognitive radio networks, this chapter models the available channel opportunity and proposes an adaptive opportunistic channel access (AOCA) schedule algorithm. Based on the channel state information sensed, available channel opportunity is modeled in single channel and multichannel scenario, respectively. The schedule algorithm can adaptively schedule channel sensing leveraging the MAC layer decisions and maximize channel utilization without imposing any additional burden on cognitive users. Different from other CR algorithms, AOCA algorithm provides cognitive users with QoS support. The QoS is identified as terminals'buffer space and queue length along with the collision ratio with other users. The simulation results demonstrate that the proposed channel schedule scheme can utilize the channel adaptively and flexibly in CR networks. Therefore it can achieve good efficiency.2. In order to utilize the dynamic channel opportunity flexibly and efficiently in cognitive radio networks, a multi-channel adaptive MAC protocol is presented. The proposed protocol employs the concept of competing control channel (CCC) and reserving control channel (RCC) to improve the low utilization and lack of expansibility in related works. In order to access the channel, cognitive users reserve the sub-frame of RCC through CCC, which obligates the access opportunity for different traffic. Then they apply the data channel based on the required bandwidth using RCC. The channel is distributed and recycled by updating a channel state table. Simulations show that the proposed protocol can effectively schedule the accessing of users and exhibit good scalability. Compared with other fixed control channel based protocol, it significantly reduces the probability of collision and congestion, thereby improves the end-to-end delay and network throughput.3. For the sake of executing vertical handoff for cognitive user without interfering primary user while offering the desired QoS and eliminating the influence caused by hidden channel and exposed channel simultaneously, this paper proposes a flexible vertical channel handoff algorithm for heterogeneous cognitive radio networks. This algorithm is very flexible and effective. It can adaptively schedule channel sensing by utilizing the concept of spectrum pooling. The key QoS parameter adopted in this algorithm is channel bandwidth which denotes the heterogeneity of the networks. The handoff process is analyzed using Markov model. We evaluate the major performance metrics such as handoff blocking probability, handoff cost and collision probability by simulation. The results indicate the proposed algorithm can significantly improve the performance and provide stable communication in the synchronous and asynchronous CR networks.4. With the intent of efficiently occupying under-utilized spectrum, radio environment map (REM) based CR networking is proposed to facilitate the distributed spectrum sensing. In this chapter, we identify the security threats and propose a chaos sequence and channel encoding based adaptive authentication protocol for REM-based CR networks. In the duration of distributed data aggregating and decision results distributing, authentication information is secret data and sensing information is useful data. Employing channel encoding techniques and chaos sequence, authentication data is embedded into channel data as random noise. The error of host data caused by secret data can be corrected via error correction encoding technique. The receiver can then use the secret information extracted from channel data to authenticate if the received data is sent by the user claimed. To the best of our knowledge, that is the first attempt to provide authentication mechanism for REM-enabled CR network.