| The cognitive radio networks (CRN) is proposed based on the technologies of computer networks, electronic communications and control theory in the face of scarce spectrum resources and a variety of heterogeneous wireless access technologies. By sensing, analyzing, reasoning and deciding the past and current situations of the networks, the nodes in CRN are able to adjust their radios’parameters intelligently and dynamically. For this ability, the cognitive radio networks can solve the problems of the spectrum scarcity and heterogeneous network effectively.Media access control (MAC) protocol decides the method how the nodes in the networks receive and send data by shared wireless channels. Whether the MAC protocol can use the limited channel effectively plays a very important role in the performance of the cognitive radio network. Focusing on designing and implementation an excellent MAC protocol in cognitive radio networks, the key technologies that should be considered are studied and analyzed in this paper.This paper studies and analyzes the multi-channel MAC protocols in cognitive radio networks from the following aspects:Firstly, the traditional multi-channel MAC protocols based on IEEE 802.11 are studied in this paper. The nodes in the CRN can select free channel dynamically according to the changing spectrum, so that the MAC protocol in CRN is naturally based on multi-channel. The paper concludes the classification mechanism of the traditional multi-channel MAC protocols, analyzes its designing method, and provides the foundation for the adoption of these methods to the designing of cognitive multi-channel MAC protocols.For the reasons of the spectrum variety and coexistence with the primary users, much more aspects should be considered when designing a multi-channel MAC protocol in CRN. The key technologies, including power control, spectrum allocation, spectrum handoff and cross-layer design are introduced and studied in this paper. The power control is used to reduce the interference to the primary users and increase the spectrum multiplexing. The joint design of power control, access technology and spectrum allocation is illuminated. In addition, the models of spectrum allocation, including graph coloring model, pricing and game theory are explained. An important side when designing a MAC protocol in CRN is the sensing policy and access policy which is researched deeply.According to the topology of the cognitive radio networks, the MAC protocols can be classified into two types:centralized and distributed. For centralized MAC protocols, one of the key technologies that should be considered is the channel allocation. This paper proposes a protocol called IDSAP, which is based on greedy algorithm. The simulation results prove that it can increase the throughtput of the network.This paper pays more attention to the distributed MAC protocols in CRN. Based on the key technologies, three new cognitive multi-channel MAC protocols are proposed. The first protocol is CR-MMAC, which is an improved MAC protocol based on MMAC. In CR-MMAC, there is a dedicated control channel. The second protocol is DCRMAC-PC, which is a multi-channel MAC protocol with power control for multi-hop mobile Ad Hoc networks. In the phase of spectrum sensing, two sensing policies:random sensing policy and stack based sensing policy are considered and in the phase of channel negotiation, power control is considered; The third protocol is CR-PRMAC, which is a parallel rendezvous multi-channel MAC protocol for distributed cognitive radio networks. Nodes in CR-PRMAC can communicate control frame with multiple channel while CRMMAC and DCRMAC with only one. So CR-PRMAC proposed in this paper can avoid the bottlenecks of dedicated control channel. All the proposed MAC protocols are simulated with NS2 and simulation results prove them working well.At last, this paper gives the performance analysis to the different type cognitive multi-channel MAC protocols. |
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