ABSTRACT
Contents 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216 8.2 Existing Cognitive Radio MAC Layer Protocols . . . . . . . . . . . . . . . . . . . . 217
8.2.1 Dynamic Open Spectrum Sharing MAC Protocol (DOSS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 8.2.1.1 Detecting the Presence of Primary Users . . . . . . . . . . 217 8.2.1.2 Setting up Three Operational Frequency Bands . . 217 8.2.1.3 Spectrum Mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 8.2.1.4 Spectrum Negotiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 8.2.1.5 Data Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
8.2.2 Common Spectrum Coordination Channel Protocol (CSCC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
8.2.3 Distributed Channel Assignment Protocol (DCA) . . . . . . . . . . 219 8.2.4 Slotted Seeded Channel Hopping Algorithm (SSCH) . . . . . . . 219
8.3 MAC Layer Spectrum Sharing Issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 8.4 Handling of CR Hidden and Exposed Terminal Problem. . . . . . . . . . 226 8.5 The Use of MAC Layer Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 8.6 Control Channel Saturation Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 8.7 MAC Layer Security. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
8.8 Optimization MAC Layer for Cross-Layer Design . . . . . . . . . . . . . . . . . . 230 8.9 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
8.1 Introduction The cognitive radio (CR) concept has been defined as “the point at which wireless personal digital assistants (PDAs) and the related networks are sufficiently computationally intelligent about radio resources and related computer-to-computer communications to detect user communications needs as a function of use context and to provide radio resources and wireless services most appropriate to those needs” [1]. Many regulatory bodies like the Federal Communications Commission (FCC) in the United States have observed that the radio spectrum is inefficiently utilized. According to the FCC, a cognitive radio is defined as one that can sense its environment and then alter its operating frequency, power, and modulation techniques in order to use the spectrum efficiently. A congnitive radio has the following features: (a) it should be able to identify and detect the channel in the available band and to tune itself to that particular channel; (b) after identifying the channel, it should then establish the network connection and operate in that particular channel; (c) to obtain the best throughput, the primary aspect for any type of system, CR implements better bandwidth for efficient data transmission and also error control and correction schemes to obtain the best throughput; and (d) in order to optimize the received signal strength it can adjust the direction of its antenna.
