ABSTRACT
CONTENTS 11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
11.1.1 Characteristics of CR-VANETs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 11.1.2 Applications of CR-VANETs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 11.1.3 CR-VANETs Network Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
11.2 Channel Acquisition Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 11.2.1 Spectrum Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
11.2.1.1 Per-Vehicle Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 11.2.1.2 Geolocation-Based Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 11.2.1.3 Cooperative Spectrum Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
11.2.2 Spectrum Decision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 11.3 The Routing Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
11.3.1 Routing Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 11.3.1.1 Single-Path Routing Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 11.3.1.2 Multipath Routing Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
11.3.2 Routing Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 11.3.2.1 Opportunistic Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 11.3.2.2 End-to-End Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
11.4 Simulating End-to-End Protocols in CRAHNs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 11.4.1 NS2-CRAHN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
11.4.2 CRE-NS3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 11.5 Open Research Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
11.5.1 Design of Global Routing Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 11.5.2 QoS Routing and Realtime Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 11.5.3 Security-Based Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 11.5.4 More Accurate PU Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
11.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
The abundance of spectrum resources available for cognitive radio networks (CRNs) and the unpredictable activities of licensed users, i.e., primary users (PUs), make channel allocation an inherently dynamic multi-objective optimization problem. A CRN has to choose an operating channel that is not being used by PUs, meets its Quality of Service (QoS) demands, has no interference from other CR users or networks, have low PU activities, etc. This selection process becomes even more challenging for cognitive radio vehicular ad hoc networks (CR-VANETs) due to the absence of a central network coordinator, and the fast changing network topology and spectral environment [1, 2]. This chapter studies spectrum-aware routing techniques for CR-VANETs. This class of CRNs should accommodate a wide range of QoS classes, including the delay-intolerant safety information, while operating in a very dynamic environment that makes the process of establishing and maintaining reliable routing paths a highly complicated process [3, 4]. To tackle this issue, this chapter starts by identifying the main distinguishing features of CR-VANETs. The process of reliable spectrum acquisition is then studied as a prerequisite to route establishment. The chapter then discusses the various metrics and algorithms used to build routing paths using both end-to-end approaches and opportunistic approaches. Route maintenance is then studied, where we develop a rigorous mathematical model for the losses incurred due to the unpredictable activities of PUs. A comparative study is then conducted using a network simulator. In this study, we compare the performance of the various routing techniques, quantify the losses incurred due to PU activities, and devise some insights into proactive route maintenance.
