86 Copyright © 2013, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited. Chapter 5 Spectrum Sensing in Emergency Cognitive Radio Ad Hoc Networks ABSTRACT Ad hoc networks are infrastructure less networks which are self organizing and adaptive. Such networks can be used in emergency situations like disaster management and military applications. Usage of cogni- tive radios as the wireless terminals in ad hoc networks in emergency situations has distinct advantages. Better bandwidth, interoperability, avoidance of interference, and ant-jamming capabilities are a few such advantages. Ad hoc networks with cognitive radios are wireless terminals used in emergency situ- ations and can be referred to as Emergency Cognitive Radio Ad Hoc Networks (Emergency CRAHNs). In this chapter, the authors discuss emergency CRAHNs and the specifc requirements that must be met by the spectrum sensing mechanism used by them. In particular, the authors discuss collaborative spec- trum sensing methodology; where in multiple cognitive radios operate together such that reliability of spectrum sensing in improved. This collaborative sensing in ad hoc networks can be either of centralized or distributed architectures, both of which are discussed in this chapter. INTRODUCTION Ad hoc networks are infrastructure less networks that are formed or de-formed on the fly without any need of system administration. That is, they are self-organizing and adaptive (Toh, 2007). Ad hoc networks find application in emergency scenarios like disaster management and military. In emergency situations, it is required for a mobile group to communicate with each other on peer to peer basis. These communication links must be reliable and provide redundant paths to cater for operations under communication link failures. For example, in S.E. Fireworks disaster in Enschede, the Netherlands (May 2000), a fireworks depot exploded and destroyed a large part of the city, 23 people were killed and more than a thousand were injured. Fire brigade, police and relief workers in the medical chain experienced severe communica- tion problems, both internally and with each other, Sasirekha GVK International Institute of Information Technology, India Jyotsna Bapat International Institute of Information Technology, India DOI: 10.4018/978-1-4666-4221-8.ch005