ABSTRACT
Contents 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5.2 Channel Assignment in Cellular Networks . . . . . . . . . . . . . . . . . . . . . . . . . 111 5.3 Channel Assignment in Cognitive Radio Networks . . . . . . . . . . . . . . . . 113 5.4 Some Research Problems in Cognitive Radio Networks . . . . . . . . . . . 114
5.4.1 Complexity Analysis of Channel Assignment Algorithms . . 114 5.4.2 Network Selection for Secondary Users. . . . . . . . . . . . . . . . . . . . . 116 5.4.3 Secrecy Capacity of Cognitive Radio Networks. . . . . . . . . . . . . 118
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
5.1 Introduction The development of software-defined-radio-(SDR) enabled1 cognitive radio networks has facilitated dynamic sharing by users of the available spectrum on an opportunistic basis. Users belonging to one network can sense spectrum opportunities in another network and contend for the unused spectrum in the new network. These users thereby become secondary users in the new network. Users that originally subscribed to the second network are called primary users. The combined interference caused by all
the secondary users to existing primary users should be below a specified threshold. Applications of this idea to ultra-wideband wireless networks are presented by Lansford2. Liu and Wang3 present the characteristics of spectrum-agile networks and study them using two metrics: (1) the effective nonopportunistic bandwidth and (2) the space-bandwidth utilization. Akyildiz et al.4 present a comprehensive survey of cognitive radio networks.
