Distributed Shared Spectrum Techniques for Cognitive Wireless Radio Networks

Cognitive radios (CR) offer the promise of being a disruptive technology innovation that will enable the future wireless world. CR techniques are being applied in many different communications systems. They promise to improve the utilization of radio frequencies making room for new and additional commercial data, emergency, and military communications services. Today's wireless networks are characterized by a fixed spectrum assignment policy. However, a large portion of the assigned spectrum is used sporadically and geographical variations in the utilization of assigned spectrum ranges from 25% to 75% with a high discrepancy in time. The limited available spectrum and the inadequacy in the spectrum usage necessitate a new communication standard to utilize the existing wireless spectrum opportunistically. This innovative networking standard is referred to as NeXt Generation (xG) Networks as well as Dynamic Spectrum Access (DSA) and cognitive radio networks(CRN). Cognitive Radio Networks are composed of wireless devices able to opportunistically access the shared radio resource. The core of such networking paradigm is the capability of cognitive radio to monitor the spectrum occupation to exploit spectrum holes for transmission. Spectrum sensing refers to the technique used by cognitive radios to scan the spectrum. in addition, the xG network roles such as spectrum management, spectrum mobility and spectrum sharing are explained in detail. The influence of these functions on the performance of the upper layer protocols such as routing and transport are investigated and open research issues in these areas are also summarized. In the end, challenges for the security, cross-layer design issues and future scope of of xG Network are concluded.