Spectrum Utilisation and Management in Cognitive Radio Networks

In recent years, the demand for radio spectrum for wireless communication is growing due to increase in number of users and popularity of data and multimedia services. This has been observed in the recent auctions completed word wide for the vestige of radio spectrum. The radio spectrum has been assigned to different services and it is very much difficult for the emerging wireless technologies to get entry due to rigid spectrum policy and heavy opportunity cost. The inefficient prevailing spectrum management causes the artificial spectrum scarcity. The measurement campaigns conducted worldwide have confirmed this by showing that the considerable amount of radio spectrum
is underutilized.

Dynamic Spectrum Access (DSA) and the spectrum refarming are the two viable solutions for the problem of spectrum scarcity. In DSA, unlicensed user opportunistically uses the vacant licensed spectrum with the help of Cognitive Radio. Cognitive Radio is a key enabling technology for DSA. In Cognitive Radio paradigm, secondary user (SU) i.e. unlicensed user locate the vacant licensed spectrum of licensed user i.e. Primary user (PU) and uses it without harmful interference to the PUs. The secondary use of licensed spectrum provides efficient use of spectrum. Spectrum refarming means the recovery of spectrum from its existing users for the purpose of re-assignment, either for new uses, or for the introduction of new spectrally efficient technologies. Spectrum
refarming is a spectrum management tool that can satisfy new market demands and increase spectrum efficiency.

Evaluation of the spectrum usage is the first step toward the future deployment of cognitive radio. Several spectrum usage measurement campaigns have been performed mainly in USA and Europe. The results of these campaigns are not directly applicable to India since the geographical characteristics, and the social environment is different in India. The spectrum usage situation and
therefore the Cognitive Radio in India are unclear. We address this in the thesis and present empirical work and modeling in the context of Cognitive Radio.

The empirical work include the design of the measurement setup and the short and longer time span measurement campaigns at different locations in India with practical scenarios of Cognitive Radio. We evaluate the spectrum usage in different bands allocated to wireless services based on the real time data collected from the measurement. We find a significant amount of spectrum is
underutilized and opportunities for the secondary use. We provide the temporal and spatial properties of the spectrum occupancy. From the extensive measurement we characterize the use of spectrum and identify the potential candidate bands for Cognitive Radio. We present the model which
has ability to reproduces the statistical characteristics of the spectrum usage.

The cognitive access of unused TV band i.e. TV white spaces is the excellent opportunity to not only to counteract the spectrum scarcity problem but also for the new cognitive radio applications. Recently the secondary access to TV white spaces is allowed by American regulatory body FCC. From the occupancy measurement of TV band, we find a significant amount of spectrum is underutilized and opportunities for the secondary use in India. In this work, we address the technical and regulatory requirements for Cognitive Radio operation in TV white space band and its implications on spectrum regulation in the context of Indian scenario.

We point out the extensive use of spectrum in the mobile cellular services showing the popularity of these services. We suggest the demand of additional spectrum for these services can be meet through the digital dividend spectrum released from spectrum refarming in TV band. The developed spectrum sharing model derives some important statistics which are beneficial in analyzing the
performance of the DSA systems.