PhD Theses

PhD theses from CMI

Spectrum Utilisation and Management in Cognitive Radio Network


The demand for radio spectrum for wireless communication is growing due to increase in number of users and popularity of data and multimedia services. Dynamic Spectrum Access (DSA) and the spectrum refarming are the two viable solutions for the current problem of spectrum scarcity. Cognitive Radio (CR) is a key enabling technology for DSA. In CR paradigm, secondary user (SU) i.e. unlicensed user locates 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.

Evaluation of the spectrum usage is the first step toward the future deployment of CR. 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 CR in India are unclear. We address this in the thesis and present reference empirical spectrum occupancy measurements in India and modelling in the context of CR. The work includes the design of the measurement setup and the short and longer time span measurement campaigns at different locations in India with practical scenarios of CR. 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. We present stochastic duty cycle model based on measurement to identify the potential for CR.

The cognitive access of TV white spaces is an excellent opportunity not only to counteract the spectrum scarcity problem but also for the new CR applications. We find a significant amount of spectrum is underutilized and opportunities for the secondary use in India from the spectrum occupancy measurement of TV band. In this work, we propose wireless broadband connectivity to rural areas in India using TV whitespaces and technical and regulatory requirements for CR operation in TV band. We also present implications of CR on spectrum regulation in the context of Indian scenario.
We point out the extensive use of spectrum by the mobile cellular services in India showing the popularity of these services. We suggest the demand of additional spectrum for these services can meet through the digital dividend spectrum released from spectrum refarming in TV band. Finally, the developed CTMC based spectrum sharing model derives some important statistics which are beneficial in analyzing the performance of the DSA systems.


Date of defense: 11.11.2013


PhD theses