PhD, University of Cincinnati, 2009, Engineering : Computer Science and Engineering

In a cognitive radio network (CRN), bands of a spectrum are shared by licensed (primary) and unlicensed (secondary) users in that preferential order. It is generally recognized that the spectral occupancy by primary users exhibit dynamical spatial and temporal properties. In the open literature, there exist no accurate time-varying model representing the spectrum occupancy that the wireless researchers could employ for evaluating new algorithms and techniques designed for dynamic spectrum access (DSA). We use statistical characteristics from actual radio frequency measurements, obtain first- and second-order parameters, and define a statistical spectrum occupancy model based on a combination of several different probability density functions (PDFs). One of the fundamental issues in analyzing spectrum occupancy is to characterize it in terms of probabilities and study probabilistic distributions over the spectrum. To reduce computational complexity of the exact distribution of total number of free bands, we resort to efficient approximation techniques. Furthermore, we characterize free bands into five different types based on the occupancy of its adjacent bands. The probability distribution of total number of each type of bands is therefore determined. Two corresponding algorithms are effectively developed to compute the distributions, and our extensive simulation results show the effectiveness of the proposed analytical model. Design of an efficient spectrum sensing scheme is a challenging task, especially when false alarms and misdetections are present. The status of the band is to be monitored over a number of consecutive time periods, with each time period being of a specific time interval. The status of the sub-band at any time point is either free or busy. We proved that the status of the band over time evolves randomly, following a Markov chain. The cognitive radio assesses the band, whether or not it is free, and the assessment is prone to errors. The errors (open full item for complete abstract)

Committee: Dharma Agrawal (Advisor); Raj Bhatnagar (Committee Member); Chia-Yung Han (Committee Member); Yiming Hu (Committee Member); Marepalli Rao (Committee Member) Subjects: Computer Science

Doctor of Philosophy, The Ohio State University, 2017, Electrical and Computer Engineering

Increasing demand for supporting more wireless services with higher performance and reliability within the frequency bands that are most conducive to operating cost-effective cellular and mobile broadband is aggravating current electromagnetic spectrum congestion. This situation motivates technology and management innovation to increase the efficiency of spectral use. If primary-secondary spectrum sharing can be shown possible without compromising (or while even improving) performance in an existing application, opportunities for efficiency may be realizable by making the freed spectrum available for commercial use. While both active and passive sensing systems are vitally important for many public good applications, opportunities for increasing the efficiency of spectrum use can be shown to exist for both systems. This dissertation explores methods and technologies for remote sensing systems that enhance spectral efficiency and enable dynamic spectrum access both within and outside traditionally allocated bands.

Committee: Joel Johnson (Advisor); Emre Ertin (Committee Member); Graeme Smith (Committee Member) Subjects: Electrical Engineering; Electromagnetics