Under the contemporary spectrum usage regulations, radio frequency bands are allocated statically to licensed users in a large geographical area and over a long period of time. Recent investigations have revealed that such static spectrum allocation has led to very poor usage of the overall spectrum. Cognitive radio has emerged as a new communication paradigm to improve the utilization of the radio spectrum. It is defined as an intelligent wireless communication system that allows coexistence of unlicensed users with the licensed ones as long as the perceived interference at the licensed user is capped below some acceptable level. In addition, the users in this system adopt efficient communication protocols to enhance spectral efficiency. We employ cooperative mechanisms wherein multiple users cooperate in order to accomplish the following tasks: 1) Cooperative spectrum sensing: In this task, the licensed users do not actively engage. Instead, the unlicensed users passively monitor the activity of the licensed users and transmit only during their absence. 2) Cooperative spectrum management: The licensed and unlicensed users can benefit from cooperation with each other, e.g., they can assist each other in transmission via relaying. In this fashion, they can save power or bandwidth and therefore, the whole network can accommodate more users. \end{itemize} In the first part of this thesis, we focus on cooperative spectrum sensing. We first study the performance of the optimal distributed detectors as the number of samples increases and identify the conditions under which the highest or lowest asymptotic performance is achieved. For each condition, we study several suboptimal detectors and obtain novel asymptotic expressions for their performance. We then consider distributed detection of an Orthogonal Frequency-Division Multiplexing (OFDM) signal source. We propose different optimal and suboptimal frequency-domain detectors and derive closed form expressions for their performance. These frequency-domain detectors, despite their lower computational complexity, outperform the state-of-the-art time-domain detectors. Finally, we consider distributed spectrum sensing in mixture-Nakagami fading channels. We propose several novel detectors that significantly outperform the traditional detectors. In all these cases, we prove that the suboptimal detectors are asymptotically optimal, i.e., their performance converges to the Uniformly Most Powerful (UMP) tests as the number of samples increases. In the second part of the thesis, we focus on cooperative spectrum management. We study the problem of cooperative relay selection and power allocation and determine the conditions, in terms of channel gains and network geometry, under which such cooperation leads to an increase in rate, or a reduction in power and bandwidth usage. Lastly, we propose cooperative protocols that exploit these results and greatly enhance spectrum efficiency. / Thesis (Ph.D, Mathematics & Statistics) -- Queen's University, 2013-06-04 18:23:24.845

ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, California / This paper presents a methodology for the management of interference and spectrum for iNET. It anticipates a need for heavily loaded test environments with Test Articles (TAs) operating over the horizon. In such cases, it is anticipated that fixed and ad hoc networks will be employed, and where spectrum reuse and interference will limit performance. The methodology presented here demonstrates how this can be accomplished in mixed networks.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / Automatic spectrum management and monitoring systems are very useful to manage frequencies at test ranges and assure interference-free transmission of telemetry signals. Spectrum management systems assign telemetry frequencies using database information on available and occupied channels and analysis tools which can determine whether a data link will support telemetry. Modern, DSP-based spectrum monitoring systems, in fixed or mobile configurations, automate the process of performing spectrum occupancy to verify clear channels and identify and locate sources of interference; they are integrated with and utilize the management system database. Such systems are important to assure reliable communications channels for telemetry.

Thesis (M.M. (ICT Policy and Regulation))--University of the Witwatersrand, Faculty of Commerce, Law and Management, Graduate School of Public and Development Management, 2013. / Radio frequency spectrum, a scarce national strategic asset, has not enjoyed the necessary attention and protection it deserves. Spectrum has been managed by the same approach over the last two decades and it is only recently that attention has been given to it due to the pressure of increased competition and technological advancements. The purpose of this study was to explore the policy and regulatory approaches to the management of radio frequency spectrum prevalent in South Africa today. Internationally there is a shift from the traditional command and control spectrum management approaches to more market-based mechanisms, such as auctions and spectrum trading. The South African approach has been marked by delays in the usage of spectrum as a result of the current institutional arrangements where there is an apparent overlap between the policy and regulatory function. The study concludes that the delays could be circumvented by separating the spectrum allocation and assignment into policy and regulatory functions respectively. Efficient spectrum management policy and regulation is important for the next stage of electronic communications revolution because of the advances in the technology such as broadband and agile radio.

Radio spectrum is becoming scarce resource due to increase in the usage of wireless communication devices. However studies have revealed that most of the allotted spectrum is not used effectively. Given the demand for more bandwidth and the amount of underutilized spectrum, DSA (Dynamic Spectrum Access) networks employing cognitive radios are a solution that can revolutionize the telecommunications industry, significantly changing the way we use spectrum resources, and design wireless systems and services. Cognitive radio has improve the spectral efficiency of licensed radio frequency bands by accessing unused part of the band opportunistically without interfering with a license primary user PU. In this thesis we investigate the effects on the quality of service (QoS) performance of spectrum management techniques for the connection-based channel usage behavior for Secondary user (SU). This study also consider other factors such as spectrum sensing time, spectrum handoff and generally distributed service time and channel contention for different SUs. The preemptive resume priority M/G/1 queuing theory is used to characterize the above mentioned effects. The proposed structure of the model can integrate various system parameters such spectrum sensing, spectrum decision, spectrum sharing and spectrum handoff. / Sajid Mahmood 0046-762788990 Mujeeb Abdullah 0046-760908069

Opportunistic spectrum access has become a high priority research area in the past few years. The motivation behind this actively researched area is the fact that the limited spectrum available is currently being utilized in an inefficient way. The complete wireless spectrum is assigned and reserved, but not necessarily being used. At the same time, the demand for innovation in wireless technology is growing. Since there is no room in the wireless spectrum to allocate significant frequency bands for future wireless technologies, the only recourse is to increase utilization of the spectrum. To achieve this, we must find a way to share the spectrum. Spectrum sharing techniques will require coordination between all the layers of the protocol stack. The network and the wireless medium are inextricably linked and, thus, both must be considered when optimizing wireless network performance. Unfortunately, interactions in the wireless medium can lead to non-convex problems which have been shown to be NP-hard. Techniques must be developed to tackle the optimization problems that arise from wireless network analysis. In this document we focus on analyzing the spectrum sharing problem from two perspectives: cooperative game theory and non-convex optimization. We develop a cooperative game theory model to analyze a scenario where nodes in a multi-hop wireless network need to agree on a fair allocation of spectrum. We show that in high interference environments, the utility space of the game is non-convex, which may make some optimal allocations unachievable with pure strategies. However, we show that as the number of channels available increases, the utility space becomes close to convex and thus optimal allocations become achievable with pure strategies. We propose the use of the NBS and show that it achieves a good compromise between fairness and efficiency, using a small number of channels. We also propose a distributed algorithm for spectrum sharing and show that it achieves allocations reasonably close to the NBS. In our game theory analysis, we studied the possible outcomes of the spectrum sharing problem and propose the NBS as a desirable outcome and propose an algorithm to achieve the NBS spectrum allocation. However, the expression used to compute the NBS is a non-convex optimization problem. We propose an optimization model to solve a class of problems that incorporate the non-convex dynamics of the wireless medium that occur when the objective is a function of SINR. We present two case studies to show the application of the model to discrete and continuous optimization problems. We propose a branch and bound heuristic, based on the RLT, for approximating the solution of continuous optimization problems. Finally, we present results for the continuous case study. We show simulation results for the heuristic compared to a time constrained mixed integer linear program (MILP) as well as a nonlinear optimization using random starting points. We show that for small networks the MILP achieves the optimal in reasonable time and the heuristic achieves a value close to the optimal. We also show that for large networks the heuristic outperforms the MILP as well as the nonlinear search. / Ph. D.

Multi-antenna systems with resource allocation based on transmit and receive precoding matrices have proven to enhance the spectral efficiency of cellular systems. In this thesis, we extend these concepts to a spectrum sharing system with primary users and secondary users. The spectrum sharing area is modeled as an array of transmit and receive antennas, with the transmit power constraint defined as a function of the interference threshold of the primary user. The area covered by a database enabled spectrum access system is represented as spatial bins, which are regions of predefined sizes. Each bin is assumed to have a single secondary user base station and all the resources of that bin (i.e., available frequencies, transmit power, etc.) are consumed by this secondary user in that bin. With these assumptions, the service area of the database can be represented by a grid of secondary users. Such a grid of secondary users forms a array of transmit antennas with secondary users in each bin. Furthermore, the set of bins with its secondary users at the edge of the exclusion zone of the primary user are assumed to create an array of receive antennas. These receive antennas act as sensors that will measure the interference power at the edge of the exclusion zone of the primary users. So the overall system of secondary user base station transmit and receive antennas can be modeled as a multi-element antenna array system. A regulatory interference threshold (I_th) is defined for protection of the primary user at the edge of exclusion zones. This interference threshold is used by the resource allocation algorithms in the spectrum access system to calculate the transmit and receive precoding matrices for the secondary user antenna array. Using multiple-input multiple-output theory, the receive antenna array will measure the interference from the transmit antenna array and a feedback mechanism will update the resource allocation to keep the power at the receive array below the interference threshold of the primary user. For each array, the transmit/receive matrix is a beamforming vector which consists of a set of weights, one for each antenna. Furthermore, a codebook-based strategy is used by the spectrum access system database to choose a transmit matrix from the codebook which minimizes the interference at the primary user. The overall spectrum sharing system can be represented by a model based on four design parameters, namely, Δ = (I_th, P, V, B), where P is the transmit power constraint, V are the transmit and receive beamforming matrices, and B is the matrix with active secondary user base stations of the antenna array or the quality of service level of the secondary users. The Δ parameter is called the system index of the spectrum sharing system. We apply the multi-antenna model to the challenging problem of spectrum sharing where the primary users operational parameters, such as transmit power levels, waveform types, and service modes, can change with time. Moreover, there are several types of primary users in different bands. Most of these users are federal government systems and their operational parameters are not available to the spectrum access system database. Our framework is useful in sharing spectrum with federal primary users, since only the interference threshold is needed for sharing their bands. Furthermore, we quantify the uncertainty in the availability of these bands for secondary users and the variations in achievable capacity with sharing spectrum in these bands. / Ph. D. / The goal of this thesis is to build a Protected Shared Access Model (PSAM) through database enabled Spectrum Access System (SAS). A model for the SAS is proposed, which is based on our vision for the SAS as a more dynamic and responsive architecture as a geolocation database than the current TVWS database. Major functions and capabilities of the model include, calculations of exclusion zone (EZ) of primary users with different operational parameters, use interference estimation techniques for predicting interference levels that will be generated by the new secondary users (SUs) and existing systems operating in the database service area, allocate location based transmit power levels and provide an algorithm for communications among the PUs, SUs, and the SAS to implement management and authorization framework of spectrum resources to different types of SUs. The selection of a propagation model is of utmost importance in spectrum sharing studies. Existing literature on EZs with simplified propagation models does not consider the effect of LOS interference between the PU to SU link and SU to PU link on peak points in the terrain area around the PU. The use of a terrain profile based model captures the essence of propagation over irregular terrain. Terrain regions that are far away from the PU may have a LOS between the PU and SU. So its not only the nearest area where the PU/SU can get interference, but interference is present from areas further away on high grounds having a direct LOS with the PU antenna. The exclusion zone computation with terrain profile based propagation model captures this effect, and it is the same effect that makes the shape of the exclusion zone irregular. So the propagation model used in spectrum sharing studies must be able to use the terrain for the specific geographical area for precise propagation calculations, and provide statistical reliability parameters for the computed propagation values for area of interest. For a multi-tier shared access model with incumbent access (IA) users, priority access (PA) users and general authorized access (GAA) users. The SU interference tolerance thresholds varies by the type of SU's i-e., PA users like public safety systems and mission critical users have low tolerance for interference and hence need to operate further from the PU. While GAA users like commercial broadband systems have higher interference tolerances and can operate closer to the PU. This multi-tier shared access model requires varying levels of interference protection from PU, that can be provided with multiple exclusion zones defined for different types of SU's. We propose the concept of differential spectrum access hierarchy, and define it in the context of a multi-tiered EZs that are based on quantiles of tolerable interference levels for different tiers of SUs. We also quantify and show the gain in SU capacity (or throughput) obtained by using multi-tiered EZs for different tiers of SUs. Using simulation results, we show that the size of EZs can be significantly reduced with the use of a terrain profile-based propagation model that takes into account terrain profile for signal attenuation between PUs and SUs in the P2P link. The exclusion zones involve the use of interference test points at the circumference of the protection contour of the PU. They are monitoring test points that the SAS uses with a propagation model and locations of SUs to calculate interference. Consider a model of Figure 5.1, the coexistence environment with PU, SU and the SAS with a database. As more SUs enter the system, their transmit powers creates interference for the PUs. In the event of SU interference exceeding a predefined threshold level at any of the test points, the SAS uses an interference based power control algorithm to turnoff the nearest dominant interferer's. Turning off the dominant interferers eliminates interference generated by that node at the PU. This nearest node interference cancellation significantly reduces the outage probability at the PU. Unlike existing metrics for spectrum utilization efficiency that considers separate metrics for PU interference protection and maximum use of the band for secondary use, we define a new metric for spectrum utilization efficiency. This metric uses utility functions and cost functions to measure the impact of secondary use of the spectrum on PUs as well as the degree of satisfaction SUs can achieve from reuse of such spectrum. The new spectrum utilization metric is used to evaluate tradeoffs between interference protection of PUs and SU spectrum utilization.

Unmanned Aerial Vehicles (UAV) are expected to be deployed both by government and industry. Rules for integrating commercial UAVs into a nation's airspace still need to be defined, safety being the main concern. As part of this thesis, the communication needs of UAVs as important requirement for UAV integration into the national airspace is considered. Motivated by recent prediction of UAV quantities, revealing the importance of Micro UAVs (MAV) and Small UAVs (SUAV), the thesis determines spectral requirements for control and non-payload communication (CNPC). We show that spectral efficiency, particularly in the downlink, is critical to the large-scale deployment of UAVs. Due to the limited range of small SUAV and MAV systems, communication between air and ground elements of these UAVs is established through radio Line-of-Sight (LoS) links. Ultimately, efficient LoS UAV systems are based on a better understanding of channels in the downlink, i.e. air-to-ground (A2G) channels, and also on efficient waveform as well as spectrum management implementation. Because of limited research in wideband aeronautical channel modeling, we have derived an A2G channel prototype applicable to SUAV and MAV. As part of the research at Wire- less@VT in designing and prototyping Orthogonal Frequency Division Multiplexing (OFDM) waveforms, this thesis derives the optimal parameters for SUAV and MAV A2G channels. Finally, the thesis discusses concepts that relate flight route with spectrum management as well as opportunities for a more dynamic spectrum allocation for UAV communication systems. / Master of Science

International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California / Reduction in available radio frequency (RF) spectrum for use in aircraft testing has steadily increased the probability of interference. The increase in users and required bandwidth generates requirements for increased monitoring and active management of the RF spectrum. The detection of background RF emissions and monitoring of authorized users will be used by future range test engineers to make decisions on when and where to conduct test missions to minimize the probability of interference. The detection of authorized users exceeding their allotted RF spectrum as well as unknown emitters should include: the general geographic area of potential interference, and times of transmission. This paper outlines the development of a complete system for wide-band RF monitoring to identify and locate active emissions. The RF surveillance system proposed must be inexpensive, easy to maintain, support large area coverage, and monitor wide bandwidths at long range. The system should contain software for emitter identification, which will determine where the current background and authorized RF transmissions occur and how they might effect authorized transmissions, and specialized software to alert spectrum managers of potential interference scenarios in real time based upon the daily schedule.

Spectrum access protocols have been proposed recently to provide flexible and efficient use of the available bandwidth. Game theory has been applied to the analysis of the problem to determine the most effective allocation of the users’ power over the bandwidth. However, prior analysis has focussed on Shannon capacity as the utility function, even though it is known that real signals do not, in general, meet the Gaussian distribution assumptions of that metric. In a non-cooperative spectrum sharing environment, the Shannon capacity utility function results in a water-filling solution. In this thesis, the suitability of the water-filling solution is evaluated when using non-Gaussian signalling first in a frequency non-selective environment to focus on the resource allocation problem and its outcomes. It is then extended to a frequency selective environment to examine the proposed algorithm in a more realistic wireless environment. It is shown in both scenarios that more effective resource allocation can be achieved when the utility function takes into account the actual signal characteristics. Further, it is demonstrated that higher rates can be achieved with lower transmitted power, resulting in a smaller spectral footprint, which allows more efficient use of the spectrum overall. Finally, future spectrum management is discussed where the waveform adaptation is examined as an additional option to the well-known spectrum agility, rate and transmit power adaptation when performing spectrum sharing.