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A Gold code sequence generator suitable for use in a code division multiple access spread spectrum communication application is designed. A dual, single return shift register configuration is used to generate Gold code sequences. The code sequences are generated by the mod-2 addition of two linear maximal length pseudo-random noise codes, each of which corresponds to a sixth-order primitive polynomial. A computer model of the design is used to generate all 65 possible members of the Gold code sequence family. A tabulation of all sequences and their initial condition “keys” is provided, along with a designation as to which code sequences are balanced. The mathematical basis of maximal length sequence generation is developed, using first the matrix characterization of a shift register generator, and then switching to the alternate treatment of a shift register generator as a polynomial division engine. The link between the matrix representation and the polynomial representation via the characteristic equation, the use of the generating function, and the three mathematical properties required of polynomials which are capable of generating maximal length sequences are described. Gold’s algorithm for selecting preferred polynomial pairs is presented, as is his technique for determining the characteristic phase of a maximal length sequence. The actual Gold code generator is then designed and modeled in software. All Gold code sequences output from the generator are tabulated. The family of sequences is evaluated in terms of its randomness properties. Finally, the results of computer analysis of the auto and cross-correlation characteristics of the family is summarized.

The radio spectrum dependent applications are facing a huge scarcity of the resource. To address this issue, future wireless systems require new wireless network architectures and new approaches to spectrum management. Spectrum sharing has emerged as a promising solution to address the radio frequency (RF) spectrum bottleneck. Although spectrum sharing is intended to provide flexible use of the spectrum, the architecture of the existing approaches, such as TV White Space [1] and Citizen Broadband Radio Services (CBRS) [2], have a relatively fixed sharing framework. This fixed structure limits the applicability of the architecture to other bands where the relationship between various new users and different types of legacy users co-exist. Specifically, an important aspect of sharing that has not been explored enough is the cooperation between the resource owner and the opportunistic user. Also in a shared spectrum system, the users do not have any information about the availability and duration of the available spectrum opportunities. This lack of understanding about the shared spectrum leads the research community to explore a number of core spectrum sharing tasks, such as opportunity detection, dynamic opportunity scheduling, and interference protection for the primary users, etc. This report proposes a Primary-Secondary Cooperation Framework to provide flexibility to all the involved parties in terms of choosing the level of cooperation that allow them to satisfy different objective priorities. The cooperation framework allows exchange of a probabilistic assurance: Spectrum Opportunity Duration Assurance (SODA) between the primary and secondary operations to improve the overall spectrum sharing experience for both the parties. This capability will give the spectrum sharing architectures new flexibility to handle evolutions in technologies, regulations, and the requirements of new bands being transitioned from fixed to share usage. In this dissertation we first look into the regulatory aspect of spectrum sharing. We analyze the Federal Communications Commission's (FCC) initiatives with regards to the commercial use of the 150 MHz spectrum block in the 3.5 GHz band. This analysis results into a Spectrum Access System (SAS) architecture and list of required functionalities. Then we address the nature of primary-secondary cooperation in spectrum sharing and propose to generate probabilistic assurances for spectrum opportunities. We use the generated assurance to observe the impact of cooperation from the perspective of spectrum sharing system management. We propose to incorporate primary user cooperation in the auctioning and resource allocation procedures to manage spectrum opportunities. We also analyze the improvement in spectrum sharing experience from the perspective of the primary and secondary users as a result of cooperation. We propose interference avoidance schemes that involve cooperation to improve the achievable quality of service. Primary-secondary cooperation has the potential to significantly influence the mechanism and outcomes of the spectrum sharing systems. Both the primary and secondary operations can benefit from cooperation in a sharing scenario. Based on the priorities of the primary and secondary operations, the users may decide on the level of cooperation that they are willing to participate. Also access to information about the availability and usability of the spectrum opportunity will result in efficient spectrum opportunity management and improved sharing performance for both the primary and secondary users. Thus offering assurances about the availability and duration of spectrum opportunity through primary-secondary cooperation will significantly improve the overall spectrum sharing experience. The research reported in this dissertation is expected to provide a fundamental analytical framework for characterizing and quantifying the implications of primary-secondary cooperation in a spectrum sharing context. It analyzes the technical challenges in modeling different level of cooperation and their impact on the spectrum sharing experience. We hope that this dissertation will establish the fundamentals of the spectrum sharing to allow the involved parties to participate in sharing mechanisms that is suitable to their objective priorities. / PHD / As the world of technology steps into the era of ubiquitous communication to anything and everything, a system's ability to wirelessly communicate in a heterogeneous environment plays a significant role in shaping our ways of life. The wireless communication systems and standards are evolving at an unprecedented rate to cope up with the explosive growth for uninterrupted mobile broadband service demand and the increasing diversity of high quality of service (QoS) use cases ranging from social communication and professional networking to cyber security and public safety. The rapid evolution of wireless communication systems and service applications has resulted in high demand for new and dedicated spectrum blocks in both the licensed and unlicensed bands. Also the predicted future wireless systems and applications indicate important characteristics of future broadband traffic demand: nomadic and sporadic bursty demand. But the existing static spectrum assignment limits the potential of the radio frequency spectrum resource. It imposes the challenge of spectrum scarcity onto radio spectrum dependent applications and technologies. This unprecedented increase in mobile data traffic along with the nomadic and sporadic bursts in data demand will disruptively shape the spectrum usage philosophy of the future wireless communication networks. It calls for new wireless network architectures and new approaches to spectrum management. Spectrum sharing has emerged as a promising solution to address the radio frequency (RF) spectrum bottleneck. Although spectrum sharing is intended to provide flexible use of the spectrum, the architecture of the existing approaches have a relatively fixed structure in the mechanism for which spectrum is shared. This fixed structure limits the applicability of the architecture to other bands where the relationship between various new users and different types of legacy users co-exist. Specifically, an important aspect of sharing that has not been explored enough is the cooperation between the resource owner and the opportunistic user. Also in a shared spectrum system, the users do not have any information about the availability and duration of the available spectrum opportunities. This lack of understanding about the shared spectrum leads the research community to explore a number of core spectrum sharing tasks, such as opportunity detection, dynamic opportunity scheduling, and interference protection for the primary users, etc. In this dissertation we propose a Primary-Secondary Cooperation Framework that provides flexibility to all the involved parties in terms of choosing the level of cooperation and allow them to satisfy different objective priorities. The cooperation framework allows exchange of a probabilistic assurance: Spectrum Opportunity Duration Assurance (SODA) between the primary and secondary operations to improve the overall spectrum sharing experience for both the parties. This capability will give the spectrum sharing architectures new flexibility to handle evolutions in technologies, regulations, and the requirements of new bands being transitioned from fixed to share usage. Based on their operational priorities, the users may decide on the level of cooperation that they are willing to participate. Also access to information about the availability and usability of the spectrum opportunity influences the mechanism and outcomes of the spectrum sharing systems to benefit both the Primary and Secondary users. Thus offering assurances about the availability and duration of spectrum opportunity through primary-secondary cooperation will significantly improve the overall spectrum sharing experience. The research reported in this dissertation is expected to provide a fundamental analytical framework for characterizing and quantifying the implications of primary-secondary cooperation in a spectrum sharing context. It analyzes the technical challenges in modeling different level of cooperation and their impact on the spectrum sharing experience. We hope that this dissertation will establish the fundamentals of the spectrum sharing to allow the involved parties to participate in sharing mechanisms that is suitable to their objective priorities.

One scheme for reliability-based design that is growing in popularity for civil and naval applications is the load and resistance factor design (LRFD). Our goal in this research is the development of a simulation to predict the remaining strength of structural composites subjected to variable fatigue loading and environmental exposure. The results of this simulation can then be used in LRFD to determine appropriate material factors of safety for engineering design applications. The work so far focuses on modeling the response of the material to fatigue damage only. A general phenomenological modeling approach is described and applied in two experimental studies using E-glass/vinyl ester composite materials. Strength distributions are modeled using Weibull statistics and residual strength is modeled using a strength-life equal rank assumption and a Monte-Carlo style simulation. The model provides good residual strength distribution fits to constant amplitude fatigue data and worked well for ordered block spectrum loading using a 735,641 cycle, 22 stress level spectrum. However, applying a randomized spectrum produced unexpected results with every specimen failing after 200,000 to 400,000 cycles while the model predicts identical residual strength when compared with the block loading case. This work points to a need for focus on developing a better understanding of load order impacts in design of composite structures based on constant amplitude fatigue tests. A future approach toward more detailed micro-mechanics fatigue damage modeling is suggested to enable better modeling of residual strength of laminates subjected to random loading fatigue. / Master of Science

ITC/USA 2015 Conference Proceedings / The Fifty-First Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2015 / Bally's Hotel & Convention Center, Las Vegas, NV / Spectrum sharing between Federal and commercial users is a technique proposed by the FCC and NTIA to open up the 3.5 GHz band for wireless broadband use and small cell technology is one of the candidates for its' realization. The traffic on small cells is temporal and their chances of interfering with other services in shared spectrum are limited. DoD has a documented requirement of 865 MHz by 2025 to support telemetry but only 445 MHz is presently available. DoD is conducting researches to realize test and evaluation spectrum efficient technology with the aim to develop, demonstrate, and evaluate technology components required to enable flight and ground test telemetry operations. This paper will provide an overview on spectrum sharing using small cell technology for LTE-Advanced and dynamic spectrum access would be briefly described. Research challenges for protocols and algorithms would be addressed for future studies.

Ultrawideband and cognitive radio are two of the most important approaches that are shaping the future of wireless communication systems. At a first glance, the aims of UWB and cognitive radio do not seem to be overlapping significantly, however, there is a strong synergy between the capabilities of UWB and the goals of cognitive radio. One of the objectives of this thesis is to shed the first light on the marriage of these two important approaches.Ultrawideband (UWB) is a promising technology for future short-range, high-data rate wireless communication networks. Along with its exciting features including achieving high data rates, low transmission power requirement, and immunity to multipath effects, UWB is unique in its coexistence capability with narrowband systems.In this thesis, the details of practical UWB implementation are provided. Regarding the coexistence of UWB with licensed narrowband systems, narrowband interference (NBI)avoidance and cancelation techniques in the literature are investigated. It is aimed to emphasize that UWB is a strong candidate for cognitive radio, and this fact is proven by providing two different approaches in which ultrawideband is combined with cognitive radio to maximize the performance of unlicensed communications.

abstract: Dynamic spectrum access (DSA) has great potential to address worldwide spectrum shortage by enhancing spectrum efficiency. It allows unlicensed secondary users to access the under-utilized spectrum when the primary users are not transmitting. On the other hand, the open wireless medium subjects DSA systems to various security and privacy issues, which might hinder the practical deployment. This dissertation consists of two parts to discuss the potential challenges and solutions. The first part consists of three chapters, with a focus on secondary-user authentication. Chapter One gives an overview of the challenges and existing solutions in spectrum-misuse detection. Chapter Two presents SpecGuard, the first crowdsourced spectrum-misuse detection framework for DSA systems. In SpecGuard, three novel schemes are proposed for embedding and detecting a spectrum permit at the physical layer. Chapter Three proposes SafeDSA, a novel PHY-based scheme utilizing temporal features for authenticating secondary users. In SafeDSA, the secondary user embeds his spectrum authorization into the cyclic prefix of each physical-layer symbol, which can be detected and authenticated by a verifier. The second part also consists of three chapters, with a focus on crowdsourced spectrum sensing (CSS) with privacy consideration. CSS allows a spectrum sensing provider (SSP) to outsource the spectrum sensing to distributed mobile users. Without strong incentives and location-privacy protection in place, however, mobile users are reluctant to act as crowdsourcing workers for spectrum-sensing tasks. Chapter Four gives an overview of the challenges and existing solutions. Chapter Five presents PriCSS, where the SSP selects participants based on the exponential mechanism such that the participants' sensing cost, associated with their locations, are privacy-preserved. Chapter Six further proposes DPSense, a framework that allows the honest-but-curious SSP to select mobile users for executing spatiotemporal spectrum-sensing tasks without violating the location privacy of mobile users. By collecting perturbed location traces with differential privacy guarantee from participants, the SSP assigns spectrum-sensing tasks to participants with the consideration of both spatial and temporal factors. Through theoretical analysis and simulations, the efficacy and effectiveness of the proposed schemes are validated. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2017

With the rapid proliferation of new wireless communication devices and services, the demand for the radio spectrum is increasing at a rapid rate, which leads to making the spectrum more and more crowded. The limited available spectrum and the inefficiency in the spectrum usage have led to the emergence of cognitive radio (CR) and dynamic spectrum access (DSA) technologies, which enable future wireless communication systems to exploit the empty spectrum in an opportunistic manner. To do so, future wireless devices should be aware of their surrounding radio environment in order to adapt their operating parameters according to the real-time conditions of the radio environment. From this viewpoint, spectrum sensing is becoming increasingly important to new and future wireless communication systems, which is designed to monitor the usage of the radio spectrum and reliably identify the unused bands to enable wireless devices to switch from one vacant band to another, thereby achieving flexible, reliable, and efficient spectrum utilisation. This thesis focuses on issues related to local and cooperative spectrum sensing for CR networks, which need to be resolved. These include the problems of noise uncertainty and detection in low signal to noise ratio (SNR) environments in individual spectrum sensing. In addition to issues of energy consumption, sensing delay and reporting error in cooperative spectrum sensing. In this thesis, we investigate how to improve spectrum sensing algorithms to increase their detection performance and achieving energy efficiency. To this end, first, we propose a new spectrum sensing algorithm based on energy detection that increases the reliability of individual spectrum sensing. In spite of the fact that the energy detection is still the most common detection mechanism for spectrum sensing due to its simplicity. Energy detection does not require any prior knowledge of primary signals, but has the drawbacks of threshold selection, and poor performance due to noise uncertainty especially at low SNR. Therefore, a new adaptive optimal energy detection algorithm (AOED) is presented in this thesis. In comparison with the existing energy detection schemes the detection performance achieved through AOED algorithm is higher. Secondly, as cooperative spectrum sensing (CSS) can give further improvement in the detection reliability, the AOED algorithm is extended to cooperative sensing; in which multiple cognitive users collaborate to detect the primary transmission. The new combined approach (AOED and CSS) is shown to be more reliable detection than the individual detection scheme, where the hidden terminal problem can be mitigated. Furthermore, an optimal fusion strategy for hard-fusion based cognitive radio networks is presented, which optimises sensing performance. Thirdly, the need for denser deployment of base stations to satisfy the estimated high traffic demand in future wireless networks leads to a significant increase in energy consumption. Moreover, in large-scale cognitive radio networks some of cooperative devices may be located far away from the fusion centre, which causes an increase in the error rate of reporting channel, and thus deteriorating the performance of cooperative spectrum sensing. To overcome these problems, a new multi-hop cluster based cooperative spectrum sensing (MHCCSS) scheme is proposed, where only cluster heads are allowed to send their cluster results to the fusion centre via successive cluster heads, based on higher SNR of communication channel between cluster heads. Furthermore, in decentralised CSS as in cognitive radio Ad Hoc networks (CRAHNs), where there is no fusion centre, each cognitive user performs the local spectrum sensing and shares the sensing information with its neighbours and then makes its decision on the spectrum availability based on its own sensing information and the neighbours’ information. However, cooperation between cognitive users consumes significant energy due to heavy communications. In addition to this, each CR user has asynchronous sensing and transmission schedules which add new challenges in implementing CSS in CRAHNs. In this thesis, a new multi-hop cluster based CSS scheme has been proposed for CRAHNs, which can enhance the cooperative sensing performance and reduce the energy consumption compared with other conventional decentralised cooperative spectrum sensing modes.

Radiofrequency spectrum is a finite resource that consists of the frequencies in the range 3 kHz to 300 GHz. It is used for wireless communication and supports several applications and services. Whether it is at the personal, community or society level, and whether it is for applications in consumer electronics, building management, smart utility networks, intelligent driving systems, the Internet of Things, industrial automation and so on, the demand for wireless communication is increasing continuously. Together with this increase in demand, there is an increase in the quality of service requirements in terms of throughput, and the reliability and availability of wireless services. Industrial wireless sensor networks, for example, operate in environments that are usually harsh and time varying. The frequency spectrum that is utilised by industrial wireless protocols such as WirelessHART and ISA 100.11a, is also used by many other wireless technologies, and with wireless applications growing rapidly, it is possible that multiple heterogeneous wireless systems will need to operate in overlapping spatiotemporal regions in the future. Increased radiofrequency interference affects connectivity and reduces communication link quality. This affects reliability and latency negatively, both of which are core quality service requirements. Getting multiple heterogeneous radio systems to co-exist harmoniously in shared spectrum is challenging. Traditionally, this has been achieved by granting network operators exclusive rights that allow them to access parts of the spectrum assigned to them and hence the problems of co-existence and limited spectrum could be ignored. Design time multi-access techniques have also been used. At present, however, it has become necessary to use spectrum more efficiently, to facilitate the further growth of wireless communication. This can be achieved in a number of ways. Firstly, the policy that governs the regulation of radiofrequency spectrum must be updated to accommodate flexible, dynamic spectrum access. Secondly, new techniques for multiple-access and spectrum sharing should be devised. A revolutionary new communication paradigm is required, and one such paradigm has recently emerged in the form of Cognitive Radio technology. Traditional methods to sharing spectrum assume that radios in a wireless network work together in an unchanging environment. Cognitive radios, on the other hand, can sense, learn and adapt. In cognitive radio networks, the interactions between users are taken into account, in order for adjustments to be made to suit the prevailing radio environment. In this thesis, the problem of spectrum scarcity and coexistence is addressed using cognitive radio techniques, to ensure more efficient use of radio-frequency spectrum. An introduction to cognitive radio networks is given, covering cognitive radio fundamentals, spectrum sensing, dynamic spectrum management, game theoretic approaches to spectrum sharing and security in cognitive radio networks. A focus is placed on wireless industrial networks as a challenging test case for cognitive radio. A study on spectrum management policy is conducted, together with an investigation into the current state of radio-frequency spectrum utilisation, to uncover real and artificial cases of spectrum scarcity. A novel cognitive radio protocol is developed together with an open source test bed for it. Finally, a game theoretic dynamic spectrum access algorithm is developed that can provide scalable, fast convergence spectrum sharing in cognitive radio networks. This work is a humble contribution to the advancement of wireless communication. / Thesis (PhD)--University of Pretoria, 2016. / Centre for Telecommunication Engineering for the Information Society / Electrical, Electronic and Computer Engineering / PhD / Unrestricted