Software radio is a technique for implementing reconfigurable radio systems using a combination of various circuit elements and digital hardware. By implementing radio functions in software, a flexible radio can be created that is capable of performing a variety of functions at different times. Numerous digital hardware devices are available to perform the required signal processing, each with its own strengths and weaknesses in terms of performance, power consumption, and programmability. The system developer must make trade-offs in these three design areas when determining the best digital hardware solution for a software radio implementation. When selecting digital hardware architectures, it is important to recognize the requirements of the system and identify which architectures will provide sufficient performance within the design constraints. While some architectures may provide abundant computational performance and flexibility, the associated power consumption may largely exceed the limits available for a given system. Conversely, other processing architectures may demand minimal power consumption and offer sufficient computation performance yet provide little in terms of the flexibility needed for software radio systems. Several digital hardware solutions are presented as well as their design trade-offs and associated implementation issues. / Master of Science

The rapid rise in computational performance offered by computer systems has greatly increased the number of practical software defined radio applications. The addition of FPGAs to these flexible systems has resulted in platforms that can address a multitude of applications with performance levels that were once only known to ASICs. This work presents an embedded heterogeneous scalable cluster platform with software defined radio applications. The Xilinx Zynq chip provides a hybrid platform consisting of an embedded ARM general-purpose processing core and a low-power FPGA. The ARM core provides all of the benefits and ease of use common to modern high-level software languages while the FPGA segment offers high performance for computationally intensive components of the application. Four of these chips were combined in a scalable cluster and a task assigner was written to automatically place data flows across the FPGAs and ARM cores. The rapid reconfiguration software tFlow was used to dynamically build arbitrary FPGA images out of a library of pre-built modules. / Master of Science

Software defined radio (SDR) is a rapidly developing field enabled by continuing improvements in digital electronics. Software defined radio has been used extensively in communication systems due to its flexibility and cost effectiveness. Recently, SDR has been incorporated into radar systems, particularly for ionospheric research. This study investigated the benefits and design of a high frequency (HF) SDR receiver for the next generation of Super Dual Auroral Network (SuperDARN) radars. This work analyzed digital beamforming and waveform design approaches that would be enabled by the adoption of a SDR based radar design and found that these techniques could improve the performance of SuperDARN radars. This work also developed a prototype receiver to demonstrate the feasibility of a SDR based SuperDARN radar. The hardware selection for this receiver leveraged low-cost commercial off-the-shelf software defined radios and amplifier designs supplemented by custom filters. The software implementation utilized GNU Radio, an open source SDR and signal processing platform, to process and record receiver data. A prototype was successfully designed and constructed using the Red Pitaya software defined radio. This prototype included a 4 channel receiver which was evaluated in the laboratory setting and tested at the Blackstone, Virginia radar site. A comparison of results from the prototype receiver and the existing hardware showed promise for the use of this platform in future ionospheric research. / M.S. / Software defined radio (SDR) is a rapidly developing field which uses software to perform radio signal processing traditionally accomplished by hardware components. Software defined radio has been used extensively in communication systems due to its flexibility and cost effectiveness. Recently, SDR has been incorporated into radar systems, particularly for space science research. This study investigated the benefits and design of a SDR receiver for the next generation of Super Dual Auroral Network (SuperDARN) radars. This work analyzed radar design approaches that would be enabled by the adoption of a SDR framework and found techniques that could improve the performance of SuperDARN radars. This work also developed a prototype receiver using low-cost commercial off-the-shelf software defined radios to demonstrate the feasibility of a SDR based SuperDARN radar. A prototype was successfully designed and constructed using the Red Pitaya software defined radio. This prototype was evaluated in the laboratory setting and tested at the Blackstone, Virginia radar site. A comparison of results from the prototype receiver and the existing hardware showed promise for the use of this platform in future space science research.

Wireless communications technology ranging from satellite communications to sensor networks has benefited from the development of flexible, SDR platforms. SDR is used for military applications in radio devices to reconfigure waveforms, frequency, and modulation schemes in both software and hardware to improve communication performance in harsh environments. In the commercial sector, SDRs are present in cellular infrastructure, where base stations can reconfigure operating parameters to meet specific cellular coverage goals. In response to these enhancements, industry leaders in cellular (such as Lucent, Nortel, and Motorola) have embraced the cost advantages of implementing SDRs in their cellular technology. In the future, there will be a need for more capable SDR platforms on inexpensive hardware that are able to balance work loads between several computational processing elements while minimizing power cost to accomplish multiple goals. This thesis will present the development of a random access MAC protocol for the IRIS platform. An assessment of different SDR hardware and software platforms is conducted. From this assessment, we present several SDR technology requirements for networking research and discuss the impact of these requirements on future SDR platforms. As a consequence of these requirements, we choose the USRP family of SDR hardware and the IRIS software platform to develop our two random access MAC implementations: Aloha with Explicit ACK and Aloha with Implicit ACK. A point-to-point link was tested with our protocol and then this link was extended to a 3-hop (4 nodes) network. To improve our protocols' efficiency, we implemented carrier sensing on the FPGA of the USRP E100, an embedded SDR hardware platform. We also present simulations using OMNeT++ software to accompany our experimental data, and moreover, show how our protocol scales as more nodes are added to the network. / Master of Science

Modern wireless communications systems are constantly evolving and growing more complex. Recently, there has been a shift towards software defined radios due to the flexibility soft- ware implementations provide. This enables an easier development process, longer product lifetimes, and better adaptability for congested environments than conventional hardware systems. However, this shift introduces new attack surfaces where vulnerable implementa- tions can be exploited to disrupt communications or gain unauthorized access to a system. Previous research concerning wireless security mainly focuses on vulnerabilities within pro- tocols rather than in the radios themselves. This dissertation specifically addresses this new threat against software radios and introduces a new security model intended to mitigate this threat. We also demonstrate example exploits of waveforms which can result in either a denial-of-service or a compromise of the system from a wireless attack vector. These example exploits target vulnerabilities such as overflows, unsanitized control inputs, and unexpected state changes. We present a defense-in-depth security architecture for software radios that protects the system by isolating components within a waveform into different security zones. Exploits against vulnerabilities within blocks are contained by isolation zones which protects the rest of the system from compromise. This architecture is inspired by the concept of a microkernel and provides a minimal trusted computing base for developing secure radio systems. Unlike other previous security models, our model protects from exploits within the radio protocol stack itself and not just the higher layer application. Different isolation mechanisms such as containers or virtual machines can be used depending on the security risk imposed by a component and any security requirements. However, adding these isolation environments incurs a performance overhead for applications. We perform an analysis of multiple example waveforms to characterize the impact of isolation environments on the overall performance of an application and demonstrate the overhead generated from the added isolation can be minimal. Because of this, our defense-in-depth architecture should be applied to real-world, production systems. We finally present an example integration of the model within the GNU Radio framework that can be used to develop any waveform using the defense-in-depth se- curity architecture. / Doctor of Philosophy / In recent years, wireless devices and communication systems have become a common part of everyday life. Mobile devices are constantly growing more complex and with the growth in mobile networks and the Internet of Things, an estimated 20 billion devices will be connected in the next few years. Because of this complexity, there has been a recent shift towards using software rather than hardware for the primary functionality of the system. Software enables an easier and faster development process, longer product lifetimes through over- the-air updates, and better adaptability for extremely congested environments. However, these complex software systems can be susceptible to attack through vulnerabilities in the radio interfaces that allow attackers to completely control a targeted device. Much of the existing wireless security research only focuses on vulnerabilities within different protocols rather than considering the possibility of vulnerabilities in the radios themselves. This work specifically focuses on this new threat and demonstrates example exploits of software radios. We then introduce a new security model intended to protect against these attacks. The main goal of this dissertation is to introduce a new defense-in-depth security architecture for software radios that protects the system by isolating components within a waveform into different security zones. Exploits against the system are contained within the zones and unable to compromise the overall system. Unlike other security models, our model protects from exploits within the radio protocol stack itself and not just the higher layer application. Different isolation mechanisms such as containers or virtual machines can be used depending on the security risk imposed by a component and any security requirements for the system. However, adding these isolation environments incurs a performance overhead for applications. We also perform a performance analysis with several example applications and show the overhead generated from the added isolation can be minimal. Therefore, the defense-in-depth model should be the standard method for architecting wireless communication systems. We finally present a GNU Radio based framework for developing waveforms using the defense- in-depth approach.

In the last decade the world has seen a steadily increasing number of Cube Satellites deployed to Low Earth Orbit. Traditionally, these cubesats rely on Amateur Radio communications technology that are proven to work from space. However, as data volumes increase, the existing Amateur Radio protocols, combined with the restrictions of use for the Amateur Radio Spectrum, as well as the trend to build one control station per cubesat, result in a bottle neck effect whereby existing communications methods are no longer sufficient to support the increasing data volumes of the spacecraft. This Masters Thesis work explores the concept of deploying a network of distributed ground station receiver nodes for the purposes of increasing access time to the spacecraft, and thereby increasing the potential amount of data that can be transferred from orbit to the ground. The current trends in cubesat communications will be analyzed and an argument will be made in favor of transitioning to more modern digital communications approaches for on orbit missions. Finally, a candidate ground station receiver node design is presented a possible design that could be used to deploy such a network. / Master of Science

Element CXI's Elemental Computing Array (ECA) delivers faster reconfiguration time and higher computational density than Field Programmable Gate Arrays (FPGAs) with similar computational power. It provides higher computational power than Digital Signal Processors (DSPs) with similar power consumption and price. It also utilizes a library-based graphical development environment promoting ease of use and fast development. In this thesis, the design and implementation of a ZigBee receiver on an Element CXI ECA-64 platform is presented. The ZigBee receiver is evaluated through simulations and implementation on an ECA device. During the design and implementation of the ZigBee receiver, some design experience and tips are concluded. The design methodology on the ECA is studied in detail to assure the implementation's correctness, since the methodology of the ECA is different from that of other platforms. / Master of Science

Software Defined Radios are computer based systems that emulate the behavior of traditional radio systems by processing digitized radio signals. A SDR replaces the traditional fixed hardware radio with a system that may be reconfigured, both during operation to provide greater flexibility and by providing software upgrades to add new capabilities without requiring new hardware. These are powerful reasons for using SDR technology; however this flexibility comes at the cost of increased hardware cost and greater power consumption compared with traditional hardware radios. This report presents measurements of memory and processor usage for a Software Communication Architecture (SCA) waveform running on an OMAP starter kit and a desktop PC. The process used to build software, originally targeted for a desktop computer, on an embedded machine with a different processor architecture is described. OSSIE, an open source SCA implementation developed at Virginia Tech, was ported to the ARM processor by adding support for building OSSIE into the OpenEmbedded build system. Once the port for the OMAP starter kit was complete, it became possible to easily re-target OSSIE for a variety of other hardware platforms. For testing purposes a simple waveform capable of transmitting several common digital modulation formats was developed. A SCA device for the Universal Software Radio Peripheral was developed to interface the waveform to the antenna. One method to reduce the cost and power consumption is to limit the amount of memory used in the radio. This reduces both cost and power consumption. This report describes the memory manager portion of the Linux kernel and how it helps reduce the memory used by the system. The exmap tool for accurately measuring memory usage is described and used to measure the memory usage of the OSSIE based test waveform. These techniques help radio developers measure and reduce the amount of memory required for the SDR, reducing system cost and power consumption. Finally, the oprofile was used to measure relative processor usage of the waveform components. Oprofile can also provide details about specific sections of waveform code that use the most processor cycles. This information helps the radio designer reduce the number of processing cycles required. This allows the hardware to use a lower speed part, or add more capability to the radio design. / Master of Science

With interoperability issues plaguing emergency responders throughout the country, Cognitive Radio (CR) offers a unique solution to streamline communication between police, Emergency Medical Technicians (EMT), and military officers. Using Software Defined Radio (SDR) technology, a flexible radio platform can be potentially configured using a Cognitive Engine (CE) to transmit and receive many different incompatible radio standards. In this thesis, an interface between a Cognitive Engine and an SDR platform is described which modifies (i.e., configures) the radio's operation. The interface is based upon communicating information via eXtensible Markup Language (XML) data files that contain the radio's Physical (PHY) parameters. The XML data files have been designed such that more development can be made to its structure as this research develops. The GNU Radio and the Universal Software Radio Peripheral (USRP) serve as the SDR platform for an example implementation. The example implementation involves importing XML data files into the SDR for quick configuration. Three configuration examples are used to describe this process. / Master of Science

Software radios have evolved as multimode, programmable digital radios that perform radio functions using digital signal processing algorithms. They have been designed as software programmable radios using a combination of various hardware elements and structures. In this dissertation a {em{soft radio}} refers to a completely configurable radio that can be programmed through software, to change the radio behavior including the hardware functionality. Conventional software radios achieve flexibility through software with the use of static hardware. While these radios have the flexibility to operate in multiple modes, the hardware is not used efficiently. This inefficient utilization of hardware frequently limits the flexibility of software radios and the number of modes the radio can support. Soft radios however, attempt to gain flexibility through the use of reconfigurable hardware. The same piece of hardware can be configured to perform different functions based on the mode the radio is operating in. While many soft/software radio architectures have been suggested and implemented, there remains a lack of a formal design methodology that can be used to design and implement reconfigurable soft radios. Most designs are based on ad hoc approaches which are appropriate only for the problem at hand. After examining the design issues of a soft radio an architecture, called the {em{Layered Radio Architecture}}, is developed with the use of stream based processing and run-time reconfigurable hardware. These choices aid in maximizing performance with minimum hardware while keeping the architecture robust, simple, and scalable. The reconfigurable platform enables {em hardware paging} through reusability hardware. The stream-based approach gives a uniform modular structure to the processing modules and defines the protocol for interaction between various modules. The architecture describes a formal yet open design methodology and makes it possible to incorporate all of the features of a software radio while minimizing complexity issues. The layered architecture also defines the methodology for incorporating changes and updates into the system. The layered radio architecture assumes run-time reconfigurability of the hardware. This feature is not supported by existing commercial reconfigurable hardware, like FPGAs. An Custom Computing Machine (CCM), called Stallion that supports fast run time reconfiguration, has been developed at Virginia Tech. This dissertation describes the deficiencies of existing commercial reconfigurable hardware and shows how the Stallion is capable of supporting the layered radio architecture. The dissertation presents algorithms and procedures that can be used to implement the layered radio architecture using existing hardware. The architecture is validated with the implementation of two receivers: A single user CDMA receiver based on complex adaptive filtering and a W-CDMA downlink rake receiver with channel estimation. Performance analysis of these receivers show that it is important to keep the paging ratio high while maximizing utilization of the processing elements. The layered radio architecture with the use of Stallion can support existing high data rate systems. / Ph. D.