VTechWorks staff will be away for the winter holidays starting Tuesday, December 24, 2024, through Wednesday, January 1, 2025, and will not be replying to requests during this time. Thank you for your patience, and happy holidays!

Browsing by Author "Sweeney, Dennis G."

Now showing 1 - 20 of 70
  • Thumbnail Image
    2GHz W-CDMA Radio Transceiver
    Cheung, Tze Chiu (Virginia Tech, 1998-12-15)
    A radio transceiver has been designed and built for a W-CDMA experimental system operating at 2GHz. The radio is an RF front-end for mobile terminals. The radio provides the functions of modulation and demodulation to enable transmitting and receiving digital information through the air link. The radio comprises one transmitter in conjunction with transmit power control (TPC), two independent receivers in conjunction with automatic gain control (AGC) and automatic frequency control (AFC), and one common synthesizer. Data exchange between the radio and the baseband processor takes place in an 8-bit digital format. Digital-to-analog converters (DAC) at the transmitter and analog- to-digital converters (ADC) at the receivers provide the interface between the radio and the baseband processor. DACs are also used to convert the 7-bit command codes from the processor to analog signals for the TPC, AGC and AFC. The radio transceiver is designed to meet the stringent requirements imposed by the W-CDMA system. The 70dB TPC enables the adaptive power control for combating the near-far problem. The high linearity of the transmitter provides the use of linear modulation with less than 40dBc adjacent channel power suppression. The 0.03125ppm tuning resolution of the AFC maximizes the receiver sensitivity. The 80dB AGC produces a constant demodulated signal level to the ADC regardless of the RF signal level. This thesis documents the design methodology for this radio transceiver.
  • Thumbnail Image
    A 60 Ghz Mmic 4x Subharmonic Mixer
    Chapman, Michael Wayne (Virginia Tech, 2000-10-31)
    In this modern age of information, the demands on data transmission networks for greater capacity, and mobile accessibility are increasing drastically. The increasing demand for mobile access is evidenced by the proliferation of wireless systems such as mobile phone networks and wireless local area networks (WLANs). The frequency range over which an oxygen resonance occurs in the atmosphere (~58-62 GHz) has received recent attention as a possible candidate for secure high-speed wireless data networks with a potentially high degree of frequency reuse. A significant challenge in implementing data networks at 60 GHz is the manufacture of low-cost RF transceivers capable of satisfying the system requirements. In order to produce transceivers that meet the additional demands of high-volume, mobility, and compactness, monolithic millimeter wave integrated circuits (MMICs) offer the most practical solution. In the design of radio tranceivers with a high degree of integration, the receiver front-end is typically the most critical component to overall system performance. High-performance low-noise amplifiers (LNAs) are now realizable at frequencies in excess of 100 GHz, and a wide variety of mixer topologies are available that are capable of downconversion from 60 GHz. However, local oscillators (LOs) capable of providing adequate output power at mm-wave frequencies remain bulky and expensive. There are several techniques that allow the use of a lower frequency microwave LO to achieve the same RF downconversion. One of these is to employ a subharmonic mixer. In this case, a lower frequency LO is applied and the RF mixes with a harmonic multiple of the LO signal to produce the desired intermediate frequency (IF). The work presented in this thesis will focus on the development of a GaAs MMIC 4-X subharmonic mixer in Finite Ground Coplanar (FGC) technology for operation at 60 GHz. The mixer topology is based on an antiparallel Schottky diode pair. A discussion of the mechanisms behind the operation of this circuit and the methods of practical implementation is presented. The FGC transmission lines and passive tuning structures used in mixer implementation are characterized with full-wave electromagnetic simulation software and 2-port vector network analyzer measurements. A characterization of mixer performance is obtained through simulations and measurement. The viability of this circuit as an alternative to other high-frequency downconversion schemes is discussed. The performance of the actual fabricated MMIC is presented and compared to currently available 60 GHz mixers. One particular MMIC design exhibits an 11.3 dB conversion loss at an RF of 58.5 GHz, an LO frequency of 14.0 GHz, and an IF of 2.5 GHz. This represents excellent performance for a 4X Schottky diode mixer at these frequencies. Finally, recommendations toward future research directions in this area are made.
  • Thumbnail Image
    Adaptive Arrays and Diversity Antenna Configurations for Handheld Wireless Communication Terminals
    Dietrich, Carl B. (Virginia Tech, 2000-02-15)
    This dissertation reports results of an investigation into the performance of adaptive beamforming and diversity combining using antenna arrays that can be mounted on handheld radios. Handheld arrays show great promise for improving the coverage, capacity, and power efficiency of wireless communication systems. Diversity experiments using a handheld antenna array testbed (HAAT) are reported here. These experiments indicate that signals received by the antennas in two-element handheld antenna arrays with spacing of 0.15 wavelength or greater can be combined to provide 7-9 dB diversity gain against fading at the 99% reliability level in non line-of-sight multipath channels. Thus, peer-to-peer systems of handheld transceivers that use antenna arrays can achieve reliability comparable to systems of single-antenna handheld units, with only one-fifth the transmitter power, resulting in lower overall power consumption and increased battery life. Similar gains were observed for spatial, polarization, and pattern diversity. Adaptive beamforming with single- and multi-polarized four-element arrays of closely spaced elements was investigated by experiment using the HAAT, and by computer simulation using a polarization-sensitive vector multipath propagation simulator developed for this purpose. Small and handheld adaptive arrays were shown to provide 25 to 40 dB or more of interference rejection in the presence of a single interferer in rural, suburban, and urban channels including line-of-sight and non line-of-sight cases. In multipath channels, these performance levels were achieved even when there was no separation between the transmitters in azimuth angle as seen from the receiver, and no difference in the orientations of the two transmitting antennas. This interference rejection capability potentially allows two separate spatial channels to coexist in the same time/frequency channel, doubling system capacity.
  • Thumbnail Image
    Adaptive Digital Predistortion with Applications for LMDS Systems
    Johnson, Daniel Eric (Virginia Tech, 2000-08-25)
    A limiting factor in the widespread deployment of LMDS systems is the limited distance of current systems. Rain attenuation and limited transmitter power are the primary causes of the limited distance. Adaptive digital predistortion is presented as a method of increasing effective transmitter power. A background on LMDS link design, non-linear amplification, and predistortion is presented to assist the reader. A developed simulation uses AM-AM and AM-PM characteristics obtained from laboratory measurements of a 28 GHz amplifier to determine the effect of several predistortion implementation options and to confirm the feasibility of the proposed architecture. The potential impact of this predistortion architecture on LMDS system design is considered. The presented multi-stage predistortion architecture is found to be capable of implementation at Msymbol/second rates utilizing a FPGA or custom IC and a moderate speed digital signal processor.
  • Thumbnail Image
    Adaptive power control as a fade countermeasure on satellite links
    Sweeney, Dennis G. (Virginia Tech, 1993)
    Satellite systems in the 20/30 GHz band are very susceptible to outages due to rain-induced fades. In order to reduce the impact of these fades, it has been proposed that the power of the uplink station transmitter be adjusted during the fade to compensate. This dissertation will explore some of the issues involved in implementing this uplink power control (ULPC). Fade slope is examined as a parameter to predict signal strength during a fade. A fade slope model based on fade physics is presented, but it strongly suggests that fade slope is not an appropriate parameter for ULPC. Real time scaling of attenuation from the downlink to the uplink shows more promise for ULPC. Differences in drop size distributions during a rain storm will result is different scaling factors. If the downlink attenuation is limited to 6 dB at 20 GHz, real time scaling can be accomplished. A scaling type ULPC algorithm driven by downlink attenuation is tested on 66 hours of OLYMPUS 20/30 GHz fade data. A similar algorithm driven by uplink attenuation is tested and the performance of the two algorithms is presented and compared.
  • Thumbnail Image
    Air Surveillance for Smart Landing Facilities in the Small Aircraft Transportation System
    Shea, Eric Joseph (Virginia Tech, 2002-04-18)
    The Small Aircraft Transportation System (SATS) is a partnership among various organizations including NASA, the FAA, US aviation industry, state and local aviation officials, and universities. The program objectives are intend to reduce travel times by providing high-speed, safe travel alternatives by making use of small aircraft and underused small airports throughout the nation. A major component of the SATS program is the Smart Landing Facility (SLF). The SLF is a small airport that has been upgraded to handle SATS traffic. One of the services needed at SLFs is air surveillance of the airspace surrounding it. This thesis researches the different surveillance techniques available for use at the SLFs. The main focuses of this paper are an evaluation of the Traffic Alert and Collision Avoidance System (TCAS) when used as a ground sensor at SLFs and the design of a Position and Identification Reporting Beacon (PIRB). The use of the TCAS ground sensor is modeled in Matlab and the results of that model are discussed. The PIRB is a new system that can be used in conjunction with the Automatic Dependent Surveillance-Broadcast (ADS-B) system or independently to provide position information for all aircraft using GPS based positioning.
  • Thumbnail Image
    Analysis of Atmospheric Effects Due to Atmospheric Oxygen on a Wideband Digital Signal in the 60 Ghz Band
    Valdez, Adelia Christina (Virginia Tech, 2001-07-09)
    As lower microwave frequency bands become saturated with users, there is a motivation for the research of applications that utilize higher frequencies, especially the 60 GHz band. This band is plagued with high atmospheric absorption due to atmospheric oxygen, but has a lot of bandwidth, which makes it desirable for multi-media applications. Recently, research of wideband digital links within the 60 GHz band gained the interest of the wireless communication industry when the FCC announced that a license is not required for a wideband digital signal in this band. Previous research on 60 GHz signals focused on how much attenuation due to atmospheric oxygen exists in the link. But a look at the physical properties of atmospheric oxygen reveals both the reason why atmospheric oxygen absorbs electromagnetic waves and how pressure affects atmospheric oxygen. Atmospheric oxygen resonates at 60 GHz due to transitions between its three closely spaced rotational states. These transitions, combined with the magnetic dipole moment of atmospheric oxygen, cause attenuation and phase dispersion in electromagnetic waves. At lower pressures, the individual resonance lines of atmospheric oxygen appear in the attenuation and the phase dispersion plots. As pressure increases, the resonance lines broaden and contribute to neighboring resonant lines. The effect of attenuation and phase dispersion in a wideband signal becomes greater at lower atmospheric pressures, which results in signal distortion. The signal distortion leads to more bit errors and results in the presence of inter-symbol interference (ISI) in the received signal. This thesis aims to analyze the effects of atmospheric oxygen on a wideband digital link, especially at lower pressures and higher data rates. In order to simulate the effects of atmospheric oxygen in the atmosphere, an empirical atmospheric model was used, which characterizes the behavior of oxygen under various atmospheric pressures. A wideband communication system was simulated with the absorption and dispersion due to atmospheric oxygen represented as a transfer function and placed in the link part of the system. Eye diagrams were used to view the impact of the atmospheric oxygen attenuation and phase dispersion in the signal. Also bit error rate plots were computed in order to determine the extra margin needed.
  • Thumbnail Image
    Analysis of the Effect of the August 2017 Eclipse on the Ionosphere Using a Ray-trace Algorithm
    Moses, Magdalina Louise (Virginia Tech, 2019-08-05)
    The total solar eclipse over the continental United States on August 21, 2017 offered a unique opportunity to study the dependence of the ionospheric density and morphology on incident solar radiation. Unique responses may be witnessed during eclipses, including changes in radio frequency (RF) propagation at high frequency (HF). Such changes in RF propagation were observed by the Super Dual Auroral Radar Network (SuperDARN) radars in Christmas Valley, Oregon and in Fort Hays, Kansas during the 2017 eclipse. At each site, the westward looking radar observed an increase in slant range of the backscattered signal during the eclipse onset followed by a decrease after totality. In order to investigate the underlying processes governing the ionospheric response to the eclipse, we employ the HF propagation toolbox (PHaRLAP), created by Dr. Manuel Cervera, to simulate SuperDARN data for different models of the eclipsed ionosphere. Thus, by invoking different hypotheses and comparing simulated results to SuperDARN measurements, we can study the underlying processes governing the ionosphere and improve our model of the ionospheric responses to an eclipse. This thesis presents three studies using this method: identification of the cause of the increase in slant range observed by SuperDARN during the eclipse; evaluation of different eclipse obscuration models; and quantification of the effect of the neutral wind velocity on the simulated eclipse data.
  • Thumbnail Image
    Antifragile Communications
    Lichtman, Marc Louis (Virginia Tech, 2016-08-16)
    Jamming is an ongoing threat that plagues wireless communications in contested areas. Unfortunately, jamming complexity and sophistication will continue to increase over time. The traditional approach to addressing the jamming threat is to harden radios, such that they sacrifice communications performance for more advanced jamming protection. To provide an escape from this trend, we investigate the previously unexplored area of jammer exploitation. This dissertation develops the concept of antifragile communications, defined as the capability for a communications system to improve in performance due to a system stressor or harsh condition. Antifragility refers to systems that increase in capability, resilience, or robustness as a result of disorder (e.g., chaos, uncertainty, stress). An antifragile system is fundamentally different from one that is resilient (i.e., able to recover from failure) and robust (i.e., able to resist failure). We apply the concept of antifragility to wireless communications through several novel strategies that all involve exploiting a communications jammer. These strategies can provide an increase in throughput, efficiency, connectivity, or covertness, as a result of the jamming attack itself. Through analysis and simulation, we show that an antifragile gain is possible under a wide array of electronic warfare scenarios. Throughout this dissertation we provide guidelines for realizing these antifragile waveforms. Other major contributions of this dissertation include the development of a communications jamming taxonomy, feasibility study of reactive jamming in a SATCOM-type scenario, and a reinforcement learning-based reactive jamming mitigation strategy, for times when an antifragile approach is not practical. Most of the jammer exploitation strategies described in this dissertation fall under the category of jammer piggybacking, meaning the communications system turns the jammer into an unwitting relay. We study this jammer piggybacking approach under a variety of reactive jamming behaviors, with emphasis on the sense-and-transmit type. One piggybacking approach involves transmitting using a specialized FSK waveform, tailored to exploit a jammer that channelizes a block of spectrum and selectively jams active subchannels. To aid in analysis, we introduce a generalized model for reactive jamming, applicable to both repeater-based and sensing-based jamming behaviors. Despite being limited to electronic warfare scenarios, we hope that this work can pave the way for further research into antifragile communications.
  • Thumbnail Image
    Biologically Inspired Cognitive Radio Engine Model Utilizing Distributed Genetic Algorithms for Secure and Robust Wireless Communications and Networking
    Rieser, Christian James (Virginia Tech, 2004-09-29)
    This research focuses on developing a cognitive radio that could operate reliably in unforeseen communications environments like those faced by the disaster and emergency response communities. Cognitive radios may also offer the potential to open up secondary or complimentary spectrum markets, effectively easing the perceived spectrum crunch while providing new competitive wireless services to the consumer. A structure and process for embedding cognition in a radio is presented, including discussion of how the mechanism was derived from the human learning process and mapped to a mathematical formalism called the BioCR. Results from the implementation and testing of the model in a hardware test bed and simulation test bench are presented, with a focus on rapidly deployable disaster communications. Research contributions include developing a biologically inspired model of cognition in a radio architecture, proposing that genetic algorithm operations could be used to realize this model, developing an algorithmic framework to realize the cognition mechanism, developing a cognitive radio simulation toolset for evaluating the behavior the cognitive engine, and using this toolset to analyze the cognitive engineà ­s performance in different operational scenarios. Specifically, this research proposes and details how the chaotic meta-knowledge search, optimization, and machine learning properties of distributed genetic algorithm operations could be used to map this model to a computable mathematical framework in conjunction with dynamic multi-stage distributed memories. The system formalism is contrasted with existing cognitive radio approaches, including traditionally brittle artificial intelligence approaches. The cognitive engine architecture and algorithmic framework is developed and introduced, including the Wireless Channel Genetic Algorithm (WCGA), Wireless System Genetic Algorithm (WSGA), and Cognitive System Monitor (CSM). Experimental results show that the cognitive engine finds the best tradeoff between a host radio's operational parameters in changing wireless conditions, while the baseline adaptive controller only increases or decreases its data rate based on a threshold, often wasting usable bandwidth or excess power when it is not needed due its inability to learn. Limitations of this approach include some situations where the engine did not respond properly due to sensitivity in algorithm parameters, exhibiting ghosting of answers, bouncing back and forth between solutions. Future research could be pursued to probe the limits of the engineà ­s operation and investigate opportunities for improvement, including how best to configure the genetic algorithms and engine mathematics to avoid engine solution errors. Future research also could include extending the cognitive engine to a cognitive radio network and investigating implications for secure communications.
  • Thumbnail Image
    Bluetooth Frequency Hop Selection Kernel Impact on "Inter-Piconet" Interference
    Ballagh, Jason (Virginia Tech, 2003-04-29)
    The Bluetooth wireless transmission standard provides a low-power data link between electronic devices over relatively short ranges. These links, also known as piconets, transmit using frequency hopping spread spectrum (FHSS) to send information over the air. As more applications for Bluetooth technology become available, the number of Bluetooth devices will continue to increase. With this increase in use, there will be a decrease in performance that can be attributed to Bluetooth "inter-piconet" interference. To date, very little has been published on the subject of inter-piconet interference. Previous studies have derived mean packet error rates for an increase in the number of piconets present. To come up with the mean rate, many papers make the assumption that the probability of a Bluetooth device hopping to a channel is random. However, making this assumption does not explain what happens in real time. This research gives some insight into what really happens when multiple piconets are interfering in real time. Bluetooth devices actually use a frequency hopping algorithm to determine the hopping sequence. This algorithm has been implemented in software to test various aspects of inter-piconet interference. Previous studies have shown that synchronizing the clocks among neighboring piconets will result in an increase in performance. This study shows that there are cases where synchronization alone will not provide sufficient improvement. Experimental testing has been conducted to validate some of the simulated results. Adjacent channel interference was observed during experimentation. This contradicts previous research, which has assumed that adjacent channel interference is insignificant.
  • Thumbnail Image
    A broadband Microwave Transceiver Front-end for an Airborne Software Defined Radio Experiment
    Blair, Arthur Paul Jr. (Virginia Tech, 2015-01-26)
    This document describes the design, simulation, construction, and test of a wideband analog transceiver front-end for use in an airborne software defined radio (SDR) experiment. The transceiver must operate in the GSM-1800 and IEEE 802.11b/g WiFi frequency bands and accommodate beamforming. It consists of a transmitter and dual band receiver. The receiver input is fed by a helical antenna and the outputs are digitized for use in the SDR. The transmitter is fed by a complex baseband output from a Digital-to-Analog Converter (DAC) and its output fed to another helical antenna. The requirements for the transceiver were driven by a spectral survey of the operating environment and the physical and electrical limitations of the platform. The spectral survey showed a great disparity in the received power levels between the signals of interest and potential interferers. Simulations of several candidate receiver architectures showed that meeting the needs of the experiment would require a high degree of linearity and filtering. It was found that the receiver requirements could be met by a single downconversion with high order filters and passband sampling. A series of analyses determined the requirements of the individual components that make up the system. Performance was verified by simulations using measured data of the individual components and lab tests of the assembled hardware. Suggestions for improved performance and expanded operation are made.
  • Thumbnail Image
    Channel Impulse Response and Its Relationship to Bit Error Rate at 28 GHz
    Miniuk, Mary (Virginia Tech, 2003-12-19)
    Over the years, the Internet has become increasingly popular and people's dependence on it has increased dramatically. Whether it be to communicate to someone across the world, find blueprints, or check sports scores, the Internet has become a necessary resource for everyone. In emergency situations, this need increases further. After the terrorist attacks on the Pentagon, it took several days to restore communications. This is not an acceptable time frame when people's lives are at stake. Virginia Tech's Center for Wireless Telecommunication has developed a prototype of a rapidly deployable high bandwidth wireless communication system at 28 GHz (Local Multipoint Distribution Service frequency). This system provides a large bandwidth radio link to a disaster zone up to 5 km away and puts Ethernet speeds and 802.11 accesses to users within hours. Because of the possible variability in locations that the system can be deployed, it is necessary to find the most useable channel at the site as quickly as possible. In addition to 28GHz radio links, the system also has a built-in channel sounder that measures and captures the channel impulse response of the current channel. Until now, there has been limited research on the relationship between the channel impulse response and the usability of the channel quantified using bit error rate. This thesis examines several different channels captured by CWT's channel sounder and simulates the BER using Cadence's SPW with time-domain models of the channels. This thesis goes on further to show that BER greatly depends on the channel impulse response and the symbol rate.
  • Thumbnail Image
    Characterization and Evaluation of Non-Line-of-Sight Paths for Fixed Broadband Wireless Communications
    Gallagher, Timothy M. (Virginia Tech, 2004-05-13)
    Channel impulse responses collected on the Virginia Tech campus show combinations of specular multipath and diffuse scattering at LMDS frequencies. An algorithm is presented that estimates link performance based on the channel impulse response. Presented and analyzed are representative impulse responses (one is primarily specular in nature and one shows significant diffuse scattering) to show that the proposed algorithm is appropriate for analyzing channels exhibiting either of these characteristics. Monte Carlo simulations logged the sequence number of each bit error to gain an understanding of the distribution of errors over time. The results show that for these static channels the errors occur randomly rather than in bursts, leading to the conclusion that average bit-error rate statistics are appropriate for channel characterization. Zero-Forcing (Z-F) and Minimum Mean Square Error (MMSE) equalizers employed on these channels had a significant impact on the link quality. In many cases, the performance of the MMSE equalizer performed only slightly better than the Z-F equalizer. However, when deep nulls were present in the channel response, the MMSE equalizer performed significantly better. Algorithms for determining the number of taps necessary to approach an optimum equalization are presented for both types of equalizers and a '98%' rule of thumb is presented. The algorithm's role in adaptive and cognitive radio systems is discussed and two applications are presented to illustrate its utility.
  • Thumbnail Image
    Collision study for the one-way IVDS channel
    Harmon, Andrew James (Virginia Tech, 1996-08-05)
    A collision study is performed to compare the interference rejection characteristics of two spread spectrum receivers, one employing a sliding correlator and the other using a more sophisticated matched filter design. The testing involves using two similar transmitters, one acting a the jammer, to test the collision dynamics of each receiver. Packet data from both transmitters contain identical spreading codes. Data from the testing is analyzed and the receivers' jamming margin, capture, and process gain qualities are compared as to which system best optimizes a one-way channel. Motivation for the collision study stems from researching a one-way communication link for the Interactive Video Data Service ( IVDS ) project currently being developed by the Center for Wireless Telecommunications ( CWT ) at Virginia Tech. A novel retransmission technique has previously been developed which discusses the probability of packet collisions on the channel and uses a computer program to simulate the channel model. This thesis will provide more information as to what happens in packet collisions as well as determine which receiver type offers the greatest interference rejection.
  • Thumbnail Image
    A Comparison Between Synchronous CDMA and Orthogonal Frequency Division Multiplexing (OFDM) for Fixed Broadband Wireless Access
    Chheda, Shital Ratilal (Virginia Tech, 2002-04-25)
    The growth of broadband Internet access has paved the way for the development of many new technologies. As the cost of implementing broadband access soars, the best alternative will be to use fixed wireless for these services. This thesis addresses the possibility of 3rd Generation (3G) mobile cellular wireless systems as the basis for fixed broadband wireless service. Two of the 3G technologies aimed at providing fixed broadband wireless access are Time Division Synchronous Code Division Multiple Access (TD-SCDMA) and Orthogonal Frequency Division Multiplexing (OFDM). This thesis aims to provide a preliminary study on using TD-SCDMA and OFDM for broadband wireless systems. Currently, there is not enough theory and information to establish the feasibility of using either of these technologies for broadband wireless access. First, the basic features and background on synchronous CDMA and OFDM are presented for the reader to better understand these technologies. Then, an example TD-SCDMA system is described, and some analytical and experimental results are presented. Finally, TD-SCDMA's technologies, along with this system's attributes, are compared analytically to that of Vector OFDM (VOFDM).
  • Thumbnail Image
    A Coverage Area Estimation Model for Interference-Limited Non-Line-of-Sight Point-to-Multipoint Fixed Broadband Wireless Communication Systems
    RamaSarma, Vaidyanathan (Virginia Tech, 2002-09-19)
    First-generation, line-of-sight (LOS) fixed broadband wireless access techniques have been around for several years. However, services based on this technology have been limited in scope to service areas where transceivers can communicate with their base stations, unimpeded by trees, buildings and other obstructions. This limitation has serious consequences in that the system can deliver only 50% to 70% coverage within a given cell radius, thus affecting earned revenue. Next generation broadband fixed wireless access techniques are aimed at achieving a coverage area greater than 90%. To achieve this target, these techniques must be based on a point-to-multipoint (PMP) cellular architecture with low base station antennas, thus possessing the ability to operate in true non-line-of-sight (NLOS) conditions. A possible limiting factor for these systems is link degradation due to interference. This thesis presents a new model to estimate the levels of co-channel interference for such systems operating within the 3.5 GHz multichannel multipoint distribution service (MMDS) band. The model is site-specific in that it uses statistical building/roof height distribution parameters obtained from practically modeling several metropolitan cities in the U.S. using geographic information system (GIS) tools. This helps to obtain a realistic estimate and helps analyze the tradeoff between cell radius and modulation complexity. Together, these allow the system designer to decide on an optimal location for placement of customer premises equipment (CPE) within a given cell area.
  • Thumbnail Image
    Decoder Board Hardware/Software Development in Wireless Interactive Video Data Service System
    Goedde, Todd William (Virginia Tech, 1997-09-18)
    The Interactive Video Data Service (IVDS) system allows consumers to browse the Internet, request information on products or services, make purchases, indicate preferences, and perform other interactive applications. To provide this service, the IVDS system has three subsystems: Consumer Control (CC), Cell Repeater (CR), and Host subsystem. In the CC subsystem, an IVDS transceiver box is placed near a television set. Once the consumer sends a command to the transceiver box using a standard television/VCR/Cable remote control, the transceiver box receives information embedded in the television audio, and then transmits the information to the CR subsystem as a radio frequency (RF) spread spectrum message. The CR subsystem decodes the spread spectrum message and forwards it to the Host subsystem for processing. Located in the CR subsystem, a custom designed circuit board, called the decoder board, uses surface mounted components to decode and packetize the spread spectrum message for transfer to the CR main processor. This paper provides a functional description of the hardware components on the decoder board, and describes the hardware/software developed for interfacing the decoder board to the radio receiver and to the CR main processor. Hardware modifications were needed to correct timing problems between components. Software was developed to initialize the components for downconverting, despreading, and demodulating spread spectrum messages, and to packetize them for transfer to the CR main processor. This paper also discusses the tests used to verify both the performance of the decoder board software and the operation of the hardware components.
  • Thumbnail Image
    Design and Implementation of a Practical Aircraft Position and Reporting Identification Beacon (PRIB)
    Lee Yan, Yuen On (Virginia Tech, 2003-04-28)
    A transponder is a device that is used for tracking aircraft by mean of a secondary radar system, but it can be turned off deliberately, and it is an expensive item for small aircraft. These weaknesses have fatal consequences, as was shown with the terrorist attack on September 11 th , 2001, where four commercial aircraft under the control of international terrorists were used as missiles against the United Stated of America, killing thousands of people. These factors have shown a need for the development of an efficient aircraft tracking system, which does not rely on transponders. To this end a new tracking aircraft system is proposed, which will be referred to as the Positioning and Reporting Identification Beacon (PRIB) system. Due to size, mass, power, and financial constraints, the design must be small, light, power efficient, and cost-effective. The PRIB will acquire the aircraft's position from a dedicated GPS receiver and then transmit this information to a base station at a different location using a radio link. This thesis presents the design of a PRIB unit in light of the system constraints. In addition to the hardware design, the software needed by the unit to control and communicate with the ground stations is presented. The performance of the PRIB is analyzed and ways in which a PRIB could be manufactured using commercial off-the-shelf parts is discussed.
  • Thumbnail Image
    Design and Implementation of a Swept Time Delay Short Pulse (SSTDSP) Wireless Channel Sounder for LMDS
    Rieser, Christian James (Virginia Tech, 2001-07-17)
    This thesis describes the theoretical development, design, and implementation of a novel measurement system, called a Sampling Swept Time Delay Short Pulse (SSTDSP) wireless channel sounder, capable of real time in field performance characterization of high speed fixed wireless links. The SSTDSP sounder has been designed to provide vital performance metrics for fixed point high data rate applications in the 28 GHz LMDS band at a fraction of the cost and complexity of existing wideband channel sounders. The SSTDSP sounder monitors the behavior of the LMDS channel by sampling the impulse response of the channel in real time. This digitized impulse response is used to assemble a power delay profile and render real-time channel performance metrics such as the mean excess delay, RMS delay spread, maximum excess delay for a given multipath threshold, and coherence bandwidth. The SSTDSP sounder is capable of recording these metrics through three modes of operation - continuous channel monitoring, single instant channel snapshot, or data logging. Swept time delay time dilation processing is combined with precise sample and hold gating to reduce the analog to digital converter sampling rate required to digitize the nanosecond short pulses from 2 Gsps to 1 Msps, while retaining the required effective Nyquist sampling rate of 2 Gsps. This dramatically reduces the memory, digital signal processing, and data logging storage requirements as well as the overall cost of the sounder system. The thesis presents the theory behind channel sounding and discusses whether there is a "bounce path" available to LMDS. Several existing channel sounding methods are compared for this application. A number of specific design and performance criteria from each of these methods are synthesized to produce the Sampling Swept Time Delay Short Pulse Sounder architecture. The design and implementation process used to realize the SSTDSP sounder is presented, including a system overview, module details, and algorithm development details. A calibration and measurement test procedure is outlined and system verification results are presented. Current work in progress on the test platform and future improvements to the modular system are outlined, as well as conclusions and future implications of the system.