No description available.

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

International Telemetering Conference Proceedings / October 26-29, 1992 / Town and Country Hotel and Convention Center, San Diego, California / The Air Force Flight Test Center (AFFTC) at Edwards, California has installed the Edwards Digital Switch (EDS). The EDS is a DS-1 switch capable of switching voice, encrypted voice, and Time Space Position Information (TSPI) data. Communicating encrypted voice and TSPI data reliably from the EDS to any other communication system requires the two systems operate using the same frequency reference. The need to communicate with other test ranges and over commercially leased lines using the EDS requires synchronization to a standard frequency source. The current synchronization method used at the AFFTC is unacceptable for the EDS. A hierarchal system of synchronization networking will be implemented to provide a common reference to each of the systems interfacing the EDS. The Master Timing Station (MTS), which provides synchronization reference to most of the AFFTC resources, is aging and must be upgraded. The upgrade of the MTS and the restructuring of the synchronization signal distribution will be completed simultaneously. Traceability to the United States Naval Observatory (USNO) and the National Bureau of Standards (NBS) is required to provide the necessary synchronization to allow the EDS to interface reliably with other systems. The Global Positioning System (GPS) is being considered as the primary source for frequency calibration traceable to the USNO and NBS.

This dissertation was conducted as part of the efforts related to WPI's Precision Personnel Location (PPL) project, the purpose of which is to locate emergency personnel in hazardous indoor environments using radio location techniques. The current PPL system prototype uses a radio transmitter worn by the personnel, indoors, and receivers on reference units, outdoors. This dissertation proposes a new system architecture with bidirectional radio transmissions to replace the current unidirectional system architecture. This allows the development of a synchronization scheme that can extract additional Time of Arrival (TOA) information for estimating the location of personnel. This dissertation also describes an extension of the multi-signal fusion technique previously used that incorporates this TOA information. At the cost of a more complicated mobile unit design, resultant benefits of this approach include rejection of signal reflectors as solutions, improved accuracy with limited reference unit geometries, improved noise rejection and significant computation reduction. In this dissertation the mathematical underpinnings of this approach are presented, a performance analysis is developed and the results are evaluated in the context of experimental data.

This thesis was conducted as part of the efforts related to WPI's Precision Personnel Location (PPL) project, the purpose of which is to locate emergency personnel in hazardous indoor environments using radio location techniques. A unique signal processing algorithm, sART, developed within the PPL project provides means to determine precise position estimates of a wideband transmitter from multipath corrupted signals captured by distributed receivers. This algorithm has synchronization requirements that can not be met without extraordinary expense and complexity by direct means. This thesis develops digital signal processing that achieves the necessary synchronization to satisfy the sART algorithm requirements without additional implementation complexity. The mathematical underpinnings of this solution are introduced and the results are evaluated in the context of experimental data.

Thesis (Ph. D. in Biomedical Engineering)--Vanderbilt University, Dec. 2007. / Title from title screen. Includes bibliographical references.

In this thesis, two signal-to-noise-ratio (SNR) estimators are analyzed for orthogonal frequency division multiplexing (OFDM) systems with imperfect synchronization. The two SNR estimators under investigation are the maximum likelihood estimator (MLE) and the second- and fourth-order moments estimator (MME). Mathematical analysis shows that the performance of MME is not affected by the advanced timing offset while a fixed bias of MLE is induced. Mathematical analysis also shows that the same frequency offset induces different bias for the two estimators under investigation. Finally, a novel carrier frequency offset and timing offset tracking scheme based on SNR estimation is proposed in this thesis.

Recent government regulations for Enhanced 911 locating of wireless handsets require accuracy to within 50 and 300 meters. Two technologies under consideration are triangulation using existing wireless base stations and location using global positioning satellites (GPS). Satellite positioning is the leading candidate, however, reception of GPS signals within large buildings is difficult and considerable research is devoted to this topic. Conventional GPS receivers require line of sight to at least four satellites and, under outdoor conditions, the expected signal level is about -160 dBW. Within large buildings, detection is very difficult because there is high thermal noise and some satellite signals can be attenuated to less than -185 dBW while others can suffer little attenuation. In order to construct the pseudo-ranges necessary for position finding, the receiver must synchronize to the incoming codephase of each satellite and must operate with substantial Doppler frequency offset caused by satellite motion.<p> This thesis investigates the application of a parallel non-coherent spread spectrum synchronizer previously implemented as a very-large-scale integration (VLSI) circuit. The circuit processes one millisecond of incoming signal and uses a segmented matched filter (SMF) by which the segmentation provides some tolerance to Doppler shift. The thesis presents simulation results of averaging for tens of seconds. Through simulation, the SMF is compared with a transversal matched filter (TMF) under conditions of no Doppler shift; coherent and non-coherent integration are discussed. The simulation is conducted at 290 K (17°C) such that the Boltzmann noise is -204 dBW/Hz, with a GPS signal bandwidth of 2 MHz and signal level of -185 dBW, and the receiver input signal-to-noise ratio (SNR) is -44 dB.<p> The SMF is applied using differing segment lengths to high-sensitivity GPS data from indoor and urban simulated GPS data. The results demonstrate the SMFs ability to tolerate Doppler frequency offsets while allowing for long integration times to detect the weak GPS signals.

Pilot Symbol Assisted Modulation (PSAM) is a good method to compensate for the channel fading effect in wireless mobile communications. In PSAM, known pilot symbols are periodically inserted into the transmitted data symbol stream and the receiver uses these symbols to derive amplitude and phase reference. <p> One aspect of this procedure, which has not received much attention yet, is the frame synchronization, i.e. the method used by the receiver to locate the time position of the pilot symbols. In this study, two novel non-coherent frame synchronization methods are introduced in which only the magnitude of received signal is used to obtain the timing of the pilot symbol. The methods are evaluated for both AWGN and frequency non-selective slow Rayleigh fading channels. <p> One synchronization technique is derived by standard maximum likelihood (ML) estimation formulation, and the other is obtained by using maximum a Posteriori probability (MAP) with a threshold test. Signal processing in the receiver uses simplifying approximations that rely on relatively high signal-to-noise ratio (SNR) as consistent with the reception of 16-QAM. Computer simulation has been used to test the acquisition time performance and the probability of false acquisition. Several lengths and patterns of pilot symbol sequences were tested where every 10th symbol was a pilot symbol and all other symbols were randomly selected data symbols. When compared with the other published synchronizers, results from this study show better performance in both AWGN and fading channels. Significantly better performance is observed in the presence of receiver frequency offsets.

With the advent of OFDM for WLAN communications, as exemplified by IEEE 802.11a, it has become imperative to have efficient and reliable synchronization algorithms for OFDM WLAN receivers. The main challenges with synchronization deal with the delay spread and frequency offset introduced by the wireless channel. In this work, rigorous research is done into OFDM WLAN synchronization algorithms, and a thorough synchronizer implementation is presented. This synchronizer performs packet detection, frequency offset estimation, and time offset estimation. Competing timing offset estimation algorithms are compared under a variety of channel conditions, with varying delay spreads, frequency offsets, and channel SNR. The metrics used to select between competing algorithms are statistical variance, and incremental hardware complexity. The timing offset estimation algorithms chosen are a dropoff detection algorithm for coarse timing offset estimation, and a quantized cross-correlator with a maximum detector for fine timing offset estimation.