Orthogonal Frequency Division Multiplexing (OFDM) is fast becoming the signal modulation technique of choice for many commercial and military wireless applications. Its resilience to cochannel interference and bandwidth efficiency make it ideal for many different applications. With its increasing popularity among disparate facets of society, it becomes likelier that enemy militaries and/or nonmilitary combatants will utilize the technique or a system that uses the technique. In light of this development, the need to develop techniques and algorithms to enable detection becomes apparent. This thesis will attempt to develop a model for OFDM and measure its performance in a multipath, outdoor environment with low signal-to-noise ratio, high noise and cochannel interference. Because of the unpredictability of the outdoor environment and the proliferation of various OFDM standards, the simulation will utilize only one algorithm for modeling outdoor environments and the IEEE 802.11a standard.

The ability to sense and monitor a variety of environmental conditions using un-tethered sensors offers a significant change over traditional sensing systems that need to be strategically positioned and have topologies engineered. As such, recent research into wireless sensor networks has attracted great interest due to its diversity of applications, ranging in areas such as home, health, environmental and military applications. In this thesis, the evaluation of a routing protocol developed by Crossbow Technologies called XMesh, is presented. The main components of the routing protocol are described and the routing algorithm explained. Experiments were conducted to determine the connectivity ranges of motes in different transmission power settings. The relationship of mote transmission power and network connectivity is presented. An energy efficiency study looked at the means of extending the lifespan of the network. Although, packet losses during the period of a node failure were significant, the routing protocol showed that it was able to adapt and reorganize to provide reliable and stable routing in a network.

In this thesis a method is developed to estimate and remove group delay caused by the transmission channel in the case of a burst signal. The signal of interest is modeled as burst white noise, and no information about any underlying symbol structure or rate is assumed. The regions of transition between the signal present and the signal not present are used to estimate the group delay of the transmission channel. Once estimated, the group delay can be removed using an all-pass lter with the proper phase characteristics.

This thesis investigates the fundamentals of multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) radio communication systems with space-time codes. A MISO system and MIMO systems were designed using multicarrier delay diversity modulation (MDDM). MDDM was incorporated with orthogonal frequency division multiplexing (OFDM). The design was implemented with binary phase shift keying (BPSK). Matlab was used to simulate the design, which was tested in both an additive white Gaussian noise (AWGN) channel and in a slow fading frequency nonselective multipath channel with AWGN. The receiver design was incorporated with the maximal ratio combiner (MRC) receiving technique with perfect knowledge of channel state information (CSI). The theoretical performance was derived for both channels and was compared with the simulated results.

Integrated Power Systems will be used on future naval combatants. These systems will allow unprecedented control of shipboard power to propel the ship, sense the battle-space, and engage the enemy. One crucial enabling technology is robust power conversion modules like the hybrid dc to ac inverter. This thesis is a further exploration of the hybrid inverter scheme consisting of a six-step voltage-source inverter (VSI) and a hysteresis controlled current-source inverter (CSI). The six-step controller was redesigned to make it independent of the hysteresis controller. The hysteresis controller is fed a reference signal extracted from the total output current. The signal is filtered and modified by the closed-loop system such that the total output current approaches a perfect sine wave limited only by bandwidth. The modified closed-loop controller was compared to a previous Naval Postgraduate School effort and found to improve current total harmonic distortion from 3.2% to 1.8%. This thesis proves that existing power electronic technology can be used to produce high-fidelity waveforms for high-power Naval Propulsion Drives (50-100 MW).

In this research, a continuous analog generalized impedance converter (GIC) 4th order band pass filter is investigated in detail. Various classroom software aids such as MATLAB, P-SPICE and MAPLE are utilized to simulate varies circuit parameter changes in ideal and non-ideal GIC filter, such as network sensitivity, effects of resistor value, capactor value and reduction of gain bandwidth product (GBWP), on the center frequency and Q factor. All simulated results are used to evaluate the actual circuit implementation prior to future GIC filter chip fabrication. A composite operational amplifier utilizing the BiCMOS standard operational amplifier that was designed and introduced in a previous thesis is presented and its improved performance is investigated. The composite amplifier (C20A2) is designed using Silvaco EXPERT and simulated with Silvaco SmartSpice. The results show the gain bandwidth product (GBWP), common mode rejection ratio (CMRR), and open loop gain are considerably improved. This sets the basic foundation for future students to incorporate the newly designed composite operational amplifier into the GIC filter to further enhance filter performance.

The purpose of this thesis is to implement the CAF-Map method of geolocation in MATLAB. This method is a modification to the traditional Cross Ambiguity Function (CAF) based TDOA, FDOA geolocation where TDOA and FDOA are determined by locating the peak in the CAF plane and then the peak's information is fed to a Least Squares like geolocation tool to determine the emitters geolocation. This method omits the step in which the geolocation is determined with the "post processed" CAF peak information and instead maps the CAF surface directly to the earth's surface. In this thesis, the traditional CAF based geolocation is explained and the limitations are discussed. After this, the development of the CAF-Map method is explained and the algorithm is presented. This thesis explores the use of the CAF-Map method as a geolocation alternative to the traditional TDOA, FDOA methods and demonstrates its ability to geolocate co-channel emitters.

Recent military applications have demanded photodetectors with high sensitivity, high selectivity and multispectral capability for detection and identification of the target. These characteristics have been found in quantum well infrared photodetectors (QWIP). Driven by these applications, a QWIP photodetector capable of detecting simultaneously infrared emissions within near infrared (NIR), mid wavelength infrared (MWIR) and long wavelength infrared (LWIR) was studied, modeled, designed and characterized. Using the envelope function approximation, the mathematical model of the quantum phenomena in semiconductor heterostructures was derived. A computational tool was developed to solve self-consistently the Schodinger-Poisson equation using the shooting method, allowing the theoretical evaluation of the absorption coefficient. A three-color (NIR, MWIR and LWIR) GaAs-based QWIP sample and a two-color (NIR and MWIR) InP-based QWIP sample were designed, both comprised of stacks of uncoupled wells for each band detection. The 67 layers of the GaAs sample was grown using molecular beam epitaxy (MBE). Intersubband absorption in the sample was measured for the MWIR and LWIR using Fourier transform spectroscopy (FTIR) and the measured peak positions, found at 5.3 æm , 8.7 æm , and 13.8 æm are within 0.3 æm of the theoretical values, indicating that the model accurately predicts the absorption wavelengths. A twodimensional ordered grating pattern was selected and optimized separately for both MWIR and LWIR desired peaks. Finally the photodetector device configurations were designed to permit to the measurement of the NIR band through photocurrent spectroscopy and performance analysis. The fabrication and characterization of the prototypes are a matter for future work.

The primary objective of this these was to study the feasibility of using a MEMS accelerometer to monitor vibration signatures of a machine to determine if the machine is operating properly. The secondary objective was to investigate the self test features of the accelerometer used in the vibration monitoring. An Efector Octavis accelerometer sensor was used in this study. It was used to monitor a small air pump and an air conditioning (AC) system. The sensor provided the amplitude for the frequency spectrum of the motor vibration. A reference signal was calculated by taking an average of the spectrum over 30 seconds. Two methods (a ratio of cross-correlation coefficients and a spectral distance) were used to compare the reference to the sensor data. The spectral distance method proved to be the better of the two. Using this method, the system could sense when the pump or the AC unit were malfunctioning. The self test feature involved exciting the Built in Self Test (BIST) pin of the accelerometer with a signal generator. Then the impulse response of the accelerometer was measured from the output pin using an oscilloscope.

This thesis studies the performance of Multiple-Input, Multiple Output (MIMO) systems that use Space-Time Block Coding (STBC). Such systems can be employed to improve the bit error rate (BER) performance of wireless communication systems and counter the detrimental effects of channel fading and other distortion phenomena. We propose a systematic method for designing a space-time orthogonal MIMO scheme that employs an arbitrary number of transmitting and receiving antennas, and we evaluate (through simulation) the performance improvements that can be attained by employing our design approach. We present a general formula for determining the rate (i.e., the ratio of the number of symbols transmitted to the number of symbol intervals required) of systems that employ our design. Additionally, this thesis analyzes the relationship between channel correlation and antenna spacing for the case of MIMO systems that use a linear antenna configuration, and, through simulation studies, we show how such systems can take the advantage of the multipath phenomenon to reduce the detrimental effects of channel correlation.