Thesis. 1978. M.S.--Massachusetts Institute of Technology. Alfred P. Sloan School of Management. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND DEWEY. / Bibliography: leaf 79. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by William Howard Hanot. / M.S.

The rapid evolution of current and upcoming high speed and complex communications networks often necessitates flawless time synchronization among the network nodes in order to guarantee performance. GPS based synchronizers have long been used for synchronizing telecommunications equipment, currently providing an accuracy of up to 10ns. Such high accuracy demands excellent operation from GPS timing receivers. Interference is an important threat to GPS performance. Any degradation in performance, due to the introduction of interference, can cause these receivers to provide a low quality timing solution, or to lose lock with incoming GPS signals altogether. This consideration motivates the study of the performance of GPS timing receivers in the presence of harmful interference. This work is devoted to the theoretical and practical investigations of the effects of RF interference on GPS-based synchronizers and their impacts on communications networks. Contributions made during this work include: a) Identification of the processes and the parameters involved in producing a timing solution which are vulnerable to interference; b) experimentbased confirmation of a hypothesis about the effects of interference on GPS timing receivers; c) identification of the effects of degraded synchronization on the performance of communications networks, especially CDMA and GSM cellular networks, which rely upon GPS based synchronizers; and d) proposal of a method to predict and avoid communications network performance degradation.

Thesis (MSc)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

The object of this research is to develop a solution for band-limited channels. Backplane channels and GPON channels are investigated to apply an equalization technique. Different lengths of backplane channels are measured with different signal speeds to investigate the channel performance. Also a GPON system with different fiber lengths is designed and set up in a lab to measure the BER performance. The GPON system utilizes a Fabry-Perot laser for the most economical solution. After the circuits are fabricated, they are inserted into the system to measure the performance of the channels with equalizers. Both the backplane and the GPON system show successful channel improvement in measured eye diagrams and BER. To expedite the procedure and eventually build an adaptive system which could be inserted and self-optimizing, we found it essential to monitor the output of the equalizer. A novel analog way to achieve this goal is suggested. All the equalizers mentioned in this dissertation have one summing node to add up all the values from VGAs. This structure is very efficient, but in the event that there are too many VGAs, it draws too much current through the one node. This issue is dealt with by the design of two nine tap equalizers, which are compared to assess the difference in performance between the unbalanced structure and the balanced structure.

This dissertation provides the conceptual development, modeling and simulation, physical implementation, and measured hardware results for a practicable digital coherent chaotic communication system. Such systems are highly desirable for robust communications due to the maximal entropy signal characteristics that satisfy Shannon's ideal noise-like waveform and provide optimal data transmission across a flat communications channel. At the core of the coherent chaotic communications system is a fully digital chaotic circuit, providing an efficiently controllable mechanism that overcomes the traditional bottleneck of chaotic circuit state synchronization. The analytical, simulation, and hardware results yield a generalization of direct sequence spread spectrum waveforms, that can be further extended to create a new class of maximal entropy waveforms suitable for optimized channel performance, maximal entropy transmission of chaotically spread amplitude modulated data constellations, and permission-based multiple access systems.

Fiber-optic networks are continually evolving to accommodate the ever increasing data rates demanded by modern applications and devices. The current state-of-the art systems are being deployed with 100 Gb/s rates per wavelength while maintaining the 50 GHz channel spacing established for 10 Gb/s dense wavelength division multiplexed (DWDM) systems. Phase modulation formats (in particular quadrature phase shift keying - QPSK) are necessary to meet the spectral efficiency (SE) requirements of the application. The main challenge for phase modulated optical systems is fiber nonlinearities, where changes in intensity of the combined optical signal result in changes to the fiber's refractive index. Limiting launch power is the primary means to avoid dramatic intensity fluctuations, a strategy which in turn limits the available signal-to-noise ratio (SNR) within the channel. Continuous phase modulation (CPM) is a format in which data is encoded in the phase, while the amplitude is constant throughout all transmission (even during transitions between symbols). With the goal of reducing the impact of nonlinearities, the purpose of this research was to identify a set of CPM signals best suited for high speed fiber-optic transmission, and quantify their performance against other formats. The secondary goal was to identify techniques appropriate for demodulation of high speed fiber-optic systems and implement them for simulation and experimental research. CPM encompasses a number of variable parameters that combine to form an infinite number of unique schemes, each of which is characterized by its own SE, minimum distance, and implementation complexity. A method for computing minimum distance of DWDM-filtered CPM formats is presented and utilized to narrow down to a range of candidate schemes. A novel transmitter design is presented for CPM signal generation, as well as a number of novel reception techniques to achieve proper demodulation of the CPM signal from the coherent optical receiver. Using these methods, the identified range of candidate schemes was compared in simulation to the conventional QPSK format, showing that some modest gain can be expected from CPM. Through these and other simulations, it is revealed that fiber nonlinearities depend on the aggregate sum of all wavelengths rather than the imposition of each separate carrier on its neighbors. Therefore the constant envelope of CPM does not directly impact the nonlinearities since multiple carriers will photonically interfere and result in intensity fluctuations regardless of modulation format. Additionally, dispersive effects in fiber decompose the underlying channels so that the intensity throughout propagation is nearly Gaussian distributed, regardless of format. The benefits gained from CPM are thus limited to schemes that attain a higher minimum distance than alternative formats (in the given channel passband), and for optically compensated links in which low dispersion is maintained throughout the fiber link.

The dissertation presents novel methodologies to realize a multi-band and multi-standard receiver with an interference-cancellation capability. First, the receiver specifications are derived from the wireless communication standard. These specifications are then used to obtain the required amount of TX leakage cancellation by using a proposed frequency selective feedback topology with multi-band capability. The effectiveness of this technique is demonstrated by the measurement of prototype integrated circuit (IC). To make the IC operate for multi-standard, another novel technique is also proposed for a channel-selection filter. With a proposed interpolated resistor bank, the active-RC channel-selection filter has programmable gain and pseudo-continuous bandwidth, which reduce the total power consumption and silicon area of the receiver. The measured result of a prototype silicon chip shows the effectiveness of the technique. With these two topologies, a multi-band multi-standard receiver that uses low power can be realized at a cost.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Computer Science." Includes bibliographical references (p. 121o-128).

Thesis (M.A. in Security Studies (Homeland Security and Defense))--Naval Postgraduate School, December 2009. / Thesis Advisor(s): Bergin, Richard. Second Reader: Munks, Jeffrey. "December 2009." Description based on title screen as viewed on January 27, 2010. Author(s) subject terms: Interoperable communications; multi-discipline, multi-jurisdictional radio communications; risk and governance; shared governance; policy and consensus teams, Monterey Police Department. Includes bibliographical references (p. 71-73). Also available in print.