For acquisition of narrow-beam free-space optical (FSO) terminals, a Global Positioning System (GPS) is typically required for coarse localization of the terminal. However, the GPS signal may be shadowed, or may not be present at all, especially in rough or unnameable terrains. In this study, we propose a lidar-assisted acquisition of an unmanned aerial vehicle (UAV) for FSO communications in a poor GPS environment. Such an acquisition system consists of a lidar subsystem and an FSO acquisition subsystem: The lidar system is used for coarse acquisition of the UAV, whereas, the FSO system is utilized for fine acquisition to obtain the UAV’s accurate position. This study investigates the optimal allocation of energy between the lidar and FSO systems to minimize the acquisition time. Here, we minimize the average acquisition time, and maximize the cumulative distribution function of acquisition time for a fixed threshold. We learn that an optimal value of the energy allocation factor exists that provides the best performance of the proposed system.

The technique of direct sequence spread spectrum (DS/SS) has been widely used in commercial mobile communication systems. The efficiency of DS/SS system is highly dependent on the accurate and fast synchronization between the incoming and locally generated PN (pseudo-noise) codes. The code synchronization is processed in two steps, acquisition (coarse alignment) and tracking (fine alignment), to bring the delay offset between the two codes. Conventionally, for code synchronization, most of techniques were proposed based on the correlation property of PN codes. Recently, the different approach, by using the adaptive LMS filtering scheme, has been proposed to reduce the hardware complexity and to improve the performance of code synchronization, especially for a long PN code. In this thesis, a new coherent adaptive code synchronization scheme is proposed, where the adaptive constrained LMS (CLMS) algorithm with the maximum tap-weight (MTW) test method is devised for code acquisition. The statistics of weight vector of the proposed CLMS scheme are derived to evaluate the performance, in terms of mean acquisition time (MAT). Analytical and simulation results verify that the proposed scheme for code acquisition outperforms the one using the conventional LMS filtering schemes, under the integer and non-integer time delay cases. Moreover, the setting of threshold value is derived for code acquisition, which is independent of the values of signal-to-noise ratio (SNR) and time delay. Next, the CLMS scheme is proposed associated with the direct delay estimation (DDE) formula for code tracking. This approach does achieve a good delay-tracking performance, which is verified via computer simulation. Simultaneously, the hardware complexity can further be reduced due to that a code-tracking loop implemented by the interpolation method is not required.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / Range to an orbiting satellite from a ground reference point (ground station) can be determined by measuring the round trip time for a waveform transmitted to the satellite and returned to the ground station (Turnaround Ranging) and more recently by using the Global Positioning System (GPS). This paper first summarizes and compares the two approaches. The paper then describes and analyzes a new turn-around ranging system which uses a flexible ranging waveform that provides spectral compatibility with existing Military, NASA, and Commercial satellite uplink/downlink signals.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / Bit errors often occur in a wireless communications link when impairments alter the transmitted signal. It is advantageous to be able to predict how well a system will tolerate transmission problems. This paper details laboratory performance measurements and comparisons in terms of evaluating configurations of a digital receiver for Feher patented Quadrature Phase Shift Keying (FQPSK-B) demodulation. The transmitted signal is subjected to calibrated levels of impairments while the receiver performance is monitored in real-time.

The aim of this thesis is to graphically interpret navigation messages from a prototype of global navigation satellite system. The resulting application is implemented in Python programming language for Windows operating system and follows requests from researchers developing the prototype. Necessary terminology together with graphical user interface programming possibilities of object-oriented language Python is a base for theoretical background of this text. Practical part of this research describes a solution for receiving generated messages from the prototype as well as their storing and filtering into useful information. Further, the design of graphical user interface of the application for prototype interactions and other tools used for its configuration are included.