Search results

(1 - 2 of 2)
CHARACTERIZING GPS PHASE LOCK LOOP PERFORMANCE IN WIDEBAND INTERFERENCE USING THE DISCRIMINATOR OUTPUT DISTRIBUTION
Title
CHARACTERIZING GPS PHASE LOCK LOOP PERFORMANCE IN WIDEBAND INTERFERENCE USING THE DISCRIMINATOR OUTPUT DISTRIBUTION
Creator
Stevanovic, Stefan
Date
2018, 2018-05
Description
The use of the Global Positioning System (GPS) has accelerated in recent years. In its inception, GPS was used exclusively by the military for...
Show moreThe use of the Global Positioning System (GPS) has accelerated in recent years. In its inception, GPS was used exclusively by the military for navigation. Today, with the emergence of extremely capable electronics and microprocessors, GPS has been integrated into many aspects of life. It is currently widely used by both the military and various civilian industries for applications that require navigation as well as precise timing. Some applications of GPS include ground vehicle and aircraft navigation, banking, power transmission, and agriculture. As a result, disruptions in GPS availability have the potential to disrupt many services and industries around the globe, and even threaten the safety of life. Reliable operation can be interrupted by radio frequency interference (RFI), which can come from natural and manufactured sources. This work describes new techniques to evaluate the performance of GPS receivers that may be subjected to RFI events. The example application motivating this work is Ground Based Augmentation System (GBAS) reference station receivers subjected to broadband interference, for example, from nearby use of personal privacy devices (PPDs). PPDs most commonly emit broadband interference, and GBAS ground based reference receivers have expe- rienced tracking discontinuities as a result [Pul12]. These events can cause navigation service interruptions to aircraft on nal approach. To ensure continuity of the nav- igation service, GBAS reference stations must be able to track GPS signals in the presence of wideband interference. The objective of this work is to develop the PLL analysis tools required to design PLLs capable of tracking through RFI events, while reducing the need for time-consuming simulations and experimental validation. Instead, simulation and experimental validation can be reserved for PLL designs which are much more likely to be successful. The techniques described in this work are valid for any GPS application in which the receiver cannot tolerate cycle slips in the phase-lock loop (PLL). The methodology is directly applicable to ground-based reference receivers for differential GPS systems, as well as other ground-based receivers that require high continuity of service. It is also relevant to moving receivers, if the additional dynamic stresses on the PLL are also taken into account. The PLL discriminator output (DO) distribution is used to characterize GPS PLL tracking performance, in contrast to the phase jitter metric widely used in prior work and literature. Both the DO variance and the bias on the mean of the DO distribution are shown to be superior to the jitter metric in predicting phase-lock. And, it is shown that the bias in the DO mean is the most effective measure of cycle slip probability. Studying the discriminator output distribution also provides a means of comparing different techniques to extend PLL averaging time beyond the length of a navigation data bit, without time-consuming direct simulation and experimental validation. Experimental results are presented to validate the theoretical analysis and simulations. The observed tracking results are consistent with the theoretically predicted system performance. The DO bias is superior to the variance metric in its ability to predict loss of phase-lock.
Ph.D. in Mechanical and Aerospace Engineering, May 2018
Show less
MACHINE VISION NAVIGATION SYSTEM FOR VISUALLY IMPAIRED PEOPLE
Title
MACHINE VISION NAVIGATION SYSTEM FOR VISUALLY IMPAIRED PEOPLE
Creator
Yang, Guojun
Date
2021
Description
Visually impaired people are often challenged in the efficient navigation of complex environments. Moreover, helping them navigate intuitively...
Show moreVisually impaired people are often challenged in the efficient navigation of complex environments. Moreover, helping them navigate intuitively is not a trivial task. Cognitive maps derived from visual cues play a pivotal role in navigation. In this dissertation, we present a sight-to-sound human–machine interface (STS-HMI), a novel machine vision guidance system that enables visually impaired people to navigate with instantaneous and intuitive responses. This proposed system extracts visual context from scenes and converts them into binaural acoustic cues for users to establish cognitive maps. The development of the proposed STS-HMI system encompasses four major components: (i) a machine vision–based indoor localization system that uses augmented reality (AR) markers to locate the user in GPS-denied environments (e.g., indoor); (ii) a feature-based object detection and localization system called the simultaneous localization and mapping (SLAM) algorithm, which tracks the mobility of users when AR markers are not visible; (iii) a path-planning system that creates a course towards a destination while avoiding obstacles; and (iv) an acoustic human–machine interface to navigate users in complex navigation courses. Throughout the research and development of this dissertation, each component is analyzed for optimal performance. The navigation algorithms are used to evaluate the performance of the STS-HMI system in a complicated environment with difficult navigation paths. The experimental results confirm that the STS-HMI system advances the mobility of visually impaired people with minimal effort and high accuracy.
Show less