Gary A. McGraw

Geometry extra-redundant almost fixed solutions: A high integrity approach for carrier phase ambiguity resolution for high accuracy relative navigation

Carrier phase (CP) real time kinematic (RTK) GPS techniques have become widely used in high accuracy relative positioning applications. CP RTK can achieve centimeter-level accuracy by resolving the integer carrier phase cycle ambiguities, creating extremely precise ranging measurements. However, in applications that require high integrity in addition to high accuracy, proving the probability of correct fix (PCF) of the CP ambiguities can be an impediment to the relative positioning system achieving high service availability. In this paper a new algorithmic approach, called geometry extra-redundant almost fixed solution (GERAFS), for high accuracy and high integrity commercial or military GPS relative navigation applications is described. The GERAFS technique relies on the fact that occasional incorrect CP ambiguity fixes can still be acceptable from accuracy and integrity perspectives. A method for quantifying the integrity protection levels associated with these so-called ldquoalmost fixed solutionsrdquo is developed. The centimeter level positioning accuracy with high integrity achieved with GERAFS is demonstrated with simulated and recorded test range GPS sensor data.

Modeling of tracking loop noise and dynamics for efficient simulation of spread spectrum ranging systems

The problem of efficiently simulating thermal noise and dynamic tracking errors in spread spectrum ranging receivers is addressed. A Gauss-Markov state space model is derived which simultaneously satisfies the conflicting requirements of high fidelity and fast-time operation. Initial validation results are presented.

Meta-image navigation augmenters for unmanned aircraft systems (MINA for UAS)

GPS is a critical sensor for Unmanned Aircraft Systems (UASs) due to its accuracy, global coverage and small hardware footprint, but is subject to denial due to signal blockage or RF interference. When GPS is unavailable, position, velocity and attitude (PVA) performance from other inertial and air data sensors is not sufficient, especially for small UASs. Recently, image-based navigation algorithms have been developed to address GPS outages for UASs, since most of these platforms already include a camera as standard equipage. Performing absolute navigation with real-time aerial images requires georeferenced data, either images or landmarks, as a reference. Georeferenced imagery is readily available today, but requires a large amount of storage, whereas collections of discrete landmarks are compact but must be generated by pre-processing. An alternative, compact source of georeferenced data having large coverage area is open source vector maps from which meta-objects can be extracted for matching against real-time acquired imagery. We have developed a novel, automated approach called MINA (Meta Image Navigation Augmenters), which is a synergy of machine-vision and machine-learning algorithms for map aided navigation. As opposed to existing image map matching algorithms, MINA utilizes publicly available open-source geo-referenced vector map data, such as OpenStreetMap, in conjunction with real-time optical imagery from an on-board, monocular camera to augment the UAS navigation computer when GPS is not available. The MINA approach has been experimentally validated with both actual flight data and flight simulation data and results are presented in the paper.

A low SWaP implementation of high integrity relative navigation for small UAS

Several aerial platforms rely on decimeter-level relative position accuracy for various applications including automatic takeoff and landing, precision targeting, and airborne refueling. For such applications, a Real Time Kinematic (RTK) GPS system provides a relatively low cost, robust, and reliable solution. Current commercial RTK products are inherently susceptible to jamming and spoofing. The Selective Availability Anti-Spoof Module (SAASM) implementations to date typically relied on relatively large and complicated architectures which would be difficult to port into a small (Groups 1-3) Unmanned Aircraft System (UAS) due to Size, Weight, and Power (SWaP) constraints. This paper describes the architecture, algorithms, and testing approach from Rockwell Collins high integrity relative navigation system including a SAASM-based RTK implementation for small UAS. A variant of the system was implemented for the Navys Small Tactical Unmanned Aircraft System (STUAS) program. The STUAS system performed its first successful ship-based launch and recoveries on the U.S.S. Mesa Verde using Rockwell Collins high integrity relative navigation system in February of 2013.

Analysis of dynamic response requirements for GNSS landing systems

An important issue in the development of future Global Navigation Satellite System (GNSS) Landing Systems (GLSs) is the dynamic response characteristics of GLS airborne equipment. To be compatible with existing airborne systems which use the Instrument Landing System (ILS), it is desirable for the dynamic properties of the GLS guidance signal to be equivalent to ILS. Specific concerns include dynamic tracking capability, frequency response characteristics, and sampled-data issues. This paper develops a methodology for modeling carrier-smoothed code GLS dynamic response characteristics. Comparing GLS characteristics with ILS requirements shows that not all ILS requirements can be met. However, a detailed autoland simulation evaluation of trade-offs in GLS dynamic response characteristics show that ILS-equivalent landing system performance can still be achieved.