Stand‐alone GPS receiver velocity algorithms and flight test results are presented. A dual‐frequency GPS receiver was subjected to aircraft dynamics of up to 1 g (9.8 m/s2), with aircraft bank angles of up to 45 deg. Velocity errors were determined for static and in‐flight conditions. In‐flight results were evaluated against a postprocessed, differential kinematic GPS solution and by an assessment of the velocity estimation residuals. Differences between the stand‐alone velocity solution and the postprocessed differential velocity solution were found to be at the 2–4 mm/s level (1 s̀) for horizontal velocity components and 9.7 mm/s (1 s̀) for vertical velocity. Since these differences include noise contributions from three GPS receivers, stand‐alone velocity errors are expected to be smaller than the results reported here. This is also indicated by the stand‐alone velocity residual biases, which were found to be on the order of 0.1 mm/s or less, while residual standard deviations ranged from 0.8 to 3.2 mm/s.

The paper describes a fully autonomous relative navigation solution for urban environments (indoor and outdoor). The navigation solution is derived by combining measurements from a two‐dimensional (2D) laser scanner with measurements from inertial sensors. This derivation relies on the availability of structures (lines and surfaces) within the scan range (80 m depth, typically). Navigation herein is performed in completely unknown environments. No map information is assumed to be available a priori. Indoor and outdoor live data test results are used to demonstrate performance characteristics of the laser/inertial integrated navigation. Relative positioning at the cm‐level is demonstrated for indoor scenarios where well‐defined features and good feature geometry are available. Test data from challenging urban environments show position errors at the meter‐level after approximately 200 m of travel (between 0.6% and 0.8% of distance traveled).

GPS P-Code has a higher chipping rate, better accuracy, and anti-jamming property than C/A code. Traditionally, GPS P-Code acquisition depends on handover from C/A code. This potentially needs long acquisition time. Moreover, when C/A code is not available, it is no longer possible to acquire GPS P-Code through handover from C/A code. The purpose of this paper is to describe a new overlap average method to facilitate hardware design of fast direct P-Code acquisition. It allows the rapid code phase search to acquire GPS P-Code signals, and also decreases the hardware resource requirement. The small size FFT in the proposed methods is very promising for fast FPGA hardware system design using FFT cores. The simulation results and theoretical analysis are included demonstrating the overall performance of the proposed method.

SUMMARYAttitude and heading determination using GPS interferometry is a well-understood concept. However, efforts have been concentrated mainly in the development of robust algorithms and applications for low dynamic, rigid platforms (e.g. shipboard). This paper presents results of what is believed by the authors to be the first realtime flight test of a GPS attitude and heading determination system. The system is installed in Ohio University's Douglas DC-3 research aircraft. Signals from four antennas are processed by an Ashtech 3DF 24-channel GPS receiver. Data from the receiver are sent to a microcomputer for storage and further computations. Attitude and heading data are sent to a second computer for display on a software generated artificial horizon. Demoinstration of this technique proves its candidacy for augmentation of aircraft state estimation for flight control and navigation as well as for numerous other applications.

[1] The second-order ionosphere error in GPS range measurements is determined by the electron densities and the geomagnetic field projection onto the GPS signal propagation direction along the GPS signal propagation path. It can be a delay or an advancement error. This paper presents the second-order error analysis based on an extensive collection of electron density profiles measured by the Arecibo incoherent scatter radar and geomagnetic field vectors generated using the International Geomagnetic Reference Field model. The results indicate that the 56-500 km altitude range contributes a maximum of À1.1 cm for GPS L1 signals arriving from the zenith at Arecibo. For signals coming from the north and south at 10 degree elevation angles, the maximum errors are 0.9 cm and À3.4 cm, respectively. The maximum of the mean values of the second-order error computed using the entire data set are À0.55 cm, 0.48 cm, and À1.74 cm for a signal arriving from the zenith, from the north at 10 degrees elevation, and from the south at 10 degrees elevation, respectively. The paper also discusses the diurnal patterns and geomagnetic activity dependency of the second-order error. Finally, the International Reference Ionosphere model is used to obtain an upper bound estimation of error contributions from the 500-2000 km altitude range.Citation: Morton, Y. T., Q. Zhou, and F. van Graas (2009), Assessment of second-order ionosphere error in GPS range observables using Arecibo incoherent scatter radar measurements, Radio Sci., 44, RS1002,