High-fidelity model development for navigation warfare simulation studies

Simon N. Gouldsworthy, Paul D. Groves and Michael Wells

Abstract:	A software project is under development that models propagation of electromagnetic (EM) signals over terrain from Global Positioning System (GPS) jamming equipment and the capability and accuracy of simulated GPS and Inertial Navigation System (INS) equipment to form a navigation solution under the modelled conditions. The purpose of the software tool is to predict, in a static or dynamic environment, the likely navigation accuracy over a period of simulated time that would be possible given different combinations of navigation equipment and jammers. The EM propagation model performs diffraction calculations using modelled terrain profiles to determine the path loss that occurs when GPS jamming radiation propagates from a transmission point to a reception point. The propagation model takes into account radiation frequency, bandwidth, polarisation and waveform. Environmental factors such as refractivity profiles and clutter are included in the diffraction calculations to provide an accurate estimate of path loss. Obscuration of EM signals by the host platform body is modelled to a fidelity controlled by the user. Obscuration modelling applies to both GPS signal reception (if platform mounted) and to jamming signal transmission (if the jammer is platform mounted). Platform mounted receivers and jammers can undertake simulated, pre- determined flight trajectories where platform attitude, signal obscuration and antenna gain orientation are taken into account at discrete points in simulated time to calculate interference levels at the GPS receiver. Antenna gain patterns can be associated with GPS jammers and with the GPS reception system. The GPS reception system can be modelled as a simple Fixed Reception Pattern Antenna (FRPA) or as a Controlled Reception Pattern Antenna (CRPA) array with realistic geometry (eg array elements flush to curved surfaces) and with an associated modelled antenna control unit. For CRPA array modelling, a key aspect in predicting navigation performance under jamming is modelling the practical limitations on cancellation performance. The CRPA model employed is based on the digital architectures that will be used in the future and takes into account the limitations of the antenna array, the radio frequency (RF) conversion electronics, the analogue-to- digital (A/D) converters and the digital signal processing. The GPS constellation and propagation model takes a base set of orbital parameters for any number of satellites (ingested directly from System Effectiveness Model (SEM) or Yuma almanacs if desired) and performs calculations to predict satellite positions at any required point in time. Ionospheric propagation, tropospheric propagation, ephemeris and residual satellite clock errors are all modelled. The GPS receiver model comprises code and carrier correlator-discriminator models, code and carrier tracking control functions for up to 12 satellite signals and a receiver clock error model. The correlator-discriminator models account for the effects of interference and receiver noise. The tracking control function includes the capability to adapt the tracking loop bandwidths to the interference level. By comparing the pseudo-ranges and pseudo-range rates output by the receiver model with their truth counterparts, it is determined whether the receiver is correctly tracking code and carrier. An INS model comprising a low order navigation equations function and accelerometer and gyro error models has also been implemented. This is used to aid code tracking when carrier tracking is not available and to provide a guide to navigation accuracy when GPS tracking is lost.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	643 - 654
Cite this article:	Gouldsworthy, Simon N., Groves, Paul D., Wells, Michael, "High-fidelity model development for navigation warfare simulation studies," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 643-654.
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