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Advanced GPS Hybrid Simulator (AGHS)

The AGHS is a hybrid software, digital and radio frequency (RF) GPS simulator design. The AGHS architecture leverages NAVSYS’ Digital Storage Receiver (DSR) data recorder and remodulator capability to allow record and playback of real-world GPS signals from field tests. The hybrid simulator can also be used to generate simulated digital signal sets using profiles generated by NAVSYS’ MATLAB Signal Simulation capability. The recorded signals can either be played back as an RF signal into GPS receivers under test or can be directly played back as a digital signal into a compatible digital GPS receiver, such as the NAVSYS HAGR product. Data can be recorded and played back from either a single antenna element or from an array of antenna elements. This allows both the signal characteristics and the signal wavefront to be preserved in a test environment.

The AGHS is available on a lease basis only. For terms and conditions, please contact Debbie Westra.

The AGHS architecture is illustrated at right, with a description of the key components below.

Advanced GPS Hybrid Simulator
AGHS Architecture
AGHS Architecture

Key components

Digital Storage Receiver: DSR-220
A key component of the AGHS is the Digital Storage Receiver (DSR). NAVSYS' latest generation DSR product has the capability of storing the complete GPS spectrum (20 MHz) with up to 12-bit resolution. The DSR-220 in one of its configurations can record up to 3 hours of 8-bit L1 and 8-bit L2 at 56 Msps input data. Up to 3 hours of single bit data from 16 L1 antenna elements at 56 Msps can be recorded. The block diagram shows the way the DSR is utilized for system development and test.

RF Remodulator
The RF remodulator card provides the capability to remodulate the digital GPS data onto an RF carrier for playback into a conventional GPS receiver. The remodulator card includes eight channels to allow simultaneous playback into multiple antenna elements. By configuring the AGHS with two cards, both L1 and L2 remodulation can be performed. The RF remodulation capability allows the AGHS to operate as a wavefront simulator playing back either pre-recorded GPS signals or digitally simulated signal profiles.

MATLAB Signal Simulation Generation
The AGHS uses MATLAB as the primary user interface for generating simulated GPS profiles to drive AGHS. The inputs for the GPS profile can be entered either as a sequence of waypoints from which a trajectory is interpolated and satellite range and Doppler is computed using the specified satellite ephemeris, or as an option, the raw satellite measurements can be provided instead. User inputs spreading code, signal strength, jamming, etc., are input. The satellite to be simulated can be specified by loading an almanac or ephemeris GPS file. The AGHS MATLAB tools will compute the visible satellites throughout the trajectory; generate the estimated range, carrier phase and Doppler observations; and generate a navigation data file for modulation on the simulated signals. The AGHS will also compute the spatial offsets for an antenna array (if specified) based on the user trajectory and the simulated satellite locations. The simulation files that are used by the AGHS can also be generated from recorded DSR flights or from a flight simulator, such as the Microsoft flight program that uses a joystick as input.

MathWorks Simulink Control
The primary interface to the AGHS is the MathWorks Simulink. The graphical inteface of Simulink has proven to be of great value in the control of the simulation being performed. NAVSYS is developing a user interface for our AGHS and High-gain Advanced GPS Receiver (HAGR) products with the MathWorks Simulink tool. Simulink is a platform for multidomain simulation and model-based design of dynamic systems. It provides an interactive graphical environment and a customizable set of block libraries that let you accurately design, simulate, implement and test control, signal processing, communications and other time-varying systems. We are using the Simulink interface to control and set up our AGHS products and to control the GPS receiver under test.

Simulink interface
Simulink Interface
Advanced features
  • INS and IMU simulation
  • GPS wavefront simulation
  • Jammer wavefront simulation
  • Integrity failure simulation
  • RAIM failure simulation
  • Satellite failure simulation
  • Digital outputs to support software GPS receivers
  • Open architecture to allow user access for low level simulation customization
  • Sofware interface for insertion of future GPS signals or simulated jammer waveforms onto composite digital satellite signal profile
  • The AGHS is flexible and designed for research into new GPS innovations

Related information


High-gain Advanced GPS Receiver (HAGR). The HAGR provides a fully functional, modular, GPS digital receiver architecture that is compatible with the AGHS digital signal generation interfaces. In addition to performing the core GPS tracking and navigation functions, the HAGR also can be configured to perform digital beam steering for enhanced GPS signal tracking performance. The AGHS digital data from one or more antenna elements can be played back into the HAGR for real-time or post-test analysis. This allows the same data to be replayed using different HAGR configurations, including alternative tracking loop implementations, or using different spatial processing. The HAGR can be configured to operate using preprogrammed weights to allow test and evaluation of alternative spatial processing algorithms using the same test data set.

GPS Signal Simulation Toolbox. This MATLAB toolbox includes functions to generate simulated GPS signal scenarios and also tools to emulate the GPS tracking and navigation capability performed in a GPS receiver. This can be used to create software simulated data files for downloading to the DSR and playback through the AGHS, or for tracking and analyzing in MATLAB recorded DSR files either from live satellite tests or prerecorded digital scenarios.



An Integrated Software Defined Radio Navigation System for Space.
Proceedings of ION GNSS 2007, Ft. Worth, TX, Sept. 2007 (PDF: 760k)


Constrained Beamforming for Space GPS Navigation.
Proceedings of ION GNSS 2007, Ft. Worth, TX, Sept. 2007 (PDF: 200k)


GPS/INS/Star Tracker Navigation Using a Software Defined Radio
Proceedings of 29th Annual AAS Guidance and Control Conference, Beckenridge, CO, Feb. 2007 (PDF: 525k)


Testing of Ultra-Tightly-Coupled GPS Operation Using a Precision GPS/Inertial Simulator.
Proceedings of ION GNSS 2005, Long Beach, CA, Sept. 2005 (PDF: 524 KB)


Architecture and Performance Testing of a Software GPS Receiver for Space-based Applications.
Proceedings of IEEEAC, Big Sky, MT, Mar. 2004 (PDF: 797 KB)


Advanced GPS Hybrid Simulator Architecture.
Proceedings of ION 57th Annual Meeting 2001, Albuquerque, NM, June 2001 (PDF: 475 KB)


Modeling and Simulation of GPS Using Software Signal Generation and Digital Signal Reconstruction
Proceedings of ION Technical Meeting, Anaheim, CA, Jan. 2000 (PDF: 162 KB)


Digital Storage Receivers for Enhanced Signal Processing.
Proceedings of the ION GPS ‘99, Nashville, TN, Sept. 1999 (PDF: 252 KB)

Brochure Advanced GPS Hybrid Simulator (AGHS) (PDF: 167 KB)
Debbie Westra
toll free: 866.4.NAVSYS (866.462.8797)
or 719.481.4289

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