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Session C3: Military PNT User Equipment Advances

Interfacing External Sensors to GPS/GNSS enabled Inertial Navigation Systems
Paul E. Myers, Orolia Defense and Security
Location: Ballroom C
Date/Time: Tuesday, Jun. 13, 8:55 a.m.

Integrated GPS/GNSS enabled Inertial Navigation Systems INS are designed to provide accurate positioning, attitude, and orientation measurements. These INS are used in manned and unmanned vehicles. These integrated Position, Navigation and Timing (PNT) systems utilize a variety of sensors such as commercial GPS/GNSS receivers, M-Code GPS receivers, Inertial Management Units (IMUs), Barometers, compass/magnetometers, odometers, or wheel-tick sensors to determine position and orientation and compensate for GPS/GNSS denied environments. However, most of these products are highly integrated into a single product or device.
This session discusses interfacing GPS/GNSS enabled Inertial Navigation Systems to external sensors. The future is distributed. Networking, the need to allow cost-effective technology upgrades and more open and collaborative standards like Victory are driving system integrators and INS vendors to open their interfaces and architectures to interface to devices outside their box.
In this session we share our experiences of how Orolia Defense and Security has integrated external sensors to our VersaPNT to provide Resilient Position, Navigation, and Timing. There are different ways to integrate external sensors. In our cases considered, we use ethernet networking or accessing external sensors using our VersaPNT’s Pin Matrix which provides access to RS-232 Serial, RS-422 Serial, RS-485 Serial, and General-Purpose Input and Output pins and Pulse Per Second Input/Output pins.
We first describe how we integrated a Wheel-Tick Sensor using our Pin-Matrix General Purpose Input pins to measure pulses from Hall-Effect Sensors. This vehicle sensor is monitored by means of a FPGA logic which counts the pulses from the Hall-Effect Sensors using the duty cycle to determine forward or backward motion. A software application is used to convert counts to rotations and rotations to distance forward or backward.
The next sensor integration described is interfacing to an external IMU. External IMUs are integrated using serial interfaces or ethernet. The benefits of an External IMU are more accurate IMU technologies than small formfactor MEMs IMUs can be used in navigation engine filter solutions.
A serial bi-directional protocol is used when both configuring the IMU and reading data is required. Otherwise only a receive serial port and any required control signals to the IMU are used. Some External IMUs provide input and/or output synchronization pulses to allow the IMU Output messages to be synchronously polled. When integrating an external sensor such as IMU considerations of the Lever Arm and Orientation in your design is an important consideration.
Integrating external sensors over ethernet is demonstrated by means of hardware-in-the-loop testing of a VersaPNT using a BroadSim Solo simulator. The BroadSim Solo is used to provide GPS/GNSS RF Simulation input to the GPS/GNSS receiver in the VersaPNT and at the same time to generate simulated IMU messages over ethernet. These simulated Ethernet IMU messages are received and input into the VersaPNT’s Navigation Engine filter.
Use of an external Inertial Navigation System (INS) to determine the navigation and attitude solution rather than use the VersaPNT’s internal navigation engine is considered. These external INS require information from the VersaPNT’s GPS/GNSS, or Military GPS receivers and possibly a synchronizing 1PPS signal and Date/Time. The VersaPNT is used to output proprietary, NMEA-0183, ICD-GPS-153C SAASM GPS or ICD-GPS-153D M-Code GPS messages as input to the external INS. The external INS navigation and attitude solution is provided as input to the VersaPNT software.
Finally, the integration of Victory into our VersaPNT software is discussed. Several Victory services are discussed, and the data required from the VersaPNT software is described.

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