Inside GNSS Media & Research

JUL-AUG 2018

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Page 18 of 59 J U L Y / A U G U S T 2 0 1 8 InsideGNSS 19 ther canned or real-time mode with an in- tercard carrier-phase with minimal error. The simulator can generate a GNSS solu- tion and up to four coherent jamming sig- nals (i.e., CW, pulsed CW, swept CW FM noise and pulsed FM noise) per frequency band (i.e., L1 + L2) for each CRPA antenna element (up to seven), which are referenced to the phase center of the antenna. Further, the simulator contains up to seven complete GPS L1/L2 output ele- ments that can be individually delayed. In total, the simulator can produce up to 32 complete GPS channels (16 for L1 and 16 for L2) and up to eight jammer waveform types (four for L1 and four for L2) per fre- quency, per antenna element (up to seven) for a total of 224 GPS channels and 56 jammer channels. The RF to each antenna element is then offset from the antenna's phase center by a lever arm correction. Through simulator system synchronization, the GPS signals and the jamming signals for each antenna element are coherent (in-phase) with each other, creating a GPS/jamming signal waveform that is seen by the CRPA anten- na. The GPS/jammer waveforms are gen- erated separately for each CRPA antenna element thus ensuring a coherent solution. BEYOND THE WAVEFORM Besides tailoring a coherent waveform, the multi-output wavefront simulator includes options for simulating potential conditions and customizing CRPA antenna patterns. Within the CAST 5000, the operator can model each CRPA element separately and support either 2-D or 3-D antenna gain patterns. The type of pattern used is both selectable and modifiable. As well, antenna gain pattern entry is an interac- tive process that allows the user to define an independent azimuth gain, elevation gain and phase. The simulator allows the user to specify up to 99 antenna gain models per scenario. The CAST 5000 also supports a vehicle silhouette (antenna shading due to vehicle structure) function that lets the user inter- actively define shadows from vehicle com- ponents (e.g. tailfins, wings) in individual five-degree points about the vehicle body. WITHIN THE RAIM RANGE The CAST 5000 is also equipped to simu- late all types of receiver autonomous in- tegrity monitor (RAIM) events (i.e., range step, drift and noise) to evaluate the integ- rity of the GPS signals. In the case of a range step event, the simulator adjusts the pseudorange of the designated satellite by the defined range step at the designated simulation time and for all subsequent pseudorange values for the designated satellite until another RAIM range step event is executed. In addition to adjusting the satellite pseudo- range by the designated range step, the sat- ellite pseudorange rate will be adjusted by the range step size divided by the update period of the signal simulator—ensuring a smooth transition to the new pseudorange. For a range drift event, the simulator adjusts the pseudorange and pseudorange rate of the designated satellite to the drift rate starting at the designated event time and continuing for the defined event peri- od. Once the final pseudorange (resulting from the range drift) has been achieved, the simulator will make a total range ad- justment to all subsequent pseudoranges for the satellite until another RAIM event occurs. Note, a range drift event will only result in changes to the pseudorange and pseudorange rate of the designated satellite. Similarly, for a range noise event, the simulator adjusts the pseudorange and pseudorange rate of the designated sat- ellite by a random rate change at every simulator update cycle for a defined noise period. As each pseudorange rate change is computed, the pseudorange for the period is adjusted for the rate change. When all pseudorange rate adjustments have been made, the final pseudorange adjustment is made to all subsequent pseudoranges until another RAIM event occurs. Range noise will be computed at random times, with user entered magnitudes, and at a fixed noise rate (0.01 meters/second). When the operator has completed and confirmed RAIM event entry in the simu- lation, the event is placed and sorted in the RAIM conditions list for time and satellite PRN number order. AN END-TO-END SIMULATION The customizable CA ST 5000 GPS Wavefront Generator can tailor each er- ror source to a simulation as required. Since the RF cable plugs directly into the antenna electronics, the operator can test the equations that are driving the antenna electronics. And of course, the CAST 5000 is designed to recreate anomalies, allowing repeatable play back to help understand and solve a problem. The CAST 5000 simulator is ideal for aircraft integrators, avionic manufactur- ers, navigator manufacturers who build embedded INS/GPS (EGI) systems. The simulator lets operators test individual receivers, embedded GNSS/INS (EGI) and combined EGIs w ith additional equipment—or an entire system. From a CRPA-equipped helicopter with dual EGI to a UAV with a CRPA antenna, the CAST 5000 GPS Wavefront Generator is built to test the interference boundaries of your CRPA-equipped GNSS receiver. ◆ About CAST Navigation As GNSS/INS simulation specialists, CAST Navigation is one of the leading innovators in GNSS/INS simulation in the world. Its carefully-designed navigation simulators are honed by engineers into powerfully accurate aviation testing tools, EGI integration tools, EGI diagnostic tools, EGI support equipment, JDAM testing and more. The company offers full-service training, upgrade, maintenance and repair services to help you make the most of our technology.

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