GPS World - September 2007 - (Page 58)
MILITARY & GOVERNMENT | Warfighter ther tie the system design together. This spiral engineering process, shown in the opening graphic, is designed to accelerate development, reduce government costs, and enable rapid analysis. JPALS, and so on; Reduce the number of satellites required for an accurate PNT solution; Investigate antenna electronics and micropower (fuel cell) integrations. Goals The operational goal is to develop a highly resilient positioning, navigation, and timing system that takes advantage of a CSAC in an integrated configuration. This can be applied to human assets, networks, and other platforms as necessary. The goals are: Improve jamming resistance, integrity monitoring, anti-spoofing, fault detection; Direct Y-code and M-code acquisitions through precise-time aiding; Accelerate reacquisitions, especially within challenging environments; Modify Kalman filter architecture with precise time aiding: add particle filtering; Improve vertical accuracy for coupled beam-forming antenna integrations, Battlespace Benefits Development of the Nugget allows warfighters and warfighting platforms to navigate in waters and terrains that can be unattainable with current standalone GPS receivers. It allows warfighters to navigate with fewer interruptions and faster reacquisitions when GPS signal degradations occur. Further, the Nugget’s precise-time feature enables battlefield synchronization for communication systems and networks. In future platform integrations, the Nugget’s ubiquitous positioning, navigation, and timing sensor suite will enable netcentric synchronization for command, control, communications, computers, intelligence, surveillance and reconnaissance (C4ISR) systems. RANDY ROLLO, project manager (right), and senior engineer Matt Nicholson sit behind the chip-scale atomic clock test fixture in SSC San Diego’s Central Engineering Activity Laboratory. The bifurcated approach to spiral engineering of the Nugget, developed with MEMS technology, satisfies the size, weight and power requirements of unmanned vehicles and dismounted soldiers. Manufacturers The new CSAC being characterized by CEA comes from Symmetricom Corp. The field programmable gate array receiver testbed comes from Xilinx. RANDY ROLLO is Navigation Nugget project manager in the Global Positioning System and Navigation Systems Division of SSC San Diego. What It Means If I have a tiny (cubic centimeter) atomic clock in my GPS receiver and it is synchronized with the atomic clocks on orbit, so we are both BY DON JEWELL using the same timing reference, I have eliminated one of the major equations my on-board computer has to process and I can accomplish things like: Significantly decrease my TTFF . Significantly decrease position error for time and altitude with fewer satellites in view. Significantly increase my anti-jamming and anti-spoofing capability. More accurately synchronize with the RF communications signal from the satellite (which are really low in signal strength) and with augmentation systems. Significantly decrease GPS reacquisition time when the signal is lost under a jungle canopy, in a building, underground, or in a jamming or interference environment. 58 GPS World | September 2007 Add the capability to have my GPS transceiver become part of a communications network: I’m now a network resource and am connected to a network. A bit more here about the network. If you have a GPS with a CSAC and all its inherent advantages, but those around you don't, but you are connected to a network, then you can broadcast your corrections and more precise time to others on that network and everyone can benefit — another benefit of having a GPS transceiver versus just a GPS receiver. There are many more advantages, but they get to be a bit esoteric and beyond my capability to explain adequately here. You can buy an atomic clock the size of a pack of cards, but it is prohibitively expensive; or you can buy an extremely accurate quartz oscillator on a card, again about the size of a deck of cards, from Trimble that supplies 1x10-11 for several hours. While small, it is large for what I call the Perfect Handheld GPS Transceiver (PHGPST), but not too large for some surveying equipment or the equipment many telcos and businesses use today. Will it get smaller? I think and hope so. The CSAC has come about only because of years of intensive research primarily by U.S. government research laboratories and because of dedicated individuals like Randy Rollo at SPAWAR. But there has also been a significant commercial research component — companies, for example, like Symmetricom, which has successfully competed in this timing arena and been awarded sponsorship over the years by DARPA. The folks at SPAWAR actually have a CSAC working in a GPS receiver and I hope to see that one of these days soon and report on that specifically. But in the real world, SPAWAR, NIST, and DARPA will not manufacture CSAC in the quantities necessary for commercial production, so it will be companies like Symmetricom that produce the CASC that we will, hopefully, see in our PHGPST one day. The bottom line is: when it comes to GPS, time and size matter. www.gpsworld.com
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