CAST Navigation: Signal Diversity and the PHGPST

May 8, 2012  - By

As loyal readers are aware, I have long been an advocate of signal diversity as a solution to many of the ills that plague the GPS user, especially outdated user equipment. Signal diversity potentially provides users with more signals and signal origins. More signals improve availability, the number-one user criteria by a huge margin, and serve as a defense against jamming and spoofing. Signal diversity also provides security and integrity, resulting in accurate and reliable GPS-derived data.

For users to take full advantage of signal diversity, they must have the best software-defined user equipment available. And the best equipment, if it were available today, would be the PHGPST or Perfect Handheld GPS Transceiver, which has so often been a popular topic of discussion over the last several years. I cannot count the thousands of letters and emails from warfighters, first responders, and civil users who immediately see the value of software-defined receivers and want to know where to purchase the PHGPST. For now, some early GPS software-defined user equipment does exist, but to reach the goal of the PHGPST, receiver manufacturers must first be able to accurately and reliably simulate/generate all the diverse PNT (position, navigation and timing) signals available, which include some signals not ordinarily categorized as PNT signals today. Certainly not an easy task; however, there is hope. Recently, I heard about a small GNSS/INS simulation company that may be paving the way to the PHGPST — CAST Navigation in Tewksbury, Massachusetts.

CAST Navigation

CAST Navigation, which qualifies under current federal acquisition guidelines as a small company, bills itself as, and my military contacts confirm that they are indeed, a leading provider of GPS signal simulators, as well as a company that supports navigation system research, development, integration and testing at commercial and military laboratories worldwide. CAST develops cutting-edge GNSS/INS simulation systems with an expert staff that provides their customers with the latest technology and knowledgeable, experience-driven support.

Tough Industry

Those of you who are real GPS techies should not have to think very hard to call up the names of at least three GPS–PNT signal simulation companies that have gone belly-up in the past five to ten years, and some of those memories are just plain painful for the U.S. military and industry alike. This can really be a tough business.

According to Susan Gove, vice president of CAST Navigation, “…the signal simulation field is certainly not an easy business and it is extremely competitive, but we have been around for a long time and are doing well,” which is exactly why a company like CAST Navigation — which has survived and grown for the last 25+ years with an outstanding track record — is of such interest when it comes to PNT signal diversity and the PHGPST.

Add the fact that recent Information Assurance (IA) and cyber security requirements have just made the GNSS business tougher for all concerned and a reliable, professional, flexible GNSS/INS signal simulation company becomes critically important to the industry as a whole. According to John Clark, VP for Engineering at CAST Navigation, “…our scenario-based software simulations, which include jamming, interference, multipath signals and spoofing allow for simultaneous and multiple scenarios — indeed, almost any battlefield signal perturbation the user needs to simulate is doable with our hardware and software. In fact, we routinely help our customers tailor scenarios for specific needs, and our customer feedback mechanism tells us our customers are extremely happy and productive with CAST Navigation’s scenario-driven software capabilities.”

cast_1000-W . Credit: Cast
The CAST-1000 GPS Simulation System.

Signal Diversity

A major requirement for signal diverse solutions to GNSS issues — to include jamming, unintentional interference and high masking angles — is the right antenna. Conventional wisdom says the right antenna is a Controlled Radiation Pattern Antenna or CRPA. Ideally, the right CRPA will eventually be capable of receiving all space-based PNT and SBAS signals (GPS, GLONASS, Galileo, Beidou, WAAS, EGNOS etc.) as well as ground-based cellular and LF (low frequency) and/or eLORAN signals. The CAST-5000 Wavefront simulator allows companies and the military to perform a full end-to-end test of a platform’s CRPA, the antenna electronics, and the GPS receiver before that receiver is ever deployed to the field. So it is a must-have capability for the truly signal diverse GPS receiver manufacturer. But to be honest, GPS signals are still key; they are still the gold standard for PNT. I am not aware of any GLONASS-only receivers on the market today, nor am I aware of any Galileo-only receivers being planned. GPS is the key component for available, reliable, and accurate PNT data.

Recently at the Munich Satellite Summit, all the European receiver manufacturers were touting GPS receivers with the Galileo/GLONASS option. Even if the marketing brochures list Galileo or GLONASS first in the name, a little probing makes it obvious that the primary baseline PNT system is GPS with augmentations. So although signal diversity is the goal and more and more systems are, to some extent, signal diverse or signal-diverse capable today, the reality is that GPS is still the Gold Standard. If we are ever to truly enjoy signal diversity and all the associated benefits, PNT signal generators and simulators will be a key developmental tool. To that end and with affordability in mind, CAST Navigation has the capability or is in the process of developing simulations for many of the diverse signals mentioned to include SAASM signals for the U.S. military and our allies.

Simulations and Predictions

For the past several years the DoD and several government agencies have made good use of a very functional PDOP (positional dilution of precision) prediction algorithm and tool named GIANT. General Dynamics originally developed the GIANT program under contract to the U.S. government. Currently, GIANT is being enhanced primarily by LINDQUIST, with the help of select government agencies; with the recent integration of Google Maps, GIANT is proving to be a very useful tool for the warfighter and first responder. Amazingly CAST Navigation has a very similar product that is available for all users to include the U.S. military. The CAST product is called TOP or Terrain Obscuration Program. Like GIANT it provides a real-time determination of satellite visibility based upon the terrain (presented in a 3-D visualization) surrounding the actual position or predicted position of specific GPS receivers, fixed or mobile.

TOP170map . Credit: Cast
(Click to enlarge.)

While this concept sounds a bit academic at first, when you see it in action and talk to warfighters and planners who have benefited from GIANT first hand, it is clearly a mission-success parameter as well as a life-saving capability. For years GIANT was purely a flat Earth planning tool, and while it was useful, the addition of real-time processing, Google Maps, and DTED data have made both GIANT and TOP incredibly useful programs. Both programs help ensure GPS user equipment, applications, and weapon systems are more accurate, since signal availability is now predictable. The first time I saw the new GIANT tool in action, it literally took my breath away, and now that capability is available for everyone with the TOP product from CAST Navigation. Knowing first-hand what both GIANT and TOP are capable of for warfighters and first responders, I cannot now imagine a government, commercial, or civil planner, who must utilize or install GPS equipment or systems that depend on GPS capabilities, that would not benefit from these groundbreaking programs. In a natural or urban canyon situation, with high masking angles, installing GPS receivers or antennas with the greatest visibility would be pure guesswork without a program like TOP that guides planners and installation engineers with real-time data extrapolating optimal PNT reception locations, both fixed and mobile, over time.

sgx_high-W . Credit: Cast


Combine the capability of GIANT or TOP with a portable or handheld GPS signal generator/simulator, such as the new handheld CAST SGX, and users are able to accurately characterize and predict the effects of area terrain and masking angles on any GPS receiver prior to actually venturing into the field. Users are able to determine which receivers will function optimally and produce the most reliable results in any physically constrained or sky-challenged environment. For both government and civil users, the fidelity of TOP and GIANT are a direct function of and only constrained by the Digital Terrain Element Data (DTED) access authorized for specific users.

The CAST SGX (signal simulator/generator) is a GPS signal device housed in a portable lightweight handheld enclosure. In other words, it is a portable handheld GPS signal device at home in the laboratory, running on house current, or in the field running on long-life batteries. Regardless of the power source, the CAST SGX is capable of generating GPS L1 signals (with P-Code options) of up to 16 GPS satellites, which are more than most users would normally have in view at any one time.

The CAST SGX is an important new development in GPS signal simulation and generation. Historically GPS signal simulators/generators have been huge, heavy and complicated pieces of laboratory equipment requiring a Ph.D. to run properly, and users were tied down to evaluating GPS receivers only where the unwieldy GPS signal simulator/generator was located. Now with the portable CAST SGX, the signal generator can go where the receivers are located and real-world data can be collected in real time. The scenarios the SBAS (satellite based augmentation system) capable SGX have made available are extraordinary, and I have purposefully not speculated on the military possibilities as those speculations become classified in a hurry. But just allow your imagination to wander a bit and you will see what I mean.

SGX Software

The optional CAST-XGen Plus software, which I have not had a chance to personally test but hope to in the near future, has the capability to integrate with Google Maps and reportedly gives the user the ability to generate advanced customized scenarios for use with the SGX device. The software allows for complete control over atmospheric effects, the GPS almanac, ephemeris and all satellite error sources to include masking angles and multipath. So you don’t actually have to take the SGX device out into the field, but the great part is now you can. Ruminate on that for awhile and the possibilities appear endless.

According to Susan Gove, the handheld SGX is proving to be a huge success, and the SGX along with CAST Navigation software products will be available at the ION 2012 Joint Navigation Conference
 (ION JNC) June 12-15, at the Crowne Plaza Hotel in Colorado Springs, Colorado. Be sure to stop by and take a look at this amazing new product.

Bottom Line

I am impressed by what I have learned about CAST Navigation. They are a small, agile, innovative GNSS/INS simulation company that has brought much needed portability and availability of GPS signals and simulation to operators, planners, and system designers worldwide. CAST Navigation hopefully has a bright future and may well play a key role in the future of the availability and integrity of GPS signals for users globally. They may also help blaze the path to the PHGPST. Check them out at ION JNC.

Until next time, happy navigating.


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About the Author: Don Jewell

Don Jewell served 30 years in the United States Air Force, as an aviator and a space subject-matter expert. Don’s involvement with GPS and other critical space systems began with their inception, either as a test system evaluator or user. He served two command assignments at Schriever AFB, the home of GPS, and retired as Deputy Chief Scientist for Air Force Space Command. Don also served as a Politico Military Affairs Officer during the Reagan administration, working with 32 foreign embassies and serving as a Foreign Disclosure Officer making critical export control decisions concerning sophisticated military hardware and software. After retiring from the USAF, Don served seven years as the senior space marketer and subject-matter expert for two of the largest government contractors dealing in space software and hardware. Don currently serves on two independent GPS review teams he helped found, and on three independent assessment teams at the Institute for Defense Analyses, dealing with critical issues for the U.S. government. Don has served on numerous Air Force and Defense Scientific Advisory Boards. He writes and speaks extensively on technical issues concerning the U.S. government. Don earned his Bachelor’s degree and MBA; the Ph.D. is in progress.