2C or not 2C: An Important Signal Question

January 9, 2013  - By
Don Jewell

Don Jewell

With apologies to the Bard of Avon, as I paraphrase his prose, 2C or not 2C — that is the question for millions of GPS users and has been for several years. Indeed, over the past seven years hardly a week has gone by without an email or inquiry about the status of the GPS L2C signal.

The name “L2C” refers to the radio frequency used by the signal (1227 MHz, or L2) and the fact that it is for civilian use, but of course it will also be used by the military. There are also two military signals on the L2 frequency. In the past couple of months inquiries concerning L2C have become an almost everyday occurrence. Plus I have it on good authority that it was a topic of conversation at recent a PNT EXCOM or Executive Committee Meeting.

However, when I started making inquiries I was met with an interesting dichotomy. One group of users actually laughed and accused me of having a Don Quixote complex and tilting at windmills, since this debate has been continuing for over seven years, while other more sanguine user groups are seriously interested in the future of L2C. Here is what I discovered.

What is L2C?

According to the official U.S. government website concerning GPS, “L2C is the second civilian GPS signal, designed specifically to meet commercial needs. When combined with L1 C/A [ed. coarse acquisition] in a dual-frequency receiver, L2C enables ionospheric correction, a technique that boosts accuracy. Civilians with dual-frequency GPS receivers enjoy the same or better accuracy as the military. For professional users with existing dual-frequency operations, L2C delivers faster signal acquisition, enhanced reliability, and greater operating range. L2C broadcasts at a higher effective power than the legacy L1 C/A signal, making it easier to receive under trees and even indoors. The Commerce Department estimates L2C could generate $5.8 billion in economic productivity benefits through the year 2030. The first GPS IIR(M) satellite featuring L2C launched in 2005. Every GPS satellite fielded since then has included an L2C transmitter.”

Problems

So while this would appear to be a “no brainer” as it were, especially the $5.8 billion in economic benefits, it appears the Global Positioning System is actually at a crossroads and the decision makers are apparently on the horns of a dilemma. For some groups of users, the laudable global PNT (position, navigation and timing) gold standard is looking a bit tarnished of late but has an opportunity to shine once again. The question and future perception of GPS by many global users simply revolves around implementing full navigation messages on signals that are already in place, namely L2 and L5 with CNAV and M-code with MNAV. So, what’s the issue, you say? The signals are there, and in the case of L2C and M-code, have been for seven years — simply upload a full navigation message and be done with all the ambiguity that has become unwelcome baggage for these modern day signals. Au contraire, mon ami, if it were only that simple.

Now grant you this, should be a simple decision, but remember this is the U.S. government we are talking about — apropos failed budgets, endless continuing resolutions, health care fiascos, and the fiscal cliff — important but in the end actually simple decisions all. Unfortunately, history reflects when the U.S. government is involved, nothing is ever easy and timely decisions are hard to come by. So as not to confuse anyone, especially the players, let’s take this process one step at a time and see what all the fuss is about, shall we?

Problem Statement: The L2C and M-code signal capability has been on orbit for more than seven years, since 2005. In 2009, the 2SOPS began uploading and broadcasting a Message Type Zero on L2C, which, while not a navigation message, does put data on the channel. What users are now asking for is the full navigation message on L2C or CNAV, which is a modern-day navigation message and will have significant advantages for all users. Plus, the signal would be available to potentially more than 3 billion users versus the small subset today that utilizes the L2C carrier phase for RTK (real-time kinematic) operations. Indeed, when compared to the L1 C/A (coarse acquisition) signal, L2C has 2.7 dB greater data recovery (with a navigation message) and 0.7 dB greater carrier tracking.

The bottom line is that, with the addition of a valid and updated CNAV message on L2C, all users, the military included, would immediately have ten more potential navigation signals available, and that number would grow with each new GPS launch. Obviously, the same is true for military users with M-code and for all users with an L5 capability. However, the upgrade process needs to start somewhere, and L2C is the obvious choice since there are essentially no M-code receivers available today and there are approximately between 450,000-500,000 L2C capable receivers already in the hands of users.

Assets

Hardware – Simply put, there are currently 10 satellites (SVs) capable of broadcasting a full navigation message or CNAV message on the L2 signal and MNAV message on the M-code signal, also on L2 and three L5 CNAV capable SVs:

7 – IIRM SVs (does not include SVN-49 which, while capable, is currently in residual and/or test status).

3 – IIF SVs (same capabilities as the IIRMs and also capable of broadcasting an L5 signal with CNAV).

While the lack of L2C monitor stations has historically been used as a reason for not broadcasting the new CNAV navigation messages, today there are literally more than one hundred L2C- and L5-capable monitoring stations, which includes the NASA JPL (Jet Propulsion Laboratory) monitoring stations. Logs from several independent monitoring stations show that at any given time there are from one to three L2C SVs visible for the majority of global users, including our warfighters, who in the mountains of Afghanistan need all the signal availability we can provide.

Plus, of the estimated 450,000-500,000 fully capable L2C receivers, several thousand of those are in the hands of our warfighters. Trimble started building in the L2C and L5 CNAV capability as far back as 2003, a full two years before the first L2C launch, for users that wanted the option. However, that option has never been fully tested with live on-air CNAV coded transmissions and they need to be. More on testing later.

From a global user perspective, Japan has essentially leapfrogged the U.S., since the L2C and L5 signals with full CNAV messages are already being broadcast on the Japanese QZSS navigation satellite QZSS-1.

Software was initially thought to be an issue, but according to my sources, the current MNAV or M-code full navigation message is remarkably similar, as to be almost identical to the CNAV messages for L2C and L5, and MNAV has already been shown to work well on the ten GPS SVs capable of broadcasting the M-code signal. Granted, it is not fully integrated into the current OCS or operational control system known as AEP or Architecture Evolution Plan, but then not many future capabilities are, so this is really not an issue since manual processes abound in the current OCS. The L2C, L5 and M-code full navigation messages are supposedly still part of the plan for OCX or the future operational control system for GPS, which should be up and working sometime in early 2017. This would be twelve years after the L2C and M-code signal capability was first placed on orbit.

Timelines

Given those timelines, some would say, hey that’s only four years from now, maybe five if you count testing, and the full navigation message might actually be turned on. But, alas, rumors abound that there is a government agency apparently objecting to the immediate activation of L2C and L5. This agency, and it is not hard to ferret out exactly which one, wants extensive testing to ensure there will be no complications with the WAAS or Wide Area Augmentation System broadcasts, and as an alternative plan it proposes waiting until all the L5 satellites are on orbit before activating navigation messages on L2C or L5. Let’s do the math – that’s 24 L5 SVs, before the L2C and L5 PNT signals are activated with full navigation messages. At one launch per year, the current GPS launch rate, and it matters not whether it is a IIF or a III, and with three L5 SVs already on orbit, that effectively means we will see all 24 L5 SVs on orbit sometime in 2034, if indeed the II-F SVs are truly the first 30-year GPS SVs. If not, then it could be as late as 2037.  However, given the average life span of GPS SVs today, it is more than likely that by 2037 every single L2C, L5 and M-code capable satellite on orbit today will have been disposed of without ever having broadcast any of the new signals for which they were designed. Now, how’s that for a lachrymose plan?

Fortunately, this alternate long-term “plan’ has not a prayer of passing, dare I utter the words, the dreaded Washington Post test. Never having purposely written anything for the Washington Post, even though several of my articles have been quoted and misquoted there, it is still a force to be reckoned with in our nation’s capital, simply because the Washington Post continually asks the question, “Is this a wise use of taxpayer’s money?” The answer for the alternative GPS L2C and L5 plan is obvious.

Personnel and monetary issues are always mentioned in the context of new GPS capabilities; however, I have no doubts that the absolutely superb blue suit operators, tacticians and support contractors at 2SOPS are more than capable of performing the simple actions of uploading the new navigation messages on their own.

Sure, times are tough but the blue suit operators and their on-site support staff, at the 2SOPS, have proven themselves time and again to simply be the best in the business. They have brought GPS SVs back from the dead, they (with Braxton Technologies Software) maintain residual satellites that everyone thought for years was an impossible task, and they have saved SVs for important missions that everyone else thought should have been abandoned. We don’t give the fine men and women at Schriever AFB, the 50th Space Wing and the 2SOPS (2nd Space Operations Squadron) enough credit, and I am not about to sell them short. I am convinced the signals in question can be uploaded with full navigation messages, tested and made operational, even if only on a test basis, within six months without expensive outside help.

Full-Scale Testing

This brings us back to the full testing proposal, which actually makes a lot of sense. We (all users) need immediate full scale and extensive operational evaluations that confirm “we have it right” with the CNAV and MNAV data messages. We should encourage manufacturers to participate in this testing process to ensure their GPS devices meet specifications and are not flawed because of a misinterpretation of an interface specification. The GPS equipment manufacturers would be the first to embrace this approach. The manufacturers and users need open-air full-scale testing with valid CNAV messages being broadcast by numerous satellites to ensure they have coded the L2C, L5 and M-code receivers properly.

Immediate testing is the key here, because otherwise under one proposed plan we will only find out if there is a problem with full end-to-end testing of the L2C CNAV signal and user equipment 13 years after manufacturers began fielding the supposed and promised capability. Under the wait for L5 FOC (full operational capability) plan, we won’t find out if the implementation of specifications are correct for another 20-plus years. Personally, I find this to be unacceptable. We need to begin the immediate six-month test plan now. 

The aviation community has the mantra, “Test it as you fly it.”  We should not do any less.  A full six-month evaluation is absolutely appropriate and should be undertaken now. We cannot afford to repeat the 5.5C debacle. [ed. click to read more about 5.5C].

Users, of course, are the prime concern. If you or your organization, including the military, can benefit from 23 more navigation signals today (and three additional signals each year from now until 2034), one of them being the strongest GPS signal to ever be broadcast (L5 with CNAV), and you want/need those signals active now, then please let us know. You may email me at djewell@gpsworld.com.

Stand up and Be Heard

Although some of my comments have been a bit tongue-in-cheek, this is indeed your chance to be heard and to make a difference. Let there be no mistake: there is no other PNT system in existence today, planned or unplanned, on the drawing boards or on PowerPoint slides that approaches the capability, availability, reliability, longevity, accuracy and integrity of the Global Positioning System. The folks at Air Force Space Command have been and continue to be admirable stewards. We just need to let them go about their business without undue restrictions.

Dare to Compare

If you want to know exactly how the GPS compares to other PNT systems, consider that the Russian GLONASS (Globalnaya Navigatsionnaya Sputnikovaya Sistema), which came into existence in 1979 only one year after the first GPS launch, has only been Fully Mission Capable (FOC) as a global PNT system for about two years, and that dubious status is literally day-to-day as it teeters on that magic number of 24 available SVs broadcasting multiple PNT signals simultaneously. Contrast that to the GPS, which currently has 32 active SVs with several additional SVs in residual status. Three GPS SVs are nearing, have attained or will soon attain 20 years on orbit. One of our SVs has been on orbit for more than 22 years. GLONASS has serious problems merely attaining an average SV life of less than five years on orbit. Even the vaunted Chinese are experiencing serious technical, longevity and integrity issues with their multiple PNT constellations. It is just not as easy as it sounds. So yes, GPS is the global PNT gold standard, and its stewards must always strive to improve and lead the way. The GPS must continue to grow and innovate or risk being left behind. This is your chance to contribute to that leadership role. Let your opinion be heard.

Until next time Happy New Year, happy navigating, and keep those card, letters and emails coming.

 

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Don Jewell

About the Author:

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.

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