Tag: Survey Scene

2009 – The Year of the Other GNSS

Being December, it’s time for my look into next year. It’s become somewhat of a tradition for me and this year is no different. What does 2009 have in store for the GNSS user?

GPS will push forward in 2009 with the launch of the two remaining IIR-M satellites and launch of the first IIF satellite which will, incidentally, introduce a new civil frequency, L5, to the world. Those are very important milestones, but is it enough to grab the headline as the 2009 GNSS of the Year?

Nope.

It’s been a couple of years since I published a column titled “GLONASS — the Comeback Kid”.

Indeed, at that point the GLONASS program was building steam, albeit slowly. The problem was that although the Russian government was launching six satellites a year, there were still many legacy GLONASS satellites that were being decommissioned. The launch rate was barely keeping up with the rate of attrition. For this reason the GLONASS constellation has fluctuated between 10 and 14 operational satellites for many years. That is changing. In 2009, GLONASS will reach heights we’ve not experienced before.

With almost all of the legacy GLONASS satellites decommissioned and the Russians still launching new GLONASS satellites at a rate of six per year, it won’t be long before the GLONASS constellation starts to look really, really good. Currently, there are 17 operational GLONASS satellites and three more are scheduled to launch later this month on their annual Christmas Day present to the GNSS world. Assuming the Russians bring them online within 60 days or so after launch, you’ll have 20 GLONASS satellites at your disposal in the first quarter of 2009. There are still some adjustments forthcoming to the constellation due to legacy satellites, according to Sergey Revnivykh of the Russian Space Agency (RSA), so “18 satellites in January/February is nominal.” In other words, we’ll have 20 with a possibility of it dropping to 18.

Even with 17, the benefits are shining bright for RTK users. Nothing illustrates this better than a couple of plots using mission planning software (provided by Trimble Navigation free of charge via website). These plots are based on my location in Portland, OR USA using an elevation mask of 10 degrees.

Figure 1: Satellite visibility chart based on using GPS satellites only (plot date is Dec. 15, 2008).

 

Figure 2: Satellite visibility chart based on using GPS and GLONASS satellites (plot date is Dec. 15, 2008).

The evolution of GLONASS isn’t a complete surprise. GLONASS was declared operational in 1993, the same year as GPS. However, Russia’s political and economic struggles relegated GLONASS to the back burner and the program began a long, steady decline to a skeleton of what it once was. At its lowest point, in 2002, there were only eight operational satellites.

As Russia’s economic and political climate stabilized (some say that oil has contributed largely to the revitalization of GLONASS), Russia brought the GLONASS program back to the front burner in 2001 when it announced an ambitious plan to revitalize the program by 2010. The plan was to fly 30 GLONASS satellites by 2010.

As with many long-term plans, especially a multi-year, publicly financed plan to spend billions, the devil is in the details . . . and execution is the devil. Well, nearly eight years later, the Russians seem to have executed their plan quite well. It wasn’t an easy road with quick results, either. As I mentioned above, the attrition rate of GLONASS satellites was high most of this decade, so they had to be very aggressive in developing and launching new satellites just to keep their head above water.

This is not to say there haven’t been any problems along the way. I’ve heard several complaints from users of excessive RTK initialization times that were eventually traced back to troubled GLONASS satellite data. For example, a few months ago Topcon issued a Service Bulletin regarding “GLONASS Satellite 9.” The bulletin states that it is “not (currently) broadcasting a P2 signal. This may have an effect on RTK performance. It may cause the receiver to stay in float for a longer period of time.”

Looking Beyond 2009

I reported in 2007 that Russia was on the path to bringing GLONASS closer to GPS with respect to compatibility. Currently, GPS uses the CDMA (Code Division Multiple Access) signal-processing scheme while GLONASS uses the FDMA (Frequency Division Multiple Access) signal-processing scheme. They aren’t compatible at all . . . sort of like CDMA (Sprint) vs. GSM (AT&T) networks for mobile phones. They just don’t work together, so manufacturers essentially have to build two receivers (one for GPS and one for GLONASS) in one box. While it’s impressive that manufacturers have been able to squeeze such amazing functionality into small boxes, it’s a complicated design.

Russia has announced its commitment to support CDMA on the next generation of GLONASS satellites (GLONASS-K). While this will go a long way in making GPS/GLONASS receivers easier/cheaper to design/build, Russia and the U.S. are in discussions to even take it a step further towards interoperability with GPS L5 and the future L1C signal. However, keep in mind the space business works at a different pace than most businesses. It will be well into the next decade before we see any GLONASS satellites broadcasting CDMA signals.

GLONASS funding is also looking pretty solid at this point. Last September, it was announced that Russian Prime Minister Vladimir Putin signed a budget directive allocating 67 billion rubles (US $2.6 billion) to further develop GLONASS with the majority being steered towards adding satellites. Compare that with the GLONASS budget in 2007 being 9.9 billion rubles ($418.25 million) and 4.7 billion rubles ($200 million) in 2006.

Congratulations

Because of GLONASS’s exceptional value to the survey/construction user community in 2009, GLONASS has indeed earned my vote as GPS World magazine’s award of 2009 GNSS of the Year. Remember, the purpose of this particular column is to look forward into the future instead of a year in review. I believe that in 2009 GLONASS will add even greater value to the survey/construction user than we have ever seen.

The GNSS Election ’08: a Victory for the Surveyor

At the annual ION GNSS conference in Savannah, Georgia, in September, GPS World magazine hosted its third annual Leadership Dinner. Many of the world’s leading GNSS experts attend this dinner. Those experts include research scientists, professors from renowned universities, and heads of companies, as well as influential government representatives and GNSS consultants.

Earlier this year, Alan Cameron, GPS World editor in chief, was mulling ideas for the theme of this year’s GPS World Leadership Dinner. He said he’d like to dovetail off of this year’s U.S. presidential election. I threw some ideas at him, as did other editors and associates.

Richard Langley, University of New Brunswick GNSS guru and GPS World Innovation column editor, had this great idea of a two-party system for the 2008 GNSS Election. Thus, the Satellites Party (Blue) and the Signals Party (Red) were born.
In the election planning stages, an idea for a third party, the Power Party (Green), was floated by Len Jacobson but not enough support was garnered to add it to the general ticket, so to speak. The Power Party was in favor of boosting power on all satellites while keeping the number of satellites and existing signals as they are today.

As much as the election was designed for entertainment value, the arguments from both parties are real world, and from people waist-deep in GNSS receiver and infrastructure development.

The Satellites Party position statement: We pledge to implement a total GNSS constellation of 60 satellites, all broadcasting signals that exist on-air today.

The Signals Party position statement: We pledge to implement full operating capability of L2C, L5, L1C, Galileo’s range of signals, and GLONASS CDMA, broadcast solely from the satellites on orbit today.

Leading the Satellites Party were Greg Turetzky, SiRF director of marketing, new product technology, and IP; Yatin Acharya, Texas Instruments GPS hardware and software systems product manager; and Per-Ludvig Nomark, NordNav founder and currently a Cambridge Silicon Radio fellow of GPS software. Leading the Signals Party were Javad Ashjaee, Javad GNSS president and CEO, and David Wither, Sarantel Ltd. CEO.

As you may recall, I was scheduled to moderate the election along with fellow contributing editor Don Jewell. Hurricane Ike had other plans for me. My flight to Savannah was canceled because it was routed via Houston. Alas, ION GNSS 2008 was not meant for me.

Perhaps it was a blessing in disguise. During the election planning process, I had conferred with Alan privately: “Do I, as a moderator, need to remain objective during the debate?” I queried, knowing full well what the answer would be.

“Yes, my friend, you do,” said Alan.

Perhaps that was the beginning of the end for me, at least in my mind.

Past newsletter columns and other GPS World articles presented way too much incriminating evidence that my objectivity was not just tainted, but downright biased. It reminded me of a writing competition in a journalism class where my paper was promptly returned to me with the words “not objective” scratched in red ink across the entire page by the first evaluator who read it. I was not born lacking neither an opinion nor the desire to express it. I would make a horrible news reporter.

Back to the Debate

Javad Ashjaee made some powerful and convincing arguments for the Signal Party. He says the signal quality (read: accuracy) is the foundation from which everything is built.

“We are the party of building infrastructure. They are party of building toys. They are worried about finding their friends in the middle of downtown New York. We are the party of building roads, generating accurate maps, growing your food by automating agriculture, and synchronizing your power stations. We are even working on automatically landing aircraft to use the air space more efficiently,” said Ashjaee.

“The latest figure from Col. David Madden, the GPS lead commander, it says costs between $60 million to $70 million to build a GPS satellite, and $200 million is the cost of launching the vehicle, and then add the cost to monitor it and keep it in orbit and a dozen monitoring stations,” Ashjaee continued. “In its lifespan it will cost over $300 million dollars. These guys have no sense for money. They are spoiled brats, especially that Turetzky there (laughs), who want to spend $300 million dollars to play on their cellphones or do those fox games at night in the middle of canyons, of urban canyons, like in New York. I mean, they want to do that with their 99-cent chipsets and they want us to spend $300 million dollars.”

Hmmm … interesting. Save money by plugging more signals into the same satellites. Makes sense. Leverage off of what you have rather than creating something new. Sort of like adding more memory to the computer you own instead of buying a new computer.

For the Satellite Party, Greg Turetzky made equally enlightening and convincing arguments. Essentially, quality doesn’t matter if you are unable to benefit from it.

“We already have an L1 signal. We already have an L2 signal. We already have GLONASS signals. How many signals do we really need? I’m not arguing for one; I’ve got three. I don’t need a whole lot more. What I need, then, is to put satellites in the proper orbits, so that they can access all the different people all over the world who have and need more signals on the same satellites. This way we can actually leverage all the investment that we’ve made in the receivers that we already have.

“All the people here in the audience, who — I know you don’t own survey receivers, so I won’t go there — but how many of you own a Garmin or a TomTom? Right, or a PND?” Turetsky continued. “How many of you would like if next year it just worked better? You didn’t have to do anything? You don’t have to buy anything new, you don’t have to change any software, just all of a sudden there are more satellites in better orbits all over the world, anywhere you go. It just works better. This is what my party is about — improving the life of every single one of you without costing you an additional penny for everything you’ve already purchased.”

Fellow Satellite Party member Per-Ludvig Normark chimed in: “I just want to sort of look at, if you don’t see a signal, you don’t see a signal. What is the point of actually throwing in more signals, if you don’t see the first one? I mean it doesn’t really help you. I would argue that you need more satellites to see more signals. That is really what we need. That is what we should focus on.”

Good points, huh? Especially from Mr. Normark. That theme seems to cross all applications of satellite navigation, whether low-cost vehicle navigation or high-precision construction staking.

Election Results

The electorate was offered the opportunity to ask questions of each party.

Alison Brown of NavSys asked: “Would either party bring forward a collaboration between our American and European brethren in bringing more capability to the end user?”

Greg Turetzky responded for the Satellite Party responded: “Absolutely. What we’re after is launching more of the satellites that we’ve already designed and built rather than designing and building new things that we’re not quite sure how they’re going to work, whether or not they’re going to be successful or delivered on time, and spending a lot of money to deliver new systems that we’re not really sure what the benefit will be.”

Representing the Signal Party, Javad Ashjaee rebutted: “Greg, for how many years do you suggest that we freeze and build the same Model T?”

For a group of rocket scientists, these people are pretty funny. There were 123 delegates in attendance who were registered (attendance confirmed by their dinner order) to cast their ballot. No mail-in ballots were accepted.

Satellite Party: 62
Signal Party: 46

Of course, the election results are being disputed. See the Letters to the Editor section in the December 2008 issue of GPS World. In a move to unify the two parties and soften party boundaries, President-Elect Greg Turetzky has created a new cabinet post, Minister of Accuracy, and offered it to Dr. Ashjaee.

Epilogue

The light-hearted debate mixed with real-world issues made this event a one-of-a-kind in the GNSS industry. Although I wasn’t in attendance, I listened to the audio recording and read the transcripts.

In reality, nations around the world are pushing forth with both the Satellite Party and Signal Party initiatives. There are both more satellites and more signals on the horizon. The hunger for positioning, whether it’s for car navigation, indoor pedestrian navigation, or geodetic surveying, is continuing to grow and push the capabilities of the existing satellite navigation systems. It’s not dissimilar to computing horsepower. It seems that just as we have enough processing power to efficiently run the software we operate, new software packages are introduced that demote our six-month-old computer into the under-powered category.

Oh, What to Buy in These Challenging Times

I receive many requests for advice and/or recommendations from folks who are looking to buy GPS/GNSS equipment for survey and construction. Of course, if they haven’t told me, the first question I ask is, for what type of project are they are planning to use the equipment?

Some are typical projects like topographical surveys and construction staking, while others are not-so-typical. But no matter what type of project it is, the common denominator is the need for high precision data. It may be real-time or post-processed, networked or base-to-rover, single frequency or dual frequency, single constellation or multi-constellation, machine control or man-pack – it could be any of the above, as well as other configurations. But … no matter what … it has to deliver high precision results.

Although it may not seem like it, there is a myriad of GPS/GNSS equipment that will provide high precision, or centimeter (cm)-level positioning. To people who are knee-deep in the industry like you and I, it’s a daunting enough task to wade through all the different GPS/GNSS products to find the one that fits the best. To a first-time purchaser, it can be absolutely confusing and mind-numbing to sift through the brochures, Web sites and flyers.

To further complicate the purchasing process, prices can vary widely. I’ll give you an example. Within the past few months, I’ve been forwarded copies of quotes provided to prospective purchasers of GPS/GNSS equipment and asked to comment on them. You might be amazed at the variation in price.

Two quotes in particular caught my attention. One was for a Spectra Precision Epoch 25 RTK system. Spectra Precision is owned by Trimble Navigation. The Spectra Precision Epoch product line is distributed by Tripod Data Systems (TDS), which is also owned by Trimble. The other quote was for a Trimble-branded R8 GNSS system. The R8 GNSS is Trimble’s top-of-the-line GPS survey system with all the bells and whistles you can get these days on a GPS survey system. I’ve used the R8 GNSS and it’s a sweet ride.

Essentially, the Epoch 25 and R8 GNSS can accomplish the same tasks. Both are dual-frequency RTK systems. The Epoch 25 is dual frequency, GPS-only (no GLONASS), and doesn’t support GPS modernization (L2C and L5). The R8 GNSS supports GPS modernization (L2C and L5) and it supports GLONASS. The R8 GNSS is a much sexier package. It is a single, lightweight unit with the radio/GSM modem fully integrated inside a single unit. The Epoch 25 is essentially two pieces instead of one; the receiver itself and the antenna with a cabled connection between the two. There are other subtle differences, but like I said, for the most part they can both accomplish the same tasks and deliver the same precision, although the GLONASS option on the R8 GNSS has some definite benefits in terms of working in areas where the sky is obscured.

What do you think the price difference is between the two systems?

The R8 GNSS system quote was U.S. $56,900. The Epoch 25 system quote was U.S. $19,000. That’s a big difference.

 

This isn’t meant to pick on Trimble, because the entire industry is the same. In fact, there is a saying I’ve heard for years: “If you don’t like today’s price, check again next Tuesday.” That’s especially true in these economic times when there are fewer potential purchasers of GPS/GNSS equipment so manufacturers and dealers must add more incentive to attract buyers.

When considering purchasing GPS/GNSS equipment, price isn’t the only thing. Local support is an important consideration for most buyers. Local support means technical support as well as sales support (spare parts, etc.). For some buyers who aren’t as technically savvy, it’s obviously even more important. Another variable is that some dealers are more technically competent than others. It doesn’t do you any good if you know more about the system than the local tech representative of the company that sold it to you.

Which GPS/GNSS Equipment Is Right for Me?

Answering this one question will help point you in the right direction:

Do I need the results in real-time, or can I wait until I process the data back in the office (or with a laptop in the field)?

The answer to this question will make a big difference in the type of systems you should consider. Also, the answer might not be so easy. If you are making a first-time purchase for your surveying firm, you may not know what type of projects your business will be working on a year from now. If you really think you’ll be doing a lot of construction staking and sizeable topo surveys, then it’s pretty clear that RTK is the way to go. If you aren’t sure, then a lower cost pair of single frequency receivers may be the way to go. The return on investment (ROI) for those is pretty quick because they are reasonably inexpensive compared to a full-blown RTK system.

Systems for post-processing (a pair of single-frequency receivers) can be purchased for well under U.S. $10,000 and deliver centimeter-level horizontal/vertical measurements. Establishing site control is a good example of how those can be used. However, staking of any kind requires real-time kinematic (RTK) positioning. Also, while post-processing can be used for topographic surveys, RTK is a much more efficient tool when the projects are larger.

Essentially, RTK trades money for time (e.g., you pay more for the equipment but it takes less time to complete the task), while post-processing trades time for money (e.g., you pay less for the equipment but spend more time to complete the task). I know I’ll get a few letters about that because there are some exceptions, but they are generally true statements.
As you see in the example above in comparing the R8 GNSS and the Epoch 25 system, “full-blown RTK systems” can carry significantly different price tags. These days, there are generally three different levels of RTK survey systems:

1. L1-only RTK. A relatively new technology, this is an entry-level RTK survey system for under U.S. $15,000. It’s suited well for environments that are ideal GPS conditions, such as wide-open construction sites with a clear view of the sky. The distance between base and rover is generally limited to 10 km, or about (six miles).

2. Legacy L1/L2 RTK systems. These are the traditional RTK GPS systems like the one I own and like the Epoch 25 system mentioned above. They use L2 in addition to L1, so a longer distance between base and rover is achievable. They are the traditional dual-frequency receivers. They don’t accommodate the new GPS signals being broadcast and planned (L2C and L5), nor can they utilize neither the Russian GLONASS system nor the planned Galileo system. Prices for these systems typically range from U.S. $19,000 to $35,000.

3. Advanced GNSS RTK systems. These are the state-of-the-art RTK survey systems that utilize all signals being broadcast by GPS and GLONASS, as well as taking into account future GPS (L5), GLONASS and Galileo signals (as much as possible). These bleeding-edge systems will allow you to push the envelope as far as possible with satellite positioning. Due to the additional signals they are able to utilize, you will be able to use these systems at times when the other two can’t perform due to lack of satellite signals. Prices for these systems typically range from U.S. $35,000 to U.S. $60,000.

It’s tough to cover a topic such as this in a single column, so I’m sure I’ll visit it again. Maybe some of you will email and perhaps I can write about some specific case studies and publish some sort of purchase decision analysis for GPS/GNSS equipment. I’ve also got a few case studies I could include in such a discussion. Given the economic climate, I think this issue will be discussed often throughout 2009, at least.

Questions from the Webinar:
Is Dual-Frequency GPS — As We Know It — Becoming Obsolete?

First of all, I’d like to thank everyone who attended my webinar a couple of weeks ago. I received many, many questions during the presentation and answered a few of these during the event, but there was no way I could handle them. But most were very good questions that deserve answers, so I’ve devoted this column to answering those I couldn’t address at the time.

Oh yeah, kudos to you who attended; it was the most well-attended webinar to date for GPS World! I really enjoyed it and look forward to the next one in February or so of 2009. The focus on this last webinar was about the Department of Defense decision to discontinue supporting P(Y) on GPS L1 and L2 for civilian users after December 31, 2020.

You can view the archived presentation here.

Col. Mark Crews (ret.), former GPS Chief Engineer, is now retired but was kind enough to comment on some of the following questions that were submitted during the webinar, along with Don Jewell, GPS World’s Military and Government editor, and Richard Langley, the magazine’s Innovation editor.

I should note that it has come to my attention that it is possible the U.S. government might be able to create a “work-around” before 2021 so that the Civil P(Y) sunset date becomes a non-issue. In other words, your legacy dual frequency GPS receivers may end up operating past December 31, 2020 without any problems. Be assured that I will stay on top of this issue and keep you (the readers) up-to-date on any changes regarding Civil P(Y) sunset.

Question #1: Do you think that there will be a program to convert units to new technology like the television change to digital?

Gakstatter: With respect to a government subsidy of sorts? I don’t believe there will be.

Question #2: How do these codes affect the data gathered? And how is the new code going to differ?

Gakstatter: I assume you’re referring to post-processing. L2C and L5 are completely new codes so more data is being collected. It really won’t affect that way you collect data in terms of the user interface. Length of data collection sessions will probably be shorter.

A couple of years ago, I wrote an article about the benefit of the new codes. Some of the information in the article is dated now, but it is still fundamentally relevant. You can view the article here.

Question #3: Explain how civilian receivers such as the Ashtech Z-12 tracks the P(Y) code.

Gakstatter: I can’t speak specifically as to how Ashtech’s Z-Tracking technology works, but fundamentally I believe it reconstructs the full L2 carrier wavelength in addition to cross-correlating the P-code with L1 and L2.

Question #4: How will this affect L1-only receivers using base corrections and getting RTK accuracy?

Gakstatter: It won’t affect L1-only receivers.

Question #5: Will the new codes be better under heavy canopy or forested areas?

Gakstatter: L2C and L5 should improve operation in and around trees, but that’s not necessarily a good thing. Don’t be fooled into thinking you can operate reliably at the centimeter level under heavy tree canopy. That will never happen with only GPS. As I stated in the webinar, the real solution for that environment is the integration of other technologies such as pseudolites, inertial navigation, gyros, lasers, etc. I think those technologies will eventually be small and cheap enough to integrate into a GPS/GNSS receiver to allow seamless operation in GPS-impossible environments at the centimeter level.

Also, more help than L2C and L5 would be the addition of more satellites via GLONASS and Galileo. In this case, I believe that quantity trumps quality. Yes, L2C and L5 are better, but it doesn’t matter how good they are if the receiver can’t track them because of obstructions.

Question #6: Are these upgradeable or will we have to buy complete new equipment sets?

Gakstatter: It depends on the product you have and the level of manufacturer support. If you recently purchased a GPS L1/L2 receiver, I would suspect the manufacturer will probably offer an upgrade to at least L2C without having to completely replace your receiver.

If your L1/L2 is several years old and the manufacturer has discontinued support of that product, then the best you can hope for is some sort of trade-in credit towards the purchase of a new system.

Question #7: Would a receiver that could track L1, L2, L2C, and L5 obtain a worse fix on just L2C and L5 alone?

Gakstatter: I have no idea. In theory, it should perform better than the L1/L2 receivers of today because of better code structure, increased signal strength and better ability to mitigate ionospheric error. The frequency separation of L2 and L5 is not as great as that between L1 and L2 (or L5), so the dual-frequency iono correction potentially might not be quite as good. However, there won’t be enough satellites broadcasting L2C/L5 for at least another decade, so we won’t know until then!

Question #8: Are receiver providers creating units that can be upgraded, or will we be looking at a complete setup replacement (as soon as we are using the stated three codes)?

Gakstatter: Most major manufacturers of survey receivers have models that can track and use L2C, since that’s a signal that’s being broadcast today. Some say certain models are L5-ready. Likely, those will need to be tweaked with firmware when the actual L5 signal broadcasts.

Question #9: Is there a simple-to-understand one page document that may explain all of this to a procurement agent so they know what to consider when purchasing GPS equipment? Does the same exist to pass onto engineers?

Gakstatter: Hmmm … not that I know of, so I’ll try to create one. Email me in a month or so at [email protected].

Question #10: Will this change have any effect on our equipment before 2010?

Gakstatter: No. The semi-codeless sunset date is set for December 31, 2020. The only changes happening before 2010 are that a couple of more Block IIR-M satellites will be launched. The IIR-M broadcasts L2C in addition to L1 C/A. Also, in 2009 the first Block IIF satellite will be launched. The Block IIF will broadcast L2C and L5 in addition to L1 C/A.

Question #11: Will there be new criteria for CORS?

Gakstatter: The National Geodetic Service (NGS) is updating their GNSS strategy and moving toward supporting all broadcast signals (GPS and others). You may want to take a look at their five year and ten year plans.

Question #12: Is there likely to be a gradual degradation in the L2 signal availability in the years approaching the sunset date as the older satellites are lost from the system and replaced by the newer birds?

Gakstatter: I defer to the GPS World’s military and government editor Don Jewell and retired GPS Chief Engineer Col. Mark Crews (ret.). Both say there will be no degradation of the L2 signal, gradual or otherwise.

Question #13: I had read an article that basically stated more frequencies would yield higher accuracies, especially vertical, over more satellites. Is this an accurate statement?

Gakstatter: I don’t believe just adding more signals to the same number of satellites will significantly improve accuracy. I believe that more satellites (thus improved satellite geometry) is the best way to improve accuracy, especially vertical. With a full constellation of GPS, GLONASS and Galileo, the number of satellites in view and the PDOP numbers would be incredibly good for high precision users.

Comment from Dr. Richard Langley, Editor of GPS World’s Innovation column:

Recall that delta-subscript v = VDOP x delta-subscript p where delta-subscript p is the measurement accuracy (pseudorange or carrier phase), if we can reduce delta-subscript p, then we can also reduce delta-subscript v. So yes, reducing VDOP with more satellites will help more but improvements in signal structure and receiver technology will also help. L5 signals, for example, should have lower multipath contamination and also less noise at low elevation angles.

Question #14: Why does L5 require a new antenna?

Gakstatter: It is broadcast on a significantly different frequency (1176.4 5Mhz) than L1 (1575.42 Mhz) and L2 (1227.60 Mhz).

Question #15: What effect will this have on static processed data?

Gakstatter: None with respect to the user interface. Behind the scenes, more data is collected and the algorithms of the post-processing software will change significantly. You may see a slight improvement in accuracy. .

Question #16: So how do you make yourself ready?

Gakstatter: I’ll be writing more about this in the future. Like I said in my webinar, twelve years from now is a long time. There is no rush to take action.

Question #17: With reference to my last question (Question #13), presumably no more L2 birds are being launched in the future; what is their expected lifespan?

Gakstatter: All planned GPS satellites include L2. It’s important to note that L2 isn’t being rendered obsolete. The government is simply reserving the right to change P(Y) on L2 which was originally designed for the military.

L2C code is the future of L2 for civilian users.

Question #18: Do you expect the government/public/DOT VRS CORS systems to be upgraded and established with L2C and/or L5 by the sunset date for the L1/L2 signal?

Gakstatter: I’d refer you to the NGS 10 year plan with respect to CORS. Otherwise, it is up to each individual public or private network (RTK or otherwise) to ensure their network is prepared to handle the sunset date of December 31, 2020.

Question #19: Let’s say I have my semi-codeless system L1/L2 and everything is fine on January. 1, 2021, but on January 2, 2021 I have an issue. What’s my alternative at that point?

Gakstatter: You might be able to use L1-only for post-processing, but you may even have an issue with that.

Question #20: If not planning to already, let listeners know what to spec now in new purchases to ensure equipment will work past 2020.

Gakstatter: I will work on that.

Question #21: Do antennas (ex. Trimble Zephyr) become obsolete, or just the receiver board itself? Or do both components become obsolete?

Gakstatter: It depends on which Zephyr model you are referring to. The newest Zephyr 2 supports:

• GPS: L1, L2, L5
• GLONASS: L1, L2, L3
• Galileo: E1, E2, E5, E6

This antenna will not be affected. In fact, all GPS dual-frequency antennas of today will be fine in tracking L1 and L2C. Only if you desire to utilize L5 might you need a new antenna.

Question #22: What happens to the old satellites? Do they just burn up as their orbit degrades and they approach earth?

Gakstatter: I deferred to the GPS World’s military and government editor Don Jewell and retired GPS Chief Engineer Col. Mark Crews (ret.):

There are definitely some people who believe that we should de-orbit all our satellites, but unless the satellite is just a few hundred miles above us in a Low Earth Orbit (LEO), it is simply not possible. The GPS satellites orbit in the Medium Earth Orbit (MEO) regime which is 20,200 kilometers (~12,000 miles), on average, above the surface of the Earth. When a satellite becomes too old or fails for some reason, it is boosted into a slightly higher orbit plane which puts it out of the way of any operational GPS satellites.

In recent years, through solid engineering and strategic thinking, some of the GPS satellites that were still functional, but would have normally been boosted up to a higher orbit, have been left in the operational MEO orbit plane and put to sleep or in standby mode for future use. Just recently some of these older GPS satellites have been reactivated. If we were to allow the satellites orbit to naturally decay from MEO, we will have been in our graves for thousands of years by the time they reach the Earth’s atmosphere, where they would burn-up on reentry.

Further comment from Dr. Richard Langley:

There is also the potential for collisions of dead satellites from different constellations (GPS, GLONASS, Galileo, etc.) as a result of the satellites drifting out of their assigned orbit bands over the next 100 years or so. The GLONASS folks are studying this and it was mentioned during Sergey Revnivykh’s presentation at the ION GNSS 2008 CGSIC meeting.

Question #23: Are there receivers on the market now anticipating the change?

Gakstatter: Yes, there are many survey receivers on the market right now that can utilize L2C and are prepared for L5. They are typically the premium-priced receivers offered by the manufacturers.

Question #24: Can you give a brand/model example of a GIS sub-foot receiver that might be affected?

Gakstatter: Trimble GeoXH, ProXH.

Question #25: Will L1 receivers using real time reference networks (e.g. Trimble GNSS VRS) be affected?

Gakstatter: I don’t believe there will be any affect.

Question #26: How will the CORS network be affected?

Gakstatter: Please refer to the NGS 10 year plan. I believe the NGS is preparing well for the transition. However, NGS doesn’t have control over most of the CORS stations. That’s a different story.

Question #27: Can you talk in general about accuracy comparison of the new L2C and L5 capabilities with current legacy RTK accuracy? Will we still need base stations?

Gakstatter: I touched on this in the webinar a bit. I don’t believe you’ll see a substantial increase in accuracy. I think you’ll see a substantial increase in reliability and robustness of the positions.

The way to achieve greater accuracy (vertical in particular) is more observations (eg. GLONASS and Galileo).

Question #28: Would GPS World plan on researching GPS manufacturers and their products that DO NOT support L2C at this time? We sell NovAtel OEMV and they have L2C, but what about the OEM4 we sold two years ago? An article on this would be nice as I can’t find it on their spec sheet.

Gakstatter: I think this is a good idea and the subject has been raised before. I’m not sure when it will happen, but I believe I will do something along these lines.

Question #29: Do you have any recommendations for a small startup land survey company? Wait for the new technology to come out or purchase what’s out there now?

Gakstatter: Well, I think it’s more of a business issue than a technology issue. I’ll make a bunch of assumptions when answering. Personally, I’d try to keep your capital investment as low as possible at this point.

If you only need post-processing, then a pair of L1-only static receivers is a relatively small investment (well under $10,000). Or, one GPS dual frequency receiver will do, and use an online positioning service like OPUS.

If you need RTK (real-time, centimeter-level positioning for staking/topo), then the price tag goes up. Do you have access to an RTK network? If so, then you only need an RTK rover and a data plan from a wireless provider like Sprint, AT&T, T-Mobile, etc.

If you need RTK and no RTK Network access, then you’ll need a RTK reference station also. Again, the price tag goes up. Another piece of equipment to consider (maybe in lieu of GPS) would be a robotic total station.

It all depends on what kind of projects your company will be involved in the majority of the time.

Question #30: Comment: GPS tech changes significantly every 1.5 to 2 years, while the useful lifetime of a receiver is on the order of 6 to 8 years. Proper planning will make this a non-issue.

Gakstatter: In general, I agree there’s plenty of time to plan for the transition. However, the fact is that some GPS equipment purchased in the early 1990’s is still working today and some legacy equipment purchased today will still be operating twelve years from now. This is especially true for survey receivers because the price tag is so high.

Question #31: Will my L1/L2 receivers still be able to collect L1 data for static computations?

Gakstatter: I believe they will, but caveat emptor.

Question #32: If I upgrade to L2C and not L5, what will my limitations be?

Gakstatter: You will be no worse off than you are today.

Question #33: Can we expect an increase in vertical positioning accuracy with the new L2C and L5 frequencies?

Gakstatter: I don’t believe so. For better vertical accuracy, the best bang for your buck will be more satellites (eg. GLONASS, Galileo). However, as stated in the answer to Question #13, there will be some gain in accuracy due to improvements in the code structure of both L2C and L5.

Question #34: Are the new satellites capable of maintaining our legacy signals, or is it totally out of the question?

Gakstatter: It’s not that the government wants to eliminate any signals, but rather they reserve the right to alter the military P(Y) signal on L2. After December 31, 2020, it may behave just like it does today or it may not, so yes, they do have the capability to have the satellites behave as they do today.

Question #35: Comment: I’m like your friend who expected his last purchase to carry him through to retirement. The way my retirement account is growing (negatively) I may still be carrying a range rod when this change occurs.

Gakstatter: I empathize. Maybe I’ll join you.

Question #36: will we still need two receivers to use RTK techniques?

Gakstatter: I also talked about this question during the webinar a bit. Yes, there will still be a need, but I think it will be more ubiquitous than it is today, primarily because of the proliferation of RTK networks and wireless communications technology. Because of this, I think you’ll see the need to operate your own RTK reference station diminishes significantly.

Question #37: How will this affect my processing software, such as Ashtech Office?

Gakstatter: Well, you’ll be okay until December 31, 2020. If there is an upgrade path that supports L2C, that might be a good move if your receiver supports L2C.

Question #38: How much will it cost, upgrading to L5?

Gakstatter: Please check with your local dealer or the manufacturer of your equipment.

Question #39: Does adding L1C into the mix have a great advantage?

Gakstatter: With respect to interoperability with Galileo, yes. With respect to the L1C code itself, it will be superior to its predecessor, L1 C/A, much like L2C/L5 and offer enhanced code and carrier tracking.

Question #40: With L2C only (no L5), is the cross correlation with the L1 C/A or will there be a new code on L1 as well?

Gakstatter: There is no new code on L1 at present. The two civilian codes are L1 C/A (the original) and L2C. On Block III GPS satellites, L1C is planned. Basically, a new and improved L1 C/A.

Question #41: How much is the difference between maintaining the legacy signals and not maintaining the signals?

Gakstatter: Again, I deferred to the GPS World’s military and government editor Don Jewell and retired GPS Chief Engineer Col. Mark Crews (ret.):

I assume you are talking about the difference in costs here, but this is really not a question pertinent to this issue, as we are currently not planning on doing away with any current signals. Both the L1 and the L2 signal structure, coded and codeless, will still be broadcast for the foreseeable future. The issue is that, after December 31, 2020, the flex-power capability may cause temporary problems in codeless and semi-codeless civilian receivers for periods of time while the satellites are in flex-power mode.

However, your question is pertinent in the general sense, as there are new GPS signals and frequencies coming on-board and there are those who believe that some of the old signal structures should be abandoned for the newer more capable signals. So far there have been no decisions made to abandon any of the current signals, only to make them stronger and more robust, with more anti-jam and anti-interference capabilities, which is one of the functions of flex-power that serves the war fighter.

There is also the possibility that flexible power mode will be modified by 2021 in such a way that it will not cause a L2 phase shift and affect civilian receivers that are using semi-codeless techniques.

Question #42: Is there a minimum baseline requirement for differential processing (RTK or otherwise) with dual frequency receivers? Will the change from L1/L2 to L1/L5 alter this?

Gakstatter: The minimum baseline won’t change. There really isn’t one for dual frequency GPS ,although very short baselines sometimes fare better with L1-only rather than L1/L2.

With regard to legacy L1/L2 vs. L1/L2C/L5, I believe you’ll have more robust solutions with the latter, and longer baseline processing will be enhanced.

Question #43: If we need dual frequency receivers for survey quality, wouldn’t three frequencies enhance ambiguity resolution and/or accuracy and precision?

Gakstatter: I believe ambiguity resolution will be enhanced (e.g. quicker and more reliable) due to better ionospheric correction with three frequencies. With regards to accuracy, I don’t see a significant improvement. As I mentioned before, the best way to enhance accuracy/precision (especially vertical) is signals from more satellites (e.g. GLONASS, Galileo, or GPS).

Question #44: After the sunset date will dual frequency not work at all, or just give bad data? How will we know if the signal has changed?

Gakstatter: Your receiver won’t be able to correctly resolve the integer ambiguity because of the phase shift. You won’t know until it happens. It’s not a permanent state either. Legacy receivers may work just fine for periods of time, but then may not for periods of time.

Referring back to the answer to Question #41, it is also possible that the US Government will find a way to resolve this situation where we will not see a phase shift at all.

Question #45: Will this enhance my L1 handheld accuracy at all?

Gakstatter: No. L1 C/A will remain the same.

Question #46: Comment: I know several surveyors who need to hear this conference. It was great. Please publish on the ‘net for access or email to us for distribution. Thank you.

Gakstatter: Thanks for listening and taking the time to comment. Pls feel free to forward this email or the links embedded in this email to those whom you think are interested. You can take in the webinar via the archived version here.

If I didn’t fully answer your questions or if it spawned more, please don’t hesitate to email me more questions and comments.

Well, if the economy is going to tank …

… at least our industry outlook is pretty good for the next five years. Hmmm … I guess I should clarify, because the survey/construction business is clearly slowing here in the United States (I probably don’t need to tell you that). But, if you want to look at a bright spot through all of the gloom and doom of today’s global economy, the GNSS industry is looking really good for the next five years.

Ok, I first need to apologize in advance for the shameless self-promotion, kind of. I co-authored a market research report on high precision GNSS which we just completed. The report covers the period 2008-2012 and discusses market growth, technology, trends, etc. for only high-precision (10cm or less) GNSS. Not just receivers themselves, but associated services such as augmentation (RTK Networks), distribution (dealers) and others.

Just in the course of writing this column twice a month, I often find myself humbled when writing about GNSS issues. The “more I learn, the more I learn how little I know” cliché really applies here. Authoring the report was no different and perhaps even more challenging because of its 214-page length and breadth of topics covered. It really opens one’s eyes as to how far GNSS has weaved its way into our lives and, even more enlightening, how far it still has to go.

Another thought: I just received an email from the people upstairs asking for bullet points to take to the budget meetings in hammering out the 2009 GPS World magazine budget. I really started thinking to myself; GNSS is one of the few industries I can think of that, even in a horrible global economy, is still going to experience growth over the next five years. We are fortunate indeed. Seriously, think of the executive running Starbucks. Imagine their forecasts for 2009? The first place people will look is to save is that $4 per day.

Looking at the hard numbers, the global value of GNSS goods and services in 2008 will end up being approximately $3 billion (all figures are in U.S. dollars). It’s predicted that it will grow to $6 billion to $8 billion by 2012. $6 billion is realistic growth, assuming a global economic downturn and softening of some commodity prices, which is already happening. A particularly bright spot is the robust agriculture market, where there is renewed growth in precision agriculture for GNSS, primarily in high-end RTK applications.

Looking at the above graphic, the compound annual growth rate (CAGR) in a realistic or expected scenario is 19 percent, while the optimistic CAGR is 23 percent. A significant portion of that growth is driven by widespread adoption of GNSS as a productivity tool. GNSS is transforming from a niche tool used in niche industries to an essential productivity tool in global industry sectors such as mining, agriculture and construction.

Breaking the growth down further, the traditional GNSS markets you are familiar with will experience the slowest growth: 16 percent to 21 percent CAGR. That’s to be expected given the steady adoption rate over the last twenty years.

Machine control applications will experience a growth of 23 percent to 28 percent CAGR. This isn’t a big surprise, as you’ve probably experienced the adoption of this technology in your daily work if you haven’t been involved with it yourself.

The highest growth area will be precision GNSS data services with a CAGR of 33 percent to 38 percent. This includes the GNSS reference station infrastructure and wireless communications needed to deliver data services over a region, such as with RTK networks and RTK clusters. Technology innovation and development will enable precise positioning with less complexity and lower cost, thus encouraging adoption and stimulating growth.

The steady shift in user demographics, continued evolution of space-based systems and precise positioning techniques combined with the growth of dedicated precision GNSS infrastructure and associated services are a recipe for a dynamic and rapidly changing business environment.

So, if you’re looking for a bright light in the darkness of global financial instability, GNSS is one to talk about – and you’re right in the middle of it.

If you want to read more about the report, there’s a 20-page abstract you can download from GPS World’s site by clicking here. You’ll have to fill out a short form in order to download the PDF, but the price is right, as in free.

Back to the Subject of Solar Activity

This is one of the more humbling subjects I’ve written about. As I mention above, as much as I write and try to stay on top of subjects, I seem to be a step behind at times. Fortunately, readers offer their help in times of need.

John Sumption from Colorado commented on my last column regarding solar activity. He opined:

It’s well worth noting that Solar Cycle 24 has not lived up to any of its advanced billing. In fact, so far, it’s been quite a dud.

A maximum in 2011 is now virtually impossible. A maximum in 2012 is unlikely. The 11-year solar cycle usually comprises four years of rise time to maximum, and seven years of fall time to minimum. Solar Cycle 23 maximum was in 2000. It has already been eight years of fall time, and Solar Cycle 24 has so far been anemic at best. Yesterday and today a couple very small sunspecks appeared, too small and insignificant to be officially counted, and they have already faded to invisibility.

There is active discussion across the blogosphere about Solar Cycles 23 and 24 and the possible implications. The official NOAA/NASA panel predictions you mention are expected to be “updated annually” as they say on the website. In conjunction with a Space Weather Workshop in May, the panel simply reiterated its predictions, there being insufficient data on which to base a significant change.

As you know the panel originally issued a split decision; six of the panelists predicting larger than normal, six predicting smaller. The lack of Solar Cycle 24 activity continues to outpace the official predictions, and so far, even the six low-side forecasters seem to have overestimated Cycle 24.

An updated prediction from this group should not be expected before Spring 2009. However, theirs is not the only forecast. IPS, the Australian Space Weather Agency, recently acknowledged the lack of activity and pushed their forecast another six months down the road.

Jan Janssens maintains a table which contains most of the published predictions. Note that this table has not been updated in the past 12 months, as Solar Cycle 24 continues to behave unexpectedly, and forecasters have little or no additional insight on which to base new predictions.

You’ll see in the table, no. 8, by Maris et al, reasons that Solar Cycle 24 will be small, because of the loss of energy through intense solar flares during the declining phase of Cycle 23.

One of the most highly-experienced solar forecasters, Ken Schatten, has been wondering if the energy lost to the solar wind through low-latitude coronal holes – which are unusual at solar minimum – has left the sun with too little energy to produce more energetic spots.

Finally, an unpublished paper (but you can find it on the web) by Livingston and Penn of the Kitt Peak Observatory notes the trend of decreased contrast between sunspots and the sun, and that if the trend continues, sunspots would vanish entirely by 2015.

Now, you can choose to agree or disagree,  but I think John’s correct in that, so far, Solar Cycle 24 is not gearing up to be what pessimists (or optimists, depending on your attitude) that it might be. Further, he adds:

I also should have mentioned this – from a NASA media teleconference last week about the Ulysses solar probe mission. I think the results would tend to support Schatten’s idea of the sun having an energy “leak” somewhere.

Thanks for the insight and links, John.

Solar Activity: Is There Aspirin for This GNSS Headache?

Like the hurricane/cyclone/typhoon seasons that occur every year around the globe, one fact of life about GNSS is space weather and the solar cycle. For professionals who use GNSS on a regular basis, it’s easy to forget about it since it’s not an annual event. In fact, those of you who have been using GNSS for only the past five years haven’t experienced it at all. Why? It’s an 11 year cycle, and it’s starting to heat up.

How does Solar Activity affect GNSS?

There are many, many papers on this subject that can offer you a lot of depth on this subject; just google “solar cycle GPS.” In my Eric Gakstatterish sort of way, I’ll write a brief description of how it affects GNSS.

The effect on GPS signals as they pass through the ionosphere is the largest single source of error that we see in GNSS today. Essentially, free electrons contained in the ionosphere affect the propagation of the signal as it passes through. Since the signals are traveling at the speed of light and GNSS is based on nanosecond timing, it doesn’t take much interference to introduce error.

For a graphic and more detailed information on the ionosphere, click here.

Modeling the Total Electron Content (TEC) of the ionosphere is something you may have heard of when reading about GNSS. TEC is directly affected by solar activity, and thus the solar cycle.

The solar cycle is an 11-year cycle of solar activity. Following is a nice graphic from the U.S. National Oceanic and Atmospheric Administration (NOAA) that’s on their Solar Cycle 24 web page. Solar Cycle 24 is the name of the solar cycle we are entering into.

From the graphic above, you can see the height of the next solar cycle will occur in the 2011-2012 timeframe. That’s when the TEC will be the most dynamic and the most difficult to model. You might also note that there are two prediction curves (along with their uncertainties); this is because even the experts can’t agree on just how big the next cycle will be.

 

Which GNSS users will it affect the most?

GPS L1 (single frequency) users will be affected the most. GPS uses a rough model, often referred to as Klobuchar (a scientist’s name), in an attempt to the model the ionosphere and minimize the effect for single frequency users. When the model closely resembles the actual TEC, then the TEC has minimal effect on single frequency accuracy and you are a happy user. When the actual TEC is much different than the Klobuchar estimate, that’s when the problem occurs. It’s sort of like that moment when you figure out you estimated 200 man-hours on a project that will take 500 man-hours … oops.

During the low point of the solar cycle is when the TEC is easiest to predict. Looking at the chart above, we are currently at the low point and really have been in a nice place since about 2004. Over the next two or three years, it’s going to change dramatically as the character of the cycle is such that it rises sharply in the beginning.

Autonomous GPS (using no correction source) accuracy has been very good these past couple of years (2-3 meters under ideal conditions). Because it’s been so good, some of you are relying on it for mapping. The increase in solar activity will affect you the most.

You will see some really funky data.

For those of you professional single-frequency GPS receivers who have built up confidence in your sub-meter mapping receivers, you need to be particularly aware. It would not be out of the ordinary for your DGPS-corrected position to have an error of more than 10 meters. That includes WAAS, DGPS beacon, commercial DGPS services, and post-processed solutions. In theory, if the accuracy of DGPS corrections (SBAS, DGPS) deteriorates sufficiently, you should be forewarned. However, how your particular piece of equipment handles that warning is up to each manufacturer.

Practically speaking, those errors aren’t going to occur on a daily basis. That would only occur during extreme solar storms. In fact, that order of magnitude will probably be quite rare, but certainly additional error in the 0.5-meter or 1-meter range will be more common than what you see now. The fantastic performance we are seeing today from autonomous GPS as well as SBAS isn’t just because of improved technology; it’s also due to the fact that we are in low point in the solar cycle.

Users of dual-frequency GPS receivers and multiple-frequency GNSS receivers will be affected less, but still affected. Ambiguity resolution will take longer (or not be achievable at all) during periods of heightened solar activity. However, these systems will fare better than their single-frequency brethren as multiple frequencies and shorter baseline distances typical of multiple-frequency users make it much easier to model the TEC.

Interestingly enough, this solar cycle ,with its effects diminishing after about 2016, should be the last one where we will have such concern. Think about it: it will be 2023 or so before Solar Cycle 25 starts to crank up. At that time, L2C, L5 and GPSIII will be in full bloom, not to mention Galileo and GLONASS, so the ability of our GNSS equipment to model and mitigate the effects of TEC will be much more advanced than it is today.

What can you do about it in the meantime?

First of all, educate yourself and understand your equipment’s exposure to solar activity. Here are some great links.

GPS World article from May 2003

NOAA Solar Cycle 24 Prediction issued April 2007

NASA feature article on the beginning of Solar Cycle 24

www.spaceweather.com

My esteemed GPS World colleague Richard Langley from the University of New Brunswick has also tackled this subject; he can provide you with the Richard Langleyish, scientific perspective.

Next, towards the end of 2009, make it a point to start checking up on solar activity. A great place for Europeans to do this is at the Royal Meteorological Institute of Belgium’s website. The U.S. National Weather Service also operates the Space Weather Prediction Center. Also, note that for those users along the equator, your area is more susceptible to dynamic TEC changes.

There is no doubt you will hear more and more about the impending solar cycle as it ramps up: more research, more data collection, and more analysis. Some space weather experts say this cycle will be worse than the last, some say it won’t. However, there’s one thing they all agree on: we won’t know until it’s here.

ION GNSS Conference – Not This Year

Well, it wasn’t meant to be. Hurricane Ike made sure of that.

I travel quite a bit and I never fly Continental Airlines, but there aren’t a lot of choices when flying to Savannah, Georgia from Portland, Oregon. So a couple of months ago, I booked my flight to Savannah on Continental with a connection in Houston, Texas.

Hurricanes and Houston don’t mix well this time of year. Anyway, Hurricane Ike wreaked havoc on southeast Texas. Houston’s airports were closed for the weekend (my flight was supposed to depart last Sunday). Continental, being a small airline with limited routes, couldn’t get me to Savannah until Wednesday night at the earliest. Other airlines were jammed up trying to reroute people around the Hurricane-affected airports.

So be it … no ION conference for me this year. Too bad, it’s my favorite conference of the year because I get to see where companies and organizations are putting their research effort which, in turn, gives me a good idea where GNSS technology for surveying/construction is heading.

At ION, one of the things I was scheduled to do was give a presentation at the Civil GPS Service Interface Committee (CGSIC) meeting on Monday. This year is the first time the CGSIC is allocating GPS World a slot on the agenda. The topic of my presentation was entitled “WAAS for Mapping: It Works Where You Work.” So, instead of presenting it at ION this year, here you go.

First of all, let me tell you that even though the applications featured are focused on WAAS, this is really about SBAS (satellite-based augmentation systems) in general. That includes MSAS (Japan), EGNOS (Europe) and soon, GAGAN (India).

Trends in GPS mapping

The user community expects GNSS technology products to become smaller, cheaper, simpler, and higher performance.

For the most part, we have seen that trend develop in the past decade. GPS mapping products have migrated from heavy, backpack-based systems with a medium-sized dome antenna, DOS-based data collector, VHS recorder batteries, antenna cable, data collector cable, and power cable to the small handheld devices and small receiver boxes of today. Likewise, prices have fallen considerably. The market prices for a sub-meter mapping system are 50 percent to 60 percent 60 less than a decade ago.

The GPS mapping user community is moving away from post-process differential correction and towards real-time correction.

The reason is quite simple: simplicity and cost. Post-processing is a pain and it’s expensive. It’s not just the cost of the software and software maintenance contracts, it’s the personnel training to stay current on the software, it’s the cost of time to post-process and it’s the cost of not having real-time data in the field. Yes, there is a cost of not having timely data.

One of the arguments for post-processing is that it’s more accurate. From a pure scientific standpoint, that’s a correct statement, but it’s crazy to make that sort of general statement. I could show you data that shows that statement is correct and also incorrect. Like most answers to GPS accuracy questions, the answer is, it depends: it depends on the receiver, it depends on the application, it depends on your personnel qualifications, etc.

SBAS makes real-time GPS correction simple and cheap, as in free. WAAS has matured over the last five years since it was declared operational from providing 1 meter to 3 meter accuracy to where it is today, providing accuracies of well under a meter in the continental United States, Alaska, Mexico, and most parts of Canada. The simplicity and low-cost of SBAS makes sub-meter mapping attainable by a larger percentage of the user community.

All WAAS (SBAS)-Enabled Receivers Aren’t Created Equal

One of the common experiences with WAAS (SBAS) in mapping applications is that the user will attempt to use a consumer-grade GPS unit (eg. Garmin) and, predictably, the performance will be poor. Consumer-grade GPS units aren’t designed for accuracy. They are designed for fast satellite acquisition, low-power consumption, low-cost, and easy user interface.

I don’t know if you’ve been paying attention, but the newer consumer-grade GPS units don’t mention SBAS like they used to. It’s because the difference between autonomous positioning and WAAS-corrected positioning isn’t a significant issue with respect to the average GPS consumer who is navigating from point A to point B. Go look at the mapping Handhelds section on the Garmin website. There is no mention of WAAS in the specs. The reason? Garmin doesn’t care about WAAS for the ground user.

If the GPS manufacturer does care about WAAS for ground users, there is a lot they can do to optimize the use of WAAS (SBAS) so it can perform in environments where a standard WAAS-enabled receiver couldn’t dream of working. One technical paper on this subject was published by Stanford University and presented at the ION conference in 2006. Euiho Kim, Todd Walter, and David Powell from Stanford presented a paper entitled Optimizing WAAS Accuracy/Stability for a Single Frequency Receiver.

Some manufacturers have done this and more to exploit WAAS so it can be used in environments where a receiver implementing the traditional use of WAAS couldn’t. I can write about this until I’m blue in the face, but the proof is how the user community is using WAAS with high-performance receivers in applications where many people say WAAS can’t be used. I know of a few of them around North America and have provided a short synopsis of each to give you an idea.

Applications of WAAS in North America

Company: J.D. Irving Ltd.
Employees: 15,000
Industry: Forest products
Location: Eastern Canada
Application: harvesting timber
User Statement: “The general misconception is that WAAS doesn’t work under forest canopy. (For us) It’s proven to be a false assumption if the right receiver is used.”

Company: American Forest Management, Inc.
Employees: 250
Industry: Forest management
Location: Virginia to Texas, Maine to Michigan
Application: Area calculations, forest road work, land owner mapping
User Statement: “Our field efficiency has drastically increased due to reliable reception and ease of use … office productivity also increased because of real-time correction.”

 

Company: Portland General Electric
Employees: 2,600
Industry: utility
Location: Oregon
Application: utility pole mapping
User Statement: “Four years ago, we started out using low-end WAAS receivers, but switched to mapping-grade WAAS receivers after 60 days due to accuracy problems. 225,000 poles and four years later, we are still using the same WAAS receivers.”

Company: State of Minnesota
Employees: a bunch
Industry: state government
Location: Minnesota
Application: mapping abandoned chemical facilities
User Statement: “Approximately 500 facilities were mapped using a Bluetooth, sub-meter WAAS GPS and a Windows Mobile data collector. Wireless technology eliminated connectivity problems and the receivers had COAST technology, consistently giving us submeter, real-time results, even in areas that had poor visibility.”

Company: U.S. National Park Service
Industry: federal government
Location: sub-arctic Alaska
Application: map archaeological sites
User statement: “Many mapping grade GPS users still do not feel good about relying on WAAS. You can always post-process, but after reading these numbers, some may ask why bother?”

Other Related Trends in Real-Time GPS Mapping

Not only is WAAS (SBAS) being exploited by some manufacturers of sub-meter GPS mapping equipment, some manufacturers have introduced survey receivers that also exploit WAAS, but use another satellite observable for centimeter-level positioning rather than using the WAAS correction itself.

In optimal scenarios, this potentially adds another two observables when resolving ambiguities for RTK positioning.When manufacturers start designing products around a technology, it speaks highly of the future of that technology.

RTK networks (RTN) are experiencing explosive growth around the world.

It’s a relatively new technology that will add to the proliferation of real-time users for both RTK and sub-meter mapping systems. RTN’s primarily cover metro areas at this time, but some countries have recently announced the implementation of country-wide RTNs. Look for more editorial coverage on this in the future.

Commercial DGPS services have shifted from offering L1 sub-meter DGPS products to decimeter L1/L2 products in certain regions in the world.

DGPS signal providers have recognized that WAAS/SBAS fills the requirement for sub-meter corrections where it’s available. They haven’t stopped offering L1 sub-meter DGPS corrections, but certainly have shifted their focus to the GPS L1/L2 market.

On The Not-So-Positive Side of Things

We’ve enjoyed many years of relatively quiet ionospheric activity. In a sense, we’ve taken for granted the awesome increase of GPS accuracy (both autonomous and DGPS). This is going to change as the next solar cycle cranks up. It’s an 11 year cycle that began early this year and will reach its high point in 2011 or 2012.

What’s so bad about solar activity?

For GPS users, errors induced by significant ionospheric activity can be measured in meters or even tens of meters even if you are using a DGPS correction source such as WAAS, beacon or RTN. Some experts say the next solar cycle will be worse than average. Some say not. All of them say “we won’t know until it’s here.”

Read more about Solar Cycle 24 here. The subject is worthy of an entire article; which I will write in the coming months.

Be sure to watch the live coverage that my fellow editors will be providing from the ION GNSS conference in Savannah this week.

Civil P(Y) follow-up and ION GNSS

I figure it’s about time for a follow-up newsletter on the Civil P(Y) sunset proposal by the GPS Wing.

In June, I wrote a very important column about the GPS Wing proposing to discontinue supporting P(Y) on L1/L2 for civilian users after December 31, 2020. Essentially it would mean that many dual frequency receivers of today will be rendered obsolete after that date.

The U.S. Department of Commerce attempted to solicit comments from the public regarding the proposal. You can view the responses here. I was somewhat surprised at how few responses were submitted.

It is predictable that equipment manufacturers are in favor of the proposal. There is significant upside for them in terms of new equipment sales and little downside, if any at all. The objections again, predictably, are from the users in the trenches who have invested a significant amount of their own capital into high precision GPS equipment.

I can see a several reasons for the lack of responses:

• Users aren’t aware of that impact this may have on their operations.
• It’s too far in the future for users to be concerned.
• It’s far enough in the future that users feel technology will change and render this a non-issue.

Of course, I think it’s a little bit of all three. The first is the one that concerns me the most. That’s why I supported an extension to the comment period (30 days). I strongly believe there is a general lack of awareness of the subject at all, not to mention the impact it will have. If surveyors/technicians around the world haven’t been keeping up with the trade publications these past three months, they have no clue what’s in store for them.

The second and third assume the user is educated on the issue and has made conscious decision not to be concerned.

A few of you asked for a list of specific model numbers which will be affected. I’m working on one, but I don’t think it will ever be comprehensive enough to be 100 percent complete. What I tell people is that if the receiver isn’t able to utilize at least L2C (preferably L5 also), then it’s considered a legacy receiver and will be affected by the GPS Wing’s proposal. If you have any question as to whether your receiver can utilize L2C, you should contact the manufacturer of the equipment. Keep in mind that most companies begin to phase out support for older products (so called EOL or end of life models) after a few years, and some manufacturers may no longer exist at all.

If you confirm your receiver uses legacy technology, I wouldn’t be in a panic to take action now. I have a feeling that manufacturers will offer some sort of trade-in program at some point. It may not be for another 7 to 10 years from now, but I think they will. The exception would be that if prices for high precision GNSS receivers drop dramatically (looking out 7 to 10 years from now) because of fierce competition, they will be so low that manufacturers won’t be able to afford it. But then you probably won’t care as much anyway.

As I mentioned in the last newsletter (about the ESRI conference), I spoke briefly with Col. Madden, Commander of the GPS Wing, about the Civil P(Y) sunset proposal. Quite a straight-forward guy if I can say so. He says that maintaining backward compatibility in GPS is becoming increasingly expensive and that they have to draw the line somewhere.

“Whether it’s 10 or 20 years, we don’t care,” said Madden. “But we need to put a marker down.” He said it currently costs $2.5 million per day to maintain GPS. In 2009, he said that cost will rise to $3.5 million to $4 million per day.

The December 31, 2020 date is not final yet, but all indications are that it will indeed be the date. I should learn more at the Institute of Navigation (ION) GNSS conference held in Savannah, Georgia in a couple of weeks.

I’m at ION

Speaking of the ION GNSS conference, I’m on the agenda for the CGSIC meeting prior to the conference. The DOT has been pushing their NDGPS agenda pretty hard this past year to try to save the program. That’s fine, but I get a little ticked off every time I hear them tell people that WAAS isn’t a valid technology for mapping. Hey, if you think NDGPS is the way to go for you, then talk about NDGPS and stop trying to bring down other programs to further your cause.

So anyway, I think a little equal time is in order. I’ll be presenting on how WAAS is being used for mapping. I picked out a half a dozen or so organizations around North America that are using WAAS with high performance GPS receivers. There are some neat examples of where WAAS is being used in places you might not think possible, and also how WAAS is being used by centimeter-level GPS equipment to speed up initialization times.

I’m sorry I can’t include examples of EGNOS (Europe) and MSAS (Japan) users in the presentation, but I’ve only got 15 to 20 minutes. But I’ll be sure to mention EGNOS, MSAS, and GAGAN as well. I know you are all alive and well.

Be sure to follow the live coverage that I and my fellow editors will be providing from Savannah the week of Sept. 15-19.

Attending the Annual ESRI Networking Conference

As much as surveyors, engineers and constructors may not appreciate geographic information systems (GIS) technology, at some point everyone should attend at least the ESRI Survey/Engineering Summit and the first couple of days of the ESRI User Conference held every summer in San Diego, California. This is not a GIS sales pitch. It’s a networking sales pitch. When other conferences are struggling to maintain attendance levels, the ESRI conferences seemingly never fail to grow in attendance. This year, it attracted some 15,000 people from 120 countries. That means gobs of GIS people, and also gobs of surveyors and engineers.

The Survey/Engineering Summit is a much smaller subset with some 500 attendees, and takes place the weekend before the User Conference. This year, it was the first weekend in August. Although relatively small in size, the conference is significant enough to attract someone the caliber of Col. Dave Madden as a keynote speaker. Col. Madden is the U.S. Air Force GPS Wing Commander, and as such he’s in charge of GPS. With a fiscal 2009 budget of $1.5B, it is the fourth largest budget in the U.S. Air Force. That means he has some clout, and that’s the quality of speaker that the ESRI conferences have the ability to attract.

It’s All About Networking

Most times, I’m like you: worried about the day-to-day stuff of running a business or department, or just getting stuff done on time and on budget. CEUs are hard enough to keep up with, not to mention taking a few days off during prime outdoor season (and spending a chunk of change) to attend a GIS conference.

But I tell you what; this is the place to mix it up with all kinds of people beyond your local association chapter. Not that there’s anything wrong with that, but I guarantee that networking with 15,000 people will open your eyes a lot wider than networking with 25 people. If you’re looking to expand your business, whether it’s GIS-related or not, you will probably meet someone in San Diego who is doing it already.

Take, for example, Michael Dennis of Geodetic Analysis LLC. Have a question about geodesy? Here’s a guy who gave a presentation entitled “GPS, Geodesy and the Ghost in the Machine.” Part of his presentation included dissecting National Geodetic Survey (NGS) Datasheets. Mind you, there’s a half dozen NGS people in the crowd! Sort of like giving a presentation on Windows to Bill Gates, isn’t it? That’s the kind of expertise walking around at this conference.

While I’m on the subject of NGS, they had a whole pack of people there. Soon-to-retire director Dave Zilkowski gave a lunch-time presentation to approximately 200 attendees. Want to talk to the manager for CORS at NGS? He was there. Want to talk to someone at NGS about network RTK? Bill Henning was there. Want to talk to someone at NGS about OPUS? Yep, there too.

What other opportunity do you have to sit down and have some face time with this caliber of people?

Back to Col. Madden

The theme of his presentation was about how the GPS Wing needs to improve on executing their strategy. A big part of what he was alluding to was keeping the schedule on target for the different programs. For example, there’s no navigation message on L2C and he said there won’t be until 2011, when the control segment (OCS) systems are upgraded. There won’t be a navigation message for L5 either until 2011, even though the first Block IIF (L5) satellite will be launched next year. It’s a good example of the space segment (satellites) and control segment (ground infrastructure) not being in sync. The L2C pilot carrier is available now, so carrier phase users (centimeter-level) are still able to use L2C carrier while utilizing the navigation message from L1.

When he was on the subject of keeping schedules, I asked Col. Madden about launch schedules — more specifically, keeping the schedule that they set. He said two things.

First of all, they need to do a better job of giving realistic launch dates. They move a lot. The seventh Block IIR-M satellite was due to launch last June and has been pushed out until October. The eighth, and last, Block IIR-M satellite was pushed out until December. Also, the first Block IIF satellite, in which an early 2009 date has been floated for quite some time, doesn’t look like it will be put into orbit until August 2009 or later.

Secondly, and most importantly, he said it’s all about the $$. Launching satellites is an expensive business. He said “it takes $60 to 70 million to build a GPS satellite and its $200 million for the launch vehicle.”

As successful as GPS is, Col. Madden is fighting for budget dollars like other program managers. As I mentioned above, he’s got the fourth largest budget in the US Air Force. When Congress looks at areas to save money, it’s easy for someone to say “Just cut 10 percent from GPS and we’ll save $150 million!” Also, it doesn’t help that there are now 31 operational satellites, way more than the guaranteed minimum constellation of 24. The problem is that, as high precision users, we need every one of those 31 operational satellites. We need to continue to raise our hand from the back of the room and be counted.

I know it’s hard, but plan for the ESRI conference next July. I know, I know, it’s prime field season. But, give it a chance and you can take a lot from it. Like I wrote above, don’t look at it as a GIS conference, but rather a networking conference. It may change your business model or even your career path. You’ll have the opportunity to talk to more people than you have in years.

The Latest from Moscow and JAVAD GNSS

It seems every industry has at least one person’s first name that, when spoken, sparks recognition from anyone who has a reasonable amount of experience in that field. In the computer database industry, everyone knows that “Larry” is Larry Ellison of Oracle fame. In GNSS, Charlie Trimble has a street named after him, not to mention a company bearing his name. But no person’s first name carries as much recognition in the industry as Javad.

I attended the First Annual JAVAD GNSS User Conference in Moscow a couple of weeks ago. The company is putting together a serious effort in order to compete in the survey/construction/engineering industries.

Javad is a name synonymous with high-quality, high-precision GNSS receivers — and with some amount of controversy. No matter what you think of the history and circumstances, you have to appreciate the fine GNSS technology produced under the guidance of Dr. Javad Ashjaee.

JAVAD GNSS is, perhaps, his most ambitious endeavor since he started Ashtech some 21 years ago.

The reason I believe it’s his most ambitious effort since Ashtech is because although Javad’s companies have a proven history of providing high quality, state-of-the-art GNSS receivers to the world, everyone in the survey/construction industry knows that while a solid GNSS receiver is important, the software makes the solution. Solid data-collection software and PC processing software is a “must-have” in order to compete with the Trimbles, Leicas, Topcons, and Magellans of today.  A big reason Ashtech always played second fiddle to Trimble wasn’t due to the quality of the receivers themselves. In fact, many viewed Ashtech receivers as superior to Trimble’s in that era. But Trimble’s heavy emphasis and investment in developing a complete software solution and a powerful distribution channel are key reasons that Trimble is valued at ~$4 billion today.

While you can debate whether Javad GNSS will ever achieve the same success as Trimble, you can’t argue about the effort that Dr. Ashjaee is putting forth. He doesn’t need to work and probably has enough money to last a couple of lifetimes, but I think he’s a competitor and he wants to win.

First Annual JAVAD GNSS Conference

The new Javad receiver design appears very nice from an ergonomic standpoint. The RTK communications antenna appears to be missing, but it’s actually integrated inside the rangepole. Last year, Javad bought ArWest Communications Corp., a maker of narrow-band and spread-spectrum radios, so JAVAD GNSS has the flexibility to integrate RTK communications in creative ways. Also, with a Bluetooth interface to the data collector, no external cables are required.

In true Javad style, the Triumph series has 216 channels capable of tracking all existing signals and is prepared to track new signals as they come online, such as GPS L5 and Galileo E1/E5.

From listening and talking with other attendees, there appear to be four areas they see where Javad is trying to set himself apart from the rest of the manufacturers:

1. Pricing. Javad’s innovative pricing scheme. You can look for yourself at http://www.javad.com, although you might be somewhat confused with all of the options. The bottom line is that the system will be pretty competitive. Something unique, though, is that pricing is the same for every country in the world.

1. “Instantaneous” RTK initialization. It’s hard to buy into this one at face value until I (or you) have tried it in true field conditions. Many other systems have pretty quick RTK initializations. “Instantaneous” re-initializations after loss in tree canopy or next to buildings would be very nice, and if it performs true to specs, would be an advantage.

1. In Band Interference Rejection (IBIR). The claim is that RTK users experience times during the day when RTK doesn’t work, due to local RF (radio frequency) interference. In my experience, the most common RTK problem, by far, is the communications link between the base and rover, whether that link be UHF, VHF, spread spectrum, or GSM/CDMA. What Javad is referring to is jamming or harmonic interference at the GNSS frequencies that prevent your GNSS receiver from processing the signals from the satellites. Personally, I’ve never experienced this type of interference, that I’ve been aware of. Any time I’ve had a problem with RTK, I’ve always been able to trace it back to the RTK communications link. So, I’m not sure there is measurable upside to this claim.

1. Superior use of GLONASS. You can read the explanation that JAVAD GNSS lays out in the company’s advertisement in GPS World. I can see that they are in a great position to capitalize on GLONASS given the long history that Javad has in Moscow. But the proof lies in how it performs in the field, so the jury is out on this one. I’ve used several GPS/GLONASS system in the field, and all performed superior to my GPS-only system. Whether Javad’s GPS/GLONASS technology is superior to other GPS/GLONASS receivers on the market is something we need more data on before that conclusion can be drawn. However, it is clear there is some wiggle room here, especially when it comes to resolving biases when the rover GNSS unit is of a different manufacturer than the manufacturer of the RTK network infrastructure receiver. Each manufacturer handles this differently and perhaps JAVAD GNSS has found a novel method.

I haven’t mentioned the “antenna umbrella” that many of you have seen in advertisements or read about. First of all, this isn’t required in order to use JAVAD GNSS equipment. The Triumph-1 pictured earlier is the standard configuration. The “antenna umbrella” you’ve seen is used with the Triumph-4 (not released yet) so the user can benefit from multi-baseline redundancy and integrity with one GNSS receiver.

The Triumph-4 includes four GNSS receivers, three accelerometers, and three gyros to allow positioning in adverse conditions. I really like the idea of the accelerometers and gyros to augment the GNSS measurements. I think this is the wave of the future. But I don’t think the antenna umbrella concept is going to fly, at least for mobile production work like topo surveys, construction staking, and high-precision GIS. I could maybe envision it for geodetic control, deformation monitoring, and machine control, given the right type of packaging.

A Word about GLONASS

Sergey Revnivykh from the Russian Federal Space Agency gave the audience an update on GLONASS. He reasserted the Russian government’s commitment to GLONASS and its intent to support CDMA to ensure “compatibility and interoperability with other GNSS and augmentations.”

GLONASS currently has 12 operational satellites. Only one of those twelve is a legacy satellite that will probably fail in the next year. The other eleven are GLONASS-M satellites with a “guaranteed” life of seven years. Revnivykh says Russia expects to launch six more GLONASS satellites this year. Finally, it looks like we are moving beyond the GLONASS constellation vacillating between nine and fourteen satellites. We should have seventeen solid GLONASS satellites to with work in 2009. Another six GLONASS satellites are planned for launch in 2009, so by December 2009, the number of operational GLONASS could reach twenty-three.

Post-conference Social Event

A Saturday party took place at a lakehouse (the traditional Russian dacha, with modern accoutrements) about 90 minutes from Moscow. A tour bus ferried conference attendees and JAVAD employees to the catered event with activities ranging from miniature golfing to boat rides on the lake. Entertainment was provided by a Brazilian dance troupe and capped off by a trio of opera performers. It was a very well put-together family-oriented event.

Javad Ashjaee in middle, wearing cap

 

 

Software Receivers May Hold the Key to Multi GNSS

It’s not often that I read a technical paper that really catches my attention to the point that I read and reread it, then write the authors to probe further. That happened to me last week.

I’m on the IGS (International GNSS Service, formerly International GPS Service) email distribution list. IGS is a consortium of 200 world-wide agencies that combine resources and share GPS/GLONASS data in order to generate precise GPS and GLONASS products. According to the IGS website, you can think of the organization as the highest precision international civilian GPS community.

The IGS GNSS Tracking Network

If you’re signed up, IGS will occasionally send out informative emails about current GNSS events. To subscribe to IGSMAIL send an email to [email protected] with a line in the body following this format (substituting your own email address):
subscribe igsmail [email protected].

Last week, I received IGSMAIL-5791. It was a notice that a paper was posted from the IGS 2008 Workshop held in Miami, Florida last month. The paper was entitled Considerations for Future IGS Receivers. It was authored by Todd Humphreys of Cornell University, Larry Young at NASA’s Jet Propulsion Lab (JPL), and Thomas Pany with University FAF Munich, Germany.

It’s a great paper to read if you are interested in the future of high-precision GNSS receivers. It touches on a lot of the subjects (GPS modernization, Galileo, GLONASS, etc.) that I’ve been writing about for awhile and also an interesting subject that I haven’t written about: GNSS software receivers.

IGS is interested in being the gold standard of GNSS data: orbits, clocks, reference frame positions, and ionosphere/troposphere maps. A noble goal for sure, but most of the commercial GNSS applications don’t require the sort of accuracy the IGS is chasing after. Nonetheless, the paper discusses many of the issues that face the commercial GNSS industry, and even takes into account the very recent proposal by the Department of Defense to cease support of L1/L2 P(Y) semicodeless. Also, IGS isn’t heavily involved in real-time kinematic (RTK) applications, which have become very prevalent in the commercial GNSS industry.

After reading the paper, I formulated a few questions and sent them to the authors. They promptly answered and I thought it would be insightful to include them in this column.

Eric Gakstatter (EG): You touch on GLONASS and Galileo a bit, but don’t delve into current constellations, launch schedules, etc. This leads the reader to believe that you value GPS modernization over an increased number of observables from other GNSS (GLONASS, Galileo). Is that a correct assumption? The “more signals from the same number of space vehicles (SVs) vs. today’s signals on more SVs” debate is a hot one right now. Which do you value more?

Larry Young: (LY) More satellites with at least two-frequency signals definitely trumps more signals per satellite. For ground uses I believe the limited number of satellites currently reduces our ability to estimate, for example, a spacially and temporally varying tropospheric delay.

We concentrated on GPS because:

1. We have excluded the current FDMA GLONASS signals as less accurate for high-accuracy science applications, but look forward to including possible future CDMA signals from GLONASS.
2. We expect the Galileo signals will be very useful, but there are as of yet only two prototype Galileo satellites in orbit. Actually, we went to some length to describe benefits from the Galileo signal structure. I think any launch schedule for Galileo is even less certain than the schedule for GPS replenishment.

 

(Editor’s Note: Larry’s reference to FDMA GLONASS accuracy (the current GLONASS architecture) doesn’t mean that GPS/GLONASS receivers sold today are less accurate than GPS-only receivers sold today for real-time kindematic RTK/machine control applications. Companies that design GPS/GLONASS receivers have developed methods to mitigate the internal biases that exist in the GLONASS broadcast signals.)

EG: How did you determine 16 as the minimum requirement for the number of L2C SVs in orbit?

Todd Humphreys (TH): We tried to temper the pressure to modernize the IGS network with an understanding that the IGS is a volunteer federation with enormous inertia, and so can’t be expected to respond to drastic requirements upheavals. The presence of 16 L2C-capable SVs (which implies 8 L5-capable SVs) on orbit is what triggers Event 2 in the minimum requirements schedule. The primary changes brought on by Event 2 are:

1. newly incorporated IGS receivers must be L5-capable
2. newly incorporated receivers are no longer required to track L2 P(Y).

Change 1. keeps the IGS current by beginning to measure and characterize the L5 signal. Change 2. is meant to begin the inevitable conversion to a network that does not use P(Y)-code tracking. Change 2. also reduces the barrier to entry into the IGS network. By not requiring L2 P(Y) tracking, we open the IGS network to receivers without semicodeless tracking capability, such as some software receivers. It’s also a recognition that commercial receivers capable of P(Y) tracking will likely be more rare and more expensive after Event 2, given that semicodeless P(Y) tracking is slated for obsolescence.

EG: Given the intention of the U.S. Department of Defense (DoD) regarding semicodeless access, do you think it will halt all development of GNSS software receivers in that area, and that they will focus purely on L1 C/A, L2C and L5 (and L1C)?

TH: The paper mentions that software receiver developers are not as keen on codeless/semicodeless techniques as they are on standard coded tracking for two reasons:

1. Software receiver designers want to get the most performance they can from their limited computational resources and so it makes sense to concentrate on coded tracking.
2. The restrictions on use of proprietary codeless/semicodeless tracking techniques makes these techniques less attractive than standard coded tracking.

Add to this that the DoD plans to discontinue semicodeless access by around 2020, and you can see why semicodeless tracking hasn’t been on the forefront of most software receiver developers’ minds.

On the other hand, the IGS minimum receiver requirements schedule proposed in the paper would require semicodeless-capable receivers until 8 IIF SVs are in orbit (making a total of 16 L2C-capable SVs on orbit). Hence, if software receiver developers want to see their products used as stand-alone receivers in the IGS before then, they’ll have to provide semicodeless tracking.

Thomas Pany (TP): Semicodeless access is an interesting topic on its own and software receiver research will continue on it (at UniFAF we got funding for it).

LY: JPL needs to track P-codes in its software receiver in order to get the best accuracy for surface-reflection experiments. When this is done with post-processing, we are able – and others should be able – to obtain the actual Y-code chip sequences that had been used. We also implement semi-codeless processing into software receivers. Sometimes it’s just handy to have both the L2C and P2 signals, for example, to investigate effects of long-delay multipath.

What is a GNSS software receiver?

I think a real interesting part of this paper, and one I haven’t touched on yet, is the discussion of software GNSS receivers. A friend of mine has been putting the software receiver bug in my ear for some time. I’ve been dismissing it for the most part because he and I have been speaking in terms of the consumer GPS market. I hadn’t really thought of it with respect to the market for high precision commercial GNSS receivers, especially those that are in fixed installations like CORS.

First of all, one of the reasons today’s complex GNSS receivers are so small is because there is a high level of electronics integration. What that means is that engineers design many different processing functions into one or two custom integrated chips. These chips are called application specific integrated circuits (ASICs). Using ASICs help reduce the size, cost and power consumption of complex electronic products such as GNSS receivers.

The Cornell University GRID GNSS software receiver based on DSP technology.

But an ASIC is not required to build a GNSS receiver. Granted, without an ASIC or two it might be larger and more power hungry, but you can build one nonetheless. A GNSS software receiver doesn’t mean you get a GNSS receiver delivered on a $2 DVD either. No sir, there are still plenty of electronic components involved. The core difference is that instead of one or two ASICs, there would be a series of off-the-shelf discrete components. There are essentially two different approaches in designing a GNSS software receiver; one uses a digital signal processor (DSP) and the other uses a field programmable gate array (FPGA). Sometimes both a DSP and FPGA are used in a design. The GNSS software is loaded in the DSP and/or FPGA and this is how the GNSS software receiver gets its name.

Essentially, a GNSS software receiver is a design where all signal processing that comes after the analog radio frequency front-end is completely software re-configurable.

Why use a GNSS software receiver?

Higher power consumption, larger size and higher chip count doesn’t seem like a good argument in favor of GNSS software receivers. So what is? I posed that question to the paper’s authors.

EG: What is the major attraction of GNSS software receivers? Cost? Flexibility?

TH: From the point of view of the IGS, the major attractions are flexibility and transparency. The IGS’s goal is to deliver gold standard GNSS orbits, clocks, reference frame positions (and thereby contribute to gold standard Earth orientation parameters), and iono/tropo maps. For this, we need transparency into receiver operation so that we can better model the statistics of the receiver products that we use. Better yet, we’d like to implement our own specialized tracking loops and other specialized receiver features. Software receivers offer us this transparency and flexibility.

Although it probably takes a back seat to transparency and flexibility, price is certainly an attraction. For example, the ASTRA software receiver mentioned in the paper is planned to be offered for around $1,200 (hardware) plus $200 or so per receiver for a software maintenance contract. This is about 10 times less expensive than the traditional receivers that the IGS buys. If ASTRA and others can really deliver at such reduced prices, you may see an exciting densification of IGS sub-networks for tropospheric and ionospheric study.

EG: Do you think there is a strong possibility that GNSS software receivers are technically able to replace traditional GNSS receivers in fixed GNSS infrastructure environments (eg. CORS, IGS, JPL, SoPAC, etc.)?

TH: Absolutely. The JPL BlackJack receiver is arguably the best-performing GPS receiver on the planet today, and it’s essentially a software receiver with an FPGA-based correlation engine (see the Montenbruck reference in the paper for a comparison of the BlackJack against other receivers). I suspect that the reference-frame receivers sold by some traditional vendors are, in fact, software receivers in the mold of the BlackJack. I predict a market-wide convergence toward FPGA/DSP-based software GNSS receivers over the next decade as the FPGS/DSP price per transistor count continues to fall.

The real question is what kind of access the IGS will have to the software of these receivers. The traditional model is that the IGS has no control over their receiver’s software aside from setting a few parameters and downloading the occasional vendor-provided firmware update. Suppose vendors instead license their source code to the IGS, or provide “plug-ins” for IGS-specific routines. Such transparency and flexibility is just what the IGS needs to carry out its demanding mission.

EG (following-up on Humphreys’ comment on a market-wide convergence toward GNSS software receivers over the next decade): If a vendor can sustain its business by licensing their source code, then it will happen. The alternative is a Linux-type approach where the development is a shared effort. The commercial demand will be great enough that I think one of these models will materialize.

TP: If an open-source software receiver emerges in the near future, it has to overcome the following difficulties, which are not easy to solve (at least this is our experience at the University FAF Munich).

1. The front-end development has to be done and drivers have to be developed.
2. The software requires assembler programming skills including multi-threading.
3. The software needs to have a high stability to run 24 hours per day with basically no failure. This all applies for FPGA, DSP or general-purpose based receivers, and are eventually most easily solved on the general-purpose processor.
4. Last but not least, you have to implement competitive signal processing algorithms to achieve results similar to commercial receivers. So if one succeeds with all this stuff, it’s questionable, if the software will be free of charge.

EG: I guess network RTK users would see some upside (to a densified reference station infrastructure)? How about static post-processing users? Maybe longer baselines?

TH: Accurate estimates of SV clocks and orbits don’t depend strongly on dense networks. By extension, network RTK users or static post-processing users won’t see marked improvement just because the surrounding network is denser. What improvements come from denser networks will be due to a better characterization of the troposphere and its gradients. Such improvements will indeed allow longer baseline carrier-phase-differential techniques. One could imagine a dense regional network making possible carrier-phase-differential techniques with millimeter-level accuracy on baselines of up to 100 km. Whether this will be of great commercial interest, I can’t say. As a researcher, I’m interested!

If the user has a single-frequency receiver, then dense networks help to mitigate both ionospheric and tropospheric errors in his RTK or static-post-processing solution.  If the user has a dual-frequency receiver, then he won’t see much reduction in his ionospheric errors, but will still benefit from reduced tropospheric errors.

EG: Can you tell me a little bit about the computing platform required for a GNSS L1/L2/L5 receiver?

TP: I strongly believe that a modern standard PC (four cores) has all the required processing power to do all-in-view L2P(Y) tracking at least with cross-correlation in addition to track the civil signals on L1/L2, but to which extent the computational resources can be exploited strongly depends on the developers’ capabilities. It’s my experience that PhD candidates who typically have a background in geodesy or communications are normally not experts in assembler language. For this type of work an experienced game programmer would eventually be more qualified.

TH: Right now, a full L1/L2/L5 receiver requires either a multiple-core approach (see the description of the University FAF Munich receiver in the paper) or an FPGA. The wide bandwidth L5 signal drives this requirement. Tracking L5 requires 10 times more computational power than narrow-band tracking of L1 and L2C.

EG: Do you have a schedule in place to perform the testing described in item 6. A. (from the paper)? Compare the performance of a software GNSS receiver with a traditional ASIC-based receiver?

TP: A University FAF Munich software receiver will be installed at a EUREF site in Germany in September or October this year. I expect that the data will be available to IGS.

TH: A dual-frequency version of the Cornell GRID receiver will be tested against traditional dual-frequency receivers in November of this year. It will be deployed to Brazil for ionospheric scintillation study in December of this year.

Imagine All the Signals, Living in Harmony

Imagine if you had a GNSS software receiver and a new signal such as L5 comes online. You wouldn’t need to change your receiver hardware (except the antenna), no boxes to unpack, no new hardware to figure out, only load new GNSS processing software into the DSP/FPGA.

But I think low cost, rather than flexibility; might drive the GNSS software receiver into the commercial markets eventually. Not necessarily on the user equipment side of things such as machine control or portable applications, but rather on the infrastructure side of the business, such as CORS and other regional as well as world-wide networks where power and size can be traded for cost. Like Humphreys said, being 1/10th the cost of traditional GNSS receivers makes it feasible to create very dense networks of reference stations.

 

PNT Advisory Board on the Virtues of 30 Plus

Last fall, I wrote a column about the Civil GPS Service Interface Committee (CGSIC). Essentially, CGSIC is the forum for the civil community to communicate with the people who manage the GPS, and vice versa. In this column, I’d like to climb up the ladder, so to speak, and talk about the Space-Based Positioning, Navigation and Timing (PNT) National Executive Committee.

The PNT Executive Committee was established by the president to “advise and coordinate federal departments and agencies on matters concerning” GPS. Specifically, its functions, according to the website, are to develop a national space-based PNT strategy, develop a five-year national space-based PNT plan, and conduct an annual assessment of the adequacy of the federal government’s department and agency budgets and schedules.

Let me be clear, the Civil Global Positioning System Service Interface Committee (CGSIC) and NAVCEN are still together the clearinghouse for the public to communicate with the people who administer GPS and vice versa. That hasn’t changed. But monitoring PNT Committee activities, reading various presentations given by PNT Committee representatives, and reading minutes from PNT Committee advisory board meetings can give one a view into the thoughts of those who influence GPS policy.

A Case in Point.

Some of you in the user community have been around GPS for a decade or longer. You may recall that back in the 90’s, the U.S. government attitude towards other countries developing their own GNSS was quite cold and unsupportive.

Since then, this attitude has changed 180 degrees. The U.S. GPS folks are reaching out and embracing GNSS development elsewhere. Joint working groups have been established that include U.S. GPS representatives and technical folks from the various GNSS programs to promote compatibility and interoperability between GPS and these other GNSS.

There is no better example of this than when the United States and Russia formed the GPS-GLONASS Interoperability and Compatibility Working Group in December 2004. Remember that GPS and GLONASS were both deployed during the height of the Cold War, so no technical communication (at least non-adversarial) was possible at that time. Fast forward to 2007 when the Russian Space Agency indicated that GLONASS would be migrating towards CDMA so GLONASS would be compatible with GPS and other GNSS in development. This is a truly remarkable turnaround.

Last September at the Institute of Navigation (ION) GNSS conference, Alice Wong, Senior Advisor on GNSS with the U.S. State Department, discussed many of the international cooperation arrangements the United States has with countries developing a GNSS. She made two revealing and significant statements. “The number of space-based signal providers will grow from two countries (the United States and Russia) to at least six or more by 2020,” she said. The United States has recognized that although it may have set the gold standard for GNSS, it’s growing beyond what it can control. That leads to Wong’s second statement, which described the U.S. attitude towards GNSS development and operation.

Interoperable = Better Together than Separate

I didn’t intend for this to become a column on U.S. international GNSS policy, but rather to illustrate the tremendous amount of information and links to be found on the PNT.gov website.

Beside the presentations by PNT representatives, another part of the PNT.gov that’s very interesting to monitor is the PNT Advisory Board. NASA (National Aerospace and Space Administration) established the board on behalf of the PNT Executive Committee. The board members are non-government GPS experts who provide advice on GNSS from a technical as well as program and policy perspective. There are some well-known and well-qualified individuals on the board. Some you would know by name, such as Charlie Trimble (formerly of Trimble Navigation) and Brad Parkinson of Stanford University. But there are also many others from industries outside of surveying/construction that you may not recognize, but that represent significant industries or offer valuable perspectives.

The board meets at least twice a year and PNT.gov publishes minutes from the meetings. Reading the minutes from these meetings is an interesting look at how future GPS policy may be shaped.

The minutes from the March 2008 meeting (all 31 pages) are now available at PNT.gov. Please note that the board meetings aren’t limited to the PNT Advisory Board members. The meetings are open to the public, although audience members are asked not to interrupt the speakers. In the minute appendices, one can view a list of all who attended the March 2008 meeting.

In reading the minutes, one sees that a substantial part of the discussion centered on the optimal number of satellites and configuration of those satellites. To wit:

• Gerhard Beutler, President, International Association of Geodesy

“Further, he reported that the scientific community, organized in IAG, was committed to exploiting the full potential of all GNSS systems: this, he said, required combining all systems measurements in a single analysis; placing laser reflectors on all GPS/GNSS satellites; and expanding the GPS constellation to 30-plus equally-spaced satellites.”

• Bard Parkinson, Stanford University

“Dr. Parkinson, panel chair, said the Independent Review Team (IRT) had identified the Big Five essential GPS performance criteria: assured availability, resistance to interference, accuracy, bounded inaccuracy (in particular, the limit on the “wild result”), and integrity.”

• Michael Shaw, director, National Coordination Office for Space-Based PNT

“Mr. Shaw commented that to meet a 30-satellite standard, 34 to 36 satellites would be required. Dr. Parkinson said he believed 33 would be sufficient; at present, he said, the commitment to 24 was not always maintained. Dr. Parkinson added that if the Federal government committed to 30, and didn’t always make it, ‘we would forgive you.’”

• Capt. Joe Burns, United Airlines

“Capt. Burns from United Airlines commented that the improvements in civil aviation expected from a space-based air traffic control system would not be realized with the current constellation. Dr. Parkinson urged civil aviation to undertake and make public a cost/benefit analysis on the subject: he asked Capt Burns how many satellites he believed were required. Capt. Burns said at least 27, preferably 30. Ms. Neilan said it appeared all present believed 30 satellites were needed. She asked Dr. Parkinson if his analysis had been intended to prompt persons at DoD to reconsider whether the 21 plus 3 constellation was indeed adequate to their needs. Dr. Parkinson said he did not know what affect his study might have.”

The discussion time spent on the number of optimal GPS satellites is positive and I think it speaks to the future of what we can expect. Even though we enjoy 31 satellites today, the DoD only guarantees a 24-satellite constellation. I also like the fact that Parkinson is staying on target with the same message of the Big Five that I first heard at the ION GNSS 2006 conference.

If you get a chance, take a break and read through the minutes. It’s worth the time.