Survey & Construction Newsletter, Late December - GPS Survey & Construction

Survey & Construction Newsletter, Late December - GPS Survey & Construction: "

Dec 18, 2008 By: Eric Gakstatter GPS World

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.