LightSquared Saga, and Recent Solar Activity

March 2, 2011 - By Eric Gakstatter

This week I’m following up on my article from a couple of weeks ago about the potential effects of LightSquared’s plans. As a user of high-precision GPS receivers (particularly GPS L1 sub-meter, but also dual-frequency), you should be particularly concerned about this issue. I’ll tell you why. Also, I have a note on recent the solar activity.

LightSquared

The reasons you should be concerned about LightSquared’s plans are two-fold:

1. Consumer GPS receivers and professional-grade GPS receivers designed for higher performance (mapping, surveying, etc.) aren’t necessarily designed the same way. High-performance GPS receivers use a wider bandwidth radio design.

For example, the GPS L1 frequency is 1575.42 MHz. Many high-performance GPS receivers use a wide bandwidth radio that scans +/- 20 MHz from 1575.42 MHz. That equates to a range of 1555 MHz to 1595 MHz. LightSquared’s frequency spectrum is 1525 MHz to 1559 MHz. Clearly, there’s overlap, which is another word for interference. On top of that, LightSquared plans on a broadcast strength of 1,500 watts from a tower located down the street. The GPS broadcast signal strength is about 30 watts from a satellite located some 19,000 kilometers away in outer space. Who’s going to win that battle?

I’m not an aerospace engineer or an RF (radiofrequency) engineer, but I don’t think it takes one to see the potential impact of LightSquared’s service on high-performance GPS receivers. At the very least, it warrants an in-depth technical study.

2. Neither the policymakers nor LightSquared know about or understand the user community of high-performance GPS receivers comprised of hundreds of thousands of high-end GPS receivers. They think the GPS user community is comprised of auto navigation and mobile-phone users. They don’t understand that we are the infrastructure people. We use GPS in a way that they don’t understand, but is so critical to our infrastructure. It’s not their fault, but you can’t assume they know, so it’s up to us to inform them. You have to speak up.

Here’s a perfect example. Click on the following link to view a report presented by LightSquared last week in Taipei, Taiwan, at a 3GPP conference.

“Final Report on Overload Characteristics of GPS Receivers in Proximity to LightSquared’s L-band Terrestrial Base Stations (BTS) and User Equipment (UE)”

The best part about this report is the following statement from the Executive Summary:

“Although results have been provided to date of a limited number of devices (6), LightSquared proposes to close the study at this stage as a more comprehensive study, covering a wider variety of GPS receivers than those involved in cellular applications, has now been initiated under the auspices of the FCC [2]. This study will be conducted by a cross-industry group led by LightSquared and USGPSIC, the reports of the study having complete public visibility.”

Granted, I understand the Taipei conference was focused on the impact of LightSquared’s plan on mobile phones using GPS, but if this is the extent of their testing, it’s alarming. Furthermore, it’s relatively easy to acquire and operate an inexpensive consumer GPS receiver. Can you picture LightSquared attempting to test a sub-meter GPS L1 receiver or a RTK setup? GPS, GLONASS, SBAS, DGPS, real-time, post-processing, and the myriad of receivers on the market need to be tested. Although it’s likely not possible to test all equipment on the market, it’s not prudent to leave anything to chance. If, one year from now, you wake up and find out your $10,000 RTK receiver doesn’t work like it used to, it will be too late to do much about it. It takes very little time to voice your concern now to your elected officials so the appropriate attention is given to high-precision users.

The good news is that Trimble Navigation is involved, along with the Federal Aviation Administration, with the U.S. GPS Industry Council and will be working closely with LightSquared in a Technical Working Group to better understand the impact that LightSquared’s system would have on GPS. Trimble and the FAA aren’t the only parties involved in the working group, but they are the parties that understand the needs of the high-precision user.

The Technical Working Group’s first report is due March 15, 2011. Time is short, so don’t delay.

Use these guidelines to take action. It is a call to action from Dr. Joe Paiva, veteran of surveying since the 1980s with whom many of you are familiar.

Solar Activity

As you’ve probably heard, we’re entering the next solar cycle, which is due to peak in May 2013.

I want to periodically touch on this subject as the solar activity is going to increase over the next few years, and if the solar activity (geomagnetic storms, not sunspots) is severe enough, it will have an effect on GPS accuracy and tracking. Regardless of what you’ve heard in the mainstream media in recent months, the last event serious enough to affect GPS operations was in December 2006. That’s not to say that things aren’t heating up.

But the recent activity does highlight the fact that “the Sun has become, somewhat suddenly, more eruptive,” according to Joe Kunches, of NOAA’s Space Weather Prediction Center. “We’ve been fortunate so far, in that the terrestrial effects — and impacts to GPS — have been very minimal. The most obvious sign of this has been the brilliant auroras up north.”

“The video shows a large prominence eruption — billions of tons of plasma being strewn off the Sun. Some of it is drawn by gravity and rains back to the surface — the rest of it escapes. It’s the blown-away plasma that forms the coronal mass ejections that, when properly pointed, go by the Earth and cause problems for GPS,” said Kunches.

Click on the following image to view a 15-second video of a solar flare that occured on February 24, 2011.

Credit: NASA/GSFC/SDO

From NASA:

When a rather large-sized (M 3.6 class) flare occurred near the edge of the Sun, it blew out a gorgeous, waving mass of erupting plasma that swirled and twisted over a 90-minute period (Feb. 24, 2011). This event was captured in extreme ultraviolet light by NASA’s Solar Dynamics Observatory spacecraft . Some of the material blew out into space and other portions fell back to the surface. Because SDO images are super-HD, we can zoom in on the action and still see exquisite details. And using a cadence of a frame taken every 24 seconds, the sense of motion is, by all appearances, seamless. Sit back and enjoy the jaw-droppi
ng solar show.

March 17, 2011 Webinar: A Closer Look at L5: The Future of High-Precision GNSS

Last year, the first GPS IIF satellite was launched. It became the first GPS satellite to broadcast the new L5 civilian signal/frequency. At 1176 MHz, it is further separated from L1 and L2 and located in the protected Aeronautical Radionavigation Services band, so there is no possibility of commercial interference like we see today with the LightSquared controversy. The availability of GPS L5 will usher in a new era of inexpensive, accurate GNSS receivers and will be the future of high-precision GNSS receivers, and quite possibly single-frequency receivers. I will also discuss the international support of L5 from other GNSS in development such as Galileo, Compass, QZSS, as well as SBAS (WAAS/EGNOS/MSAS).

I’ll be presenting some interesting new material in the webinar such as graphics illustrating how many satellites (GPS and others) are projected to be broadcasting L1 and L5 just four years from now. It will be well worth 60 minutes of your time.

Thanks, and see you next time.

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