Public Knowledge Sides with LightSquared
Public Knowledge filed comments to the FCC that clearly sided with LightSquared in their dispute with GPS device makers. When it comes to wireless broadband that uses spectrum that was once designated for satellite usage, Public Knowledge wrote:
“the costs of updating a legacy spectrum regime should not necessarily be borne by new entrants”
The “LightSquared vs. GPS” dispute is a problem that has no easy answer. On the one hand, GPS makers like Garmin manufactured GPS devices with no receive-side filters to block out neighboring frequencies. The result is GPS devices that require guard bands on the order of 50 MHz (two sides combined) and the GPS devices listen to frequencies allocated to LightSquared. This wasn’t a problem when LightSquared broadcast their signals from Satellite orbit with signal levels reaching earth that were comparable to the GPS satellites. But with terrestrial wireless base stations that are on the order of 100,000 times stronger due to higher transmit power and closer proximity, the GPS devices with no receive side filters will experience interference.
While Garmin and other GPS makers are a major source of the problem (lack of FCC regulation on radio receivers is another), the reality is there are tens of millions of GPS devices in the hands of consumers that would face interference if LightSquared was permitted to go forward with its terrestrial transmitter broadband service. That means consumers will need new GPS receivers in their cars and smartphones with receiver filters that filter out LightSquared. And someone – either the GPS makers, the consumers, or LightSquared – will need to pay for this, should LightSquared be permitted to go forward with terrestrial transmitters. Furthermore, it isn’t possible to build a perfect receiver filter, particularly when the power difference between satellite and terrestrial transmitters is so great. Filters can’t filter out all neighboring frequencies, and will unfortunately filter some of the GPS signal as well.
Garmin is screaming that LightSquared’s proposed terrestrial wireless network will interfere with existing GPS devices and customers’ devices will suffer interference. LightSquared will scream that Garmin and other GPS devices are listening to spectrum allocated to LightSquared. Both assertions are correct, but the consumer will be very angry should they be forced to replace devices at a nontrivial cost. And can LightSquared or the GPS makers even afford the necessary upgrades (in the unlikely event that both assumed equal responsibility)? The short term answer might be “no.” and the new LightSquared terrestrial wireless network may have to wait until some long term solution materializes.
Some clarification is needed here:
1. “…the GPS devices with no receive side filters will experience interference.”
I’d like to know which GPS receiver you know of that has no “receive-side filter”? Every GPS receiver is designed with filters. The problem is that the MSS band has historically been used for low-power satellite-to-earth communications and the filters were designed to handle that scenario. Who would reasonably expect the same filter to be able handle a neighboring signal a billion times stronger?
2. Many high-end GPS receivers were designed to specifically use the MSS band because LightSquared (and Inmarsat) sells satellite-to-earth data communication services to the GPS industry. It’s ironic that they are saying GPS receivers are “looking in our spectrum” when they were (and continue to) soliciting business from high-end GPS users. If they want to discontinue that service (they haven’t), that’s fine, but don’t characterize it as “sloppy GPS receiver design.”
3. You are right, the issue is the installed base of GPS receivers. In the high-end GPS receiver market alone, this is a multi-billion dollar proposition that is very complex. It’s not like a consumer throwing away their Garmin unit and buying another for $100. The high-end GPS receivers sell for $10,000-$30,000 each. It will destroy a huge number of small, professional services businesses in which high-end GPS receivers are their largest capital expenditure. That’s not even considering the investment by Fed/State/local entities.
Read my comments to the FCC for a better understanding.
http://fcc.us/nZoGO9
Sincerely,
Eric Gakstatter
Eric, thanks for your comments. I think with the filter issue, the point is that the filters were not adequate. They were adequate for neighboring satellite signals but not neighboring terrestrial signals. This is a problem of poor planning and it’s not easy to pin the blame if there’s anyone to blame at all.
On your second point, I was not aware before that LightSquared sells services to GPS users. It’s a good point.
The point of my blog post is that the issue is far more complex than the Public Knowledge comments.
No filters for GPS receivers exist today that can handle a signal that powerful in neighboring spectrum. That doesn’t mean they couldn’t be developed, but no one knows. Most say that GPS performance would take a hit if such a filter was possible. You’re correct in that with proper planning, the issue would be less serious than it is today. But the lack of proper notification prevented any sort of reasonable planning. That falls on the FCC. In my comments to the FCC, I give an example of how this sort of situation was handled properly in 2008.
Yes, I’ve communicated a little with Harold Feld of PK. While his intentions may be good and he’s done a fair amount of homework, he’s out of his league on this one. I don’t blame him. It’s a complex issue and difficult for many to understand.
Thx, Eric
“No filters for GPS receivers exist today that can handle a signal that powerful in neighboring spectrum”
Are you saying that we can’t reduce the neighboring broadcast of terrestrial transmitters to a level significantly below that of the passband, so that the signal to noise ratios for the GPS signal is greater than one?
Hi George,
Of course, if you reduce the terrestrial broadcast strength to a point, it becomes very feasible. I don’t know what that level is. I’ve heard of the original ATC discussions with MSV (LightSquared predecessor) that ~1,800 tower density broadcasting @ ~80 watts was acceptable with existing GPS equipment so I imagine with newly developed filters, one could go much higher than that and somewhat more dense…maybe even to the reduced levels that LightSquared is proposing (50% reduced power of the original proposal if I remember correctly). However, that still leaves the issue of the replacement cost of legacy GPS equipment. That’s the tough one. Only time (unless someone has a couple of billion to throw at it) can solve that one, and LightSquared doesn’t have time to give.
Thx, Eric
I think LightSquared wanted a few thousands watts ERP for their terrestrial towers. Taking it down to 80 watts ERP would require very high tower density.
Agreed. That’s one of the problems of going to lower power output. I’m not sure what the 50% reduction does to the tower density. They don’t talk about that. At original power levels, the heavily-populated urban tower density was already at 400-800 meters.
[…] had a great discussion about the ugly problem of GPS interference last week and why it can’t be oversimplified. […]
[…] had a great discussion about the ugly problem of GPS interference last week and why it can’t be oversimplified. […]
[…] had a great discussion about the ugly problem of GPS interference last week and why it can’t be oversimplified. […]
Do you know of any satellite based services in this frequency band that Light Squared does NOT hose?
No doubt, the FCC staffer who approves the LightSquared deployment will leave the FCC and go to a well paid job at LightSquared, just as Baker went to Comcast after ruling in their favor!
http://www.nextgov.com/nextgov/ng_20110610_6517.php
“He also said more details on a previously issued report on the interference LightSquared caused to GPS receivers that first responders used with a LightSquared transmitter mounted on a 100-foot tower at Holloman Air Force Base, N.M. In this instance, a GPS receiver in a police cruiser lost its signal 600 feet from the tower and the GPS receiver in an ambulance showed the vehicle was moving at a speed of 9 mile per hour, when in fact it was stopped.
General Motors OnStar system, installed in close to 6 million vehicles, and used for emergency road services and GPS-based turn-by-turn navigation, experienced “significant degradation of service” during the Holloman tests, which ran from April 14 to 17, Bunce said.
NASA’s Jet Propulsion Lab determined that the LightSquared system showed “significant interference” to GPS receivers at a distance of 185 miles, he added.”
History and Background about LightSquared, their promises, and claims that even their other frequencies hose GPS receivers
http://www.wirelessindustrynews.org/news-jul-2011/2623-072811-win-news.html
Broadcast Engineering Journal recommends against deployment of LightSquared
http://broadcastengineering.com/ott/report-recommends-against-lightsquared-07132011/