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4G Broadband May Jam GPS
mferrare noted some rumblings that 4G Broadband may jam GPS. There's a slew of technical bits in an report (PDF). 4G broadband frequencies (1525-1559MHz) are next door to GPS frequencies (1559-1610MHz). Test results won't be out until June.
All the GPS satellites transmit on the same frequency, 1.575ghz for L1 and 1.227ghz for L2. The only variance from this is Doppler shifts from the user to satellite perspective.
Just to specify, that was all assuming that the study isn't crap, and that properly designed GPS receivers could infact be affected.
Don't worry about bandwidth overlap (guaranteed to happen with some poorly designed transmitters and antennas) worry about all the other electronic devices which aren't meant to transmit RF but blast it out all over the bands.
I have recently got into amateur radio and some bands are locally unusable due to something as simple as a transformer power supply blasting out many watts of RFI.
The slow death of radio bands to RFI is like the "death" of stargazing due to light pollution.
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CINC, 4th Penguin Legion
Depending on the type of bandwidth and modulation within those specific carriers (specifically at or very near 1559 MHz), they could be interfering with each other.
Using a more highly-compressed modulation type (ie qpsk or 8psk vs. bpsk) with viable harmonic filtering should eliminate any "side lobes" and therefore interference at low power levels. Filtering at the satellite and/or cell tower side should also be present, further eliminating possible treading across bands.
This sounds like a problem between frequency management, poor choices of modulation, excessively wide bandwidth on carriers, and simple bandpass-style filtering. Certainly not difficult to overcome, but one of these technologies is going to have to budge in the correct direction, and I doubt GPS will be the one to do so.
What else can happen when an unstoppable force collides with an immovable object?
Feh. It wouldn't be the first time these dimwits at the FCC screwed up. I remember installing 928.8... MHz SCADA (you know, the telemetry that runs your water, electricity, gas...) and it worked great. About nine months later, the FCC allowed 929 MHz paging. In a very short span of time we had enough energy coming down the antenna line to light a neon bulb. They were licensed for 3 kW ERP. Our remotes were licensed for 5 W + some gain from a small Yagi.
The master receivers went deaf from the continuous blast of high powered paging traffic. A Cavity filter can't do much to get rid of strong signals only 200 kHz away at 900 MHz.
Yeah, the FCC screwed up. They had no knowledge of the state of the art of receivers. We bought receivers engineered for sensitivity, not strong signals, because at the time, there were no other significant strong signal sources on that band. The state of the art took a while to catch up. We ended up solving the problem by re-licensing our channels for horizontal polarization. The pager stuff remained vertical. We got 20 dB of immunity from them and that was enough.
And to the jerkwads at the FCC who thought this was acceptable: DO YOU LIKE WATER? DO YOU LIKE ELECTRICITY? DON'T DO THIS TO US!
spit...
Nearly fifty percent of all graduates come from the bottom half of the class!
You're right. The report is likely to be bogus.
If this is true it means the up and coming cash cow and one of the largest payola maker for representatives is now default for US. Yes, that means UAVs are now unsafe for operation. That also means IFR aviation traffic in inclement weather is many cases is now impossible. It means the entire GPS and navigation markets have been destroyed.
Simply put, if in fact there is any proof that GPS can be compromised by 4G deployment, the FCC will be forced to move 4G to another frequency. Period.
Can you imagine headline, "FCC sued for string of airliner crashes - negligent homicide charges filed against head." And that's just the tip of the iceberg.
No bones about it. *IF* its even remotely true, 4G would be forced to change. Otherwise both safety of the masses and economic damage is just too massive to ignore. Not to mention the possibility of criminally negligent charges.
and according to TFA
The data point is best completely ignored. Outages like that do periodically occur and are well documented. Furthermore, they have occurred long before 4G was deployed. Such a failure could have been anything from wiring problem, faulty antenna, or even a software glitch.
But, it says it happened 5.6 miles from the transmitter, it almost certainly means the article is completely confused. Which if true, means GPS IS NOT BEING JAMMED. PERIOD. For them to be that close to a transmitter means they are in space, which simply isn't likely. Likely, they are talking about WAAS, which is not GPS in of itself. Rather, WAAS is ground based signal correction/enhancement which is used to increase GPS accuracy; but GPS still works without it.
If in fact 4G interferes with WAAS, expect the FCC force 4G to new frequencies as without WAAS, some GPS IFR aviation approaches can not be legally or safely performed. Simply put, air safety and speed is likely to trump high speed wireless broadband. Worst case this means some approaches may become obsoleted and unlikely to affect anyone else other than pilots.
AM Radio could interfere with aircraft beacons, since they're right next to each other!
Please. We've been allocating spectrum for things for a long time. Interference can be monitored and controlled. Do you really think that mobile telephone companies would put up with broadcasters puking all over their spectrum? Or vice versa? Or either putting up with amateur radio interference?
Or, perhaps worst of all, do you think the Hams would put up with someone interfering with their spectrum? They can triangulate secret government projects accidentally using their shortwave spectrum.
Yes, interference happens from all sorts of places. You'll likely find that devices in your adjacent spectrum are less likely to interfere than other sources of interference.
-- Erich
Slashdot reader since 1997
Contrary to what the headline and summary implies, "4G" doesn't always use 1500Mhz. In fact, I'd never heard of a 1500Mhz cellular network until now. Apparently a startup called "Lightsquared" has bought that patch of spectrum and wants to roll out an LTE network. No other 4G network is in that frequency range. For example, Verizon's LTE network is at 700Mhz and Sprint's Wimax network is 2500Mhz.
So, really, this is no concern to anyone but Lightsquared. Either there's no interference and they can go ahead with their rollout, or there is interference and the FCC has to step in. In either case, the other 4G networks are unaffected.
"A week in the lab saves an hour in the library"
This could be somewhat worrisome to us urban geocachers. It's gonna be harder to use the multi-billion dollar military satellite network to find that little tupperware container.
Dude, your GPS receiver is 14 seconds off!
People who use GPS for accurate timing need to be aware that GPS doesn't account for leap-seconds. As such, GPS is ahead of UTC by about 14 seconds. You can read more about the problem here.
It gets more complicated, however, as some receivers correct for this. You can read more about the correction here.
Some have wondered how accurate the time display is on Garmin GPS receivers such as G-12XL, G-II+, and the G-III. Here is an answer provided by Garmin Engineering. This also explains why the GPS can be locked for awhile and still differ from UTC by 11 or 12 seconds. (This answer applies to other brands of GPS receivers as well.)
Start of Garmin quote>
Provided the unit has collected current leap second count from the navigation message, (current leap second difference from GPS time is only broadcast once in a 12.5 minute Nav. message), or current leap second has not changed since the last time the unit collected this variable, the time displayed on the front of the unit should be accurate to within 1 second of UTC.
>end of Garmin Quote
Joe Mehaffey comments:
This means that IF your GPS does not have (or does not save) the leap second offset from last time it was operated, your time may be off by perhaps 12 seconds until the complete NAV MESSAGE is received by the GPS. Jack and I have observed that "typically" Garmin GPS receivers display time which is delayed from about 1/2 to 1 second behind UTC. Lowrance GPS receivers are usually between 1 and 2 seconds delayed behind UTC. In both cases, this is a result of the display driver subroutine having low priority as the "GPS internal clock" is within a few nanoseconds of correct.
Similarly, the NMEA time output on the serial link is typically delayed a second or two depending on various factors.
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I would stress too much about this. Anything that has even a remote chance of interfering with the US military's use of GPS is never going to be deployed. Period.
It's time to learn old fashioned orientation again! When driving on car trips as a child, when we got lost, my father would always ask, "Where's the sun?" This to figure out in what direction we were traveling. He grew up on a large, remote ranch, so he learned this skill from my grandpa. Now if some other broadcaster starts sending something that interferes with the Earth's magnetic field . . . the rest of us will be in big trouble.
I'll just mention that to the Alaska Airlines pilots who are shooting GPS assisted landings into Juneau and Ketchikan (next to mountains) or Sitka (where the airport hangs out over the ocean AND abuts the mountains). I'm sure they still carry their sextants in their flight bags.
Faster! Faster! Faster would be better!
You fail to understand the issue. Lightsquared's transmitters could screw up GPS service for EVERYONE. The FCC waived their own rules to allow this, rollout. If you RTFA (I know I know, this is slashdot) you would see the large distances a single transmitter can jam GPS devices at.
The GPS manufacturers and 4G companies are colluding to get us all to buy new GPS devices and GPS-enabled phones with better band-pass filters!