Re: [ntp:questions] GPS Weakness Could Sink Wireless
Jan Ceuleers wrote: Interesting Light Reading article on the degree to which infrastructure (in casu wireless networks) is dependent on GPS timing signals, how little is needed to jam GPS (intentionally or otherwise), and what the impact of such jamming would be. It also talks about how PTP might or might not mitigate some of these issues. http://www.lightreading.com/mobile/mobile-security/were-jamming-gps-weakness-could-sink-wireless/d/d-id/706895 I spent 2.5 years as the architect of a national cell phone network replacement project so I do know a little about this issue: The core do use GPS to sync up the central time servers, but they also have Rb local osc, which means that even if you were able to jam the GPS reception in all the areas that have reference gps receivers, you would also have to wait long enough so that the Rb clocks would drift apart. For the GSM/3G/4G networks we have we don't need to know exactly what the time is (unlike the US CDMA setup which do need single-digit us time sync), we only need to keep the frequencies the same, and these only need to match up at the 20 ppm level in order to be able to do seamless base station handovers at bullet train speeds. 20 ppm is a _lot_ compared to the stability of an Rb osc, it would take at least some months before things got that bad, and if you had an adversary who could do wide-area GPS denial over several months, without getting detected and caught, then you have a _real_ problem. Terje -- - Terje.Mathisen at tmsw.no almost all programming can be viewed as an exercise in caching ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
unruh un...@invalid.ca wrote: On 2013-12-12, Rob nom...@example.com wrote: Jan Ceuleers jan.ceule...@computer.org wrote: Interesting Light Reading article on the degree to which infrastructure (in casu wireless networks) is dependent on GPS timing signals, how little is needed to jam GPS (intentionally or otherwise), and what the impact of such jamming would be. It also talks about how PTP might or might not mitigate some of these issues. http://www.lightreading.com/mobile/mobile-security/were-jamming-gps-weakness-could-sink-wireless/d/d-id/706895 It depends on the structure of the network and the required accuracy. Remember that the usual GPS jamming methods are quite local in nature. You can jam my GPS but that won't take out my DCF77 receiver or the three GPS-synced servers I have configured as internet NTP sources. If they are in the same locality (or, depending on the strength of the jamming, local could mean within a few Km) they could also be jammed. Could could could But how can the jammer know what sources the victim is using? And where the receivers are located? When they want to jam everything for sure, they could just detonate a nuclear weapon in the ionosphere above the victim. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
John Hasler wrote: In any case designers of things like cell towers should no more assume that GPS is always just there than they should assume that electric power is always just there. This is a _basic_ shortcoming in CDMA as designed and in use. ( think of it as the NTSC of mobile phone systems ;-) uwe ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
I wrote: In any case designers of things like cell towers should no more assume that GPS is always just there than they should assume that electric power is always just there. Uwe writes: This is a _basic_ shortcoming in CDMA as designed and in use. ( think of it as the NTSC of mobile phone systems ;-) But Terje points out above that they use Rb oscillators so short (or medium) term loss of GPS by cell towers is not actually a problem. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
John Hasler wrote: I wrote: In any case designers of things like cell towers should no more assume that GPS is always just there than they should assume that electric power is always just there. Uwe writes: This is a _basic_ shortcoming in CDMA as designed and in use. ( think of it as the NTSC of mobile phone systems ;-) But Terje points out above that they use Rb oscillators so short (or medium) term loss of GPS by cell towers is not actually a problem. you still have the higher requirement of syncronicity limiting your design. uwe ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
[ntp:questions] GPS Weakness Could Sink Wireless
Interesting Light Reading article on the degree to which infrastructure (in casu wireless networks) is dependent on GPS timing signals, how little is needed to jam GPS (intentionally or otherwise), and what the impact of such jamming would be. It also talks about how PTP might or might not mitigate some of these issues. http://www.lightreading.com/mobile/mobile-security/were-jamming-gps-weakness-could-sink-wireless/d/d-id/706895 ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
There are many things that could be done to mitigate the GPS jamming and interference problem. Unfortunately, few if any are being done by anyone outside the military. These include: 1) Better front-end selectivity 2) Better front-end dynamic range 3) Directional antennas for fixed sites such as cell towers -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
On 12/12/13 13:57, John Hasler wrote: 1) Better front-end selectivity 2) Better front-end dynamic range I don't really see how these help against all but the crudest jammers, which transmit pure CW carriers or are off frequency. 3) Directional antennas for fixed sites such as cell towers That might help a bit, if you rejected signals near the horizon (which are good for navigation, but may be bad for time). However, to get full benefit from directionality, you'd need to run large phased arrays and steer their beams to track the individual satellites. As most military users want the navigation data, they would be better off with steerable beams. The military also have the advantage of a broader, L2 signal, with a cryptographic chipping code. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
I wrote: 1) Better front-end selectivity 2) Better front-end dynamic range David Woolley writes: I don't really see how these help against all but the crudest jammers, which transmit pure CW carriers or are off frequency. Better dynamic range means that the jammer must be closer or more powerful. Both it and better selectivity help against out-out-band interference, which is one of the concerns (probably a more serious one than jamming) (and most jammers *are* going to be of the crudest sort). I wrote: 3) Directional antennas for fixed sites such as cell towers David Woolley writes: That might help a bit, if you rejected signals near the horizon (which are good for navigation, but may be bad for time). Signals near the horizon are weak and have gone through a lot of atmosphere. You don't really want them for any purpose if you can find better (and you can unless you are in the [ant]arctic). However, to get full benefit from directionality, you'd need to run large phased arrays and steer their beams to track the individual satellites. As most military users want the navigation data, they would be better off with steerable beams. 99.9% of jammers and 99.99% of interference sources are going to be on the ground. A well-designed fence (shielding, really) with a cutoff at, say, 30 degrees above the horizon can easily knock them down 100db or more. Due to the use of spread-spectrum jamming GPS has no effect as long as it stays within the dynamic range of the receiver (spoofing is a different issue entirely, and *much* more difficult to achieve). My point is that this weakness is more of a design weakness in commercial receivers than a fundamental weakness in GPS. In any case designers of things like cell towers should no more assume that GPS is always just there than they should assume that electric power is always just there. -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
In article 87vbyugh88@thumper.dhh.gt.org, John Hasler jhas...@newsguy.com wrote: In any case designers of things like cell towers should no more assume that GPS is always just there than they should assume that electric power is always just there. So long as they're still running IS-2000 CDMA, GPS is at least a formal requirement. But for intermittent interference or signal interruptions, a receiver with a good oscillator will have enough hold-over accuracy to meet the actual protocol requirements. -GAWollman -- Garrett A. Wollman| What intellectual phenomenon can be older, or more oft woll...@bimajority.org| repeated, than the story of a large research program Opinions not shared by| that impaled itself upon a false central assumption my employers. | accepted by all practitioners? - S.J. Gould, 1993 ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
Jan Ceuleers jan.ceule...@computer.org wrote: Interesting Light Reading article on the degree to which infrastructure (in casu wireless networks) is dependent on GPS timing signals, how little is needed to jam GPS (intentionally or otherwise), and what the impact of such jamming would be. It also talks about how PTP might or might not mitigate some of these issues. http://www.lightreading.com/mobile/mobile-security/were-jamming-gps-weakness-could-sink-wireless/d/d-id/706895 It depends on the structure of the network and the required accuracy. Remember that the usual GPS jamming methods are quite local in nature. You can jam my GPS but that won't take out my DCF77 receiver or the three GPS-synced servers I have configured as internet NTP sources. Nor will it take out my peer server that itself has DCF77 and some other internet time sources, that are again synced to different other servers. Of course it is possible to jam everything, just not very likely. In a mobile network, it should be possible to get time information both from the local GPS receiver and via the glass/microwave link as a backup. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
On 2013-12-12, Rob nom...@example.com wrote: Jan Ceuleers jan.ceule...@computer.org wrote: Interesting Light Reading article on the degree to which infrastructure (in casu wireless networks) is dependent on GPS timing signals, how little is needed to jam GPS (intentionally or otherwise), and what the impact of such jamming would be. It also talks about how PTP might or might not mitigate some of these issues. http://www.lightreading.com/mobile/mobile-security/were-jamming-gps-weakness-could-sink-wireless/d/d-id/706895 It depends on the structure of the network and the required accuracy. Remember that the usual GPS jamming methods are quite local in nature. You can jam my GPS but that won't take out my DCF77 receiver or the three GPS-synced servers I have configured as internet NTP sources. If they are in the same locality (or, depending on the strength of the jamming, local could mean within a few Km) they could also be jammed. Also, transmitting time via a network (whetehr wired or radio) can have a fair amount of jitter so it depends on the accuracy that the wireless towers need. If it is seconds no problem. If it is nanoseconds, you just won't get that. Nor will it take out my peer server that itself has DCF77 and some other internet time sources, that are again synced to different other servers. Of course it is possible to jam everything, just not very likely. The article talks about a truck driving by the airport (ie a few km) jamming the airport. And that was a trucker probably unwilling to spend more than a 100 dollars on his jamming gear. In a mobile network, it should be possible to get time information both from the local GPS receiver and via the glass/microwave link as a backup. But does it have the required accuracy? I do not know. ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
unruh writes: The article talks about a truck driving by the airport (ie a few km) jamming the airport. And that was a trucker probably unwilling to spend more than a 100 dollars on his jamming gear. And the jammed receivers probably weren't worth much more than that (though the airport undoubtedly paid a lot more for them). -- John Hasler jhas...@newsguy.com Dancing Horse Hill Elmwood, WI USA ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] GPS Weakness Could Sink Wireless
unruh un...@invalid.ca wrote: The article talks about a truck driving by the airport (ie a few km) jamming the airport. And that was a trucker probably unwilling to spend more than a 100 dollars on his jamming gear. Is this the incident? http://www.theregister.co.uk/2013/08/12/feds_arrest_rogue_trucker_after_gps_jamming_disrupts_newark_airport/ After Bojczak parked near the ground station for the system, FAA staff noticed jamming in the restricted 1559 to 1610MHz band. rick jones -- It is not a question of half full or empty - the glass has a leak. The real question is Can it be patched? these opinions are mine, all mine; HP might not want them anyway... :) feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH... ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
