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GPS, GLONASS, Galileo, Beidou
Oct. 14th, 2011 02:05 pmI just had a small surgery and a doctor recommended me not talk and not to walk outside for one day.
So I am reading a new novel by Gibson, "Zero history", bought it last week in Powells. In first 50 pages, the protagonist tells someone that GPS are especially inaccurate near the "sensitive sites". I have noticed that GPS is indeed sensitive to current US military agenda. E.g. since our wedding trip in Jordan, I never had observed better GPS reception, not even close. I assume that helped US military in the region at that time.
But making results less accurate? My GPS receiver is a passive device (I hope) it just gets time signals from satellites (clock, ephemeris, almanac). The public time signals are broadcasted so they can be degraded but that distorted signal would cover a great land area, not just near a sensitive site.
What else? I have only few hypothesis, sorted by likelihood as I understand it.
1. Selective GPS jamming by ground station near sensitive site.
2. GPS vendor makes sure it reduces accuracy when near sensitive site. How to add sensitive sites when chip is already in the market?
3. Like for M-code, a directional high gain antenna can broadcast distorted data to specific small region.
4. GPS receiver is not a passive device, aaaahhh black helicopters are chasing me!
Anything else?
While I think 1. is most likely, Re: 2, open source GPS anyone, may be via SDR?
So I am reading a new novel by Gibson, "Zero history", bought it last week in Powells. In first 50 pages, the protagonist tells someone that GPS are especially inaccurate near the "sensitive sites". I have noticed that GPS is indeed sensitive to current US military agenda. E.g. since our wedding trip in Jordan, I never had observed better GPS reception, not even close. I assume that helped US military in the region at that time.
But making results less accurate? My GPS receiver is a passive device (I hope) it just gets time signals from satellites (clock, ephemeris, almanac). The public time signals are broadcasted so they can be degraded but that distorted signal would cover a great land area, not just near a sensitive site.
What else? I have only few hypothesis, sorted by likelihood as I understand it.
1. Selective GPS jamming by ground station near sensitive site.
2. GPS vendor makes sure it reduces accuracy when near sensitive site. How to add sensitive sites when chip is already in the market?
3. Like for M-code, a directional high gain antenna can broadcast distorted data to specific small region.
4. GPS receiver is not a passive device, aaaahhh black helicopters are chasing me!
Anything else?
While I think 1. is most likely, Re: 2, open source GPS anyone, may be via SDR?
