On Jan 3, 10:51*pm, Sam Wormley <sworml...@gmail.com> wrote:
> Expert Advice: Give Us This Day Our Daily Bread
>
> http://www.gpsworld.com/GNSS%20Syste...e-us-day-our-d...
>
> > Across transportation, agriculture, industry, commerce, and finance, GPS has replaced earlier technologies, opened up innovative applications, andled to new ways of doing old things. GPS now plays a key role in the critical infrastructures of all industrialized nations, from the most sophisticated telecommunications system to the production of a simple loaf of bread.
>
> GNSS Is Threatened by Rising Levels of Radio Interference
>
> > The First Threat
> > The first component of the Triple Whammy comes from the new satellite systems themselves. Each satellite transmitting in the GPS frequency band increases the noise level there. Satellite navigation receivers must find andlock onto the extremely weak signal that reaches the Earth, digging it outfrom the background noise of the cosmos. And the other GPS satellites add to the noise level.
> > The Second Threat
> > Conflicts between nations as their new GNSSs compete for radio spectrumalso threaten GNSS viability.
>
> > The frequency bands available to satellite navigation are essentially L2, L5, and the principal one we use currently, L1. On L1, the European Galileo system and the Chinese Compass system occupy the same areas. Now, that’s very desirable if the two systems are to share receivers. But they also compete for that spectrum, and there is conflict between Compass and Galileo.
> > This battle for spectrum is a highly complex engineering problem. But chiefly, the spectrum wars are political, even emotional.
>
> > The Third Threat
> > Communications systems compete with GNSS for spectrum: witness the current Lightsquared case of a powerful new broadband system. For existing receivers, including those in government systems and aviation, it seems there is no fix for its devastating interference. Lightsquared is driven by rich and powerful commercial forces; it could well win this fight.
> > Communication technologies will continue to press upon the satellite navigation spectrum. Lightsquared will likely erode spectrum gaps between communications and navigation services, the so-called guard bands.
>
> See:http://www.gpsworld.com/GNSS%20Syste...e-us-day-our-d....
Thinking out loud.
If it were up to me, on the L1 band, I would leave GPS broadcasting
only L1 C/A, Galileo broadcasting only L1C, QZSS broadcast only L1C,
and optimize GPS sats position, we don't need 12 birds in view (with
lots of pairs), we need 7-9 birds in view with better spacing. By
better spreading the positioning, there's less over crowding of the
spectrum due to GPS itself. GPS III would broadcast L1C on just 2-3
satellites, just for testing, until they have enough birds for a jump
right to FOC. Then we'll be in 2025-2030, and technology will have
figured the interference issue out.
And finally, have GLONASS broadcast L1 CDMA using the current TDMA
frequency (neighbor to GPS, close enough receivers can use a single
radio circuit). And have Beidou broadcast using the same GLONASS
frequency. This way, the overcrowding just wouldn't exist... But, with
GNSS receiver improvements over the next 20 years, this might end-up a
non-issue.
L2C will only be broadcast by GPS + QZSS, so no overcrowding there. L5
will be broadcast by GPS+Galileo+QZSS+SBAS+GLONASS, being a 10megachip
code, will that make interference more or less severe ?
And when GPS IV comes, get rid of the current L1 C/A signal and use
L1C only. Perhaps reuse the C/A band for a SBAS like signal, a
composite of worldwide SBAS providers (using cross linked structure
but with constant updates instead of only ad hoc).
Marcelo
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