Techniques to use both L1 and L2

Techniques to use both L1 and L2 are fundamental to high-grade GPS
receivers, and I believe the patents related actually protect this small
community to grow under the canopy of low-cost GPS receivers.

I remembered many years ago I was told that the techniques could be
roughly divided into 5 categories:
1. Completely codeless.
2. Squaring
3. code-aided squaring
4. cross-correlation (by Trimble)
5. Z-tracking (by Ashtech)

I think the top 3 techniques are pretty much dead now due to their poor
performance, and 5 is the most popular one used at the GNSS
manufacturers so far. Please correct me if I am wrong or I missed any
technique.

My question is, if most manufacturers use 5 or 4, are they required to
pay royalty to Ashtech or Trimble? Otherwise will they be sued and how
they settle down the lawsuit? I guess NovAtel, Javad, and Septentrio use
Z-tracking in their dual-freq products, and I am not sure how Hemisphere
GPs does.

For other companies typically working on single-frequency low-cost
receivers, what prevents them from penetrating into the dual-frequency
receiver market?

Thanks.

Johnson

On 10-07-20 14:22 , Johnson wrote:


Demand. There is not that much for the small practical gain in accuracy
or other performance areas. I'd also guess that the demand is so small
that the incremental cost of adding L2 would drive up the unit price
considerably for a very slow to start market.

--
gmail originated posts are filtered due to spam.

Alan Browne wrote:
Is it the cost or the IP infringement the biggest concern for the giant
companies?

Moving forward what we need is triple carrier GPS receivers without
any usage of P(Y) tracking.
Those can achieve sub meter accuracy by just using multiple signals to
perform iono corrections.
Perhaps use WAAS for iono correction for older satellites that don't
even have L2C and until L2C signals are set healthy.
This way NO patent issues should apply.

I'm not talking about millimeter / centimeter accuracy applications,
since then we would be talking carrier phase techniques which might be
patented (guessing).

The biggest advantage of those designs is apart from the antenna, they
should be very cheap to manufacture.
The same chipset could be used on cheaper hiking products (with lower
gain antennas), and more expensive survey/airplane products (with
higher gain, more expensive antennas).
There's no reason the higher end products for surveying should cost
more than US$ 1000 per unit, with lower end products eventually
costing the same as current cheap units.

This way, demand would be there. Imagine Garmin launching higher end
ground/air navigation L2C/L5 ready products circa 2013.

Those products could be Galileo ready, since since Galileo also uses
L1 and L5 bands.

Anyhow since L2C won't be oficially available until more 11 GPS
satellites are launched (need 18 L2C capable satellites for initial
operational capability), and the OCX phase I is operational (current
USAF monitoring stations don't monitor L2C / L5 signal health)

The main reason this might not happen this soon is Moore's law. The
longer GPS chipset designers wait, lower power consumption, lower
hardware costs, smaller size they can achieve. By the timeframe L5
reaches FOC (full operation, at least 24 satellites), your typical GPS
chipset will include a general purpose CPU, or be a radio only
expansion with the main CPU doing all the hard GPS signal tracking
work, and will use less than one square inch of board space.

Remember that DOD is planning to eventually shutdown the P(Y) signal.
We should be planning to move away from that.
Plus L1 / L2C / L5 tracking will provide better accuracy than the best
semi-codeless techniques, since L2c and L5 provide dataless components
for optimal carrier phase tracking, and L2c have higher effective gain
than L1, and L5 has the same chirp rate than the P(Y) on each
component, arguably making for an even better signal than the current
P(Y) signals.

Eventually when the GPS constellation consists of only GPS IIF and
better satellites, we should achieve 20-50 cm accuracy without carrier
phase techniques depending on satellite geometry. With GPS+Galileo,
20cm accuracy should be achievable 24x7 as long as there is sufficient
sky view.