Hi I read the patent and understand how you can get timing off of a WAAS sat. The carrier does not need to have fancy steering on it to enable that function. The thing that it does not show is doing carrier phase off of a WAAS sat.
Bob On Jul 10, 2013, at 9:54 PM, David I. Emery <[email protected]> wrote: > On Wed, Jul 10, 2013 at 07:45:39PM -0400, Bob Camp wrote: >> Hi >> >> If the WAAS birds are run in a fashion that gives a true GPS payload >> performance, why not assign them a SN 32 or below and use them? >> >> If the WAAS birds are not in the "right numbers", why bother to set them up >> and spend the bucks to make them behave like a nav sat? What's the payoff? > > > The patent cited here recently explains... for fixed timing > purposes and basic anti jam a simple directional antenna pointed at the > WAAS bird allows rejection of many interferers without elaborate and > expensive active steered phased array nulling technology. > > And because - given a known fixed ground position - timing and > frequency can work with only one bird visible, this allows > timing/frequency using just the WAAS signal (or signals, they do provide > more than one WAAS frequency). > > And potentially if the timing accuracy via the hosted payload is > respectable at least for the needs of many fixed time/frequency users > this might supply a solution MUCH less resistant to local (nearby) > interferers than the usual more or less hemi pattern GPS antenna would - > as fixed dishes with considerable gain toward the satellite could be > used and in most places they would point well above the horizon and > could be shielded by nearby structures to further reduce jamming > susceptibility from jammers (intentional or unintentional) below or at > the horizon for the site. For timing/frequency users (certainly an > important subset of the GPS user population) this provides some > protection by antenna pattern that is hard to obtain otherwise (and > users interested in higher precision or redundancy of timing could still > just use another GPS timing system based on normal hemi GPS antennas as > the primary - using the normal SVs - and rely on the dedicated dish > pointed at the WAAS bird only as backup in the event of jamming). > > The choice of using different spreading codes from the normal > GPS set for WAAS or using a slightly different one is an overall system > architecture decision... which I guess was made in favor of not tying > up codes for regular SVs for the WAAS birds. But AFAIK a receiver with > suitable firmware could still extract pseudo ranges and use them. > > I guess there is an issue in any frequency translation scheme > with the relationship of carrier and code phase... a homodyne > distortion... due to the random phase of the LO(s)... but this too can > be predistorted on the ground to come out right and that kept in line > via closed loop tracking of the downlink from a ground site. > > I do understand that this insight into a potential further use > of WAAS beyond its use as a data channel and propagation beacon seems > to have happened later and not initially. > > -- > Dave Emery N1PRE/AE, [email protected] DIE Consulting, Weston, Mass > 02493 > "An empty zombie mind with a forlorn barely readable weatherbeaten > 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in > celebration of what could have been, but wasn't and is not to be now either." > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
