[time-nuts] New Japanese GPS accuracy

[jimlux]

On 1/4/11 12:53 PM, Hal Murray wrote:
>
> jimlux at earthlink.net said:
>> Similar in concept to waas or tass, the satellite provides a nav signal and
>> differential corrections.
>
>> One of the goals is to make a nav system that performs well (sub meter) in
>> urban canyons, which conventional gps does not
>
> I thought the idea with waas was to correct for the delays through the
> ionosphere by measuring the error at a known (nearby?) location and
> broadcasting the correction.  The idea is that a nearby location would have
> similar delays and similar errors.
>
> I thought the problem with urban canyons was multi-path and blocked signal.
> How is a correction for ionospheric delays going to help that?
>
> I must be missing something interesting.
>


I'm looking for the GPS World article now that describes it..

But it was designed to address some peculiar needs of Japan, which is 
basically long and skinny oriented north south.  A WAAS like scheme from 
Clarke Orbit doesn't work well for them because the satellite is at low 
elevation angles (45 degrees), so you don't "see" it even on the bounce 
in a canyon that is east west oriented. A satellite that is effectively 
"overhead" solves the problem.

I seem to recall that it also transmits a conventional nav signal which 
can be used in the solution as well