[time-nuts] New Japanese GPS accuracy

Hal Murray hmurray at megapathdsl.net
Tue Jan 4 20:53:27 UTC 2011

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.

phk at phk.freebsd.dk said:
> >As far as I know, it is a geo-synchronous polar orbiting D-GPS system.
> Duh!  "Sun-synchronous" of course. 

The original crunchgear article said they needed 3 satellites to get 24 hour 

I can't picture an orbit pattern that's going to use 3 satellites.  Geosync 
would work with one satellite, but Japan is fairly far north.  Are they doing 
something like picking the orbit height and inclination angle so that the 
satellite period is 24 hours and over Japan rather than the equator at the 
right time?

These are my opinions, not necessarily my employer's.  I hate spam.

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