Re: [gpsd-dev] [PATCH 5/9] Define TTFF

[Gerry Creager - NOAA Affiliate]

Yo! Sanjeev

On Fri, Apr 17, 2015 at 9:56 PM, Sanjeev Gupta <address@hidden> wrote:

On Sat, Apr 18, 2015 at 4:21 AM, Gary E. Miller <address@hidden> wrote:

> WIthout an almanac... any almanac, often including expired ones, the
> receiver cannot do more than open its correlator and attempt to snag
> onto a spreading signal with a recognizable Gold-code. Then it can
> start receiving data.

Which with a 66 channel receiver is not a big deal.  Just try them
all at once.

Please see:  http://bit.ly/1ITXBPt  (URL shortened, goes to Google Books)

Sec 3.3.3

The section seems to describe how a modern (2009) receiver brute-forces, in parallel, the entire constellation, and needs no almanac a priori.

May I suggest that my $25 receiver outperforms the best that Gerry could get the NOAA to buy, or Eric could dream of, when this documentation was written?

At the time I was doing the serious research, I had the best Trimble could provide to the University where I worked (this was pre-NOAA). And you could assume  that, for L1 code-phase, you're correct. Retrieving L1/L2 and carrier phase data took a bit more processing. Still, there are better, more capable receivers than the Trimble 7000's and 4800's I did some work with.

And, today, I'd be lucky to get NOAA to buy a Garmin if I said I needed a receiver for something... unless I wrote a proposal, justified it, held a seminar, and underwent at least 2 reviews. 

 

We still need to define these terms, if for no other than that reason so that people like me can drift into the project, but increasing receiver sensitivity and multi-channel design mean that the users of gpsd will never be able to see, or use, these distinctions.

But knowing the history allows someone like you to drift in, and understand WHY some of this nonsense is ongoing. Standards don't change quickly. A silly idea today might have been borne out of necessity a decade ago.

gerry

--

Gerry Creager

NSSL/CIMMS

405.325.6371

++++++++++++++++++++++

“Big whorls have little whorls,

That feed on their velocity; 

And little whorls have lesser whorls, 

And so on to viscosity.” 

Lewis Fry Richardson (1881-1953)