On Feb 3, 9:21�pm, TheGlimmerMan Archie > I am currently working on our Archie > battlefield tracking and comms solutions. What kind of security and handlers does your employer provide to keep their pet sociopath from becoming a public embarassment?
Reported SNR of GPS Receivers
Started by ●February 2, 2011
Reply by ●February 4, 20112011-02-04
Reply by ●February 4, 20112011-02-04
In article <2e11c5b1-4eeb-426a-b9c2-067a57605627@d12g2000vbz.googlegroups.com>, Rune Allnor <allnor@tele.ntnu.no> wrote:> On Feb 3, 6:05�am, Sound Consulting > <Sound_Consulting@_rm_Sounds.wa.com> wrote: > > In article > > <e900b2b6-72e1-4a28-9aa1-43d2508ce...@a28g2000vbo.googlegroups.com>, > > �Rune Allnor <all...@tele.ntnu.no> wrote: > > > > > On Feb 3, 4:50�am, Tim Wescott <t...@seemywebsite.com> wrote: > > > > On 02/02/2011 07:00 PM, brent wrote: > > > > > On Feb 2, 7:20 pm, Tim Wescott<t...@seemywebsite.com> �wrote: > > > > >> Does anyone happen to know at what point in the signal chain a GPS > > > > >> receiver measures SNR, if it reports SNR at all? > > > ... > > > > > Higher end (including aviation) GPS have SNR reporting. �It is > > > > > important to monitor the signal to noise ratio degradation on > > > > > airplanes when �other avionics are turned on. > > > > > > > I believe the SNR calculations are done by looking at the stability of > > > > > the data at the very end of the receiver chain. > > > > > I would *guess* that the variance of the reported position > > > *formally* depends on the SNR + system-specific factors. > > > If one were able to control the system-specific factors > > > 'sufficiently well' one would probably be able to estimate > > > SNR from variance in position. > > > > Isn't the data in a digital format before it is used to determine > > position? �I don't see how you can determine signal to noise based on > > errors in a digital stream - rather, you can determine error rate, but > > that is distinct from SNR. > > > > Also, doesn't position depend upon the combination of several inputs? � > > It doesn't make sense to use variance in position to determine SNR when > > you can't really know which of the many inputs are responsible for the > > error. > > The error rates depend on the SNR of the recieved signal. If the > error correction system is seen to be too busy correcting errors, > it's at least an indication that the numbers in the associated > data stream might be viewed with some suspicion. An error correcting > system can only handle so much - there might be errors coming through > if the SNR is low enough.My point is that packets with errors should never be used to calculate position, and thus any variance in position cannot be used to determine the error rate. At least I see no reason to assume that digital errors would cause the position to vary. Also, I should point out that error detection is much easier than error correction, and I assume that GPS has bullet-proof error detection. You are correct that error correction has its limits, but error detection should not be difficult at all. Brian Willoughby Sound Consulting
Reply by ●February 4, 20112011-02-04
On Feb 4, 11:19�am, Sound Consulting <Sound_Consulting@_rm_Sounds.wa.com> wrote:> In article > <2e11c5b1-4eeb-426a-b9c2-067a57605...@d12g2000vbz.googlegroups.com>, > �Rune Allnor <all...@tele.ntnu.no> wrote: > > > > > > > On Feb 3, 6:05�am, Sound Consulting > > <Sound_Consulting@_rm_Sounds.wa.com> wrote: > > > In article > > > <e900b2b6-72e1-4a28-9aa1-43d2508ce...@a28g2000vbo.googlegroups.com>, > > > �Rune Allnor <all...@tele.ntnu.no> wrote: > > > > > On Feb 3, 4:50�am, Tim Wescott <t...@seemywebsite.com> wrote: > > > > > On 02/02/2011 07:00 PM, brent wrote: > > > > > > On Feb 2, 7:20 pm, Tim Wescott<t...@seemywebsite.com> �wrote: > > > > > >> Does anyone happen to know at what point in the signal chain a GPS > > > > > >> receiver measures SNR, if it reports SNR at all? > > > > ... > > > > > > Higher end (including aviation) GPS have SNR reporting. �It is > > > > > > important to monitor the signal to noise ratio degradation on > > > > > > airplanes when �other avionics are turned on. > > > > > > > I believe the SNR calculations are done by looking at the stability of > > > > > > the data at the very end of the receiver chain. > > > > > I would *guess* that the variance of the reported position > > > > *formally* depends on the SNR + system-specific factors. > > > > If one were able to control the system-specific factors > > > > 'sufficiently well' one would probably be able to estimate > > > > SNR from variance in position. > > > > Isn't the data in a digital format before it is used to determine > > > position? �I don't see how you can determine signal to noise based on > > > errors in a digital stream - rather, you can determine error rate, but > > > that is distinct from SNR. > > > > Also, doesn't position depend upon the combination of several inputs? � > > > It doesn't make sense to use variance in position to determine SNR when > > > you can't really know which of the many inputs are responsible for the > > > error. > > > The error rates depend on the SNR of the recieved signal. If the > > error correction system is seen to be too busy correcting errors, > > it's at least an indication that the numbers in the associated > > data stream might be viewed with some suspicion. An error correcting > > system can only handle so much - there might be errors coming through > > if the SNR is low enough. > > My point is that packets with errors should never be used to calculate > position, and thus any variance in position cannot be used to determine > the error rate. �At least I see no reason to assume that digital errors > would cause the position to vary. > > Also, I should point out that error detection is much easier than error > correction, and I assume that GPS has bullet-proof error detection. �You > are correct that error correction has its limits, but error detection > should not be difficult at all.I'm just speculating. I don't know error correction and I don't know the specifics of GPS, so I might be totally lost. I am only projecting the principles I know from other fields, where internal variables can be used to estimate the quality of the desired computed result. Run
Reply by ●February 4, 20112011-02-04
On Thu, 03 Feb 2011 11:23:35 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:>On Thu, 03 Feb 2011 19:50:39 +0200, upsidedown@downunder.com wrote: > >>On Wed, 02 Feb 2011 16:20:47 -0800, Tim Wescott <tim@seemywebsite.com> >>wrote: >> >>>Does anyone happen to know at what point in the signal chain a GPS >>>receiver measures SNR, if it reports SNR at all? I'm assuming that it'd >>>be doing so after despreading and bit detection. >> >>When the GPS system was first revealed to the general public, there >>was claims of systems working down to -20 dB SNR :-). >> >>Of course, this was calculated comparing the signal power to the >>thermal noise in 1.023 MHz bandwidth. However, since the actual >>despread net data rate is only 50 bit/s, that -20 dB SNR would >>translate to something like +23 SNR :-). >> > >I designed a PLL data extractor that could function on a TACAN signal >at around -6dB SNR (all analog, of course ;-). That's the one that >Gardner (of PLL book fame) opined couldn't work, until I demonstrated >it to him. > >I was 28 at the time, and a wee bit scared of confronting Gardner. > >But I had already cleaned Larry Huelsman's clock a few years before, >proving his paper on desensitizing NIC's was a bunch of crap, so I was >experienced :-) > > ...Jim Thompson| James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | Hi Jim, You're in Phoenix, huh? Not wanting to be accused of not adding something useful to this thread, I'll add the following. One of the scariest movies ever made was Stanley Kubrick's 'The Shining', starring Jack Nicholson as the main character Jack Torrence. My favorite scene in the movie was the super-weird conversation between Jack and the ghost of Delbert Grady in the Overlook Hotel's men's room. The interior of men's room was painted with an unbelievably garish all-red color. A truly strange, other-worldly, room. That men's room was modeled after a Frank Lloyd Wright-designed bathroom in Phoenix�s famed Arizona Biltmore Hotel. The next time I'm in Phoenix I'm gonna visit the Biltmore Hotel to check out that men's room. (I hope Mr. Grady doesn't show up though.) [-Rick-]
Reply by ●February 4, 20112011-02-04
On Thu, 3 Feb 2011 21:45:16 -0800 (PST), Greegor <greegor47@gmail.com> wrote:>On Feb 3, 9:21�pm, TheGlimmerMan >Archie > I am currently working on our >Archie > battlefield tracking and comms solutions. > >What kind of security and handlers does >your employer provide to keep their pet >sociopath from becoming a public embarassment?The idiot greegor can fuck off and die.
Reply by ●February 4, 20112011-02-04
Rune Allnor wrote: [snip]> > The error rates depend on the SNR of the recieved signal. If the > error correction system is seen to be too busy correcting errors, > it's at least an indication that the numbers in the associated > data stream might be viewed with some suspicion. An error correcting > system can only handle so much - there might be errors coming through > if the SNR is low enough.But in many digital systems the relationship between SNR and error rate is nonlinear. There's a knee in the curve, beyond which the error rate rises dramatically. Watching the SNR as it approaches this knee might be useful. -- Paul Hovnanian paul@hovnanian.com ---------------------------------------------------------------------- Have gnu, will travel.
Reply by ●February 4, 20112011-02-04
Rune Allnor wrote: [snip]> > The error rates depend on the SNR of the recieved signal. If the > error correction system is seen to be too busy correcting errors, > it's at least an indication that the numbers in the associated > data stream might be viewed with some suspicion. An error correcting > system can only handle so much - there might be errors coming through > if the SNR is low enough.But in many digital systems the relationship between SNR and error rate is nonlinear. There's a knee in the curve, beyond which the error rate rises dramatically. Watching the SNR as it approaches this knee might be useful. -- Paul Hovnanian paul@hovnanian.com ---------------------------------------------------------------------- Have gnu, will travel.
Reply by ●February 5, 20112011-02-05
On Feb 3, 9:21=A0pm, TheGlimmerMan Archie > I am currently working on our Archie > battlefield tracking and comms solutions. G > What kind of security and handlers does G > your employer provide to keep their pet G > sociopath from becoming a public embarassment? Archie > The idiot greegor can fuck off and die. Is it a big locked gorilla cage or a pedded cell?
Reply by ●February 7, 20112011-02-07
Archie > I am currently working on our Archie > battlefield tracking and comms solutions. G > What kind of security and handlers does G > your employer provide to keep their pet G > sociopath from becoming a public embarassment? Archie > The idiot greegor can fuck off and die. G > Is it a big locked gorilla cage or a pedded cell? Does DRS Technologies or other Defense Contractors hire brain disorder or mental case people for defense work? http://www.drs-ts.com/article-armycontract.htm You do BRAT? ( What does BRAT stand for? Beyond Line-Of-Sight Reporting and Tracking (US Army) ) It's more like you ARE a BRAT, Archie! Then again, if you Google battlefield tracking, lots of the hits are for computer games by Electronic Arts and others. Is Archie living a rich fantasy life?
