[OpenSource_GPS] Doppler calculation result

[Long Nguyen]

Hi Cliff,

Thanks for your reply, but it seems not the problem I face with. It happens
with all channels for a short time and then everything comes normal. I
checked my collected almanac data with the data provided as yuma format (
http://www.navcen.uscg.gov/ftp/GPS/almanacs/yuma/ ) and they match well. 

I think the problem is about the time because my pseudorange results are
always wrong (negative or too big). I checked the nav_fix function and I
found that you program the TIC register everytime running nav_fix. What is
your purpose?

I also have some more uncertainties:

1/ at the beginning, we have t_count==0 then frame_ready=1, although the
message=0 for all bits, but it also be taken into account in nav_mess
function, and also give valid data (because parity_check also give valid
result). because t_count maybe not start from 0 then this problem occurs
again when t_count==1500 but many of data bits are not collected. Does this
make sense for the message data? and should we add more condition for
frame_ready, (for example add: if (.......&&(n_frame!=0) frame_ready=1;)

2/ in tracking algorithm, when state changes from acquition to confirm, you
push back 1 chip to narrow the "band", and if we cannot find the signal so
it will return to acquition state and push forward 1 chip. How about just
push forward 1/2 chip for full scanning?

3/in acquisiton state, if (code_slew==2044) then you change the frequency.
It seems you didn't check the last code slew, because the code_slew
increases AFTER correlating, then if code_slew==2044, that mean you have
just increased this value have not yet correlated with this slew. 

I don't want to make you sleep when reading this, so I stop now although I
still have so many things that I want to ask.

Thank you,

Best Regard,

Long


Clifford Kelley wrote:
> 
> Long,
> 
> The only possibility that comes to mind is that the almanac may have
> somehow been corrupted.  Take a look at the almanac entry for that
> satellite and see if it looks reasonable compared to the other satellites.
> 
> Best regards,
> 
> Cliff
> 
> -----Original Message-----
>>From: Long Nguyen <phuclong79 at yahoo.com>
>>Sent: Sep 16, 2006 7:52 AM
>>To: opensource_gps at lists.psas.pdx.edu
>>Subject: [OpenSource_GPS] Doppler calculation result
>>
>>
>>Hi guys,
>>I knowledge the maximum doppler could not be larger than 10kHz, due to
>>relating speed between Satellite and Receiver. But when using GPS
Opensource
>>V1.17, I found out the result doppler when running in Warmstart sometimes
>>exceed 10kHz far off, few hundred Khz. 
>>I have considered the doppler calculation in program and it seems correct.
>>What should be the problem? 
>>Thanks a lot
>>-- 
>>View this message in context:
http://www.nabble.com/Doppler-calculation-result-tf2282455.html#a6340576
>>Sent from the OpenSource GPS forum at Nabble.com.
>>
>>
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