Re: question on parity

Thanks Georg,

I'm sorry for i'm still puzzlling on that.
I think the process like this: ephemris data -> struct NAV -> sf[6][11] -> 
sfp[6][11] ->msg[1500];
So, sf[6][11] was encoded data, and sfp[6][11] was encoded data adding 
parity.
what was described in the reference book is: last two parity bits of Word 
#2 of every subframe should be zero.(James Bao-Yen Tsui, Fundmantal of 
Global Positioning System Receivers....P86)
So, at the receiver, when checking this two bits, the subframe must be 
encoded and parity added and should not be _decoded_ HOW.
also when HOW was decoded, it only has 24 bits, the last 6 was parity.

Thanks for answering..




>From: Georg Beyerle <[email protected]>
>To: [email protected]
>CC: [email protected]
>Subject: Re: [OpenSource_GPS] question on parity
>Date: Mon, 26 Jul 2004 12:25:32 +0200
>
>Hello Si Chuanyu,
>
>
>I haven't looked at OpenGPSSim for a long time. I'll try to
>answer your question from what I still remember...
>
>I assume what you did was something like that:
>
>     ./bin/ogsencdec nav-01-template-01-06.txt
>
>and then
>
>     ./bin/ogsxmit -n nav-01-template-01-06
>
>However, the 'transmitter' program 'ogsxmit' inputs
>the _encoded_ navigation data stored in the file
>'nav-01-template-01-06'. So the last two bits of sf[1][2]
>could be anything. As Cliff already said it's the _decoded_
>HOW word that should end with 00 (or 11).
>
>
>Regards
>
>Georg
>
>At 16:34 21.07.2004, you wrote:
> >It looks like you are using Georg Beyerle's data and code which may be
> >somewhat different from OpenSource GPS.
> >
> >Georg, can you take this question?
> >
> >Thanks,
> >
> >Cliff
> >----- Original Message -----
> >From: "si chuanyu" <[email protected]>
> >To: <[email protected]>
> >Sent: Tuesday, July 20, 2004 12:53 AM
> >Subject: Re: [OpenSource_GPS] question on parity
> >
> >
> >> thanks Kelley.
> >>
> >> yes, you said it.
> >> but in my side, when i use nav-01-template-01-06.txt as input, after
> >> encoding and parity adding, sf[1][2]'s last two bit was "ff 01" in the
> >> memory. so it is 01 or 10(polarity is unkown)
> >> I've tried several time and get the same result. I used Visual Studio 
6.0
> >> for development.
> >>
> >> I added a break point in ogsxmit.cpp 's main function after read the 
nav
> >> bit from nav-01-template-01-06 into buffer NavBit[], and watched the
> >memory
> >> contents in the debug window, and get NavBit[58]=ff NavBit[59]=01;
> >> so I am wondering why this ocurr? could you please give me some
> >information
> >> on that?
> >>
> >> Thank you very much!
> >>
> >>
> >> >From: "Clifford Kelley" <[email protected]>
> >> >Reply-To: "Clifford Kelley" <[email protected]>
> >> >To: "si chuanyu"
> >> <[email protected]>,<[email protected]>
> >> >Subject: Re: [OpenSource_GPS] question on parity
> >> >Date: Tue, 8 Jun 2004 21:48:17 -0700
> >> >
> >> >I'm not sure which reference you are referring to but the last two 
bits
> >of
> >> >HOW when decoded should be 00.  If the polarity is unknown it could 
be
> >11.
> >> >The reference to check with is ICD-GPS-200.
> >> >
> >> >Cliff
> >> >----- Original Message -----
> >> >From: "si chuanyu" <[email protected]>
> >> >To: <[email protected]>
> >> >Sent: Monday, June 07, 2004 2:37 AM
> >> >Subject: [OpenSource_GPS] question on parity
> >> >
> >> >
> >> > > hi
> >> > >    I found in the reference that the sum of the last two bits of 
HOW
> >in
> >> > > each subframe should be +2 or -2. but in the reference code, after
> >> >encoding
> >> > > the subframe and adding parity, the last two bits of subframe[][2] 
was
> >> 1
> >> >or
> >> > > -1. thus in the receiver, we can't pass parity check. what's the
> >> problem
> >> > > with that? do I missed something else? thanks a lot!
> >> > >
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> >> > >
> >> >
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