PRC as a amplifier in GPS question.

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Could you please help to understand
1) what is the relationship of background noise and PRC noise
2) Could anyone explain how does it work?

Thank you very much




Re: PRC as a amplifier in GPS question.


could anyone please kindly explain this for me.
"when the code from the receiver matches with the code from the satellite,
the signal is loud compared to background noise (amplified)"



Re: PRC as a amplifier in GPS question.


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The Psuedo-Random Code spreads the L1 carrier (as in CDMA), so that when the
receiver applies the correct code (each GPS satellite has a different code)
to the received signal, the L1 'pops out'.

What text are you using? There should be an explanation of how information
theory is used on the coded signal to 'amplify' the signal while leaving the
noise at essentially zero.

Ken



Re: PRC as a amplifier in GPS question.


i read from this site
http://www.ictp.trieste.it/~radionet/ghana1998/GPS/DECODING.HTM

Could you please explain that "infomation theory"?
how does receieved signal compare to background noise to achieve a
amplification?



Re: PRC as a amplifier in GPS question.


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Hmm, the only other half-decent site I found in a quick search had the same
text!

The 'amplification' is 'virtual' - you are really taking enough samples over
a period of time so as to reduce the errors. Assume you look at a signal
containing noise. Because the noise in it is random, and the PRC code is by
definition also 'random', if you sample and compare the signal with the PRC
over time, they should match just as often as they don't match.

But now if you add the signal from a GPS satellite (which looks like noise
because it uses a PRC for coding), and if the PRC we sample with matches the
satellite's, then there will be times when the sample of the  PRC from the
satellite adds to the noise correctly so that we start to get more matches
with the PRC we are sampling with. There only has to be a small number of
times in a sample period when we get the benefit of added matches, but we
can then sample over longer time periods to get lots more matches. In this
way we can resolve the GPS signal from the noise. In the text they make a
fairly spurious, in my opinion, comparism back to a figure of amplification.
What you are really improving is your bit-error rate. It equates to the same
thing, but I don't think they say that part particularly well. My opinion
only.

Is that any clearer than what you read on that site? It's basically the same
words, I can't think of any other way to put it off-hand.

Are you studying for a course or just curious?

Cheers.

Ken



Re: PRC as a amplifier in GPS question.



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same
over
by
PRC
the
amplification.
same
same

Ken I know next to nothing about the topic except in a general way, and it
made perfect sense to me. Thank you.

Cheers
Jim



Re: PRC as a amplifier in GPS question.


Hi,
I suggest a book on spread spectrum may be of use. Try "Spread spectrum
systems.." by Dixon.

The gain you are referring to is called Process Gain. When the received
signal is run through a matched filter or autocorrelator, the energy of the
original signal is reconstructed. The gain acheived is dependant on the chip
rate and bandwidth used.

This concept is also used widely in radar systems. Using a low power spread
or chirped pulse can be run through a matched filter to produce a high power
narrow pulse, providing better jammer to noise ratio, lower probability of
intercept and better range resolution.

If you look for LPI radar or Spread Spectrum, you should find answers.

In essence, the energy of a carrier signal is spread over a wide band width
using the PN code, this will effectivly reduce the energy in any given
bandwidth (W/Hz) and so for a receiver that has no matched filter, the
signal may at or below the thermal or terrestrial noise floor of that
receiver. When the signal is passed through a matched filter the energy of
the spread signal becomes coherent and reconstructs the original signal.

Cheers
Greg


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Re: PRC as a amplifier in GPS question.


thank all guys...
According from the web
http://www.ictp.trieste.it/~radionet/ghana1998/GPS/DECODING.HTM
What I am thinking is, the PRC is sending in a period(100s), and compare
itself and take the averaging to get a better quality. is it correct?
But the thing is, how can the PRC and background noise ampilify the signal
to make the receiver size smaller?
Thank you for all helps..

I am doing a uni assignment about PRC in spread spectrum system.



Re: PRC as a amplifier in GPS question.


Amm...
When the recieved signal matched the satellite signal, the recieved
signal(PRC) compare to background noise, when recieved signal compare to
background noise, energy of the
recieved signal is reconstructed, therefore the amplitcation is achieved.

Please correct any mistake. Thank you.



Re: PRC as a amplifier in GPS question.


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Your University should have access to the IEEE Transactions on
Communications (1982) which have a detailed account of spread-spectrum
systems. This will probably help you more at this stage than more words
saying the right thing.

Good luck.

Ken



Re: PRC as a amplifier in GPS question.


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the
chip
spread
power
width

The website explanation is terribly thin and I need clarification. Can you
tell me if this is on the right track :

The receiver pattern runs at a slightly different speed to the satellite
pattern so the two can "strobe" or correlate against each other.  Every time
they slide to the correct position, a pulse is produced.  The pattern of
those produced pulses is decoded to produce the GPS information.

Roger Lascelles



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