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)"

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

i read from this site

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

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

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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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

thank all guys... According from the web

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.

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.

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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

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