# Understanding time delay estimation for GPS?

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1. Mar 14, 2017

### Nate Duong

I really need help to understand these questions which is highlight, for the GPS situation, I hope anyone who has been working in this situation before, please help me to have a clear understanding about "time delay estimation":

Here is the scenario:

1. Suppose I know precisely I have transmit the signal (data), I know the sampling, I know the time correspond to the very 1st point, I can go through the sign the time every single measurement, that I just transmitted. Now, I received the signal (data), I have section of data and in there somewhere is the signal that transmitted. Unlike, as the transmit, I know the time correspond to the very 1st point in my receive data:
what would I do to get the time delay?
what steps do we follow?

2.
In there, somewhere, I don’t know where exactly, but in there somewhere is transmitted the signal and I want to estimate time delay between the transmit and receive. So, I want to look at:
what you need to do that?
What math. operation do I need to use to compute that time delay?

3.If I say:"I want to compute xcorr between 2 vectors". So, this xcorr is twice sum of the length – 1:
what do I do when I have xcorr output?

4.I take 2 vectors, and I compute even longer vector use xcorr, so now I compute the longer vector but I want a number, I don’t want a vector, I want a time delay estimation:
what do I do with the xcorr solved like a MATLAB?

5.If I say xcorr(x,y), x has certain length and y has certain length, the result is the length of x plus length of y and minus 1. So, now I have a long vector:
what do I do then to determine the time delay?
what the signal look like and what xcorr look like?
what do I do when I have xcorr to determine the time delay?

6.I know that have xcorr with bunch of complex number but I need only one real number. The real number that I want is the time delay. I take input data, I take received signal, I compute xcorr, then I do something to help myself to get the time delay. Result to that is single real number. But these are general ideas, I need to answer those question.

7.I have read this link: http://dsp.stackexchange.com/questi...-oscilloscope-signals-using-cross-correlation . It's really help my understanding, but they way he answered very high level, I think I need to understand the basic first, then continue with this link.

Please help me for these questions.

Thank you very much, everyone

2. Mar 14, 2017

### Buzz Bloom

Hi Nate Duong:

I am not sure I understood all of your questions, but I think the following might be helpful.
There is a lot of information there that seems to be related to your questions.

Regards,
Buzz

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