Understanding time delay estimation for GPS?

In summary, the conversation is about time delay estimation in the context of the GPS system. The speaker is seeking help to understand the process and steps involved in estimating the time delay between transmission and reception of a signal. They mention using xcorr and ask for guidance on what to do with the output to get a single real number representing the time delay. They also mention a link to a website that they found helpful but are looking for a more basic understanding before delving into it.
  • #1
Nate Duong
126
3
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
 
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  • #2
Nate Duong said:
Please help me for these questions.
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
 

1. What is time delay estimation for GPS and why is it important?

Time delay estimation for GPS is the process of accurately measuring the time it takes for a signal to travel from a satellite to a receiver on Earth. This is crucial for GPS systems to accurately determine the location of an object, as the time delay helps calculate the distance between the satellite and the receiver. If time delay estimation is not accurate, it can result in incorrect location data and navigation errors.

2. How does time delay estimation work for GPS?

Time delay estimation for GPS is based on the principle of triangulation, where multiple satellite signals are used to calculate the position of a receiver. The receiver measures the time it takes for a signal to travel from the satellite to the receiver, and this time delay, along with the known position of the satellite, is used to calculate the distance between the two. By using signals from multiple satellites, the receiver can accurately determine its position.

3. How is time delay estimation affected by environmental factors?

Environmental factors such as atmospheric conditions and satellite orbit can affect the time delay estimation for GPS. The ionosphere, a layer of the atmosphere, can cause signal delays due to its varying density. Satellite orbit errors can also impact the accuracy of time delay estimation. These factors must be carefully accounted for in the GPS system to ensure accurate location data.

4. How is time delay estimation for GPS different from other navigation systems?

Unlike other navigation systems that use signals from stationary ground-based transmitters, time delay estimation for GPS relies on signals from multiple satellites in orbit. This allows for more accurate and precise location data, as well as the ability to determine velocity and time information. GPS is also globally available, making it a widely used and reliable navigation system.

5. What are some current advances in time delay estimation for GPS?

There is ongoing research and development in improving time delay estimation for GPS, including the use of advanced algorithms and techniques to reduce errors caused by environmental factors. Additionally, new satellite systems such as Galileo and BeiDou are being developed to provide even more accurate and reliable time delay estimation for GPS. Advances in technology are constantly being made to enhance the performance and capabilities of GPS systems.

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