Data transmission via standard audio cable

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Valerio Marcucci
Valerio Marcucci 2016-8-31
评论： Walter Roberson 2022-1-12
Hi, I'm trying to transmit an image from a computer to another using Matlab and a standard aux cable. On the transmitter I get the binary matrix of the image in b&w with im2bw, convert it into an electrical signal (1 -1) and use the QPSK modulation, without using Matlab predefined functions (just by multiplying half of the bits for cos(2*pi*f*t) and the other for sin(2*pi*f*t) ). Then I use sound while I use audiorecorder on the receiver, so that I get data on the other pc and then I make the demodulation.
This said, here it is an example of my results:
Original file
Transmitted image
Received image without filters
Received image with a low pass filter (not sure it's well done)
Received image with a band pass filter (not sure it's well done)
The obvious question is how to receive the correct image?
More in detail,
1) can you suggest me a good filter (with matlab code)? I'm using it before demodulating the received signal, is it right?
2) I'm "cheating" on reconstructing the image, because I already know what the specific dimensions of this particular image are (width and height), but if my transmission would be far more noiseless, I would transmit the dimensions before transmitting data. Do you think I can solve this problem using a FEC method like Hamming or Reed Solomon?
3) I see Mickey's head is cut off on the received images, and I think the problem is due to the delay between the start of recording and the start of transmission, but if you help me with point 2) (increasing the precision) I should be able to say to the receiver what is the beginning of data by means of a pattern
4) Any other suggestion is really appreciated!
Thanks a lot to everyone who tries to help me
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yanqi liu
yanqi liu 2022-1-12
may be use base64 encode and decode to make image to string and bits，then transfer it
Walter Roberson
Walter Roberson 2022-1-12
@yanqi liu
They are already using im2bw() so they only have bits anyhow.

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