Hello,
My ultimate goal is to use the correlation estimator block for synchronization using a preamble in order to send packets of digital data from one sdr to another, both running gnu-radio. In order to understand how the correlation estimator works, I am looking at the provided example "example_corr_est_and_phase_sync." It looks like this example is using a BPSK modulation scheme and I am trying to modify it to work with QPSK instead to make sure I know how it works, but I am running into problems. I have four questions:
1.)
I do not understand the purpose of the "tag marking delay" entry in the correlation estimator block. How should this value be determined?
2.)
How does the correlation estimator "talk to" the costas loop and Polyphase Clock Sync blocks? Is there something going on behind the scenes here that I cannot see? Is it somehow passing the frequency/phase correction information to these blocks?
3.)
I think my main issue is that I do not understand how to format the "Data Vector" entry in the "Modulate Vector" block. This is my (probably incorrect) understanding:
I want my preamble symbols to be [1+1j, 1+1j, 1+1j, -1-1j, -1-1j, 1+1j, -1-1j]
My constellation object has the following parameters:
Symbol Map: [0,1,2,3]
Constellation Points: [(-1-1j),(-1+1j),(1-1j),(1+1j)]
Therefore, my desired preamble would map to: [3,3,3,0,0,3,0]
So, in the "Data Vector" box in the "Modulate Vector" block, I should enter:
[0x3,0x3,0x3,0x0,0x0,0x3,0x0]
4.)
Why is the Modulate Vector block needed at all? Why can I not simply enter
[1+1j, 1+1j, 1+1j, -1-1j, -1-1j, 1+1j, -1-1j] into the field for "Symbols" in the correlation estimator block?
Disclaimer:I am relatively new to gnu-radio and this is my first time using the mailing list.