Boundary alignment (follow up)

[lannan jiang]

Hi everyone,

    Two days ago I asked something about boundary alignment, and I have been 
trying many stuff in GRC to solve this. I am stuck on this for days and any 
help will be appreciated. Below is a description of what I wish to do. 
   
   1) My transmission and receiving chain are like this: signal source -> 
constellation modulator -> Adalm Pluto Tx-> Antenna -> Adalm Pluto Rx -> 
Polyphase Clock Sync -> CMA equalizer -> Costas Loop -> decoding. As for 
modulation scheme, I am using QPSK.
    2)  Now I just want to transmit  one byte output from the signal source, 
and following with one byte of a known pattern, and then one byte output from 
the signal source, etc. Then at the receiver, because i already know the known 
pattern, I need to sync to the known pattern in order to align the bytes, which 
will allow me to hear clean audio at the receiver.
    3) There are three things I am looking for: 
       a.  I have been looking for a SIMPLE way  to prepend a known pattern at 
the transmitter, and send it with the output bytes of a signal source.  Is 
there any block that might work to do this in GRC?
       b.  I have been trying to see if i can write an embedded python block to 
prepend a known pattern, but I am having a hard time trying to understand the 
input_items of the block, and how i can add a known pattern iteratively.
       c. If i can successfully send the known pattern with my data to the 
receiver, is there any easy way to parse at the receiver?

  Thank you in advance! 
  Lannan

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