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  _  _     _____                ___     __   _   
 | \| ||  |  ___||     ___     / _ \\  | || | || 
 |  ' ||  | ||__      /   ||  | / \ || | '--' || 
 | .  ||  | ||__     | [] ||  | \_/ || | .--. || 
 |_|\_||  |_____||    \__ ||   \___//  |_|| |_|| 
 `-` -`   `-----`      -|_||   `---`   `-`  `-`  
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Text this: LDPC code and PPM modulation in free space optical communication system