Bit Error Floor Reduction for MQAM Signals in the Presence of Phase Error

We propose a method to form a non-uniform decision boundary (NUDB) for
$M$
-ary quadrature amplitude modulation (MQAM) signals to reduce bit error floor (BEF) in the presence of phase error. We put our focus on angle distances between MQAM symbols and adjacent decision boundaries to observe minimum angle distance, and derive optimum intervals for the decision boundaries to maximize the minimum angle distance. Through computer simulations, we verify that the proposed NUDB shows lower BEF than a conventional uniform decision boundary by 56% and 15% smaller for 16QAM and 64QAM, respectively.