Optimal Rotated M-PSK Signaling for Multi-User Receive Diversity System Over Correlated Rician Fading Channels

In this letter, a two-user receive diversity non-orthogonal multiple-access (NOMA) wireless communication system is considered with the transmitter utilizing a rotated
$M$
-ary phase-shift keying (
$M$
-PSK) modulation for data modulation over correlated Rician fading channels. A maximum ratio combining scheme followed by an optimum maximum-likelihood rule is employed for received data detection at each user end. Further, a simple separation scheme is proposed to eliminate the use of successive interference cancellation at the receiver end of the NOMA system. The receiver structure is utilized to derive a closed-form expression for the symbol error probability which is minimized by obtaining the optimal rotation angle of the
$M$
-PSK constellation. The variations of the optimal rotation angle with system parameters are studied by numerical results which lead to novel modulation schemes for the considered system.