Performance Analysis of Adaptive M-PSK Communications Using Equal Gain Combining

Channel estimation at the receiver is essential for Variable Rate (adaptive) modulation schemes and this prohibits systems that are less complex from using (adaptive) variable rate and/or variable power transmissions. Providing a solution to this problem, we introduce a variable-rate (VR) M-PSK modulation scheme, for communications over fading channels, without channel gain estimation at the receiver. The choice of the constellation size is based on the signalplus-noise (S+N) value rather than on the signal-to-noise ratio (S/N). It is analytically shown that S+N can serve as an excellent simpler criterion, alternative to S/N, for determining the modulation order in adaptive systems. In this way, low complexity transceivers can use VR transmissions to increase their spectral efficiency under an error performance constraint. As an application, we utilize the proposed adaptive modulation scheme in equal gain combining (EGC) diversity receivers.