Analysis of Channel Noise in Orthogonally Multiplexed QAM Systems

The paper deals with the background for the analysis and performance evaluation of orthogonally multiplexed QAM (OQAM) systems in the presence of noise, intersymbol interference and interchannel interference. The main result of the analysis is that the noise at the decision points is always stationary, regardless of the time-varying characteristics of the OQAM system. However, unless the filters are ideal (bandlimited and with a square-root Nyquist-shape) and the carriers are properly chosen, the noises of different branches are correlated even in the presence of an ideal channel. Hence a vector estimate method should be used instead of the classical scalar threshold detectors. Furthermore, the intersymbol interference and interchannel interference impulse responses have been evaluated. Again, the interesting result is that both relationships are time-invariant regardless of the system parameters