AWGN : Recombining AWGN to obtain new AWGN
My guess is your professor is trying to teach you about how noise in a dual-pol QAM system affects decoder performance. In such a system, there are 4 uncorrelated AWGN noise channels (XI,XQ,YI,YQ). It could also be that your professor is trying to teach you about linear impairments and their properties.