On the capacity of multiple-input multiple-output gaussian X channels

Finding the capacity region of a Gaussian X network is an open problem in information theory. In this study, the authors characterise the capacity regions of 2 × 2 user multiple-input multiple-output Gaussian X channels for very strong interference and generally strong interference. Moreover, the sum capacity is established for noisy interference. Sufficient conditions for Gaussian X networks to have very strong interference, generally strong interference and noisy interference are derived.