Theoretical analysis on spectral efficieny of semi-orthogonal downlink communications in mobile cellular systems

This paper is concerned with spectral efficiency analysis on semi-orthogonal downlinks in mobile cellular systems. The analysis is implemented based on the exact hexagonal-cell model which is practically generalized to multi-tier cellular systems. New explicit closed-form expressions are obtained for the spectral efficiency and the probability of error. These are used to investigate the impacts of fading, the level of background noise, the degree of orthogonality, as well as the conditions of the propagational path. From the numerical results, it is found that the spectral efficiency depends heavily on the condition of propagational path, whereas the impact of orthogonality seems dominant in comparison to those of background noise and propagational path.