Random matrices and the impact of imperfect channel knowledge on cooperative base stations

Base station cooperation is a very promising technique for reducing inter-cell interference and enhancing spectral efficiency in next generation cellular systems. However, imperfect precoding at the base stations is limiting the potential gains. In this paper, we present a downlink signal model with impaired zero-forcing precoding and analyze self-user signal and inter-user interference. Properties of Wishart-distributed random matrices are used for calculating the average inverse eigenvalues. We provide closed-form expressions for signal to interference ratio (SIR) bounds, which are found inversely proportional to the mean square error of the base station´s channel knowledge. Further, it is found that the SIR increases with the ratio of number of base stations to number of users. Numerical evaluation agrees with analytical results.