Downlink performance limitations of cellular systems with coordinated base stations and mismatched precoder

Coordination of base stations is a promising technique for reducing inter-cell interference in next-generation cellular systems. For the downlink of such systems, the authors study the degradation of zero-forcing precoded transmissions caused by imperfect channel estimation and channel variation over time. They derive exact expressions for the mean power of the desired signal received by an arbitrary user and of the interference caused by the mismatched precoder. By using these expressions, they show that for attaining a given signal-to-interference power ratio (SIR) these systems are limited by a maximum feedback delay of updated channel state information. Finally, they present a procedure to calculate the maximum tolerable feedback delay and to determine the separation between the non-precoded pilot symbols for guaranteeing a desired SIR.