In a distributed antenna system (DAS), the number of physical antennas is usually larger than that of the antenna ports supported by LTE/LTE-A RS pattern in each cell. Systems and methods are directed to a RS transmission scheme in which the RRHs (or RRH groups) are dynamically scheduled and mapped to the antenna ports for RS transmission based on user density distribution such that the accuracy of the channel state information (CSI) estimation in the DAS is optimized.