A base station includes a reference signal sequence generator configured to generate a reference signal sequence for a reference signal for each of n antenna ports using one initialization seed cinit with n being a positive integer. The initialization seed is defined as: cinit=(└ns/2┘+1)·(2NIDcell+1)·216+NIDgroup, where ns is a first slot number in a subframe, NIDcell is a cell identifier of the base station, and NIDgroup is a group identifier. The base station also includes a transmit path circuitry configured to transmit a downlink grant and the reference signal. In some embodiments, the group identifier NIDgroup is a one-bit group identifier dynamically indicated in a codepoint in the downlink grant transmitted by the base station.