Orthogonal multi-user, multiple input, multiple output (MU-MIMO) multiplexing capacity for demodulation reference signals (DMRSs) is increased without increasing the overhead in resource elements per physical resource block by using length-4 orthogonal cover codes (OCC-4). A base station switches between legacy DMRS antenna port mappings and OCC-4 mapping based upon either a transmission mode or a channel station information process configuration field value.