RS ports can be doubled in NR by using the DM-RS configuration with two adjacent symbols and orthogonal cover codes in the time domain. DM-RS sequences corresponding to different ports are orthogonal due to the use of different subcarriers (e.g. following a comb pattern) or by using different orthogonal cover codes. The actual number of orthogonal antenna ports depends on the type of DM-RS with a maximum of 12 DM-RS antenna ports, allowing efficient MU-MIMO transmission schemes for up to 12 UEs. In the time domain, the DM-RS structure is also configurable and may include one or multiple DM-RS occasions with the first DM-RS symbol always located at the beginning of the transmission to enable early channel estimation processing. For efficient PDSCH or PUSCH transmission in scenarios with medium and high mobility, NR supports a max- imum of three additional DM-RS occasions within a slot, thus allowing more frequent channel estimation updates. The channel estimation using DM-RS in downlink can be per- formed based on the unit of precoding resource group, which may include two, four, or all contiguous scheduled PRBs. The actual physical resource block group (PRG) size in NR can be configured for the UE by higher layers, for example, RRC, or dynamically indicated by the DCI. For uplink transmission, the PRG always corresponds to all scheduled PRGs. The DM-RS sequence for the CP-OFDM waveform is modulated by QPSK using Gold sequences and for the DFT-s-OFDM waveform by low PAPR constant amplitude zero auto- correlation sequences. Depending on the number of allocated PRBs for uplink transmis- sion, DM-RS is modulated by QPSK using either a low PAPR Zadoff-Chu sequence or a low PAPR CGS similar to LTE. The constant modulus property of the sequences in frequency domain guarantees perfect autocorrelation in the time domain for DM-RS and therefore optimal channel estimation performance. 3.5.7.3 PT-RS PT-RS is used for fine granularity tracking of the phase in time, which helps to suppress RF impairments such as phase noise (3