Phase Tracking Reference Signal (PTRS)
The phase noise of a transmitter increases as the frequency of operation increases. The PTRS plays a crucial role especially at mmWave frequencies to minimize the effect of the oscillator phase noise on system performance. One of the main problems that phase noise introduces into an OFDM signal appears as a common phase rotation of all the sub-carriers, known as common phase error (CPE).
PTRS stands for Phase Tracking Reference signal
It’s main function is to track phase of the Local Oscillator at transmitter and receiver.
PTRS enables suppression of phase noise and common phase error specially at higher mmwave frequencies.
It is present both in uplink (in NR-PUSCH) and downlink (in NR-PDSCH) channels.
Due to phase noise properties, PTRS has low density in frequency domain and high density in time domain.
PTRS is associated with one DMRS port during transmission. Moreover it is confined to scheduled BW and duration used for NR-PDSCH/NR-PUSCH
The NR system typically maps the PTRS information to a few subcarriers per symbol because the phase rotation affects all sub-carriers within an OFDM symbol equally but shows low correlation from symbol to symbol
The system configures the PTRS depending on the quality of the oscillators, carrier frequency, Sub Carrier Spacing, and modulation and coding schemes that the transmission uses