Targetting for the great goal of the 5th generation (5G) system, the new radio (NR) system, proposed by the 3rd generation partner project (3GPP), has employed a variety of cutting-edge technologies, including advanced channel coding schemes, e.g., low density parity code (LDPC) and polar code, higher-order modulation schemes, e.g., 256QAM, etc. Considering the fact that the lower frequency spectrum has already been so crowded and overutilized, NR decided to explore higher frequency band, e.g., million meter wave (mmWave). After all, much richer spectrum resources are available at higher frequency bands than lower frequency spectrum.
As is well-known, high frequency transmission suffers severe attenuation loss in the propagation, which remarkably limits the effective coverage and transmission distance. Fortunately, higher frequency spectrum has shorter wave length. Given an aperture size, much more antennas can be equipped in higher frequency transmission than those in lower frequency transmission. In this way, more antennas can yield larger beamforming gain and complement the attenuation loss in the transmission over the higher frequency bands. In a word, higher frequency enables the dense deployment of antennas, i.e., massive multi-input multi-output (M-MIMO), or equivalently large-scale MIMO (LS-MIMO); while M-MIMO extends the transmission distance and coverage of the higher frequency bands. Therefore, M-MIMO and higher frequency transmission are usually jointly utilized and have been the focus of the research and discussion in the 3GPP standardization.
Generally, an oscillator always produces phase noise, which is essentially an impairment of the oscillator. Nevertheless, the phase noise soars as the operation frequency grows. In the NR system, which operates on higher frequency spectrum, the impact of phase noise cannot be ignored. Instead, the phase noise must be accurately estimated and complemented before data detection. To this end, a dedicated reference signal, termed phase tracking reference signal (PTRS) has been proposed to track the fluctuation of the phase noise.
This report intends to cover the detail relating to PTRS. The remaining of this report is structured as follows. Section #sec:pn-model briefly introduces the models of phase noise, and Section #sec:presence-density provides the configuration of PTRS, including its presence and density in the time and frequency domain. The number of PTRS supported is given in Section #sec:port-num. The PTRS port association follows in Section #sec:port-association. Then, resource mapping and sequence generation are presented in Sections #sec:res-map and #sec:seq-gen respectively. In Section #sec:pn-estim-compl, the methodology of phase noise estimation and complementation are described in details. Finally, Section #sec:summary summarizes the report.
For clear description, following denotation conventions are adopted throughout the document. \(\otimes\) is the operator of circular convolution. $\mathcal{F}_N \left\{ \cdot \right\} $ is the $N$-point fast Fourier transformation (FFT) operator. Radio resource control (RRC) signaling and downlink control indicator (DCI) parameters are illustrated as blue and orange phrases, respectively.
