In this case, the UE needs the CSI-RS to calculate the CSI and report it back in the UL direction. At lower frequencies, the system uses a modest number of active antennas for MU-MIMO and adds FDD operations. During MIMO operations, NR uses different antenna approaches based on the carrier frequency. The design of SRS and its frequency hopping mechanism is same as used in LTE.Ĭhannel State Information Reference Signal (CSI-RS)Īs a DL-only signal, the CSI-RS the UE receives is used to estimate the channel and report channel quality information back to the gNB.Multiple SRS symbols allow coverage extension and increased sounding capacity.In time domain, it spans 1/2/4 consecutive symbols which are mapped within last six symbols of the slot.SRS refers to Sounding Reference signal and uplink only signal.The system uses the SRS for resource scheduling, link adaptation, Massive MIMO, and beam management. Channel State Information describes how the NR signal propagates from the UE to the gNB and represents the combined effect of scattering, fading, and power decay with distance. 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 usesĪs a UL-only signal, the SRS is transmitted by the UE to help the gNB obtain the channel state information (CSI) for each user.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.Moreover it is confined to scheduled BW and duration used for NR-PDSCH/NR-PUSCH PTRS is associated with one DMRS port during transmission.Due to phase noise properties, PTRS has low density in frequency domain and high density in time domain.It is present both in uplink (in NR-PUSCH) and downlink (in NR-PDSCH) channels.PTRS enables suppression of phase noise and common phase error specially at higher mmwave frequencies.It’s main function is to track phase of the Local Oscillator at transmitter and receiver.PTRS stands for Phase Tracking Reference signal.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). The PTRS plays a crucial role especially at mmWave frequencies to minimize the effect of the oscillator phase noise on system performance. The phase noise of a transmitter increases as the frequency of operation increases. Multiple orthogonal DMRSs can be allocated to support MIMO transmission.DMRS can be beamform the DMRS, kept within a scheduled resource, and transmit it only when necessary in either DL or UL.DMRS is specific for specific UE, and transmitted on demand.DMRS design and mapping is specific to each Downlink and Uplink NR channels vize NR-PBCH, NR-PDCCH, NR-PDSCH, NR-PUSCH, NR- PUSCH.It is used by a receiver for radio channel estimation for demodulation of associated physical channel.DMRS refers to demodulation reference signal.In high-mobility scenarios to track fast changes in channel, it might increase the rate of transmission of DMRS signal (called “additional DMRS”). The network presents users with DMRS information early on for the initial decoding requirement that low-latency applications need, but it only occasionally presents this information for low-speed scenarios in which the channel shows little change. Additionally, multiple orthogonal DMRSs can be allocated to support MIMO transmission. The system can beamform the DMRS, keep it within a scheduled resource, and transmit it only when necessary in either DL or UL. The DMRS is specific for specific UE, and used to estimate the radio channel. In NR, reference signals are transmitted only when it is necessary where as in LTE constantly exchanging reference signals to manage the link. DMRS has been introduced for both downlink and uplink channels.New Reference Signal PTRS has been introduced for Time/Frequency tracking.In NR, there is not Cell specific Reference Signal (C-RS).Reference Signals Mapping with associated with different physical channel is depicted in following figure. Channel State Information Reference Signal (CSI-RS).To increase protocol efficiency, and to keep transmissions contained within a slot or beam without having to depend on other slots and beams, NR introduces the following four main reference signals.
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