To increase 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 as compared to LTE.
What’s new in NR compare to LTE
In NR, there is not Cell-specific Reference Signal (C-RS)
New Reference Signal PTRS has been introduced for Time/Frequency tracking DMRS has been introduced for both downlink and uplink channels
In NR, reference signals are transmitted only when it is necessary whereas in LTE constantly exchanging reference signals to manage the link.
What is reference signal:
Most of the channels (e.g, PDSCH, PDCCH, PBCH etc) is for carrying special information (a sequence of bits) and they have some higher layer channel connected to them, but Reference Signal is a special signal that exists only at PHY layer. This is not for delivering any specific information. The purpose of this Reference Signal is to deliver the reference point for the downlink power.