Reference Signals(RS) are crucial components in both LTE  and NR wireless communication systems. In LTE, various types of Reference Signals are utilized, and these signals serve similar fundamental roles in NR. However, despite their similarities, there are notable differences between the Reference Signals used in LTE and those in NR. These differences are significant and can be described in detail as follows:

• In NR, there is no CRS (Cell Specific Reference Signal). The CRS in LTE is used for various purposes, such as channel estimation, cell identification, and synchronization across the cell. Its absence in NR reflects a shift in design philosophy, as NR relies on other mechanisms and signals to achieve similar functionalities, optimizing for the demands of 5G networks, such as higher data rates, lower latency, and improved efficiency.
• In NR, there is a new reference signals  Phase Tracking Reference Signal, PBCH Reference Signal, Time/Frequency Tracking Reference Signal and DMRS (Demodulation Reference Signal) for various channels(e.g, PDCCH, PDSCH etc) are some examples of the new reference signals

• Type of Reference Signal
• How to Detect Reference Signal
• Reference

Type of Reference Signal

There are various types of Reference Signals in NR (New Radio), and the types of reference signals along with their roles can be summarized in a diagram. The diagram illustrates the structure and interaction of reference signals within the NR protocol stack, spanning across different layers and channels.

At the physical layer (PHY), the diagram highlights several key reference signals and their association with specific physical channels. The reference signals, marked in red, are integral to the operation of NR and are used for tasks such as channel estimation, synchronization, and phase tracking.

Overall, the diagram effectively maps out the various types of reference signals in NR—such as DMRS, PT-RS, PBCH Reference Signal, CSI-RS, SRS, and others—and their roles in supporting the physical channels and ensuring robust, high-performance communication in 5G networks.

The picture stacks the three layers. Logical channels and the MAC blocks are at the top, and transport channels are in the middle. The physical channels run along the bottom, with their reference signals attached. The legend marks a red oval as a reference signal, and the arrows below each channel give its direction.

Every channel that has to be demodulated carries its own DMRS. The signals drawn outside a channel box are the ones that exist for measurement rather than for demodulation.

• DMRS appears once per channel : PBCH, PDCCH, PDSCH, PUSCH and PUCCH each carry their own, and none of them shares one with another channel.
• PT-RS rides with the data channels only : it is drawn inside the PDSCH and PUSCH boxes, and nowhere else.
• CSI-RS and SRS stand alone : neither sits inside a channel box, because both exist to measure the channel rather than to demodulate one.
• PRACH carries no reference signal : the preamble is the signal, so nothing is attached to it.
• The arrows give the direction : CSI-RS points down and SRS points up, which is the whole difference between the two.

List of all NR reference signal can be summarized as follows. The details of each reference signal will be posted as separate page.

Two rows in that table need a note. The first is TRS, which is not a signal of its own in 38.211. It is an NZP-CSI-RS resource set with trs-Info set, so its physical structure is the CSI-RS one and its configuration lives in 38.331. Clause 7.4.1.6 of 38.211 is the RIM reference signal, which is a different thing entirely.

The second is what the list leaves out. 38.211 also defines positioning reference signals at clause 7.4.1.7 and the RIM reference signals at 7.4.1.6, and neither appears above. Both are real downlink reference signals, and neither is needed for the cell search the next section walks through.

• The clause column is the useful one : it is the string to paste into a search box, and it is where each signal is actually specified.
• Downlink and uplink split the clause number : the downlink signals sit under 38.211 clause 7.4.1 and the uplink ones under 6.4.1.
• TRS is a configuration, not a signal : it is a CSI-RS resource set with trs-Info, so no 38.211 clause defines it separately.
• The list is not complete : positioning reference signals and RIM reference signals are both defined in 38.211 and both are absent from it.

How to Detect Reference Signal

Based on this definition, NR Cell Search procedure can be broken down to several steps as follows : (Even though it may seem simple process, this is very complicated process if you go in detail. First, try to understand overall procedure as described below and then follow through the linked pages for further details for each of the steps).

1) UE tunes to a specific frequency (How UE select this specific freuqency to tune to ?)

2) UE tries to detect SSB and decode PSS, SSS. If UE fails at this step, it goes to step i) and passes at this step, go to next

3) Once UE successfully detect PSS/SSS, it can construct the resource grid for SSB

4) From the resource grid, it can decode PBCH DMRS.

5) From SSB resource grid with the help of PBCH DMRS, it can decode PBCH / MIB

6) Based on MIB.pdcch-ConfigSIB1, find the location of CORESET0 (CORESET for PDCCH/DCI for SIB1 transmission) and SearchSpace information. This CORESET0 finding is done by predefined parameters as described here.

7) Blind decode DCI 1_0 in the SearchSpace.

8) Based on the contents of the DCI 1_0. (NOTE : In order to interpret the DCI 1_0 for SI RNTI, UE need to have some additional table like TimeDomainResourceAllocation which is usually configured in RRC message (e.g, SIB1, RRCConfiguration etc). But this step is before decoding any RRC message. It implies that UE should know of TimeDomainResourceAllocation from predefined tables in 3GPP. Refer to [NOTE 1] in SI-RNTI DCI 1_0 for further details )

9) Detect and decode PDSCH carrying SIB1.

10) decode SIB1 and other SIBs (if SIB1 carries information on other SIBs).

11) Once the SIB1 is decoded, UE can figure out various other fundamental information like channel bandwidth, center frequency of the channel etc as shown here.

12) Based on the information obtained from SIB1 (i.e, Channel bandwidth, subcarrier spacing), UE can construct the resource grid for the entire bandwidth.

13) Proceed to RACH procedure

14) If RACH procedure is successfully done, UE can receive and decode RRC Setup.

15) Based on the information from RRC Setup, UE can figure out exact resource element for DMRS for other channels (e.g, PDCCH, PDSCH, PUSCH etc) and other signals (e.g, CSI-RS, TRS, SRS etc)

Reference

[1] 38.211 v19.4.0 : NR - Physical channels and modulation. Clause 7.4.1 holds the downlink reference signals and clause 6.4.1 the uplink ones. The clause numbers in the table above were checked against it.

[2] 38.214 v19.4.0 : NR - Physical layer procedures for data. It carries the UE assumptions for a CSI-RS resource set configured with trs-Info.

[3] 38.331 v19.3.0 : NR - Radio Resource Control (RRC) protocol specification. The field trs-Info belongs to NZP-CSI-RS-ResourceSet.