The UE needs measurement gaps to perform measurements when it cannot measure the target carrier frequency while simultaneously transmitting/receiving on the serving cell. In NR, the measurements that the UE performs can be gap-assisted or non-gap-assisted. The network configures an RRC CONNECTED UE to perform measurements and UE report measurement report
In 5G NR, RSRP measurement is performed and reported at layer 1 (Physical Layer) and layer 3 (RRC layer). 5G capable devices can provide SS-RSRP measurements at Layer 1 when sending Channel State Information (CSI) and at Layer 3 when sending an RRC measurement report to gNB.
5G measurements facts
For Downlink channel sounding, 5G NR uses two main downlink signals that a UE measures:
- SSB (Synchronization signal PBCH block): it is transmitted with a low duty cycle on a limited bandwidth as compared to LTE’s cell-specific reference signals (CRS) that are sent on the entire channel bandwidth. These measurements are used to determine path loss and average channel quality.
- CSI-RS (Channel State Information – Reference Signal): it is used for tracking rapidly changing channel conditions to support mobility and beam management.
In general, measurements in FR1 (Frequency Range 1) are from UE’s antenna connector. In FR2 (Frequency Range 2) measurements are based on the combined signal from antenna elements mapped to a given receive branch. Although a UE can be configured for measurements early on, measurement reports can be sent to the network only after AS security activation.
Parameters measured by a 5G UE:
- SS-RSRP (Synchronisation Signal – Reference Signal Received Power): It is the Average power of resource elements carrying secondary synchronization signals. In addition, resource elements of PBCH-DMRS and CSI-RS can be included in this.
- SS-RSRPB: it is similar to SS-RSRP but for each antenna connector or for each receiver branch.
- SS-RSRQ: it is the quality of the signal received and it is measured over the same resource block.
- SS-SINR: it is SS-RSRP over average noise plus interference power.
- Measurement objects: it specifies what is required to be measured. For NR, it may include cell-specific offsets, blacklisted cells that are to be ignored, and whitelisted cells that are to be considered for measurements.
- Reporting configurations: it could be periodic or event-triggered. It specifies how reporting should be done.
- Measurement ID: it identifies how to report measurements of a specific object.
- Quantity configuration: it specifies parameters for layer 3 filterings of measurements.
- Measurement Gaps: periods that UE may use to perform measurements.