Synchronisation Signal – Reference Signal Received Quality (SS-RSRQ) measurements can be used for
- Cell Selection,
- Cell Reselection
- Mobility procedures.
- In contrast to RSRP measurements, RSRQ measurements arc not used when reporting Channel State Information (CSF).
SS RSRQ = SS-RSRP/(RSSI-N)
where, N is the number of Resource Blocks across which the Received Signal Strength Indicator (RSSI) is measured, i.e. RSSI / N defines the RSSI per Resource Block. The RSSI represents the total received power from all sources including interference and noise.
The RSRP and RSSI are both measured across the same set of Resource Blocks
This equation is similar to the equation used by LTE. However, there are some significant differences in the measurement methods. In the case of LTE, RSRP is measured from the Cell specific Reference Signal (CRS) and the RSSI is measured from symbols which include the CRS. This means that RSSJ / N can never be less than the RSRP, so RSRQ is always less than I and is a negative number when expressed in dB.
In the case of cell selection, 3GPP does not constrain the time domain resources used to measure the RSSJ. In all other cases, the time domain resources are confined to a subset of the symbols belonging to the SS/PBCH Block Measurement Time Configuration (SMTC).
This implies that the SMTC defines a time window which includes the Secondary Synchronisation Signal. The Base Station can use the SS-RSSI Measurement parameter structure presented to configure a subset of the SMTC which excludes the SS/PBCH Block.
RSRQ measurements are filtered at Layer 3 to remove the impact of fast fading and to help reduce short term variations in the measurement results. This filtering is specified by 3GPP within TS 38.331.
3GPP TS 38. 133 specifies the mapping between the reported and measured SS-RSRQ. The measured values of RSRQ can be either positive or negative when expressed in dB.
When using Frequency Range I, the reference point for the measurement is the UE antenna connector, i.e. it is assumed that the UE has a single antenna element per receive path rather than an antenna array.
When using Frequency Range 2, the measurement is based upon the combined signal strength from all antenna elements belonging to a single receive path, i.e. it is assumed that the UE has an antenna array for each receive path.
Layer 3 measurements can be either ‘beam level’ or ‘cell level’. Both can be reported to the Base Station within an RR C: Measurement Report message. Beam level results are evaluated and reported after Layer 3 filtering.