RSRQ 3GPP Definition
RSRQ or Reference Signal Received Quality is defined as the ratio N×RSRP/(E-UTRA carrier RSSI), where N is the number of RB’s of the E-UTRA carrier RSSI measurement bandwidth. The measurements in the numerator and denominator shall be made over the same set of resource blocks.
- N is the number of Physical Resource Blocks (PRBs) over which the RSSI is measured, typically equal to system bandwidth
- RSSI is pure wideband power measurement, including intracell power, interference and noise (noise + serving cell power + interference power during RS symbol)
E-UTRA – RSSI (Carrier Received Signal Strength Indicator), comprises the linear average of the total received power (in [W]) observed only in OFDM symbols containing reference symbols for antenna port, in the measurement bandwidth, over N number of resource blocks by the UE from all sources, including co-channel serving and non-serving cells, adjacent channel interference, thermal noise etc.
- The reporting range of RSRQ is defined from -3…-19.5dB: See Graph and Table below
The reference point for the RSRQ shall be the antenna connector of the UE. If receiver diversity is in use by the UE, the reported value shall not be lower than the corresponding RSRQ of any of the individual diversity branches.
So we have that RSRQ depends on serving cell power and the number of Tx antennas
Applicable for: RRC_CONNECTED intra-frequency, RRC_CONNECTED inter-frequency
As you know from the definition of RSSI (RSRP and RSRQ-Measurement in LTE), it contains all sorts of power including:
- power from co-channel serving & non-serving cells
- adjacent channel interference
- thermal noise
Therefore, (N x RSRP)/RSSI indicates “What is the portion of pure RS power over the whole E-UTRA power received by the UE“.
As you see, this is not the direct measurement, it is a kind of derived value from RSRP and RSSI. By dividing RSRP by RSSI, it could give some information about interference as well in addition to the strength of the wanted signal.
Since this is the ratio of two different power value, the unit of RSRQ is dB and the value would be always negative (because RSSI value will always be larger than N x RSRP)
UE usually measures RSRP or RSRQ based on the direction (RRC message) from the network and report the value. When it report this value, it does use the real RSRQ value.
It sends a non-negative value ranging from 0 to 34 and each of these values are mapped to a specific range of real RSRQ value as shown in the following table from 36.133.