RSRP (Received Signal Reference Power) is defined as the measured power level at one specific RE. I.E. UE in cell centre would have a RSRP level at -65dBm.
RSSI (Received Signal Strength Indicator) is defined as the total measured power for all REs that carries RSRP across the whole measured spectrum.
RSRQ (Received Signal Received Quality) is defined using equation (NPRB * RSRP ) / RSSI
1. RSRP, RSSI and RSRQ of antenna port 0 and 1 CRS
Relation between RSSI and RSRP depends on channel bandwidth. For 10MHz system, there are in total 50 PRBs and for each PRB, the first symbol has 2 REs that transmitting CRS, thus in total there are 100 subcarriers of first symbol that is transmitting CRS. RSSI is 100 times RSRP. Converted in to dB is 10log100 = 20dB. So for UE in cell centre, if RSRP is -65dBm, RSSI is -65dBm+20dBm=-45dBm. Ideally, RSRQ = (NPRB * RSRP ) / RSSI = -3dB. However, due to interferences, RSRQ is always lower than -3dB and RSSI is always higher than 20dB of RSRP.
2. RSRP, RSSI and RSRQ of antenna port 0 and antenna port 1 with 2 CRS
For 10MHz system, 50PRBs, each first symbol has 4 CRS (2 for antenna port 0 and 2 for antenna port 1), in total, there will be 200 subcarriers that carry cell reference signal. RSSI is 200 times RSRP. Converted in to dB is 10log200 = 23dB. So for UE in cell centre, if RSRP is -65dBm, RSSI is -65dBm+23dBm=-42dBm. Ideally,1 RSRQ = (NPRB * RSRP ) / RSSI = -6dB. However, due to interferences, RSRQ is always lower than -6dB and RSSI is always higher than 23dB of RSRP.
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