RSSI represents the total received wide-band power measured over entire bandwidth by UE. RSSI is not reported to eNodeB. It is computed to be used for the calculation of RSRQ in LTE system. RSSI is also a power and its measurement unit is dBm same as RSRP.
LTE系统中RSSI是UE在全带宽上测量到的功率；RSSI不直接上报，而是换算成RSRQ上报eNodeB；
与RSRP相同，RSSI也是功率测量指标，计量单位为dBm;
RSSI=Serving Cell Power + Neighbour Co-Channel Cells Power + Thermal Noise (1)
RSSI=服务小区功率+同频邻小区功率+热噪声功率
Under full Load condition the RSRP (dBm)= RSSI – 10*log (12*N) (2)
全加载场景下:RSRP(dBm)=RSSI-10*log (12*N)
Bandwidth | 1.4 MHz | 3 MHz | 5 MHz | 10 MHz | 15 MHz | 20 MHz |
No. of Resource Blocks (N) | 6 | 15 | 25 | 50 | 75 | 100 |
Scaling Factor: 10*log(12*N) | 18.57 | 22.55 | 24.77 | 27.78 | 29.54 | 30.72 |
图表1.带宽与噪声系数
Using Above equation one can say that if RSRP is -70 dBm and the cell is fully loaded (20MHz) and there is not interference from other cell then RSSI measured by UE should be -70 dBm +30.72 = -39.28 dBm. Let’s say the UE is experiencing 10dBm power from a Neighbour cell operating at same frequency then the RSSI should be -39.28 dBm +10 dBm = -29 dBm
根据公式(2)当RSRP=-70dBm时，20MHz带宽的小区无干扰时;
UE测量到的RSSI=-70dBm+30.72=-39.28 dBm;
而当UE接收到同频邻区的功率为10dBm时，
根据公式（1） RSSI=-39.28 dBm +10 dBm = -29.28 dBm
So from the above calculation it can be concluded that if UE is seeing only one cell then there is relation between RSRP and can be directly scaled by the factor for particular bandwidth given in the table, but UE start seeing more signal on the same frequency from other cell then RSSI value become even better.
通过公式，当网络中仅有一个小区时UE可以直接获得全带宽的RSRP；
而UE接收到多个同频小区信号时RSSI将会更高。
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