RSRP, RSSI, SINR and RSRQ in LTE
RSRP, RSSI, SINR and RSRQ in LTE
Lets have a discussion on some basic terms used like RSRP, RSSI, SINR and RSRQ in LTE.
RSRP(Reference Signal Received Power):-
RSRP (Reference Signal Receive Power) is the average power of Resource Elements (RE) that carry cell specific Reference Signals (RS) over the entire bandwidth, so RSRP is only measured in the symbols carrying RS. Its typical range is around -44 to -130dbm. This measurement is used in RRC Idle/Connected, Cell Re selection/Selection, handover scenarios. Following is an example of one downlink radio frame. The red part is the resource elements in which reference signal is being transmitted. RSRP is the linear average of all the red part power.
RSRP(Reference signal Receive Power)
RSRP Range
Since this measures only the reference power, we can say this is the strength of the wanted signal. But it does not gives any information about signal quality. RSRP gives us the signal strength of the desired signal, not the quality of the signal. For quality of the signal information another parameter called ‘RSSQ’ is used in some case.
Reference signal receive quality (RSRQ):
Although RSRP is an important measure, on its own it gives no indication of signal quality. RSRQ is defined as (N x RSRP)/RSSI, where N is the number of RBs over the measurement bandwidth. 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. The RSSI parameter represents the entire received power including the wanted power from the serving cell as well as all co-channel power and other sources of noise. Measuring RSRQ becomes particularly important near the cell edge when decisions need to be made, regardless of absolute RSRP, to perform a handover to the next cell. Reference signal receive quality is used only during connected states. Intra- and inter-frequency absolute RSRQ accuracy varies from ±2.5 to ±4 dB, which is similar to the inter frequency relative RSRQ accuracy of ±3 to ±4 dB.
RSRQ in LTE
RSSI (Received Signal Strength Indicator):
RSSI (Received Signal Strength Indicator) is a parameter which provides information about total received wide-band power (measure in all symbols) including all interference and thermal noise.
RSSI is the total power UE observes across the whole band. This includes the main signal and co-channel non-serving cell signal, adjacent channel interference and even the thermal noise within the specified band. This is the power of non-demodulated signal, so UE can measure this power without any synchronization and demodulation.
Following is an example of one downlink radio frame. The red part is the resource elements in which reference signal is being transmitted. Blue and light blue part is for synchronization signal. Yellow part is for PDCCH. Green part is for MIB. Whitepart is PDSCH where user data is being transmitted. RSSI is the total power for all color and any possible noise/interference existing over all these area.
So it would be safe to write that, in LTE, RSRP provides information about signal strength and RSSI helps in determining interference and noise information. This is the reason, RSRQ (Reference Signal Receive Quality) measurement and calculation is based on both RSRP and RSSI.
RSSI in LTE
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