RSSI varies with LTE subcarrier activity - the greater the data transfer activity, the higher the RSSI.But that does not actually translate to stronger signal to the end user. For example, even if all other factors were equal, VZW 10 MHz LTE bandwidth RSSI would measure 3 dB greater than would Sprint 5 MHz LTE bandwidth RSSI.
RSSI varies with LTE downlink bandwidth.To conclude, here are a few takeaways about RSSI and RSRP as signal strength measurement techniques for LTE: Thus, that superficially weak -102 dBm RSRP signal level that we saw previously would actually be roughly -82 dBm if it were converted to RSSI. Or, to put it another way, RSRP measures about 20 dB lower than what we are accustomed to observing for a given signal level. 10 × log 100 = 20), RSSI tends to measure about 20 dB higher than does RSRP. Since the logarithmic ratio of 100 subcarriers to one subcarrier is 20 dB (e.g. So, the sector depicted here exhibits no data traffic it is transmitting only the periodic reference signals on 100 subcarriers, which you can clearly count in the graph: The LTE downlink graph comes from a Sprint site in the Kansas City area in late April, well before Sprint stopped blocking devices from live LTE sites. To illustrate, I captured this power vs frequency sweep with a spectrum analyzer. In other words, of the 300 subcarriers, 100 transmit periodic reference signals. And of those subcarriers, one in three carry LTE reference signals. A 5 MHz bandwidth downlink, which is the configuration that Sprint is deploying, contains 300 subcarriers. To understand why, we need to learn the differences between two types of signal measurement: Received Signal Strength Indicator (RSSI) and Reference Signal Received Power (RSRP).įirst, an LTE downlink is divided into subcarriers. But -102 dBm is actually relatively healthy LTE signal level. Were measuring CDMA1X or EV-DO, then, yes, -102 dBm would be nearing the margin of usable signal. For example, see this screenshot from an HTC EVO 4G LTE (under Settings - About -Network As Sprint LTE 1900 has become live and discoverable in numerous markets over this past weekend, some of our readers, especially those who are using Android 4.0 ICS based ROMs, have expressed concern at the seemingly low signal levels that they have encountered.
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