How are good, fair, poor and bad defined for signal strength?

Question

How are good, fair, poor and bad defined for signal strength in terms of dBm, in most Android phones or telecommunication community?

Are they defined the same for mobile network and for WiFi network?

Thanks.

Answer 1

I can answer this for WiFi: received signal strength indicator (RSSI) in the 802.11 standard is only required to be orderable. This means for a single device you can tell when its reported value x is greater than its reported value y, but not by how much because there may be no real scale. Every device can report different values for the same real signal power, and the values across devices are not directly comparable because they can each use different values and they may have no scales. A device is only required to be able to tell a signal is stronger or weaker than another signal.

For reference, see https://en.wikipedia.org/wiki/Received_signal_strength_indication

Answer 2

It depends on the technology of the Mobile i.e. CDMA 1xEVDO (verizon & sprint 3G), UMTS (AT&T and T-Mobile 3G), LTE (all carriers 4G LTE) In General for 3G -116dBm to -108dBm is bad -108dBm to -103dBm is poor, -103dBm to -95dBm is fair and pretty much anything > -98dBm is good to very good. For LTE it's -120dBm to -115dBm poor, -115dBm to -105dBm bad, -105dBm to -95dBm fair and greater then -95dBm good

None of this however is an absolute to guarantee quality of service (QoS). There are many factors that go in to QoS. In urban areas there is much more interference from various sources including the Operators own network that affect speech quality and throughput speed.