Today on The Academic Minute: Erik Born, assistant professor of German studies, explores the history behind it.Įrik Born is an Assistant Professor in the Department of German Studies at Cornell University. On Cornell University Week: The wireless icon is ubiquitous in today’s world. Displaying SNR would correlate more to link "quality".Erik Born, assistant professor of German studies. lower than 10 dB it starts to get very slow.įrom my experience in various environments (calm or noisy, close or far) it seems Apple shows the signal strength. The larger this value, the better the link quality SNR larger than 25 dB is good to excellent. It's the "distance" between the two power levels (signal - noise). The SNR (signal to noise ratio) measured in dB or percent. The value is somewhere between -70 dBm (very noisy) and -100 dBm (almost no disturbers). It varies with the interference of other access points and other disturbers. The noise level or noise floor measured in dBm or mWatt. Unfortunately, a lot of people (including Apple, see class CWInterface) mix the RSSI and the signal strength. Being able to handle different chip vendors with varying max raw RSSI, the OS might normalizes the raw RSSI to a normalized RSSI range e.g. Atheros uses raw RSSI values 0.127, Broadcom 0.60) The larger the RSSI, the stronger the signal. The mapping of RSSI value to absolute signal strength is defined by the HW vendor of the WiFi chip. This value correlates loosely the signal strength. The RSSI (received signal strength indicator) value without unit. In reality, the value is somewhere between -40 dBm (close to the AP) to -110 dBm (far away). It varies with the distance to the access point. The absolute signal strength, a power level measured in dBm or mWatt. So you have a 15db to 25db signal OR as diagnostics calls it SNR which isn't that good but isn't really bad either.Īs Apple is not very explicit on what it actually shows with the bars, I can only tell you my observations. Also an increase in RF intereference from microwave ovens, cordless phones, walls, ceilings, etc, which would increase the noise level, would also decrease the overall SNR value.
The calculated SNR value, as measured from a wireless client, would decrease as the range to the base station increases due to applicable free space loss. For example, a signal level of -53dBm and a noise value of -90dBm would yield an SNR of 37dB (i.e., SNR = Signal - Noise = -53 -(-90) = 37) Both of these values are typically represented as negative numbers. SNR is the signal level (in dBm) minus the noise level (in dBm). One method to calculate signal quality is to compute the Signal-to-Noise Ratio (SNR). While you have a good signal strength, your throughput speed ( Tx Rate ) isn't that fast. So if you're asking for a scale I think its around 10 to 12.5 RSSI per bar. Not sure if it will go to -100 since you don't have a signal then ) 50 will show all the bars and -90 will show gray bars. Most people will see a number between about -50 and -80, with around -50 being excellent.
The higher the number ( closer to 0 ) the better your signal strength.įor Apple devices they used a scale of -100 to 0. RSSI or Received signal strength indication is what is used for the display of the bars.