Generally, signal quality above 25-30% is usable. It is based on signal strength and SNR margin. It can be calculated differently, depending on the OS/device used. It is the percentage of the best theoretical ideal quality in regards to your local noise. Signal Quality this is a percent value between 0% and 100%, with the higher numbers representing better link quality. Utilizing full 54 Mbps data rate, for example requires at least 25 dBm of SNR margin. SNR margin = signal(dBm) - noise(dBm) For example, if singal ( RSSI) = -55dBm, and noise = -85dBm, then: (-55dBm signal) - (-85dBm noise) = 30 SNR margin Higher SNR/SNR margin numbers represent cleaner signals, with less noise. SNR margin is simply calculating the difference between signal ( RSSI) and noise to get the SNR margin as a positive number expressed in db. Many DSL modems and wireless devices (notably dd-wrt open source router firmware) use SNR margin, only denoted as ' SNR'. SNR margin is often confused and used interchangeably with SNR. noise margin) is the ratio by which the signal exceeds the minimum acceptable amount (minimum SNR) to sustain a certain speed. Signal-to-noise ratio ( SNR) is defined as the power ratio between a signal (meaningful information) and the background noise (unwanted signal): SNR = signal / noise The more commonly used SNR margin, as described below is sometimes abbreviated as simply SNR as well. Typical environments range between -100dBm and -80dBm. The closer this value is to -120, the better, because that means there is little to no interference. This value is measured in decibels from zero to -120. Noise (dBm) in wireless communications is a combination of all unwanted interfering signal sources, such as crosstalk, radio frequency interference, distortion, etc.

EIRP = Tx power (dBm) + antenna gain (dBi) - cable loss (dB). EIRP (Effective Isotropic Radiated Power) is the actual amount of signal leaving the antenna, measured in dB.

Cisco can use range between 0 to -100, Atheros may use 0 to -127. Notes: RSSI values can be different depending on the chip vendor. Anything below -85dBm is generally unusable, and over -50dBm can be considered perfect. For wireless data communications, normal range is -45dBm to -87dBm. Smaller negative numbers represent a cleaner/stronger signal. RSSI) is the usable strength of the radio waves, expressed in decibels relative to a milliwatt between 0dBm (strongest) and -120dBm (weakest).

Rssi values wifi