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iOS 4.1 restores limited Field Test mode
Authored by: westont on Sep 10, '10 12:41:13PM

Most likely this is showing the signal level in dBm which is the decibel representation of the signal power relative to a 1mW reference level. i.e.1mW = 0dBm. Negative values indicate levels less than 1mW, positive values indicate levels greater than 1mW. A 10dBm difference means a factor of 10 difference in signal level. For example +30dBm = 1000mW = 1W. Likewise -30dBm = 0.001mW = 1μW.

The receive sensitivity of mobile phones will vary according to the technology in use (GSM, CDMA, W-CDMA etc.) but as reference point, the GSM standards specify a mobile receive sensitivity of -102dBm to -104dBm depending on the band of operation (900, 1800, 1900 etc.) and mobile power class. This figure accounts for Rayleigh fading and an implementation margin and assumes a receiver Noise Figure of 6dB but, of course, some mobiles perform better than this.

It is important to remember that this Rx sensitivity figure represents performance in a thermal noise limited environment. The presence of network generated noise on the operating channel (especially at cell edges) results in a interference limited environment which the network operator must allow for in the design and planning of the network.

Hope that helps !

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