Contains several forms for calculation of Power in terms of dBm, Loss in a co-axial cable, theoretical antenna gain, radiated power from antenna, free space loss, receiver sensitivity, signal-to-noise ratio, Fresnel ellipsoid, and a lot more.
Signal to Noise Ratio Example
Receiver sensitivity is not the only parameter for the receiver, we have also
to take into account the signal to noise power ratio. It's the minimum power
difference to achieve between the wanted received signal and the noise (thermal
noise, industrial noise due for example to microwave ovens, interering noise due
to other WLAN on the same frequency band). It is defined as:
Signal/Noise Ratio [dB] = 10 * Log10 (Signal Power [W] / Noise Power [W])
If the signal is more powerful than the noise, signal/noise ratio (also
called S/N ratio) will be positive. If the signal is buried in the noise, the
ratio will be negative. In order to be able to work at a certain data rate the
system needs a minimum S/N ratio:
- Orinoco PCMCIA Silver/Gold: 11Mbps => 16 dB ; 5.5 Mbps => 11 dB ; 2
Mbps => 7 dB ; 1 Mbps => 4 dB.
If the noise level is very low then the system will be limited more by the
receiver sensitivity than by the S/N ratio. If the noise level is high then it
will be the Signal/Noise ratio that will count to achieve a given data rate. If
the noise level is high we will need more received power. In normal conditions
whithout any other WLAN on the frequency and whithout industrial noise the noise
level will be around -100dBm. For example to achieve a 11 Mbps data rate with an
Orinoco 802.11b card we would need a received power 16dB higher (S/N ratio) so a
level of -100+16=-84 dBm but in fact the minimum receiver sensitivity is at -82
dBm...higher than -84. It means in that case the mimimum receiver sensitivity is
the limiting factor for the system.
http://www.swisswireless.org/wlan_calc_en.html
