The IEEE-802.11 Wireless LAN protocol
We'll next examine devices implementing the IEEE-802.11
family of wireless networking protocols,
and get an appreciation of some of the security challenges.
Often of interest is not simply the maximum possible transmission rate,
but the distance over which WiFi may operate.
We need an understanding of the transmission power, propagation,
and signal loss over distance and through objects.
The unit dBm is defined as power ratio in decibel (dB) referenced to
one milliwatt (mW). It is an abbreviation for dB with respect to 1 mW and
the "m" in dBm stands for milliwatt.
dBm is different from dB. dBm represents absolute power, whereas dB is a
ratio of two values and is used to represent gain or attenuation. For
example, 3 dBm means 2 mW, and 3 dB means a gain of 2. Similarly, -3 dBm
means 0.5 mW, whereas -3 dB means attenuation of 2.
A WiFi access point (AP) will typically transmit at up to 100mW,
and a receiving device will typically be able to discern arriving signal
from noise until -90dBm.
CITS3002 Computer Networks, Lecture 5, Wireless Networks (WLANs), p1, 25th March 2020.