Tutorial
Wireless LAN Technology and
Network Implementation
Signal
Strength and Signal-to-Noise
When
a signal is sent into space, it mixes with radio noise. Once
this happens, it is difficult to separate the two. A good
analogy for signal to noise is having a measuring cup that
contains one cup of water and one cup of cooking oil. You have
two cups of liquid, but only one cup of oil on the top.
In radio communications, you may have two units of
signal strength, but if one unit is noise, you really have one
useable unit of signal. The
relationship in proportions of signal to noise is called
signal-to-noise ratio. The
lower the signal-to-noise ratio, the lower the overall data
performance.
In
Figure 4, we see a radio signal and noise for a fixed carrier
signal.
Figure
4: Carrier with Noise
Figure
5 shows how a spread spectrum signal would look with noise.
The suppressed carriers operate just above the typical
noise floor, making spread spectrum look like noise to the
untrained eye. The
receiving stations must detect the carrier shift pattern and
match their demodulation patterns to the existing modulation
pattern in order to recover data.
Figure
5: Spread Spectrum Signal and Noise
<<
Previous page Next
page >>
Page 3 of 6
