In a
spread-spectrum system, the process gain (or "processing gain") is the ratio of the spread (or RF) bandwidth to the unspread (or baseband) bandwidth. It is usually expressed in
decibel
The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a po ...
s (dB).
For example, if a 1 kHz signal is spread to 100 kHz, the process gain expressed as a numerical ratio would be / = 100. Or in decibels, 10 log
10(100) = 20 dB.
Note that process gain does not reduce the effects of wideband thermal noise. It can be shown that a direct-sequence spread-spectrum (
DSSS) system has exactly the same bit error behavior as a non-spread-spectrum system with the same modulation format. Thus, on an
additive white Gaussian noise
Additive white Gaussian noise (AWGN) is a basic noise model used in information theory to mimic the effect of many random processes that occur in nature. The modifiers denote specific characteristics:
* ''Additive'' because it is added to any nois ...
(AWGN) channel without interference, a spread system requires the same transmitter power as an unspread system, all other things being equal.
Unlike a conventional communication system, however, a DSSS system does have a certain resistance against narrowband interference, as the interference is not subject to the process gain of the DSSS signal, and hence the signal-to-interference ratio is improved.
In
frequency modulation (FM), the processing gain can be expressed as
:
where:
: ''G''
p is the processing gain,
: ''B''
n is the
noise bandwidth,
: Δ''f'' is the peak frequency deviation,
: ''W'' is the sinusoidal modulating frequency.
Signal processing
{{telecomm-stub