Process Gain

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 decibels (dB).

For example, if a 1 kHz signal is spread to 100 kHz, the process gain expressed as a numerical ratio would be 100,000/1,000 = 100. Or in decibels, 10log10(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 (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:

Gp is the processing gain

Bn is the Noise Bandwidth

Δf is the peak frequency deviation and

W is the sinusoidal modulating frequency.

Spread spectrum in Digital Communications
Main articles
  • Spread spectrum
  • Code division multiple access (CDMA)
History
Hedy Lamarr
Commercial use
More...
Spread spectrum Methods
  • Direct-sequence spread spectrum (DSSS)
  • Frequency-hopping spread spectrum (FHSS)
  • Chirp spread spectrum (CSS)
  • Time-hopping spread spectrum (THSS)
CDMA Schemes
  • W-CDMA
  • TD-CDMA
  • TD-SCDMA
  • DS-CDMA
  • FH-CDMA
  • MC-CDMA
Major implementations
  • Space Network (NASA)
  • GPS
  • Galileo
  • GLONASS
  • Bluetooth
  • Cordless phones: DECT
Cellular
EV-DO Mobile
IS-95 (aka cdmaOne)
CDMA2000 (aka IS-2000)
Also
Qualcomm
Verizon
Major concepts
  • PN (pseudorandom noise) code
  • Chip
  • Near-far problem
  • Power spectral density (PSD)
  • Process gain
  • Rake receiver
  • Low probability of intercept
See also
Digital communication
Modulation
Statistical multiplexing
Waveform


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