Spread-Spectrum Radio Technology - WaveRider NCL1135 User Manual

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Spread-Spectrum Radio Technology

Spread-spectrum communications systems differ from conventional narrowband
communications systems because these systems use a much larger transmission bandwidth
to send the same amount of information.
There are two primary forms of spread spectrum—direct sequence and frequency hopping.
The NCL1135 uses direct-sequence spread-spectrum (DSSS). In DSSS systems, the
transmitted information, along with a digital spreading sequence, are used to modulate the
transmit carrier. The received signal is de-spread using the same digital spreading sequence,
and the information recovered.
Although spread spectrum appears complex and uses a wider bandwidth, DSSS offers the
following advantages for its use:
• Reduced power spectral density — Spreading over a wider bandwidth reduces the
spectral density (power per Hz of bandwidth) of the transmitted signal, allowing
simultaneous operation of many spread spectrum systems in the same frequency
band and geographic area. The reduced spectral density also allows you meet the
regulatory emissions requirements in frequency bands such as the ISM band.
• Transmission security — It is technologically more difficult to surreptitiously recover
(or jam, in the case of military communications systems) spread-spectrum signals
than it is to recover conventional narrowband signals.
• Interference suppression — The same mechanism that de-spreads the desired signal
in the receiver, also spreads undesired signals, which then appears to the receiver as
lower levels of RF noise.
For more information about spread spectrum communications, contact the WaveRider
Customer Support Centre.
APCD–NC003–1.0
Chapter 1 NCL1135 Overview
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