User Manual

1 NCL1135 Overview
APCD–NC003–2.0A 3
1.3 About Spread-Spectrum Radio Technology
Spread-spectrum communications systems differ from conventional narrowband
communications systems because they 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.