Spread Spectrum
Techniques for Wireless
Communication
Axel Acuna
Spread Spectrum
 Methods by which a signal generated with a particular
bandwidth is deliberately spread in the frequency domain,
resulting in a signal with a wider bandwidth.
 These techniques are used for a variety of reasons:
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Establishment of secure communications
Increasing resistance to natural interference, noise and jamming
Prevent detection
Limit power flux density
How It Works?
 Spread spectrum uses wideband, noise-like signals that are
hard to detect, intercept, or demodulate.
 Spread-spectrum signals are harder to jam (interfere with)
than narrow band signals.
 This technique:
 decreases the potential interference to other receivers (anti-jam,
or AJ).
 while achieving privacy low probability of intercept (LPI).
 Spread spectrum generally makes use of a sequential noiselike signal structure to spread the normally narrowband
information signal over a relatively wideband (radio) band of
frequencies.
 The receiver correlates the received signals to retrieve the
original information signal.
 Direct sequence and frequency hopping are the most
commonly used methods for the spread spectrum
technology.
 DSSS: Direct Sequence Spread Spectrum
 FHSS: Frequency Hopping Spread Spectrum
DSSS
 The carrier of the direct-sequence radio stays at a fixed
frequency.
 Narrowband information is spread out into a much larger (at
least 10 times) bandwidth by using a pseudo-random chip
sequence.
 Uses the same amount of transmit power and carry the same
information as narrowband
 The power density of the DSSS signal is much lower than the
narrowband signal, making it more difficult to detect.
FHSS
 FHSS achieves the same results provided by DSSS by using
different carrier frequency at different time.
 The receiver and the transmitter must be synchronized in
time and frequency in order to ensure proper transmission
and reception of signals.
 FHSS is better than DSSS radio when dealing with multipath.
Since the FHSS does not stay at the same frequency.
Questions?