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:
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?
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