What is the fundamental principle and use of spread spectrum?

Question

What will be an ideal response?

Answer 1

In the spread spectrum transmission technique, the frequency spectrum of a
data-signal is spread using a code uncorrelated with the signal. As a result, the
bandwidth occupancy is much higher than required. Spread Spectrum uses wide
band, noise-like signals. Spread Spectrum signals use fast codes that run many
times the information bandwidth or data rate. These special “Spreading” codes
are called “pseudo Random” or “Pseudo Noise” codes. They are called Pseudo
because they are not real Gaussian noise.
Spread Spectrum transmitters use similar transmitting power levels to narrow
band transmitters. Because Spread Spectrum signals are so wide, hey transmit at a much lower spectral power density, measured in Watts per Hz, than
narrowband transmitters. This lower transmitted power density characteristic
gives spread signals a big plus. Spread and narrow band signals can occupy the
same band, with little or no interference. This capability is the main reason for
all the interest in the Spread Spectrum today.

A number of advantages are:
Low power spectral density. As the signal is spread over a large
frequency-band, the Power Spectral Density gets very small, so other
communications systems do not su¤er from the interference problem.
However the Gaussian Noise level is increasing.
Interference limited operation. In all situations the whole frequencyspectrum is used.
Privacy due to unknown random codes. The applied codes are – in
principle - unknown to a hostile user. This means that it is hardly possible
to detect the message of another user.
Applying spread spectrum implies reduction in multi-path effects.
Random access possibilities. Users can start their transmission at any
arbitrary time.
Good anti-jam performance.