Concept of spread spectrum :- Spread-spectrum techniques are methods by which a signal (e.g. an electrical, electromagnetic, or acoustic signal) generated with a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth.
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Spread spectrum systems are intended to provide such secure and reliable communication. In this system the spectrum of the transmitted signals spreaded over a very wide bandwidth. This achieved in these systems by modulating for a second time, an already modulated signal in such a way as to spread the power of the transmitted spread spectrum signal over a very large bandwidth.