What is spread spectrum technique? Name two standard spread spectrum techniques and state the main difference in their principles of operation.
Spread-spectrum techniques are methods by which 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. This results in a much greater bandwidth than the signal would have if its frequency were not varied.
Two standard spread spectrum techniques are:
Direct sequence (DS): DS spectrum is typically used to transmit digital information. A common practice in DS systems is to mix the digital information stream with a pseudo random code.
Time hoping: In a time hopped signal, the carrier is on-off keyed by the pseudo-noise (PN) sequence resulting in a very low duty cycle. The speed of keying determines the amount of signal spreading.
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