Spraed spectrum methods FHSS and DSSS

Spread spectrum method used for digital tx over air

1. DSSS
2. FHSS

Fhss

• the data signal is modulated with a narrowband carrier signal that "hops" in a random but predictable sequence from frequency to frequency.
•  The signal energy is spread in time domain rather than frequency domain.
• This technique reduces interference because a signal from a narrowband system will only affect the spread spectrum signal if both are transmitting at the same frequency at the same time.

DSSS

•  Also known as direct sequence code division multiple access (DS-CDMA),
• Stream of information to be transmitted is divided into small pieces, each of which is allocated across to a frequency channel across the spectrum.
• Data signal is combined with high bit rate sequence also called chipping code ,divides the data according to a spreading ratio.
• The redundant chipping code helps the signal resist interference and also enables the original data to be recovered if data bits are damaged during transmission.