Spread Spectrum refers to a system originally developed for military applications, to provide secure communications by spreading the signal over a large frequency band. Spread spectrum uses wideband, noise-like signals that are hard to detect, intercept, or demodulate.

The Spread spectrum signal occupies a larger bandwidth than that of a normal signal, therefore the name spread spectrum Signal. This signal uses some kind of coding. The spectrum spreading at the transmitter and dispreading at the receiver is obtained with the help of this code word.

The spread spectrum signal is pseudorandom in nature and so it appears like random noise. Therefore the normal receiver cannot demodulate this signal. Only a specially designed receivers can demodulate it to recover the information.

Types of SS Based on the kind of spreading modulation, spread spectrum systems are broadly classified as-

(i)Direct sequence spread spectrum (DS-SS) systems

The information signal in DSSS transmission is spread at baseband and then the spread signal is modulated by a carrier in a second stage.

(ii)Frequency hopping spread spectrum (FH-SS) systems

Another basic spread spectrum technique is frequency hopping. In a frequency hopping (FH) system, the frequency is constant in each time chip; instead it changes from chip to chip.

(iii)Time hopping spread spectrum (TH-SS) systems.

(iv) Hybrid systems