SPREAD SPECTRUM

SPRED SPRECTRUM modulation is a techinique where by a modulated waveform is modulated second time in such away

so as to generate an expanded bandwidth(widebamd) signal, that not significantly interfere with other signals.bandwisth expansion

is achived by a second modulation and it is independent of message oe information transmitted.

It also can be defined as, spread spectrum is a transmission techinique in which a pseudo noise code, indepedent of

information data employed as amodulation waveform to spread the signal energy over the bandwidth much greater than the signal information

bandwidth. At the reciver the signal is dispresed using a synchronised replica of the pseudo noise code.

The spread spectrum signals used for the transmission of digital information are distinguished by the characteristic thst their

bandwidth 'w' is greatr than the information rate 'R' bits/sec. i.e, the bandwidth expansion factor [Be=(W/R)] for a spread spectrum signal is much

greater than unity. The large redundancy inherent inspread spectrum signal is required to over come the interference encounted over some

radio and satellite channels. It is achived by using suitable coding techiniques, thus that coding is the important element in the design of

spread spectrum modulation.

A second important element employed in the design of spread spectrum signal is pseudo-randomness, it makes the signal

appear similar to random noise and difficult to demodulate the receivers other than intended ones.

USES OF SPREAD SPECTRUM COMMUNICATION:

1. Suppressing the the determined effects due to jamming, interference arising from other users of the channel, and self interference due to multipath                                   propogation
2. acheving the message privacy in the presence of other listeners
3. Hiding a signal my transmitting in the low power, and thus making difficult for a unidirectional receiver to detect in the presence of noise

ADVANTAGEOF SPREAD SPECTRUM MODULATION:

1. IMPROVED INTERFERENCE REJECTION
2. Code division multiplication for CDMA application
3. low density power spectrum for signal hidding
4. High resolution ranging
5. secure communication .
6. antijam capability.
7. Increased capacity.
8. lower cost of implemention.
9. readily aviable IC components.

APPLICATION SPREAD SPECTRUM

• MILITARY APPLICATION SYSTEMS

1. 1. It allows to transmiter to transmit message to a receiver without the message being detected by unauthorised receivers.
   2. To achive this spread spectrum modulation decreases the transmitted power sectral density to an unauthorised receiver.

• COMMERCIAL COMMUNICATION SYSTEM

transmitted over the same thereby increasing the number of users

• IT IS USED IN SATELLITE COMMUNICATION AND LAN