Mumbai University > Electronics and Telecommunication Engineering > Sem 6 > Data Communication

Marks: 10 Marks

Year: Dec 2016

Types of spread spectrum:-

1. DSSS:- (Direct sequence spread spectrum)

2. FHSS:- (Frequency hop spread spectrum)

DSSS:- It combines spread spectrum modulation with BPSK. It is the process of modifying phase of the carrier according to changes in spread information signal.

DSSS Transmitter:

DSSS Receiver:-

Advantage of DSSS system:

1) This system has very high degree of discrimination against the multipath signal. Therefore interference called by multipath reception is minimized successfully.

2) The performance of DSSS system in presence of noise is superior to other system such as FHSS system.

3) This system combats the intentional interferance (jamming) most effectively.

Disadvantage of DSSS:-

1) With the serial search system, the acquasition time is too large This makes DSSS system slow.

2) The sequence generated at the PN code generator output must have high rate. The length of such ssequence needs to be long enough to make the sequence truely random.

3) The channel bandwidth required is very large, but this bandwidth is less than that of FHSS system.

4) The synchronization is affected by the variable distance between the transmitter and receiver.

Applications of DSSS system:-

1) To combact intentional interferance (jamming)

2) To reject unintentional interference

3) To minimize self interferance due to multipath propogation

4) In the law probability of intercept signal

5) In obtaining message privacy

6) Code division multiple access with DSSS.

Features of DSSS:-

1) It provides good security against potential jamming or interpretation

2) The DSSS is extremely effective against narrow band jamming signals.

3) The narrowband communication signal can coexist with DSSS system.

4) The DSSS system is not very effective against broadband interferance.