6 April 2018

What is direct sequence spread spectrum

Direct sequence spread spectrum (DSSS) is spread spectrum modulation technique used in telecommunication to reduce overall signal interface. 

Direct sequence spread spectrum (DSSS) is one type of channel access method is better known as direct sequence CDMA. This is mainly used in IEEE 802.11b and also used  Zigbee technology. 

Overview : 
  • The term DS/SS stands for direct sequence spread spectrum
  • In this method, the pseudo-random code is used when the signal can be detected at the receiver end. If avoid unauthorized signal access.
  • The DS/SS is affected by the near-far problem. This problem occurs because of the unequal power that is received by the user.
  • It is a very sensitive technology.
  • Many users can be used in the same band with a better signal to noise ratio. 
  • DS/SS is used point to point scenario.
  • The DS/SS signal spectrum is spread over a wide band while the PSD is small, Hence, it is simple to hide the signal within the noise floor.
  • DS/SS delivers capacity of about 11 Mbps.
Advantages of  DS/SS :
  • It has the best noise and antijam performance.
  • Simple hardware implementation.
  • It supports high coverage range due to low SNR requirement at receiver.
  • Do not require high-speed fast setting frequency synthesizer.
  • It has the best discrimination against multi-path signals.
  • The unidentified receivers find it difficult to detect the direct sequence type of signals.
  • It can be employed in point to point the application at the rate of 11 Mbps.
Disadvantages of DS/SS :
  • DS/SS has a longer acquisition time.
  • It requires a wideband channel with small phase distortion.
  • The pseudo noise generator must generate a sequence at high rates.
  • Near-far problem.
  • Fast code generator needed.
  • The system is prone to error at lower compared to FH/SS.
Application of DSSS :

The application of direct spread spectrum analysis is listed below.
  • DSSS is used in the low probability of intercept signal.
  • It obtains message privacy.
  • It is used military and much commercial application.
  • It can support the unique spreading codes support code division multiple access.
  • Support various decision-making level.
  • To reject unintentional interference.
  • To minimize self-interference due to the multi-path propagation.
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