/    /  CDCS – Spread Spectrum

Spread Spectrum

 

Spread spectrum is a technique used for wireless communication, in which, the frequency of the transmitted signal is deliberately varied, and it generates a much greater bandwidth than the signal would have if its frequency were not varied. 

It is widely used in telecommunication and radio signals as it can easily reduce noise and other signal issues. 

 

Advantages of Spread Spectrum:

  1. Spread spectrum signals are spread over a wide range of frequencies, and collected and sent back to the receiver. 
  2. Spread spectrum signals are resistant to jamming and difficulty intercepting.
  3. It has greater bandwidth utilization ability. 

 

Types of Spread Spectrum:

There are two types of spread spectrum:

  • Frequency Hopping Spread Spectrum (FHSS)
  • Direct Sequence Spread Spectrum(DSSS)

Frequency Hopping Spread Spectrum (FHSS)

In Frequency Hopping Spread Spectrum, the entire bandwidth is divided into many channels and arranged continuously. The slots are selected randomly and the signals are transmitted based on their occupancy.

It can be further classified into two types:

  1. Slow hopping
  2. Fast hopping

Advantages of FHSS:

  1. It is highly efficient.
  2. It is resistant to narrowband interference. 
  3. The time needed for acquisition is shorter. 
  4. It can be easily programmed to avoid certain parts of the spectrum. 
  5. It gives a large bandwidth. 
  6. The implementation is simpler. 

Disadvantages of FHSS:

  1. It is less robust.
  2. It needs complex frequency synthesizers.
  3. It supports lower data rate. 
  4. It supports lower coverage range. 

Direct Sequence Spread Spectrum(DSSS)

DSSS is a spread-spectrum modulation technique used to reduce signal interference. In DSSS, the message bits are modulated by a bit sequencing process known as a spreading sequence known as chip. 

It can be classified into two types:

  • Wide Band Spectrum
  • Narrow Band Spectrum

Advantages of DSSS:

  1. It is less reluctant to noise. 
  2. It provides discrimination against multipath system.
  3. It avoids jamming effectively. 

Disadvantages of DSSS:

  1. Performance is low  as it takes large acquisition time. 
  2. It needs wide-band channels with small phase distortion. 

Reference