Question

How does infrared light communication differ from radio wave communication? Discuss a few salient features of both. [ 3 marks] Why does spread-spectrum result in reduced interference and fewer errors? [ 3 marks] What is the purpose of using Barker code in DSSS systems? [ 2 marks]

Answer 1

How does infrared light communication differ from radio wave communication ?

Answer :-

• Inrared light only function through line of sight , where as radio wave can effecively be used from a long distance .
• A remote control uses infrared light to change the channel on your TV , while radio waves are used to receive TV shows .
• Radio waves have a longer wave length then infrared light .

Feature of both :-

Infrared light :-

• Frequency - Between 300 GHz to 400 Thz.
• Wavelength - Between 1mm to 750nm .
• Distance - About 10-30 meters .
• Modulation - Pulse Position modulation .
• Data rate - Serial Infrared support 300 to 115200 bps and Fast infrared support 4Mbps.

Radio Wave :-

• Radio waves are type of electromagnetic radiation with wavelength in the electromagnetic spectrum longer than infrared light .
• They have frequencies from 300 GHz to low as 3 kHzand corresponding wavelength from 1 milimiter to 100 kilometer .

Why does spread-spectrum result in reduced interference and fewer errors ?

Answer :-

• The spread of energy over a wide band, or lower spectral power density, also makes spread-spectrum signals less likely to interfere with narrowband communications.
• Since the total integrated signal density or signal-to-noise ratio (SNR) at the correlator's input determines whether there will be interference or not.
• Direct Sequence Spread Spectrum (DSSS) is a spread-spectrum modulation technique primarily used to reduce overall signal interference.
• The direct-sequence modulation makes the transmitted signal wider in bandwidth than the information bandwidth.
• After the despreading or removal of the direct-sequence modulation in the receiver, the information bandwidth is restored, while the unintentional and intentional interference is substantially reduced.

What is the purpose of using Barker code in DSSS systems ?

Answer :-

• Providing DSSS transmission security or Inhancing security .