Fixed Frequency, FHSS, and DSSS

The essence of this method of spreading is that the RF carrier frequency remains fixed while the signal being transmitted has been spread. The transmitter does not operate at the bit rate of the digital information, but rather at the higher bit rate associated with the coded signal. This causes the side lobe energy (Figure 3) to increase as the size of the spreading PN code increases. As more bits are added to the spreading code, more energy is transferred into the side lobes, thereby reducing the amplitude of any individual lobe. Notice that with a "suitable" size spreading code, it is possible to drop the energy in any single side lobe to less than a spectrum analyzer's noise floor, thereby essentially becoming undetectable.

Figure 3. A general design for a direct-sequence spread spectrum (DSSS) radio

Wise Guy is the problem-solving persona of WINA, the Wireless Industrial Networking Alliance ( www.wina.org) . Send your questions to wiseguy@questex.com.

1 2 

• Home
• News
• E-Mail Newsletters
  • Subscribe to e-mail newsletters
  • Newsletter Archives
• White Paper Library
• Sensors TV
• Opinion
  • Sensors Insights
  • Mel's Picks
  • Older Departments
• Technical Articles
  • Tutorials
  • Technologies in Depth
  • Case Studies
  • Intelligent Systems
• Inside Sensors
  • About Us
  • Sensors News
  • Sensors TV
  • White Paper Library
  • Sensors Expo
  • Resources
  • Contact Us
  • Award Program
  • Events Calendar
  • Discussion Forum
  • Media Kit
  • Advertising
• Browse by Topic
  • Sensor Type
  • New Products
  • Tutorials
  • Technology in Depth Articles
  • Case Studies
  • DA & Control
  • Industrial Networking
  • Archives
• Sensors Expo