Robertson Stephens

1
Engineering for Frequency Re-Use and Spectrum
Efficiency
Broadband Wireless World Forum February 20, 2001
Mort Cohen Director of Marketing mcohen_at_centerpoin
t.com [phone]
2
Market Drivers

• Medium and high capacity radios
  represent gt40 of
• P-P radio sales

• PMP networks are striving to increase the number
  of subscribers per hub

• Carriers want to lower their spectrum usage fees
  

• Higher capacity backhaul will be required for
  future mobile networks

3
Improving Network Performance

• Benefits of Frequency Re-Use
• Minimize spectrum usage
• Minimize intercellular interference
• Minimize interference among closely
• spaced radios or buildings

• Benefits of Spectral Efficiency
• Increase spectrum usage flexibility
• Minimize spectrum usage fees
• Increase network traffic handling
• capacity

4
Enhancing Re-use and Spectral Efficiency

• Modem
• Higher Order Modulation (QAM)
• Use of Forward Error Correction (FEC)
• Hub Antenna
• Narrower Main Beam
• Suppressed Sidelobes
• Increased Cross Polarization Discrimination
• Subscriber Antenna
• Narrower Main Beam
• Increased Cross Polarization Discrimination

5
Enhancing System Gain with FEC
Use of FEC Typically Increases System Gain by 6
to 8 dB
6
QAM Modulation vs. Distance (OC-3)
23 GHz w/60cm ant both ends - ITU Region D
(19mm/hr)
7
System Gain vs. Distance (DS3/E3)
16-QAM system offers 10-50 improvement in
distance compared to 4-FSK systems (depending on
rain region)
23 GHz w/60cm ant both ends - ITU Region F
(28mm/hr) - ITU Region K (42 mm/hr)
8
P-P Antenna Performance
Highly directional antennas facilitate frequency
reuse 39 dB gain on boresight, unwanted
signals attenuated 25 dB as little as 10 off
boresight
9
Summary

• Market factors are driving medium and high
  capacity radio systems to
• More flexibility in selecting between capacity
  delivered, spectral efficiency, and link distance
• Concatenated Reed-Solomon and Trellis Code
  Modulation for increased system gain
• QAM rather than FSK modulations for improved
  spectral efficiency
• Higher performance antenna systems
• More robust links

Frequency reuse and spectral efficiency will
become increasingly more important in future
radio systems