EECS 6590

1
Multi-channel, multi-radio wireless networks

• EECS 6590

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Single Channel Capacity

• Theoretical upper limit of the per node
  throughput capacity

• Theoretically achievable capacity of every node
  in a random static wireless ad hoc network with
  ideal global routing and scheduling

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Single Channel Capacity (2)
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Single Channel Capacity (3)

• Experimental results from CSMA/CA MAC on a string
  topology.
• Throughput 1 / n

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Reasons

• Exposed terminal problem (main factor!)
• Hidden terminal problem
• High error rate on wireless channel
• MAC characteristics
• etc.

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Solution

• Multi-channel, multi-radio
• Use multiple frequencies to transmit on.
• 802.11a has 12 non overlapping channels in the
  5GHz range.
• each channel is 20MHz wide
• 5.200 GHz, 5.180 GHz, 5.220 GHz, 5.240 GHz, 5.260
  GHz, 5.280 GHz, 5.300 GHz, 5.320 GHz, 5.745 GHz,
  5.765 GHz, 5.785 GHz, 5.805 GHz
• Use multiple antennas to transmit and receive at
  the same time
• wireless routers

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Orthogonal Channels in IEEE 802.11b
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Multi-channel Multi-radio Networks
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Why use multi-channel, multi-radio?
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Design Issues
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Design Issues (2)
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Design Issues (3)
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Radio Usage Policy

• Static binding
• Channel assignment algorithm must ensure that the
  number of channel assigned to a node is the same
  as the number of radios.
• Hybrid

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Radio Usage Policy (cont.)

• Another hybrid scheme

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Protocols
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Summary

• Multiple channels and multiple antennas will
  increase throughput.
• Any solution should support
• distribution of load across channels
• maintaining node connectivity
• broadcast abilities

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References
10) Wireless Mesh Networking book, chapters 1
and 2