Multihop MAC Protocol for MC-CDMA based WLANs confidential

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Multihop MAC Protocol forMC-CDMA based
WLANsconfidential
ComNets FFV

• Georgios Orfanos
• RWTH Aachen University, Chair of Communication
  Networks
• 31.03.2006

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Outlook

• MC-CDMA
• C-DCF
• Smart Backoff
• Parallel transmission
• MAC layer relaying function
• Multihop guard interval, extended NAV
• Simulated scenario and parameters
• Simulation results
• Comparison with DCF
• Conclusions

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MultiCarrier Code Division Multiple Access

• Combination SS and OFDM
• Frequency spreading
• Frequency diversity
• IFFT / FFT realization of multicarrier modulation
• Multipath robustness
• Cyclic prefix
• Simultaneous transmissions in the same frequency,
  through division of the spectrum in parallel
  channels gt codechannels
• Spreading factor 4

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C-DCF

• CSMA / CA with 4 parallel codechannels
• multichannel system
• Selection of codechannel
• random
• first transfer on cch1
• Data transfer DCF
• NAV per codechannel
• each station monitors optionally one or all
  codechannels
• Power control over RTS / CTS
• for all data frames

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Smart Backoff

• Backoff procedure spanning over many cchs
• Backoff Time Random aSlotTime
• Another cch seems idle
• Another cch is determined idle
• No cch is idle

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Parallel transmission

• 1 codechannel 1/4 of frequency channel capacity
• Parallel (multichannel) transmission for high load

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MAC layer relaying function

• Multihop connections up to 3 hops
• Fig. multihop connection from station 1 to
  station 4
• Multihop packet handled per station as own packet
• MAC header contains the addresses of all
  forwarding stations
• Spatial reuse possible

Mac frame Format
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6
6
6
6
2
6
0-2312
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Frame Control Duration/ ID Address 1 Address 2 Address 3 Sequence Control Address 4 Frame Body FCS
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Multihop guard interval, extended NAV

• Multihop guard interval to prioritize forwarder
• Duration of one complete transmission window
• Smart Backoff at forwarders for bottleneck
  avoidance
• Combined with parallel transmission
• Extended NAV
• Duration, cch, MSs

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Simulated scenario and parameters
Parameter Value
Max. TxPower 17dBm
Spreading Factor 4
Cwmin 31 slots
Cwmax 255 slots
Number of Subcarriers 48 Data 4 Pilot
Subcarrier Spacing 0.3125 MHz
Channel Bandwidth 20 MHz
Carrier Frequency 5.25 GHz
Noise Level -93dBm
Path loss Factor 3.5
TxRate Data 12 Mbps
TxRate Control 12 Mbps
RTS/CTS enabled
Symbol Interval 4 µs 3.2 µ 0.8 µs
Guard Interval 0.8 µs
Preamble 16 µs
Max. Propagation Delay 0,15 µs
PDU Length 1024 Byte
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Simulation results (I)Mean values

• Achievable throughput allies with theoretical
  calculation 2,5 Mbit/sec/cch
• Depends on number of hops

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Simulation results (II)CDF of delay per hop

• left 1,25 Mbit/sec
• right 0,75 Mbit/sec (saturation throughput)

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Simulation results (III)CDF of end-to-end delay
per connection

• left 1,25 Mbit/sec
• right 0,75 Mbit/sec (saturation throughput)

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Comparison with DCF (I)Throughput
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Comparison with DCF (II)End-to-end delay
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Conclusions

• Multihop guard interval
• prioritizes the relaying MS on medium access
• reduces the end-to-end delay of the multihop
  connection
• Smart Backoff at forwarding MSs
• reduces the medium access time
• enables parallel transmission in many cchs, that
  increases the available capacity and reduces the
  bottleneck effect.
• In multi-channel, multihop environments applying
  carrier sensing NAV timer per cch (channel) is
  not enough
• the cch specific NAV per cch and MS proposed is
  then necessary.

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• Thank you for your attention !
• Georgios Orfanos
• orf_at_comnets.rwth-aachen.de
• Any questions?