MAC enhancements to 802'11a

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MAC enhancements to 802.11a

• EE206a Student Presentation 4
• Yen-Cheng Kuan
• Chih-Chieh Han
• yckuan, simonhan_at_ee.ucla.edu

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Link Adaptation in DCF

• Goodput is a step function of SNR in a given PHY
  mode
• High SNR gt high goodput
• Low SNR gt zero goodput
• PHY mode selection
• Higher PHY mode gt higher SNR is needed gt high
  goodput
• Lower PHY mode gt low goodput
• Fragmentation may help
• More fragments gt shorter packet size gt low
  packet error rate gt less retransmission and high
  control overhead
• Less fragments gt more retx and low control
  overhead

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Useful Terminologies

• DCF (Distributed Coordination Function) Ad Hoc
  mode
• PCF (Point Coordination Function) Access Point
  mode
• PLCP (Physical Layer Convergence Procedure)
• MAC (Medium Access Control)
• LLC (Logical Link Control)
• MSDUs (MAC Service Data Units) Data from LLC
• MPDUs (MAC Protocol Data Units) Fragments of
  MSDU
• PPDUs (PLCP Protocol Data Units) PLCP preamble
  PLCP header MPDU
• TPC (Transmission power control)

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MAC Timing Diagram
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DCF Assumptions

• One transmitter and one receiver
• Queue always backlogs with 2304-octet long MSDU
• No retry limit for each frame
• All OFDM symbols are transmitted at the same
  power level
• Neglect the air propagation delays
• ACK frame uses the same rate as data frame
  received

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802.11a PHY
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802.11a PHY Characteristics
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PPDU frame format
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Goodput Analysis
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Implementation
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Energy Efficient PCF

• Transmission power should not be constant
• Can use less power when path loss is low
• PHY mode should be dynamic
• The lower the path lose, the higher PHY mode can
  be used

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PCF assumptions

• Exponential E-P (efficiency power level) curve

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PCF Timing diagrams
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Implementation