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Overview of Previous Analysis for WAVE

Overview of Previous Analysis for WAVE. Justin McNew jmcnew@technocom-wireless.com. Traditional Scanning. Passive scanning Requires waiting for Beacon reception Beacons are not required for WAVE communications (see document 0135 )

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Overview of Previous Analysis for WAVE

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  1. Overview of Previous Analysis for WAVE Justin McNew jmcnew@technocom-wireless.com Justin McNew, TechnoCom

  2. Traditional Scanning • Passive scanning • Requires waiting for Beacon reception • Beacons are not required for WAVE communications (see document 0135) • Introduces excessive latency for public safety applications that require immediate access to information transmitted in mobile environments • Active scanning • Requires excessive transmissions by mobile units • Clogs communications channels with densely populated OBU (mobile stations) Justin McNew, TechnoCom

  3. Authentication & Association • Authentication and association also affect latency of critical public safety applications (see document 0135) • Not utilized for most public safety applications • Requires Beaconing mechanism • Joining a network is not required to communication with WAVE devices Justin McNew, TechnoCom

  4. Channelization • 10 MHz versus 20 MHz channels • 75 MHz allocation results in excessive unused bandwidth with 20 MHz channels • Seven 10 MHz channels provides ability to dedicate more channels to specific applications • Leftover 5 MHz reserved for future FCC allocation of spread spectrum ISM band below 5.85 GHz • Licensing of channels more robust (less overlap) • Utilize half-rate solution consistent with 802.11j • Consistent with expected delay spreads in outdoor and mobile environments Justin McNew, TechnoCom

  5. Basic MAC Simulations • Altered existing simulation models to represent WAVE environment and 10 MHz channels • No Beacons or association • 6 Mbps data rate (QPSK modulation) • Simple simulation used to confirm 802.11 can work for WAVE Justin McNew, TechnoCom

  6. Characteristics Value Comments aSlotTime 16 s Calculated as aCCATime + aRxTxTurnaroundTime + AirPropagationTime + aMACProcessingDelay aSIFSTime 32 s Doubled from standard 802.11a value aCCATime  8 s Doubled from standard 802.11a value aRxTxTurnaroundTime  2 s Same as standard 802.11a value aRxTxSwitchTime  1 s Same as standard 802.11a value aAirPropagationTime  4 s Quadrupled to support up to 1200 meter range aMACProcessingDelay  2 s Same as standard 802.11a value aPreambleLength 40 s Doubled from standard 802.11a value aPLCPHeaderLength 8 s Doubled from standard 802.11a value aCWmin 15 Same as standard 802.11a value aCWmax 1023 Same as standard 802.11a value PHY Parameters Justin McNew, TechnoCom

  7. Basic Simulation Results (cont’d) • Generic simulation • Randomly distributed nodes. • 10, 30, 50, 70, and 90 OBUs with 1 RSU • Network traffic • Unicast traffic sent from OBUs destined to RSU • Each OBU starts in different time (exponentially distributed with mean of 10 sec.) • Exponentially distributed inter-arrival time with mean of 0.1 sec • Average payload size of 64 bytes (smaller than anticipated) Justin McNew, TechnoCom

  8. Basic Results Justin McNew, TechnoCom

  9. Realistic Simulation Case • OBU enter communication zone of an RSU at a reasonably consistent rate • OBU service table (OST) sent in response to periodically broadcast RSU service table (RST) Single Exchange represented by Exchange Success Rate (ESR): RSU OBU RST Broadcast Delay Unicast OST Justin McNew, TechnoCom

  10. System Stability • An excessive number of OBU entering a communication zone will result in significant exchange failures • E.g. if 5 new OBUs enter the zone, the total number of OBUs that must be processed is the number of new OBUs plus the number of OBUs that failed for the last RST transmission • Failures can result from collisions of RSTs and/or OSTs • Realistically, not more than around 10 to 15 OBU can arrive in a communication zone on a large freeway within a 100 ms period Justin McNew, TechnoCom

  11. Simulation Parameters • Packet characteristics • RST Size: 490 bytes • Unicast OST size: 490 bytes • Vehicle to Vehicle: • Broadcast OST size: 250 bytes • Broadcast OST period: 100 ms • Randomly distributed over 100 ms interval (uniform) • 6 Mbps data rate Justin McNew, TechnoCom

  12. Simulation Results RST Period Justin McNew, TechnoCom

  13. Summary • 802.11 can support WAVE applications • Requires disabling various MAC features in certain instances • Beacons, authentication & association • 10 MHz channels used in WAVE frequency band • Simulations indicate adequate capacity is available Note: Resulting recommendations presented in document 0135 Justin McNew, TechnoCom

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