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IEEE 802.11 based Vehicular Communication Simulation Design for NS-2

IEEE 802.11 based Vehicular Communication Simulation Design for NS-2 . Qi Chen, Daniel Jiang, Vikas Taliwal, Luca Delgrossi DaimlerChrysler Research and Technology North America, Inc. Content. DSRC Overview and Motivation for IEEE 802.11 based VANET Simulations

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IEEE 802.11 based Vehicular Communication Simulation Design for NS-2

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  1. IEEE 802.11 based Vehicular Communication Simulation Design for NS-2 Qi Chen, Daniel Jiang, Vikas Taliwal, Luca Delgrossi DaimlerChrysler Research and Technology North America, Inc.

  2. Content • DSRC Overview and Motivation for IEEE 802.11 based VANET Simulations • Wireless Simulation Design in the Default NS-2 Distribution • Improvements to NS-2 • Simulation Example and Comparison

  3. Critical Safety of Life High Power Public Safety Control Channel Ch 172 Ch 174 Ch 176 Ch 178 Ch 180 Ch 182 Ch 184 5.850 5.860 5.870 5.880 5.890 5.900 5.910 5.920 Frequency (GHz) Service Channels Service Channels Overview of DSRC • The Dedicated Short Range Communication (DSRC) spectrum is allocated for vehicle-to-vehicle and infrastructure-to-vehicle communication in the U.S. • DSRC is meant to save lives and improve traffic flow, and also to provide value through private applications

  4. IEEE 802.11 based simulation for DSRC • DSRC is an IEEE 802.11 based technology • Based on IEEE 802.11a and standardized as IEEE 802.11p WAVE • DSRC research needs a IEEE 802.11 based simulation tool that addresses: • The unbounded nodes distribution • More precise RF modeling • DSRC specific protocol parameters

  5. NS-2 Simulator Usage NS-2 Simulator Analysis Output Trace File TCL Configuration Script

  6. Wireless Communication Support in NS-2 Application Application LL LL Mobile Node1 Mobile Node2 MAC80211 MAC80211 RF Model WirelessPhy WirelessPhy Wireless Channel

  7. Wireless Communication Support in NS-2, Cont. Application Application Application Pkt LL LL LL Sender Recv1 Recv2 MAC802.11 MAC802.11 MAC802.11 RF RF RF WirelessPhy WirelessPhy WirelessPhy Pkt Pkt Wireless Channel

  8. NS-2 Reception Logic Details • Shortcomings • PHY works without a state machine, i.e. no operating mode support • Channel condition is not monitored by PHY. The RxThresh is a fixed value • All packets that are stronger than RxThresh are sent to MAC, no matter if those packets are really receivable • No preamble detection mechanism is supported • Flawed PHY/MAC behavior MAC 802.11 Receiver Pr RF Model Pr> RxThresh? WirelessPhy Pkt: Pr Pt, SenderInfo RecvInfo Pkt: Pt, SenderInfo

  9. Reception Logic in Improved NS-2 • WirelessPhy • WirelessPhy works with operating mode Txing/Rxing/Idle • A Noise Monitor exists in WirelessPhy to record the current observed interference level (power other than the signal) • MAC 802.11 • Carrier Sense Signalings are added to the interface between MAC and WirelessPhy • Only the receiving packet is delivered to MAC layer • If reception fails, WirelessPhy sets error flags in the receiving packet MAC 802.11 Mobile Node Pkt CS.Signaling RF Model WirelessPhy NM TXing RXing Idle

  10. TXing TXing RXing RXing Idle Idle TXing RXing Idle Reception Logic in Improved NS-2 Cont. • An incoming packet is dropped if the operating mode is TXing or RXing • If the operating mode is Idle, WirelessPhy is ready to detect frame’s preamble • Pr is calculated in the same way • Pr is compared to the current interference level • If one preamble is captured, WirelessPhy switches to RXing mode and then setup a receiving timer according to the duration of the receiving packet • During receiving, noise level is updated and SINR is checked again if any new interference is on the channel MAC80211 Receiver Pr Pr/Noise > 4dB? (for Preamble detection) RF Model WirelessPhy NM Pkt Pt, SenderInfo RecvInfo Pkt: Pt, SenderInfo Pkt: Pt, SenderInfo

  11. BUSY BUSY BUSY BUSY IDLE IDLE IDLE IDLE Pkt CS.BusyIndication NM CS.IdleIndication NM Carrier Sensing mechanism • MAC 802.11 utilizes both logical and physical carrier sense mechanism • With CS.Signalings, MAC maintains a correct channel state • If an incoming packet can not be received, its power is recorded by the Noise Monitor. The power from different overlapping interference source is considered to be additive • If cumulative noise level > CSThresh, CS.BusyIndication is sent to MAC • MAC will set the channel state to BUSY • When Noise Monitor’s current noise level drops below CSThresh, Channel State is set to Idle with a CS.IdleIndication from PHY • Channel State is set to Busy if a MAC is receiving a packet • The MAC internal logic depends on the channel state Channel State MAC 802.11 Mobile Node RF Model WirelessPhy NM NM NM Pkt 1 Pkt 2

  12. Noise Monitor Observation and SINR based reception decision • Additional Simplifications • Uniform received power over an entire frame • SINR based frame reception decision • Uncorrelated received power among nearby nodes

  13. Behavior comparison Behavior comparison Received Power Frame 3 Frame 1 Frame 2 Carrier Sense Threshold Time Default NS-2 Distribution Code MAC_Coll MAC_Recv MAC_Coll MAC802.11 RX_State Channel Busy Channel Busy Channel Busy MAC802.11 Channel_State Modified NS-2 Code RX_Recv RX_Idle RX_Recv MAC802.11 RX_State RXing Idle RXing WirelessPhy State

  14. Features of the improved NS-2 • Corrected the flawed PHY/MAC behaviors • Implemented wireless interface operating modes • Allowed preamble detection for a MAC frame • Provided each mobile node its local view of the wireless channel • Support cumulative interference • Noise Monitor sends Carrier Sense Signaling to control MAC channel state • Made a clear cut between PHY and MAC • MAC doesn’t have to deal with power comparisons • Packet arriving in wrong operating mode is not visible to MAC anymore

  15. Simulations with improved NS-2 • Simulation Settings • Simulation scenario contains 500 vehicular nodes placed pseudo-uniformly on a single lane road. The vehicle density is 200 cars per km road. All simulations run for 10 seconds. Each vehicle has a messaging frequency of 10Hz. The frame payload (i.e. besides MAC/PHY overhead) is 250 Byte. • The intended transmission range in these simulations is 200 m. A receiver at the distance of 200 m would have a 75% reception rate if there is no interference whatsoever.

  16. Breakdown of the drop events • Further analysis of reception probability and the drop reasons. • Drop Reasons: • POW: Insufficient Power • TXB: Arriving at TXing • RXB: Arriving at RXing • COL: The receiving packet was collided • BER: Insufficient Power to decode the frame payload

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