IEEE 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 1.DSRC Overview and Motivation for IEEE based VANET Simulations 2.Wireless Simulation Design in the Default NS-2 Distribution 3.Improvements to NS-2 4.Simulation Example and Comparison

3 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 Ch 172 Ch 174 Ch 176Ch 178Ch 180 Ch 184 Ch 182 Frequency (GHz) Control Channel Service Channels Critical Safety of Life High Power Public Safety

4 IEEE based simulation for DSRC DSRC is an IEEE based technology Based on IEEE a and standardized as IEEE p WAVE DSRC research needs a IEEE based simulation tool that addresses: 1.The unbounded nodes distribution 2.More precise RF modeling 3.DSRC specific protocol parameters

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

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

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

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 WirelessPhy MAC RF Model Receiver Pkt: Pt, SenderInfo Pt, SenderInfo RecvInfo Pr Pr> RxThresh? Pkt: Pr

9 WirelessPhy MAC Mobile Node TXingRXingIdle NM RF Model 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 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 Pkt CS.Signaling

10 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 frames 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 WirelessPhy MAC80211 RF Model Receiver Pkt: Pt, SenderInfo Pt, SenderInfo RecvInfo Pr Pr/Noise > 4dB? (for Preamble detection) Pkt TXingRXingIdleTXingRXingIdle Pkt: Pt, SenderInfo NM TXingRXingIdle

11 Carrier Sensing mechanism MAC 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 Monitors 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 WirelessPhy MAC Mobile Node NM RF Model Pkt CS.BusyIndication Channel State Pkt 1 Pkt 2 BUSYIDLE NM CS.IdleIndication BUSYIDLEBUSYIDLE NM BUSYIDLE

12 Noise Monitor Observation and SINR based reception decision Additional Simplifications 1.Uniform received power over an entire frame 2.SINR based frame reception decision 3.Uncorrelated received power among nearby nodes

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

14 Features of the improved NS-2 1.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 2.Support cumulative interference Noise Monitor sends Carrier Sense Signaling to control MAC channel state 3.Made a clear cut between PHY and MAC MAC doesnt 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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