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

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.

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Content

1. DSRC Overview and Motivation for IEEE 802.11 based VANET Simulations

2. Wireless Simulation Design in the Default NS-2 Distribution

3. Improvements to NS-2

4. Simulation Example and Comparison

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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 176 Ch 178 Ch 180 Ch 184Ch 182

Frequency (GHz)

5.8

50

5.8

60

5.8

70

5.8

80

5.8

90

5.9

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5.9

10

5.9

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Control Channel

Service Channels Service Channels

Critical Safety of Life

High Power Public Safety

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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:1.The unbounded nodes distribution2.More precise RF modeling3.DSRC specific protocol parameters

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NS-2 Simulator Usage

TCL ConfigurationScript

NS-2Simulator

Output Trace File

Analysis

Road A

Road B

Road C

Reception Probablity Comparison

0%

20%

40%

60%

80%

100%

0 50 100 150 200 250 300

Distance From the Sender (m)

Rec

epti

on

Pro

bab

ility

BPSKQPSK16QAM

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Wireless Communication Support in NS-2

WirelessPhy

MAC80211

LL

Application

MobileNode1

Wireless Channel

WirelessPhy

MAC80211

LL

Application

RFModel

MobileNode2

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Wireless Communication Support in NS-2, Cont.

WirelessPhy

MAC802.11

LL

Application

RF

Sender

Wireless Channel

WirelessPhy

MAC802.11

LL

Application

RF

Recv1

Pkt

WirelessPhy

MAC802.11

LL

Application

RF

Recv2

Pkt Pkt

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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 802.11

RF Model

Receiver

Pkt: Pt, SenderInfo

Pt, SenderInfoRecvInfo

PrPr> RxThresh?

Pkt: Pr

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WirelessPhy

MAC 802.11

MobileNode

TXingRXing Idle

NMRF 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 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

Pkt CS.Signaling

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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

WirelessPhy

MAC80211

RF Model

Receiver

Pkt: Pt, SenderInfo

Pt, SenderInfoRecvInfo

PrPr/Noise > 4dB?

(for Preamble detection)

Pkt

TXingRXing IdleTXingRXing Idle

Pkt: Pt, SenderInfo

NM

TXingRXing Idle

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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

WirelessPhy

MAC 802.11

MobileNode

NMRF Model

PktCS.BusyIndication

Channel State

Pkt 1

Pkt 2

BUSY IDLE

NMNM

CS.IdleIndication

BUSY IDLEBUSY IDLE

NMNM

BUSY IDLE

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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

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MAC_Recv

RXing RXingIdle

MAC802.11 RX_State

Frame 1 Frame 2Frame 3

Received Power

TimeCarrier Sense

Threshold

MAC_Coll

WirelessPhy State

RX_Recv RX_RecvRX_IdleMAC802.11 RX_State

Channel BusyMAC802.11 Channel_State

Default NS-2Distribution Code

Modified NS-2Code

Behavior comparison

MAC_Coll

Channel BusyChannel Busy

Behavior comparison

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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 doesn’t have to deal with power comparisons Packet arriving in wrong operating mode is not visible to MAC anymore

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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.

Reception Prbability Comparison

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20%

40%

60%

80%

100%

0 50 100 150 200 250 300 350

Distance From the Sender (m)

Recep

tio

n P

rob

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Default NS-2

ImprovedNS-2

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Breakdown of the drop events

Broadcast Reception and Drop Breakdowns

0% 20% 40% 60% 80%

100%

0 50 100 150 200 250 300 350 Distance From the Sender (m)

POW TXB RXB COL BER

Received

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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