aspects of vehicular wlan implementation

July 2005DENSO INTERNATIONAL AMERICA, INC. LA Laboratories

1

Aspects of Vehicular WLAN Implementation

Roger Berg

Vice President - Technology and Product Development

DENSO INTERNATIONAL AMERICA, INC.

LA Laboratories


2

Contents• Identify

– Use cases– Application Requirements– Necessary Technology

• Innovate– Technology Solutions

• Prioritization• Channelization• Synchronization• Latency

• Implement– Simulation– Feasibility Platform HW & SW

• Insure– Test and Evaluation– Comparison to analytical and simulated results


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Cooperative sensors

sensor range extension

limited sensor range

autonomous sensors

However, US vehicle crash

related death rates have flattened.

Safety improvements have come from crash mitigation.

Motor vehicle crashes are the leading cause of death for every age from 2 to 33 years old.

The trend and focus must move from

crash mitigation to crash prevention.

Identify: United States Vehicle Safety Scenarios

Goal for 2010: < 1.0 fatalities / 100 M VMT

United States Vehicle Fatalities

0

10,000

20,000

30,000

40,000

50,000

60,000

fata

litie

s /

ca

len

da

r y

ea

r

0

1

2

3

4

5

6

fata

litie

s /

10

0 M

VM

T


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Identify: VSC in the USA

DSRC WAVEUS DOT envisions DSRC unitsin every new motor vehicle for life saving communications capability

DSRC is proposed as the critical communications link

For interoperabilitynation wide…

a public standardof operation

must be created

WIRELESS ACCESS FOR VEHICULAR ENVIRONMENTS

Government wants to have standard capable for both V2V and V2R communications.

Specification

Feasibility

Development

1998 2006 2009

February 2004 FCC authorized75 MHz in the 5.9 GHz bandfor exclusive use of ITS.

Safety

MobilityReduce US Transportation

inefficiency 3.6 Billion hours of vehicle

delay / yr 5.7 Billion gallons of wasted

fuel

$70B/yr

Reduce highway fatalities

US DOT #1 priority $230B/yr


5

Identify: Applications & Requirements

ISO TC204 WG16 WAVE IEEE 1556 SAE VSCC ICDN NAWG ITS OTHER

Highest Priority (1)Cooperative Forward Collision Warning

Curve speed warning (rollover warning)

Electronic Brake Lights

GPS correction

Intersection collision warning

Left turn assistant

Platooning

Pre-crash sensing

SOS services

Stop Sign Movement Assistance

Tractor-Trailer Interface

Traffic signal violation warning

High Priority (2)Animal Crossing Zone Information

Cooperative Adaptive Cruise Control

Curve speed warning

HighwayRail Intersection Warning

Hybrid Intersection Collision Warning

Intelligent Traffic Lights

Intersection Collision Avoidance

Keep Clear' Warning

Lane Change Assistant

Low Parking Structure Warning

Merge Assistant

Pedestrian Crossing Information

Pedestrian/Children Warning

Rollover Warning

School Zone Warning

Stop Sign Warning

Vehicle-based Road Condition Warning

V-to-V Intersection Collision Warning

Work Zone Warning

Medium-High Priority (3)Emergency electronic brake lights

Instant Problem Messaging

Intelligent On-ramp Metering

Onboard Safety Data Transfer

Sign Information

Stop Sign Movement Assistant

V-to-V Road Feature Notification

Focus:requirements of groups of applications (range

of required values)

Focus:requirements of groups of applications (range

of required values)

Latency, range, mobility, security,

…

Latency, range, mobility, security,

…


6

Identify: Vehicular applications requirements

Top 7 Vehicle Safety Applications

• Intersection Collision Warning and Avoidance (Vehicle-to-Roadside-to-Vehicle)

• Left Turn Assistance (Vehicle-to-Vehicle)

• Cooperative Forward Collision Warnings (Vehicle-to-Vehicle)

• Pre-crash sensing (Vehicle-to-Vehicle)

• Emergency Electronic Brake light Signaling (Vehicle-to-Vehicle)

• Curve Speed/Rollover Warnings (Vehicle-to-Roadside-to-Vehicle)

• Pre-crash Sensing (Vehicle-to-Vehicle)

Preliminary Common Communications System Requirements• 50 - 100 ms access latency and update rates• 250+ km/hr mobility• Scalable on the basis of vehicle traffic density• Dynamic message routing• 10 - 500 m radio link range• Shared communication channel • Message payload 2 - 5 kbytes• Data rates 2 - 12 Mbps


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Identify: Technology improvement

Channelization Scheme for Vehicle/Public Safety & Private Applications

Channelization solution to:• provide priority to vehicle/public safety message traffic• provide guaranteed and configurable message latency • allow channel capacity to be adaptively allocated

CH 1725860 MHz

CH 1745870 MHz

CH 1765880 MHz

CH 1785890 MHz

CH 1805900 MHz

CH 1825910 MHz

CH 1845920 MHz

ServiceChannel

High PriorityVehicle Safety

ServiceChannel

ServiceChannel

ServiceChannel

ServiceChannel

ServiceChannel

ControlChannel


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Innovate: i-Channel Main Goals

• Prioritization– Public/Vehicle Safety is guaranteed highest priority– Channelization latency is predictable and configurable

• Synchronization– RSU not necessary for synchronization– Messaging is organized into Safety/Non-Safety time slots– Provides synchronization in overlapping RSU communication zones– No restrictions EXCEPT channel switching priority based on i-Channel rules– Non-Safety operation is flexible as long as i-Channel rules are followed

• Adaptive Channel Access– Allows available system capacity to be allocated to Non-Safety when Public

Safety is not needed– Allows full system capacity to be allocated to Public Safety when necessary

Main Features: Prioritizes Safety, reduces latency, supports non-RSU communications.


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1. Safety Slot:• An adaptive time slot. • High-Priority Safety Messages transmitted only during Safety time slot. • Lower Priority Safety Messages may also be transmitted during the Safety time slot. • 802.11e QoS ensures highest priority messages get first access to RF medium. • OBUs and RSUs monitor the Safety Channel during the Safety time slot. • All devices stay on Safety Channel until High-Priority Safety Messages have not been

transmitted or received for a predetermined period of time. • Once this predetermined time expires, Safety time slot ends, Non-Safety time slot begins.

Innovate: Safety & Non-Safety Systems

Separate the Safety and Non-Safety operations.

2. Non-Safety Slot:• A fixed time slot. Guarantees return to Safety Channel to meet latency requirements. • OBUs and RSUs may change channels at will. • High-Priority Safety Messages may not be transmitted, even if tuned to the Safety Channel.

SAFETY (ADAPTIVE) NON-SAFETY (FIXED)


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Innovate: Architectural Concept

Focus: Specification of control mechanism for channel/system isolation.

SafetyCH Non-Safety CH(s)

i-ChannelChannel

ManagementEntity

MAC/PHYMain Radio

Non-Safety SystemAccess

Channel Mux/Demux (CHMUX)

Safety SystemAccess

Non-Safety SystemUpper-Layers

Safety SystemUpper-Layers


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Innovate: i-Channel Parameters

TNS-TX Time left over for Non-Safety Communication. This time period is fixed to TNS – (2 x TTUNE).

TIDLE Idle time that follows the last High Priority Safety Message (TX or RX).

TTUNE Time allocated for receiver settling after a channel change.

TNS Time allocated for Low Priority Non-Safety Communication. This time period is fixed.

TNS

TIDLE

Last HP

TTUNE

Tc = One Adaptive I-Channel Cycle

First HP

First LP or NS

Last LP or NS

TTUNETNS-TX


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Non-Safety Channel(s)

Safety Channel

Zoom Out

HP S LP SHP S LP S HP S LP S

Paused

HP S LP S

Tune Back to Non-Safety Channel.

Tune to Safety Channel;

Complete all pending High-Priority Safety (HP S);

While verifying all High-Priority Safety has been completed, exchange Low-Priority Safety (LP S);

HP S LP S HP S LP S

Paused

Fixed Durationfor Non-Safety

Adaptive Durationfor HP Safety

Paused

Time

DSRC Band

>> x2

Innovate: i-Channel Cycle

Fixed Durationfor LP


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1) T idle InitInnovate: i-Channel Timing

Channel Switch timing is derived solely from HP Safety Messages.

Non-Safety Channel(s)

Safety Channel

Idle Timer [ms]

0

(1) Idle Timer is initialized upon entering the Safety Slot.

HP Safety Message from Radio 0


Legend

LP Safety Message from Radio 1


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T idle = 1.5


Idle Timer [ms]

1.5


Innovate: i-Channel Timing



Legend



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2) HP Radio 0


Idle Timer [ms]

0

(2) Idle Timer is reset every time a HP Safety message is received OR transmitted by any OBU or RSU in the network.


Radio 0 HP




Legend



16

T idle = 1.0


Idle Timer [ms]

1.0



Radio 0 HP




Legend



17

HP Radio 1


Idle Timer [ms]

Radio 0 HP Radio 1 HP



0




Legend



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T idle = 3.5


Idle Timer [ms]



3.5





Legend


Radio 1 LP


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T idle Timeout


Idle Timer [ms]


(3) The Idle Timer times out when it reached a predetermined value. Then, the radio MAY tune away from safety.

(4) Even if the radio does not tune away during the fixed non-safety period, HP Safety messages SHALL NOT be sent during that time.


Timeout



Radio 1 LP



Legend



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Nodes enter High Awareness mode (HA) periodically

Innovate: How do nodes and networks synchronize?

High Awareness = Stay on Safety Channel during Non-Safety period.

Nodes enter HA, e.g. every 1 or 2 seconds, andNodes enter HA, e.g. every 1 or 2 seconds, andstay on the safety channel during the next NS period stay on the safety channel during the next NS period

looking for other nodes within communication distance.looking for other nodes within communication distance.

HP NSLP HP HALP HP NSLP HP NSLP HP NSLP HP NSLP HP NSLP HP NSLP

HP NSLP HP NSLP HP NSLP HP HALP HP NSLP HP NSLP HP NSLP HP NSLP

HP NSLP HP NSLP HP NSLP HP NSLP HP NSLP HP NSLP HP HALP HP NSLP

HP HALP HP NSLP HP NSLP HP NSLP HP NSLP HP NSLP HP NSLP HP NSLP

t0 tf

Nodes in a network enter High Awareness mode at different times

Node 0

Node 1

Node 2

Node 3


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Innovate: Follow the Leader

TNS = TSRCHTIDLE

Last HP

Go to High Awareness

THA Timeout

In High Awareness “Follow Me” Returning

TIDLE

HPTX

Following Searching

Follow Me!

LEADER

FOLLOWERS

Other Network Detected

RX Follow Me Packet

Last HP

Last HP

TIDLE

TIDLE

“Follow the Leader” allows two clusters to join very quickly.


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Innovate: i-Channel Multiple Networks

Radio 0

Radio 1

Radios in the same network (i.e. synchronized)

Radios in different networks (i.e. unsynchronized)

i-Channel High-Awareness Mode

HP S LP S High-Awareness (instead of NS) HP S LP S

HP STX

RX F

F Acquire Radio 0 Network LP SHP S

Networks Merged


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Innovate: High Awareness

Simulation data shows switching times independent of network size and mobility

Equal Size ClustersUnequal Size Clusters

Equal Size ClustersUnequal Size Clusters

THA = 1.0 THA = 1.0


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• All channel switching causes delays,

• unless a radio is camped on a channel continuously.

• All 802.11 systems have delays for medium access.

• CSMA/CA access and back-off and

• impacts of hidden nodes, interference, propagation delay, …

• 802.11 packet latency depends on circumstances, environment, number of nodes, dynamics, loading, …

• How can we isolate these impacts to determine the performance of a given channel switching method?

How can we effectively compare channel switching methods?

Implement: Channelization Latency Problem


25

Implement: Useful Measure of Latency

DEFINITION: Channelization latency is the component of packet latency attributable to delays caused by the multi-channel management system.

Time delay between:• Packet arrival in MAC transmit queue from upper layer, and

• Radio tuned to channel corresponding to that MAC queue.

Thus, Packet Latency =Channelization latency

+ Queue delay

+ Access delay

+ Propagation delay

+ Process delay in receiver

Channelization Latency is a measure of the efficiency of the channel switching.


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Implement: Expected Latency (analytic)

___ HP Safety___ LP Safety___ Non-Safety

• Computation of expected value of channelization latency according to:

• Probability of packet arrival relative to channel switching system time;

• Probability of channel change latency given load.

T_IDLE = 0.005

T_NS = 0.050

T_TUNE = 0.002

Expected Latency for HP and LP Safety and Non-Safety


27

Implement: Measured Latency (simulations)

• Measured actual channelization latency from ns2 simulations with varying degrees of high priority safety load.

T_IDLE = 0.005

T_NS = 0.050

T_TUNE = 0.002


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ITS / DSRC prototyping

Implement: feasibility platform


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WAVE Prototype Communications Module Support Tool

10 / 20 MHz BandWidth

Selection

WAVE Frequency Channel Selection Variable Data

Rate

Adjustable TX Pout (1dB incremental)

Implement: Tools for prototype

T-ns setting T-idle setting T-High Awareness setting

t-ns


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Insure: Expected vs. Measured Latency (prototype)

Measurements using radio module prototype confirm Analytical & Simulation analysis.

Measured packet latency from WRM prototypes with very low loading and few units:• low loading approximates zero queue delay; • few units approximates zero access delay;• thus, packet latency approximates channelization latency.

0102030405060708090

100110120130140150

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Safety Offered Load

Late

ncy (

ms)

Measured HP Safety Expected HP Safety Measured LP Safety

Expected LP Safety Measured Non Safety Expected Non Safety

T_IDLE = 0.005

T_NS = 0.100

T_TUNE = 0.002


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Insure: Other Evaluation Tools

Link Window Field Test

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

0 10 20 30 40 50 60 70 80 90 100

Time (Sec)

Th

rou

gh

pu

t (M

bp

s)

-95

-90

-85

-80

-75

-70

-65

-60

-55

-50

-45

-40

RS

S (

dB

m)

Rx_Thruput_M bps

RSS

Link Window Field Test

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

0 10 20 30 40 50 60 70 80 90 100

Time (Sec)

Th

rou

gh

pu

t (M

bp

s)

-95

-90

-85

-80

-75

-70

-65

-60

-55

-50

-45

-40

RS

S (

dB

m)

Rx_Thruput_M bps

RSS

Automatic data plotting


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1 50 99 148 197 246 295 3440

2

4

6

8

10

12

14

16

18

20

22

24

26

28

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Index into RSU Drive-Away Time (in 1/4 sec increments)

Measured Broadcast Throughput by Burst Rate Vs 1/4 Sec Time IndexOBU driving away from RSU (54Mbps burst data not available)

483624181296

6

24

18

12

9

48

36

Th

rou

gh

pu

t in

Mb

ps

Rates (Mbps)

802.11a Burst Max Ad Hoc UDP-BRate (Mbps) Throughput (Mbps)

54 28.448 26.536 22.124 16.818 13.412 9.69 7.5

6 5.2

Link Window Distance ~ 2000 meters

1 50 99 148 197 246 295 3440

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

Index into RSU Drive-Away Time (in 1/4 sec increments)

Measured Broadcast Throughput by Burst Rate Vs 1/4 Sec Time IndexOBU driving away from RSU (54Mbps burst data not available)

483624181296

6

24

18

12

9

48

36

Th

rou

gh

pu

t in

Mb

ps

Rates (Mbps)

802.11a Burst Max Ad Hoc UDP-BRate (Mbps) Throughput (Mbps)

54 28.448 26.536 22.124 16.818 13.412 9.69 7.5

6 5.2

Link Window Distance ~ 2000 meters

99.3% 98.5%99.9% 99.3% 99.8% 98.2%

88.1%

76.6%

67.2%

99.4% 98.3% 99.3%97.5%

95.7%

85.8%

74.7%

66.1%

98.0%96.1%

98.2%96.6% 95.8%

85.9%

72.4%

63.0%

95.9% 94.6% 95.4%93.1%

91.8%

82.5%

70.3%

61.4%

55%

60%

65%

70%

75%

80%

85%

90%

95%

100%

Avera

ge P

SR

(%

)

6 9 12 18 24 36 48 54

802.11A Burst Rates (Mbps)

Packet Size(Bytes)

Average V2V PSR Vs 802.11A Burst Rate (Mbps) & Packet Size (Bytes), 40% link blockage

99.8% 99.6%

89.5%

78.8%

69.4%

97.2%V2V PSR

STATISTICS

98.5%99.3%99.9% 99.3% 99.8%

98.2%96.4%

99.3% 98.5%99.9% 99.3% 99.8% 98.2%

88.1%

76.6%

67.2%

99.4% 98.3% 99.3%97.5%

95.7%

85.8%

74.7%

66.1%

98.0%96.1%

98.2%96.6% 95.8%

85.9%

72.4%

63.0%

95.9% 94.6% 95.4%93.1%

91.8%

82.5%

70.3%

61.4%

55%

60%

65%

70%

75%

80%

85%

90%

95%

100%

Avera

ge P

SR

(%

)

6 9 12 18 24 36 48 54

802.11A Burst Rates (Mbps)

Packet Size(Bytes)

Average V2V PSR Vs 802.11A Burst Rate (Mbps) & Packet Size (Bytes), 40% link blockage

99.8% 99.6%

89.5%

78.8%

69.4%

97.2%V2V PSR

STATISTICS

98.5%99.3%99.9% 99.3% 99.8%

98.2%96.4%

Insure: Other Evaluation Tools


33

Conclusion

• Identified– Application requirements are the center point– Analyze technology deficiencies

• Innovated solutions– Prioritize, channelize, synchronize with low latency

• Implemented– Simulation and feasibility HW & SW

• Insured– Match theory/simulation to implementation results– Test tools validate innovative implementation

aspects of vehicular wlan implementation

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