Vehicular Networks: Emerging Standards and Performance of Safety Applications Tamer ElBatt* San Diego Research Center (A wholly Owned Subsidiary of Argon ST)
[email protected] (858) 623 9424 ext. 382
*
This work was done at HRL Laboratories, LLC and funded by General Motors Corporation
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Collaborators
Siddhartha Goel Jijun Yin Gavin Holland Vikas Kukhsya Fan Bai Hariharan Krishnan Jayendra Parikh
(HRL) (HRL) (HRL) (HRL) (GM) (GM) (GM)
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Agenda
Background
I. Vehicular Communication Standards
II. Safety Applications
Cooperative Collision Warning (CCW)
III. Performance Evaluation
IEEE 802.11p/Dedicated Short Range Communications (DSRC) IEEE 1609.4: Multi-channel Operation IEEE 1609.3: Networking Services
Large-scale Simulations Extreme vehicular densities Performance metrics: Application-perceived latency
Conclusions 3
Motivation
US government’s commitment to save lives and improve traffic flow FCC Report and Order, Nov. 2002: “… operations related to the improvement of traffic flow, traffic safety and other intelligent transportation service applications, in a variety of public and commercial environments.”
Opens room for introducing new value-added vehicle-based applications Safety: Cooperative Collision Warning, Traffic Violation Warning, Hazard Warning, …
Convenience: Free-flow Tolling, Trip Planning, Traffic Probe, … Commercial: Cooperative Content Download, Infotainment, Media Streaming,
…
Development of a variety of licensed and unlicensed wireless access technologies
IEEE 802.11 a/b/g/p (DSRC) (Mesh network extensions) Mobile WiMax (IEEE 802.16e) and 3G Cellular IEEE 802.20
Interplay of these factors gives rise to “Connected Vehicle” Vision 4
Connected Vehicle
A connected vehicle constitutes one of the building blocks of future ubiquitous, broadband wireless access
Resource richness (energy, processing, storage) Information richness (variety of sensors, vision, GPS) Mobility (opportunistic communications)
Connected to whom? to do what?
Connected to vehicles nearby to exchange messages, e.g. warning Connected to an infrastructure to upload/download data, …
Single-hop Multi-hop
Connectivity type depends on the application type, vehicle speed, …
Some applications rely on infrastructure, others do not Unlicensed WiFi should be utilized for entertainment, as opposed to safety
VANET technologies are driven by applications which dictate the technical challenges and research agenda
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I. Vehicular Communication Standards
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Standards Under Development
IEEE 802.11p/DSRC/WAVE
IEEE 1609.4
Networking Services
IEEE 1609.2
Multi-channel sub-layer
IEEE 1609.3
PHY & MAC
Security Services (confidentiality, authenticity, integrity)
IEEE 1609.1
Resource Manager (interoperability, memory, user interface devices, …) 7
Dedicated Short Range Communications (DSRC/802.11p) Wireless Access for Vehicular Environment (WAVE)
What is DSRC?
Why DSRC?
High data rate (≤ 27 Mbps), short range (≤ 1000 m), multi-channel wireless standard based on 802.11a PHY and 802.11 MAC 1st standard draft developed by ASTM in 2003 and currently being evaluated by IEEE 802.11 TGp/WAVE
Operate in the 75 MHz licensed spectrum at 5.9 GHz allocated by FCC in 1999 for Intelligent Transportation Systems (ITS) applications Avoid intolerable and uncontrollable interference in the ISM unlicensed bands, especially for safety applications
Major Differences from IEEE 802.11a:
Licensed band operation Outdoor high-speed vehicle applications (up to 120 mph) 7 channels for supporting safety and non-safety applications 10 MHz channel bandwidth 8
DSRC Band Plan at 5.9 GHz Shared Public Safety/Private Short Rng Control Med Rng Service Service 44.8 dBm
Power Limit Power Limit
33 dBm
Power Limit
23 dBm Uplin k Downlink
5.925
5.920
5.915
5.910
Public Public Safety Safety/ Private Intersections Ch 182 Ch 184 5.905
Public Safety / Ch 180 Privat e 5.900
5.890
Private
5.880
Private
5.875
Safety/ Ch 176
5.870
Safety/ Ch 174
Control Channe Chl 178
5.895
Public
5.885
Public
5.865
5.860
5.855
5.850
5.845
5.840
5.835
5.830
Public Safety Veh-Veh Ch 172 5.825
Dedicated Public Safety High Intersection Avail s 40 dBm
Frequency (GHz) Canadian Special License Zones*
DSRC Supports 1 control channel (CCH) and 6 service channels (SCH) 9
DSRC Stakeholders
Joint Initiative by Government, Industry and Standards Bodies
Government:
Industry:
FCC, US DOT Vehicle Infrastructure Integration (VII), NHTSA, …
Automakers: CAMP (a.k.a Vehicle Safety Communication Consortium) OEM and suppliers: DENSO (supplied DSRC-compliant test kits to CAMP) Chip makers: Atheros, … System Integrators
Standards Bodies:
IEEE, SAE, ASTM, ISO
VII Initiative: coordinate road-side units (RSU) and onboard unit (OBU) deployment
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DSRC-Related Standards
IEEE 1609.4
(Multi-channel Operation) How to utilize multiple channels to prioritize different applications? Channel assignment and switching mechanisms Use of one vs. multiple radios onboard each vehicle One radio/vehicle
CCH Interval and SCH Interval Distributed synchronization
(GPS outage)
IEEE 1609.3 (Networking Services) Supports two protocol stacks
Standard Internet (IPv6) Wave short Message protocol (WSMP)
(only on SCHs) (on any channel)
Managing WAVE BSSs to coordinate visits to SCHs Interfacing between applications and low layers (multiple channels/radios, MAC,…) 11
Fundamental Questions
Does DSRC have the potential for supporting low-latency (~100s ms) vehicular safety applications? Is best effort DSRC MAC scalable under high vehicle density interference-limited scenarios?
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II. Safety Applications
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Example Applications Application Name
User Benefit
Slow Vehicle Advisor
Safety
Emergency Electronic Brake Light
Safety
V2V Post Crash Notification
Safety
Road Hazard Condition Notification
Safety
Cooperative Collision Warning
Safety
Cooperative Violation Warning
Safety
Congested Road Notification
Convenience
Traffic Probe
Convenience
Free Flow Tolling
Convenience
Parking Availability Notification
Convenience
Parking Spot Locator
Convenience
Remote Vehicle Personalization
Commercial
Content Download
Commercial
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Application Classification (Wireless Networking Perspective)
Objective: group large number of applications, with similar properties, to the same ”generic” class
Identify 7 generic application classes Short Message Broadcasts
Class1: Event-Driven Class 2: Periodic Class 3: On-demand
(e.g. hazard warning) (e.g. CCW) (e.g. parking helpers)
On-demand Short Message Unicasts
Simplifies simulation and modeling of the generic classes Maximize the reuse of common protocol modules across different stacks
Class 4: Secured Transactions Class 5: Non-secured Transactions
(e.g. toll collection) (e.g. vehicle diagnostics)
Large-volume Content Download/Streaming
Class 6: File Download Class 7: Video/Media Streaming
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Vehicle Safety Using Wireless Communication
Vehicle safety research is shifting its focus towards crash avoidance and collision mitigation (Active vs. Passive Safety) Traditional sensors, like radars, have the following limitations:
TRADITIONAL SENSORS
5 3 1
7
4
6 8
2
Limited range (sense immediate vehicles) Limited Field of View (FOV) Expensive
Cooperative collision warning systems explore the feasibility of using wireless comm. (e.g. DSRC) for vehicle safety
COOPERATIVE COLLISION WARNING (CCW)
“360 Degrees Driver Situation Awareness” using wireless comm.
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Cooperative Collision Warning (CCW)
Requirements:
Radio platform GPS with ~1-1.5m resolution to properly associate vehicles with lanes
Forward Collision Warning (FCW) Host Vehicle (HV) utilizes messages from the immediate Forward Vehicle in the same lane to avoid forward collisions
Lane Change Assistance (LCA) Host Vehicle utilizes messages from the Adjacent Vehicle in a neighboring lane to assess unsafe lane changes
Electronic Emergency Brake Light Host Vehicle utilizes messages to determine if one, or more, leading vehicles in the same lane are braking
Host Vehicle Forward Vehicle Next Forward Vehicle Adjacent Vehicle
Focus on single-hop broadcast CCW applications as a 1st step
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CCW Application Modeling
Application Model
Single-hop periodic broadcasts over UDP Broadcast rate: 10 packets/sec Packet size = 100 Bytes payload
All vehicles broadcast, according to the above model, a small message bearing status information (e.g. location, velocity)
FCW: Measure the quality of reception at a randomly chosen HV for messages transmitted only by the FV
HV ignores messages from other vehicles, based on their relative location
Host Vehicle Forward Vehicle
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III. Performance Evaluation
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What dominates the latency of periodic broadcast applications?
Packet-level Metrics:
Per-packet Latency (PPL): defined as the time elapsed between generating a packet at the application of the sender and successfully receiving the same packet at the application of the receiver
Important metric for network and protocol designers However, it does not reveal much about the latency of periodic applications
Problem: Application requirements are not given in terms of packetlevel metrics
Application-level Metrics:
Packet Inter-Reception Time (IRT): defined as the time elapsed between two successive successful reception events for packets transmitted by a specific transmitter
Directly related to the pattern of consecutive packet losses
Strong need for performance metrics that bridge the gap between the networking and automotive communities
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Simulation Setup
Simulation Tool: QualNetTM Protocol Stack:
Wireless Channel Model:
Exponential decay with distance Path loss = 2.15 out to a distance of ~150m (experimental measurements) BER vs. SNR performance of DSRC measured using DSRC test kits from DENSOTM
Transmission Power: 16.18 dBm (range ~150 meters) Simulation time: 30 sec
PHY/MAC: DSRC @ 6 Mbps data rate, single-channel operation Transport: UDP Application: single-hop broadcast @ 10 packets/sec broadcast rate
Each vehicle broadcasts 290 messages throughout a simulation run
Mobility: straight freeway # simulation runs: 20
CI ≤ 3% and 19% for the gathered Shown to yield statistically significant results ( 2 * Mean performance metrics) 21
Freeway Mobility Scenarios
High Density Scenario: (1920 vehicles) One Side of the freeway
Stationary vehicles Vehicle separation = 5m
On the other side:
Avg vehicle speed = 25 mph Avg vehicle separation ~10m
mile 1 1mile
• Low Density Scenario: (208 vehicles) • Avg vehicle speed = 65 mph • Avg vehicle separation ~61m
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FCW Performance for a chosen pair of vehicles (High Density) • Cumulative Packet Reception: • ~ 46 packets lost out of 290 sent • But, Max. # consecutive packet losses is only 3
• Inter-Reception Time (IRT): • Max. ~400 msec, Min. ~100 msec
• Per-packet Latency (PPL): • Max. ~17 msec, Min. ~0.321 msec
• Max. IRT stats over 20 runs: Mean = 372.1 ms, SD = 66.3 ms, 95% CI = 58.1 ms • IRT and PPL vary over vastly different ranges (due to consecutive pkt losses) 23
FCW Performance for a chosen pair of vehicles (Low Density) • Cumulative Packet Reception: • Only 7 packets lost in total • No consecutive packets losses
• Max. Inter-Reception Time (IRT): • Max. = 200 msec, Min. = 100 msec
• Per Packet Latency (PPL): • Max. ~1 msec, Min. ~0.321 msec
• Max. IRT stats over 20 runs: Mean = 238 ms, SD = 74.4 ms, 95% CI = 65.2 ms • Performance gap between extreme densities is small 24
FCW periodic broadcast interval optimization
Motivation: balance the factors contributing to the application metric, packet Inter-reception time (IRT)
# consecutive packet losses: favors low broadcast rates Inter-broadcast interval: favors high broadcast rates
Scenario: ~2000 vehicles periodically broadcasting on a 1 mile freeway, 150 m Tx range, 100 Bytes payload
Different Broadcast intervals:
50, 100, 200, …, 700 msec
Conjecture: There is an optimal broadcast interval that minimizes IRT 25
DSRC Performance Trends with Distance
Objective: Characterize the behavior of packet success probability with increasing distance from the Host Vehicle
Transmission Range is fixed
All vehicles are stationary
Measured at a randomly chosen Host Vehicle
150m comm. range is divided into 10 concentric bins at 15m, 30m, 45m, ….
Host Vehicle
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Packet Success Probability at the Host Vehicle
• Success probability varies considerably with distance • Good reception from nearby vehicles • Even at the edge of the reception range (150m), success probability ~ 38%
Quality of reception at HV strongly depends on the distance to the relevant sender, as specified by the application 27
Concluding Remarks
DSRC, and related standards, constitute only a step towards realizing the ultimate Connected Vehicle vision
Applications are the main drivers for VANETs
How to optimally allocate heterogeneous wireless access resources to a vehicle?
Strong need to understand, characterize, classify, and model automotive applications from a wireless networking perspective
Need for performance metrics (e.g. IRT) that bridge the gap between the networking and automotive research communities
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Research Directions
Capacity of single-/multi-hop vehicular networks supporting broadcast/geocast applications?
Enhance capacity using cross-layer optimizations (MIMO, beam forming, multiple channels, …)
Vehicle naming/addressing (e.g. Geo-based)
Configurable protocol stacks that opportunistically configure the underlying agile radio depending on the interference conditions and application requirements/constraints
Protocols and applications for sparsely connected networks (i.e. low market penetration) 29
References [1] J. Yin, T. ElBatt, G. Yeung, B. Ryu, S. Habermas, H. Krishnan, T. Talty, “Performance Evaluation of Safety Applications over DSRC Vehicular Ad Hoc Networks,” 1st ACM Mobicom VANET Workshop, Oct. 2004 [2] T. ElBatt, S. Goel, G. Holland, V. Kukshya, H, Krishnan, J. Parikh, “Communications Performance Evaluation of Cooperative Collision Warning Applications,” IEEE Plenary session, Task Group P, July 2005 [3] T. ElBatt, S. Goel, G. Holland, H. Krishnan, J. Parikh, “Cooperative Collision Warning Using Dedicated Short Range Wireless Communications,” 3rd ACM Mobicom VANET Workshop, Sept. 2006 [4] J. Yin, G. Holland, T. ElBatt, F. Bai, H. Krishnan, “DSRC Channel Fading Analysis From Empirical Measurement” 1st ChinaCom VehicleComm Workshop, Oct. 2006 [5] F. Bai, T. ElBatt, G. Holland, H. Krishnan, V. Sadekar, “Towards Characterizing
and Classifying Communication-based Automotive Applications from a Wireless Networking Perspective” 1st IEEE Globecom AutoNet Workshop, Dec.
2006
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Thank You! http://www.geocities.com/telbatt
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