Vehicular Ad-hoc NETwork (VANET) Speaker: Yi-Ting Mai Contact
Vehicular Ad-hoc NETwork (VANET) Speaker: Yi-Ting Mai Contact info. :[email protected] Date: 2010/05/04 Outline Overview of VANETs Physical Layer and MAC protocols for VANETs Broadcast Routing Protocols for VANETs Applications for VANETs 2 Why Vehicular Networks? Safety On US highways (2004):
42,800 Fatalities, 2.8 Million Injuries ~$230.6 Billion cost to society Combat the awful side-effects of road traffic In the EU, around 40,000 people die yearly on the roads; more than 1.5 millions are injured Traffic jams generate a tremendous waste of time and of fuel Most of these problems can be solved by providing appropriate information to the driver or to the vehicle 3 Why Vehicular Networks? (cont.) Efficiency Traffic jams waste time and fuel In 2003, US drivers lost a total of 3.5 billion hours
and 5.7 billion gallons of fuel to traffic congestion Profit Safety features and high-tech devices have become product differentiators 4 5 What is a VANET? Roadside base station Emergency event
Inter-vehicle communications Vehicle-to-roadside communications 6 A taxonomy of vehicular communication systems 7 Inter-vehicle communication (IVC) Systems IVC systems are completely infrastructure-free; o nly onboard units (OBUs) sometimes also called
in-vehicle equipment (IVE) are needed. 8 IVC systems Single-hop and multihop IVCs (SIVCs and MIVCs) . SIVC systems are useful for applications requiring short-range communications (e.g., lane merging, a utomatic cruise control) MIVC systems are more complex than SIVCs but can also support applications that require long-ran ge communications (e.g., traffic monitoring) 9 IVC systems
a) Single-hop IVC system b) Multihop IVC system 10 Vehicular Communication Internet Gateway Vehicle Internet Future Vehicular Communication Scenario
11 Vehicular Communication-DSRC In 2003, FCC established the service and license rules for Dedicated Short Range Communication s (DSRC) Service. DSRC is a communication service that uses the 5.9 GHz band (5.850-5.925 GHz band) for the use of public safety and private application. The vehicular related services and communication standa rds enable vehicles and roadside beacons to form VANE Ts (Vehicular Ad Hoc Networks) in which the mobile node s (vehicles) can communicate each other without central access points. 12
VANETs vs. MANETs A VANET consists of vehicles to form a network which is similar to a Mobile Ad Hoc Network (MANET). However, there are following differences between these two networks. Vehicles mobility Vehicles move at high speed but mobility is regular and predictable Network topology High speed movement makes network topology dynamic No significant power constraint Recharging batteries from vehicle Localization Vehicles position estimate accurately through GPS systems or on-board
sensors 13 Features of VANETs The characteristics of VANETs can be summarized after c omparing with the MANETs. Dynamic topology Nomadic nodes with very high speed movement cause frequent topology variation Mobility models Vehicles move along original trajectories completely different from typical MANET scenarios Infinite energy supply Power constraint can be neglected thanks to always recharging batteries
Localization functionality Vehicle can be equipped with accurate positioning systems (GPS and G ALILEO) integrated by electronic maps 14 Operating Environment According to the environments of operating vehicles, the VANETs can be established in the following situa tions: City environments, disaster situations, extreme weather c onditions, and so on. For instance: City environments, have certain unique characteri stics: Many tall buildings obstructing and interfering the transmission signals, In the highway scenario, vehicles are closer together than, thus incur in
terference if their transmission range are large, The topology is usually two dimensional (e.g. with cross streets). 15 Scopes of VANETs (1/2) Communication range of VANETs Short/medium-range communication systems (vehicle-to-vehicle or vehicle-to-roadside) Applications of VANETs The VANETs vision includes vehicular real-time and safety application s, sharing the wireless channel with mobile applications from a large, d ecentralized array of commercial service providers. VANET safety applications include collision and other safety warnings. Non-safety applications include real-time traffic congestion and routing information, high-speed tolling, mobile infotainment, and many others.
16 Scopes of VANET (2/2) VANET research issues
Safety and non-safety applications Roadside-to-vehicle and vehicle-to-vehicle communication Communication protocol design Channel modeling Modulation and coding Power control and scalability issues Multi-channel organization and operation Security issues and countermeasures Privacy issues Network management Simulation frameworks & real-world testbeds 17 Threat model
Presented in SeVeCom (Secure Vehicular Communicatio n) project An attacker can be: Insider / Outsider Malicious / Rational Active / Passive Local / Extended Attacks can be mounted on:
Safety-related applications Traffic optimization applications Payment-based applications Privacy 18 Attack 1 : Bogus traffic information Traffic jam ahead Attacker: insider, rational, active 19
Attack 2 : Generate Intelligent Collisions SLOW DOWN The way is clear Attacker: insider, malicious, active 20 Attack 3: Cheating with identity, speed, or position Wasnt me!
Attacker: insider, rational, active 21 Attack 4: Jamming Roadside base station Jammer 22 Attack 5: Tunnel Wrong information
Physical tunnel or jammed area 23 Attack 6: Tracking A 3 * A enters the parking lot at time t3 * A downloads from server X
A B 2 A 1 * A at (x1,y1,z1) at time t1 * A communicates with B * A refuels at time
t2 and location (x2,y2,z2) 24 Protocols of Layers in VANETs In this topic, we introduce the physical layer and the 802 .11 related MAC protocols. Afterwards, the routing proto cols between vehicles are presented.Finally, the applica tions of VANETs are proposed. The physical layer and the 802.11 related protocols. The physical layer and the MAC layer of DSRC/802.11p 802.11 DCF Routing protocols Position-based Routing (Unicast)
Geocasting Routing (Multicast) Broadcast Routing Applications of VANETs. 25 Physical Layer and MAC protocols for VANETs Physical/MAC Layers DSRC/802.11p Dedicated Short Range Communication (DSRC) was released in 2002 by the American Society for Testing and Materials (ASTM). In 2003, the standardization moved to IEEE Forum and changed the name from DSRC to WAVE
(Wireless Ability in Vehicular Environments), which was also known as 802.11p. 27 DSRC/802.11p Physical Layer (1/4) DSRC/802.11p The standard of 802.11p is based on IEEE 802.11a PHY layer and IEEE 802.11 MAC layer Seven 10 MHz channels at 5.9GHz one control channel and six service channels Vehicle to vehicle Service channel
Service channel Control channel CH 172 CH 174 CH 176 CH 178 Optionally combined
5.875 5.865 5.855 Frequency (GHz) Intersection 28 DSRC/802.11p Physical Layer (2/4) DSRC/802.11p vs. 802.11a 802.11a is designed for high data rate multimedia
communications in indoor environment with low user mobility. DSRC PHY uses a variation of OFDM modulation scheme to multiplex data. high spectral efficiency, simple transceiver design and avoids multi-path fading 29 DSRC/802.11p Physical Layer (3/4) DSRC/802.11p vs. 802.11a DSRC/802.11p reduces the signal bandwidth from 20MHz to 10MHz. all parameter values are doubled in time domain in order to increase the robustness (e.g. timeout increase) to ISI caused by the multi-path delay spread and Doppler spread effect
Data rates are between 6 and 27 Mbps Transmit power level are changed to fit requirements of outdoor vehicular communications communication ranges up to 1000 meters 30 DSRC/802.11p Physical Layer (4/4) Parameters DSRC/802.11p 802.11a Information data rate Mb/s
1/2, 1/3, 3/4 Number of subcarriers 52 (=48+4) 52 (=48+4) OFDM symbol duration 8s 4s Guard time
1.6s 0.8s FFT period 6.4s 3.2s Preamble duration 32s 16s
Subcarrier frequency spacing 0.15625MHz 0.3125MHz 31 Revolution and Design in 802.11 DCF The revolution of 802.11 DCF can be described in the following. The design of avoiding collisions: The design to solve the collisions including collisions incurred by the terminal problem. The improvement design to IEEE 802.11 DCF
32 The Design of Avoiding Collisions The design of avoiding collisions In mobile wireless networks, the objectives of MAC protocols is to avoid collisions, process contention, and re-tramsit lost packets to increase the overall throughput. In previous works, the design of avoiding collisions can be described in the following. Carrier Sense Multiple Access Protocols, CSMA: A mobile node uses carrier sensing technology to detect whether there is any node using the channel before transmitting data to avoid collisions. The problems in the CSMA: hidden- and exposed- terminal problems Terminal problems: Hidden terminal problem Exposed terminal problem
33 Medium Access Control (MAC) LAN(Ethernet) CSMA/CD Carrier Sense Multiple Access with Collision Detection WLAN(802.11) CSMA/CA (Carrier Sensing Multiple Access/Collision Avoidance) 34 CSMA/CD CSMA/CD (Carrier Sense Multiple Access/ Collision Detection)
Data ACK MH MH 42 The Designs to Solve the HiddenTerminal Problem The Designs to Solve the Hidden-Terminal Problem The design of using busy tone channel The design of MACA (IEEE 802.11 DCF) 43
The Design with Busy Tone Channel Protocol Each node equipped with an extra busy tone channel to send out the busy signals when the node is processing data transmission. When a node would like to transmit data, it detects weather there are nodes issuing the signals by other nodes in its range. If a node detects no signal, it can process the transmission. Problems Needed an extra busy tone channel. The hidden-terminal is solved, but the exposed-terminal problem still exists. 44
IEEE 802.11 DCF To solve the hidden-terminal problem, MACA proposed the Multiple Access Collision Avoidance protocol, which is adapted by the IEEE 802.11 MAC to be the IEEE 802.11 DCF. Contention period Handshake period Data period ACK period contention 4
1 6 3 8 4 Sender Receiver Others handshake
data SIFS RTS ACK data SIFS CTS SIFS ACK NAV Defer Access
45 Contention Period of IEEE 802.11 DCF Contention period Interval Frame Space, IFS Short IFS, SIFS) CTS, ACK, or Poll Response PCF (PIFS) DCF (DIFS) 46 Handshake period of IEEE 802.11 DCF
Handshake period In MACA, before processing data transmission, a sender broadcasts a RTS (Request To Send) signal to inform its neighbors that it will send out data. When a neighbor except the sender and the receiver receives the RTS signal, it use the NAV (Network Allocation Vector) to exhibit itself to issue signals to avoid occurring interference of data transmission. When the receiver receives the RTS, it will reply a CTS (Clear To Send) signal if it accepts the RTS request. Similarly, when a neighbor of the receiver except the sender receivers the CTS, it uses the NAV to exhibit itself to send any signal. 47
Data and ACK Periods of IEEE 802.11 DCF Data period After completing the handshaking period, the sender and the receiver can transit data, while the neighbors of these two nodes are exhibited by the NAV until the finishing data transmission. ACK period After the completion of data transmission, the receiver sends a ACK to the sender to show that the data has been received. At the same time, all neighbors are in the listening status for contending the channel. 48 IEEE 802.11 DCF and Problems
With the protocol (IEEE 802.11 DCF) mentioned above can solve the hidden-terminal problems The problems of IEEE 802.11 DCF The exposed-terminal problems exists. The number of contention nodes during the contentio n period increases. The length of backoff time period. 49 Exposed-Terminal in IEEE 802.11 DCF With IEEE 802.11 DCF, the nodes are exhibited by NAV increase. Therefore, the problem of exposedterminal becomes more serious than CSMA. In CSMA, only node C is exhibited to send or receive data.
In IEEE 802.11 DCF, nodes C and D are exhibited. (a) C A B D C A
B D (b) 50 The Power Control Design The design of controlling power to improve the exposedterminal problem. With detecting the strength of signals, the power of data transmission can be controlled to fit the distance between two nodes. With the decrease of exhibited area, the exposed-terminal problem can be improved. D
C A B E F D C A
B E F 51 The Power Control Design Problems: With controlling power, the problem of exposedterminal can be improved, the hidden-terminal problem may occur. 52
The Spilt-Channel Design to Improve the Problem of Contending for the Channel Spilt-channel design Two pipeline stages of contending for the channel. Nodes that would like to send data contending at the first stage. If nodes pass the first one, they can contending for the channel at the second stage. The number of nodes contending for the channel is reduced. To avoid occurring starvation, the protocol uses the weight schemes to make some nodes enter the second stage directly. 53 Influence of the Backoff Time
The length of backoff time: If the node density in IEEE 802.11 DCF is high, to a void collisions in the contention period, the backoff ti me should be increase. If the node density in IEEE 802.11 DCF is low, too lo ng backoff time incurs the time waste of waiting. 54 Dynamic Adjustment of Backoff Time Schemes: Dynamic adjustment for the backoff ti me to reduce the waste of bandwidth utilization.
Three kinds of the dynamic adjustments Successful history records. Polling the neighbors Statistical method: With the statistic list, the length of backoff time can be decided according to the statistic list. 55 DSRC/802.11p MAC Layer (1/2) DSRC/802.11p MAC MAC layer of DSRC is very similar to the IEEE 802.11 MAC based on CSMA/CA with some minor modifications. DSRC involves vehicle-to-vehicle and vehicle-toinfrastructure communications.
56 DSRC/802.11p MAC Layer (2/2) Vehicle-to-Vehicle relative speed : low absolute speed: high multi-hop relay (a) distributed mobile multihop network Vehicle-to-Infrastructure high download rates over a short duration (b) centralized one-hop network 57
Communication architecture Hot Spot ADSL/WiFi WiMax/3.5G TTS Server V-I communication DSRC/802.11 V-V communication Workstation
V-I communication DSRC/802.11 V-V communication 58 Broadcast Routing Protocol for VA NETs Broadcast Routing In Inter-Vehicle Communication Systems (IVC) broadcasting is an efficient method to spread messages. The reasons of occurring broadcast storm
In a broadcasting network, the situations of contentions and collisions often take place if an efficient broadcasting scheme is not used. The result incurred by broadcasting is called broadcast storm. 60 Broadcast Storm In VANETs, broadcast is used for disseminating the traffi c information Detour route
Accident alert Construction warning etc Some messages will be periodically broadcasted by road side unit (RSU) for several hours or even some days. The problem of broadcast storm in VANET is more serious tha n that in MANET 61 Broadcast Routing Message Dissemination Ideal solution: Minimum Connected Dominating Set, which minimizes pack et rtx and preserves network connectivity. Realistic solutions: trade-off between robustness and redundancy.
The important concern in designing a broadcast scheme in VANET. How to design broadcast algorithm to efficiently transmit messages to the t arget nodes. To design a broadcast algorithm to make the desired vehicles to receive th e message as soon as possible. 62 Four Broadcasting Strategies Different broadcasting strategies to select the forwarding nodes:
Probability-based Location-based Neighbor-based Cluster-based 63 Broadcast Routing 1. Probability-based: A given PDF determines the decision, for example depending on the number of copies a node has received. The strategy is often dynamic. PDF = probability distribution function 64
Broadcast Routing Probability-based Car A PDF = 0.8 Car B PDF = 0.5 Forwarding Node choose 65 Broadcast Routing Location-based The selection criterion is the amount of additional area that would be covered by enabling a node to forward.
Some proposal also computes position prediction as useful input information. 66 Broadcast Routing Location-based Target Car A Car B wants to turn right Forwarding Node choose 67
Broadcast Routing Neighbor-based A node is selected depending on its neighbors status (for instance, the status concerns how a neighbor is connected to the network). 68 Broadcast Routing Neighbor-based Target Car A Collect the information of neighbors
Car B Forwarding Node choose 69 Broadcast Routing Cluster-based Nodes are grouped in clusters represented by an ele cted cluster-head. Only cluster-heads forward packet s. Nodes in the same cluster share some features (e.g., relative speed in VANETs). Reclustering on-demand or periodically.
Assistance for Safe Navigation Traffic safety Detecting dangerous situations Sending warning messages to other cars using adhoc networking Traffic management services Traffic congestion Weather forecast Road works 73 Assistance for Safe Navigation (1/3) There are some components must be included into a smart car. 74
Assistance for Safe Navigation (2/3) Overview of the demonstrator routing architecture 75 Assistance for Safe Navigation (3/3) A danger situation: The system sends the warning message immediately after there are cars accident occurring. 76
Intelligent IntelligentVehicle Vehicle Intelligent IntelligentDriving Driving Advanced AdvancedSafety SafetyFeatures Features Innovated Services Vehicle Infotainment Service UNS
UNSLife Life Signal exchanging facilities GPS/RDS/DVB/DAB +
Ubiquitous UbiquitousUse Use ETC/ CVO Multi-Modal Navigation/ Reservation Mobile Business services
RDS/DVB/DAB GSM/GPRS/3G/ 3.5G/WiMAX WiFi/DSRC Service terminals LBS/ Social Networking WiFi/Cellular/DSRC
Hot Spot Urban Nomadic/pedestrians T elematics Source: adapted from TEEMA, 2007/12 E-call/ Maintenance & warrantee Safety Warning/ Mitigation 77
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