A taxonomy of wireless networks

2008/10/1

Examples

4 2008/10/1

Ad Hoc Networks • Non-infrastructure

• Fixed and Mobile Nodes

• Special Classes of Ad Hoc NetworksVehicular Ad Hoc NetworksVehicular Ad Hoc NetworksWireless Mesh Networks

Wireless Sensor Networks

Bluetooth Scatternets…

What is a VANET(Vehicular Ad hoc NETwork)?

Roadside base station

Emergency event

Inter-vehicle communications

Vehicle-to-roadside communications

A taxonomy of vehicular communication systems

Inter-vehicle communication (IVC) Systems • IVC systems are completely infrastructure-free;

only onboard units (OBUs) sometimes also called in-vehicle equipment (IVEIVE) are needed.

IVC systems• Single-hop and multi-hop IVCs (SIVCs and MIVCs).• SIVC systems are useful for applications requiring

short-range communications (e.g., lane merging, automatic cruise control)

• MIVC systems are more complex than SIVCs but can also support applications that require long-range communications (e.g., traffic monitoring)

IVC systems

a) Single-hop IVC system b) multi-hop IVC system

Roadside-to-Vehicle Communication (RVC) Systems • RVC systems assume that all communications take

place between roadside infrastructure (including roadside units [RSURSUs]) and OBUs.

• Depending on the application, two different types of infrastructure can be distinguished

Sparse RVC (SRVC) system Ubiquitous RVC (URVC) system

RVC Systems –SRVC • SRVC systems are capable of providing

communication services at hot spots.• A busy intersection scheduling its traffic light, a gas

station advertising its existence (and prices), and parking availability at an airport, are examples of applications requiring an SRVC system.

• An SRVC system can be deployed gradually, thus not requiring substantial investments before any available benefits.

RVC Systems -URVC • A URVC system : providing all roads with high-speed

communication would enable applications unavailable with any of the other systems.

• Unfortunately, a URVC system may require considerable investments for providing full (even significant) coverage of existing roadways (especially in large countries like the United States)

Hybrid Vehicular Communication(HVC) Systems• HVC systems are proposed for extending the range

of RVC systems.• In HVC systems vehicles communicate with

roadside infrastructure even when they are not in direct wireless range by using other vehicles as mobile routers.

• An HVC system enables the same applications as an RVC system with a larger transmission range.

• The main advantage is that it requires less roadside infrastructure. However, one disadvantage is that network connectivity may not be guaranteed in scenarios with low vehicle density.

IVC vs. MANET (1/6)MANETs are wireless multihop networks that

lack infrastructure, and are decentralized and self-organizing

IVC systems satisfy all these requirements, and are therefore a special class of MANETs

IVC vs. MANET (2/6)There are several characteristics that

differentiate IVCs from the common assumptions made in the MANET literature:ApplicationsAddressingRate of Link ChangesMobility ModelEnergy Efficiency

IVC vs. MANET (3/6)Applications

While most MANET articles do not address specific applications, the common assumption in MANET literature is that MANET applications are identical (or similar) to those enabled by the Internet.

In contrast, as we show later, IVCs have completely different applications. An important consequence of the difference in the applications is the difference in the addressing modes.

IVC vs. MANET (4/6)• Addressing

Faithful to the Internet model, MANET applications require point-to-point (unicast) with fixed addressing; that is, the recipient of a message is another node in the network specified by its IP address.

IVC applications often require dissemination of the messages to many nodes (multicast) that satisfy some geographical constraints and possibly other criteria (e.g., direction of movement). The need for this addressing mode requires a significantly different routing paradigm.

IVC vs. MANET (5/6)• Rate of Link Changes

In MANETs, the nodes are assumed to have moderate mobility. This assumption allows MANET routing protocols (e.g., Ad Hoc On Demand Distance Vector, AODV) to establish end-to-end paths that are valid for a reasonable amount of time and only occasionally need repairs.

In IVC applications, it is shown that due to the high degree of mobility of the nodes involved, even multi-hop paths that only use nodes moving in the same direction on a highway have a lifetime comparable to the time needed to discover the path.

IVC vs. MANET (6/6)• Mobility Model

In MANETs, the random waypoint (RWP) is (by far) the most commonly employed mobility model. However, for IVC systems, most existing literature recognized that RWP would be a very poor approximation of real vehicular mobility; instead, detailed vehicular traffic simulators are used.

• Energy EfficiencyWhile in MANETs a significant body of literature

is concerned with power-efficient protocols, IVC enjoys a practically unlimited power supply.

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 fuelMost of these problems can be solved by

providing appropriate information to the driver or to the vehicle

EfficiencyTraffic jams waste time and fuelIn 2003, US drivers lost a total of 3.5 billion

hours and 5.7 billion gallons of fuel to traffic congestion

ProfitSafety features and high-tech devices have

become product differentiators

Examples

Emergence of Vehicular NetworksIn 1999, US’ FCC allocated 5.850-5.925 GHz band to

promote safe and efficient highways Intended for vehicle-to-vehicle and vehicle-to-infrastructure

communicationEU’s Car2Car Consortium has prototypes in March 2006

http://www.car-to-car.org/Radio standard for Dedicated Short-Range

Communications (DSRC)Based on an extension of 802.11

OBU for each equipped vehicle(Assumptions)• A central processing unit (CPU) that implements

the applications and communication protocols• A wireless transceiver that transmits and

receives data to/from the neighboring vehicles and roadside

• A GPS receiver that provides relatively accurate positioning and time synchronization information

• Appropriate sensors to measure the various parameters that have to be measured and eventually transmitted

• An input/output interface that allows human interaction with the system

A Modern Vehicle (GPS) Positioning system

Forward radar

Communication

facility

Rear radar

Computing platform Display Human-Machine Interface

A modern vehicle is a network of sensors/actuators on wheels !

Event data recorder (EDR)

Applications for VANETsPublic Safety ApplicationsTraffic Management ApplicationsTraffic Coordination and Assistance ApplicationsTraveler Information Support ApplicationsComfort ApplicationsAir pollution emission measurement and

reductionLaw enforcementBroadband services

Applications (details)Applications (details)

Congestion DetectionVehicles detect congestion when:

# Vehicles > Threshold 1Speed < Threshold 2

Relay congestion informationHop-by-hop message forwardingOther vehicles can choose alternate routes

Congestion Detection

Deceleration WarningPrevent pile-ups when a vehicle decelerates

rapidly

Public Safety Applications (1/2)Public safety applications are geared

primarily toward avoiding accidents and loss of life of the occupants of vehicles.

Collision warning systems have the potential to reduce the number of vehicle collisions in several scenarios.

Public Safety Applications (2/2)Safety applications have obvious real-time

constraints, as drivers have to be notified before the information is no longer useful. Either an MIVC or a URVC (SRVC for intersections) can be used for these applications. It is possible that, depending on the communication range, an SIVC may be sufficient for these applications.

In terms of addressing, the destinations in these applications will not be individual vehicles, but rather any relevant vehicle. The zone of relevance (ZOR) (also known as the target area) is determined by the particular application.

Traffic Management ApplicationsTraffic management applications are

focused on improving traffic flow, thus reducing both congestion as well as accidents resulting from congestion, and reducing travel timeTraffic monitoringTraffic light schedulingEmergency vehicles

Traffic Coordination and AssistanceApplicationsPlatooning (i.e., forming tight columns

of vehicles closely following each other on highways)

Passing and lane change assistance may reduce or eliminate risks during these maneuvers, since they are often the source of serious accidents.

Traveler Information SupportApplicationsLocal information such as local updated maps,

the location of gas stations, parking areas, and schedules of local museums can be downloaded from selected infrastructure places or from other “local” vehicles. Advertisements with, for example, gas or hamburger prices may be sent to approaching vehicles.

Road warnings of many types (e.g., ice, oil, or water on the road, low bridges, or bumps) may easily be deployed by authorities simply by dropping a beacon in the relevant area.

Comfort Applications (1/4)This class of applications may be motivated

by the desire of passengers to communicate with either other vehicles or ground-based destinations such as Internet hosts or the public service telephone network (PSTN).

Comfort Applications (2/4)Targeted vehicular communications allow

localized communications (potentially multi-hop) between two vehicles. Voice, instant messaging, or similar communications may occur between the occupants of vehicle caravans traveling together for long distances, or between law enforcement vehicles and their “victims.”Note that this application does not scale to

large network sizes.

Comfort Applications (3/4)Vehicle to land-based destination communications is

arguably a very useful capability as it may enable an entire array of applications, from email and media streaming to Web browsing and voice over IP.Unfortunately, land-based access requires a URVC

system that may be prohibitively expensive in the near future.

Comfort Applications (4/4)Tolls for roads and bridges can be collected

automatically. Many nonstandard systems exist and work well.

Parking payments can be made promptly and conveniently.

Repair and maintenance records can be recorded at the garages performing them.

Multimedia files such as DVDs, music, news, audio books, pre-recorded shows can be uploaded to the car’s entertainment system while the car is in the garage.

The relationship among the IEEE1609 and IEEE 802.11 standards

UPPERLAYERS

LOWERLAYERS

WAVESECURITYSERVICES

NETWORKLAYER

IEEE 1609.1,et al

IEEE 1609.3 IEEE 1609.2

IEEE 1609.4IEEE 802.11p

MEDIUM

DSRC Spectrum AllocationIn 1999, the U.S. Federal Communication

Commission allocated 75MHz of Dedicated Short Range Communications (DSRC) spectrum at 5.9 GHz to be used exclusively for vehicle-to-vehicle and infrastructure-to-vehicle communications.

802.11 WAVE modeA station in WAVE mode can send and receive data

frames with the wildcard BSSID with “To DS” and “From DS” fields both set to 0, regardless of whether it is a member of a WAVE BSS.

A WAVE BSS (WBSS) is a type of BSS consisting of a set of cooperating stations in WAVE mode that communicate using a common BSSID. A WBSS is initialized when a radio in WAVE mode sends a WAVE beacon, which includes all necessary information for a receiver to join.

A radio joins a WBSS when it is configured to send and receive data frames with the BSSID defined for that WBSS. Conversely, it ceases to belong to a WBSS when its MAC stops sending and receiving frames that use the BSSID of that WBSS.

A station shall not be a member of more than one WBSS at one time. A station in WAVE mode shall not join an infrastructure BSS or IBSS, and it shall not use active or passive scanning, and lastly it shall not use MAC authentication or association procedures.

A WBSS ceases to exist when it has no members. The initiating radio is no different from any other member after the establishment of a WBSS. Therefore, a WBSS can continue if the initiating radio ceases to be a member.

MULTI-CHANNEL OPERATIONS (P1609.4)SCOPE

“…describes multi-channel wireless radio operations, that uses the IEEE 802.11p, WAVE mode, medium access control and physical layers, including the operation of control channel and service channel interval timers, parameters for priority access, channel switching and routing, management services, and primitives designed for multi-channel operations.”

NETWORKING SERVICES (P1609.3)SCOPE

“…define services, operating at the network and transport layers, in support of wireless connectivity among vehicle-based devices, and between fixed roadside devices and vehicle-based devices using the 5.9 GHz DSRC/WAVE mode.”

RESOURCE MANAGER (P1609.1)SCOPE

“…describe the services and interfaces, including security and privacy protection mechanisms, associated with the DSRC Resource Manager operating at 5.9GHz band authorized by the Federal Communications Commission (FCC) and to satisfy the Intelligent Transportation System (ITS) wireless communications requirements.”

Security Services for Applications and Management Messages (P1609.2)SCOPE

defines secure message formats and processing of secure messages, within the DSRC/WAVE system.

defines methods for securing WAVE management messages and application messages, with the exception of anonymity-preserving vehicle safety messages.

describes administrative functions necessary to support the core security function.

Issues of VANETSecurityDSRC and collision warningBroadcast and routingInformation disseminationData accessAddress configuration

Suk-Bok Lee, Gabriel Pan, J.S Park, Mario Gerla and Songwu Lu,

ACM MobiHoc, 2007

Secure Dissemination FrameworkSSD: Signature-Seeking Drive

Secure incentives for cooperative nodesNo tamper-proof h/w assumptionsNo game theoretic approachesLeverages a PKI (public key infrastructure)A set of ad dissemination designs

SSD: OverviewSSD: Overview

u

Vehicular Authority (VA)

Certified Ad

Request for Ad permission

Ad Distribution Point (ADP)

ADI

After verifying ADI, Vehicle u may agree to disseminate the ad.

SSD: Overview SSD: Overview Rw

w

v

ADI

Rv u

Vehicle-Vehicle Communication

Vehicle ukeeps forwarding ADI

In return, receiving vehicles v, wprovide signed-receiptsto u.

While driving its way, u may collect as many receipts as it forwards ADI.

SSD: OverviewSSD: OverviewVehicular Authority (VA)

Transaction Record Charge

Colleted receipts

ADI

Rw Rv .

.

. Receipts are exchangeable with virtual cash at Virtual Cashier (e.g. gas station) ;predefined amount of cash is reserved for each receipt-providing node, too.

VA charges the restaurantsuch virtual cash induced by ADI’s

Uncooperative ModelSelfish nodes

Seek to maximize their own profitMalicious nodes

Try to intentionally disrupt the systemWe may encourage selfish nodes to

participate in the network with an incentive model, yet malicious nodes try to

attack the weak point of the model.Secure incentive !

Ad Dissemination Models

One-level advertisement• Local advertising• Most users receive the ad, with reasonable # of

forwarding nodes

Multi-level advertisement

• Intensive advertising over the wide area

Yong Ding, Chen Wang, and Li Xiao,ACM VANET, 2007

A Static-Node Assisted Adaptive Routing Protocol in Vehicular NetworksMulti-hop routing

protocols in vehicular networksMDDV [VANET’04],

VADD[Infocom’06]Basic Idea

Use geographic routingMacro level: packets

are routed intersection to intersection

Micro level: packets are routed vehicle to vehicle

S

D

MotivationUnder high vehicle densities

Both MDDV and VADD work well

Under low vehicle densitiesWhen a packet reaches an

intersection, there might not be any vehicle available to deliver the packet to the next intersection at the moment.

MDDV: not consideredVADD: Route the packet

through the best currently available path A detoured path may be

taken

S

XY Z

D

SADV DesignBasic Idea:

A packet in node A wants to be delivered to a destination

The best path to deliver the packet is through the northward road

The packet is stored in the static node for a whileThe packet is delivered northward when node C

comes

SADV DesignTransactions of packets at

static nodesForward the packet along

the best pathIf the best path is not

available currently, store the packet and wait

Buffer managementTransactions of packets in

vehicles along roadsGreedy geographic

forwarding used to route the packet to the next static node

Yang Zhang, Jing Zhao and Guohong Cao,ACM VANET, 2007

The Big PictureVehicular Ad-hoc Networks -

VANETMoving VehiclesRoadSide Units (RSU)

Local broadcasting infostations 802.11 access point

ApplicationsCommercial AdvertisementReal-Time TrafficDigital Map Downloading

TaskService Scheduling of Vehicle-

Roadside Data Access

ChallengesBandwidth Competition

All requests compete for the same limited bandwidth.

Time ConstraintVehicles are moving

and they only stay in the RSU area for a short period of time.

Data Upload/DownloadThe miss of upload

leads to data staleness.

Assumptions and Performance MetricsAssumptions

Location-aware and Deadline-awareThe RSU maintains a service cycleService non-preemptive

Performance MetricsService Ratio

Ratio of the number of requests served before the service deadline to the total number of arriving requests.

Data Quality Percentage of fresh data access.

Tradeoff !!!

Naive Scheduling PoliciesFirst Come First Serve

(FCFS): the request with the earliest arrival time will be served first.

First Deadline First (FDF): the request with the most urgency will be served first.

Smallest Datasize First (SDF): the data with a smallest size will be served first. workload

D*S SchedulingIntuition

Given two requests with the same deadline, the one asking for a small size data should be served first.

Given two requests asking for the data items with same size, the one with an earlier deadline should be served first.

Basic IdeaAssign each arrival request a service value based on

its deadline and data size, called DS_value as its service priority weight.

DS_value=(Deadline − CurrentClock)*DataSize

Implementation of D*S

Dual-ListSearch from the top of

D_listSet MinS and MinDSearch D_List and

S_list alternativelyStops when the

checked entry goes across MinD or MinS, or when the search reaches the halfway of both lists.

Download Optimization: BroadcastingObservation

several requests may ask for downloading the same data item.

wireless communication is broadcast in nature.Basic Idea

delay some requested data and broadcast it before the deadlines, then several requests may be served via a single broadcast.

the data with more pending requests should be served first.

DSN_value=(Deadline − CurrentClock)*DataSize/Number

D*S/N: Selection of Representative DeadlineWhen calculating

their DSN value, we need to assign each pending request group a single deadline to estimate the urgency of the whole group.

The Problem of D*S/NData Quality !!!

DSN_value=(Deadline − CurrentClock)*DataSize/Number

For upload request, it is not necessary to maintain several update requests for one data item since only the last update is useful.

Number value of update requests is always 1, which makes it not fair for update requests to compete for the bandwidth.

D*S/N can improve the system service ratio but sacrifice the service opportunity of update requests, which degrades the data quality for downloading.

Upload Optimization: 2-Step Scheduling

Basic Ideatwo priority queues: one for the update requests and

the other for the download requests.the data server provides two queues with different

bandwidth (i.e., service probability).Benefits of Using Two Separate Priority Queues

only need to compare the download queue and update queue instead of individual updates and downloads.

update and download queues can have their own priority scheduling schemes.

ReferenceChien-Chung Shen, “Vehicular Ad hoc Networks (VANET),” 「車載資通訊」短期課程 , 國立台北大學三峽校區 , 2007.陳宗禧教授 , “Data Dissemination, Service Discovery, and

Applications in Vehicle Ad Hoc Networks ,“「車載隨意行動網路」學界短期課程推廣暨產學座談會 , 私立淡江大學 , 2008.Daniel Jiang and Luca Delgrossi, “IEEE 802.11p: Towards

an International Standard for Wireless Access in Vehicular Environments,” Vehicular Technology Conference, 2008. VTC Spring 2008. IEEE11-14 May 2008 Page(s):2036 – 2040.

Tom Kurihara, “IEEE DSRC Application Services (P1609),” doc:IEEE 802.11-07-2134-00-000p, 2007.