Vehicular Communication Technology 22.09.2018 Vehicular Communication Technology

Vehicular Communication Technology Motivation Safety and transport efficiency In Europe around 40,000 people die and more than 1.5 millions are injured every year on the roads 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 22.09.2018 Vehicular Communication Technology

Vehicle Communication (VC) VC promises safer roads, … more efficient driving, 22.09.2018 Vehicular Communication Technology

Vehicle Communication (VC) … more fun, … and easier maintenance. 22.09.2018 Vehicular Communication Technology

Vehicular Communication Technology Smart Vehicle 22.09.2018 Vehicular Communication Technology

Approaches to vehicular communication Communication using Communication using dedicated infrastructures cellular systems Direct Communication 22.09.2018 Vehicular Communication Technology

Vehicular Ad Hoc Network (VANET) A network with minimal or no infrastructure Self-organizing Each node can act as the source of data, the destination for data and a network router Vehicular Ad Hoc network (VANET) Uses equipped vehicles as the network nodes Nodes move at will relative to each other but within the constraints of the road infrastructure 22.09.2018 Vehicular Communication Technology

Differences VANETs from MANETs Rapid Topology Changes High relative speed of vehicles => short link life Frequent Fragmentation Chunks of the net are unable to reach nodes in nearby regions Small Effective Network Diameter A path may cease to exist almost as quickly as it was discovered (reactive routing) Limited Redundancy The redundancy in MANETs is critical to providing additional bandwidth In VANETs the redundancy is limited both in time and in function 22.09.2018 Vehicular Communication Technology

Vehicular Ad Hoc Network (VANET) Message propagates to destination using a number of intermediate links 22.09.2018 Vehicular Communication Technology

Vehicular Ad Hoc Network (VANET) If vehicle mobility causes links to break, message rerouted using a different path 22.09.2018 Vehicular Communication Technology

Vehicular Communication Technology Why use VANETS? Easier deployment Decreased dependency on fixed infrastructure Sparse network of roadside beacons Permit gradual introduction of technology Location-oriented services can be provided with little or no running costs to the users 22.09.2018 Vehicular Communication Technology

Lot of Involved Parties 22.09.2018 Vehicular Communication Technology

Major problems in this area Communication / Networking Localization 22.09.2018 Vehicular Communication Technology

Requirements on vehicular communication Mobility Delay bounded (real-time) Scalability Bandwidth efficiency Cost Fairness Any time, any place, any hosts (GPS unequipped vehicles, standardization between cars’ manufactures) 22.09.2018 Vehicular Communication Technology

Addressing the challenges Physical Layer limited bandwidth Link Layer congestion control, latency, throughput, fairness and scalability Network (Routing) Layer rapid topology changes and network fragmentation 22.09.2018 Vehicular Communication Technology

Dedicated Short Range Communications (DSRC) DSRC operates at 5.9 GHz 22.09.2018 Vehicular Communication Technology

DSRC – Operating Characteristics IEEE 802.11p protocol (802.11a modification for VC) Maximum range: 1000 m Vehicle speeds up to 100 mph Low latency: 50 ms Application priority: 8 levels Channel 172: vehicle safety only 22.09.2018 Vehicular Communication Technology

Vehicular Communication Technology How does DSRC work? Road-Side Unit (RSU) Announces to OBUs 10 times per second applications it supports on which channel On-Board Unit (OBU) Listens on Channel 172 Executes safety applications first Then switches channels Executes non-safety applications Returns to Channel 172 and listens 22.09.2018 Vehicular Communication Technology

Channel allocation (MAC) Existing MAC protocols (CSMA/CA, MACA, MACA-BI) are contention-based => not delay bounded Proposed MCS/CDMA Each vehicle senses all the spreading codes, finds a code that is not used by nearby vehicles, and transmits data using the selected code Search for free code, contention for free code (if vehicles > codes) => large delays 22.09.2018 Vehicular Communication Technology

Channel allocation (MAC) Location-based Channel Access (LCA) The geographical area is divided into a cellular structure Each cell has a unique channel associated with it Multiple access scheme, such as CSMA/CA and MCS/CDMA, can be used within each cell Main design parameters: cell size and channel reuse distance Advantages: no central station for channel assignment, no wait before transmit, no contention for free channels, reuse of channels => delay bounded, fairness, bandwidth efficiency, scalability and mobility 22.09.2018 Vehicular Communication Technology

Vehicular Communication Technology Routing Schemes Proactive (table-driven) Each node attempts to maintain a current representation of the network topology Advantage: lower message latency (routes are immediately available) Disadvantage: bandwidth overhead (to maintain routes), restricted scalability Reactive (source-driven, on-demand) Routes are requested by source nodes only when needed Advantage: bandwidth economy (no control messages for non-active routes) Disadvantage: latency (establishing a route) Hybrid ZRP – proactive within zone, reactive outside zone 22.09.2018 Vehicular Communication Technology

Major problems in this area Communication / Networking Localization 22.09.2018 Vehicular Communication Technology

Vehicular Communication Technology GPS 22.09.2018 Vehicular Communication Technology

Vehicular Communication Technology Space Segment 22.09.2018 Vehicular Communication Technology

Vehicular Communication Technology How does GPS work? 22.09.2018 Vehicular Communication Technology

How do we compute Position? GPS is a Distance (Range) Measuring System Stable Frequency Standards in the Satellites and Receivers Able to compute a Clock Offset Velocity of Radiowave is known Thus Distance = V x T Since the coordinates of the Satellites are known at any point of time, with 4 ranges the position of the GPS Antenna can be computed 3-D Trilateration: Distance, Distance, Distance and Distance Intersection 22.09.2018 Vehicular Communication Technology

Vehicular Communication Technology DGPS Differential GPS can improve accuracy from several meters to a few centimeters 22.09.2018 Vehicular Communication Technology

Vehicular Communication Technology However… Vehicles may be unequipped with GPS or sometimes cannot obtain line-of-sight access to satellites (in tunnels) In order to discover their position (or at least driving direction), GPS-U vehicles can use communication with GPS-E vehicles GPS-U periodically broadcasts PREQ message to its one-hop neighbors When GPS-E receives PREQ, it sends back PREP message including its current position The knowledge of the exact position depends on the number of neighbors sending PREP messages GPS-U can compute its exact position if it receives at least three PREP from three different vehicles (by triangulation) 22.09.2018 Vehicular Communication Technology

Vehicular Communication Technology Thank You! 22.09.2018 Vehicular Communication Technology