1 Introduction
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We propose a cross-layer architecture for the Post Collision Notification (PCN) application.
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We show the impact of the application on the mobility patterns of vehicles after the notification messages are disseminated by means of the Distributed Robust Geocast protocol.
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We conduct a set of simulations and obtain experimental results that demonstrate the effectiveness of the proposed design for the PCN application.
2 Related work
3 Characterization of the post collision notification application
3.1 PCN application layer
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Parameters initialization: The application layer of the PCN is responsible of the initial phase, including parameters definition, such as: operational range of the application (in miles or kilometers), beacon intervals (in seconds) and the connection establishment with the Global Positioning System (GPS) or urban mobility simulator.
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Data encapsulation: We propose a set of messages, so called the WaveAppMsg, following the modular design. A WaveAppMsg packet contains an identification number (ID), the header field, the data and an optional field. The data correspond to the geographical coordinates of the emergency event; for PCN, an additional field is employed to indicate the accident status, showing that either the accident is ongoing or it has been successfully resolved.
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Accidents detection: To avoid collisions with new arrival vehicles in the scene of a previous accident, PCN detects and notifies when there is a stopped vehicle on the road due to an accident. According to the speed and deceleration, PCN calculates an abruptly halt and triggers the notification event called accident signal.
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Triggering of the sending mechanism: PCN starts the data dissemination process once the event trigger -accident signal- is launched right after the accident’s detection. This layer also defines the periodicity and the amount of packets to send through the VANET.
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Vehicle position retrieval: PCN requires the up-to-date geographical location of the vehicle, so as to deliver reliable information about an occurred accident within actual coordinates. The application layer employs geo-data from a GPS or a road network simulator.
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Data storage: Once data are delivered to the destination, each recipient node stores the information related to the accident. The reason is to update nearby drivers about road events and to maintain traffic data for statistical and mobility purposes.
3.2 Network requirements for PCN
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Participants: it specifies if it is a Vehicle-to-Vehicle (V2V) or a Vehicle-to-Infrastructure (V2I) communication.
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Latency: it defines the total delay experienced from the time the packet is sent by the source to the moment it is delivered to the recipient: low (< 100 ms) and medium (> 100 ms). This parameter provides message priority information.
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Region of interest: it describes the geographical range of the application: long (> 1500 m), medium (~1000 m) and short (< 500 m).
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Geo-location: it describes if the vehicle’s position in the geographical coordinate system is necessary to perform any data process.
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Recipient pattern: it describes the message receiver’s pattern. In other words, it says to whom the messages emitted have to be transmitted. The pattern can be one-to-many, one-to-a-zone, one-to-one, and many-to-one.
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Trigger: it states how the application is triggered. There are three different modes; Beacon mode (periodic), event-triggered mode (event driven), and user-initiated-on-demand mode (user-initiated).
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Routing protocols: this network attribute is highly related to the Recipient pattern criterion. There are four different categories: broadcast (one-to-many) and geocast (one-to-a-zone) for safety applications, and unicast (one-to-one) and aggregation (many-to-one), which are more suitable for commercial applications. As we want to cover the direct neighbor of the crashed vehicle with PCN messages, we will favor the geocast routing scheme.
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Message packet format: it specifies the network packets format used to encapsulate application messages. There are two standards from which the application’s designer can choose, the Internet Protocolv6 (IPv6) or the WAVE Short Message Protocol (WSMP) [12].
Parameter | Value |
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Participants | Car-to-Car (V2V) |
Max. End-to-End delay | Low (< 100 ms) |
Infrastructure | Not required |
Region of interest | Medium (< 1500 m) |
Geo-location | GPS/Simulator |
Recipient pattern trigger | One-to-a-zone |
Time-to-live | Event-triggered |
Routing protocol | Multi-hop |
Packet format | Geocast |
Channel frequency | WAVE Short Message (WSM) Control Channel (CCH) |
4 Geocast routing scheme for the PCN application
4.1 DRG protocol aspects
4.2 Forwarding mechanism of DRG
5 Simulation tools and ICT for vehicular communications research
5.1 Simulation setup of PCN application on the V2V domain
5.2 Simulation scenario
Parameter | Car | Truck |
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Acceleration (m/s2) | 2,6 | 2,6 |
Deceleration (m/s2) | 4,5 | 3,5 |
Max. Speed (m/s) | 14 | 11 |
Min. Gap (m) | 3 | 3 |
Length (m) | 3 | 5 |
Driver’s Dawdle σ | 0,5 | 0,5 |
Parameter | Value |
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Application | |
Beacon interval | 0,1 s |
Routing data length | 320 bit |
Max. power | 20 mW |
Connection Mng daturation | −89 dBm |
Mac carrier frequency | 5,890e9 Hz |
Mac. 1609.4. Tx power | 20 mW |
Mac1609.4. bitrate | 18 Mbps |
Phy 80211p sensitivity | −89 dBm |
Phy 80211p. Max Tx power | 10 mW |
Antennas' high | 1895 m |
Simulation area | 4500 m × 6000 m |
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End-to-End Delay: it is the time elapsed since a packet is sent by the application layer at the source node until the recipient node’s application layer receives the packet [23]. The latency is a common metric used to show the effect of larger areas to cover and also the impact of nodes on the performance of the protocol.