VANETs (Vehicular ad-hoc networks) are getting closer and closer to being a reality in everyday life. This technology based on vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications allows vehicles to connect through short/medium-range wireless links thus creating decentralised ad-hoc networks that supports messaging between cars.
VANETs’ messages will carry some standardised data about vehicles (e.g. their positions headings speeds…) so to enable innovative on-board services primarily addressing drivers’ safety and comfort such as advanced driver assistance systems (ADAS) real-time route optimisation traffic management in response to actual congestions travel-related information systems…
Thanks to work by IEEE and ETSI VANETs will use the correct adaptation of WiFi. As a transmission and medium access technology: IEEE 802.11p is the standard that defines enhancements required to support Intelligent Transportation Systems applications. The reasons for IEEE 802.11p’s success are pretty straightforward: (1) it has essentially the same structure as 802.11 a/b/g/n – hence it is widely known and WiFi intellectual properties can be reused; (2) it intrinsically supports some of the requirements of a MAC protocol for VANETs; more specifically it is decentralised reactive to topology changes involves a low protocol overhead supports priority and prevents blocking states.
Moreover various international (DRIVE C2X and TeleFOT) and national (SCOREF and simTD) field operational tests (FOTs) have been carried out successfully demonstrating IEEE 802.11p’s capabilities in real scenarios.
While it is clear that IEEE 802.11p will work and be sufficient tomorrow there is someone who is already thinking about solutions for the day after tomorrow.
Some recent studies (ETSI TR 102 861: Intelligent Transport Systems (ITS); On the Recommended Parameter Settings for Using STDMA for Cooperative ITS; Access Layer Part and ETSI TR 102 862: Intelligent Transport Systems (ITS); Performance Evaluation of Self-Organising TDMA as Medium Access Control Method Applied to ITS; Access Layer Part) have highlighted that VANETs based on IEEE 802.11p will show a poor performance under heavy congestion and in presence of obstacles (hence with hidden terminals) with a medium level of congestion. In both cases the determinism (delay delivery rate fairness among nodes) drops to unsatisfactory levels due to a large number of uncoordinated transmissions. These weaknesses will not be dramatic in the first years of the VANET era since only few nodes will be initially equipped but indeed new solutions facing these issues must be challenged today.
Since the main threat comes from wireless medium congestion today two main approaches are being studied by ETSI: Decentralised Congestion Control (DCC) (ETSI TS 102 687 v1.1.1 (2011-07) Intelligent Transport Systems (ITS); Decentralised Congestion Control Mechanisms for Intelligent Transport Systems operating in the 5 GHz range; Access layer part) and alternative MAC solutions.
However DCC is expected to mitigate the problem of protocol congestion but actually it has not been extensively studied yet and moreover it represents a partial solution since it does not solve the issue of hidden terminals. Conversely new MAC solutions are not obvious because they should solve the issues left open by IEEE 802.11p – concerning scalability determinism and hidden terminals – while preserving its main benefits of and moreover with a good backward compatibility with 802.11p (in order to preserve the investments of chipset makers).
Within ETSI STF395 alternative solutions (namely MS-Aloha and STDMA) based on slotted connection-oriented and decentralised protocols (i.e. TDMA – Time Division Multiple Access) were studied. Slotted protocols are indeed a very promising approach for VANETs: they provide determinism and reliability.
In particular MS-Aloha (developed and patented by ISMB) solves both the issues of hidden terminals and scalability (by a multi-hop slot allotment) and has already a unique proposal for backward compatibility. ISMB is looking for opportunities to investigate the practical feasibility and answer the question “Might it be the key to VANET 2.0?”.
This article has been written by Francesco Fileppo and Riccardo M. Scopigno – MLW Research Area Istituto Superiore Mario Boella Turin (IT)
About Instituto Superiore Mario Boella
Istituto Superiore Mario Boella (ISMB – www.ismb.it) is a research & innovation center operating in the Information and Communication Technologies (ICT) domain. Founded in 2000 by Compagnia di San Paolo and Politecnico di Torino today ISMB relies on the technological and process competences of around 150 researchers working in close cooperation with companies academia and Public Administration.
ISMB is organised in Research Areas focused on core sectors of ICT. Satellite navigation systems (Navigation Technologies) wireless sensor networks and pervasive systems (Pervasive Technologies) broadband communications and electromagnetic simulation (Multi-Layer Wireless Solutions) optical fibers (Photonics) cloud computing and applications for mobile devices (Information System Architectures & SW Technologies) and new paradigms for Information Management and Innovation Development.
Since 2010 ten years after its foundation ISMB has extended its activities to process innovation orienting its focus on priority themes of the European agenda. Such an evolution aims at exploiting excellences and results obtained by Research Areas into Strategic Programs that are interdisciplinary by nature. Smart Energy Smart City and Smart Health are the strategic programs tackled by ISMB representing the first step of a broader action aimed at high-value social projects.
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Original Publication Date: Tue 27 Nov 2012