Ad-Hoc Networks
▶ Introduction
 

A Vehicular Ad hoc Network (VANET) is a form of Mobile Ad hoc Network (MANET). VANETs are distributed, self-organizing communication, and are characterized by high mobility, variable node density, and no limitation of energy and storage resources. In a vehicular network, vehicles are equipped with On-Board Units (OBUs) and roads are equipped with Road Side Units (RSUs). OBUs communicate with each other and with the RSUs in ad hoc manner. There are mainly two types of communication in vehicular networks: Vehicle-to-Vehicle (V2V) which is also called InterVehicle Communication (IVC) and Vehicle-to-RSU (V2R) or Vehicle-to-Infrastructure (V2I).

Fig. 1. VANET architecture


The US Federal Communication Commission allocated 75 MHz of the spectrum in the 5.9 GHz band, including one control channel (CCH) and six service channels (SCHs) for safety and non-safety applications, respectively.

The applications of VANETs fall into two categories, namely safety applications and non-safety applications. Safety applications have strict requirements on communication reliability and delay. On the other hand, non-safety applications are more throughput-sensitive instead of delay-sensitive. The requirements for different applications are shown in Table. 1.

Table 1. DSRC Application Requirements

Fig. 2. Frequency channel layout of a 5.9 GHz WAVE system


Wireless Access in Vehicular Environment (WAVE) is designed for an ITS on 5.9 GHz frequency with the IEEE 802.11p and IEEE 1609 standard family. The IEEE 1609.4 is the standard of the multi-channel operation for WAVE MAC. As shown in Fig. 2, each 100 ms Sync Interval (SI) allocates 50 ms for the CCHI and 50 ms for the SCHI, including 4 ms Guard Interval (GI) for switching between CCH and SCH. Nodes broadcast SMsgs or negotiate the SCHs on the CCH during the CCHI. Then, nodes switch to the negotiated SCHs for their non-safety messages transmissions. This channel access scheme has a high contention during the CCHI, and the resource of SCHs cannot be utilized during this interval.

The WAVE architecture is developed based on the IEEE 802.11p which deals with PHY and MAC and the IEEE 1609 which deals with the higher-layer protocols. The IEEE 1609 Family has defined four standards for WAVE:
IEEE 1609.1: Resource Manager
IEEE 1609.2: Security Services for Applications and Management Messages
IEEE 1609.3: Networking Services
IEEE 1609.4: Multi-Channel Operations



▶ Research Issues

 
  • Multi-channel MAC for VANETs: improve the non-safety application’s throughput.
  • Safety application dissemination in VANETs: Reliable, contention-free and delay-bounded transmission for safety applications.
  • Routing in VANETs: deals with highly dynamic topology, network partitions and time sensitive transmissions.


  • ▶ References

     
    1. Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, Amendment 6: Wireless Access in Vehicular Environments, 2010.
    2. IEEE 1609 - Family of Standards for Wireless Access in Vehicular Environments (WAVE)
    3. ZaydounYahyaRawashdeh and Syed Masud Mahmud, “Communications in Vehicular Networks”, www.intechopen.com
    4. Qing Xu , Tony Mak , Jeff Ko and Raja Sengupta. “Vehicle to Vehicle Safety Messaging in DSRC”, Proceedings of VANET 2004, USA.
    5. Ning Lu, YushengJi, Fuqiang Liu and Xinhong Wang. “A Dedicated Multi-Channel MAC Protocol Design for VANET with Adaptive Broadcasting” Proc. IEEE Wireless Communications and Networking Conf. (WCNC), 2010.
    6. Qing Wang, SupengLeng, Huirong Fu and Yan Zhang, “An IEEE 802.11p-based Multi-channel MAC Scheme with Channel Coordination for Vehicular Ad Hoc Networks”, IEEE Trans. on Intelligent Transportation Systems (ITS), 2011.
    7. C. Han, M. Dianati, R. Tafazolli, X. Liu and X. Shen. “A Novel Distributed Asynchronous Multi-Channel MAC Scheme for Large-Scale Vehicular Ad Hoc Networks”, IEEE Trans. on Vehicular Technology, vol. 61, p. 3125 - 3138, 2012.


    ▶ Achievements

     
    1. Duc Ngoc Minh Dang, ChoongSeon Hong, "A Multi-channel MAC Protocol for VANETs", KIISE 2012, CNU, Korea, Nov. 2012.
    2. Duc Ngoc Minh Dang, Hanh Ngoc Dang, Cuong T. Do, ChoongSeon Hong, "An Enhanced Multi-channel MAC for Vehicular Ad Hoc Networks", WCNC 2013, Shanghai, China, Apr 7-10, 2013 (accepted)