Computer Laboratory

Technical reports

Vehicular wireless communication

David N. Cottingham

January 2009, 264 pages

This technical report is based on a dissertation submitted September 2008 by the author for the degree of Doctor of Philosophy to the University of Cambridge, Churchill College.

Abstract

Transportation is vital in everyday life. As a consequence, vehicles are increasingly equipped with onboard computing devices. Moreover, the demand for connectivity to vehicles is growing rapidly, both from business and consumers. Meanwhile, the number of wireless networks available in an average city in the developed world is several thousand. Whilst this theoretically provides near-ubiquitous coverage, the technology type is not homogeneous.

This dissertation discusses how the diversity in communication systems can be best used by vehicles. Focussing on road vehicles, it first details the technologies available, the difficulties inherent in the vehicular environment, and how intelligent handover algorithms could enable seamless connectivity. In particular, it identifies the need for a model of the coverage of wireless networks.

In order to construct such a model, the use of vehicular sensor networks is proposed. The Sentient Van, a platform for vehicular sensing, is introduced, and details are given of experiments carried out concerning the performance of IEEE 802.11x, specifically for vehicles. Using the Sentient Van, a corpus of 10 million signal strength readings was collected over three years. This data, and further traces, are used in the remainder of the work described, thus distinguishing it in using entirely real world data.

Algorithms are adapted from the field of 2-D shape simplification to the problem of processing thousands of signal strength readings. By applying these to the data collected, coverage maps are generated that contain extents. These represent how coverage varies between two locations on a given road. The algorithms are first proven fit for purpose using synthetic data, before being evaluated for accuracy of representation and compactness of output using real data.

The problem of how to select the optimal network to connect to is then addressed. The coverage map representation is converted into a multi-planar graph, where the coverage of all available wireless networks is included. This novel representation also includes the ability to hand over between networks, and the penalties so incurred. This allows the benefits of connecting to a given network to be traded off with the cost of handing over to it.

In order to use the multi-planar graph, shortest path routing is used. The theory underpinning multi-criteria routing is overviewed, and a family of routing metrics developed. These generate efficient solutions to the problem of calculating the sequence of networks that should be connected to over a given geographical route. The system is evaluated using real traces, finding that in 75% of the test cases proactive routing algorithms provide better QoS than a reactive algorithm. Moreover, the system can also be run to generate geographical routes that are QoS-aware.

This dissertation concludes by examining how coverage mapping can be applied to other types of data, and avenues for future research are proposed.

Full text

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BibTeX record

@TechReport{UCAM-CL-TR-741,
  author =	 {Cottingham, David N.},
  title = 	 {{Vehicular wireless communication}},
  year = 	 2009,
  month = 	 jan,
  url = 	 {http://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-741.pdf},
  institution =  {University of Cambridge, Computer Laboratory},
  number = 	 {UCAM-CL-TR-741}
}