UCAM-CL-TR-741: Vehicular wireless communication
tech-r...@cl.cam.ac.uk
Vehicular wireless communication
David N. Cottingham
Technical report UCAM-CL-TR-741, University of Cambridge,
Computer Laboratory, PhD thesis, January 2009, 264 pages.
This document is now available at
http://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-741.html
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.
--
University of Cambridge, Computer Laboratory,
Technical Reports (ISSN 1476-2986)
http://www.cl.cam.ac.uk/techreports/