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Constructing Accurate, Space-Efficient, Wireless Coverage Maps for Vehicular Contexts
David N. Cottingham, Robert K. Harle, Andy Hopper
4th International Wireless Internet Conference (ICST WICON) 2008, November 2008, Hawaii, USA
Wireless connectivity for vehicles is a fast-growing market, with a plethora of different network technologies already in use. Surveys of the numbers of IEEE 802.11b/g access points in cities point to hundreds to thousands of networks within each square kilometre, with coverage areas that are not easily predicted due to the complexities of the urban environment. In order to take advantage of the diversity in wireless networks available, we need data concerning their coverage. Methods of generating such coverage maps that are accurate, space-efficient and easy to query are not a well addressed area. In this paper, we present and evaluate, using a large corpus of real-world data, novel algorithms for processing large quantities of signal strength values into coverage maps that satisfy such requirements.
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PDF (346 KB) (subject to the ICST Copyright terms)
Vehicular Wireless Communication
David N. Cottingham
Ph.D. dissertation, University of Cambridge Computer Laboratory, September 2008
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.
Dissertation PDF (3.77 MB)
Technical Report UCAM-CL-TR-741 PDF (3.6 MB)
Multi-Carrier Burst Contention (MCBC): Scalable Medium Access Control for Wireless Networks
Bogdan Roman, Frank Stajano, Ian Wassell, David N. Cottingham
Wireless Coommunications & Networking Conference (WCNC) 2008, Pages 1667--1672, March 2008, Las Vegas, USA
With the rapid growth of WLAN capability for mobile devices such as laptops, handhelds, mobile phones and vehicles, we will witness WLANs with very large numbers of active nodes for which very efficient medium access control techniques will be needed to cope with high loads and mobility. We propose a high performance solution based on an innovative node elimination algorithm that uses short and unmodulated bursts of energy during contention -- no data is exchanged. We also present a modified OFDM PHY layer, based on IEEE 802.11a, which allows sensing and bursting on individual subcarriers. We show that the protocol maintains a very low overhead and collision probability which lead to high and virtually constant network throughput at all analyzed network loads, even beyond 500 nodes. The protocol is validated by extensive simulation, comparing it against the IEEE 802.11a and SYN-MAC protocols.
PDF
(454 KB)
Exploiting Contextual Handover Information for Versatile Services in NGN Environments
Edson D. S. Moreira, David N. Cottingham, Jon Crowcroft, Pan Hui, Glenford Mapp, Renata M. P. Vanni
IEEE Second International Conference on Digital Information Management (ICDIM), Pages 506--512, October 2007, Lyon, France
Users in ubiquitous and pervasive computing environments will be much more empowered in ways to access and to control their navigation. Handover, the vital event in which a user changes the attachment point in a Next Generation Network, is an important occasion and the conditions and environment in which it is executed can offer relevant information for businesses. This paper describes the capabilities of a platform which intends to exploit contextual handover information offering a rich environment that can be used by access and content providers for building innovative context-aware multi-provided services. Based on ontologies, the technique not only eases the building of versatile services but also provides a comprehensive source of information both for enriching user navigation in the network as well as for the improvement of the provider's relationship with their customers.
PDF (1.282 MB)
Y-Comm: A Global Architecture for Heterogeneous Networking (Invited Paper)
Jon Crowcroft, David Cottingham, Glenford Mapp, Fatema Shaikh
3rd Annual International Wireless Internet Conference (WICON 2007), October 2007.
In the near future mobile devices with several interfaces will become commonplace. Most of the peripheral networks using the Internet will therefore employ wireless technology. To provide support for these devices, this paper proposes a new framework which encompasses the functions of both peripheral and core networks. The new architecture is called Y-Comm and is defined in a layered manner like the OSI model.
PDF (176 KB)
A Survey of Technologies for the Implementation of National-Scale Road User Charging
David N. Cottingham, Alastair R. Beresford, Robert K. Harle
Transport Reviews, Volume 27, Number 4, pages 499--523, Routledge, July 2007 (DOI: 10.1080/01441640701214304).
This paper surveys the technologies available for constructing a pervasive, national-scale road pricing system. It defines the different types of road pricing, the methods by which a vehicle's position can be determined, and then examines possible pricing regimes in the context of their technological requirements and implications. The issue of enforcement and the distribution of pricing policies are considered, and further complexities are outlined. An examination of the security aspects of such systems is made, focusing particularly on the need to ensure privacy using technological, rather than solely procedural, methods. The survey concludes that a pervasive, national-scale deployment is unlikely to be technically achievable in the short term.
PDF (365 KB)
(subject to the Taylor & Francis Copyright terms)
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MIPv6 Experimental Evaluation using Overlay Networks
Pablo Vidales, Carlos J. Bernardos, Ignacio Soto, David Cottingham, Javier Baliosian, Jon Crowcroft
Computer Networks, Volume 51, Number 10, Pages 2892--2915, Elsevier, July 2007.
Article on Science DirectThe commercial deployment of Mobile IPv6 has been hastened by the concepts of Integrated Wireless Networks and Overlay Networks, which are present in the notion of the forthcoming generation of wireless communications. Individual wireless access networks show limitations that can be overcome through the integration of different technologies into a single unified platform (i.e., 4G systems).
This paper summarises practical experiments performed to evaluate the impact of internetworking (i.e. vertical handovers) on the Network and Transport layers. Based on our observations, we propose and evaluate a number of inter-technology handover optimisation techniques, e.g., Router Advertisements frequency values, Binding Update simulcasting, Router Advertisement caching, and Soft Handovers. The paper concludes with the description of a policy-based mobility support middleware (PROTON) that hides 4G networking complexities from mobile users, provides informed handover-related decisions, and enables the application of different vertical handover methods and optimisations according to context.
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Performance of IEEE 802.11a in Vehicular Contexts
David N. Cottingham, Ian J. Wassell, Robert K. Harle
IEEE Vehicular Technology Conference (VTC), Spring 2007. April 2007, Dublin, Ireland, Pages 854--858.
A key component of intelligent transportation is the provision of adequate network infrastructure to support vehicle-to-vehicle and vehicle-to-roadside communication. In this paper we report on performance evaluations carried out using the IEEE 802.11a protocol at 5.2 GHz between a moving vehicle and a fixed base station. We concentrate our evaluation on realistic urban speeds and environments, observing that performance at very low speeds is degraded due to the presence of null zones. We vary the modulation scheme and analyse the spread of resulting throughputs. Our results have implications for multimedia and other real-time applications that will utilise vehicle-to-roadside connectivity.
PDF (175 KB)
(subject to the IEEE Copyright terms)
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A Vision for Wireless Access on the Road Network
David N. Cottingham, Jonathan J. Davies
4th International Workshop on Intelligent Transportation (WIT). March 2007, Hamburg, Germany.Metropolitan area wireless networks are currently being deployed in major cities around the world, whilst in tandem there has been much research into vehicle-to-roadside communication. New applications for vehicular networking become possible as blanket, low-cost, wireless networks begin to exist across cities, resulting in Connected Traffic, rather than isolated Connected Cars. We examine the nature of these applications, classifying them according to their distinguishing characteristics, and discussing their demands on the network architecture required. We then outline our current work on the language and compiler support required for the application developers in order to deploy applications on such networks. Also, we discuss current work on coverage mapping algorithms in order to enable better prediction of network conditions. Finally, we describe our forthcoming WiMAX deployment to create a larger-scale vehicular access testbed, and the Sentient Vehicles project. This work has important implications for the implementors of wireless networks on roads, and for developers designing applications to harness such connectivity.
PDF (100 KB)
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A Research Platform for Sentient Transport
David N. Cottingham, Jonathan J. Davies, Brian D. Jones
Works in Progress item in IEEE Pervasive Computing Magazine, Volume 5, Number 4, Oct-Dec 2006, Pages 63--64Describes the Sentient Vehicles project at the Computer Laboratory.
PDF (2.3 MB)
(subject to the IEEE Copyright terms)
A Sensor Platform for Sentient Transportation Research
Jonathan J. Davies, David N. Cottingham, Brian D. Jones
1st European Conference on Smart Sensing and Context (EuroSSC) 2006, Enschede, The Netherlands
(LNCS volume 4272, pages 226--229, 2006)This paper describes experiences and lessons learnt in the creation of a vehicle-based sensor platform, as part of research into sentient computing. We outline the requirements of such a platform; the sensors that have been deployed in it; the on-board infrastructure to facilitate logging and the deployment of context-aware applications; and the external communications provision. We focus particularly on the lessons learnt in the deployment, justifying and evaluating our approach. This analysis will be of use to others considering similar sensor platform deployments. We conclude with an outline of our ongoing research.
PDF (56 KB)
An Architectural Framework for Heterogeneous Networking
Glenford Mapp, David N. Cottingham, Fatema Shaikh, Pablo Vidales, Leo Patanapongpibul, Javier Balioisian, Jon Crowcroft
International Conference on Wireless Information Networks and Systems (WINSYS) 2006, Setubal, PortugalThe growth over the last decade in the use of wireless networking devices has been explosive. Soon many devices will have multiple network interfaces, each with very different characteristics. We believe that a framework that encapsulates the key challenges of heterogeneous networking is required. Like a map clearly helps one to plan a journey, a framework is needed to help us move forward in this unexplored area. The approach taken here is similar to the OSI model in which tightly defined layers are used to specify functionality, allowing a modular approach to the extension of systems and the interchange of their components, whilst providing a model that is more oriented to heterogeneity and mobility.
PDF (142 KB)
The Sentient Van
David N. Cottingham, Jonathan J. Davies, Brian D. Jones
Internal DTG Poster, December 2005
The sentient van project has created a vehicular platform into which many different sensors and applications are integrated, allowing re- search into Intelligent Transportation Systems (ITS), network con- nectivity on the move, and congestion charging. This poster overviews the infratructure deployed in the van, and the current research work being carried out.
PDF (419 KB)
Is Latency The Real Enemy in Next Generation Networks?
David N. Cottingham & Pablo A. Vidales
In Proc. First International Workshop on Convergence of Heterogeneous Wireless Networks (ConWiN) 2005, Budapest, Hungary.This paper positions the idea that apart from the network vertical handover latency effects on the TCP/IP stack, there is another challenge that shadows ubiquitous networking. The TCP-connection adaptation time required when roaming between two disparate wireless technologies can be even longer than the total handover period. Thus, the impact of the adaptation time needs to be minimised and considered when dealing with seamless networking in heterogeneous environments. We present an experimental testbed that has been used to characterise the latency during vertical handover. Later, we introduce the concept of adaptation time (ta) and show the experimental value of ta, obtained from the collected traces. Finally, we discuss the effects of ta on the TCP/IP stack during heterogeneous handovers. We conclude the paper proposing some solutions to minimise the adaptation time.
PDF
(389 KB)
Congestion-Aware Vehicular Traffic Routing Using WiFi Hotspots
David N. Cottingham, Jonathan J. Davies, Alastair R. Beresford
Proc. Communications Innovation Institute Workshop, May 2005, Cambridge, UK
Congestion on roads in the UK costs the economy an estimated £12 billion a year, a figure that is set to rise with increasing commuting distances and distance selling volumes. In cities, congestion on key routes must be managed to ensure smooth traffic flow, even at peak times.
We have investigated how vehicles' routes can be improved by using congestion data collected on the vehicles and distributed by wireless access points. Vehicles exchange data with these access points at regular intervals to provide near real-time information.
Our results show that even for a very simple topology (2 route alternatives), the improvements in average journey time can be up to 6%. With more complex cities the benefits will be far more significant.
Poster PDF (1.3 MB) Handout PDF (51 KB)
Research Interests in the DTG
David N. Cottingham
Presentation to the Digital Technology Group, January 2005, Cambridge, UK.A brief description of my research topics and interests. This is not by any means exhaustive and is very high-level, as it was a 5 minute presentation.
Powerpoint (66 KB)Possible Directions for Intervehicular Networking Research
This is for internal use only: please come and talk to me if you're interested in the data aggregation and networking issues involved.Collaborative Power Management in Wireless Mesh Networks
David N. Cottingham Part II Dissertation, University of Cambridge Computer Science Tripos, June 2004, Cambridge, UK.My undergraduate final year dissertation. Mobile nodes in mesh networks draw on limited energy resources. In most mesh routing protocols the metric used is latency. Hence, some nodes' energy resources become more rapidly exhausted than others', due to their location on low latency (and therefore high traffic) routes. In this project an energy-aware routing protocol was created, supporting reliable communication, that increased average node lifetime, and lowered the standard deviation in energy reserves throughout the network. These characteristics are crucial in applications where the failure of any one node is unacceptable: instead all fail approximately simultaneously, which then defines the length of a maintenance cycle.
PDF (2.3 MB)