Mike Warrington

• Deputy Head of Department
• Head of Radio Systems Research Group
• Head of Resources
• Head of Research Committee
• Coordinator of BEng/MEng Electrical and Electronic Engineering Degree
• Coordinator of BEng/MEng Communications and Electronic Engineering Degree

Professor of Radio Communications Engineering
Radio Systems Research Group

BSc (Durham), PhD (Leicester), CEng, FIET
T: +44 (0)116 252 2561
F: +44 (0) 870 130 2578
E: emw@le.ac.uk

Location: Room 10, R Block, Engineering

Main Research Interests:
Professor Warrington is head of the Radio Systems Group. The Group specialises in experimental studies of the influence of the propagation medium on radio systems and on the development of techniques to overcome or to take into account propagation related system performance limitations. An underlying theme of the projects is the development of a
better understanding of the effects of the atmospheric (principally the ionospheric) environment on the propagation characteristics of radio waves, and the development of techniques to account for these effects in radio system operation, development and planning. All of Professor Warrington's projects are experimentally based and involve the development, deployment and operation of equipment at a number of sites away from Leicester, for example over-sea paths in the Channel Islands in support of UHF studies and long distance paths (often in the Arctic) in support of investigations within the HF band.

Ionospheric radiowave propagation
Ionospheric radio wave propagation effects are of longstanding interest. Currently investigations have the following emphasis:

• An EPSRC supported experimental programme with transmitting equipment deployed in Sweden and Finland, and a direction finding receiver deployed near Leicester with
the aim of improving the ionospheric models of the trough. In addition, the delay and Doppler spread characteristics of the received signals are being measured, information which is of direct relevance to the operation and planning of digital communications systems (such as those used by shortwave broadcasters) operating in the HF frequency band. Appropriate statistical information to aid system planning will be input to the International Telecommunication Union.

• Continued development (currently supported by the abovementioned EPSRC grant) of our northerly-latitude engineering model, and its incorporation into prediction tools for use by the operational community and for system planning purposes. Plans are in hand to extend this work as part of a major international initiative to improve communications with civil aircraft operating on trans-polar routes.

• A new experimental programme currently being devised to further investigate the influence of ionospheric structures (convecting patches, etc) on various radio systems. This work is a development from the studies outlines earlier, and is in collaboration with the US Airforce Research Laboratory and a number of scientists at the Istituto Nazinale di Geofisica e Vulcanologia, Rome.

Adaptive multi-channel reception / HF MIMO
One of the major limitations in the performance of HF long range radio communications operating over paths subject to severe ionospheric distortion (e.g at northerly latitudes) is the imposition of large delay and Doppler spreads on the signal. The magnitude of these dispersions is such as to severely limit the data throughput capabilities of communication systems. Techniques have been investigated whereby the signals from several receivers connected to a spaced element antenna array are combined in such a way as to reduce the apparent level of dispersion by means of spatial filtering. Initial studies yielded very promising results and a paper on this topic was awarded
the 2002 IEE Maxwell Premium Prize.

Recent developments, in particular by the mobile radio community, with the aim of exploiting multi-path propagation to increase the data throughput through the use of multiple
antennas at both the transmitter and receiver (a so-called MIMO system) have been made for systems operating in the UHF radio bands with some significant success. The application of this technology to systems operating in the HF band has not yet received significant attention, and in order to address this issue a new experimentally based investigation with EPSRC support has been initiated. The project is being undertaken jointly with Durham Uiversity, and involves active collaboration with the University of Rennes 1. If, as we anticipate, our investigations in this area lead to useful improvements in HF communication capability, then we will be in a world-leading position to exploit this technology for systems operating within that radio band.

VHF / UHF propagation over sea paths
Measurements over two periods in excess of a year have recently been made to investigate the propagation characteristics of VHF and UHF signals propagating over the
sea. Initial studies were undertaken at frequencies around 300 MHz, of particular interest for communications between ships at the extreme limits of propagation. Subsequently, the study has been extended to 2 GHz to aid the development of tools available for the planning and operation of UHF systems, and appropriate statistical data have been provided to the International Telecommunication Union to improve the recommendations used by the industry in the planning of future systems.

Several issues arose when modelling the propagation characteristics observed in the experimental programmes. Whilst it is well known that local meteorological conditions
play an important role in determining the propagation characteristics of these types of radio link, we found that under certain conditions the atmospheric structure is well
understood and the propagation can be modelled to a reasonable accuracy whereas under other atmospheric conditions this is not the case. Proposals are currently being
developed for further funding to address this issue.

Recent Publications:
• N.Y. Zaalov, E.M. Warrington and A.J. Stocker. The simulation of off-great circle HF propagation effects due to the presence of patches and arcs of enhanced electron
density within the polar cap ionosphere. Radio Science, 38, (3), 1052, doi:10.1029/2002RS002798, 2003.
• N.Y. Zaalov, E.M. Warrington and A.J. Stocker. A ray-tracing model to account for off-great circle HF propagation over northerly paths. Radio Science, 40, doi:
10.1029/2004RS003183, 2005.
• E.M. Warrington and A.J. Stocker. Measurements of the Doppler and multipath spread of HF signals received over a path oriented along the mid-latitude trough. Radio Science
38, (5), 1080, doi:10.1029/2002RS002815, 2003.
• C.Y.D. Sim and E.M. Warrington. Signal strength measurements at frequencies of around 300 MHz over two sea paths in the British Channel Islands. Radio Science, 41,
RS3005, doi:10.1029/2004RS003207, 2006.