27 November 2012
My research interest is focused on developing practical and theoretical frameworks for modelling antenna-channel interactions necessary to produce high-performance wireless systems in terms of spectral efficiency and energy efficiency. I put great emphasis on the characterisation of the transmission properties of wireless communication systems by studying the fundamental characteristics of propagation channels, their deterministic and stochastic behaviours as well as the underlying mechanisms. In my research I try to combine signal processing and electromagnetic theory by exploiting the spatial, the directional and the wave polarisation domains of the transmitted signals. As a part of my doctoral dissertation I developed a formalism based on mathematical physics offering an exploration framework for antenna-channel interactions. It integrates a deterministic modelling of antennas with a characterization of the stochastic propagation channels on the basis of the fundamental laws of physics. As a result of this research I have discovered physical limitations on the antenna gain patterns in wireless propagation channels.
The Multiple Input Multiple Output (MIMO) technologies achieve system performance improvement by applying spatial processing techniques at the multiple antennas at both the transmit side and receive side of the communication link. Their performance depends on both the propagation channel and the antennas used for each specific application. My approach is based on a solution to Maxwell's equations given by a spherical vector wave (svw) multi-modal expansion of the electromagnetic field, and the scattering matrix representation of an antenna that provides a full description of all its properties as a transmitting, receiving or scattering device. In this Letter, I have obtained the antenna patterns that maximise the signal-to-noise ratio (SNR) of a communication link when maximum ratio combining (MRC) is applied at both the transmitter and the receiver. In the MRC, signals are weighted is such a way that the SNR per branch is maximised. The svw multi-modes have been used as the diversity branches. As a result, under these conditions, I have also derived the maximum SNR of the communication link when the antennas excite up to a desired multi-pole order of the svw multi-modes.
The development of IMT-Advanced is intended to bring significant enhancements to the existing 3GPP and WIMAX standards in terms of system throughput and quality of service in general. These enhancements require ultra-high spectral efficiency which is enabled, among others, by MIMO technologies. The main applications are systems that use multiple antennas at both the receiver and the transmitter sides of a communications, a sensor or a radar system.
This work shows the potential improvements in one specific application such as the joint MRC at the receiver and the transmitter. The next step is to provide experimental data and prototypes that put into work these results. Moreover, new performance metrics that integrates the different aspects of the performance of the devices and systems are being developed.
Antenna-channel interactions are required to be understood from different points of view. For example, the interaction with the environment is essential for developing energy efficient communications systems and devices. The environment should here be understood to comprise the user’s body as well. The development of new cost-efficient ways to test the performance of small and large antenna systems on communication devices are also of great interest to me.
I believe that a multi-disciplinary approach is required to bring a change of paradigms in the way we communicate among each other, how devices communicate among themselves and how we communicate with devices. Information theory, signal processing and electromagnetic theory will necessarily get closer in the way we solve new more demanding technical challenges. This, of course, is already happening.
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