# Research

### Research Interests

Information Theory, Communication Theory, Coding Theory, Iterative Decoding, Fading Channels, Multiuser Detection, Digital Signal Processing, Wireless Communications, Satellite Communications, Free-Space Optical Communciations.

### Current Research Projects

Finite-Length Information Theory
European Research Council, Starting Grant 2011-2016 Shannon's Information Theory establishes the fundamental limits of information processing systems. A concept that is hidden in the mathematical proofs most of the Information Theory literature, is that in order to achieve the fundamental limits we need sequences of infinite duration. Practical information processing systems have strict limitations in terms of length, induced by system constraints on delay and complexity. The vast majority of the Information Theory literature ignores these constraints and theoretical studies that provide a finite- length treatment of information processing are hence urgently needed. When finite-lengths are employed, asymptotic techniques (laws of large numbers, large deviations) cannot be invoked and new techniques must be sought. A fundamental understanding of the impact of finite-lengths is crucial to harvesting the potential gains in practice. This project is aimed at contributing towards the goal of providing a unified framework for the study of finite-length Information Theory. The approach in this project will be based on information- spectrum combined with tight bounding techniques. The results of this project will be of benefit to areas such as communication theory, probability theory, statistics, physics, computer science, mathematics, economics, bioinformatics and computational neuroscience. |

Mismatched Decoding in Information Theory with Applications to Channel Modelling
Marie Curie Career Integration Grant, 2012-2016 The recent trend to communicate over short temporal durations undermines two key assumptions in the underlying communication-theoretic analysis, namely: 1) perfect knowledge of the stochastic nature of the channel may be difficult to acquire, a state of affairs which renders impossible the use of optimum decoding rules; 2) efficient analytical techniques valid for infinitely long transmission durations, such as large-deviation theory, are loose and of difficult theoretical justification and ought therefore to be replaced by tools valid for arbitrary transmission lengths. Similarly, the coding schemes used to attain the entropy or capacity limits often turn out to be inefficient. This projects aims at addressing these challenges by devising new tools, theoretical and practical, which expand the validity and usefulness of previous communication-theoretic methods. These new tools are inspired by common practice in two adjacent disciplines, i.e. physics (electromagnetic and quantum electrodynamics) and probability, and besides have the potential to impact not only the field of information theory, but quantum information theory and applied probability. |

### Past Research Projects

Achievable Information Rates of Bit-Interleaved Coded Modulation
Royal Society International Joint Project 2009-2011, with Alfonso Martinez Although widely used in the design of iterative systems, EXIT charts lack of operational meaning in terms of achievable rates. This project aims at providing such an operational meaning by using a mismatched decoding framework. Mismatched decoding theory allows for the natural modelling of iterative decoders, by which the information generated at each iteration modifies the mismatched decoding metric, and accordingly the achievable rates. More specifically, this project is aimed at exploring the precise way in which the achievable rates so determined can be related to common tools in iterative decoding analysis, such as density evolution or EXIT charts. We will apply the results to multiple-antenna, additive exponential noise, additive energy and discrete-time Poisson channels. |

Coding for Wireless Broadband Mobile Networks
Australian Competitive Grant, University of South Australia, 2005 Future wireless communication networks will need to support extremely high data rates in order to meet the rapidly growing demand for broadband applications such as high quality audio and video. Existing wireless communications technologies such as third generation cellular telephony and 802.11 wireless local area networks cannot support broadband data rates (of the order of hundreds of millions of bits per second) due to their sensitivity to severe wireless channel impairments such as the time-varying attenuation caused by user mobility. To make things even more difficult, there are limited resources such as the available frequency bandwidth, allowable transmission power and computational ability of portable devices. These difficulties may be overcome by designing clever data coding schemes (i.e. data transmission systems) specially suited for the wireless channel. In this project, we will develop new low-complexity high-performance coding schemes suitable for implementation in wireless broadband communication networks. |

Advanced Concepts for Future Broadband Wireless Networks
Department of Education, Science and Training, Australian Government, French-Australian Science and Technology Program, 2006-2008 |

Adaptive Broadband Wireless Communication
Australian Research Council Discovery Project 2008-2010, with Lars K. Rasmussen Key challenges for future broadband wireless communications networks are to provide high-data-rate wireless access, subject to limited resources in terms of available frequency bandwidth, allowable transmission power and computational ability of portable devices. Building upon our previous Discovery project, the aim of this project is to determine fundamental limits for broadband wireless communication systems, and to develop practical transmission schemes for achieving these limits. A theoretical design framework for practical coding structures will be developed, resulting in fundamental contributions to information theory and new designs for future broadband wireless applications. |