Chair of Mobile CommunicationsProfessor Harald Haas

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The University of Edinburgh
The King's Buildings
Edinburgh EH9 3JL

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h(dot)haas(at)ed(dot)ac(dot)uk

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Professor Harald Haas

Chair of Mobile Communications

School of Engineering, University of Edinburgh

Read about my Research, Li-Fi, and the future of Mobile Communications.

Recent Posts from Professor Harald Haas:

  • Major Events in First Half of 2014:

    I had the great pleasure to be involved in a number of exciting events during the first half of 2014:

  • How Li-Fi is different from RF wireless

    By Majid Safari

    Based on Maxwell's theory of electromagnetics, the light and radio propagation follow the same rules of physics. However, the optical waves have significantly smaller wavelength compared to radio waves. This is particularly important when an approximation of Maxwell's theory is required. For example, the geometric wave theory is only applicable when electromagnetic wave interacts with structures much larger than its wavelength. In effect, Geometrical or ray optics can greatly simplify the analysis of optical propagation although it fails to describe some important phenomena such as diffraction. The small optical wavelength is also responsible for higher scattering of light by particles like fog droplets. The so-called Mie scattering solution to Maxwell equations describes the scattering of the electromagnetic radiation by particles with comparable-size or larger than the wavelength. On the other hand, for particles much smaller than the wavelength, the scattering of electromagnetic waves can be explained by Rayleigh scattering.

    Read more »

  • Optical Wireless Communication: The rebirth of an ancient technology

    By Majid Safari

    When you pack a survival kit for disaster and emergency situations, what kind of tools would you include? I bet a flashlight is one of them. Besides its obvious use, a flashlight can be toggled on and off to send Morse coded signals for requesting help and rescue. It is thus a good idea to always remember the Morse code for SOS: [•••−−−••• ]. This is a simple example of optical wireless communication: a technology that has been around for a long time over a wide range of applications with very simple to very sophisticated designs.

    Optical wireless communication refers to the transmission of data using light propagating through the air (or free space) without being guided by any waveguide structure such as optical fibre. The use of smoke signalling in ancient China, optical telegraphy (Heliography) based on mirror-based sunlight reflections in 19th and early 20th century, and the invention of photophone are some of the early examples of optical wireless communication. The photophone, invented by Alexander Graham Bell in 1880 (U.S. Patent 235,199), is indeed the most sophisticated design among these primitive optical wireless systems. It could transmit human conversation carried by a beam of light (sunlight) over an atmospheric link with a distance of few hundred meters. Despite the significant interests in the invention of the telephone, Bell believed that the photophone was "the greatest invention [he has] ever made, greater than the telephone" as he told a reporter shortly before his death.

    Read more »

     

  • Energy-efficient Li-Fi

    We have developed a new algorithm that avoids the typical 50% spectral efficiency loss in visible light communications when the LED is driven close to the turn-on voltage. This is an important breakthrough because the new algorithm enables energy-efficient Li-Fi links and dimming close zero. A typical scenario where this feature is instrumental is the communication link between a mobile terminal and the Li-Fi access point (uplink) where there is no need for additional illumination as opposed to downlink scenarios where the Li-Fi access point serves two functions - broadband data communication and room illumination. This paper will be presented at ICC 2014, 10-14 June 2014, Syndey (Australia).

  • Invited Paper

    This is a pre-print of an invited paper at SPIE Photonics West, 1-6 February 2013

  • PhD Projects

    I have announced a number of new PhD projects under Vacancies!

  • Latest JLT Paper

    Complete Modeling of Nonlinear Distortion in OFDM-based Optical Wireless Communication

    A pre-print is available for download.

    Abstract

    This paper presents a complete analytical framework for modeling memoryless nonlinear effects in an intensity modulation and direct detection optical wireless communication system based on orthogonal frequency division multiplexing. The theory employs the Bussgang theorem, which is widely accepted as a means to characterise the impact of nonlinear distortions on normally-distributed signals. The current work proposes a new method to generalise this approach, and it describes how a closed-form analytical expression for the system bit error rate can be obtained for an arbitrary memoryless distortion. Major distortion effects at the transmitter stage such as quantisation and nonlinearity from the light-emitting-diode are analysed. Four known orthogonal-frequency-division-multiplexing-based modulation schemes for optical communication are considered in this study: direct-current-biased optical OFDM, asymmetrically clipped optical OFDM, pulse-amplitude-modulated discrete multitone modulation, and unipolar orthogonal frequency division multiplexing.

  • Best Paper Award at VTC Fall 2013 Las Vegas 2 5 September 2013

    A. Younis, W. Thompson, M. Di Renzo, C.-X. Wang, M. A. Beach, H. Haas and P. Grant, "Performance of Spatial Modulation using Measured Real-World Channels", VTC-Fall, 2013, 2-5 September 2013.

    A pre-print can be downloaded.

  • IEEE Proceedings Paper on Spatial Modulation

    Spatial Modulation for Generalized MIMO: Challenges, Opportunities and Implementation

    A pre-print is available for download.

    Abstract

    The key challenge of future mobile communications research is to strike an attractive compromise between wireless network's area spectral-efficiency and energy-efficiency. This necessitates a clean-slate approach to wireless system design, embracing the rich body of existing knowledge especially on Multiple-Input-Multiple-Output (MIMO) technologies. This motivates the proposal of an emerging wireless communications concept conceived for single-RF large-scale MIMO communications, which is termed as Spatial Modulation (SM). The concept of SM has established itself as a beneficial transmission paradigm, subsuming numerous members of the MIMO system-family. The research of SM has reached sufficient maturity to motivate its comparison to state-of-the-art MIMO communications, as well as to inspire its application to other emerging wireless systems such as relay-aided, cooperative, small-cell, optical wireless and power-efficient communications. Furthermore, it has received sufficient research attention to be implemented in testbeds, and it holds the promise of stimulating further vigorous inter-disciplinary research in the years to come. This tutorial paper is intended to offer a comprehensive state-of-the-art survey on SM-MIMO research, to provide a critical appraisal of its potential advantages, and to promote the discussion of its beneficial application areas and their research challenges leading to the analysis of the technological issues associated with the implementation of SM-MIMO. The paper is concluded with the description of the world's first experimental activities in this vibrant research field.

  • IEEE Webinar

    I will be giving an IEEE Webinar entitled: "Li-Fi: High Speed Wireless Communications via Light Bulbs".

    Wednesday, 19 June 2013 at 10:00am (BST).

    Free registrations can be made online.

    The presentation can be download.

  • High Speed Wireless Networking Using Visible Light

    A new article has been publishedd in the SPIE newsroom.

  • Li Fi at the Edinburgh Science Festival

    Professor Harald Haas' Li-fi talk at the Edinburgh International Science Festival.

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