Professor Jean Armstrong

AbstractThis paper investigates the effect of fractional linearmisalignment between the transmitter and the receiver for a pixelated MIMO optical wireless system using spatial orthogonal frequency division multiplexing (OFDM). The novelty of this work is in the modeling and analysis of fractional misalignment for spatial OFDM. It is shown that when the receiver is perfectly focused and when fractional misalignment is the only impairment, the received constellation points are phase shifted and attenuated. MATLAB simulations show that the impact of misalignment is the greatest when the fractional offset is equal to half of a pixel. Unlike integral misalignment, the use of equalizers cannot fully compensate the effect of fractional misalignment. It is revealed that when the fractional offset is half of a pixel, the offset causes bit error rate (BER) floor and the degradation is greater for a system with lower number of subcarriers than a system with larger number of subcarriers. We show that the BER degradation caused by fractional offset can be mitigated when a number of higher spatial.


M.R.H Mondal and J. Armstrong, Impact of linear misalignment on a spatial OFDM based pixelated system, (APCC), 2012 18th Asia-Pacific Conference on Communications, 15 October 2012 to 17 October 2012, pp. 617-622.

Abstract—White lighting LEDs offer great potential for high speed communications, especially for indoor applications. However, for their widespread adoption, two important issues need to be addressed. They are the lack of diversity in multiple-input multiple output (MIMO) systems and the small field of view of receivers. In this paper, we describe a design using a hemispherical lens in the receiver that solves these problems. By using classical optics, we derive exact expressions for the channel gain and the optical power density of the projected images. Simulation results of a typical indoor scenario show that the new system has a wide field of view, and provides adequate channel gain for angles of incidence as large as 70 degrees. We present the distribution of optical power on the imaging plane for a number of representative indoor scenarios for various receiving positions and tilted receivers. They show that the images of LEDs are clearly distinguishable. This demonstrates the presence of low channel correlations between individual transmitters and receivers. Consequently, this confirms that the new technique is capable of providing significant diversity order for MIMO optical wireless applications.

T. Q. Wang, Y. A. Sekercioglu, and J. Armstrong, "Analysis of an Optical Wireless Receiver Using a Hemispherical Lens With Application in MIMO Visible Light Communications," Journal of Lightwave Technology , vol. 31, pp. 1744-1754, 2013.

Recent papers on MIMO optical wireless communications.