Visible Light Communications: Vehicular applications by Xavier Fernando Hasan Farahneh

Author:Xavier Fernando, Hasan Farahneh
Language: eng
Format: epub
ISBN: 9780750322843
Publisher: IOP Publishing
Published: 2019-11-08T00:00:00+00:00

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IOP Publishing

Visible Light Communications

Vehicular applications

Xavier Fernando and Hasan Farahneh

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Chapter 3

Optical OFDM basics

VLC channels have inherent scattering and reflection properties and undergo destructive effects of multipath dispersion. This results in ISI and leads to a reduced data rate. In order to mitigate ISI, time domain equalization (TDE) technique is used in single-carrier and OFDM is used in multi-carrier communication systems [1]. OFDM has been implemented in many wireless RF and wireline standards and has also proved to be beneficial in VLC systems [2]. O-OFDM schemes have better optical power efficiency, reduced ISI and very low BER, compared to conventional optical modulation schemes such as OOK and pulse position modulation (PPM) [3].

MIMO systems have gained considerable attention in VLC networks due to their high data rate capabilities over longer distances despite multipath dispersion interference effects. The combination of OFDM and MIMO is considered a powerful physical layer solution for high-speed vehicular VLC systems, especially for accommodating bandwidth-hungry applications [4].

Generally, the combination of MIMO and OFDM has been mostly used for non-adaptive systems with a single type of modulation. Few existing works have studied V2V–VLC MIMO systems using optical OFDM. Adaptive transmission in VLC has been explored before, but mostly for indoor applications [5]. Researchers have usually assumed a Gaussian channel with fixed modulation schemes in outdoor environments.

This chapter intends to give a brief introduction on optical OFDM, from its fundamental concepts to the up-to-date experimental results. Also, we introduce a study of a novel VLC algorithm for a V2V communication system using the channel model given in section 2.3. We use O-OFDM with adaptive modulation schemes to mitigate ISI and to improve data rate. We consider DCO-OFDM and ACO-OFDM schemes for our VLC system. We consider practical reflectors; sunlight is considered as the main noise source; the effect of clipping noise is also considered. Moreover, the performance of the V2V–VLC system is optimized by singular value decomposition (SVD) technique. Also, we apply bit-loading algorithm to improve the performance of the system.

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