Comparison of Fourier and Trigonometric Transform based Multicarrier Modulations for Visible Light Communication

Year 2024, Volume: 19 Issue: 2, 397 - 405, 30.09.2024

Selva Muratoğlu Çürük

https://doi.org/10.55525/tjst.1452146

Abstract

It is predicted that the radio frequency spectrum will be insufficient in the near future due to the increase in wireless data. Visible Light Communication (VLC) is an alternative solution, which promises high speeds. Similar to other wireless communication systems, VLC systems prefer Multicarrier Modulation (MCM), but the signals are converted to be real and unipolar before transmission for optical communication. In this paper, two optical MCM groups that utilize Discrete Fourier Transform (DFT) and Discrete Trigonometric Transform (DTT) are questioned with respect to Bit Error Rate (BER), spectral efficiency and complexity. DFT based techniques use complex mapped signals together with their Hermitian symmetries to obtain real output signals, while DTT based techniques already output real signals when the input signal is real mapped. It is seen that DFT based techniques have lower BERs because of used mapping. DTT based techniques improve spectral efficiency, but they are limited to real mappings with higher error rates. For both transformations, the real signals are made unipolar by adding a bias (DCO-MCM), by asymmetrically clipping (ACO-MCM) or by sending positive and negative values separately (UnO-MCM). It is shown that, adding a dc bias (DCO-MCM) increases BERs, where ACO-MCM and UnO-MCM have close performances with lower BERs.

Keywords

Bit Error Rate, Discrete Fourier Transform, Discrete Trigonometric Transform, Multicarrier Modulation, Visible Light Communication.

Görünür Işık Haberleşmesi için Fourier ve Trigonometrik Dönüşüm Tabanlı Çok Taşıyıcılı Modülasyonların Karşılaştırılması

Abstract

Kablosuz verideki artış nedeniyle yakın gelecekte radyo frekans spektrumunun yetersiz kalması ön görülmektedir. Görünür Işık Haberleşmesi (VLC) yüksek hız vaat eden alternatif bir çözümdür. VLC sistemleri, diğer kablosuz haberleşme sistemlerine benzer şekilde, Çoklu Taşıyıcılı Modülasyon (MCM) tercih ederler, ancak optik iletişim için iletimden önce sinyaller gerçek ve tek kutuplu olacak şekilde dönüştürülürler. Bu makalede, Ayrık Fourier Dönüşümü (DFT) ve Ayrık Trigonometrik Dönüşümü (DTT) kullanan iki optik MCM grubu Bit Hata Oranı (BER), spektral verimlilik ve karmaşıklık açısından sorgulanmaktadır. DFT tabanlı teknikler, gerçek çıkış sinyali elde etmek için karmaşık eşlemeli sinyaller ve onların Hermit simetrilerini kullanırlar, DTT tabanlı tekniklerde ise giriş sinyali gerçek eşlenmiş ise çıkış zaten gerçek olacaktır. DFT tabanlı tekniklerin kullanılan eşleme nedeniyle daha düşük BER'lere sahip oldukları görülmektedir. DTT tabanlı teknikler spektral verimliliği arttırır ancak bu teknikler daha yüksek hata oranlarına sahip gerçek eşlemelerle sınırlıdırlar. Her iki dönüşüm için de gerçek sinyaller, bir öngerilim eklenerek (DCO-MCM), asimetrik olarak kırpılarak (ACO-MCM) veya pozitif ve negatif değerleri ayrı ayrı göndererek (UnO-MCM) tek kutuplu hale getirilir. Dc bileşen eklemek (DCO-MCM) BER'leri arttırırken, ACO-MCM ve UnO-MCM in daha düşük BER'lerle yakın performanslara sahip oldukları gösterilmiştir.

Keywords

Bit hata oranı, ayrık fourier dönüşüm, ayrık trigonometrik dönüşüm, çok taşıyıcılı modülasyon, görünür ışık haberleşmesi.

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