Software-defined implementation of multi-point transmission schemes for multi-cell VLC systems

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master_Mummadi_Ramya_2025.pdf (2.48 MB)

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School of Electrical Engineering | Master's thesis
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Date

2025-07-29

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Communications Engineering

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Master's Programme in Computer, Communication and Information Sciences

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en

Pages

98

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Abstract

This MSc Thesis presents the design, implementation, and testing of coordinated multi-point transmission schemes for multi-cell Visible Light Communication (VLC) systems using a software-defined radio (SDR) approach. The proof-of-concept that has been developed uses GNU Radio and Universal Software Radio Peripheral (USRP) hardware to assess the actual data rate performance of a VLC setup under different modulation and interference conditions. Phosphor-converted white Light-Emitting Diodes (LEDs) act as transmitters, while photodetectors (PDs) take the role of receivers to create an optical wireless access link in an indoor setting. The experiments focus on defining coverage areas, data rates, and interference management strategies in both single-cell and two-cell VLC setups. Orthogonal Frequency Division Multiplexing (OFDM) serves as the modulation scheme that allows for efficient multi-carrier transmission. Transmission schemes such as Zero-Forcing Beamforming (ZFBF) and Joint Transmission (JT) are used at the transmitter side to mitigate the co-cell interference in signal overlapping areas. The results show that practical performance is limited by the narrow electrical modulation bandwidth of phosphor-converted white LEDs, despite high theoretical data rates. The effective cell radius in a single-cell scenario is about 150 to 160 cm. In a two-cell VLC setup, however, it was possible to find distinct spatial regions for the use of the different transmission schemes, namely frequency reuse (0 to 40 cm), ZFBF precoding (40 to 70 cm), and JT (70 to 85 cm). This offers detailed insight into the spatial interference behaviour in VLC networks. This software-defined proof-of-concept framework shows that low-complexity, coordinated VLC systems can be deployed in actual multi-cell VLC indoor settings. The obtained results also emphasize that white LEDs offer secure, stable communication by directing light to narrow light spots. This setup allows multiple VLC cells to operate in a single room with minimum interference between them. Therefore, when compared to RF systems, the gain of VLC systems is expected to come from the ultra-densification of small cells to cover an indoor area, rather than the increase of data rate per individual VLC link.

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Supervisor

Hämäläinen, Jyri

Thesis advisor

Dowhuszko, Alexis

Keywords

visible light communication, software-defined radio, indoor wireless communication, orthognal frequency division multiplexing, zero-forcing beamforming, joint transmission, co-channel interference, signal-to-interference-plus-noise ratio, bit error rate

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https://urn.fi/URN:NBN:fi:aalto-202508196326

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[dipl] Sähkötekniikan korkeakoulu / ELEC