Enhanced Filterless Multi-Color VLC via QCT

Color shift keying (CSK) in visible light communication (VLC) often suffers from filter-induced crosstalk and reduced brightness. This paper proposes using quartered composite transform (QCT) with multi-color light-emitting diodes (LEDs) to improve both illumination and communication. The proposd DC-biased QCT scheme eliminates receiver optical filters, thereby removing crosstalk and significantly increasing signal-to-noise ratio (SNR). Simulations demonstrate QCT maintains high illumination quality (CRI 79.72, CCT 3462 K) while achieving over double the average illuminance compared to CSK under the same power budget. QCT also shows better bit error rate (BER) performance in low-to-moderate SNR regimes and has ability to convert multi-tap frequency-selective channel into an equivalent single-tap flat-fading channel to mitigate inter-symbol interference (ISI), proving a promising technique for brighter, high-performance, filter-less VLC.

Optimizing Visible Light Communication Efficiency Through Reinforcement Learning-Based NOMA-CSK Integration

In this paper, we explore the use of Non-Orthogonal Multiple Access (NOMA) and Color Shift Keying (CSK) for Visible Light Communication (VLC) systems. VLC is a wireless communication technology that uses visible light as the carrier signal to transmit information. It has several advantages over traditional radio frequency communication, including higher bandwidth, lower interference, and greater security. We first provide an introduction to NOMA and CSK and explain how they can be applied to VLC systems. NOMA is a technique that allows multiple users to share the same frequency channel by allocating different power levels to each user. This enables more users to connect to a single VLC transmitter simultaneously, thereby improving system capacity and spectral efficiency. CSK, on the other hand, is a modulation technique that uses different colors of light to represent digital information. By changing the color of the transmitted signal, information can be encoded and decoded at the receiver. Next, we discuss how NOMA and CSK can be combined in VLC systems by using different power levels to represent different users. This allows for more efficient use of the frequency spectrum, as multiple users can share the same channel at the same time. Additionally, we examine the potential benefits of using NOMA and CSK together in VLC systems to increase data rate. Finally, we discuss how reinforcement learning, a machine learning technique used to train agents to make decisions based on environmental feedback, can be used to optimize NOMA-CSK-VLC networks by allowing agents to learn and adapt to changing network conditions. Overall, our paper provides insights into the benefits of combining NOMA and CSK for VLC systems, highlighting the potential for improving communication efficiency and performance.

A Novel Approach to Fair Power Allocation for NOMA in Visible Light Communication

This paper addresses the growing demand for high-bandwidth wireless data transmission by exploring Visible Light Communication (VLC) as an alternative to Radio Frequency (RF) communication. In indoor scenarios, VLC systems utilize existing lighting infrastructure for high-speed data transmission. To meet the data rate demands of 5G and beyond, the paper proposes Non-Orthogonal Multiple Access (NOMA) and introduces Empirical Fair Optical Power Allocation (EFOPA) to simplify resource allocation in NOMA. EFOPA integrates NOMA with VLC, utilizing the Artificial Bee Colony (ABC) optimization algorithm for offline resource allocation planning. The approach then derives a simplified power allocation equation from ABC outcomes, ensuring fair resource distribution among users. EFOPA is compared against existing power allocation methods, demonstrating superior fairness and reduced computational complexity. Numerical evaluations reveal EFOPA consistently outperforms other methods across various channel conditions, making it a robust and efficient solution for fair power allocation in NOMA-VLC systems.

A Novel Pre-Coding Based PAPR Reduction Scheme for IM/DD Systems

Orthogonal frequency division multiplexing (OFDM) is critical for high-speed visible light communication (VLC) transmission; however, it suffers from a high peak-to-average power ratio (PAPR) problem. Among PAPR reduction techniques, pre-coding methods have shown promising advantages such as signal independence and no requirement for signaling overhead. In this paper, we present a novel pre-coding method that combines discrete cosine transform (DCT) and discrete sine transform (DST) for VLC systems using OFDM. Our proposed approach, tailored specifically for intensity modulation and direct detection (IM/DD) systems, aims to further improve the PAPR reduction while preserving bit error rate (BER) performance. Simulation results demonstrate that the proposed method achieves more than a 6 dB reduction in PAPR compared to the DCT pre-coded method without significant degradation in BER performance.

Optical OFDM Waveform Construction by Combining Real and Imaginary Parts of IDFT

In optical communication systems, orthogonal frequency division multiplexing (OFDM) is widely used to combat inter-symbol interference (ISI) caused by multipath propagation. Optical systems which use intensity modulation and direct detection (IM/DD) can only transmit real valued symbols, but the inverse discrete Fourier transform (IDFT) or its computationally efficient form inverse-fast Fourier transform (IFFT) required for the OFDM waveform construction produces complex values. Hermitian symmetry is often used to obtain real valued symbols. For this purpose, some trigonometric transformations such as discrete cosine transform (DCT) are also used, however these transformations can eliminate the ISI only under certain conditions. In this paper, we propose a completely different method for the construction of OFDM waveform with IFFT to obtain real valued symbols by combining the real and imaginary parts (CRIP) of IFFT output electrically (E-CRIP) or optically (O-CRIP). Analytical analysis and simulation works are presented to show that compared to the Hermitian symmetric system, the proposed method slightly increases the spectral efficiency, eliminates ISI, significantly reduces the amount of needed calculation and does not effect the error performance. In addition, the O-CRIP method is less affected by clipping noise that may occur due to the imperfections of the transmitter front-ends.