Periodic OFDMA: A Low-PAPR Multiple Access Scheme for Uplink Communications in 5G and Beyond

Multiple access techniques are vital for 5G and beyond. While Orthogonal Frequency Division Multiple Access (OFDMA) is standard, its high peak-to-average power ratio (PAPR) reduces energy efficiency in uplink transmissions. This paper presents Periodic OFDMA (P-OFDMA), a novel multiple access scheme with reduced PAPR and computational complexity. By assigning subcarriers in a periodic pattern across the entire frequency band, P-OFDMA enhances frequency diversity and simplifies allocation. We also introduce two precoded variants: P-OFDMA-DCT and P-OFDMA-DFT. Comprehensive simulations comparing P-OFDMA with OFDMA and SC-FDMA show that P-OFDMA-DFT consistently achieves the lowest PAPR. Furthermore, the standard P-OFDMA scheme outperforms SC-FDMA in PAPR for low subcarrier-per-user scenarios and achieves better bit error rate (BER) performance under high delay-spread conditions. Notably, P-OFDMA and its variants reduce transmitter-side processing by up to an eightfold factor compared to SC-FDMA, greatly benefiting low-complexity uplink devices. Although receiver complexity increases, the overall system processing load decreases, yielding improved energy efficiency. Thus, P-OFDMA offers a robust, energy-efficient uplink solution for future wireless networks.

Physical Layer Authentication With Colored RIS in Visible Light Communications

We study a visible light communication (VLC) system that employs a colored reconfigurable intelligent surface (CRIS) based on dichroic mirrors that reflect light at tunable frequencies. A verifier can use the CRIS to authenticate transmissions by comparing received multicolor power profiles with expected patterns. Four CRIS configuration strategies are evaluated: a deterministic cyclic pattern, static random reflectance, dynamic random reflectance, and dynamic random permutation of fixed profiles. Randomized configurations, especially dynamic ones, achieve superior authentication, enabling a novel challenge-response physical-layer authentication scheme over CRIS.

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.