Low Complex, Power E cient Modulation Schemes for VLC Systems and Hardware Implementation

Abstract

The rise of groundbreaking technologies such as massive machine-type communi cation (MTC), Internet of Things (IoT), and smart cities concepts have signi cantly emphasized the need for an alternative channel to alleviate the congestion in the Radio Frequency (RF) spectrum for wireless communication. To address this demand, Visi ble Light Communication (VLC) technology has emerged as a viable solution within the realm of optical wireless communication. VLC transmits information through the In tensity Modulation (IM) of Light Emitting Diode (LED) light and receives it through Direct Detection (DD) using a Photodiode at the receiver. Several variants of Opti cal Orthogonal Frequency Division Multiplexing (O-OFDM) have been developed within the constraints of this incoherent modulation technique in VLC, employing Hermitian symmetry. However, systems that employ IM/DD and rely on these O-OFDM modu lations encounter certain drawbacks in terms of spectral e ciency and energy e ciency and computational complexity. Furthermore, the utilization of O-OFDM schemes results in a high peak-to-average power ratio (PAPR), causing signi cant signal distortion when transmitted through nonlinear devices in the front end. Additionally, the rapid devel opment of high-speed 5G systems requires waveforms that o er exibility to meet the demands of vehicular communication technology based on VLC. These challenges em phasize the necessity for advanced multicarrier waveforms that preserve the bene ts of O-OFDM variations while e ectively addressing the aforementioned issues. A new PPAPR reduction technique called Top Samples Detection and Appending (TSDA) is proposed for an O-OFDM system. Unlike other PAPR reduction schemes such as Selected Mapping (SLM) and Partial Transmit Sequence (PTS), the TSDA technique does not rely on side information, making it more e cient and practical. The TSDA technique works by identifying and modifying the high-amplitude samples in the OFDM Abstract viii signal. It employs a two-step process: detection and appending. In the detection, the TSDA algorithm identi es the top samples with the highest magnitudes in each OFDM symbol. These top samples are the primary contributors to the high PAPR. Once the top samples are detected, the appending step modi es these samples by appending top samples at the tail of the actual sequence. This modi cation e ectively reduces the overall PAPR of the signal. Importantly, the TSDA technique achieves this without requiring any additional side information, which simpli es its implementation and reduces computational complexity. To evaluate the e ectiveness of the TSDA technique, the proposed method is compared with established PAPR reduction schemes like SLM and PTS. Performance metrics such as PAPR reduction, computational complexity, and bit error rate (BER) are considered in the comparison. Subsequently, a novel modulation scheme called LADO-OFDM for VLC systems has been introduced. The primary goal of this technique is to mitigate the mutual inter ference between even subcarriers, which are associated with DC-biased Optical OFDM (DCO-OFDM) and ACO-OFDM, during transmission. This is achieved through the uti lization of a pre-distortion technique. To assess the e ectiveness of LADO-OFDM, two generalized LED models have been examined. The investigation focuses on the impact of nonlinear clipping distortion on the LEDs bias point and dynamic range. By applying pre-distortion to the transmitted signal and adjusting the knee factor in the piecewise polynomial model and Rapps models, respectively, the LEDs dynamic range can be lin earized, thereby enhancing the performance of the system. The performance of the pro posed system is then compared to that of ADO-OFDM in terms of bit error rate (BER) and computational complexity. The comparison is based on simulation results obtained through Monte Carlo BER simulations. Consequently, a new modulation scheme called Variably-biased Asymmetrically clipped Optical OFDM (VAO-OFDM) for VLC systems is proposed. Unlike traditional constant DC bias methods, VAO-OFDM utilizes a variable bias that is dependent on speci c samples. By aligning the frequency components of VAO-OFDM with pre-de ned subcarriers, the variable bias does not cause any interference with the initially transmitted symbols. This bias design can helps to mitigate potential signal degradation and improve overall transmission quality. One notable advantage of VAO-OFDM over its counter Abstract ix parts is its reduced computational complexity. By incorporating a pre-distortion process, VAO-OFDM achieves a signi cant decrease in computational requirements compared to ADO-OFDM. This reduction in complexity allows for more e cient implementation and utilization of system resources. To validate the performance of VAO-OFDM, we conducted simulations and presented the corresponding results. Additionally, we also implemented the proposed modulation scheme on an experimental Testbed using LabView software and Universal Software-de ned Radio Peripherals (USRPs). These practical validations help to demonstrate the feasibility and e ectiveness of VAO-OFDM in real-world VLC systems. Finally, a novel modulation scheme called Variably-biased Asymmetrically-clipped Optical Conjugate-symmetric Sequency-ordered Complex Hadamard Coded Modulation (VAO-CS-CHCM) is proposed for VLC systems. The objective of this scheme is to en hance power e ciency by leveraging the bene ts of a discrete set of amplitudes gen erated through Conjugate Symmetric Sequency-ordered Complex Hadamard Transform (CS-SCHT). VAO-CS-CHCM introduces a new approach to bias design like in VAO OFDM, where the bias is dependent on speci c sample amplitudes. Additionally, the frequency domain signals of VAO-CS-CHCM are distributed across pre-de ned subcar riers, similar to the VAO-OFDM scheme which is initiated in the previous contribution. This VAO-CS-CHCM ensures that the originally transmitted symbols remain una ected by any interference, resulting in signi cant gains in power e ciency. Further, the sim ulation results are presented to evaluate the performance of VAO-CS-CHCM compared to traditional modulation schemes such as VAO-OFDM, DCO-OFDM, ACO-OFDM, and ADO-OFDMover a wide range of bit rates and normalized bandwidths. Additionally, the computational complexity of VAO-CS-CHCM is analyzed in comparison to VAO-OFDM and ADO-OFDM