Visible Light Communication (VLC) becomes a promising technology in the Optical Wireless Communication OWC field. VLC has been developed based on Optical Orthogonal Frequency Division Multiplexing (O-OFDM) in recent years. The Bit Error Rate (BER) performance for various O-OFDM is studied in this paper. The non-linearity characteristic of Light-Emitting Diode (LED), modulation constellation size, O-OFDM scheme, and channel types impacts the BER performance of VLC systems significantly. The proposed model utilizes the conVolutional encoder of 2/3 rate and seven memory cells in the transmitter with O-OFDM for BER enhancement.At the receiver, the Viterbi algorithm system is employed with hard or soft-decision decoding. The proposed system is evaluated in Line-of-Sight and Non-Line-of-Sight (NLOS) channels. In the NLOS model, Zero Forcing Equalizer (ZFE) with channel estimation is added at the receiver path for equalizing the multipath diffused components. This study proves the capability of the proposed system in mitigating the LED non-linearity and reducing BER. The simulation results show the Signal-to-Noise Ratio (SNR) enhancement of the exanimated O-OFDM-based softdecision between 7 to 10 dB for the BER 10-5 in the LOS model, and for the NLOS model, the BER can be improved from 0.02 up to 10-5 at SNR 45dB.
The increasing demand for bandwidth through modern applications and multimedia services has led to high-speed wireless communications. Optical Wireless Communications (OWC) encourages solutions that provide a higher data rate due to the large bandwidth available. In this paper, performance enhancement approaches will be studied and simulated for Visible Light Communication (VLC) as a case study. The Orthogonal Frequency Division Multiplexing (OFDM) systems are used to investigate Intensity Modulation/ Direct Detection (IM/DD) to improve the performance of VLC. The IM/DD in OWC requires positive real OFDM symbols, so there are many approaches to satisfy this requirement. This paper proposed a model of Asymmetrically Clipped DC-Biased Optical (ADO-OFDM) to use in OWC/VLC environment. The Proposed system has avoided the use of the noise cancelation technique that is used in traditional ADO-OFDM. The results show that the ADO-OFDM has the best spectral efficiency than DC-biased Optical (DCO-OFDM) and Asymmetrically Clipped Optical (ACO-OFDM). Also, it has better optical efficiency than DCO-OFDM with the equally overall Bit Error Rate (BER) at the same signal-to-noise ratio. Hamming channel coding/decoding with different code lengths is applied in various optical OFDM schemes for BER improvements. Furthermore, we simulate and analyze these optical OFDM systems with many modulation orders.
Visible light communications (VLC) and optical orthogonal frequency division multiplexing (O-OFDM) have recently been identified as hopeful wireless techniques. Asymmetrically clipped DC-biased O-OFDM (ADO-OFDM)is a modern performance enhancement technology used in VLC. This article proposes a performance improvement model using a novel approach that collaborates with ADO-OFDM and multiple-input multiple-output (MIMO) in different design scenarios. In the first scenario, the bit-error-rate (BER) performance improvement is examined using different setups of MIMO-ADO-OFDM with maximal ratio combining (MRC). 8 × 8 MIMO good performance can be attained with about 15 dB signal-to-noise ratio for BER = 10 −4 . Another scenario is to boost the spectral efficiency of MIMO-ADO-OFDM by employing spatial multiplexing (SMX). However, 8 × 8 MIMO with SMX can improve spectral efficiency eight times that of single-input single-output ADO-OFDM by fragmenting source data into numerous independent data streams. In the last scenario, multi-user MIMO is developed by adopting ADO-OFDM with zero-forcing equalisers, allowing each user to consume all available bandwidth. The proposed technologies are evaluated by comparison with other MIMO systems, different O-OFDM, and under a non-linear LED model.
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