Data Detection and Code Channel Allocation for Frequency-Domain Spread ACO-OFDM Systems Over Indoor Diffuse Wireless Channels

Future optical wireless communication systems promise to provide high-speed data transmission in indoor diffuse environments. This paper considers frequency-domain spread asymmetrically clipped optical orthogonal frequency-division multiplexing (ACOOFDM) systems in indoor diffuse channels and aims to develop efficient data detection and code channel allocation schemes. By exploiting the frequency-domain spread concept, a linear multi-code detection scheme is proposed to maximize the signal to interference plus noise ratio (SINR) at the receiver. The achieved SINR and bit error ratio (BER) performance are analyzed. A computationally efficient code channel allocation algorithm is proposed to improve the BER performance of the frequency-domain spread ACO-OFDM system. Numerical results show that the frequency-domain spread ACO-OFDM system outperforms conventional ACO-OFDM systems in indoor diffuse channels. Moreover, the proposed linear multi-code detection and code channel allocation algorithm can improve the performance of optical peak-to-average power ratio (PAPR

The Novel PAPR Reduction Schemes for O‐OFDM‐Based Visible Light Communications

In this chapter, we propose two novel peak-to-average power ratio (PAPR) reduction schemes for the asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) scheme used in the visible light communications (VLC) system. In the first scheme, we implement the Toeplitz matrix based Gaussian blur method to reduce the high PAPR of ACO-OFDM at the transmitter and use the orthogonal matching pursuit algorithm to recover the original ACO-OFDM frame at the receiver. Simulation results show that for the 256-subcarrier ACO-OFDM system a ~6 dB improvement in PAPR is achieved compared with the original ACO-OFDM in terms of the complementary cumulative distribution function (CCDF), while maintaining a competitive bit-error rate performance compared with the ideal ACO-OFDM lower bound. In the second scheme, we propose an improved hybrid optical orthogonal frequency division multiplexing (O-OFDM) and pulse-width modulation (PWM) scheme to reduce the PAPR for ACO-OFDM. The bipolar O-OFDM signal without negative clipping is converted into a PWM format where the leading and trailing edges carry the frame synchronization and modulated information, respectively. The simulation and experimental results demonstrate that the proposed OFDM-PWM scheme offers a significant PAPR reduction compared to the ACO-OFDM with an improved bit error rate

OFDM-PWM scheme for visible light communications

In this paper, we propose an improved hybrid optical orthogonal frequency division multiplexing (O-OFDM) and pulse-width modulation (PWM) scheme for visible light communications. In this scheme, a bipolar O-OFDM signal is converted into a PWM format where the leading and trailing edges convey the frame synchronization and modulated information, respectively. The proposed scheme is insensitive to the non-linearity of the light emitting diode (LED) as LEDs are switched ‘on’ and ‘off’ between two points. Therefore, the tight requirement on the high peak-to-average-power-ratio (PAPR) in O-OFDM is no longer a major issue. The simulation and experimental results demonstrate that the proposed scheme offers an improved bit error rate performance compared to the traditional asymmetrically clipped O-OFDM (ACO-OFDM)

A Novel PAPR Reduction in Filter Bank Multi-Carrier (FBMC) with Offset Quadrature Amplitude Modulation (OQAM) Based VLC Systems

The peak to average power ratio (PAPR) is one of the major problem with multicarrier-based systems. Due to its improved spectral efficiency and decreased PAPR, Filter Bank Multicarrier (FBMC) has recently become an effective alternative to the orthogonal multiplexing division (OFDM). For filter bank multicarrier communication/offset quadrature amplitude modulation-Visible light communication (FBMC/OQAM-VLC) systems is proposed a PAPR reduction technique. The suggested approach overlaps the proposed FBMC/OQAM-based VLC data signal with the existing signals. Non-redundant signals and data signals do not overlap in the frequency domain because data signals are scattered on odd subcarriers whereas built signals use even subcarriers. To reduce the effects of large-amplitude signal reduction, the suggested technique converts negative signals into positive signals rather than clipping them off as in conventional FBMC-based VLC systems. The PAPR reduction and bit error rate (BER) are realized using a scaling factor in the transformed signals. Complementary cumulative distribution function(CCDF) and BER are used to calculate the performance of the proposed approach. The presented study found that FBMC/OQAM-VLC systems to achieve a good trade-off between PAPR reduction and BER

PAPR reduction in multicarrier modulation techniques based visible light communication systems

Visible light communication (VLC) is an optical wireless communication (OWC) technology that has the potential to provide high data rate transmission for indoor applications. VLC is a promising alternative technology with a large and unlicensed spectrum to complement the congested radio frequency (RF) based communication in order to meet the exponential growth and popularity of smart devices, data intensive services and applications. The use of low-cost commercially available front-end devices further highlights the attraction of VLC system. However, nonlinear dynamic range of front-end devices and optical channel impairments limit full exploitation of VLC available modulation bandwidth. To fully benefit from the inherent resources and mitigate these limitations, multicarrier modulation (MCM) techniques are adopted. However, these techniques are affected by high peak-to-average power ratio (PAPR) which imposes constraints on the limited dynamic range of the front-end devices and the average radiated optical power. The main focus throughout this thesis is to reduce the high PAPR of MCM modulation techniques-based VLC system by implementing pilot-assisted (PA) technique. Additionally, performance of PAPR reduced modulation techniques is investigated through analytical, simulation, and experimentally. This thesis first presents background of VLC system principles including the front-end devices, VLC channel, system impairments and challenges, and employed solutions. The principles, limitations, and performance of MCM modulation variants that are implemented in this work are presented. Moreover, principles of PAPR challenge in MCM based VLC, PAPR evaluation, impact on the transmitted signal as well as the existing PAPR reduction techniques are discussed. Looking at the gap, a PA is implemented as PAPR reduction technique which is presented in this work including its implementation and performance. Following that, multiple experimental studies on PAPR reduction of PA technique are presented. Two experimental demonstrations on the efficacy of PA PAPR reduction for PAM-DMT and DCO-OFDM based VLC using a single blue LED are presented. These studies are comparing the bit-error-rate (BER) performance of the proposed systems with conventional counterparts over a range of sampling rate. This shows that, the proposed systems perform better than conventional systems without PAPR reduction. The results are validated through simulation. Other two experimental studies on the previous systems with parameters optimisation and available modulation bandwidth utilisation are presented, which show that the proposed systems outperform the conventional systems in terms of BER. This is followed by investigating the PA PAPR reduction effect on the achievable data rate of a wavelength division multiplexing (WDM) based VLC system using three different LEDs for PAPR reduced DCO-OFDM and PAM-DMT systems. The proposed systems have achieved more than 8% data rate higher than that of conventional systems without BER performance degradation. Finally, analytical investigation of clipping noise that leads to distortion in a VLC system due to front-end devices limitations is presented. To mitigate the clipping noise, PAPR of the system is reduced by the PA technique. The analytical BER performance of the system with PAPR reduction is verified through simulation and then compared to that of the conventional system without PAPR reduction at similar clipping levels. The PA proposed system shows better BER performance at all clipping levels

Doubly Orthogonal Wavelet Packets for Multi-Users Indoor Visible Light Communication Systems

Visible Light Communication (VLC) is a data communication technology that modulates the intensity of the light to transmit the information mostly by means of Light Emitting Diodes (LEDs). The data rate is mainly throttled by the limited bandwidth of the LEDs. To combat, Multi-carrier Code Division Multiple Access (MC-CDMA) is a favorable technique for achieving higher data rates along with reduced Inter-Symbol Interference (ISI) and easy access to multi-users at the cost of slightly reduced compromised spectral efficiency and Multiple Access Interference (MAI). In this article, a multi-user VLC system is designed using a Discrete Wavelet Transform (DWT) that eradicates the use of cyclic prefix due to the good orthogonality and time-frequency localization properties of wavelets. Moreover, the design also comprises suitable signature codes, which are generated by employing double orthogonality depending upon Walsh codes and Wavelet Packets. The proposed multi-user system is simulated in MATLAB software and its overall performance is assessed using line-of-sight (LoS) and non-line-of-sight (NLoS) configurations. Furthermore, two sub-optimum multi-users detection schemes such as zero forcing (ZF) and minimum-mean-square-error (MMSE) are also used at the receiver. The simulated results illustrate that the doubly orthogonal signature waveform-based DWT-MC-CDMA with MMSE detection scheme outperforms the Walsh code-based multi-user system