On the Performance of Single- and Multi-carrier Modulation Schemes for Indoor Visible Light Communication Systems

In this paper, we investigate and compare the performance of single- and multi-carrier modulation schemes for indoor visible light communication (VLC). Particularly, the performances of single carrier frequency domain equalization (SCFDE), orthogonal frequency division multiplexing (OFDM) and on-off keying (OOK) with minimum mean square error equalization (MMSE) are analyzed in order to mitigate the effect of multipath distortion of the indoor optical channel where nonlinearity distortion of light emitting diode (LED) transfer function is taken into account. Our results indicate that SCFDE system, in contrast to OFDM system, does not suffer from high peak to average power ratio (PAPR) and can outperform OFDM and OOK systems. We further investigate the impact of LED bias point on the performance of OFDM systems and show that biasing LED with the optimum value can significantly enhance the performance of the system. Bit-interleaved coded modulation (BICM) is also considered for OFDM and SCFDE systems to further compensate signal degradation due to inter-symbol interference (ISI) and LED nonlinearity.Comment: 6 Pages, IEEE Globecom conference 201

Orthogonal space time coding for IM/DD optical wireless communication with single carrier frequency domain equalization

Recently the development of optical wireless communication has received growing attention because of its unlimited bandwidth and simple implementation as compared to radio frequency communication application for indoor wireless data transmission. The objective of this thesis is to improve the performance of intensity-modulated direct- detection (IM/DD) optical wireless communications with single carrier frequency domain equalization (SCFDE) by using Orthogonal Space Time Code (OSTC). More attention has been paid to three SCFDE schemes due to their outstanding performances in practical cases. It is demonstrated that OSTC can be modified to be suitable to optical systems and provide an excellent enhancement to system performances. By applying 4x4 OSTC that was formally used extensively in radio frequency communications, the performance of optical wireless systems with SCFDE is to be improved remarkably. It is pointed out that there exist some differences of the application of OSTC in between radio frequency communications and optical wireless communications. The performances, such as Peakto-average Power ratio, complexity and Bit-error rate, are compared and discussed. Finally the optical system, which has the best performance, is proposed and extended with multiple LEDs and Photodiodes

Single carrier optical FDM in visible light communication

In this paper a comparison between a spiral and a strip shaped LED is presented in terms of the maximum link distance achievable in visible light based car to car communications (VLC-C2C). The transmitted data is recovered from the frame brightness of the video signal. The intensity modulated LED is captured from two scenarios, using a focused and unfocused camera. A data rate of 180 bps with the bit error rate performance below the FEC limit of 10-3 at a distance of 100 cm is successfully achieved, sufficient for transmitting road safety messages for VLC-C2C. It is shown that under the same conditions, the strip LED can effectively recover the data from a greater distance than its spiral counterpart

Single-carrier frequency domain equalization using subband decomposition for optical wireless communications

Optical wireless communication is intended to be applied into indoor and visual distance high-rate data transmission, which is complementary to radio frequency communications. There are specific problems and requirements in optical wireless communications compared with radio frequency communications. Single-carrier frequency domain equalization (SCFDE) is a transmission scheme which has been considered as an alternative of orthogonal frequency-division multiplexing (OFDM), because it has most of the advantages of OFDM and avoids the problems of OFDM. Subband decomposition is a multi-resolution signal analysis and synthesis method, using quadrature mirror filter (QMF) bank to convert time-domain signal to frequency-domain subbands. As a time-to-frequency transform, subband decomposition technique can be employed to frequency domain equalization. Compared with the commonly used discrete Fourier transform (DFT), subband transform is more flexible and efficient to compensate the fading of frequency-selective channels. This thesis includes the theories of SCFDE, subband decomposition, subband equalization, and optical wireless transmission scheme. Also, simulations are given to demonstrate the processing of signals and the implementation of equalizers. The results show that the transmitted signal can be effectively equalized to compensate the channel fading, and the transmission scheme is appropriate for optical wireless communications

Unipolar-pulse amplitude modulation frequency division multiplexing for visible light communication systems

Asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) has been proposed in visible light communication (VLC) systems to overcome the dc-biased optical OFDM power consumption issue at the cost of the available electrical spectral efficiency. Due to the implementation of inverse fast Fourier transform, all the optical OFDM schemes including ACO-OFDM suffer from large peak-to-average power ratio (PAPR), which degrades the performance in VLC systems as the light-emitting diodes used as the transmitter have a limited optical power-current linear range. To address the PAPR issue in ACO-OFDM, we introduce a unipolar-pulse amplitude modulation frequency division multiplexing by adopting the single carrier frequency division multiple access (SC-FDMA). This is achieved by considering a PAM as an SC-FDMA data symbol and inserting a conjugate copy of the middle and first SC-FDMA FFT output subcarriers after the middle and last subcarriers, respectively. Simulation results show that, for the proposed scheme, the PAPR is 3.6 dB lower compared with ACO-OFDM. The PAPR improvement is further analyzed with the simulation results demonstrating that the proposed scheme offers 2.5 dB more average transmitted power compared to ACO-OFDM

Performance Evaluation of a MIMO VLC System Employing Single Carrier Modulation with Frequency Domain Equalization

In this paper, a multiple input - multiple output (MIMO) visible light communications utilizing single-carrier modulation combined with frequency domain equalization is investigated. We study the repetition coding (RC) and spatial multiplexing (SMP) schemes and show that MIMO with RC offers improved performance compared with single input - single output system, however MIMO with SMP increases the spectral efficiency at the cost of bit error rate degradation

Diversity Based on Oversampling Technique for PAM-4 in Optical Wireless Communication Systems

This paper utilizes the concept of oversampling to achieve diversity for optical wireless communication (OWC) systems with four levels pulse amplitude modulation (4-PAM). We propose two contributions to the development of OWC applications. The first one is the implementation of realtime PAM-4 transmitter (Tx) using field-programmable gate array (FPGA). The second one is diversity using oversampling method which can be used to improve the system performance. In this case, each symbol is sampled more than two times, and, averages them all together.  The proposed method is fully verified by experimental demonstration for both Tx realtime implementation and the receiver (Rx). The digital PAM format from FPGA is converted to analog format by using a digital-to-analog converter (DAC). With the update rate of 400 Msps, the proposed OWC systems can provide the communication speed over 800 Mbps; and, only a few FPGA resource usages are consumed. The experimental results showed that the bit error rate (BER) free can be achieved applying diversity using oversampling with four taps. Additionally, the communication distances up to 14 m is successfully transmitted