Jin-Yuan Wang

Channel capacity and receiver deployment optimization for multi-input multi-output visible light communications

Multi-input multi-output (MIMO) technique is attractive for visible light communication (VLC), which exploits the high signal-to-noise ratio (SNR) of a single channel to overcome the capacity limitation due to the small modulation bandwidth of the light emitting diode. This paper establishes a MIMO VLC system under the non-negativity, peak power and dimmable average power constraints. Assume that perfect channel state information at the transmitter is known, the MIMO channel is changed to parallel, non-interfering sub-channels by using the singular value decomposition (SVD). Based on the SVD, the lower bound on the channel capacity for MIMO VLC is derived by employing entropy power inequality and variational method. Moreover, by maximizing the derived lower bound on the capacity under the given constraints, the receiver deployment optimization problem is formulated. The problem is solved by employing the principle of particle swarm optimization. Numerical results verify the derived capacity bound and the proposed deployment optimization scheme.

On the Performance of Spatial Modulation-Based Optical Wireless Communications

This letter focuses on a spatial modulation (SM)-based multiple input single output optical wireless communication system. In the system, both input-dependent noise and finite alphabet are employed. Based on information theory, the theoretical expressions of the mutual information and its lower bound are derived. By maximizing the minimum distance, an optimization problem for precoding design is formulated. Then, an interior point method-based iteration algorithm is proposed to solve the problem. Numerical results show that the performance of the proposed SM scheme outperforms that of the conventional, choosing the best-gain channel scheme. Moreover, the proposed precoding scheme can provide better system performance than the scheme without precoding.

Sum Rate Maximization for VLC Systems With Simultaneous Wireless Information and Power Transfer

This letter investigates the sum rate maximization problem in a downlink visible light communication system with simultaneous wireless information and power transfer. To solve this nonconvex sum rate maximization problem, we first transform it into an equivalent convex problem. Then, we provide the optimal condition and propose a low-complexity iterative algorithm, which yields the optimal solution. Numerical results show that the proposed algorithm can achieve good performance.

Improvement of BER performance by tilting receiver plane for indoor visible light communications with input-dependent noise

In this paper, an indoor visible light communication (VLC) system with the input-dependent noise is considered. In the system, the main noise is caused by Gaussian noise, however, with a noise variance depending on the current input signal strength. In the presence of the input-dependent noise, the theoretical expression of the bit error rate (BER) for the VLC using on-off keying is derived. Based on the derived BER, an optimization problem is formulated to improve the BER performance by tilting the receiver plane. The proposed optimization problem is proven to be a convex optimization problem, which can be efficiently solved by using the specialized solver such as the CVX toolbox for MATLAB. To verify the accuracy of the derived expression of the BER, all theoretical results are thoroughly confirmed by using the Monte-Carlo simulations. Moreover, simulation results show that the larger the variance of the input-dependent noise is, the worse the BER performance becomes. Additionally, the BER performance can be dramatically improved by tilting the receiver plane properly.

Novel spectral efficient OFDM for optical wireless communication

This paper presents an enhanced hybrid asymmetrically clipped optical orthogonal frequency division multiplexing (OFDM) scheme referred to as EHACO-OFDM. The scheme uses asymmetrically clipped optical OFDM (ACO-OFDM) on the odd subcarriers, pulse-amplitude-modulated discrete multitone modulation (PAM-DMT) on the imaginary parts of even subcarriers, and direct-current-biased optical OFDM (DCO-OFDM) on the real parts of even ones. Since the entire available bandwidth is utilized for data modulation, this scheme can achieve higher spectral efficiency than HACO-OFDM and ACO-OFDM. Moreover, as a smaller DC bias is introduced in our scheme, it is more power efficient than asymmetrically clipped DC-biased optical OFDM (ADO-OFDM) and DCO-OFDM. Simulation results show that EHACO-OFDM performs much better than ADO-OFDM and HACO-OFDM at high bit rates.

Enhanced hybrid asymmetrically clipped orthogonal frequency division multiplexing for optical wireless communications

Abstract. This paper presents an enhanced hybrid asymmetrically clipped optical orthogonal frequency division multiplexing (EHACO-OFDM) scheme, which benefits from the simultaneous transmission of ACO-OFDM, pulse-amplitude-modulated discrete multitone modulation, and direct-current-biased optical orthogonal frequency division multiplexing (DCO-OFDM). Since the entire available bandwidth is utilized for data modulation, this scheme can achieve higher spectral efficiency than HACO-OFDM and ACO-OFDM. Moreover, as a smaller DC bias is introduced in our scheme, it is more power efficient than asymmetrically clipped DC-biased optical OFDM (ADO-OFDM) and DCO-OFDM. A modified receiver is also designed for this system, taking advantage of an iterative algorithm and a pairwise averaging. It has been shown by simulation that our three-path simultaneous transmission scheme can surpass the existing mixed OFDM-based schemes at high data rates. In addition, compared with the noniterative receiver, the modified receiver exhibits significant gains.

A new technique for analyzing asymptotic outage performance of diversity over lognormal fading channels

Existing asymptotic analysis techniques fail to provide closed-form asymptotic outage probability expressions for lognormal fading channels due to the fact that lognormal fading channel distributions have an infinite diversity order. In this work, we develop a new analytical technique to study the asymptotic outage probability of maximum-ratio combining and equalgain combining over independent lognormal fading channels. The derived closed-form asymptotic expressions, which can be expressed in terms of the well-known Marcum-Q function, are accurate in high signal-to-noise ratio (SNR) regimes. The results reveal insights into the long-standing problem of asymptotic analyses for diversity systems over lognormal fading channels, and can help circumvent the time-consuming Monte Carlo simulation and numerical integration in large SNR region.

A New Asymptotic Analysis Technique for Diversity Receptions Over Correlated Lognormal Fading Channels

Prior asymptotic performance analyses are based on the series expansion of the moment-generating function (MGF) or the probability density function (PDF) of channel coefficients. However, these techniques fail for lognormal fading channels because the Taylor series of the PDF of a lognormal random variable is zero at the origin and the MGF does not have an explicit form. Although lognormal fading model has been widely applied in wireless communications and free-space optical communications, few analytical tools are available to provide elegant performance expressions for correlated lognormal channels. In this paper, we propose a novel framework to analyze the asymptotic outage probabilities of selection combining (SC), equal-gain combining (EGC), and maximum-ratio combining (MRC) over equally correlated lognormal fading channels. Based on these closed-form results, we show: 1) the outage probability of EGC or MRC becomes an infinitely small quantity compared to that of SC at high signal-to-noise ratio (SNR); 2) channel correlation can cause an infinite performance loss at high SNR; and 3) negatively correlated lognormal channels can outperform the independent lognormal channels. The analyses reveal insights into the long-standing problem of asymptotic performance analyses over correlated lognormal channels, and circumvent the time-consuming Monte Carlo simulation and numerical integration.

Optical spatial modulation based visible light communications with an arbitrary number of transmitters

Recently, the optical spatial modulation (OSM) technique has been proposed for visible light communication (VLC). However, its design flexibility is limited by the fact that the number of transmitters has to be a power of two, given that the number of bits mapped by the transmit antenna index at each time slot is required to be an integer. In the paper, to break the limitation on the required number of transmitters, a new bit mapping scheme for OSM based VLC with an arbitrary number of transmitters is proposed. When the number of transmitters is not a power of two, the symbols at the transmitters are mapped by different numbers of bits. By employing the pulse amplitude modulation, constellations with different modulation orders are exploited for radiated symbols so as to guarantee that the total number of bits transmitted at each timeslot remains the same. Moreover, the channel state information at the transmitters is taken into consideration in order to obtain better performance. Furthermore, a new channel adaptive bit mapping scheme is proposed. Numerical results on bit error rate performance are provided and substantiate that the proposed scheme can achieve better performance.

Fundamental Analysis for Visible Light Communication with Input‐Dependent Noise

Recently, visible light communication (VLC) has drawn much attention. In literature, the noise in VLC is often assumed to be independent of the input signal. This assumption neglects a fundamental issue of VLC: due to the random nature of photon emission in the lighting source, the strength of the noise depends on the signal itself. Therefore, the input-dependent noise in VLC should be considered. Given this, the fundamental analysis for the VLC with input-dependent noise is presented in this chapter. Based on the information theory, the theoretical expression of the mutual information is derived. However, the expression of the mutual information is not in a closed form. Furthermore, the lower bound of the mutual information is derived in a closed form. Moreover, the theoretical expression of the bit error rate is also derived. Numerical results verify the accuracy of the derived theoretical expressions in this chapter.