Xingxing Huang

8-Gb/s RGBY LED-Based WDM VLC System Employing High-Order CAP Modulation and Hybrid Post Equalizer

In this paper, for the first time, we propose the use of a hybrid post equalizer in a high-order carrierless-amplitude-and-phase-modulation-based visible light communication (VLC) system. The hybrid equalizer consists of a linear equalizer, a Volterra-series-based nonlinear equalizer, and a decision-directed least mean squares equalizer to simultaneously mitigate the linear and nonlinear distortions of the VLC system. A commercially available red-blue-green-yellow light-emitting diode (RBGY LED) is utilized for four-wavelength multiplexing. By the hybrid equalizer, an aggregate data rate of 8 Gb/s is experimentally achieved over a 1-m indoor free-space transmission with the bit error rate (BER) below the 7% forward error correction (FEC) limit of 3.8 × 10-3. To the best of our knowledge, this is the highest data rate ever reported in high-speed VLC systems.

Enhanced performance of visible light communication employing 512-QAM N-SC-FDE and DD-LMS

In this paper, a novel hybrid time-frequency adaptive equalization algorithm based on a combination of frequency domain equalization (FDE) and decision-directed least mean square (DD-LMS) is proposed and experimentally demonstrated in a Nyquist single carrier visible light communication (VLC) system. Adopting this scheme, as well with 512-ary quadrature amplitude modulation (512-QAM) and wavelength multiplexing division (WDM), an aggregate data rate of 4.22-Gb/s is successfully achieved employing a single commercially available red-green-blue (RGB) light emitting diode (LED) with low bandwidth. The measured Q-factors for 3 wavelength channels are all above the Q-limit. To the best of our knowledge, this is the highest data rate ever achieved by employing a commercially available RGB-LED.

4.5-Gb/s RGB-LED based WDM visible light communication system employing CAP modulation and RLS based adaptive equalization

Inter-symbol interference (ISI) is one of the key problems that seriously limit transmission data rate in high-speed VLC systems. To eliminate ISI and further improve the system performance, series of equalization schemes have been widely investigated. As an adaptive algorithm commonly used in wireless communication, RLS is also suitable for visible light communication due to its quick convergence and better performance. In this paper, for the first time we experimentally demonstrate a high-speed RGB-LED based WDM VLC system employing carrier-less amplitude and phase (CAP) modulation and recursive least square (RLS) based adaptive equalization. An aggregate data rate of 4.5Gb/s is successfully achieved over 1.5-m indoor free space transmission with the bit error rate (BER) below the 7% forward error correction (FEC) limit of 3.8x10(-3). To the best of our knowledge, this is the highest data rate ever achieved in RGB-LED based VLC systems.

1.6 Gbit/s phosphorescent white LED based VLC transmission using a cascaded pre-equalization circuit and a differential outputs PIN receiver.

We proposed a cascaded amplitude equalizer used for high speed visible light communications (VLC) system. With the cascaded pre-equalization circuit, the -3dB bandwidth of VLC system can be extended from 17MHz to 366MHz using a commercially available phosphorescent white LED, a blue filter and a differential outputs PIN receiver. The data rate is 1.60Gbit/s exploiting 16QAM-OFDM with 400MHz modulation bandwidth over 1m free-space transmission under pre-forward error correction (pre-FEC) limit of 3.8 × 10(-3). To our knowledge, this is the highest data rate ever achieved by using a commercially available phosphorescent white LED in VLC system.

High-speed quasi-balanced detection OFDM in visible light communication.

In this paper, we proposed and experimentally demonstrated a novel quasi-balanced detection (QBD) technique in orthogonal frequency division multiplexing (OFDM) visible light communication (VLC) system. By employing opposite signals to odd and even consecutive symbols, the nonlinearity distortion, and direct current can be eliminated efficiently. Additionally, the sensitivity of receiver can also be improved by 3dB, thus a longer transmission distance and high-order modulation formats can be received. We achieved physical data rate of 2.1-Gb/s enabled by wavelength-division-multiplexing (WDM), pre- and post-equalization, and the resulting bit error ratios (BERs) were below the FEC limit of 3.8x10(-3). The distance was above 2.5 meters that was long enough for indoor communication. Compared with conventional direct-detection optical (DDO-OFDM) and asymmetrically-clipped optical (ACO-OFDM), the BER can be enhanced by 22.2dB and 20.8dB, respectively, which shows great potential in short range and low cost access network.

Enhanced Performance of a High-Speed WDM CAP64 VLC System Employing Volterra Series-Based Nonlinear Equalizer

The light-emitting diode nonlinearity in visible light communication (VLC) systems is considered to be a major problem that deteriorates system performance. In this paper, we experimentally demonstrate a high-speed WDM CAP64 VLC system employing a Volterra series-based nonlinear equalizer to mitigate the nonlinear effect. A modified cascaded multimodulus algorithm (M-CMMA) is utilized to calculate the error function and update the weights of the nonlinear equalizer without using training symbols. An aggregate data rate of 4.5 Gb/s is successfully achieved over 2-m indoor free-space transmission with a bit error rate (BER) below the 7% forward error correction limit of 3.8 × 10-3. With the Volterra nonlinear equalizer, the Q factor of the VLC system is 1. 6 dB better than that without using the nonlinear equalizer, and the transmission distance is also increased by about 110 cm at the BER of 3.8 × 10-3. To the best of our knowledge, this is the first time that the Volterra nonlinear equalizer is utilized for high-speed carrierless amplitude and phase (CAP) modulation-based VLC systems.

2.0-Gb/s Visible Light Link Based on Adaptive Bit Allocation OFDM of a Single Phosphorescent White LED

In this paper, we present a high-speed visible light communication (VLC) system based on a single commercially available phosphorescent white light-emitting diode (LED). In this system, a preequalization circuit is used to extend the modulation bandwidth, and a differential output receiver is utilized to reduce the system noise. With adaptive bit and power allocation and orthogonal frequency-division multiplexing (OFDM), we experimentally demonstrated a 2.0-Gb/s visible light link over 1.5-m free-space transmission, and the BER is under a preforward error correction limit of 3.8×10-3. To the best of our knowledge, this is the highest white-light VLC data rate using a single phosphorescent white LED.

A Gb/s VLC Transmission Using Hardware Preequalization Circuit

In this letter, we proposed a constant-resistance symmetrical bridged-T amplitude equalizer for high-speed visible light communication (VLC) system. Using the hardware equalizer, we successfully demonstrated a gigabit per second VLC transmission over 80-cm free space based on a RGB LED. The measured bit error rates (BERs) for the signals in 64-quadratic-amplitude modulation (64QAM) single carrier modulation at 1.05-Gb/s, 64QAM-orthogonal frequency division multiplexing (OFDM) at 1.05 Gb/s, and bit and power loading OFDM modulation at 1.42 Gb/s, are under 7% pre-forward error correction (pre-FEC) limit of 3.8 × 10-3, clearly validating the feasibility of the proposed equalizer. Compared with the system without using the equalizer, the BER performance of the VLC systems can be improved at least by 1 order of magnitude. Moreover, the equalizer can be easily integrated into amplifier or LED because of its compact size and easy installation for just using passive component. To the best of our knowledge, it is the highest data rate with longest transmission distance using preequalization circuit.

1.8-Gb/s WDM visible light communication over 50-meter outdoor free space transmission employing CAP modulation and receiver diversity technology

We experimentally demonstrate a WDM VLC system employing CAP modulation and receiver diversity technology. The record aggregate data rate of 1.8Gb/s with the BER less than 3.8×10-3 is successfully achieved over 50-m outdoor transmission.

A Power-Type Single GaN-Based Blue LED With Improved Linearity for 3 Gb/s Free-Space VLC Without Pre-equalization

A new GaN light-emitting diode (LED) structure, which has a 300-nm aluminum-doped zinc oxide transparent current spreading layer epitaxial layer grown on a standard GaN LED epistack used in commercial GaN LED products, shows improved power vs. voltage (P-V) linearity and is suitable for high-data rate visible light communication. Experimentally, a single GaN-based blue LED with a mesa diameter of 150 μm and a maximum optical power of 42 mW demonstrates a 3-Gb/s free-space data transmission speed. The modulation bandwidth reaches 600 MHz under the present experimental setup. The present work proves the practicability of enhancing the LEDs free-space data transmission ability through a P-V linearity improvement at the chip level.