Yen-Liang Liu

Real-time white-light phosphor-LED visible light communication (VLC) with compact size

In this demonstration, we first demonstrate a real-time phosphor-LED visible light communication (VLC) system with 37 Mbit/s total throughput under a 1.5 m free space transmission length. The transmitter and receiver modules are compact size. Utilizing our proposed pre-equalization technology, the ~1 MHz bandwidth of phosphor LED could be extended to ~12 MHz without using blue filter. Thus, the increase in bandwidth would enhance the traffic data rate for VLC transmission. The maximum bit-rate achieved by the VLC system is 37 Mbit/s, and a video transmission at 28.419 Mbit/s is demonstrated using the proposed VLC system. In addition, the relationships of received power and signal performance are discussed and analyzed.

Theory and Technology for Standard WiMAX Over Fiber in High Speed Train Systems

In this investigation, we propose and investigate the standard WiMAX access in high speed railway (HSR) using radio over fiber (RoF) link. We also discuss the theory of mobile WiMAX at a target speed of 300 km/hr in simulation. We also analyze the effect of the Doppler frequency shift over HSR. The effective transmission fiber length in the WiMAX-RoF system was limited due to the time-division-duplex (TDD) protocol in the practical WiMAX. Thus, we also demonstrate the transmission limitation and performance of the standard WiMAX access in RoF link. The performances of throughput and packet loss at different fiber lengths are also investigated and discussed. Furthermore, a WiMAX-RoF field trial is also demonstrated based on a simple two RAUs RoF architecture. It was tested and measured in the SongShan tunnel of the Taiwan high speed railway (THSR).

Demonstration of bi-directional LED visible light communication using TDD traffic with mitigation of reflection interference

In this work, we experimentally demonstrate a bi-directional transmission link using light emitting diode (LED) visible light communication (VLC) for both downlink and uplink paths. Time-division-duplex (TDD) is proposed and demonstrated to significantly eliminate the reflection interference in VLC. A free space bi-directional transmission of 2 m using simple on-off keying (OOK) modulation with bit error rate (BER) of < 10(-5) in both directions are achieved. Moreover, the influence of reflection interference is analyzed, showing the proposed scheme can significantly eliminate the reflection interference.

Utilization of multi-band OFDM modulation to increase traffic rate of phosphor-LED wireless VLC.

To increase the traffic rate in phosphor-LED visible light communication (VLC), a multi-band orthogonal frequency division multiplexed (OFDM) modulation is first proposed and demonstrated. In the measurement, we do not utilize optical blue filter to increase modulation bandwidth of phosphor-LED in the VLC system. In this proposed scheme, different bands of OFDM signals are applied to different LED chips in a LED lamp, this can avoid the power fading and nonlinearity issue by applying the same OFDM signal to all the LED chips in a LED lamp. Here, the maximum increase percentages of traffic rates are 41.1%, 17.8% and 17.8% under received illuminations of 200, 500 and 1000 Lux, respectively, when the proposed three-band OFDM modulation is used in the VLC system. In addition, the analysis and verification by experiments are also performed.

Adaptive 84.44−190 Mbit/s phosphor-LED wireless communication utilizing no blue filter at practical transmission distance

We propose and experimentally demonstrate a white-light phosphor-LED visible light communication (VLC) system with an adaptive 84.44 to 190 Mbit/s 16 quadrature-amplitude-modulation (QAM) orthogonal-frequency-division-multiplexing (OFDM) signal utilizing bit-loading method. Here, the optimal analogy pre-equalization design is performed at LED transmitter (Tx) side and no blue filter is used at the Rx side. Hence, the ~1 MHz modulation bandwidth of phosphor-LED could be extended to 30 MHz. In addition, the measured bit error rates (BERs) of < 3.8 × 10(-3) [forward error correction (FEC) threshold] at different measured data rates can be achieved at practical transmission distances of 0.75 to 2 m.

Ring-Based WDM Access Network Providing Both Rayleigh Backscattering Noise Mitigation and Fiber-Fault Protection

In this paper, we propose and investigate a ring-based wavelength-division-multiplexing passive optical network (WDM-PON) providing both Rayleigh backscattering (RB) noise mitigation and fiber-fault protection. The proposed ring-based WDM-PON has a dual-ring architecture to protect and restore any fiber fault. Besides, the ring architecture also can mitigate the RB beat noise, since the RB and the upstream wavelengths are propagating in opposite directions. Here, we discuss and analyze the characteristics of the downstream signals using 10 Gb/s ON-OFF keying (OOK), 10 Gb/s differential phase-shift keying, and 10 Gb/s orthogonal frequency-division multiplexing (OFDM) modulations, respectively. Moreover, we also investigate the upstream traffic using the 2.5 Gb/s OOK and 10 Gb/s OFDM generated by the directly modulated reflective semiconductor optical amplifier-based optical network unit, respectively.

Performance of Long-Reach Passive Access Networks Using Injection-Locked Fabry–Perot Laser Diodes With Finite Front-Facet Reflectivities

In this study, we use the injection-locked Fabry-Perot laser diodes (FP-LDs) with front-facet reflectivities of 10% and 35% respectively, as colorless optical networking unit (ONU) in long-reach passive optical networks (LR-PONs). Here, the injection-locked FP-LD is directly modulated at 2.5 Gbit/s on-off keying (OOK) and 10 Gbit/s orthogonal-frequency-division-multiplexing (OFDM) modulations for upstream traffic transmission over 60 km of single-mode fiber (SMF). Different operating parameters for the injection-locked FP-LD to achieve higher data rate transmission are reported.

High Speed Imaging 3 × 3 MIMO Phosphor White-Light LED Based Visible Light Communication System

The phosphor light-emitting diode (LED) has been widely used not only for indoor illumination but for the optical transmitter (Tx) as well in visible light communication (VLC). However, the transmission data rate is significantly limited by the modulation bandwidth of LED because of the low-speed response of phosphor. In order to enhance the data rate of the VLC system, we demonstrate a 3 × 3 imaging multiple-input multiple-output (MIMO) VLC system. Besides, the pre-equalizer circuit is used to extend the bandwidth of the LED Tx. Orthogonal frequency division multiplexing (OFDM) with bit-loading algorithm is used. By using the proposed scheme, the original 1 MHz bandwidth commercially available phosphor white light LED can achieve 1 Gbps data rate over 1-m free-space transmission distance.

Investigation of phosphor-LED lamp for real-time half-duplex wireless VLC system

In this investigation, a 71.3 to 148.4 Mbit s−1 white phosphor-LED visible light communication (VLC) system is proposed and demonstrated under the practical transmission length of 140 to 210 cm. Here, a commercial white-light LED lamp with five cascaded phosphor-LED chips is utilized for illumination and communication simultaneously. In the measurement, we utilize the optical orthogonal frequency division multiplexing quadrature amplitude modulation (OFDM-QAM) with bit-loading algorithm and propose an optimal bias-tee circuit design to improve the modulation bandwidth from 1 MHz to 27 MHz. Moreover, a blue optical filter is not used on the client side. Finally, to realize and demonstrate the real-time transmission performance in the proposed LED VLC system, a commercial OFDM-based digital signal processor (DSP) chip is utilized on the LED lighting side and client side, respectively. Hence, the proposed real-time half-duplex VLC transmission could achieve the 70 Mbit s−1 downstream and upstream data throughputs, under a practical transmission length of 200 cm.

A practical in-home illumination consideration to reduce data rate fluctuation in visible light communication

Visible light communication based on LED has attracted more and more attention. As the primary function of LED luminaries is optimized for lighting and illumination, it challenges the communication properties of VLC. An investigation based on different in-home illumination conditions using commercially available whitelight LED luminaries to optimize both illumination and communication is highly desirable. In this work, we investigate joint illumination and communication systems to provide an in-home lighting and VLC system. We first focus on the performance constraints set by illumination properties and discuss lighting conditions using different kinds of commercially available luminaries, beam angles, and LED lamp arrangements, and consider reflections off different wall materials. Then we propose and experimentally demonstrate a white-light phosphor-based LED adaptive data rate VLC system. Finally, the achievable data rates of a joint illumination and VLC system are discussed based on the experimental results, and an environment with reduced VLC data rate fluctuation can be achieved.