High-speed Indoor Optical Wireless Communication Research Articles

Full-duplex high-speed indoor optical wireless communication system based on a micro-LED and VCSEL array.

We built a full-duplex high-speed optical wireless communication (OWC) system based on high-bandwidth micro-size devices, for which micro-LED and VCSEL arrays are implemented to establish downlink and uplink, respectively. The high-capacity downlink based on a single-pixel quantum dot (QD) micro-LED can reach a data rate of 2.74 Gbps with adaptive orthogonal frequency division multiplexing (OFDM). VCSEL-based line-of-sight (LOS) and non-line-of-sight (NLOS) uplinks are designed with lens-free receiving functions for a 2.2-m communication distance. Experimental results have been demonstrated and confirmed that both downlink and uplinks are capable of providing sufficient bandwidth for a multi-gigabit OWC. Besides, the lens-free uplink receiver can alleviate requirements for aligning and improve the mobility of the transmitter. The VCSELs implemented for both systems work with low driving currents of 140-mA and 190-mA under consideration of the human eye safety. For non-return-to-zero on-off keying (NRZ-OOK), both uplinks can achieve 2.125 Gbps with bit-error-rate (BER) lower than the forward error correction (FEC) threshold of 3.8×10-3 for Ethernet access.

Digital Orthogonal-Filters Enhanced Spatial Modulation for High-Speed Indoor Optical Wireless Communications

Spatial modulation (SM) has been proposed and studied in high-speed indoor optical wireless communication systems to improve the spectral efficiency and system capacity by exploring the spatial domain information of transmitters. However, the correct detection of active transmitter(s) is critical, and it typically requires precise channel state information (CSI) and low correlation between channel gains. To overcome this limit, in this paper an orthogonal-filters enhanced SM scheme is proposed for high-speed indoor optical wireless communication systems, where the use of orthogonal-filters can improve the correct detection of active transmitter(s) significantly. The proposed scheme is experimentally demonstrated, and results show that with 4-pulse amplitude modulation (PAM-4) and two transmitters, 7.5 Gb/s optical wireless data transmission is achieved with 2.5 GS/s symbol rate. The power penalty of proposed scheme on the receiver sensitivity is negligible, and the active transmitter(s) can be correctly detected even under high channel correlations and without CSI. The scalability of proposed orthogonal-filters enhanced SM scheme is also studied, and it is shown that higher dimensions can be realized to achieve higher spectral efficiency, which provides a promising solution in indoor optical wireless communications to achieve ultra-high bit rate.

Linear Precoding Designs for MIMO VLC Using Multi-Color LEDs under Multiple Lighting Constraints

Multiple-input multiple-output (MIMO) technology as an efficient approach to improve the transmission rate in visible light communication (VLC) has been well studied in recent years. In this paper, we focus on the MIMO VLC system using multi-color LEDs in the typical indoor scenario. Besides the correlation of the MIMO channel, the multi-color crosstalk interference and quadrangle chromaticity region are also considered to increase the practicality of this system. With the constraints of power, amplitude and chromaticity, an iterative algorithm to minimize mean-squared-error (MSE) is proposed to jointly design the precoder and equalizer. Our proposed algorithm provides an effective method to get the optimal precoder by updating optimization variables iteratively. As the equalizer matrix is fixed at each iteration, the main non-convex precoding design problem is transformed into a convex optimization problem and then solved. With the utilization of multi-color LEDs, our proposed precoding method would be promising to promote the practical applications of high-speed indoor optical wireless communication. Simulation results show that our proposed method owns better performance than conventional chromaticity-fixed schemes and zero-forcing precoding designs.

High-speed indoor optical wireless communication system employing a silicon integrated photonic circuit.

Beam-steering-based optical wireless technologies are being widely investigated due to the capability of providing high-speed wireless connectivity in indoor applications. However, high-speed indoor optical wireless systems are traditionally realized with discrete bulky components, significantly limiting their practical applications. In this Letter, we demonstrate an infrared optical wireless communication system employing a miniaturized silicon integrated photonic circuit for beam steering for the first time. Experimental results show that up to 12.5Gb/s optical wireless communication can be achieved with error-free performance over a free-space range of 140cm, and limited mobility of users can be realized. The experimental results of this Letter open the way for realizing integrated high-speed optical wireless communications.

High-speed indoor optical wireless communication system with single channel imaging receiver: erratum

High-speed indoor optical wireless communication system with single channel imaging receiver: erratum

High-speed indoor optical wireless communication system with single channel imaging receiver

In this paper we experimentally investigate a gigabit indoor optical wireless communication system with single channel imaging receiver. It is shown that the use of single channel imaging receiver rejects most of the background light. This single channel imaging receiver is composed of an imaging lens and a small photo-sensitive area photodiode attached on a 2-axis actuator. The actuator and photodiode are placed on the focal plane of the lens to search for the focused light spot. The actuator is voice-coil based and it is low cost and commercially available. With this single channel imaging receiver, bit rate as high as 12.5 Gbps has been successfully demonstrated and the maximum error-free (BER<10⁻⁹) beam footprint is even larger than 1 m. Compared with our previous experimental results with a single wide field-of-view non-imaging receiver, an improvement in error-free beam footprint of >20% has been achieved. When this system is integrated with our recently proposed optical wireless based indoor localization system, both high speed wireless communication and mobility can be provided to users over the entire room. Furthermore, theoretical analysis has been carried out and the simulation results agree well with the experiments. In addition, since the rough location information of the user is available in our proposed system, instead of searching for the focused light spot over a large area on the focal plane of the lens, only a small possible area needs to be scanned. By further pre-setting a proper comparison threshold when searching for the focused light spot, the time needed for searching can be further reduced.