Bidirectional Visible Light Communication Research Articles

Mobility Support for Full-Duplex Multiuser Bidirectional VLC Networks

In this paper, a novel and unique mobility support scheme for a color-clustered (CC) full-duplex multiuser (MU) bidirectional visible light communication (VLC) network is presented. Mobility is classified into two categories: intercluster and intracluster. In the proposed scheme, the mobility support is efficiently provided using a color filter array (CFA) at the downlink receiver. This CFA gives rise to receiver diversity in the form of selection combining yielding performance improvement. Simulations are conducted in terms of communication delay and frame loss rate relative to user speed and distance. In addition, the bit error rate (BER) performance and the data rate are analyzed in the CC MU VLC network. It is demonstrated that the proposed CFA and receiver diversity based mobility scheme in the CC MU VLC network offers superior performance in terms of BER and data rate in indoor environments.

Optical bidirectional beacon based visible light communications.

In an indoor bidirectional visible light communications (VLC), a line-of-sight (LOS) transmission plays a major role in obtaining adequate performance of a VLC system. Signals are often obstructed in the LOS transmission path, causing an effect called optical shadowing. In the absence of LOS, the performance of the VLC system degrades significantly and, in particular, at uplink transmission this degradation becomes severe due to design constraints and limited power at uplink devices. In this paper, a novel concept and design of an optical bidirectional beacon (OBB) is presented as an efficient model to counter the performance degradation in a non-line-of-sight (NLOS) VLC system. OBB is an independent operating bidirectional transceiver unit installed on walls, composed of red, green, and blue (RGB) light emitting diodes (LEDs), photodetectors (PDs) and color filters. OBB improves the coverage area in the form of providing additional or alternate paths for transmission and enhances the performance of the VLC system in terms of bit error rate (BER). To verify the effectiveness of the proposed system, simulations were carried out under optical shadowing conditions at various locations in an indoor environment. The simulation results and analysis show that the implementation of OBB improves the performance of the VLC system significantly, especially when the LOS bidirectional transmission paths are completely or partially obstructed.

Smart LED allocation scheme for efficient multiuser visible light communication networks.

In a multiuser bidirectional visible light communication (VLC), a large number of LEDs or an LED array needs to be allocated in an efficient manner to ensure sustainable data rate and link quality. Moreover, in order to support an increasing or decreasing number of users in the network, the LED allocation is required to be performed dynamically. In this paper, a novel smart LED allocation scheme for efficient multiuser VLC networks is presented. The proposed scheme allocates RGB LEDs to multiple users in a dynamic and efficient fashion, while satisfying illumination requirements in an indoor environment. The smart LED array comprised of RGB LEDs is divided into sectors according to the location of the users. The allocated sectors then provide optical power concentration toward the users for efficient and reliable data transmission. An algorithm for the dynamic allocation of the LEDs is also presented. To verify its effective resource allocation feature of the proposed scheme, simulations were performed. It is found that the proposed smart LED allocation scheme provides the effect of optical beamforming toward individual users, thereby increasing the collective power concentration of the optical signals on the desirable users and resulting in significantly increased data rate, while ensuring sufficient illumination in a multiuser VLC environment.

Color coded multiple access scheme for bidirectional multiuser visible light communications in smart home technologies

In optical wireless communications, multiple channel transmission is an attractive solution to enhancing capacity and system performance. A new modulation scheme called color coded multiple access (CCMA) for bidirectional multiuser visible light communications (VLC) is presented for smart home applications. The proposed scheme uses red, green and blue (RGB) light emitting diodes (LED) for downlink and phosphor based white LED (P-LED) for uplink to establish a bidirectional VLC and also employs orthogonal codes to support multiple users and devices. The downlink transmission for data user devices and smart home devices is provided using red and green colors from the RGB LEDs, respectively, while uplink transmission from both types of devices is performed using the blue color from P-LEDs. Simulations are conducted to verify the performance of the proposed scheme. It is found that the proposed bidirectional multiuser scheme is efficient in terms of data rate and performance. In addition, since the proposed scheme uses RGB signals for downlink data transmission, it provides flicker-free illumination that would lend itself to multiuser VLC system for smart home applications.

Network Architecture of a High-Speed Visible Light Communication Local Area Network

A novel ultrahigh-speed LED visible light communication (VLC) local area network to provide beyond 10-Gb/s optical wireless access based on star topology architecture is proposed and experimentally demonstrated for massive users. Fiber link is used as the backbone of the bidirectional VLC network. The hybrid access protocol is utilized: 1) frequency division multiplexing for downlink and uplink fiber transmission and 2) time division multiplexing for bidirectional VLC transmission. A full-duplex VLC network for eight VLC access points (VAPs) has been successfully demonstrated with the total throughput of 8 Gb/s. Each VAP is offered 500-Mb/s downstream and 500-Mb/s upstream. The measured bit error rates of downlink and uplink for all the VAPs are under 7% FEC limit of $3.8\times 10^{-3}$ over 25-km standard single mode fiber and 65-cm free space, clearly validating the promising potential of the proposed VLC network architecture for future 40- and 100-Gb/s wireless access.

Basic Study on Receiving Light Signal by LED for Bidirectional Visible Light Communications

SUMMARYLight emitting diodes (LEDs) are now used for lighting and illumination because of features such as low power consumption and long life. Lighting equipment has only LEDs, therefore it is necessary to install a photodetector to allow bidirectional communication. In this paper, we propose reception of a light signal by means of an LED for bidirectional visible light communications. We evaluate the characteristics of the LED used as a photodetector for bidirectional visible light communications through experiments. Further, we describe the newly developed experimental system that uses LEDs as a photodetector. Experiments show that an LED can be used not only as a light source but also as a photodetector for bidirectional visible light communications.

A high-speed bi-directional visible light communication system based on RGB-LED

In this paper, we propose and experimentally demonstrate a bi-directional indoor communication system based on visible light RGB-LED. Spectrally efficient modulation formats (QAM-OFDM), advanced digital signal processing, pre- and post-equalization are adopted to compensate the severe frequency response of indoor channel. In this system, we utilize red-green-blue Light emitting diodes (LEDs), of which each color can be used to carry different signals. For downlink, the low frequencies of each color are used while for uplink, the high frequencies are used. The overall data rate of downlink and uplink are 1.15-Gb/s and 300-Mb/s. The bit error ratios (BERs) for all channels after 0.7 m indoor delivery are below pre-forward-error-correction (pre-FEC) threshold of 3.8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . To the best of our knowledge, this is the highest data rate in bi-directional visible light communication system.

LED transceivers with beehive-shaped reflector for visible light communication

This paper proposes a novel beehive-shaped reflector for application to light-emitting diode (LED) transceivers for illumination and bi-directional visible light communication (VLC). By using a diffuse propagation model extended to line-of-sight and direct signals, the distribution of illuminance and the path loss of the transceiver are investigated to evaluate the performance of the beehive-shaped reflector. To verify bi-directional communication, a VLC-based image capture system, comprising a complementary metal-oxide semiconductor (CMOS) image sensor and video processor unit, is demonstrated. Real-time images captured by the CMOS camera are successfully transmitted to the monitoring system via a free-space channel at a rate of 115.2 kbps.

Basic Study on Receiving Light Signal by LED for Bidirectional Visible Light Communications

Recently the light emitting diodes (LED) have been used for lighting and illumination because of their features such as low power consumption and long life. The lighting equipments have only LED. Therefore, it is necessary to install photo detector to enable bidirectional communication. In this paper, we propose a receiving light signal by LED for bidirectional visible light communications. We evaluate the characteristics of LED used as a photo detector for bidirectional visible light communications through experiment. And, we describe the developed experimental system that uses LED as a photo detector. We show that we can use LED as not only light source but also photo detector for bidirectional visible light communications through experiment.