Smart Indoor Bidirectional Visible Light Communication with Resource Allocation and Motion Detection

Abstract

Light emitting diodes (LEDs) are becoming popular as illumination devices. The LEDs are now considered as a strong candidate for a last-mile wireless communication technology. LED based visible light communications (VLC) have many advantages such as energy efficiency, high security, the absence of electromagnetic interference and higher data rate as compared with other wireless communication technologies. Since data transmission is done via LEDs using intensity modulation techniques, VLC is able to provide very high data rates which are on the order of Gbps. Recently, VLC has led to Li-Fi (light fidelity) as a high speed wireless broadband communication technology. A successful Li-Fi deployment should have an efficient multiuser (MU) access scheme to meet the demand for simultaneous network access along with full-fledged bidirectional communications. In order to provide very efficient, high-speed and high-performance data communication in a MU bidirectional network, this thesis gives a detailed analysis of user and LED allocation schemes with mobility support in a high speed bidirectional indoor VLC environment with experimental studies. Additionally, the thesis introduces a very novel application area of VLC system, i.e. motion detection, along with fundamental analysis of the VLC system at aspects of indoor illumination, power reception, signal to noise ratio (SNR) and bit-error rate (BER) distribution in the indoor environment.

In the first study, a novel user allocation scheme which uses a predefined frame structure is analysed for a full duplex MU bidirectional VLC environment along with user mobility support. The users are allocated into separate color clusters and the user data is transmitted through the allocated color beams from the RGB (red, green, and blue) light emitting diodes (LEDs) using frame structure. At the receiving end, primary user separation is achieved by a color filter that is capable of distinguishing the colors. Similarly, for uplink data transmission, the modulation of the user data is performed using a different color from the one used to retrieve the data and transmitted through the RGB LED, resulting in a bidirectional VLC link with minimal interference. The use of color filter array (CFA) allows the users to move freely in a color clustered environment. Algorithm for achieving mobility support is also presented.

Secondly, the thesis presents a novel smart LED allocation technique for efficient multiuser VLC networks. As in a MU bidirectional 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. Therefore, in order to support an increasing or decreasing number of users in the network, the LED allocation is required to be performed dynamically. The 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.

The next study is time and frequency based double optical diversity (DOD) scheme for achieving high-speed indoor VLC system with a data rate supported up to 3 Gbit/s. The scheme utilizes color filters and selection combining (SC) at receiving end; and DOD and RGB LEDs at transmitter end. The original data and the delayed versions of this data are simultaneously transmitted by multiplying with orthogonal frequencies, in order to create diversity effect over the transmission. In addition, RGB LEDs are utilized for parallel data transmission, resulting in increased data speed. At receiver end, color filters are used to filter out for the desired signal while receiver diversity in the form of SC is performed to obtain the most probable bits.

The last study in this thesis proposes a unique and novel VLC based motion detection. The proposed motion detection is performed based on white light LEDs and an array of photodetectors from existing VLC links, thus providing VLC with three functionalities of illumination, communication and motion detection. The motion is detected by observing the pattern created by intentional obstruction of the VLC link. The VLC based motion detection can benefit smart devices control in VLC based smart home environments.

The aforementioned studies are conducted to achieve a smart indoor VLC system which is suitable for high-speed, high-performance, and efficient MU full-duplex bi-directional wireless network with mobility support along with a novel functionality of VLC i.e. VLC based motion detection.