Optical Bidirectional Beacon based Visible Light Communication in Smart Home Environments

Abstract

With the advancement of light emitting diode (LED) technology, visible light communication (VLC) emerged as a novel communication scheme for providing data communication. Using visible light as the communication medium, VLC possesses many advantages over conventional RF communications, such as large unlicensed spectral bandwidth, usability at radio frequency (RF) prohibited areas. In order to provide high-speed bidirectional data communication for the multiple users, this thesis addresses some of important issues in indoor VLC with simulation studies. Moreover, the thesis provides a fundamental analysis of the VLC system in the aspects of illumination, power reception and data rate in the indoor environment.

In the first study, a multiple channel transmission, which is an attractive solution to enhancing capacity and system performance of optical wireless communication systems, is analysed. A new modulation scheme called color coded multiple access (CCMA) for bidirectional multiuser VLC is presented for smart home applications. The proposed scheme uses RGB (red, green, blue) LED to establish a bidirectional multiuser VLC and employs orthogonal codes to support multiple users and multiple devices. The downlink transmission for data user devices and smart home devices is provided using red and green color, respectively, while uplink transmission from both types of devices is made using blue color. 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 data transmission, it provides flicker-free illumination that would lend itself to VLC based Light-Fidelity (Li-Fi) systems for smart home applications.

Secondly, the thesis presents the studies on combating the optical shadowing resulted from obstruction in the line-of-sight (LOS). 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 thesis, 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 RGB LEDs, photodetectors (PD) 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.

The last study in this thesis proposes device-to-device (D2D) communication that is considered, a promising technique to provide wireless peer-to-peer communication services. Due to increasing demand on mobile services, available spectrum for RF based communications becomes scarce. Recently, VLC has evolved as a high speed wireless data transmission technology for indoor environments with abundant available bandwidth. In this thesis, a novel VLC based D2D communication that provides wireless peer-to-peer communication is proposed. Potential low operating power devices for an efficient D2D communication over increasing distance of separation between devices is analysed. Installation of the OBBs in indoors is also proposed to enhance the performance in an environment where direct D2D communications yield degraded performance. Simulation results show that VLC plays an important role in providing efficient D2D communication up to a distance of 1 m between devices while achieving higher data rates. It is also found that the installation of OBB significantly improves the coverage distance up to 3.5 m.