Visible light communication systems supporting wireless data access and indoor positioning applications

• Main Author: Yang, Helin
• Other Authors: Arokiaswami Alphones
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Electrical and electronic engineering::Wireless communication systems
• Online Access: https://hdl.handle.net/10356/137178
• Institution: Nanyang Technological University

White light emitting diodes (LEDs) have attracted much attention recently in the lighting market for their long lifetime, low power consumption, fast switching time and reliability. Besides illumination, LEDs are also used for visible light communications (VLC) and visible light positioning (VLP). On the one hand, VLC has been emerging as a promising candidate for indoor wireless communications due to its supporting high-speed data rate, economic, electro-magnetic interference free and high security, compared with traditional radio-frequency (RF) systems. On the other hand, VLP can provide high-accuracy positioning performance compared with RF based indoor positioning systems. However, the development and deployment of indoor VLC and VLP systems face some key challenges, such as integration of VLC and VLP to provide simultaneous communication and positioning services, inter-cell interference (ICI) in indoor multi-cell VLC systems, negative effect of line-of-sight (LoS) blockages on the performance, and guaranteeing different quality of services (QoS) of various indoor devices. The goals of this thesis are to address the above mentioned challenges, and propose integrated system, robust optimized design, ICI mitigation scheme and resource management strategy to improve the system performance. The combination of orthogonal frequency division multiplexing (OFDM) and positioning algorithm can provide simultaneous communication and positioning for indoor devices, but the performance is degraded due to the high out-of-band interference (OOBI) generated from OFDM signals on adjacent subcarriers. This thesis first proposes a quasi-gapless integrated VLC and VLP (called VLCP) system based on filter bank multicarrier-based subcarrier multiplexing (FBMC-SCM). Compared with OFDM-based SCM (OFDM-SCM), FBMC-SCM is capable of mitigating OOBI and therefore requires much smaller guard band (GB) spacing. Simulations and experimental results verify that our proposed FBMC-SCM can improve the effective bandwidth utilization ratio and enhance the positioning accuracy in the integrated VLCP system, compared with OFDM-SCM. The FBMC-SCM needs extra computational complexity of signal processing compared with OFDM. An OFDM-SCM-interleaving based integrated VLCP system is further proposed, where the sinusoidal positioning signals can be placed into the idle subcarriers (called frequency holes) which have the negligible OOBI from OFDM communication signal. In order to maximize the system data rate while guaranteeing the minimum data rate and high positioning accuracy requirements, a QoS-driven optimized design with joint adaptive modulation, subcarrier allocation and weighted pre-equalization is proposed to improve the system performance. The LoS blockage issue is investigated in this thesis, and robust communication and positioning schemes are presented to maintain the system performance. Furthermore, this thesis also extends the system model into multi-cell integrated VLCP networks, where a joint VLC access point section, bandwidth allocation, adaptive modulation and power allocation approach is proposed to maximize the network data rate while guaranteeing different QoS requirements of indoor devices. The experimental results and simulations show that the presented integrated VLCP system model and solutions effectively enhance the data rate, improve the positioning accuracy and guarantee devices' QoS requirements. In indoor multi-user multi-cell multiple-input multiple-output (MIMO) VLC systems, ICI and inter-user interference (IUI) are the two key factors that could severely degrade the system performance. In this thesis, a novel joint precoder and equalizer design based on interference alignment (IA) is proposed to mitigate both IUI and ICI in multi-user multi-cell MIMO VLC systems under both perfect and imperfect channel state information (CSI). The proposed design aims to choose proper precoder and receiving equalizer to minimize the mean square error (MSE) under unique optical power constraints. Furthermore, this thesis considers optical channel estimation errors in the formulated joint optimization problem. Numerical results show that the proposed design achieves better performance under different users' locations, channel estimation errors and transmitter/receiver spacing, compared to the existing designs. In wireless indoor networks, Internet of Things (IoT) devices and industrial IoT devices may have different QoS requirements, ranging from high reliability and low-latency to high transmission data rate, leading to high complex and heterogeneous network environments. Hence, this thesis presents a heterogeneous RF/VLC network architecture to guarantee the different QoS requirements, where RF is capable of offering seamless coverage and VLC has the ability to provide high transmission data rate. Then, a joint uplink and downlink energy-efficient resource management decision-making problem (network selection, subchannel assignment and power management) is formulated as a Markov decision process. After that, a new deep post-decision state (PDS) based experience replay and transfer (PDS-ERT) reinforcement learning (RL) algorithm is proposed to learn the optimal policy. Simulation results corroborate the superiority in performance of the presented heterogeneous network, and verify that the proposed PDS-ERT learning algorithm outperforms other existing algorithms in terms of meeting energy efficiency and QoS requirements.