Research On Double Layer Visible Light Imaging Communication

Visible light imaging communication systems use liquid crystal displays(LCDs) or light emitting diode(LED) array as data transmitter. After being modulated to the intensities of the pixels, data are transmitted in parallel through the visible channel and are recovered by the imaging devices at the receiver. Typical receivers are charge coupled device(CCD) and CMOS. Visible light imaging communication systems have broad application prospects in fields such as indoor and outdoor high-speed communication systems, intelligent transportation systems, location-based services, and augmented reality. In recent years, almost all mobile phones and other smart terminals have the abilities of installing intelligent software and shooting in high performance which have laid the foundation for the popularity of visible light imaging communication. Based on the analysis of the characteristics, this dissertation mainly research on the double layer imaging system and the constructions of its applications, the main works are as follows:1. After being combined with typical visible light imaging application scenarios, a typical model of visible light imaging communication system is established, and its transmission characteristics is analyzed. The system model of imaging communication is established and the transmission characteristics of the light sources are studied. Based on the theoretical derivations to the channel gain and the system capacity, quantitative analysis and numerical simulations are exerted to the communication distance, the relative position, the lens blur, the elements layout and other factors which determine the capacity. Spatial and temporal synchronization are deeply analyzed and the spatial-temporal synchronization method is researched.2. Aiming at the differences of the transmission characteristics and the specific works of visible light imaging communication, double layer imaging system is researched; a linear complexity maximum likelihood detection algorithm is proposed and three signal constellation designs which can be applied to double layer imaging system are designed. In the double layer imaging system, the transmitted data are split into two layers that a few high priority data are transmitted on the upper layer and a lot of low priority data are transmitted on the lower layer. The basic principle of multi-layer visible light imaging communication system is studied and the signal models of transmitter and receiver are established. To solve the problem of high error rate of sum detection and high complexity of maximum likelihood detection, a fast maximum likelihood detection algorithm with linear complexity which takes advantage of the system characteristics is proposed to balance the requirements of low error rate and low complexity. Three binary constellation designs corresponding to different priority orders are presented to adjust the priorities of the data on the transmission layers flexibly. Computer simulations show that the error rate performance of the proposed ML detector obtains 6dB signal-to-noise ratio(SNR) gain over the current the detection algorithm. Three different constellation designs are able to correspond to different needs and error rates of the transmitting layers.3. The realization principle of the VLC-based invisible information casting system is studied; different approaches are analyzed; theoretical analysis and experimental tests of the feasible designs are carried; and the system is finally realized. The realization principle is introduced; the advantages and disadvantages of different processing methods and several modulations combining with the characteristics of images are analyzed; and the preferable approach method is finally achieved. The VLC-based invisible information casting system is designed and realized. The composition structure of the training sequence-based system is introduced and the spatial-temporal synchronization method towards dynamic frames is proposed and implemented. The relationships between the main parameters such as modulation depth, diversity degree, multiplexing degree, and the carrier image intensities are evaluated through experiments. The user interface and functionality of the system are introduced in detail at last.