Research On Key Techniques Of Visible Light Localization And Transmission

With the explosive growth of the content-rich application services such as augmented reality/virtual reality,high-definition video and so on,and the rapid popularity of high-performance mobile devices,smart home devices and wearable devices,the radio frequency(RF)-based wireless communication is facing the more serious“spectrum crunch".Recently,visible light communication(VLC)is widely regarded as a potential emerging technology which can effectively complement the RF wireless communication.VLC has the numerous predominate strengths,such as the wide spectrum resource,the simultaneous illumination and communication,no electromagnetic interference and so on.Based on the National Natural Science Foundation Project,the dissertation deeply studies three VLC-based popular applications:One is how to realize the effective three-dimensional visible light positioning in fully-automated application scenarios;The second issue is how to achieve the effective modulation and equalization in the low-cost high-speed VLC systems;Lastly,it is how to achieve the dimmable VLC system with high spectral efficiency.The main innovations in the dissertation are summarized as follows:1.Research on the VLC-based localizationFor the requirement of fully-automated application scenarios in the IoT era,the paper proposes a visible light three-dimensional positioning system based on hierarchical trilateral positioning and optimal selection algorithm.Firstly,the system narrows the possible spatial area according to the spatial arrangement characteristics of light-emitting diode(LED)with the known position information.Meanwhile,by selecting the suitable LEDs,it can effectively prevent the system from the positioning blind zone conditions caused by the limited field of view(FOV)of the receiver.Secondly,the hierarchical trilateral positioning and the optimal selection algorithm are jointly implemented to determine the final position in the narrowed positioning space.Finally,the high-precision thr-ee-dimensional positioning without the blind spot can be achieved.2.Research on orthogonal frequency-division multiplexing(OFDM)based VLC modulation and equalizationIn order to alleviate the increasing RF spectrum pressure and consider the limited linear dynamic range and the typical low-pass channel property of VLC,the dissertation based on the typical asymmetrically clipped optical OFDM(ACO-OFDM)and direct current biased optical OFDM(DCO-OFDM)VLC schemes proposed:(1)Discrete Hartley transform(DHT)based ACO-SCFDM VLC scheme.It adopts the DHT-spreading method to achieve PAPR reduction of ACO-OFDM signal,and uses the one-demensional constellation and the simplified signal encoding method to reduce the computational complexity.By simulation,ACO-SCFDM can reduce the requirement to DAC and enhance the tolerance to the nonlinear charateristics of LED,both of which are cost-efficient.At receiver,the joint one-tap equalization and intra-symbol frequency-domain averaging(ISFA)algorithm is used to achieve the effective channel estimation and equalization.Simulation results show that the proposed scheme has the obvious advantages of performance and complexity over the traditional ACO-OFDM one.(2)Discrete Fourier transform(DFT)based real-valued interleaved SCFDM(I-SCFDM)VLC scheme.It uses DFT-spreading method to achieve the low-PAPR DCO-OFDM signal,and reduces the encoding complexity of transmitter by simplifying the signal encoding process.I-SCFDM also inherits the strength of resisting the high-frequency attenuation of signal.The simulation results verify that the scheme has the obvious advantage of Q2 performance over the traditional DCO-OFDM one in linearity-and bandwidth-limited VLC system.Moreover,the low-cost VLC experimental platform is set up where the 3-dB bandwidth is only2.1MHz.The experimental results reveal that when a low-complexity joint frequency-and time-domain equalization is adopted at receiver,a data rate of 100 Mb/s over 2.1-m transmission is achieved without any pre-compensation of transmitter.3.Research on OFDM-based dimmable VLC with high spectralefficiencyIn the practical applications,the dimming control function of LED deteriorates the spectral efficiency of VLC system.Based on the typical ACO-OFDM and DCO-OFDM dimmable VLC schemes,the dissertation proposes two types of dimmable VLC systems.(1)Asymmetrically hybrid optical SCFDM(AHO-SCFDM)based dimmable VLC scheme.The scheme designs the polarity-adjustable signal structure with the upper and lower ACO-SCFDM layers for better adapting to the limited linear dynamic range of the LED.Compared to the traditional ACO-OFDM one,the proposed scheme increases the used subcarrier resources.Meanwhile,AHO-SCFDM inherits the advantage of SCFDM in low PAPR and resistance to the high-frequency distortion in bandwidth-limited systems.The simulation results show that the scheme can achieve the communication with high spectral efficiency in the wide dimming range.Based on AHO-SCFDM,layered/enhanced ACO-SCFDM(L/E-ACO-SCFDM)based dimmable VLC scheme is proposed for further enhancing the used subcarrier number.It can achieve the multi-layer ACO-SCFDM dimmable system.The layer amplitude,layer spectral efficiency and bias voltage are jointly optimized for maximizing the spectral efficiency of system.Benefiting from the low-PAPR property,the resistance to the high-frequency attenuation and the multi-layer structure,the scheme can achieve the efficient communication under different illumination requirements,which shows the great superiority for future practical applications of VLC.(2)Direct current biased optical SCFDM(DCO-SCFDM)based dimmable VLC scheme.The scheme adopts the low-PAPR and real-valued I-SCFDM for achieving VLC with dimming control.Based on the high spectral efficiency of DCO-OFDM,the proposed scheme mitigates the high-PAPR problem for avoiding the excess amplitude clipping within the limited dynamic range of LED.Moreover,the advantage of resistance to high-frequency distortion can further enhance the achievable spectral efficiency in the dimmable VLC system.Based on DCO-SCFDM dimmable VLC scheme,the paper proposes space-domain dimming control SCFDM(SD-SCFDM)VLC scheme.It achieves the spatial dimming by introducing the space-domain dimming factor according to spatial summing property of VLC.The proposed scheme can satisfy different illumination requirements by adjusting the number of active LED chips,which can avoid adjusting the signal amplitude and bias voltage simultaneously.Finally,simulation results verify that the achievable spectral efficiency of SD-SCFDM scheme is higher than the of its OFDM-based counterpart in the entire dimming range.Additionally,for the proposed scheme with different spectral efficiencies,the required number of LED chips in one lamp is also reduced greatly.In summary,this dissertation has been in-depth discussed and studied three important VLC application scenarios:the VLC-based localization technology,the effective VLC modulation and equalization,the dimmable VLC technology.The research results show the important significance in the 5G and future B5G practical applications.