Research On Theory And Techniques Of Efficient Transmission In Indoor Visible Light Communications

Visible light communication(VLC),which does not take up the radio frequency(RF)spectrum,has attracted considerable interests owing to its compelling advantages of license-free operations,low cost,high-speed transmission,low electromagnetic interference,high security and so on.Given the saturation of the RF spectrum and the unsatiable customer demand for high-speed data transmission,VLC is deemed to be a promising solution of realizing ubiquitous high-capacity indoor wireless coverage,which is of broad prospects for commercial application.Recently,some efficient transmitting techniques have been extensively inves-tigated in wireless communication,including multiple-input multiple-output(MIMO),orthogonal frequency division multiplexing(OFDM)and so on.In the context of VLC,a critical issue is how to optimize and design these techniques to explore their potential application advantages in VLC.This paper mainly focuses on the optimization of the techniques of MIMO and OFDM in VLC.More specifically,the main contributions of the paper are summarized as followings:Firstly,a novel VLC MIMO transceiver is investigated under the optical power constraints in the disser-tation.The model of optical power constraints,which is applicable to a wide range of modulation schemes in VLC,is established by taking into consideration the unique characteristics of VLC,including the nonlinearity of light emitting diodes(LEDs),indoor illumination and so on.These constraints imposed on transmitted signals can ensure that the LEDs operate within their limited linear dynamic ranges,thus avoiding the non-linearity distortion.Furthermore,under the minimum mean-square error(MMSE)criterion,we formulate the optimization problem of the MIMO transceiver design.An efficient solution of our design problem is derived by conceiving a projected gradient algorithm.The proposed MIMO transceiver scheme is capable of improving the system performance,whilst at the same time,achieving the functionality of dimming control to satisfy the different illumination demand.Numerical results show that the proposed scheme achieves better bit error ratio(BER)performance than the traditional scheme based on singular value decomposition(SVD).Then,in order to suppress the multiuser interference and boost the attainable system performance,the multiuser transceiver design of VLC systems is studied in the dissertation.Based on the optical constraints for MIMO transceiver proposed in Chapter 3,we deduce the specific optical constraints imposed on multiuser transceiver.Furthermore,the multiuser multiple-input single-output(MISO)transceiver design in VLC is investigated under these optical power constraints.More specifically,we formulate the transceiver design as the optimization problem that minimizes the maximum MSE between the received and legitimate transmitted user.The globally optimal transceiver scheme is first proposed,which can substantially mitigate the inter-user interference as well as maintain communication fairness for all users.Then,by introducing the zero-forcing(ZF)criterion into the design,we propose a simplified ZF transceiver,which outperforms the traditional pseudo-inverse based ZF TPC scheme of RF communication,and strikes a compelling tradeoff between the complexity imposed and the performance obtained.Based on the above work,we extend the study to the case of the multiuser MIMO transceiver design in VLC.Under the mentioned constraints,we first formulate the design problem of the multiuser MIMO transceiver.Then,a locally optimal transceiver design scheme is put forward by invoking the method of iterative optimization.Simulation results demonstrate that the proposed transceiver schemes exhibits superior performance compared to the conventional ZF and block diagonalization(BD)methods.Finally,the dissertation investigates the peak-to-average power ratio(PAPR)reduction of optical OFDM(OOFDM)in VLC.In order to avoid bandwidth expansion and significant increase in bit error ratio(BER),the tone injection method is adopted in the proposed scheme to reduce PAPR.With the aid of the theory of compressed sensing,we first investigate the linear TI scheme of DC-biased OOFDM(DCO-OFDM),which exhibits almost the same performance as the conventional TI method,but has a lower implementation com-plexity.Furthermore,we focus our attenuation on the PAPR reduction of hybrid asymmetrically clipped OOFDM(HACO-OFDM).Based on the superimposed feature of the HACO-OFDM,we propose the joint optimization of ACO-OFDM and PAM-MDT tone injection for HACO-OFDM for substantially reducing the PAPR.This is capable of providing a better PAPR reduction performance than separate tone injection ap-plied to both signal components.The performance of the proposed PAPR reduction methods is evaluated by simulation results.