Research On Space-Collaborative Coding For High-Speed Visible Light Communications

Combining lighting with communication,Visible Light Communication(VLC)is used as a means to defuse the frequency spectrum tension,the poor coverage problem and the energy consumption problem in wireless communication that is based on extensive coverage of Light Emitting Diode(LED).High-speed transmission has been an extensively attractive task in telecommunication industry,in order to improve the transmission rate,a possible way is to use array transmission,i.e.,multi-LED parallel transmission.In this paper,based on the unique advantages of indoor VLC,such as abundant space resource,channel static stability,non-negative signal and so on,space collaborative coding technique for the joint design of multiple transmitter-receiver signal parameters at different spatial locations is presented,the main research contents and results are summarized as follows:1.Catering to the need of high-speed parallel transmission for indoor VLC,a VLC multi-LED space-collaborative coding transmission model and constellation additive unique factorization that is applied to VLC are proposed,while realizing the high-speed transmission,reducing effectively the correlation of the channel and the peak-to-average power ratio of signal.As the issues,such as the low modulation depth of the traditional transmission drive circuit and the high peak-to-average power ratio in VLC system,a lighting and communications integrated effectively drive circuit and a VLC multi-LED space-collaborative coding transmission model are designed.While the differences in amplitude and time delay are set at the transmitter so that the synthetic signal received at the receiver is equivalent to a high order modulation signal,while the multiple LEDs with one receiver reach the additive unique factorization,which can reduce effectively the peak-to-average power ratio,achieve a better anti-nonlinearity performance and a higher rate.2.In order to the space-collaboration of indoor multi-LED lamps,multi-LED chips and multi-color-LED chips,under the optimal design criterion with maximizing the minimum Euclidean distance,the optimal power allocation problem is equivalent to non-convex optimization problem that is a mix of continuous variable and discrete variable,while the closed-form optimal power allocation solution is obtained through the combination of mathematical geometry and piece-wise induction.According to the differences of the channel gains and the number of the transmission,then,a power allocation scheme is derived and analyzed,increasing the identification of multi-LED parallel transmission channels for VLC system.Under the optimal design criterion with maximum likelihood detection that is to maximize the minimum Euclidean distance between the receiving vectors and the maximum symbol error rate minimization criterion with linear detection,the closed-form optimal power allocation solution is obtained for arbitrary modulation orders and channel settings through the combination of mathematical geometry and apagoge.Simulation results indicate that the proposed power allocation strategy obtains significant performance gains over the uniform power allocation system that is consistent with the theoretical analysis.While according to the closed-form allocation solution,the power allocation ratios of the transmit signals can be adaptively adjusted and generalized to power allocation schemes of arbitrary cases with a direct guiding significance.3.Aiming at improving the performance of Orthogonal Space-Time Block Codes(OSTBCs)for VLC,base on the Uniquely Factorable Constellation Pair(UFCP)and space-collaboration,constellation collaborated non-linear orthogonal space-time block codes and a fast maximum likelihood decoding algorithm with the linear decoding complexity are developed.The deployment of OSTBCs for VLC and the channel model about OSTBCs are introduced.Using the recently-developed unique factorization of signals,several UFCPs generated from cross quadrature amplitude modulation(QAM)constellations are chosen for transmission through all the transmitter antennas,with one random symbol acting as a coordinator to control all the symbols embedded in each coding matrix.The coding gains of collaborated orthogonal codes that accumulate the minimum Euclidean distances of serval constellations are calculated and some optimal constellation pairs with maximum coding gains are presented,including orthogonal codes with different antennas and UFCPs with different groups.As the fact that the proposed code is nonlinear,a fast ML decoding algorithm is developed that is also applied to the detection of collaborative nonlinear OSTBCs technology in VLC system,while its complexity is analyzed in detail.By comparing the decoding complexity of serval detection methods,it can be observed that the complexity of fast ML algorithm is still linear in terms of the square root of the cardinality of the cross QAM constellations without any performance loss.Computer simulations are performed to verify the performance of collaborative OSTBCs and the fast ML Algorithm under different conditions,and the results demonstrate that the average error rate of the collaborative nonlinear orthogonal codes outperforms that of the conventional OSTBCs.4.In view of the problem that multi-user high-speed VLC transmission is difficult to construct directly orthogonal transmission matrix,a faster-than-Nyquist(FTN)space-collaborative signal design is presented,while realizing the parallel transmission and multi-cell communication,the theoretical limit of the method is analyzed and a fast iterative receiver is developed.Indoor VLC system is a typical multi-user multi-cell system and each LED lamp is the base station of an optical cell.A FTN signal design is presented for multi-user multi-cell VLC broadcasting systems,where all the transmitters transmit independently with a properly designed time delay to achieve multiple times spectral efficiency,while avoiding the inter-user or inter-cell interference.The performance of the system is analyzed in view of the minimum Euclidean distance of symbol sequence.As the design can be seen a convolutional code structure with dynamic weights,a fast iterative receiver for the system is developed to reduce the complexity of maximum-likelihood sequence estimation decoding algorithm.Simulation results show that the proposed system obtains significant performance gains over currently available schemes,while eliminating the need of joint encoding or the definition of auxiliary signals required in previous broadcast coding schemes.