Space-Collaborative Constellation Designs And Detections For MIMO Visible Light Communications

Visible Light Communication(VLC)because of its green environmental protection and does not take up the traditional spectrum resource,which is widely researched by scholars and supported by governments around the word.In order to meet the demand brightness of light,indoor lighting is generally performed by a plurality of LED bulbs together,while each LED within the lamp further comprises a plurality of wicks,so indoor visible light communication system is a natural multi-input communication system.For a single LED visible light communication system which wicks are limited bandwidth,MIMO(Multiple-input Multiple-output)is a powerful way to enhance its transmission rate.However,in conventional MIMO VLC techniques such as repetition coding(RC),spatial modulation(SM)and spatial multiplexing(SMP),their transmission symbols are produced by each independent antenna,so their energy utilization efficiency are very low.This paper takes full advantage of rich resources of space visible light communication and the characteristic of non-negative channel signals,then designs a novel modulation technology,that is space-collaborative constellation(CC),the main research contents and results summarized as follows:1.As the energy utilization efficiency of the conventional MIMO VLC techniques is very low,we minimize the average optical power as an optimization goal under the conditions of a given transmission rate,then establish an optimal design model of constellation for VLC MIMO,and convert it to maximize the minimum Euclidean distance,and prove that the optimal space-collaborative constellation analytic formula.We design a 2×2 space-collaborative constellation based on the optimal space-collaborative constellation analytic formula,performance analysis and comparison shows that,compared with RC,SM,SMP,CC always achieves a minimal average optical power under different spectral efficiency.Numerical simulation under static channel and sports channel show that,under any correlation channel and different spectrum efficiency,the performance of CC is always better than SM and SMP,and it is also better than RC under the low correlation channel and high spectral efficiency.Meanwhile,according to the space-collaborative constellation design criterion,we also build 3×3,4×4 space-collaborative constellation and construct the corresponding mobile channel model,through performance analysis and numerical simulation demonstrates the superior performance of the multidimensional space-collaborative constellation again.2.As the computational complexity and the consuming time of space-collaborative constellation is very large in the decoding process,combined with its unique triangular structure,we have designed a fast detection algorithm with linear complexity and theoretically proved its performance is equivalent to the maximum likelihood algorithm.Firstly,we virtual extend space-collaborative constellation based on the structural characteristics of space-collaborative constellation,then design a rapid quantification for the receiving signals in the expanded square constellation.Secondly,we design a fast decision decoding algorithm for the quantized signals belong to different constellations,and also prove that the fast detection algorithm is equivalent to the traditional maximum likelihood detection algorithm theoretically.Thirdly,compared to the computational complexity of the conventional maximum likelihood detection algorithm,we analyze the computational complexity of the fast maximum likelihood detection algorithm.Finally,numerical simulations show that the BER performance of the fast ML algorithm is the same as that of the conventional ML algorithm.3.Based on the structure of the maximum likelihood detection and the decision region in the Maximum Likelihood detection,we analyze the performance of space-collaborative constellations in theory,get a general analytical formula for symbol error rate,and design a rotating-based portion of the bit mapping method of the Gray code for space-collaborative constellation.According to the divide area of constellation points in the fast ML algorithm and the layout of different constellations,we derive the transmission performance of space-collaborative constellation in detail and get a general expression of symbol error rate.By comparing space-collaborative constellations and QAM(Quadrature Amplitude Modulation)constellation layout structure similarities and differences,we get a rotating-based portion of the bit mapping method of the Gray code for space-collaborative constellation.Numerical simulations verify the correctness of theoretical derivation symbol error rate expressions.