Research On Error Propagation And Power Efficiency In NOMA-VLC Network

Light emitting diode(LED)based visible light communication(VLC)has recently attracted significant attention in both academia and industry due to the advantages of rich spectrum resources,easy implementation into existing infrastructure,and radio frequency(RF)interference-free.As a wireless broadband technology,an efficient multiple access(MA)method is essential for VLC.Especially the modulation bandwidth of current commercial LEDs is quite limited,which makes it difficult to realize large-scale high-speed VLC network.On the other hand,non-orthogonal multiple access(NOMA)has recently attracted significant attention as a promising multiple access scheme for the 5th generation(5G)wireless communication and VLC due to its superior spectral efficiency and support massive access.NOMA can achieve higher throughput by 30%to 40%and double the increase in access compared with orthogonal multiple access(OMA).However,there are still many problems with the NOMA-VLC network,include the problem of error propagation problem poor power efficiency.Thus,these two issues were studied in this paper and solutions were proposed.?A Symmetric Superposition Coding/Symmetric Successive Interference Cancellation(SSC/SSIC)scheme was proposed for the problem of error propagation.In NOMA network,user messages are superposed in the power-domain and separated by different size of power.The user with larger power can treat the signal of the user with lower power as noise and decode directly.The user with lower power need to restore and cancel the signal of the user with larger power.Hower,the demodulation error of the user with larger power will lead to the demodulation error of the user with lower power,which is called error propagation.Experiments show that more than 95%of errors in high-power users are transmitted to low-power users.This phenomenon is related to the distribution of the joint constellation generated by traditional superposition coding.Therefore,the probability of error propagation can be reduced by changing the joint constellation distribution.SSC/SSIC is proposed in this paper to solve this problem by adjusting the user signal superposition method to make the joint constellation distribution more reasonable.The experimental results show that more than 90%demodulation errors caused by EP are eliminated compared with traditional NOMA-VLC.?A Hierarchical Pre-distorted Layered Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing(HPD-LACO-OFDM)scheme is proposed for NOMA-VLC network to improve the power efficiency of traditional NOMA-VLC networks.It is not realistic to provide all users network access solely through NOMA technology since the power resources are limited.Thus,NOMA is always applied in combination with an orthogonal multiplexing technology.The orthogonal frequency division multiplexing(OFDM)is commonly selected due to its advantages of high spectrum efficiency,resistance to inter symbol interference(ISI)and flexible bandwidth allocation.DC-biased optical OFDM(DCO-OFDM)is the alternative in VLC system since negative signals cannot be transmitted in VLC.However,DCO-OFDM suffers from poor power efficiency,which limit the signal to noise ratio of the NOMA-VLC network.The other optical OFDM technologies also have problems such as poor power efficiency,poor spectral efficiency,or complex receiver.Thus,HPD-LACO-OFDM scheme is firstly proposed in this paper,which offers superior spectrum efficiency as well as optical power efficiency by generating multiple layers of ACO-OFDM signals to fill the odd subcarriers successively and eliminate the inter-layer interference with successive signal pre-distortion,and the implementation of the HPD-LACO-OFDM receiver is simple and will not impose a new burden on the complex receiver of the NOMA.The experimental results show that with the same signal power,the HPD-LACO-OFDM based NOMA-VLC network shows the best BER performance whereas the demand for DC voltage is reduced by half of the signal voltage compared to traditional DCO-OFDM based NOMA-VLC network.