Research On The Digital Signal Processing Technology For Mini-LED Visible Light Communication

430～790 THz is the communication frequency band of visible light communication(VLC).VLC can provide a large transmission capacity.Therefore,people have done a lot of research on VLC communication recently.With the discovery of blue and green light low attenuation windows in seawater,underwater visible light communication(UVLC)has been widely concerned in recent years.People widely use light-emitting diodes(LEDs)as the light source of VLC/UVLC due to their low cost and high safety.However,the modulation bandwidth of standard commercial LEDs is limited(usually only tens of MHz).Mini-LED or micro-LED achieves higher modulation bandwidth by reducing carrier lifetime and parasitic resistance-capacitance(RC)delay.Moreover,4-level single-carrier pulse amplitude modulation(PAM-4)has very low complexity,making it suitable for short-distance low-cost VLC/UVLC systems.In the PAM-4 VLC/UVLC system,linear and nonlinear damage limits the transmission capacity.In summary,a current research hotspot is using miniLED or micro-LED as the light source and adopting the digital signal processing(DSP)algorithm to achieve the high-speed PAM-4 VLC/ULC system.In this paper,we adopt the Volterra Equalizer,sparse Volterra Equalizer and noise-whitening post-filter to compensate for the damage of the system.We use the improved Gram-Schmidt(GS)orthogonal decomposition method and principal component analysis(PCA)method to reduce the computational complexity of the Volterra Equalizer.This paper proposes two kinds of noisewhitening post-filters whiten the color noise.The autoregressive(AR)model noise-whitening post-filter based on the Yule-Walker equation will introduce additional inter-symbol interference(ISI).Therefore,it is necessary to cascade the Maximum Likelihood Equalization(MLSD)based on the Viterbi Algorithm.Another noise-whitening post-filter connects the signal output at the current moment with the noise before and after this moment.It does not need to solve the Yule-Walker equation continuously and uses a simple AR coefficient acquisition method to update the noise-whitening post-filter taps.Therefore,this noise-whitening post-filter has low complexity,but it has some loss in performance.This paper builds a set of VLC/UVLC system with a transmission distance of 2 m based on a Ga N-based mini-LED with an active area diameter of 175μm and achieves the high-speed PAM-4 communication with the help of the sparse Volterra Equalizer and noise-whitening post-filter.When the driving current of the mini-LED is 50～60m A,its 3d B modulation bandwidth is 580 MHz,which is much larger than that of traditional commercial LEDs.When the PAM-4 signal with a data rate of 4.4 Gbit/s passes through a 2 m VLC system,its BER is below the 7% forward error correction(7%-FEC)threshold.This paper also realizes the data rate of 3.8 Gbit/s PAM-4 signal with BER of 3.7e-3 and the rate-distance product of 7.6 Gbit/s·m in the 2 m UVLC system.As far as we know,this is the highest speed-distance product based on a single-pixel LED.