High-speed VLC for Outdoor Free-Space Communication Proposal

January 2016 Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) doc.: IEEE 802.15-15-16-0019-00-007a Submission Title: High-speed VLC for out-door free-space communication Date Submitted: January 2016 Source: Prof. Nan Chi, Dr. Junwen Zhang Company: Fudan Univerisity Address: Fu Dan University, 220 Handan Rd., Yangpu District, Shanghai Voice: Tel: 0086-21-65642983, E-Mail: nanchi@fudan.edu.cn hustzjw@gmail.com Abstract: In response to Call for Proposals for OWC Channel Models issued by 802.15.7r1, this contribution presents the PHY technologies proposal of outdoor free space VLC long distance transmission for high rate PD communication in wireless backhaul (mobile back haul). Purpose: Call for Proposal Response Notice: discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. This document has been prepared to assist the IEEE P802.15. It is offered as a basis for Submission Slide 1 Nan Chi, Junwen Zhang, Fudan Univerisity

January, 2015 doc.: IEEE 802.15-15-16-0019-00-007a Application Scenarios: Mobile backhauling VLC outdoor free-space high speed PD communication for mobile backhaul It shares the same CAPEX/OPEX advantages with mmW More competitive with lower device cost *A typical mmW backhaul link Backhaul is a top priority for small cell deployments 80% of small cells will have wireless backhaul Cost of fiber is ~4x greater than wireless (cumulative CAPEX/OPEX) Small Cell mesh inter-connectivity over ~250m Large indoor and outdoor public spaces Characters: Large indoor/outdoor public spaces Distance: ~50 m~1 km Speed: ~Gbps Link: mainly Point-to-point * According to InterDigital Whitepaper 2013 Submission Slide 2 Junwen Zhang, Nan Chi, Fudan Univerisity

January, 2015 doc.: IEEE 802.15-15-16-0019-00-007a Targets High-speed VLC Out-door long-distance communication for mobile backhaul Data Rates Speed: ~Gbps Distance: 50m~1km, typical ~250-500 m Environment: Large outdoor public spaces Link: mainly Point-to-point To provide a Out-door VLC free-space link for high-speed user applications. Submission Slide 3 Junwen Zhang, Nan Chi, Fudan Univerisity

January, 2015 doc.: IEEE 802.15-15-16-0019-00-007a Proposal Research Route VLC Free Space Transmission Channel Model LED/PD Modulation Property Optics System design Free-space channel Key Technique for High Speed Outdoor VLC Transmission System Modulation formats equalization Technology Multiplexing Pre Equalization and post- Diversity reception technology Simulation for Outdoor Long Distance VLC Transmission System System Structure and Simulation Parameters Simulation Results and Analysis Outdoor Transmission Experiments System Structure Results and Analysis Submission Slide 4 Junwen Zhang, Nan Chi, Fudan Univerisity

January, 2015 doc.: IEEE 802.15-15-16-0019-00-007a High-speed VLC our-door modeling High-speed VLC Out-door long-distance communication for mobile backhaul:Theoretical study of system Model Tx/Rx LED and PD modulation model LED Tx model: modulation bandwidth (linear); Nonlinearity PD/APD receiver sensitivity, noise Link analysis SISO MIMO Point- to- Point Point- to- multi- Point Optical System Model LED beam, LED power, active area, beam width, multi-LED Tx Focal length and diameter of lens, Tx/Rx Angle of Half Received power, PD area, Rx Focal length/diameter of lens Free-space channel model Path loss, Distance Air Turbulence Background Noise, optical filter Fog/Rain, impact of visibility Submission Slide 5 Junwen Zhang, Nan Chi, Fudan Univerisity

January, 2015 Physical Layer of VLC system doc.: IEEE 802.15-15-16-0019-00-007a Visible light transmission Rx Module LEDModulation Demodulator Tx Module Decoder I AD Phase AD coding modulation Pre-equalization Q Baseband O to E LED Signal processing Data TX electronics LED driving circuit signal processing (coding,modulation, equalization) optics transmitter antenna RX optics receiver antenna PD electronics signal processing (decoding,demodulation, equalization), Submission Slide 6 Junwen Zhang, Nan Chi, Fudan Univerisity

January, 2015 doc.: IEEE 802.15-15-16-0019-00-007a 1. LED bandwidth limitations 2. VLC system Nonlinear LED Nonlinearity 10dB Bandwidth Inter-symbol interference LED nonlinearity Phosphor LED 10dB bandwidth<15MHz RGB LED 10dB bandwidth<25MHz Solutions Higher order modulation and pre- equaliztion Advanced post-equalization techniques Software/ hardware pre-equalization PAM OFDM Single Carrier CAP and so on ZF CMMA Volterra DFE M-CMMA RLS DD-LMS Submission Slide 7 Junwen Zhang, Nan Chi, Fudan Univerisity

VLC Channel Pre-equalization doc.: IEEE 802.15-15-16-0019-00-007a Visible light transmission Rx Module LEDModulation Tx Module Demodulator I Decoder AD Phase AD coding modulation Q Baseband O to E Signal processing LED Data Pre-equalization Pre-equalization schemes: Hardware Equalization hardware circuit design Software Equalization digital signal processing Submission

doc.: IEEE 802.15-15-16-0019-00-007a Software Pre-equalization FIR response Channel response Pre-equalization Obtain the channel knowledge(H) at the RF domain Make pre-equalization Tx*1/H at the baseband w/opre-equlization withpre-equlization Y. Wang, et al, IEEE Communication Letters, Vol. 18, No. 10 Submission

doc.: IEEE 802.15-15-16-0019-00-007a Hardware bridged-T amplitude equalizer Z11 RLC Network1 R2 R3 LED Driving Circuit Z22 Data In RLC Network2 Z11 : RLC network1 (R1, C1 and L1) Z22 : RLC network2 (R4, C2 and L2) R2 =R3 =R0 R = + 1/(1 ) S L j L 2 0 = Z Z R 21 + 11 22 R 1 4 2 1 C L 1 1 X. Huang, et al, OFC 2015, Tu2G.1 Submission

January, 2015 doc.: IEEE 802.15-15-16-0019-00-007a Hardware Pre-EQ for Gbps VLC system DC supply Blue Filter PIN White LED DC Out+ Ch1 + EA2 LE D OSC Ch2 TIA TIA - AWG Out- EA1 Bias Tee Cascaded Equalizer TX EA3 RX Lens GND QAM Demapping Channel estimation Post-equalization Serial to Parallel Parallel to Serial Serial to Parallel Parallel to Serial cos QAM Mapping -sin Downsample Syn. Ch2 Remove CP Upsample Add CP Data out Data in IFFT FFT Syn. Ch1 cos -sin OFDM modulation OFDM demodulation X. Huang, et al, Optics express, 2015 Submission Slide 11 Junwen Zhang, Nan Chi, Fudan Univerisity

January, 2015 Bit-loading based OFDM-DMT modulation for Gbps VLC doc.: IEEE 802.15-15-16-0019-00-007a Blue Filter DC supply EA2 DC supply PIN Output+ Channel1 AMP LED Arbitrary Waveform Generator + LE D Oscilloscope Channel2 TIA TIA - AMP AMP Pre-qualizer EA1 TX Bias Tee Output- RX GND AWG710 Lens EA3 54855A X. Huang, et al, IEEE Photonics Journal, 2015 Submission Slide 12 Junwen Zhang, Nan Chi, Fudan Univerisity

January, 2015 Bit-loading based OFDM-DMT modulation for Gbps VLC doc.: IEEE 802.15-15-16-0019-00-007a (a) SNR estimation (dB) 30 20 10 0 0 50 100 (b) Bit allocation 150 200 250 5 0 0 50 100 (c) Power allocation 150 200 250 5 0 0 50 100 150 200 250 Subcarrier index X. Huang, et al, IEEE Photonics Journal, 2015 Submission Slide 13 Junwen Zhang, Nan Chi, Fudan Univerisity

VLC Channel Post-equalization doc.: IEEE 802.15-15-16-0019-00-007a Visible light transmission Rx Module LEDModulation Tx Module Demodulator I Decoder AD Phase AD coding modulation Q Baseband O to E Signal processing LED Data Post-equalization Post-equalization solutions: ISI Equalization Classical DFE Modified Eqs Nonlinear Compensations Volterra series Submission

January, 2015 doc.: IEEE 802.15-15-16-0019-00-007a Volterra nonlinear equalizer 140 V-I curve of the Red Chip 120 Current (mA) 100 Measured Curve 80 Bias Voltage Current Linear Curve 60 LED nonlinearity 40 Signal Vpp 20 TOV 0 1.6 1.7 1.8 1.9 Bias Voltage (V) 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Voltage LED nonlinearity seriously degrades the system performance; The LED forward current exhibits strong nonlinearity with the bias voltage; Two factors dominate the nonlinear effects: DC bias voltage and the input signal peak-to-peak value (Vpp); Submission Slide 15 Junwen Zhang, Nan Chi, Fudan Univerisity

January, 2015 doc.: IEEE 802.15-15-16-0019-00-007a Volterra nonlinear equalizer ( ) ly n Linear Equalizer = + ( ) y n ( ) ( ) n y n y l nl 1( ) w n 2( ) w n 0( ) w n ( ) iw n ( ) y n 1 N = + ( ) ( w n x n i ) i ( ) x n Z Z 1 1 = 0 i Weights Update ( ) e n ( ) y n l Ref. Nonlinear Equalizer 1 1 NL NL w n x n k x n l ( ) ( ) ( ) ( ) w n kl 01( ) w n 00( ) w n 11( ) w n 12( ) w n 22( ) w n 02( ) w n kl = l k = 0 k ( ) n y nl ( ) n y nl Principle The Volterra series based equalizer is considered as a promising solution to mitigate the LED nonlinearity; The Volterra series expansion contains a linear term and nonlinear series. M-CMMA is utilized to update the weights of the nonlinear equalizer without using training symbols Submission Slide 16 Junwen Zhang, Nan Chi, Fudan Univerisity

January, 2015 doc.: IEEE 802.15-15-16-0019-00-007a RGB LED (LED Engine) Multiplexing for high-speed VLC (WDM VLC outdoor transmission CAP Demodulation CAP Modulation EA Bias Data out Data in Eq. LPF QAM Demapping APD 1 MRC QAM Mapping DC DD-LMS RGB LED LPF Up-Sample Red Bias M-CMMA w1 EA I/Q Separation lens& filter Eq. LPF Green Down-Sample APD 2 DC Blue ( ) ( ) Qf t If t LPF EA Bias ( ) m t ( ) m t w2 Q I Eq. LPF 50m DC Submission Slide 17 Junwen Zhang, Nan Chi, Fudan Univerisity

January, 2015 doc.: IEEE 802.15-15-16-0019-00-007a Receiver diversity technology 2r 3r Mr 1r In receiver diversity, the outputs of multiple receivers are combined which is a weighted sum of the different branches 1 2 3 M 2 the output SNR: = M i i r 2 r = 1 i = ith branch SNR: 2/ i i r = N M N 2 i N i tot i = Combiner output SNR: 1 i The goal of MRC is to find the weight to maximize the output SNR According to the Schwarz inequality, it is found that: the maximum SNR of the combiner output is the sum of SNRs in each branch: 2 1 / i i r = M M = = N i i = 1 i Submission 18

January, 2015 Out-door Long distance testing results doc.: IEEE 802.15-15-16-0019-00-007a 20 Red Chip 0 Power (dB) @3.8e-3 -20 Red Chip Green Chip Blue Chip 1E-3 -40 -60 -80 0 50 Frequency (MHz) 100 150 200 250 20 1E-4 Green Chip Power (dB) BER 0 BER -20 (a) -40 -60 1E-5 -80 0 50 100 150 200 Frequency (MHz) 20 Blue Chip Power (dB) 0 1E-6 -20 -40 -60 10 20 30 40 50 Distance (m) -80 0 50 Frequency (MHz) 100 150 200 250 Distance At the distance of 50m, the total data rate of 1.8Gb/s can be achieved with the BER less than the 7 % FEC limit of 3.8x10-3. Submission Slide 19 Junwen Zhang, Nan Chi, Fudan Univerisity

January, 2015 doc.: IEEE 802.15-15-16-0019-00-007a Conclusion In this contribution, we propose several general technique considerations for high rate PD VLC out-door communications. The out-door high-speed VLC modeling including three parts LED/PD Modulation Property Optical system design Free-space channel The results show the benefit and feasibility of the advanced pre-equalization and post-equalization technology for the high-speed VLC systems. To achieve high speed VLC out-door communication, we provide analysis and our proposals on the following aspects Adaptive Modulation formats: DMT with bit loading Multiplexing Technology using different color LED and MIMO setup Advanced Pre-/post- equalization methods Receiver-diversity reception technology Submission Slide 20 Junwen Zhang, Nan Chi, Fudan Univerisity