PWM-based PPM Format for Dimming Control in Visible Light Communication System

Transcription

1 PWM-base PPM Forat for Diing Control in Visible Light Couniation Syste Hyung-Joon Jang 1, Joon-Ho Choi 1, Z. Ghasselooy, an Chung Ghiu Lee 1,* 1 Departent of Eletroni Engineering, Chosun University, Gwangju, South Korea Shool of Coputing, Engineering an Inforation Sienes, Northubria University, Newastle upon Tyne, Unite Kingo * E-ail : lee@hosun.a.kr Abstrat We report siulation results of pulse with oulation (PWM)-base pulse position oulation (PPM) signal forat for visible light ouniation systes. For siultaneous operation of ata transission an iing ontrol, PPM ata forat is ae to PWM iing ontrol signal. To show iing ontrol, the PWM uty ratio is hange fro 40 % to 80 % uring PPM ata transission. The PWM frae rate is set to 1 khz to avoi flikering in huan eyes. The PPM ata rate is set to 0 kb/s. The wavefors, eye iagras an BER of this syste are alulate. The siulation shows the BER of is ahievable. 3 LED Laps I. INTRODUCTION Reently, any researh results on inoor optial wireless ouniation using illuination LEDs have been reporte [1-10]. Copare to onventional lighting ethos suh as fluoresent or inanesent light, LED lighting is very useful ue to its avantages suh as effiieny, low power onsuption, environental frienliness, eye safety, an no regulation for raiation. Therefore, the appliation of the raws uh attention for isplay baklight unit (BLU), ar laps, inoor olorful illuinations, et. In aition, illuination LEDs are use not only as lighting evies, but also as optial soures for inoor optial wireless ouniation systes, the so-alle visible light ouniation (VLC) systes. The VLC has several avantages that it is strong against eavesropping beause light annot penetrate the opaque wall. An, the VLC wavelength range of 380 n ~ 750 n is not regulate. Therefore, we expet that VLC an provie high transission spees in inoor ouniation along with the evelopent of LEDs with wie oulation banwith. Reently, a obine syste of Ethernet an VLC using DPPM oulation etho is reporte by Rufo et al. []. A preite noralize power istribution an spatial istribution of Q fator using on-off keying non-return-tozero (OOK-NRZ) oulation etho are reporte at 5 Mb/s ata rate in inoor iffuse ellular visible light ouniation syste by Wu et al. [3]. Grubor et al. shows results on illuinane istribution, SNR istribution, broaban broaasting using white LEDs, whih have blue LEDs an phosphorous layer [4]. Cobining PWM base iing is perfore for VLC syste base on DMT [5]. 5 Figure 1. Inoor VLC siulation environent. Sine VLC syste will at as illuination as well, the iing ontrol funtion is neee. Previously, a joint brightness ontrol an ata transission for VLC systes by Siique an Tahir [6] an a joint LED iing etho with high apaity VLC is propose base on overlapping PPM (OPPM) [7] have been reporte. Also, we have propose a ata strea of NRZ-OOK ata strea over PWM iing signal an eonstrate the operation of the syste base on that signal forat [8]. PPM is power effiient opare with NRZ sine it avois the DC an lower frequeny oponents of the spetru []. Also, it aintains the iing ontribution fro its onstant average power. PWM is an wiely use etho for brightness ontrol [6]. Therefore, we suggest the PPM ata signal base on PWM iing ontrol signal for VLC systes. We exaine the perforane of the syste using a siulation progra, evelope using MATLAB an Siulink. Previously, we reporte an experiental results on PPM ata strea over PWM iing signal [10], where the PPM ata rate was set to 1 kbits/se whereas the PWM frae rate is set to 1 khz. A siulation progra is evelope an the siulation results are reporte on eye iagra an BER urve. This paper organize as follows. In Setion II, the optial hannel is esribe. In Setion III, the signal forat is explaine in etail.

2 In Setion IV, the siulation results are shown. The illuination istribution an reeive optial power istribution on the esktop surfae are alulate. Then, the signal wavefors inluing the reovere PPM ata signal, eye iagras an BER urve are shown. Finally, we onlue the paper with Setion V. where A is the physial area of the etetor in a PD, T s (ψ ) is the gain of an optial filter, an g (ψ ) is the gain of an optial onentrator. ψ enotes the with of the fiel of vision at a reeiver. TABLE I. SIMULATION PARAMETERS II. OPTICAL CHANNEL The roo oel in Fig.1 has the size of 5 x 5 x 3. Four LED transitters are installe above.5 fro the floor. Eah LED transitter is assue to be opose of 3600 LEDs, whose enter luinous intensity is An, the reeiver is installe on the esk an the height of the esk is The refletion at eah wall is assue to be Labertian. The first-orer refletions are onsiere for siulation. The illuination represents the brightness of an illuinate esktop surfae. The luinous intensity at an angle φ is given by: I ( φ) = I(0)os ( φ), (1) where I(0) is the luinous intensity of the white LEDs, φ is the angle of irraiane, it is assue that LED lighting has a labertian raiation pattern [9], is the orer of labertian eission an is given by the sei-angle at half illuination of the LED φ as: 1 = ln ln(osφ 1 ), () A horizontal illuination E hor at a point (x, y, z) on the esktop surfae is given by: I(0)os ( φ) E =, (3) hor D os( ψ ) where D is the istane between transitter an reeiver, ψ is the angle of iniene. For assessing ouniation perforane with the propose signal forat, the reeive optial power is alulate by the hannel DC gains H (0), on irete paths an H ref (0), on reflete paths with the Eq. (4) [9]. { P H 0) + P H (0 } walls LEDs P = ( ), (4) r t where P t is the transitte power fro an LED an P r is the reeive optial power at a reeiver point. The hannel DC gain is given [9] as: H ( + 1) A os ( φ) T ( ψ ) g ( ψ )os( ψ ), 0 ψ ψ s, (5) ( 0) = πd 0, ψ > ψ t ref The optial onentrator g (ψ ) an be given [9] as: n, g ( ψ ) = sin ψ 0, 0 ψ ψ, (6) ψ > ψ where n enotes the refrative inex. The hannel DC gain on the first refletion is given [9] as H ref Sei-angle at half power 60 [eg.] Center luinous intensity 0.63 [] Nuber of LEDs 3600 (60x60) Transitte optial power 169 [W] FOV at a reeiver 60 [eg.] Refletion oeffiient of eah wall 0.7 Gain of an optial filter 1.0 Refrative inex of a lens at a PD 1.5 Detetor physial area of a PD 1.0 [ ] ( + 1) A ρa π D D 1 (0) = wall 0,, os ( φ)os( α)os( β) T ( ψ ) g ( ψ )os( ψ ) s 0 ψ ψ ψ > ψ, (7) where D 1 is the istane between an LED hip an a refletive point, D is the istane between a refletive point an a reeiver, ρ is the refletane fator, A wall is a refletive area of sall region, α is the angle of irraiane to a refletive point, β is the angle of irraiane to the reeiver. The values of physial paraeters suh as sei-angle at half power, enter luinous intensity an transitte optial power, et. are liste in Table I. The paraeters for LED is quote fro a oerial LED [11]. The optial wavefors, eye iagras an bit error ratio (BER) will be alulate using the propose signal forat base on PPM ata strea over PWM iing signal. We assue that the inoor VLC hannel is an aitive white Gaussian noise (AWGN) hannel. III. SIGNAL FORMAT The propose signal forat is shown in Fig.. The PWM signal is for iing ontrol. The with of a PWM pulse is proportional to the iing level of illuination. The PPM oulate ata signal is transitte with the

3 PWM iing ontrol signal, regarless of the ON state uring a PWM perio. To show signal shapes uring iing ontrol, we show the instant at the iing level hange fro 80 % to 40 %. experienes refletions at eah wall. The effet of refletions is ipleente in MATLAB -files an AWGN is ae using Siulink. The reore ata are use for alulation of illuination, reeive optial power istributions an wavefors. A. Illuination Distribution Figure. PPM-PWM signal forat. The binary PPM ata pulses oupy 10 % of the PWM iing perio. The PPM pulse with is 5 μs within a slot perio of 50 μs. Therefore, the guar tie is set to 40 μs. Figure 4. Illuination istribution on the esktop surfae. (Max : lx, Ave : lx, Min : lx). IV. SIMULATION RESULTS Fig. 4 shows the illuination istribution on the esktop surfae using Eq. (3). Exept orners, the average illuinane level is lux an it eets the ISO reoenation for offie work. B. Optial Power Distribution Fig. 5 shows a optial power istribution on the esktop surfae using Eq. (4). We assue LEDs with RGB threehip in a pakage [11]. Figure 3. Flow hart of siulation. Fig. 3 shows the blok iagra whih explains the siulation proess. The PWM pulses for iing an PPM pulses for ata signal are generate at Siulink bloks. The obine signal for the propose signal forat oulates LEDs an the oulate light signal Figure 5. Optial power istribution on the esktop surfae. (Max : 14.1 B, Average : B, Min : 6.65 B).

4 C. Signal Wavefors Fig. 7 shows the eye iagra of the PPM signal extrate fro the wavefor in Fig. 6. As explaine in Setion III, it is shown that the slot tie of PPM is 5 μs. Therefore, Fig. 7 shows that the slot tie of -pp is 10 μs an the guar tie is 40 μs. E. Bit error ratio (BER) Figure 6. Wavefors of PPM ata strea over PWM signal.. Figure 8. Bit error ratio. In this siulation, we assue that PWM uty ratio is set to hange between 80 % an 40 % for brightness an the PWM frae rate, whih ensures no flikering at the iing rate over 500 Hz. The PPM ata rate is set to 0 kbits/se. Fig. 6 shows the alulate signal wavefors along with flow hart in Fig. 3. The PWM an PPM signals are ae in synhronis an the propose signal wavefor is shown on the thir figure. Then, the refletion an AWGN is ae an the reovere PPM signal is shown. D. Eye iagras Fig. 8 shows the BER of this syste. We fin that the BER value of about is obtaine when E b /N o is larger than -1 B. V. CONCLUSION We have shown a siulation result on a VLC syste whih transits PPM ata strea with PWM iing ontrol signal. We alulate the optial power istribution on the esktop surfae assuing white LEDs. We propose a PPM ata signal for ata transission base on the PWM iing ontrol signal. The PWM uty ratio was set to hange between 40 % an 80 % for brightness ontrol an the PWM frae rate 1 khz. The PPM ata rate was set to 0 khz. We have shown the alulate wavefors, eye iagras an BER urve. The BER of has been obtaine. ACKNOWLEDGMENT This work is supporte by the Basi R&D Progra of Ministry of Euation, Siene an Tehnology through National Researh Founation (NRF) [ ]. Figure 7. Eye iagra of the reovere PPM signal. REFERENCES [1] T. Koine an M. Nakagawa, Funaental analysis for visiblelight ouniation syste using LED lights, IEEE Transations on Consuer Eletronis, vol. 50, pp , February 004.

5 [] J. Rufo, C. Quintana, F. Delgao, J. Rabaan an R. Perez- Jienez, "Consierations on oulations an protools suitable for visible light ouniations (VLC) hannels: Low an eiu bau rate inoor visible light ouniations links," The 8th IEEE Consuer Couniations an Networking Conferene (CCNC), pp , January 011. [3] D. Wu, Z. Ghasselooy, H. Le Minh, S. Rajbhanari an Y.S. Kavian, "Power Distribution an Q-fator Analysis of Diffuse Cellular Inoor Visible Light Couniation Systes," The 16th European Conferene on Networks an Optial Couniations (NOC), pp.8-31, July 011. [4] J. Grubor, S. Ranel, K.-D. Langer an J.W. Walewski, Broaban Inforation Broaasting Using LED-Base Interior Lighting, Journal of Lightwave Tehnology, vol. 6, pp , Deeber 008. [5] G. Ntogari, T. Kaalakis, J. W. Walewski an T. Sphiopoulos, "Cobining Illuination Diing Base on Pulse-With Moulation With Visible-Light Couniations Base on Disrete Multitone," IEEE/OSA Journal of Optial Couniations an Networking, vol. 3, pp , January 011. [6] A.B. Siique an M. Tahir, "Joint Brightness Control an Data Transission for Visible Light Couniation Systes base on White LEDs," The 8th IEEE Consuer Couniations an Networking Conferene (CCNC), pp , January 011. [7] B. Bai, Z. Xu an Y. Fan, "Joint LED Diing an High Capaity Visible Light Couniation by Overlapping PPM," 19th Annual Wireless an Optial Couniations Conferene (WOCC), pp. 1-5, May 010 [8] E.-B. Cho, J.-H. Choi, C. S. Park, M. S. Kang, S. J. Shin, Z.Ghasselooy an C. G. Lee, "NRZ-OOK Signaling with LED Diing For Visible Light Couniation Link," The 16th European Conferene on Networks an Optial Couniations (NOC), pp. 3-35, July 011. [9] J.M. Kahn an J.R. Barry, Wireless Infrare Couniations, Proeeings of the IEEE, vol. 85, pp , February [10] J.-H. Choi, E.-B. Cho, T.-G. Kang an C. G. Lee, Pulse with oulation base signal forat for visible light ouniations, The 15th OptoEletronis an Couniations Conferene (OECC), pp , July 010. [11] (LRTB G65F 6-lea MULTI LED).