visible light communication system using silicon photocell
TRANSCRIPT
Research ArticleVisible Light Communication System Using Silicon Photocell forEnergy Gathering and Data Receiving
Xiongbin Chen,1,2 Chengyu Min,1 and Junqing Guo1
1State Key Laboratory of Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, China2School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing, China
Correspondence should be addressed to Xiongbin Chen; [email protected]
Received 24 September 2016; Revised 9 December 2016; Accepted 20 December 2016; Published 11 January 2017
Academic Editor: Liang Wu
Copyright ยฉ 2017 Xiongbin Chen et al.This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Silicon photocell acts as the detector and energy convertor in the VLC system. The system model was set up and simulated inMatlab/Simulink environment. A 10Hz square wave was modulated on LED and restored in voltage mode at the receiver. Anenergy gathering and signal detecting system was demonstrated at the baud rate of 19200, and the DC signal is about 2.77V andAC signal is around 410mV.
1. Introduction
Solar cell has drawn great interest over the past 30 years,and there is a tendency to use it more widely and practically.Visible light communication is also very amazing [1] as a newkind of wireless communication technology with less energyconsumption, higher response speed, and more privacy.
Energy gathering and signal detecting system is a newidea. Energy harvesters are widely used in sensor networks.But energy gathering can be hardly seen in the VLC. Wenoticed that the silicon-based solar panels could receive VLCdata and gather energy at the same time.
Research works in this area can be found in [2]; theresearchers from Korea used a solar cell as a simultaneousreceiver of solar power and visible light communication(VLC) signals. Some research on the efficiency and frequencyresponse of solar cell had been launched.
In our works, solar cell was studied totally under visiblelight. We set up models similar to the real lighting conditionsand run simulations in Matlab/Simulink. Simulation resultsindicate that it is possible to gather energy and receive datathrough the same solar panels.
We implement the systemusing commercial components.Our experiments based on the prototype show that the solarpanels can gather energy for low power circuit and detect theVLC signal at the same time.
2. Model Analysis
In this section, we analyzed the model of LED and solar celland then formulated their relationshipwith some approxima-tions.
2.1. Model of LED Light Source. The LED conforms toLambert emission rule. When the transmitted optical poweris ๐๐ก, the received power ๐๐ (w/m2) is expressed as [3]
๐๐= {{{
๐๐ก๐ + 12๐๐2 cos๐ (๐) ๐๐ (๐) โ ๐ (๐) cos (๐) 0 โค ๐ โค ๐๐
0 ๐ > ๐๐,(1)
where ๐ is the distance between LED and PD, ๐ is theirradiance angel, ๐ is the incidence angel of PD, ๐๐ (๐) is theoptical filter gain, ๐(๐) is the optical concentrator gain, ๐๐ isthe field of view of PD, and๐ is Lambert emission order.
The SNR for VLC and the illuminance value on PD aregiven as follows:
SNR = ๐พ2๐๐signal2๐2shot + ๐thermal
2 + ๐พ2๐๐ISI2๐ธhor = ๐ผ (0) cos๐ (ฮฆ) cos (๐)
๐2 .(2)
HindawiInternational Journal of OpticsVolume 2017, Article ID 6207123, 5 pageshttps://doi.org/10.1155/2017/6207123
2 International Journal of Optics
Iph D
Id
C
IRs
V R
Rth
+
โ
Figure 1: The equivalent circuit diagram of a typical solar cell.
2.2. Model of Solar Cell. The equivalent circuit diagram of atypical solar cell is as shown in Figure 1 [4].
It can be formulated as
๐ผ = ๐1๐ผ๐ โ ๐ผ0 {exp[๐ (๐ + ๐ผ๐ ๐ )๐2๐ด๐พ๐ ] โ 1} โ ๐ถ๐๐๐๐กโ ๐ + ๐ผ๐ ๐ ๐ th
,(3)
where ๐1 is the number of solar cells in parallel, ๐2 is theseries number, ๐ผ๐ is the light current, ๐ผ0 is the diode saturationcurrent, ๐ is the output voltage of solar cell, ๐ผ is the outputcurrent, and ๐ด is a constant which is typically in the rang 1 to3. As ๐ th โซ ๐ ๐ , if set
๐พ0 = ๐ด๐พ๐๐ (4)
then (3) can be written as
๐ผ = ๐1๐ผ๐ โ ๐ผ0 {exp[(๐ + ๐ผ๐ ๐)๐2๐พ0 ] โ 1} โ ๐ถ๐๐๐๐ก . (5)
For solar cell, the light current is positively proportional withreceived illuminance power:
๐ผ๐ = ๐1000๐ผSC. (6)
๐ is the illuminance power of solar cell. The standard sunlight illuminance power at normal room temperature is1000w/mm2. ๐ผSC is the short circuit current.
We can set ๐ผ = 0, so the solar cell works in the open state;then (5) can be expressed as
๐1๐ผ๐ = ๐ผ0 [exp( ๐OC๐0๐2) โ 1]
๐ผ0 = ๐1๐ผ๐exp (๐OC/๐0๐2) โ 1 .
(7)
2.3. Model of the System. For our system, solar cell is used asthe PD. The two models can be connected by making ๐๐ = ๐.In this way, (3) can be expressed as follows:
๐ผ = ๐1 ๐๐1000๐ผSC โ๐1๐๐๐ผSC
exp (๐OC/๐2๐0) โ 1โ [exp(๐ + ๐/๐ โ โ ๐ ๐๐2๐0 ) โ 1] .
(8)
Combine (5), (6), and (7) together:
๐ผ = ๐1๐๐๐ผSC1000 {1 โ 11000 [exp (๐OC/๐2๐0) โ 1]
โ [exp(๐ + (๐/๐ ๐) ๐ ๐๐2๐0 ) โ 1]} .(9)
๐ โ is the load resistance of solar cell. In conclusion, ๐1, ๐2,and ๐3 are constants related to ๐1, ๐2, ๐ผSC, and ๐OC, so therelationship between ๐ of solar cell and the LED power canbe formulated as (11):
๐ผ = ๐๐ โ (10)
๐ = {{{๐๐ก๐ + 12๐๐2 cos๐ (๐) ๐๐ (๐) โ ๐ (๐) cos (๐)
1๐1 [1 โ
1๐2๐ โ exp(
๐๐3)] 0 โค ๐ โค ๐๐
0 ๐ > ๐๐.(11)
3. Results and Discussions
We set up the two models in Matlab/Simulink and combinedthem for simulation.
Solar cell model was simulated separately first.Themodelis based on the equations of (5), (6), and (7). Assuming that itworks in the stable room temperature at 298K, we chose solarcell AM-5308 for our experimental study. Parameters are setin Table 1.
The LED illumination model and Si photocell arraymodel were combined to simulate the practical system.Figure 2 shows that ๐OC for 4 ร 4 and ๐ผSC for 2 ร 8 arehalf of values for 4 ร 8 arrays individually. ๐OC of 2 ร 8and 4 ร 8 are 3โผ3.5 V, which possibly charge lithium battery.In Figure 3, we got the 2 ร 8 arrays solar cellโs I-V curvesthrough the simulations under different illumination from300 Lx to 1000 Lx. These numbers represent the daily sceneillumination value, including living room, library, hospital
International Journal of Optics 3
Table 1: Parameters for solar cell.
Parameter ValueAreas 3 ร 36mm2
Open circuit voltage ๐OC = 0.3VShort circuit current ๐ผSC = 15 uASeries resister ๐ ๐ = 0.0052ฮฉStandard condition ๐ธV = 100 LxParallel number of solar cells ๐1 = 2series number of solar cells ๐2 = 8Load resistance ๐ โ = 0โผ5000ฮฉCapacity 20 nFTemperature ๐ = 298KElectronic charge ๐ = 1.62๐ โ 19๐Boltzmannโs constant ๐พ = 1.38066๐ โ 23Gain of optical filter ๐๐ (๐) = 1Field of view ฮจ = 60โHalf angel of LED ฮฆ = 60โLambert constant ๐ = 1Distance ๐ = 1.0mOptical concentrator gain 1Power of LED 15WIlluminance 68 lm/W
I(A
)
1.4 ร 10โ4
1.2 ร 10โ4
1.0 ร 10โ4
8.0 ร 10โ5
6.0 ร 10โ5
4.0 ร 10โ5
2.0 ร 10โ5
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
U (V)
2 โ 8
4 โ 4
4 โ 8
Figure 2: I-V curves for different solar cell arrays (๐ธV = 300 Lx).
operating room, and sports venue. Power properties of differ-ent arrays under different illumination values are also simu-lated in Figures 4 and 5. The output power of 2 ร 8 arraysunder 300 Lx and 50Kฮฉ is 1.4 ร 10โ4W.The single receivingarea of Si photocell chip is 3 ร 36mm2. For 2 ร 8 arrays, thearea is 1728mm2. So the efficiency of the 2 ร 8 array is 8.1%.The spectral response of Si photocell chip made influence onthe received light power as our LED light is mainly made upof blue and yellow.
The output voltage in simulation and experiment isamong 2.7 V to 3.5 V. It increased to saturation state when the
I(A
)
1.4 ร 10โ4
1.6 ร 10โ4
1.8 ร 10โ4
2.0 ร 10โ4
1.2 ร 10โ4
1.0 ร 10โ4
8.0 ร 10โ5
6.0 ร 10โ5
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
U (V)
1000Lx750Lx
500Lx300Lx
Figure 3: I-V curves of 2 ร 8 arrays under different illumination.
2 โ 8
4 โ 4
4 โ 8
0 100k 200k 300k 400k 500kR (ฮฉ)
1.6 ร 10โ4
3.2 ร 10โ4
2.8 ร 10โ4
2.0 ร 10โ4
2.4 ร 10โ4
1.2 ร 10โ4
8.0 ร 10โ5
4.0 ร 10โ5
0.0
P(W
)
Figure 4: P-R curves for different solar cell arrays (๐ธV = 300 Lx).
illumination value is above 500 Lx. It is stable for supplyingpower. The simulation value and experiment matched per-fectly in Figure 6.
Then, a square signal as in Figure 7 is modulated on LEDas the transmitting data. The period of the square signal is0.1 s. The duty cycle is 50%.
The output power of the solar cell depends on the loadresistance. The maximum output power about 1.2 ร 10โ3Wcan be achieved, when load resistance is 4 kฮฉ, under illumi-nation at 300 lx. The output power of solar cell with differentload resistance is shown in Figure 8; the ๐ฅ-axis unit is 10 Kฮฉ.
The output voltage of solar cell rises to 2.5 V after severalpulses. The waveform of output voltage of solar cell undercontinuous pulse modulation is shown in Figure 9; the ๐ฅ-axisunit is 1 S.
An energy gathering and signal detecting system wasdemonstrated as Figure 10. To fit the working condition ofsolar cell, we used a 15W LED which could simulate the
4 International Journal of Optics
0 50.0k 100.0k 150.0k 200.0k 250.0k 300.0kR (ฮฉ)
P(W
)
750Lx500Lx300Lx
4.0 ร 10โ4
3.5 ร 10โ4
2.0 ร 10โ4
3.0 ร 10โ4
2.5 ร 10โ4
1.5 ร 10โ4
1.0 ร 10โ4
5.0 ร 10โ5
0.0
Figure 5: P-R curves under different illumination.
Practical voltageSimulated voltage
1000 20000 500 30002500 35001500
E๏ฟฝ (Lx)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
U(V
)
Figure 6: Comparison of simulation and experiments result forvoltage and illumination.
different indoor lighting conditions. The distance betweenthe 2 ร 8 photocell array and the 15 w LED is 1.8m. Theillumination value on photocell was 690 lx, when the LEDwas not modulated. The illumination value on photocell was637.5 lx, when the LEDwasmodulated.The baud rate of com-puterโs output was 19200. The output data was the repetitionof โA5โ in HEX form and the polarity was reversed by RS485converter chip. The yellow line in Figure 11 represents a DCcoupled output signal of the silicon photocell which is about2.77V. The green line in Figure 11 represents the AC coupledoutput signal of the silicon photocell, filtered by a 0.1๐Fcoupling capacitor. And the AC signal is around 410mV. Thebaud rate and AC amplitude could be higher after one stageamplifier circuit [5].
1
0
โ1
0 0.2 0.4 0.6 0.8 1
Initial signal
Figure 7: Initial signal.
0 0.5 1 1.5 2 2.5 3
1.2
1
0.8
0.6
0.4
0.2
0
ร10โ3
P (W)
Figure 8: Power of solar cell.
U (V)3
2.5
2
1.5
1
0.5
00 0.5 1 1.5 2 32.5
Figure 9: Voltage of solar cell.
4. Conclusion
In our works, we set up a model of solar cell VLC systemwhich was simulated in Matlab/Simulink. We had verifiedthe correction of the model and gave reasonable design tooptimize the system.
The energy gathering and signals detecting system wasdemonstrated.The data rate of it is 19200 bps.TheDC voltageof photocell was about 2.77Vwhich is enough for low voltagepower supply circuits. The AC voltage of photocell was about410mV and could be optimized by one stage amplifier circuit.It was proved that solar cell can act as energy converting anddetecting device simultaneously in VLC system.
The channel influences [6], response of solar cell tofrequency, room lighting conditions, and other factors wereignored in our model. Further studies can take these factorsinto consideration. At the same time, we will optimize thedesign for the actual application.
Competing Interests
The authors declare that they have no competing interests.
International Journal of Optics 5
Figure 10: Energy gathering and signal detecting demo system.
Figure 11: Output signals of silicon photocell.
Acknowledgments
This work is supported in part by the National Key BasicResearch Program of China (Grant no. 2013CB329204), inpart by the National High Technology Research and Devel-opment Program of China (Grant no. 2015AA033303), and inpart by Science and Technology Planning Project of Guang-dong Province, China (Grant no. 2014B010120004).
References
[1] A. Jovicic, J. Li, and T. Richardson, โVisible light communica-tion: opportunities, challenges and the path to market,โ IEEECommunications Magazine, vol. 51, no. 12, pp. 26โ32, 2013.
[2] S.-M.Kim, J.-S.Won, and S.-H.Nahm, โSimultaneous receptionof solar power and visible light communication using a solarcell,โOptical Engineering, vol. 53, no. 4, Article ID 046103, 2014.
[3] T.-H. Do andM. Yoo, โOptimization for link quality and powerconsumption of visible light communication system,โ PhotonicNetwork Communications, vol. 27, no. 3, pp. 99โ105, 2014.
[4] E. Koutroulis, K. Kalaitzakis, and N. C. Voulgaris, โDevelop-ment of amicrocontroller-based, photovoltaicmaximumpowerpoint tracking control system,โ IEEE Transactions on PowerElectronics, vol. 16, no. 1, pp. 46โ54, 2001.
[5] J. Guo, X. Chen, H. Li, Y. Huang, and H. Chen, โThe responseproperties analysis of silicon photovoltaic cell array in visiblelight communication system,โOptoelectronics Laser, vol. 26, no.3, pp. 475โ479, 2015.
[6] K. Lee, H. Park, and J. R. Barry, โIndoor channel characteristicsfor visible light communications,โ IEEE Communications Let-ters, vol. 15, no. 2, pp. 217โ219, 2011.
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