Reducing the Effects of Noise Light in a Visible Light Communication System Using Two Color LEDs

pISSN 1225-5475/eISSN 2093-7563

°√§Î≈ √∫¤°≠ 2 ^ˆ LED ^{¶ ÃΗ}

‚Ω§« μ‚ “

Ã∫£+

Reducing the Effects of Noise Light in a Visible Light Communication System Using Two Color LEDs

Seong-Ho Lee

Abstract

In this paper, we reduced the optical noise interference in a visible light communication system using two color LEDs. In the transmitter, the original and the inverted signals of the transmitted data modulated a red LED and a blue LED, respectively. In the receiver, a differential detector which is composed of two photodetectors and an optical red filter detected the mixed signal radiated from the two LEDs. In an environment that the optical noise from a fluorescent lamp exists, the signal-to-noise ratio in this system was improved by about 20dB compared to that in the conventional system which uses a single LED and a single photodetector.

Keywords : Visible light communication, LED, Two color LEDs, Optical noise, Differential detector

1. ≠ –

°√§Î≈ (VLC; visible light communication) ^{∫ °√§« ˚}

ª fl˝œ¬ §¯ª Ø∂‘∏Œ· — ≥« §¯∏Œ ∂Ì˙ Î≈ª

‚“ ˆ ÷μœ √∫¤ª ∏ˆœ¬ ‚˙ß [1,2]. VLC ^{°≠ ÁÎœ}

¬ §¯∫ ∂Ì˙ Î≈« Ø∫ª ø√° °Æfl œ‚ ßÆ° °√§

± Ι« ˚ª fl˝‘˙ ø√° ¸• ”μŒ Ø∂“ ˆ ÷¬ ‚…

ª °Æfl —Ÿ . ^{∂ÌÎ fl§ŸÃ¿Â} (LED; light-emitting diode) ^{¬ ÃØ—} VLC ° ˚’— §¯∏Œ≠ ¶¤ ◊ ∞΂˙à ¸

£‘ fl¸œÌ ÷Ÿ . LED ^{¬ ›μº«} PN ¢’°≠ ⁄¨Ê‚ª à Μ© ˚ª ˝∫œ¬ “⁄Œ≠ ©‚° ¤Ì °≠ÏÁ , ^{‚Ë˚Œ Ê}

›° ≠œÌ ˆÌà ÊÓ ‚∏« ∂Ì√≥ª °˜ κÿ °Ì ÷¬

flºÃŸ .

∂ÌÎ LED ^{¶ ÁÎœ©} VLC √∫¤ª ∏∫“ ß ¸§ÓÙ

È≠Ó˙ ∞∫ ‚∏« ∂Ì√≥à ≥°«Ó ÷¬ ØÊ°≠¬ ÃØ

— ∂Ì√≥ŒŒÕ Ø‘«¬ ‚Ω§ ßÆ° ˆ≈Œ°≠ £∑à fl

˝œ© ¸¤° 삪 ÷¬ ÊÏ° ⁄÷ fl˝—Ÿ . ^{ˆ≈«¬ ‚Ω§}

« º‚° ≈£§° Òœ© ÛÎ˚∏Œ Ç— ÊÏ°¬ ≈£§«

º‚¶ ı°√—≠ ‚Ω§« 삪 ±‘ ¯Ÿ ˆ ÷ˆ∏ , ^‚Ω§«

º‚° ≠œ© ◊ 삪 ´√“ ˆ ¯¬ ØÊ°≠¬ ‚Ω§« £∑

ª Ÿœ ˆ ÷¬ Ê»μ ‘≤ Ì¡œ© VLC ^{√∫¤ª ∏∫œ©fl}

—Ÿ .

LED « ≈£§˙ ÷Ø« ‚Ω§« ƒÂà ≠Œ ˜Ã° πà ™¬

ÊÏ°¬ ˆ≈Œ° § Õ¶ Œ¯œ© ‚Ω§ª ±‘ ˜‹“ ˆ ÷

∏Á [3,4], ≈£§° ̃Ø∫à ÷¬ ÊÏ°¬ ̧‚¶ ÁÎœ©

Ò≥˚ ÎÃœ‘ ‚Ω§ª “≈“ ˆ ÷Ÿ [5]. ^◊Ø™ VLC ^°≠Õ

∞à ∂ÌÎ LED « fl§ƒÂ∫ ¸§ÓÙ È≠Ó˙ ∞à °√§

±° ÿÁœÁ ا— ̃ʂà ¯Ó § Õ™ ̧‚¶ ÁÎœ

© ‚Ω§« £∑ª ʈœ‚° ±ˆ  Ÿ . ÃØ— ÊÏ°¬ ‚Ω÷

ƒˆ∏Ÿ Œ¿ Ù∫ ≥ÆÓ ÷ƒˆ¶ ÁΗ ›¤ƒ Ø∂ʃª Á Γ ˆ ÷Ÿ . È≠Ó« ÊÏ°¬ ‚Ω§« RF ^{÷ƒˆ° ¸¬± ÷}

ƒˆ 60 Hz ^« 2 ^{Ë° ÿÁœ¬} 120 Hz ∫–à Ό– ßÆ°

ð Òœ© Œ¿ Ù∫ ÷ƒˆŒ ˆÈ kHz Óˆ ›¤ƒ Ø∂‘∏Œ

· 120 Hz « ‚Ωª Ò≥˚ ±‘ –Æœ© ˜‹“ ˆ ÷Ÿ . ^◊Ø™

¸§Ó« ÊÏ°¬ »§‚ (electronic ballast) ^{ŒŒÕ fl˝œ¬ ‚}

Ω ßÆ° ‚Ω§« RF ÷ƒˆ° È≠Ó∏Ÿ Œ¿ Ù∫ ˆÈ kHz

≠Ô˙–‚˙Ζ≥ ¸⁄ IT ^{ÃÓ¯–˙} (Department of Electronic &

IT Media Engineering, Seoul National University of Science and Technology)

232 Gongneung-ro, Nowon-gu, Seoul 139-743, Korea

+

Corresponding Author : [email protected]

(Received : Sep. 17, 2012, Revised : Oct. 22, 2012, Accepted : Nov. 1, 2012)

This is an Open Access article distributed under the terms of the Creative Commons

Attribution Non-Commercial License(http://creativecommons.org/licenses/by-

nc/3.0)which permits unrestricted non-commercial use, distribution, and

reproduction in any medium, provided the original work is properly cited.

Óˆ –˜œ¬ ÊÏ° ÎŒ–ß . ˆÁ √fl° πà «≈«Ì ÷¬

∂ÌÎ Ì‚¬ LED ¬ ¶∞° ˚Û ˜Ã° ÷ˆ∏ Ø∂°…— Ι

¯Ã ˆÈ kHz §μŒ ÊÏ° πΔ ¸§Ó« ‚Ω÷ƒˆ∏Ÿ Œ¿

Ù∫÷ƒˆ¶ÁÎœ©›¤ƒØ∂¶œ‚°μÓ¡ÓÊÏ°πŸ .

ÃØ— °ª ≥±œ‚ ßœ© ª ÌÆ°≠¬ ‚˙Ι (base- band) ^{°≠ Œ °ˆ ˆ«} LED ¶ ÁÎœ© ‚Ω§« 삪 ±‘ 

“œ¬ ∏∂¶ ıŒÃ ¶»œÌ «Ëœ¥Ÿ . à ∏∂¬ ¤≈Œ°≠

∏ªÌ⁄ œ¬ ¯≈£ (original signal) ^{Õ Ã« ›¸≈£} (inverted signal) ^{¶ ÁÎœ© ¢¢} Red-LED ^Õ Blue-LED ^{¶ Ø∂œ© ≈£}

§ª ¸¤œÌ , ^ˆ≈Œ°≠ 2 ^{≥« §À‚‚Õ} 1 ^≥« Red ^§ ÕŒ

∏∫«¬ ˜øÀ‚‚ (differential detector) ¶ ÁÎœ© ‚Ω§«

£∑ª ŸÃÌ ≈£§ª À‚œ¬ ʃß . ^«Ë°≠¬ 1 ^≥«

LED ¶ ÁÎœ¬ ʃ° Òœ© 2 ^ˆ« LED ^{¶ ÁΑ∏Œ· ‡} 20 dB « ≈£Î‚ΩÒ« ≥±ø˙° ÷˙Ÿ .

ÃØ— ∏∂¬ ‚Ω§« 삪 πà fi¬ ØÊ°≠ ‚Ω° ≠—

°√§Î≈ √∫¤ª ∏‡œ¬ •° ±‘ ∞Γ ˆ ÷Ÿ . ^{ª ÌÆ}

« ¶ 2 ^˝°≠¬ 2 ^ˆ« LED ¶ ÁÎœ© ‚Ωª “œ¬ ¯Æ° Î œ© ÀΔ∏Ì , ^¶ 3 ˝°≠ «Ëª “≥œ¬ ¯≠Œ ¯‡œ¥Ÿ .

2. ¯Æ

Œ °ˆ ˆ« LED ¶ ÃΗ °√§Î≈ √∫¤« ∏∫μ¬ Fig.

1 ^{˙ ∞Ÿ} .

¤≈Œ°≠¬ ¸¤•ÃÕ« ¯≈£¶ ÁÎœ© LED1(Red) ^{¶ Ø}

∂œÌ , ^{ÃÕ ø√°} Inverter ¶ Îœ© ›¸» ≈£¶ ÁÎœ©

LED2(Blue) ^{¶ Ø∂‘∏Œ·} 2 °ˆ ˆ« ≈£§Ã •’«Ó ⁄Ø

¯£∏Œ ÊÁ»Ÿ . ¤≈Œ ∑°¬ È≠ÓÙ ¸§ Ó˙ ∞∫ ‚∏

« ∂Ì√≥ŒŒÕ fl˝œ¬ ‚Ω§¯Ã ≥°«Ó ÷Ÿ . ^{à ۬°}

≠¬ ˆ≈Œ° ≥°» ¯£° 2 ˆ« ≈£§˙ ‚Ω§Ã •’» Û

¬Œ ∏Á—Ÿ .

ˆ≈Œ¬ 2 ^{≥« §À‚‚Õ} 1 ^{≥« § Õ} , ^◊ÆÌ 1 ^{≥« ˜øı}

¯‚Œ ∏∫«¬ ˜øÀ‚‚° ≥°«Ó ÷Ÿ . ^ˆ≈Œ« Photo- detector1(PD1) ’°¬ § Õ° ≥°«Ó ÷Ì Photo- detector2(PD2) ’°¬ § Õ° ¯Ÿ . PD1 ^{’° ≥°» § Õ}

¬ RED-filter Œ≠ ˚ˆ« °√§±˙ Ã∏Ÿ ‰ ƒÂ° ÿÁœ¬

˚‹±∫ Œ Î˙œˆ∏ Ã∏Ÿ ™∫ ƒÂŒ ªˆ« °√§±∫

˜‹œ¬ Ø∫ª °ˆÌ ÷Ÿ . ^˚Û≠ PD1 ^∫ RED ^{≈£§˙ ‚Ω§}

à •’» ≈£¶ ˆ≈œˆ∏ Blue ^{≈£§∫ ˜‹—Ÿ} . ^›È° PD2

°¬ § Õ° ¯‚ ßÆ° ‚Ω§˙ Red ^◊ÆÌ Blue ^≈£§Ã

Œ •’» Û¬Œ ˆ≈»Ÿ . ^{˜øı¯‚«} (+) ^Õ (-) ^‘¬‹°¬

¢¢ PD1 ^˙ PD2 « À‚¸–ª Œ°œ© ˜øı¯— ƒ° ˆ≈Œ

° ¸fi»Ÿ . ÃØ— ¸Ë¶ ˆƒ˚∏Œ •ˆœÈ ƒ (1) ^{˙ ∞Ÿ} .

©‚°≠ Ì 1 ^{˙ Ì} 2 ^{¬ ¢¢} PD1 ^˙ PD2 « À‚¸–ª ™∏ªÁ , ^Ò ₁

˙ Ò 2 ¬ ¢¢ ≈£§° Η PD1 ^˙ PD2 « ¿‰μ¶ ™∏ΩŸ . C ₁₁

˙ C ₁₂ ^{¬ ¢¢} LED1 ^˙ LED2 ^ŒŒÕ PD1 ∏Œ« §·’ˈ¶ ™∏

ªÁ , C ₂₁ ^˙ C ₂₂ ^{¬ ¢¢} LED1 ^˙ LED2 ^ŒŒÕ PD2 ^{Œ« §·’Ë}

ˆ¶ ™∏ΩŸ . P ₁ ^˙ P ₂ ^{¬ ¢¢} LED1(Red) ^Õ LED2(Blue) ^{« ‚}

¬§ ¸¬ÃÁ , P N ∫ ‚Ω§ ¸¬ª ™∏ΩŸ . ^Ò _1N ^{˙ Ò} _2N ^{∫ ¢¢}

‚Ω§° Η PD1 ^˙ PD2 « ¿‰μ¶ ™∏ªÁ , C _1N ^˙ C _2N ^{∫ ¢}

¢ ‚Ω§¯∏ŒŒÕ PD1 ^˙ PD2 Œ« §·’ˈ¶ ™∏ΩŸ . R _L

∫ PD1 ^˙ PD2 « Œœ˙◊∏Œ≠ øœ— ™ª °¯Ÿ . ^Ì _out ^{∫ ˜ø}

ı¯‚« ‚¬¸–ÃÁ , G ¬ ˜øı¯‚« ¸–Ãʪ ™∏ΩŸ .

ˆ≈Œ« PD1 ^˙ PD2 ° øœ— æ˘« §À‚‚Œ ÊÏ , ^≈£§

° Η ¿‰μ° ≈« øœœ© Ò 1 = ^Ò ₂ = ^Ò _S Œ ™∏æ ˆ ÷∏Á , ^‚

Ω§° Η ¿‰μ¶ Ò 1N = ^Ò _2N = ^Ò _N ∏Œ ™∏æ ˆ ÷Ÿ . ^¤≈Œ°≠

LED1 ^˙ LED2 ° ≠Œ ›¸» ≈£¶ ÁÎœ© Ø∂œ¬ ÊÏ°

P ₂ =- P ₁ ^{à «Á} , ^ˆ≈Œ« PD1 ^’°¬ Red ÃÛ« ‰ ƒÂ∏ Î˙

œ¬ Red-filter ^{° Œ¯«Ó ÷Ó≠} Blue ^{≈£° ˜‹««Œ} C ₁₂

õ 0 ^ß . 2 ^≥« LED Áë ≈Æ° ¤ˆ≈Œ Áë ≈Æ° Òœ

© ˆ˙˜ ¤Ì , ^«— 2 ^≥« PD Áë ≈Æμ ¤ˆ≈Œ Áë ≈ Æ° Òœ© ˆ˙˜ ¤∫ ÊÏ°¬ C ₁₁ ^õ C ₂₁ ^õ C ₂₂ ^{Œ≠ ≈« øœ—}

™ª °ˆÁ , ^{à ™ª Ûˆ} C _S ^{Œ ™∏æ ˆ ÷Ÿ} .

‚Ω§¯Œ ¸§ÓÙ È≠Ó« §∫ÂÆ≥∫ °√§ Ι∏Œ ŒÕ ˚‹± Ι° ã‚Óˆ –∫ Ι° …ƒ §∫ÂÆ≥à –

˜œ«Œ [4], PD1 ^{’° ≥°»} Red-filter ° «œ© ‚Ω§« ªˆ Œ–à œŒ “≈«Óμ PD1 °≠ À‚«¬ ‚Ωƒ¸Ã § Õ°

¯¬ PD2 °≠ À‚«¬ ‚Ωƒ¸˙ ≈« øœ‘ª ∞μ« «Ëª Îœ© ÆŒœ¥Ÿ . «— ‚Ω§¯∏ŒŒÕ ˆ≈ŒÓˆ« ≈Æ°

Òœ© 2 ^≥« PD Áë ≈Æ° ≈Ï ¤∫ ÊÏ°¬ C _1N ^õ C _2N ^Ã

«Á à ™ª C _N ∏Œ ™∏æ ˆ ÷Ÿ . ÃØ— ¸Ë¶ Αœ© ƒ

(1) ª Ÿ√ §ÆœÈ ƒ (2) Õ ∞à ™∏æ ˆ ÷Ÿ .

Fig. 1. The VLC system using two LEDs.

Ì 1 = ^Ò ₁ ( C 11 P 1 + C 12 P 2 )R L + ^Ò _1N C 1N P N R L (1a)

Ì 2 = ^Ò ₂ ( C 21 P 1 + C 22 P 2 ) R L + ^Ò _2N C 2N P N R L (1b)

Ì out = G( ^Ì ₁ - ^Ì 2 ) (1c)

Ì 1 = ^Ò s C s P 1 R L + ^Ò N C N P N R L (2a)

Ì 2 = ^Ò N C N P N R L (2b)

Ì out = G ( ^Ì ₁ - ^Ì ₂ ) ^ô G ^Ò s C s P 1 R L (2c)

ƒ (2c) °≠ ∏¬ ŸÕ ∞à ˆ≈Œ« ˜øı¯‚°≠ ‚Ω§ P _N

° Ò — ‚Ω¸–∫ “≈«Ì , ^≈£§ P 1 ∏° Ò — ‚¬¸–ª Úª ˆ ÷Ωª À ˆ ÷Ÿ .

3. «Ë

Œ °ˆ ˆ« LED ¶ ÁÎœ© ‚Ω“ ø˙¶ «Ë˚∏Œ ÆŒ ÿ∏‚ ßœ© ’« Fig. 1 ˙ ∞à «Ë°¶ ∏∫œ¥Ÿ . ^¤≈•

ÃÕ« fl˝Â°Œ¬ Atmel Á« ∂éŒ‹Æ—Ø Atmega32 ^¶

ÁÎœ¥Ÿ . ¤≈•ÃÕ« ¸‚˚ ≈£¶ §≈£Œ ØØœ‚ ßœ

© ∂錋Ɨث UART ^{‹⁄¶ Îœ©} 9.6 kbps ^{Œ ‚¬»}

≈£¶ ÁÎœ© 2 ^≥« LED ^{¶ Ø∂œ¥Ÿ} . ^{«Ë° ÁΗ} 2 ^≥«

LED ^{¬ Œ} 1W ^{fi« ∂ÌÎ} LED ^ÃÁ , Helio ^Á« Red-LED ^Õ Blue- LED ^{¶ ÁÎœ¥Ÿ} . Red-LED ^{« fl§ fl…ƒÂ∫} 630 nm

ÃÌ , Blue-LED ^{« fl§ fl…ƒÂ∫} 470 nm ^Ã˙Ÿ . UART ^‹⁄

°≠ ‚¬«¬ ¤≈•ÃÕ¶ ÁÎœ© ŸŒ Red-LED ^{¶ Ø∂œ}

¥∏Á , ^{ÃÕ ø√°} Inverter ¶ ÁÎœ© ¤≈•ÃÕ¶ ›¸√≤

ƒ Blue-LED ^{¶ Ø∂œ¥Ÿ} . ^Œ LED ^{Áë ≈Ƭ ‡} 3cm ^§μ

° «μœ Ÿ¢œ© ≥°œ¥Ÿ . à ۬°≠ ¯≈£Œ Ø∂«¬

Red §≈£Õ ›¸» ≈£Œ Ø∂«¬ Blue ^{§≈£¬ ⁄د£°}

≠ •’«Ó ˆ≈Œ  ∏Œ ÊÁ«˙Ÿ .

¤≈ŒŒŒÕ ‡ 2 m « ≈Æ° ˆ≈Œ¶ ≥°œ¥Ÿ . ^ˆ≈Œ°

ÁΗ 2 ^{≥« §À‚‚} PD1 ^˙ PD2 ^{¬ Œ} Opto-sensor ^Á«

OST-1KLA ^{˜‰Æ£ˆ∫ÕÃÁ} , ^Œœ˙◊ 100 ^{ÿ°≠ ‡} 50 kHz

« ˆ≈Ι¯ª °¯Ÿ . PD1 ^˙ PD2 ^{Áë ≈Ƭ ‡} 3 cm ^§μ

° «μœ Ÿ¢œ© ≥°œ¥Ÿ . à ≈Ƭ ¤≈ŒÕ ˆ≈ŒÁë

≈Æ 2 m ° Òœ© ≈Ï ¤∫ ۬ëŒ PD1 ^˙ PD2 ^{° ≥°» ß}

°°≠ ≈£§« º‚¬ ≈« øœœŸ . ^{‚Ω§¯∏Œ¬} 100 W ^¸

§Óª ¤≈Œ« LED ∑° ≥°œ© ‚Ω§Ã ˆ≈Œ° …œ‘ £

∑ª ÷¬ ØÊ°≠ «Ëœ¥Ÿ . ^ˆ≈Œ« PD1 ^{’° Œ¯— § Õ}

¬ Kodak ^Á« No.25 Red  ^ÕŒ≠ 580 nm ^{Ãœ« ™∫ ƒÂª}

˜‹œ¬ Ø∫ª °ˆÌ ÷Ÿ . ^˚Û≠ 630 nm ^« Red ^{≈£§∫ Î}

˙œ©μ 470 nm ^« Blue ≈£§∫ ˜‹œ¬ Ø∫ª °ˆÌ ÷Ÿ .

ˆ≈Œ° ≥°— ˜øı¯‚¬ Hitachi ^{Á« ¨Íı¯‚} HA11741

ª ÁÎœ© ¶¤— Õß .

¤≈ŒŒŒÕ Æ⁄≠∞ VLC Test ^±¶ 2 ms £›ª ŒÌ ›πœ©

¸¤œ¥ª ß , ¿«Œ∫⁄¡¶ ÁÎœ© ¸¯— ¤≈Œ« Ø∂ƒ

¸˙ ˆ≈Œ« À‚ƒ¸∫ Fig. 2 ^{Õ ∞Ÿ} .

Fig. 2(a) ^¬ LED1(Red) ^{« Ø∂≈£ÃÁ} , Fig. 2(b) ^¬ LED2 (Blue) « Ø∂≈£¶ ™∏ΩŸ . ^{Œ ≈£«} High ^Õ Low ^{Û¬° ≠}

Œ ›¸«Ó 2 ^≥« LED ¶ ∏øœÌ ÷Ωª º ˆ ÷Ÿ . Fig. 2(c) ^¬

ˆ≈Œ« PD1 °≠ À‚— ¸–ƒ¸ª ™∏ΩŸ . PD1 ^’°¬ Red- filter ^{° Œ¯«Ó ÷Ó≠} LED1(Red) « ≈£§˙ ¸§Ó« ‚Ω§

à •’» ƒ¸Ã À‚«Á , LED2(Blue) « ≈£§∫ ˜‹»Ÿ . ^˚

Û≠ PD1 ^{« À‚¸–Œ} Fig. 2(c) ^{¬ ’« ˆƒ} (2a) ^{° ™∏Ω ¸–}

Ì 1 ^{° ÿÁ—Ÿ} .

Fig. 2(d) ^{¬ ˆ≈Œ«} PD2 °≠ À‚» ¸–ƒ¸ÃÁ , ^{©‚°¬ §}

 Õ° ¯∏«Œ Red ^Õ Blue ^« 2 °ˆ ≈£§˙ ¸§Ó« ‚Ω§Ã

Œ •’«Ó À‚«¬ ۬ß . ^¤≈Œ°≠ LED1(Red) ^Õ LED2(Blue) « ≈£§Ã ≠Œ ›¸«Ó ‚¬««Œ , ^ˆ≈Œ« PD2

°≠¬ Red ^Õ Blue ° •’«Ó ˆ– •ÃÕ« ≈£ƒ¸Ã Û‚«

Ó ÁÛˆÌ ¸§Ó« ‚Ωƒ¸∏ À‚«Ì ÷Ÿ . ^˚Û≠ PD2 ^{« À}

‚¸–Œ Fig. 2(d) ^{¬ ’« ˆƒ} (2b) ^{° ™∏Ω ¸– Ì} ₂ ^{° ÿÁ—Ÿ} .

’« ˆƒ (2c) ^{°≠Õ ∞Ã} PD1 ^{« ¸– Ì} ₁ ^∏ŒŒÕ PD2 ^{« ¸–}

Ì 2 ¶ ©÷‘ «È ‚Ω§∏ŒŒÕ fl˝— ‚Ω¸–à ÁÛˆÌ ≈

£¸–∏ ‚¬»Ÿ . ÃÕ ∞∫ ˙§ª «Ë˚∏Œ ∏ˆœ‚ ßœ©

˜øı¯‚« (+) ^‘¬‹˙ (-) ^{‘¬‹° ¢¢} PD1 ^{« ¸– Ì} ₁ ^˙ PD2

« ¸– Ì 2 ¶ Œ°œ© ˜øı¯œ¥Ÿ . ˆ≈Œ°≠ ˜øı¯‚¶

Î˙œÈ≠ ¤≈•ÃÕ° π∏«¬ ˙§ª ¿«Œ∫⁄¡Œ ¸¯—

·˙¬ Fig. 3 ^{˙ ∞Ÿ} .

Fig. 3(a) ^{¬ ’« ◊≤} Fig. 2(c) ^{Õ ∞Ã} PD1 ^{°≠ À‚» ¸–ƒ}

¸∏Œ≠ ‚Ω§˙ LED1(Red) « ≈£§Ã •’» Û¬¶ ™∏Ω Ÿ . ©‚°≠ À‚«¬ ‚Ω« ¸¬¬ 120 Hz « ¸¬±∏ŒŒÕ fl

˝œ¬ ‚Ω˙ 50-60 kHz « ¸§Ó »§‚ŒŒÕ fl˝œ¬ Ì÷

ƒ ‚Ωà “‘¢œ‘ Ø©÷Ÿ . ©Ø ≥« ¸§ÓÙ È≠Ó∏Œ Fig. 2. The waveforms observed on an oscilloscope ; (a) The signal to LED1 (Red), (b) The signal to LED2 (Blue), (c) The detection voltage of PD1, (d) The detection voltage of PD2.

Fig. 3. The waveforms observed on an oscilloscope ; (a) The detection voltage of PD1, (b) The output of a differential amplifier, (c) The recovered signal.

(a) (b) (c) (a) (b)

(c)

(d)

ŒÕ« ‚Ω§Ã Ø‘«¬ ÊÏ°μ ÃÈ ∂Ì√≥ Œ° 60 Hz

« ¸¬±° ¯Î∏Œ ¨·«Ó ÷Ó 60 Hz ^« 2 ^{Ë ÷ƒˆŒ} 120 Hz « øœ— ÷ƒˆ¶ °¯ ÁŒƒ ¸¬« £∑≈£ ©Ø ≥° ¸

¬±° ø‚» Û¬Œ fl∏«Ó À‚»Ÿ . ◊ ·˙ ¸º •’» ‚ Ωƒ¸∫ « Ÿ√ 120 Hz « ÁŒƒ° Ÿ¢œ‘ «Á ‚Ω§¯« ˆ

° ı°“ˆœ ‚Ω¸–« ¯¯Ã ı°œÌ , ^{◊ ¸¬¬} Fig. 3(a) ^˙

ØÁœŸ .

Fig. 3(b) ^¬ PD1 ^˙ PD2 « À‚¸–ª ¢¢ ˜øı¯‚« (+) ^Õ (-) ‘¬‹° °— ƒ ‚¬‹°≠ ¸¯— ƒ¸ª ™∏ΩŸ . ^{à ۬}

°≠¬ 120 Hz « ≠— ‚Ω§˙ Ì÷ƒ ‚Ω« º‚° ˆ˙˜ “

œÌ , ^¤≈Œ°≠ LED1(Red) ¶ Ø∂— ≈£¸–à ÛÎ˚∏Œ ≠ œ‘ À‚«¬ Û¬”ª º ˆ ÷Ÿ .

Fig. 3(a) ^Õ Fig. 3(b) ^{¶ Ò≥œÈ} 1 ^≥« LED ^Õ 1 ^≥« PD ^{¶ Á}

Îœ¬ ‚∏« ¸¤Êƒ° Òœ© 2 ^ˆ« LED ^{¶ ÁΗ ˜øÀ‚}

ʃ°≠ ≥±» ≈£Î‚ΩÒ¶ ËÍ“ ˆ ÷Ÿ .

’˙ ‹œ« LED ¶ ÁÎœ© ¸¤œ¬ ∏∂° ÿÁœ¬ Fig.

3(a) °≠ ∏È ≈£¸–« «©£ ¯¯Ã ‡ V _S,pp ^ô 0.2 V ^ÃÌ rms

¯¯∫ V _S,rms ^ô 0.11 V ^{Œ ¯§«˙∏Á} , ‚Ω¸–« «©£ ¯¯∫

‡ V _N,pp ^ô 0.36 V ^ÃÌ rms ^¯¯∫ V _N,rms ^ô 0.28 V ^{Œ ¯§«˙Ÿ} .

à ۬°≠ rms ^≈£¸– (V _S,rms ) ^Õ rms ^‚Ω¸– (V _N,rms ) ^{¶ ÁÎ}

œ© ≈£Î‚ΩÒ¶ ËÍœÈ ŸΩ ƒ (3) ^{˙ ∞Ÿ} .

›È° 2 ^ˆ« LED Õ ˜øı¯Êƒª ÁΗ Fig. 3(b) ^{°≠ ∏È}

≈£¸–« «©£ ¯¯∫ V _S,pp ^ô 6 V ^ÃÌ rms ^¯¯∫ V _S,rms ^ô 3.36 V ^{Œ ¯§«˙∏Á} , ‚Ω¸–« «©£ ¯¯∫ ‡ V _N,pp ^ô 1 V

ÃÌ rms ^¯¯∫ V _N,rms ^ô 0.79 V ^{Œ ¯§«˙Ÿ} . ^{Çœ‘ Δ˜ ≤}

Δ÷¬ ‚Ω∫–« ¯Œ∫ ˆ≈Œ« PD1 ^°≠ Red ^{§ Õ¶ ÁΑ}

∏Œ· ªˆ« °√§Î™Ã ˜‹» Û¬°≠ ˆ≈» ‚Ω§˙

PD2 °≠ § Õ¶ ÁÎœˆ  Ì ŸŒ ˆ≈— ‚Ω§« ƒ¸°

Ç— ˜Ã° ∏Áœ‚ ßÆß . ^{à ۬°≠} rms ^≈£¸–

(V _S,rms ) ^{Õ ‚Ω¸–} (V _N,rms ) ¶ ÁÎœ© ≈£Î‚ΩÒ¶ ËÍœÈ ƒ (4) ^{Õ ∞Ÿ} .

˚Û≠ — ≥« LED ^{Õ — ≥«} PD ¶ ÁΗ ¸¤∏∂° Òœ©

2 ^ˆ« LED ¶ ÁÎœÌ ˜øÀ‚— ¸¤∏∂°≠ ≥±«¬ ≈£Î

‚ΩÒ¬

Ã˙Ÿ .

Fig. 3(c) ^¬ Fig. 3(b) ^{« ¸–ª ÁÎœ©} 0 V ^ÃœÕ 5 V ^ÃÛª

¨ÆŒœ© ÷æ π∏— ƒ¸ÃŸ . à ƒ¸∫ ¤≈Œ°≠ LED1 (Red) ^{ª Ø∂œ© ¸¤—} Fig. 2(a) « •ÃÕÕ øœ— ۬ß .

ÃÕ ∞à ≠— ‚Ω§Ã ∏Áœ¬ ØÊ°≠ °√§Î≈ √∫¤ª

∏‡œ¬ ÊÏ° Œ °ˆ ˆ« LED ¶ ÃÎœÈ ‚Ω§« £∑ª ŸÃÌ ≈£Î‚ΩÒ° ≥± ª «Ë˚∏Œ ÆŒœ¥Ÿ . Fig. 4 ^¬

«Ë°≠ ÁΗ LED « ∏ø∏ŒÕ §À‚‚∏Œ« ‹¸ª ™∏

ΩŸ .

Fig. 4(a) ^{¬ ¤≈Œ° ≥°—} LED1(Red) ^Õ LED2(Blue) ^{« ∏ø}

∏ŒÃÁ , Fig. 4(b) ^{¬ ˆ≈Œ° ≥°—} 2 ^{≥« ˜‰Æ£ˆ∫Õ} PD1

˙ PD2, ^◊ÆÌ PD1 ^{’° Œ¯—} Red-filter ^{« ‹¸ª ™∏ΩŸ} .

4. ·–

ª ÌÆ°≠¬ °√§Î≈« ¤≈Œ°≠ 2 ^{°ˆ ˆ«} LED ^{¶ Á}

Îœ© ≠Œ ›¸» ≈£Œ Ø∂œ© ¸¤œÌ , ^ˆ≈Œ°≠ 2 ^≥«

§À‚‚Õ 1 ≥« § Õ¶ ÁÎœ© ˜øÀ‚‘∏Œ· ‚Ω§«

£∑ª ŸÃ¬ ∏∂¶ ıŒÃ ¶»œÌ «Ë˚∏Œ ÆŒœ¥Ÿ . ^’

˙ £‹— ˆƒª Îœ© ‚Ω§« £∑à ŸÓ¬ ¯Æ¶ “≥œ

¥∏Á , ÃÓ≠ «Ëª Îœ© ‚Ω “ø˙¶ ÆŒœ¥Ÿ .

«Ë°≠¬ — ≥« LED ¶ ÁÎœ¬ ¸¤∏∂° Òœ© Œ ≥«

LED ¶ ÁΗ ÊÏ° ‚Ω§« 삪 “‘∏Œ· ≈£Î‚Ω Ò° ‡ 20 dB ^≥±«˙Ÿ .

ÃÕ ∞∫ ∏∂¬ ÷Ø« ‚Ω§« μ‚à …— ØÊ°≠ Ò≥˚

£‹œ‘ ‚Ω§« £∑ª Ÿœ ˆ ÷Ó ‚Ω§° ≠— °√§Î≈

√∫¤ª ∏‡œ¬ •° ±‘ ∞Γ ˆ ÷Ÿ . ^{π¶ ÈÓ ⁄ø˜«}

¯È ∂Ì LED ¶ ÃΗ ´±ŒƒÂ° [2] Õ ∞∫ Ò¢Àƒ æ≠ √

∫¤ª ∏ˆœ¬ ÊÏ LED « ›¤ƒ Ø∂¶ ÁÎœˆ  Ì 2 ^ˆ«

LED ¶ ‚˙Ι Ø∂‘∏Œ· £‹œÌ ±‘ ‚Ω§« £∑ª “

≈œ¬ •° ∞Γ ˆ ÷Ÿ .

Fig. 4. The circuits used in experiments ; (a) LED circuits, (b) PD circuits.

(a) (b)

SNR 1 = 20log ( V _S,rms / V N,rms )

= 20log( 0.11 / 0.28 ) ^ô -8.1(dB) (3)

SNR diff = 20log ( V _S,rms / V N,rms )

= 20log( 3.36 / 0.79 ) ^ô 12.6(dB) (4)

‚ SNR = SNR diff - SNR ₁

= 12.6-(-8.1) = 20.7(dB) (5)

Á« ¤

à ¨∏¬ ≠Ô˙–‚˙Ζ≥ ≥ª –˙¨∏Ò ˆ¯∏Œ ˆ‡

«˙¿œŸ .

REFERENCES

[1] T. Komine and M. Nakagawa, “Fundamental analysis for visible-light communication system using LED lights”, IEEE Transactions on Consumer Electronics, Vol. 50, No. 1, pp. 100-107, 2004.

[2] S.-H. Lee, “Visible light identification system using optoelectronic feedback of a lighting LED”, J. Sensor Sci. & Tech., Vol. 20, No. 3, pp. 193-198, 2011.

[3] A. M. Street, P. N. Stavrinou, D. C. O'Brien, and D.

J. Edwards, “Indoor optical wireless systems-a review”, Opt. Quantum Electron., Vol. 29, pp. 349- 378, 1997.

[4] J. M. Kahn and J. R. Barry, “Wireless infrared communications”, Proc. IEEE, Vol. 85, No.2, pp.

265-298, 1997.

[5] S.-H. Lee, “Reducing the effects of ambient noise light in an indoor optical wireless system using polarizers” , Microwave and Optical Technology Letters, Vol. 40, No. 3, pp. 228-231, Feb. 5, 2004.

[6] D.-H. Hwang and S.-H. Lee, “Reducing the effects of noise light using inter-bit noise detection in a visible light identification system”, J. Sensor Sci. & Tech., Vol. 20, No. 6, pp. 412-419, 2011.

à ∫ £ (Seong-Ho Lee)

U 1980 ^‚ 2 ˘ —π◊¯Î–≥ ¸⁄¯–˙

( ^¯–Á )

U 1989 ^‚ 2 ˘ —π˙–‚˙¯ ¸‚ ◊ ¸

⁄¯–˙ ( ^¯–ÆÁ )

U 1993 ^‚ 2 ˘ —π˙–‚˙¯ ¸‚ ◊ ¸

⁄¯–˙ ( ^¯–⁄Á )

U 1995 ^‚ 3 ^˘ ~ ˆÁ ≠Ô˙–‚˙Ζ≥

¸⁄ IT ^{ÃÓ¯–˙ ≥ˆ}

U÷‰ ¸…–fl : ^§Î≈ , VLC, ^æ≠ ,

RFID, ^»◊™