Implementation of VLC transmitter using MCU for promotion lighting ID services

Transcription

1 Implemenaion of ransmier using MCU for promoion lighing ID services Il-Soon Jang*, Jin-Doo Jeong*, Myoung-Soon Kim*, InSu Kim*, Sang-Kyu Lim*, Tae-Kyu Kang* *Elecronics and Telecommunicaions Research Insiue, 28 Gajeong-ro, Yuseong-gu, Daejeon, 35-7 KOREA Absrac In his paper, we propose a MCU-based signal generaing mehod and a physical layer frame forma for promoion lighing ID services using visible ligh communicaion () echnology. The proposed mehod and forma for services are possible o be simply implemened by updaing he firmware of exising MCU which is in he LED lighing for dimming funcion. We ge he poenial of performing visible ligh communicaion using MCU hrough he experimens. Keywords Dimming, LED, Lighing ID, MCU, I. INTRODUCTION Tradiional luminaires such as fluorescen and incandescen are being replaced wih energy-efficien LED (Ligh Emiing Diode) lighings in hese days. The propagaion of LED lighings is able o bring on IT (Informaion Technology) fusion echnology[-2]. As one of hose areas, sudies on visible ligh communicaion () using LED lighing have being performed acively. Whereas ypical wireless communicaion use radio frequency o ransmi and receive daa, use visible ligh as carrier frequency. The advanages of LED lighing, unlike radiional lighing conrolling he brighness of he ligh by changing he supplied volage, can provide digial dimming. Digial dimming ligh uses PWM (Pulse Widh Modulaion) signal o conrol he brighness of he ligh. In ON secion of PWM signal, LED ligh is urned ON. By changing he pulse widh of PWM signal, brighness of LED ligh is conrolled. We use MCU (Main Conrol Uni) which generaes conrol signal o change he pulse widh of PWM in LED lighing. Usually On-Off Keying (OOK) modulaion is used in. OOK signal is similar o PWM signal in case he physical appearance of signal. So we can generae signal using similar mehod generaing PWM signal in MCU. This mehod can give service hrough already insalled lighing by updaing he firmware in MCU. Bu MCU-based is suiable only for shor message ransmission due o limi of processing power. In case of combining and LED lighing, some problems such as flickering and dimming conrol may occur. Occasionally sysems use line code including Mancheser code, 4B6B for rejecing flickering and VPPM (Variable Pulse Posiion Modulaion) modulaion. Random daa preven dimming-conrol in LED lighing. This paper proposes a soluion o solve hese problems of he ransmier using MCU in LED lighing. In addiion, we also propose he PHY frame forma o conrol dimming and rejec flickering. And also, we propose he PHY frame forma ha can conrol dimming and rejec flickering. The proposed sysem can ransfer only shor daa such as promoion lighing ID (Idenificaion) associaed wih a produc informaion. In he proposed sysem, promoion lighing ID is ransferred o user device wih receiver. User device displays mulimedia conens relaed wih received ID. We have esed he proposed sysem in commercial mar and described he es environmen and he resuls in his paper. II. SIGNAL GENERATION Typically radiional luminaires conrol he brighness of lighing by changing he supplied volage such as zero-en base. Dimming in digial lighing sysems including LED lighing is based on PWM signal, as shown in Figure. Brighness of lighing is dependen on pulse widh of PWM signal. In he figure, is he period of PWM signal and T c is ON secion of he period. Supplied volage, V is supplied o PN juncion of LED during ime T c in period and LED urns on. Doubling he ON secion, he brighness of lighing is wice brigher. Volage V T c Volage V n n Brighness B 2B T c Brighness Figure. Digial dimming by PWM A. MCU based PWM Signal Generaion Typically MCU has a GPIO (General Purpose Inpu Oupu) pins and can generae PWM signal using GPIO pin. GPIO pin oupus he decided logic value in MCU a TTL (Transisor- Transisor Logic) volage level. GPIO pin is conneced o he pin for LED driving shown as figure 2. The GPIO pin is conrolled by MCU main clock, so he smalles pulse widh of PWM is decided by he main clock. The inpu and oupu rae of GPIO pin is conrolled by he main clock. In case he inpu and oupu rae of GPIO pin is 4 Mbps, he smalles pulse widh of PWM, T c is.25us. n n ISBN February 6~9, 24 ICACT24

2 Programmed MCU can change he oupu of GPIO pin every sep T c. MCU GPIO pin LED Driver Figure 2. Connecion beween MCU and LED driver using MCU GPIO pin T c. In case ha he VPPM symbol is % and % of he maximum brighness, he symbol has no he ransiion of signal, so ha he symbol canno be used as a communicaion signal. If he ime duraion of one VPPM symbol is and dimming sep is % of maximum brighness, equals o T c. As MCU changes he oupu of GPIO every T c, MCU can generae one VPPM symbol every. For he condiion ha logical daa is and dimming sep is % and he brighness is % of maximum brighness, he VPPM symbol is generaed by C program as shown in he figure 4. We know ha he duraion of VPPM symbol is decided by he main clock of MCU. B. VPPM Symbol VPPM symbol is defined as in Table. Logical daa is mapped o VPPM symbol ransied from high o low, and logical daa is mapped o VPPM symbol ransied from low o high. Schemaic mechanism for VPPM in IEEE sandard is shown as figure 3[3]. TABLE. DEFINITION OF DATA MAPPING FOR VPPM Logical value Physical value d is he VPPM duy cycle (. d.9) High Low High Low < dt dt < T < (-d)t (-d)t < T The brighness of VPPM symbol is same for boh case of logical daa and, because boh signals have he same ON secion of pulse. The difference beween logical daa and is he ype of ransiion. So receiver can deec logical daa and from he ype of ransiion. Brighness 2% 4% 6% 8% 4T c 6T c 8T c 2 Figure 3. Schemaic mechanism for VPPM signal C. MCU based VPPM Symbol Generaion VPPM symbol has ON secion and OFF secion. The widh of each secion is conrolled according o he brighness of lighing. For example, if dimming sep of lighening is % of maximum brighness, he ON secion ime of VPPM symbol is 3 Figure 4. VPPM symbol generaion using C program VPPM symbols generaed in MCU are used as he ransmission signal in a visible ligh communicaion. To receive he daa wihou error a he receiver, he symbol period of he ransmiing signal mus be always same. However, he swing of symbol period prevens receiver from mainaining symbol synchronizaion. In order o always keep he symbol period of he ransmiing signal, MCU should no perform oher asks. Oher ask of MCU should be performed afer delivery of a single physical layer frame. III. PHY FRAME FORMAT Figure 5 shows he srucure of he ransmier implemened by using a MCU. Ou signal from GPIO pin of he MCU is applied o he LED driver. The MCU has a role o make PHY frame and generae ransmiing signal which is applied o he LED driver. In deail, he MCU includes he following funcion blocks. A funcion block reads he memory wih a given ID. Anoher funcion block makes he PHY frame wih hese daa. The hird block modulaes he frame wih he VPPM symbol mapping funcion. Given ID ID Loading Funcion GPIO pin MCU Driver LEDs PHY Frame Generaion Funcion VPPM Symbol Mapper Funcion Figure 5. Srucure and funcion of ransmier using MCU ISBN February 6~9, 24 ICACT24

3 A. PHY Frame Frame srucure for he promoion lighing proposed in his paper is shown in Figure 6. The frame sars wih a preamble field o indicae he saring poin of he frame. The daa field following he preamble field includes he predeermined value ha is assigned for promoing lighing. The CRC field is generaed by using a generaor polynomial CRC-5 o check he error in a frame. The CRC-5 polynomial which is used in he sysem is given by x ^ 5 + x ^ 2 +. As shown in Figure 6, he proposed frame consiss of 32-bi binary values and each bi is ransmied during 8 ime slos. The flicker effec occurs in case ha all of values during 8 ime slos are same. As shown in Figure 8, o preven his flicker effec, Mancheser coding aking value-ransiion is applied in his sysem. Figure 8. Srucure and funcion of ransmier using MCU Figure 6. PHY Frame forma of promoion lighing service For promoion lighing, he daa depends on ligh ID and hen he conens of he frame are fixed if he ligh ID is no changed. Therefore, once he CRC value relaed o ligh ID is deermined, he value can be reused for all frames. In he receiver side, he saring poin of he frame can be deeced by using his preamble which is predeermined values. The proposed sysem has been developed in ATMEGA28 8-bi processor. To mainain he duy cycle of ransmi signal for logic daa and, physical layer frame is consised of 32 bis. To exend he ID lengh is achieved by reducing he lengh of preamble and CRC, bu i causes he performance of communicaions o worse. If lighing does no suppor dimming funcion, we can use Mancheser code insead of VPPM. If Mancheser code is used, he ransmier sends 4 imes faser han VPPM-based ransmier sends daa. Also if flicker is no considered as problem, no coding scheme is needed in sysem. B. Flickering in Flicker is defined as periodic or non-periodic changes in he brighness of he ligh source which human eye can deec. When he oupu of he LED lighing have differen averages of brighness abou each of daa bi and bi as shown figure 7, flicker proecion echnology is needed on he inside of he frame. VPPM symbol mapping is a flicker proecion echnology which can suppor dimming simulaneously. Figure 7. Inra-frame flicker and iner-frame flicker in The oupu of he LED lighs in aspec of he average brighness is differen beween idle ime and daa-ransferring ime. And hen, oher echnologies o preven he iner-frame flicker anoher echnique are also required. However, we don consider iner-frame flicker because he proposed sysem ransmis packes coninuously wihou idle ime. C. VPPM Symbol mapping symbol mapping is implemened using he look-up able (LUT). According o he inpu daa, he sysem reads he corresponding values in he LUT and ransfers his value o FEM during 8 ime slos. Figure 9 describes he process of ransferring he frame o FEM. Oupu of PB5 pin ha is one of he MCU GPIO pins is conneced o FEM inpu. Depending on he value of he inpu signal, FEM par is driving he LED module (ON / OFF conrol). PHY Frame Preamble ID CRC VPPM Mapping PB5 oupu Figure 9. Srucure and funcion of ransmier using MCU D. MCU Main Program The main funcion of he MCU is implemened wih a simple srucure. Afer he iniializaion rouine is performed, he same daa is sen infiniely repeaed. Once he promoion lighing is power on, iniializaion rouine o clear he PB5 por is performed. In his implemenaion, PB5 is one of he ATMEGA28 MCU s PORT is conneced o LED lighing. All inerrup funcions are disabled o avoid he scaering of he ransmiing ime-slos due o any inerrup funcion. Whenever a paricular variable value is, PB5 is clear by he daa ransmission rouine. In conras, a paricular variable value is, PB5 is se. PB5 ou signal conrols he LED lighing in he form of ON/OFF[4]. Figure shows he operaion of main funcion for daa ransmission. Daa is already iniialized o he predeermined values, mapped o VPPM symbol and is ransmied sequenially. Transmi inerval in he infinie loop always mus have he same processing ime. If his is no guaraneed, duy cycle of daa changes. Clock synchronizer of receiver canno be performed appropriaely because of irregular duy cycle. Daa of index i is passed o PB5 hrough he send() funcion. Afer sending he Daa, index i is increased. Maximum value of index i is 255. In an 8 bi processor, when index i is 255, if i is auomaic increasing, i reurns o. Therefore ransmier ransmis Daa from index. As a ISBN February 6~9, 24 ICACT24

4 resul, ransmier can infiniely broadcas PHY frame wih shor message ID. Figure. MCU main funcion for ransmier IV. TEST AND RESULTS The proposed sysem ransferring only shor daa such as promoion lighing ID (Idenificaion) associaed wih a produc informaion was esed for proving he proposed physical layer frame and MCU ransmier. Proposed MCUbased mehod for promoion lighing sysem broadcass ID o he user erminal. User erminal receiving ID plays he conens mapped o i. User picks he promoion informaion for produc mapped o ID. ATMEGA28 MCU is used for ransmier. Typically ATMEGA28 MCU is used for PWM dimming in LED lighing. For MCU firmware updaing, AVR Sudio 4 developmen environmen and C programming language were used. GPIO pin of he MCU, PB5 sends a digial signal o deriver in he FEM. Depending on he value se for PB5, LED is ON or OFF. Daa bis is fixed o 5 in curren physical frame, bu sysem can ransfer longer daa by changing he frame srucure able o be applied o high-performance MCU. Figure shows he es environmens for proposed sysem in laboraory. For experimens, wo buil-in MCU lighing are used. Each MCU firmware saves each oher ID. To generae he CRC, MCU can perform CRC calculaion in real ime. Bu we don perform CRC calculaion in real ime, because ID value isn changed in real ime. Each MCU based ransmier ransmis each pre-calculaed physical layer frame. Receiver module Lighings of ID A Conens of ID A Conens Displayer Lighings of ID B Lighings of ID A Conens of ID B Conens Displayer Lighings of ID B Figure. Demonsraion of proposed sysem Receiver module receiving par is consised of receiving module and user erminal for displaying mulimedia conens mapped o ID. receiving module receives physical frame ha is ransmied by ransmier and gives he received physical frame o user erminal. The applicaion of user erminal checks CRC from physical frame and ges ID. As he es resul of he proposed sysem, depending on he locaion of he receiving module, he applicaion of user erminal displays he mulimedia conens mapped o he received ID. User erminal display he mulimedia conens of lighing closer o he receiving module. By using he proposed sysem, various services including indoor navigaion, noificaion on risk areas and locaion dependen game service can be developed. V. CONCLUSIONS In his paper, we designed visible ligh communicaion sysem for ransmiing shor message such as promoion ID. We implemened he MCU based ransmier applying he mehod used o generae PWM dimming signal. The designed MCU based ransmier is able o suppor he dimming funcion and ransmiing a he same ime. Also, we have proved ha implemened sysem provide he service scenario for promoing producs. According o resuls of his paper, locaion informaion service can be provided. Lighing IDs from LED lighings which exis all over he building can be used in indoor navigaion. We will propose he srucure of receiver for MCU based ransmier in nex paper. ACKNOWLEDGMENT This work was suppored by MKE / KEIT [3928, -LED lighing module developmen]. REFERENCES [] S. Rajagopal, R.D. Robers, and S.-K. Lim, IEEE visible ligh communicaion - modulaion schemes and dimming suppor, IEEE Communicaions Magazine, pp Mar. 22. [2] S. Arnon, J. R. Barry, G. K. Karagiannidis, R. Schober and M. Uysal, Advanced Opical Wireless Communicaion Sysem, pp , Cambridge Universiy Press, 22. [3] IEEE Sandard for Local and meropolian area neworks Par 5.7: Shor-Range Wireless Opical Communicaion Using Visible Ligh, IEEE Sd. 82.5, 2. [4] hp:// Il-Soon Jang is a principal member of engineering saff in he Elecronics and Telecommunicaions Research Insiue (ETRI) in Daejeon, Korea. He received his B.S degree in informaion and communicaion engineering in 997, and M.S and Ph.D. degrees in communicaion circui and sysem engineering in 999 and 25 from Chungbuk Naional Universiy, Cheongju, Korea. In 2, he joined ETRI, where he has worked on mobile communicaion sysems. He is concenraing in he area of visible ligh communicaion. He is one of he major conribuors in developing he IEEE sandard on. Jin-Doo Jeong is a senior member of engineering saff in he Elecronics and Telecommunicaions Research Insiue (ETRI) in Daejeon, Korea. He received his B.S degree in elecronic engineering in 998, and M.S degree in elecronic and communicaion engineering in ISBN February 6~9, 24 ICACT24

5 2 from Hanyang Universiy, Seoul, Korea. In 2, he joined ETRI, where he has worked on wireless personal area communicaion sysems. He is concenraing in he area of visible ligh communicaions. Myung-Soon Kim is a senior member of engineering saff in he Elecronics and Telecommunicaions Research Insiue (ETRI) in Daejeon, Korea. She received her B.S and M.S degrees in informaion and communicaion engineering in 999 and 2 from Chonbuk Naional Universiy, Jeonju, Korea. In 2, she joined ETRI, where she has worked on mobile communicaion sysems. She is concenraing in he area of visible ligh communicaion. In-Su Kim is a senior member of engineering saff a ETRI. He received his B.S. degree in 2, and M.S. and Ph.D. degrees in 22 and 28 in compuer engineering from Konkuk Universiy, Seoul, Korea. Since he joined ETRI in 29, he has worked on LED lighing conrol sysems and lighing conrol neworks. Sang-Kyu Lim is a principal member of engineering saff in he Elecronics and Telecommunicaions Research Insiue (ETRI) in Daejeon, Korea. He received his B.S. degree in Physics in 995, and M.S. and Ph.D. degrees in Elecronics Engineering in 997 and 2 from Sogang Universiy, Seoul, Korea. Since he joined ETRI in 2, he has worked on high-speed opical ransmission sysems and he microwave/millimeer-wave circui design. He is concenraing in he areas of visible ligh communicaion and lighing conrol neworks. He is one of he major conribuors in developing he IEEE sandard on. Tae-Gyu Kang, Ph.D. has been LED Communicaion Research Secion Direcor a ETRI for 23 years (or since 989) wih responsibiliy CCS No. 7 Inelligen Nework, responsibiliy Voice over Inerne Proocol, sysem lighing and responsibiliy LED Fusion echnology Visible Ligh Communicaions. Visible Ligh Communicaion is a echnology ha LED illuminaion swiches on and off repeaedly according o wireless communicaion media and is modulaion schemes. Sysem Lighing is a lighing ha has sysem capabiliies wih wireless connecion ZigBee, wired connecion DALI, muli-sensor, acive cooling, and processing/driving. He has been conribued inernaional and domesic sandard specificaion of Visible Ligh Communicaion as chairman of IEEE regulaion subcommiee, chairman of TTA visible ligh communicaion service Working Group, and edior of TTA roadmap. He is ineresed in fusion echnologies: Visible Ligh Communicaion, Inelligen Informaion Technology LED illuminaion, sysem lighing, and neworking proocols beween LED lamps. ISBN February 6~9, 24 ICACT24