International Conference on Information Sciences, Machinery, Materials and Energy (ICISMME 2015)

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1 Internatonal Conference on Informaton cences, Machnery, Materals and Energy (ICIMME 05) The ystem of Outdoor Vsble ght Communcaton wth Fast Blnd Algorthm Zheng-Guo un, Y-Jun Zhu & Yan-Yu Zhang Department of Communcaton Engneerng, Informaton cence and Technology Insttute, Henan Provnce, 45000, Chna Keywords: Outdoor VC (OVC), blnd channel estmaton, block transmsson, IM/DD, generalzed lkelhood rato test (GT). Abstract. In ths paper, we study a new fast blnd algorthm based on the generalzed lkelhood rato test (GT) prncple. It s used n an outdoor vsble lght communcaton (OVC) system that uses OOK modulaton wth ntensty modulaton and drect detecton (IM/DD) over atmospherc turbulence-nduced slow fadng channel, and we prove that the fast blnd algorthm can detect the optcal sgnal outdoor effectvely by experments Introducton As a new communcaton technology, VC has been pad a lot of attenton [] [6]. It s a data communcatons medum usng vsble lght between 400 and 800 THz ( nm). The ntensty modulaton and drect detecton (IM/DD) method s practcally utlzed n VC due to ts smple mplementaton of a low-cost recever. It can acheve the broadband transmsson wth unlcensed spectrum, allevate shortage of wreless spectrum resources [7], there are no health regulatons to restrct the transmt power. VC s more and more wdely used n human lfe, but the most technologes n VC are used ndoor. VC develops rapdly under the nfluence of lght-emttng dode (ED) development. New generaton of hgh-ntensty lght emttng dodes (EDs) whch has permtted the replacement of ncandescent-based lghts, unfolds the potental of mplementng VC system on outdoor envronment [8]. Hgh-ntensty EDs meet the demand of square llumnaton, streetlght, traffc lght and other outdoor scenes because of ts hgh lght and energy savng. Based on llumnaton equpment exstng, t can acheve hgh speed communcaton wth vsble lght. It gves an addtonal supplement to tradtonal communcaton wth releasng the communcaton pressure and provdng a better performance. The channel n the ndoor VC s statc and stable [9], but outdoor s dfferent. The optcal channel outdoor s n the complex atmospherc stuaton. The nhomogeneous of temperature and pressure lead to the atmospherc turbulence. The atmospherc turbulence makes the refractve ndex varable along the transmsson path, optcal sgnal attenuaton degrades communcaton performance. Than the sgnal transmsson rate, the channel change s more slow [0] [3]. The outdoor optcal channel s tme-varable slow fadng. The paper s organzed as follows. In ecton, A new optcal sgnal detecton algorthm s proposed. In ecton 3 we test our algorthm n the outdoor VC system. Fnally, we conclude our paper n secton 4. THE DETECTION METHOD OF OUTDOO VC In ths secton, we wll put forwards our new algorthm and compare t wth mean value algorthm, frst let me revew the mean value algorthm next.. Mean Value Detecton Ths method s common used n practce, as the probablty densty functon (PDF) of channel s 05. The authors - Publshed by Atlants Press 537

2 unknown. The channel estmaton used mean value detecton h s obtaned by r = h = () where s the block length, r s the sgnal receved. Then we get sgnal transmtted s by the decson crteron h, r >, s = () h 0, r. Fast Blnd Detecton The channel gan h and nose n n n are ndependent dstrbuton. The pdf of receved sgnal r condtoned on s and h s r hs p( r s, h) = exp (3) ps s n ( n ) (3) can be smplfed nto (4). The Eucldan dstance descrbes the error between receved sgnal vector r and emtted sgnal vector s = = = (4) r hs = r h r s + h s (4) s a non-determnstc polynomal hard (NP-hard) problem. The common method s Vterb algorthm [4] to search s wth hgh complexty. To make the NP-hard problem be lnear, we defne the sgnal sum functon. = s,0 = (5) As the sgnal s non-negatve n VC, the s only can be 0 or n OOK modulaton. When s fxed, we get the total number of symbol, ths dea s very mportant to smplfy algorthm. To make (4) mnmum, we order the receved block sgnal vector r and summate the frst terms. = r() + r() r(),( r() r()... r(), ) (6) r() Where s the order statc of receved sgnal. When s fxed, s a fxed number. ubsttutng (5) and (6) nto (4) results n = + = C r h h (7) C0 = When = 0, = 0 r, = s fxed. Our target s to search to get the mnmum. To a gven, by dfferentatng (7) wth respect to h and lettng the dervatve be equal to zero, We get the estmated value of h h = ubsttute (8) nto (7) results n C = Fnally we obtan the decson crteron (8) y (9) = 538

3 By searchng exhaustvely to ft (), we can acheve the channel estmate and the sgnal demodulaton jontly EXPEIMENT We compare the performance of the fast blnd detecton algorthm and mean value algorthm wth OOK sgnal and IM/DD. The board wth Altera Cyclone II s used as a transmtter, and Kntex-7 FPGA KC705 Evaluaton Kt wth perpheral AD chp s used as a recever. The known data s stored n transmtter and recever. The transmtter transmts data repeatedly, the recever compute the BE after recevng the sgnal. Two knds of detecton algorthm fast blnd detecton and mean value are used n recever. The processng of sgnal s shown n Fg.. The block code s used to elmnate error floor, the data whch passes through an block encoder transmts n the channel, the recever gets sgnal, the detecton algorthm s used to detecton sgnal, then the sgnal wll be decoded by block decoder. The system s shown n Fg., The dfferent dstance D=m, 0m and 00m s expermented. (0) Fg.. (a) The expermental setup. (b) The sgnal processng flow between transmtter and recever. The results are shown n Fg., Fg.3 and Fg.4. As the block code s used, there no exts error floor. The fast blnd detecton algorthm outperform mean value algorthm n all three cases. When dstance D ncreases, the gap ncreases n Fg., Fg.3 and Fg.4 because of atmospherc turbulence. Fg. 3. The comparson between fast blnd algorthm and mean value wth dstance D=0m 539

4 Fg.. The comparson between fast blnd algorthm and mean value wth dstance D=m Fg. 4. The comparson between fast blnd algorthm and mean value wth dstance D=00m CONCUION In summary, a fast blnd detecton algorthm based on GT s proposed n outdoor VC, the algorthm s tested by experments wth dfferent block length. The algorthm are sgnfcant for slow fadng channel n the outdoor VC, they can mprove system performance extremely, block code as a new method to elmnate error floor s effectve. Acknowledgements Ths work was supported n part by NNF of Chna (No. 6753) and NHTDP (863 Program) of Chna (Grant No.03AA03603), n part by Grant No. KFKT-003 of Bejng Unversty of Posts and Telecommuncatons (BUPT) eferences [] D. O. A.M.treet, P.N. tavrnou and D. Edwards, Indoor optcal wreless systems-a revew, Opt. Quantum Electron., Mar [] A. Acampora, ast mle by laser, c. Amer., Jul. 00. [3]... K.-D. a. W. J. Grubor, J., Broadband Informaton Broadcastng Usng ED-Based Interor ghtng, J. ghtw. Technol., Dec [4] M. Z. Afgan, H. Haas, H. Elgala, and D. Knpp, Vsble lght communcaton usng ofdm, n Testbeds and esearch Infrastructures for the Development of Networks and Communtes, 006. TIDENTCOM 006. nd Internatonal Conference on, pp. 6 pp, IEEE,

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