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ÇѱÛÇ¥ÁØ¸í ±¤ÇÐ Ä«¸Þ¶ó Åë½Å ¹°¸®°èÃþ ÇÁ·ÎÅäÄÝ µ¥ÀÌÅÍ À¯´Ö(PPDU) ÇÁ·¹ÀÓ Çü½Ä Á¦2ºÎ: ¿þÀ̺긴 Á÷±³ ÁÖÆļö ºÐÇÒ ´ÙÁßÈ­ ¹æ½Ä
¿µ¹®Ç¥Áظí Physical Protocol Data Unit(PPDU) Frame Format for Optical Camera Communication Part 2. Wavelet OFDM(Orthogonal Frequency Division Multiplexing(OFDM) Scheme
Çѱ۳»¿ë¿ä¾à Á÷±³ ÁÖÆļö ºÐÇÒ ´ÙÁß(Orthogonal Frequency-Division Multiplexing: OFDM)Àº ´ÙÁß ¹Ý¼ÛÆÄ ÁÖÆļö¿¡¼­ µ¥ÀÌÅ͸¦ µðÁöÅÐ ÀÎÄÚµùÇÏ´Â º¯Á¶ ¹æ½ÄÀÌ´Ù. °í¼Ó Åë½Å¿¡¼­ Áß¿äÇÑ ±â¼úÀÌ¸ç ½Éº¼ °£ °£¼·(Intersymbol Interference: ISI)À¸·Î ÀÎÇÑ ¿Ö°îÀ» Á¦°ÅÇϱâ À§ÇØ ´ë¿ªÆøÀ» Á÷±³ ºÎ¹Ý¼ÛÆÄ·Î ºÐÇÒ ÇÑ´Ù. ºÎ¹Ý¼ÛÆÄ °£ÀÇ Á÷±³¼ºÀ» ÀÌ¿ëÇÔÀ¸·Î½á OFDM ½Ã½ºÅÛÀÇ ºÎ¹Ý¼ÛÆÄ´Â ½ÅÈ£ ¼º´É¿¡ ¿µÇâÀ» ÁÖÁö ¾Ê°í ¼­·Î ÁßøµÉ ¼ö ÀÖ´Ù. ¶ÇÇÑ, Wavelet-OFDM¿¡´Â ±âÁ¸ OFDM ¹æ½ÄÀÇ Cyclic-Prefix°¡ ÇÊ¿äÇÏÁö ¾Ê´Ù.

±âÁ¸ OFDM°ú ´Þ¸® Wavelet-OFDMÀº ·Ñ¸µ ¼ÅÅÍ Ä«¸Þ¶óÀÇ ·Ñ¸µ È¿°ú¿Í ¿þÀ̺긴 º¯È¯À» »ç¿ëÇÏ¿© µ¥ÀÌÅ͸¦ Àü¼ÛÇÑ´Ù. ·Ñ¸µ È¿°ú¸¦ »ç¿ëÇÏ¿© ¹ß±¤ ´ÙÀÌ¿Àµå(LED)ÀÇ ÁøÆøÀ» Á¶Á¤ÇÏ¿© OFDM ½Éº¼ÀÇ µ¥ÀÌÅÍ ÇÁ·¹ÀÓÀ» Àü¼ÛÇÒ ¼ö ÀÖ´Ù. OFDM ½Ã½ºÅÛ¿¡ ´ëÇÑ Çª¸®¿¡ º¯È¯°ú ºñ±³ÇÏ¿© ¿þÀ̺긴 º¯È¯ÀÇ ÀÌÁ¡À» ÀÌ ¹®¼­¿¡¼­ Á¦½ÃÇÑ´Ù. ±¤ Ä«¸Þ¶ó Åë½Å(OCC)À» À§ÇØ Á¦¾ÈÇÏ´Â Wavelet-OFDM ¹æ½ÄÀÇ ±¸Á¶¿Í ÀÚ¼¼ÇÑ ³»¿ëÀ» Á¦½ÃÇÑ´Ù.
¿µ¹®³»¿ë¿ä¾à The Orthogonal Frequency-division multiplexing (OFDM) is a modulation method of digital encoding data on multiple carrier frequencies. It is an important technique in high-speed communication, and the bandwidth is divided into the orthogonal sub-carrier to eliminate the distortion caused by Intersymbol Interference(ISI). By using orthogonality among subcarriers, the sub-carrier in OFDM system can be overlapped on each other without affecting signal performance. Besides that, the Cyclic-Prefix in the conventional OFDM method is not necessary for Wavelet-OFDM.

Unlike the conventional OFDM, the wavelet-OFDM uses the rolling effect of rolling-shutter cameras and the wavelet transform to transmit data. By using the rolling effect, we can adjust the amplitude of LED to transmit the data frame of OFDM symbol. The advantages of Wavelet transform comparing with Fourier transform for OFDM system will be presented in this document. The more detail of the wavelet-OFDM scheme for OCC, we mention in the sections below. Besides that, we proposed the structure of the wavelet-OFDM.
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