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 ¡]2¡^µÜ´Ë³q¹D¡]Ricean Channel¡^¡Aµo®g¤Ñ½u»P±µ¦¬¤Ñ½u¤§ª½±µ¸ô®|¤£¨üªý¾×¡A¦ý¬O±µ¦¬¤Ñ½uªþªñ¦³¤Ï¡]´²¡^®gÅé¡A¨ä¨å«¬ªºÀô¹Ò¬°¥«°Ïµó¹D©Î¦ì©ó°ª¼ÓªL¥ßªº¤½´J¡C

 ¡]3¡^·ç§Q³q¹D¡]Rayleigh Channel¡^¡Aµo®g¤Ñ½u»P±µ¦¬¤Ñ½u¤§ª½±µ¸ô®|¨ü¨ìªý¾×¡A¦¹®É¤§±µ¦¬¨ìªº¹qªi¬°Â¶®gªi»P¨Ó¦Û¨ä¥Lª«Åé¤Ï®g©Î´²®gªi¡A¨ä¨å«¬ªºÀô¹Ò¬°¤s¸}¤U©Î¨ü¤j¼Óªý¾×ªº¦a¤è¡C

 

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µL½u¹q«H¸¹¥Ñµo®g¾÷ªº¤Ñ½u¿ç®g¨ì¾ã­Ó¦Û¥ÑªÅ¶¡¤W¶i¦æ¶Ç¼½¡C¥H¦Û¥ÑªÅ¶¡¬°¶Ç¿é¤¶½è¡A¹qºÏªi¦b¦Û¥ÑªÅ¶¡¤¤¶Ç¼½¡A¬°¤F¶Ç¼½«Ü»·¡A±`±Ä¥ÎÀW²v«Ü°ª¤§®¶Àúªi¡C¦]¦¹¡A¥²¶·¦³¤@­Ó°ªÀWµo®g¾÷¡A²£¥Í°ªÀW¸üªi¥H©Ó¸ü¸ê°T¡A¨Ã³q¹L¤Ñ½uµo®g¥X¥h¡F¦b±µ¦¬ºÝ¡A³q¹L±µ¨ü¤Ñ½u©M±µ¦¬¾÷¨Ó±µ¨ü«H¸¹©M¸ê°T¡C¤£¦PÀW¬qªºµL½u¹qªi¦³¤£¦Pªº¶Ç¼½¤è¦¡¡A¥D­n¦³¡G

¥Ñ©ó¹qºÏªi¦b¤ôÅ餤¶Ç¿éªº·l¯Ó«Ü¤j¡A¦b¤ô¤U³q±`±Ä¥ÎÁnªiªº¤ôÁn³q¹D¶i¦æ¶Ç¿é¡C¤£¦P±K«×©MÆQ«×ªº¤ô¼h§Î¦¨ªº¤Ï®g¡B§é®g§@¥Î©M¤ô¤Uª«Å骺´²®g§@¥Î¡A¨Ï±o¤ôÁn³q¹D¤]¬O¦h®|°I¸¨³q¹D¡C

µL½u³q«H¦b¦Û¥ÑªÅ¶¡¡]¹ï©óµL½u¹q³q¹D¨Ó»¡¬O¤j®ð¼h©M¤ÓªÅ¡A¹ï©ó¤ôÁn³q¹D¨Ó»¡¬O¤ôÅé¡^¤W¶Ç¼½«H¸¹¡A¦]¦¹¯à¶q¤À´²¡B¶Ç¿é®Ä²v¸û§C¡A¨Ã¥B«Ü®e©ö³Q¥L¤HºIÀò¡A¦w¥þ©Ê®t¡C¦ý¬O¡AµL½u³q«HÂ\²æ¤F¹ï¾É½uªº¨Ì¿à¡A¦]¦¹¨ã¦³¦³½u³q«H©Ò¨S¦³ªº°ª«×ÆF¬¡©Ê¡C

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C = \sup_{p_X} I(X;Y)\,

¹ï©ó«H¾¸¤ñ¬° S/N¡BÀW¼e¬°Bªº¥[©Ê°ª´µ¥Õ¾¸Án³q¹D¡A¨ä³q¹D®e¶q¬°

C = B \ \log_2 (1 + S/N)

log2(1 + S / N)¬°³q¹D¶Ç¿é«H®§ªºÀWÃЮIJv¡A§Y³æ¦ì®É¶¡¡B³æ¦ìÀW¼e¤W¯à°÷¶Ç¿éªº«H®§¶q¡A³æ¦ì¬°\mbox{bit} \cdot \mbox{Hz}^{-1} \cdot \mbox{s}^{-1}¡C¼W¤j«H¾¸¤ñ¥i¥H´£°ª³q¹Dªº®e¶q¡A³o¥i¥H³q¹L§í¨î¾¸Án©ÎªÌ¼W¥[µo®g¥\²v¹ê²{¡C°²­Y«H¾¸¤ñµL½a¤j¡A«h³q¹D®e¶q¤]ÁÍ©óµL½a¡C¤£¹L¥Ñ©ó³q¹D¤¤Á`¦s¦b¾¸Án¡A¦Ó¥Bµo®g¾÷ªº¥\²v¤£¥i¯à¨S¦³­­¨î¡A¦]¦¹³oºØ±¡ªp¤£·|¥X²{¡C¼W¥[³q¹DÀW¼e¤]¥i¥H¼W¥[³q¹D®e¶q¡A¦ý¬O³oºØ¼W¥[¤£¬OµL­­¨îªº¡C³]³q¹Dªº¾¸Án¥\²vÃбK«×¬°N0¡A«hÀHµÛ³q¹DÀW¼e B ªº¼W¥[¡A¾¸Án¥\²vN = BN0¤]ÀH¤§¼W¥[¡C°O«H¸¹¥\²v³Ì¤j¬°Es¡A«hÀW¼eµL½a¤j®É¡A³q¹D®e¶qªº·¥­­¬°

 \lim_{B \rightarrow \infty} B \log_2 \left( 1 + \frac{E_s}{B N_0} \right) \approx 1.44 \frac{E_s}{N_0}

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¤½²³¦æ°Ê¹q¸Ü¨t²Î¡B±M¥Î¦æ°Ê³q«H¨t²Î¡B¤À§G¦¡¡]§½§G«ü´§½Õ«×¡^¦æ°Ê³q«H¨t²Î¡BµL½u¹q©I¥s¨t²Î¡BµL½u¹q¸Ü¨t²Î¡BµL¤¤¤ß¿ï§}­Ó¤H³q«H¨t²Î¡B½Ã¬P¦æ°Ê³q«H¨t²Î¡B¦a¤U¦æ°Ê³q«H¨t²Î¡B¨ä¥L¦æ°Ê³q«H¨t²Î¡]µL½u¨¾µs¨¾¤õ³øĵ¨t²Î¡B¨Ø±a¦¡µL½uºò«æ³q³ø¨t²Î¤Î°Êª«¬ã¨s¨t²Î¡^¡B

¦³Ãö¦æ°Ê³q«Hªº¯SÂI±ø¦C¦p¦Z¡G¯à¦b¦æ°Ê¤¤³q«H¡F¹qªi¶Ç¼½½ÆÂø¡A¥Ñ©ó¦æ°Ê¥x¦b¤£Â_¹B°Ê¡A¾É­P±µ¨ü«H¸¹±j«×©M¬Û¦ìÀH®É¶¡¦aÂIªºÅܤƦÓÅܤơFÂø°T©M¤zÂZ¤j¡FÀW¹D¾ÖÀ½¡F±±¨î½ÆÂø¡F³q«H¹q¥x­n¤p¡B¬Ù¡B¨c¡B«K¡C

 

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°T¸¹±j«×ÀHµÛ¶Ç¼½¸ô®|¼W¥[¦Ó°I´î¡A¬°µo®g¤Ñ½u¦Ü±µ¦¬¤Ñ½u¤§¶¡ªº¥\²v®t­È¡C¸ô®|·l¥¢¡A¦bµL½u³q°T»â°ì¤¤¤£­Y¦b¦³½u³q°T»â°ì¤@¯ëªº©ö©ó¹w´ú¡CµL½u¹qªi±j«×²`¨ü©ó¸ô®|ªø«×¡B¤Ñ½u°ª«×¡BÀW²v½d³ò¡B¦a§Î°_¥ñ¥H¤Î¦p«Ø¿vª«¡B¨T¨®¡B¾ðªLµ¥¤§»Ùꪫªº¼vÅT¡C¹qªiªº¶Ç¼½¾÷¨î¦³¤Ï®g(reflection)¡A³z®g(refraction)¡A´²®g(scattering)¡B¶®g(diffraction)µ¥²{¶H¡A¥[¤W²¾°Ê³t«×³y¦¨ªº§ù¤R°Ç¦ì²¾(Doppler shift)®ÄÀ³¡A³o¨Ç±N³y¦¨°T¸¹²£¥Í§Ö³t°I¸¨(fast fading)ªº²{¶H¡C¥t¥~¡A¥Ñ«Ø¿vª«©Î¦a§Î²£¥Íªº¾B½ª±¡§Î¤]·|¨Ï°T¸¹¼È®É©Êªº¤U­°¡A¦¹²{¶HºÙ¬°ºC³t°I¸¨(slow fading)©Î¾B½ª(shadowing)¡C

數¦ì°T¸¹¦b¦Û¥ÑªÅ¶¡¤¤©Î¬O§÷料¤¶½è¤¤¶Ç¿é®É¡A±`·|¾D¹J¨ìªº¤zÂZ°ÝÃD¥]§t¡G¥æ¤¬²Å¸¹¤zÂZ(Inter Symbol Interference, ISI )¡B¤Ï®g¤zÂZ¡B串­µ¤zÂZ(Crosstalk)¡BÂø°T¤zÂZ¡B¦h­«路®|¤zÂZ(multipath fading )µ¥¡C

1. ¥æ¤¬²Å¸¹¶¡¤zÂZ¡GISI¬O數¦ì³q°T¨t²Î¤¤¥D­nªº¤zÂZ·½¡A¥¦¬O¤@ºØ¡u­¼©Ê¡vªº¤zÂZ¡A³y¦¨ISIªº­ì¦]¤@¯ë¬O³q¹D°I´î©Î°T¸¹©µ¿ð©Ò³y¦¨ªºªi§Î¥¢¯u¡A¦b³q¹D(channel)ÀW±a¼e度¦³­­¤U§K不了·|²£¥ÍISI¡A¥H¤@©w³t度¶Ç¿éªi§Î§Ç列¨ü¨ì«D理·Q³q¹Dªº¼vÅT¡A±`³y¦¨¦U²Å½X¶¡ªi§Î©µ¿ð±q¦Ó¨Ï¬Û¾F²Å½Xªºªi§Î²£¥Í­«Å|¡A³y¦¨±µ¦¬ºÝ¨ú¼Ë§PÂ_ªº¿ù»~¡C

2. ¤Ï®g¤zÂZ¡G¤Ï®g¤zÂZ»P³q¹Dªý§Ü¤Ç°t¦³«Ü±K切ªºÃö«Y¡A°T¸¹¦b³q¹D¤¤¶Ç¿é¡A³q¹Dµ¥®Äªý§Ü®e易¦]¹qÆl½u¤À±µÂIªý§Üªºº}²¾¦Ó²£¥Í不ªý§Ü¤Ç°tªº°ÝÃD¡Aªý§Üªº¬ðÅÜ·|¨Ï°T¸¹¶Ç¿é¤Þ°_¥\率ªº¤Ï®g©Î¤Ï®gªi¯Ó·l¡Aµ¥®Äªý§Ü¬°75£[ªº¦P¶b¹qÆl(coaxial)¤@¯ë¦b¶×流±Æªº²×ºÝ­n¥[¸Ë²×ºÝ¾¹(terminator)´N¬O¤@­Ó±`見ªº例¤l¡A²×ºÝ¾¹§Y¬O¬°了§l¦¬¹qÆl²×ºÝªº°T¸¹¡A²×ºÝ若¶}路·|¨Ï±o¾ã­Ó°T¸¹¥þ數¤Ï¼u²£¥Í¤zÂZ¡C

3. 串­µ¤zÂZ¡G串­µ¤zÂZ±`µo¥Í©ó½u§ô¤§¶¡ªº½u¶¡¤zÂZ¡A¦b¦P¤@±ø·F½uªº¹qÆl¤¤¡A¥i¯à§Î¦¨¹q®e©Î¹q·Pªº½¢¦X®ÄÀ³¡A¦]¦¹µo°e«H¸¹¥i¯à¸g¥Ñ½¢¦X¤è¦¡¶i¤J¨ä¥Lµo°e¾¹©Î±µ¦¬¾¹¡A串­µ¤zÂZ¹ï©ó°ªÀW°T¸¹¼vÅT¤×¨äÄY­«¡A¨ä¤@¯ë¤À¬°ªñºÝ串­µ(Near-end crosstalk¡ANEXT)¤Î»·ºÝ串­µ(Far-end crosstalk¡AFEXT)¡C

4. Âø°T¤zÂZ¡G數¦ì°T¸¹¶Ç¿é±`·|¨ü¨ì若¤zÂø°Tªº¤zÂZ¡A³o¨ÇÂø°T·½³q±`¬O®a¥Î¹q¾¹ªº¶}Ãö切´«¡A¹q°Ê¾÷±Ò°Êµ¥¹q力¹q¤l¤¸¥ó©Ò¤Þ°_ªº¬ðµo©Ê¤zÂZ¡A³q±`¬°¶Ç¾É©Ê©Î½¢¦X¤è¦¡²£¥Í©ó¶Ç¿é½u路¤§¤¤¡C¤@¯ë¦bÂø°T·½¸û¦hªºÀô¹Ò¤¤¡A¬°了½T«O±µ¦¬«H¸¹±j度¨¬¥H¹ï§Ü¥~¬ÉÂø°T·½¡A¦]¦¹©w¸qÅܰʽd³ò¤Î°T¸¹Âø°T¤ñ(S/N)»Ý落¦b¤@­Ó¥i±µ¨üªº¦X理­È¤º¡C

5. ¦h­«路®|¤zÂZ¡G¦h­«路®|¤zÂZªº°ÝÃD¤@ª½¦s¦bµL½u¶Ç¿é¨t²Î¤§¤¤¡A¦b理·QªºµL½u³q°T¨t²Î¤¤±µ¦¬¾÷ªº°T¸¹·|§¹¥þ»Pµo®g¾÷¬Û¦P¡A¹ê»Ú¤WªºµL½u¹q°T¸¹¦b¶Ç¿éªº¹Lµ{¤¤·|¸g¹L¦UºØ¤zÂZ»P°I´î¡A¦b¸g¹L¤Ï®g¡B¶®g¤Î§é®g±µ¦¬ºÝ¦¬¨ìªº°T¸¹¤w¸gÅÜ了¼Ë¡C

¤U¹Ï¤¤ 1 ¥iµø¬°µo®g¾÷¡A2 ¬°±µ¦¬¾÷¡A¦Ó©Ò¿×ªº¦h­«路®|¨Æ¹ê¤W¬O«ü°T¸¹¥Ñµo®g¾÷¨ì±µ¦¬¾÷ªº路®|¨Ã不¬°³æ¤@路®|¡A¥i¯à¨ã³Æ¦³¦hºØ路®|¡A不¦Pªº路®|¨ä¶Z離¨Ã不·|¬Ûµ¥¡A©Ò¥H±µ¦¬¾÷¦¬¨ìªº°T¸¹·|¨ã¦³不¦Pªº®É¶¡©µ¿ð¡A³o²{¶H©¹©¹®e易³y¦¨±µ¦¬ºÝªº¨ú¼Ë¿ù»~¡C

­nÁA¸Ñ¦h­«路®|²{¶H¡A­º¥ý¦Ò¼{ÀRºA(Static)¦h­«路®|Àô¹Ò¡A°²³]µo®g«H¸¹¦Ü±µ¦¬¾÷¦³兩類ªº°I´î«¬¦¡¡A不¦Pªº©µ¿ð®É¶¡·|³y¦¨兩±µ¦¬«H¸¹¬Û¹ïªº¬Û¦ì®t¡A¦³兩ºØ·¥ºÝªº±¡§Î¥i¯àµo¥Í¡G

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°w¹ï³o¨Ç±`見ªº¤zÂZ°ÝÃD¡A¥i¥H利¥Î¦UºØ½ÕÅܧ޳N±N¨ä§ïµ½¡A½ÕÅÜ(modulation)»P¸Ñ½Õ(demodulation)¬O³q°T¤¤ªº°ò¥»§Þ³N¡A±N±a¦³¸ê°Tªº°T¸¹Âà´«¦¨²Ä¤GºØ°T¸¹ªº¨BÆJºÙ¤§¬°½ÕÅÜ¡A¦Ó±N±a¦³¸ê°Tªº«H¸¹ÁÙ­ìºÙ¤§¬°¸Ñ½Õ¡F³q°T¨t²Î¥Î¨ìªº½ÕÅܧ޳N°£了¼ô±xªºASK»PFSK¥~¡A¬Û²¾½ÕÅÜ(phase shift keying)¬O±`¥Îªº§Þ³N¤§¤@¡A¦Ó¦p¤G¦ì¤¸¬Û²¾½ÕÅÜ (Binary Phase Shift Keying, BPSK)¡B¥¿¥æ¬Û²¾½ÕÅÜ(Quadrature Phase Shift Keying, QPSK)¡B¥¿¥æ´T²¾½ÕÅÜ(Quadrature Amplitude Modulation, QAM)都³Q¼sªxªº¨Ï¥Î¡C

¡i´T²¾½ÕÅÜ¡]Amplitude Shift Keying, ASK¡^¡j

ASK¬O¹B¥Î®¶´Tªº不¦P來ªí¥Ü©Ò­n¶Ç°eªº¸ê°T¡A¥H©T©wªº®¶´T¤j¤p來ªí¥Ü數¦ì°T¸¹¤¤ªº邏¿è·Ç¦ì1¤Î邏¿è·Ç¦ì0¡C

¡iÀW²¾½ÕÅÜ¡]Frequency Shift Keying, FSK¡^¡j

FSK¬O利¥Î不¦PªºÀW率來ªí¥Ü©Ò­n¶Ç°eªº¸ê°T¡A¥Ñ¤U¹Ï¤¤¥i¬Ý¥XFSK¦p¦ó¦b不¦PÀW率¤U來ªí¥Ü邏¿è1¤Î邏¿è0¡C

¡i¬Û²¾½ÕÅÜ¡]Phase Shift Keying, PSK¡^¡j

PSK³z¹L¬Û¦ìªº§ïÅÜ來ªí¥Ü¶Ç¿é°T®§ªº¤º®e¡Cªí¥Ü¦¡¦p¤U¡AA(t)¸g°ò©³°T¸¹½ÕÅÜ«á¡A±o¨ì¤@²Õ½ÕÅÜ°T¸¹Sm(t)¡A¨ä¤¤m¬O¾ã數¨ä½d³ò­­¨î¦b1¡Øm¡ØM¡A若M=2«hºÙbinary PSK (BPSK)¡AM=4 «hºÙ quadrature PSK (QPSK)¡C

¡i¤G¦ì¤¸¬Û²¾½ÕÅÜ¡]binary PSK, BPSK¡^¡j

BPSK¬OPSK¤¤³Ì°ò¥»ªº½ÕÅܤ覡¡A³oºØ¤è¦¡¬O±N¸üªi¬Û¦ì©ó0度¨ì180度¶¡ªºÅÜ´«¡A¥Hªí¥Ü³Q½ÕÅܪº¸ê料¡A¬GBPSK¨C¤@­Óbaud ¶Ç¿é1-bitªº¸ê料(i.e.1 ­Ósymbol ªí¥Ü1-bit, 1bit/symbol)¡A¤U¹Ï¥i¬Ý¥XBPSKªº狀ºA§ïÅÜ¥u¦s¦b0»P180度兩ºØ狀ºA¡C

¡i¥¿¥æ¬Û²¾½ÕÅÜ¡]Quadrature PSK, QPSK¡^¡j

QPSK¶Ç¿éªº¸ê料量¸ûBPSK來ªº¤j¡A¨C­Óbaud¥i¶Ç¿é2-bit(1­Ó symbol ¥i¥Hªí¥Ü2-bit, 2bits/symbol)¡AQPSK¥Î¤j¤p¤Î¬Û¦ìªº¸ê°T來ªí¥Ü數¦ì°T¸¹¡A¤W列說©ú¥i¥HÆ[¹î¤U¹Ï±oª¾¡C

¡i¥¿¥æ®¶´T½ÕÅÜ¡]Quadrature Amplitude Modulation, QAM¡^¡j

QAM¬O¤@ºØ°ª®Ä率ªº¸ê料¶Ç¿é§Þ³N¡A¨ä¥i¤À¬°QAM-16¡BQAM-64¡BQAM-256¡A¥Ñ¤U¹Ï¥i¥H¬Ý¥XQAM¦b¸ê料¶Ç¿é±K度¤W°ª©ó¤§«e©Ò¤¶²Ðªº¦UºØ½ÕÅܤèªk¡C

QAM-16»PQAM-64¸ê料¶Ç¿é率¤W¤À§O¬°4-bit/symbol¤Î6-bit/symbol¡A²{¤µ¦³½u¼eÀWºô路cable modem ©Ò¨Ï¥Îªº½ÕÅܤ覡§Y¬OQAM¡A¥B¦bcable modem¼Ð·Ç³W®æ¤¤¥u¨Ï¥Î¨ä¤¤4.5MHzªºÀW¼e¡A®Ú¾Ú³o¸ê料¥i¥H¹ï©óQAM¶Ç¿é³t率¦³¤@­Ó¸û¬°ª½Ä±ªº·§念¡G

       (1) QAM-16¶Ç¿é率¡Glog(16)/log(2)x4.5MHz¡Ü18Mbps¡Ü12±øT1±M½u

       (2) QAM-64¶Ç¿é率¡Glog(64)/log(2)x4.5MHz¡Ü27Mbps¡Ü18±øT1±M½u

       (3) QAM-256¶Ç¿é率¡Glog(256)/log(2)x4.5Mhz¡Ü36Mbps¡Ü23±øT1±M½u(T1±M½u=1.544Mbps)

 

¡i¥¿¥æ¤ÀÀW¦h¤u¡]Orthogonal Frequency Division Multiplexing, OFDM¡^À³¥Î©óPLCªºÀu¶Õ¡j OFDM§Þ³N³Q¨Ï¥Î©óµL½u°Ï°ìºô路5.4GHzÀW¬qªº802.11a³q°T¨ó©w¤W¡AµL½u³q°T©Ò­±¹ïªº³q°TÀô¹Ò¬Û¸û©ó¦³½u³q°T³q±`¸û¬°ÄY­V¡A³q¹D¤zÂZ¤Î°T¸¹°I´îªº±¡§ÎÄY­«¡AOFDM¦b½ÕÅܧ޳N¤W¦³§O©ó¤@¯ë±`見ªºFSK¡BBPSK¡BQPSK¡Kµ¥¡C¨ä¯S¦â¦b©ó¯à¦³®Ä¸Ñ¨M¦h­«路®|¤zÂZ¡A¥B¹B¥Î¦h­«¸üªi§Þ³N來降§C°T¸¹¤zÂZªº¼vÅT¡A¨Ã´£°ª¸ê料¶Ç¿é±K度¤ÎÀW¹Dªº利¥Î率¡A´N§Þ³Nªº¨¤度±NOFDM¹B¥Î¦bµL½u³q°T¨t²Î©Î¨ã¦³¬Û類¦ü¤zÂZ¨t²Î¬O¦³¨äÄYÂÔªº理論®Ú¾Úªº¡C

¸ê料¶Ç¿é»Ý¥ý¸g¥Ñ½ÕÅܦA³z¹L¸üªi¶Ç»¼¡A¥«­±¤W°Ó·~¹B§@ªº¨t²Î¥i¥H°Ï¤À¬°³æ¸üªi(mono-carrier)¤Î¦h­«¸üªi(multi-carrier)兩¨t²Î¡A´NADSL«D¹ïºÙ數¦ì¥Î¤á°j路©Ò¨Ï¥ÎªºDMT (Discrete Multitone)½ÕÅܧ޳N¡A§Y¬O¤@ºØ¦h­«¸üªi¨t²Î¡C

DMTªº°ò¥»·§念´N¬O±N©Ò¾Ö¦³ªº³q¹DÀW¼e¹º¤À¬°¦h­Ó¨ã¦³不¦P¸üªi°T¸¹ªº¤l³q¹D(subchannel) ¦A±N數¦ì¸ê料³z¹LQAMªº½ÕÅܤ覡¡A¤À°t½ÕÅܦܨC­Ó¤lÀW¹D¤W¡A¹ï©ó¨C¤@­Ó¤lÀW¹Dªº¶Ç¿é¸ê料量«h¨Ì·Ó¶Ç¿é½u路ªº¤zÂZ±¡ªp°µ½Õ¾ã¡A若¬Y¤@¤lÀW¹D¨ü¨ìªº¤zÂZ¤Ó¹L©óÄY­«(S/N)¤Ó¤p«h¨t²Î¥i¥HÃö³¬¦¹³q¹D¥H¹F¨ìÀW¼eªº¦³®Ä¹B¥Î¡C

¤@­Ó¦h­«¸üªi¨t²Î¨ä不®e©¿µøªº¯S¦â¦b©ó§ÜÂø°Tªº¯à力¡A¶Ç¿é³q¹D¨Æ¹ê¤W¦s¦bµÛ不¦PÀW率ªº¤zÂZ¡A¹ï©ó³æ¸üªi¨t²Î¦Ó¨¥¡A若¸üªiÀW率ÂI¨ü¨ì¤zÂZ¡A«h·|³y¦¨°T¸¹¶Ç¿é¥þ數¥¢±Ñ¡A¬Û¹ï©ó¦h­«¸üªi¨t²Î¡A¨ä¸û不易¨ü¨ì¿ï¾Ü©ÊÀW率°I´î¤Î¯¶ÀW¤zÂZªº¼vÅT¡A§Y¨Ï¶Ç¿é¸ê料¹Lµ{¤¤¦³¤zÂZ¤zÂZ¦s¦b¡A¤]·|¬O¤Ö數¤lÀW¹D¨ü¼vÅT¡A¥i¥H³z¹L¿ù»~更¥¿½X來¥[¥HÁ٭쳡¥÷¿ò¥¢ªº¸ê°T¡C

¦b°T¸¹¤zÂZ¤¶²Ð®É´¿´£¹L¦³Ãö¦h­«路®|¤zÂZªº·§念¡A°T¸¹¸g¹L不¦Pªº路®|¨ì¹F±µ¦¬ºÝ®É¡A³Ì¥ý¨ì¹Fªº°T¸¹»P³Ì«á¨ì¹Fªº°T¸¹¦³¤@©wªº

®É¶¡®ttmax¡AOFDM不¦P©ó¤@¯ë½ÕÅܤèªkªº¦a¤è´N¬O¦b©ó¥¦¯à¦³®Ä¸Ñ¨M¦h­«路®|¤zÂZªº°ÝÃD¡A¥D­nªº§Þ¥©¬O¦b¨C¤@­Ó²Å¸¹«e¥[¤W¤@¬q½w½Ä®É¶¡¡]guard time ¡^¡A³o¬q®É¶¡¥²¶·¦Ü¤Öµ¥©ótmax¡A±µ¦¬ºÝ¥²¶·µ¥«Ýtmaxªº®É¶¡¤~¯à¶}©l¨ú¼Ë¡A¹L了guard time ªº¸ê料¤~³Q»{©w¬°¥¿½Tªº¸ê料¡A¦p¦¹«OÅ@¸ê料不¨ü¤zÂZ¡A¦p¤U¹Ï©Ò¥Ü¡C

OFDM¬O¦h­«¸üªiªº¬[ºc»PDMT¬Û¦P¡A¦ý¬O¨ã³Æoverlapping subchannel¯S©Ê更Àu©óDMT¡A¦h­«¸üªi¨t²Î¦b§í¨î¿ï¾Ü©ÊÂø°T¤zÂZ¤w¦³不¿ùªº®ÄªG¡Aoverlapping subchannel 說©úOFDM½ÕÅܪkÅý¤l³q¹D¦bÀW°ì¤º¥i¦³³¡¥÷­«Å|¡A¬Û¸û©óDMTªºnon-overlapping subchannel ¨Ï¥ÎOFDMªº¨t²Î¦b¬Û¦PÀW±a裡¦³更¦nªº利¥Î率¡A¦ý¦b¸`省ÀW¼eªº¦P®É¤lÀW¹Dªº­«Å|¤]·|¤¬¬Û²£¥Í¤zÂZ(Crosstalk)¡A¾A·íªº±N¤l¸üªi¤§¶¡²£¥Í¥¿¥æ©Ê§Y¥i´î§C¦¹°ÝÃD¡A¤U¹Ï¥i¬Ý¥X¤GªÌ®t異¡C

OFDM ªº¨C¤@­Ó¤lÀW±a¹B¥ÎQAM§Þ³N¡A´£°ª¸ê料¶Ç¿éªº±K度¡A³o¨ÏOFDM¦b¦U¤è­±®Ä¯àµL論¬O¶Ç¿é©Îí©w度都Àu©ó¥H©¹ªº¦UºØ½ÕÅܧ޳N¡A802.11aµL½u³q°T¼Ð·Ç¤¤¤w±Ä¥ÎOFDM½ÕÅܾ÷¨î¡A§Ö³t¥i¾aªº數¾Ú¶Ç¿é¬O¦¨¬°¥D流ªº»ù­È©Ò¦b¡FOFDM§Þ³N¹B¥Î©ó¹q力½u³q°T¨t²Î¤W¡A¥Ñ³\¦hªº´ú¸Õ³ø§i¤¤¥i¬Ý¥X¡A¦b§ÜÂø°T¤Î°ª³t°ª±K度¶Ç¿é¦³不¿ùªº®Ä¯à¡AÅkµM¦¨¬°¤U¤@¥N³q°Tªº¥D流§Þ³N¡A¦pªí©Ò列¡C

 

 

 

 

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1¡Bºû°ò¦Ê¬ì¡X³q¹D    http://zh.wikipedia.org/zh-tw/%E9%A0%BB%E9%81%93

2¡Bhttp://chahaar.blogspot.com/2009/04/blog-post.html

3¡B¹q力½u³q°T(PLC)¨t²Î¤uµ{¨t列±M¥Z (¥|) --¹q力½u³q°T½ÕÅܶǿé§Þ³N¡A¥x¹qºî¦X¬ã¨s©Ò »Z«a§Ó³Õ¤h »P ¤u¬ã°|¸ê³q©Ò 林«T良±M®×¸g理¡C

4¡B¸ê®Æ»P¹q¸£³q°T²Ä¤Kª©  William Stallings µÛ¡B¦óÀM Ķ¡C