{"id":409,"date":"2020-04-06T09:03:36","date_gmt":"2020-04-06T07:03:36","guid":{"rendered":"http:\/\/tech.sosthe.sk\/?p=409"},"modified":"2020-04-06T22:47:33","modified_gmt":"2020-04-06T20:47:33","slug":"6-3-modulovany-prenos","status":"publish","type":"post","link":"http:\/\/tech.sosthe.sk\/index.php\/2020\/04\/06\/6-3-modulovany-prenos\/","title":{"rendered":"6.3.\u2002Modulovan\u00fd prenos"},"content":{"rendered":"

Pri prenose na ve\u013ek\u00e9 vzdialenosti je probl\u00e9m prenies\u0165 tak\u00fd skokov\u00fd sign\u00e1l, ako sa pou\u017e\u00edva pri digit\u00e1lnom prenose, lebo sa za\u010d\u00ednaj\u00fa zaob\u013eova\u0165 hrany tohto sign\u00e1lu. Pre elektromagnetick\u00e9 \u017eiarenie je prirodzen\u00e9 \u0161\u00edrenie vlnami v tvare s\u00ednusoidy. Pri modulovanom prenose sa vyu\u017e\u00edva nosn\u00e1 harmonick\u00e1 elektromagnetick\u00e1 vlna, ktorej zmena predstavuje zmenu sign\u00e1lu. T\u00fato zmenu u odosielate\u013ea realizuje na z\u00e1klade pren\u00e1\u0161an\u00fdch d\u00e1t zariadenie naz\u00fdvan\u00e9 modul\u00e1tor a u pr\u00edjemcu extrahuje digit\u00e1lne d\u00e1ta zariadenie zvan\u00e9 demodul\u00e1tor. Kombinovan\u00e9 zariadenie obsahuj\u00face modul\u00e1tor aj demodul\u00e1tor sa naz\u00fdva\u00a0modem<\/strong>.<\/p>\n

Nosn\u00fa elektromagnetick\u00fa vlnu m\u00f4\u017eeme modifikova\u0165 troma sp\u00f4sobmi. M\u00f4\u017eeme meni\u0165 amplit\u00fadu, frekvenciu a f\u00e1zov\u00fd posun. Pri amplit\u00fadovej modul\u00e1cii men\u00edme silu sign\u00e1lu, pri frekven\u010dnej modul\u00e1cii men\u00edme frekvenciu sign\u00e1lu a pri f\u00e1zovom posune za\u010diatok s\u00ednusoidy tejto vlny. F\u00e1zov\u00fd posun sa realizuje viacer\u00fdmi gener\u00e1tormi harmonickej vlny s posunom za\u010diatku vlny.<\/p>\n

\"\"<\/p>\n

Amplit\u00fadov\u00e1 modul\u00e1cia je citliv\u00e1 na zoslabovanie sign\u00e1lu na v\u00e4\u010d\u0161ie vzdialenosti, frekven\u010dn\u00e1 modul\u00e1cia je citliv\u00e1 na interferencie s in\u00fdmi elektromagnetick\u00fdmi \u017eiareniami v prostred\u00ed. F\u00e1zov\u00e1 modul\u00e1cia je najodolnej\u0161ia vo\u010di nepriazniv\u00fdm vplyvom na prenosov\u00fd kan\u00e1l.<\/p>\n

Pri prenose telef\u00f3nnymi dr\u00f4tmi sa realizuje kombin\u00e1cia v\u0161etk\u00fdch troch zmien nosnej harmonickej vlny. Ak pou\u017eijeme napr\u00edklad 3 r\u00f4zne amplit\u00fady, 4 r\u00f4zne frekvencie a 8 r\u00f4znych f\u00e1z, tak ich kombin\u00e1ciou vieme odhali\u0165 3*4*8= 96 r\u00f4znych stavov. To znamen\u00e1, \u017ee jednou kombinovanou zmenou viem prenies\u0165 viac ako jeden bit. V pr\u00edpade, \u017ee by sme mali t\u00fdchto 96 r\u00f4znych stavov a z nich vyu\u017eili 64=26<\/sup>, tak zak\u00f3dujeme jednou kombinovanou zmenou sign\u00e1lu 6 bitov. V tomto pr\u00edpade je prenosov\u00e1 r\u00fdchlos\u0165 (po\u010det bitov za sekundu) v\u00e4\u010d\u0161ia ako modula\u010dn\u00e1 (po\u010det \u010d\u00edtan\u00ed sign\u00e1lu za sekundu).<\/p>\n

6.3.1\u2002 Zvy\u0161ovanie prenosovej r\u00fdchlosti<\/h3>\n

Vid\u00edme, \u017ee zv\u00e4\u010d\u0161en\u00edm po\u010dtu stavov m\u00f4\u017eeme zv\u00e4\u010d\u0161i\u0165 prenosov\u00fa r\u00fdchlos\u0165. To prirodzene evokuje ot\u00e1zku, dokedy sa d\u00e1 zvy\u0161ova\u0165 prenosov\u00e1 r\u00fdchlos\u0165. Existuj\u00fa nejak\u00e9 teoretick\u00e9 limity?<\/p>\n

Prv\u00fdm sp\u00f4sobom je zv\u00e4\u010d\u0161ovanie modula\u010dnej r\u00fdchlosti (po\u010det \u010d\u00edtan\u00ed za sekundu), ktor\u00e1 n\u00e1sledne priamo \u00famerne zv\u00fd\u0161i aj prenosov\u00fa r\u00fdchlos\u0165. Zvy\u0161ovanie modula\u010dnej r\u00fdchlosti v\u0161ak priamo z\u00e1vis\u00ed od \u0161\u00edrky p\u00e1sma. \u0160\u00edrka p\u00e1sma je rozsah (ve\u013ekos\u0165 intervalu) frekvenci\u00ed, v ktorom sa vysiela. Pod\u013ea Nyquistovho z\u00e1kona plat\u00ed, \u017ee modula\u010dn\u00e1 r\u00fdchlos\u0165 nesmie by\u0165 v\u00e4\u010d\u0161ia ako dvojn\u00e1sobok \u0161\u00edrky p\u00e1sma. Ak m\u00e1me \u00fazke p\u00e1smo, nem\u00f4\u017eeme \u010dasto robi\u0165 zmeny\/modul\u00e1ciu. To, ak\u00fd rozsah frekvenci\u00ed m\u00f4\u017eeme pou\u017ei\u0165, je dan\u00e9 charakterom prenosov\u00e9ho m\u00e9dia. R\u00f4zne typy dr\u00f4tov dok\u00e1\u017eu kvalitne prenies\u0165 r\u00f4zne rozsahy frekvenci\u00ed.<\/p>\n

Druh\u00fdm sp\u00f4sobom zv\u00e4\u010d\u0161ovania prenosovej r\u00fdchlosti je zv\u00e4\u010d\u0161enie po\u010dtu stavov. Ich po\u010det sa v\u0161ak tie\u017e nem\u00f4\u017ee zvy\u0161ova\u0165 do nekone\u010dna, ke\u010f\u017ee jemn\u00e9 rozdiely medzi stavmi s\u00fa \u0161umom (interferenciami) a zoslabovan\u00edm sign\u00e1lu nerozl\u00ed\u0161ite\u013en\u00e9. O hornom ohrani\u010den\u00ed prenosovej r\u00fdchlosti v z\u00e1vislosti od \u0161\u00edrky p\u00e1sma, sily sign\u00e1lu a sily \u0161umu hovor\u00ed Shannonova veta:<\/p>\n

\"\"<\/p>\n

 <\/p>\n

6.3.2\u2002 Technol\u00f3gia ADSL (Asymmetric Digital Subscriber Line)<\/h3>\n

Klasick\u00e9 telef\u00f3nne dr\u00f4ty s\u00fa stavan\u00e9 na ist\u00fa kvalitu dr\u00f4tu (vysok\u00fd odstup sily sign\u00e1lu od sily \u0161umu). T\u00e1to kvalita pri vy\u0161\u0161\u00edch frekvenci\u00e1ch ako 3400 Hz kles\u00e1, ale nekles\u00e1 ve\u013emi r\u00fdchlo. Technol\u00f3gia ADSL vyu\u017e\u00edva vy\u0161\u0161ie frekven\u010dn\u00e9 p\u00e1sma a\u017e do vy\u0161e 1000 kHz s ni\u017e\u0161ou kvalitou prenosu. T\u00e1to technol\u00f3gia prenech\u00e1va frekvencie 300 \u2013 3400 Hz na anal\u00f3gov\u00fd prenos hlasu a frekvencie nad 4000 Hz vyu\u017e\u00edva na sie\u0165ov\u00fa komunik\u00e1ciu. Tieto vy\u0161\u0161ie frekvencie s\u00fa rozdelen\u00e9 do viacer\u00fdch podp\u00e1siem, v ktor\u00fdch sa pou\u017e\u00edvaj\u00fa r\u00f4zne sp\u00f4soby modul\u00e1cie vzh\u013eadom na aktu\u00e1lnu kvalitu prenosu v danom podp\u00e1sme. T\u00e1to kvalita z\u00e1vis\u00ed od r\u00f4znych \u0161umov prostredia aj od sily sign\u00e1lu (vzdialenosti od telef\u00f3nnej \u00fastredne). Prenosov\u00e9 p\u00e1smo na sie\u0165ov\u00fa komunik\u00e1ciu je asymetricky (z toho je A v n\u00e1zve ADSL) rozdelen\u00e9 na upstream a downstream, pri\u010dom downstream m\u00e1 t\u00fdmto umo\u017enen\u00e9 v\u00e4\u010d\u0161ie prenosov\u00e9 r\u00fdchlosti. Z\u00e1rove\u0148 sa t\u00fdmto rozdelen\u00edm zabezpe\u010dil \u00fapln\u00fd duplex.<\/p>\n

6.3.3\u2002 Porovnanie digit\u00e1lneho a anal\u00f3gov\u00e9ho prenosu<\/h3>\n

Anal\u00f3gov\u00fd prenos vyu\u017e\u00edva modul\u00e1ciu harmonickej (s\u00ednusoidovej) elektromagnetickej vlny a vyu\u017e\u00edva na to n\u00edzke frekvencie. Pri anal\u00f3govom prenose zis\u0165ujeme konkr\u00e9tnu hodnotu meranej veli\u010diny (frekvencia, amplit\u00fada, f\u00e1zov\u00fd posun). Pri relat\u00edvne malej zmene vplyvom \u0161umu alebo \u00fatlmu m\u00f4\u017ee d\u00f4js\u0165 k zlej interpret\u00e1cii stavu, \u010do sp\u00f4sob\u00ed skreslenie inform\u00e1cie.<\/p>\n

Digit\u00e1lny prenos sa realizuje skokov\u00fdmi zmenami sign\u00e1lu. Zis\u0165ujeme, \u010di meran\u00e1 veli\u010dina (nap\u00e4tie, pr\u00fad, intenzita svetla,\u2026) reprezentuje niektor\u00fd z m\u00e1la stavov \u2013 hodn\u00f4t sign\u00e1lu. To umo\u017e\u0148uje napr\u00edklad pri malej zmene hodnoty meranej veli\u010diny (napr. pri \u00fatlme) st\u00e1le spr\u00e1vne ur\u010di\u0165, ktor\u00fd z mal\u00e9ho po\u010dtu stavov (napr. dvoch) bol pou\u017eit\u00fd. Zis\u0165ujeme, \u010di hodnota je z nejak\u00e9ho intervalu, a tak m\u00f4\u017eeme dosiahnu\u0165 ide\u00e1lny stav prenosu bez ak\u00e9hoko\u013evek skreslenia p\u00f4vodnej inform\u00e1cie.<\/p>\n","protected":false},"excerpt":{"rendered":"

Pri prenose na ve\u013ek\u00e9 vzdialenosti je probl\u00e9m prenies\u0165 tak\u00fd skokov\u00fd sign\u00e1l, ako sa pou\u017e\u00edva pri digit\u00e1lnom prenose, lebo sa za\u010d\u00ednaj\u00fa zaob\u013eova\u0165 hrany tohto sign\u00e1lu. Pre…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11],"tags":[],"_links":{"self":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts\/409"}],"collection":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/comments?post=409"}],"version-history":[{"count":3,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts\/409\/revisions"}],"predecessor-version":[{"id":541,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts\/409\/revisions\/541"}],"wp:attachment":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/media?parent=409"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/categories?post=409"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/tags?post=409"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}