(1) Ikhodi ye-AMI
Ikhodi ye-AMI(Alternative Mark Inversion) yigama eligcwele lekhodi yokuguqula uphawu, umthetho wayo wombhalo wekhodi uwukuguqula ngokushintshana ikhodi yomlayezo “1″ (umaka) iye ku-“+1″ kanye “-1″, kuyilapho ithi “0″ ( uphawu olungenalutho) luhlala lungashintshiwe. Ngokwesibonelo:
Inombolo yomlayezo: 0 1 1 0 0 0 0 0 0 0 0 0 1 1 0 0 1 1
Ikhodi ye-AMI: 0-1 +1 0 0 0 0 0 0 0 0 0 0 0 1 +1 0 0 0 0 1 +1
I-waveform ehambisana nekhodi ye-AMI isitimela esishayelayo esinamaleveli amahle, angalungile kanye neziro. Ingabonwa njengokuwohloka kwe-unipolar waveform, okungukuthi, “0” isahambisana namaleveli aziro, futhi “1” ihambisana ngokushintshana namaleveli amahle namabi.
Inzuzo yekhodi ye-AMI ukuthi ayikho ingxenye ye-DC, futhi izingxenye zemvamisa ephezulu neziphansi zincane, futhi amandla agxilwe ku-1/2 yejubane leyadi.
(Umfanekiso 6-4); Isifunda se-codec silula, futhi iphutha lekhodi lingabonwa ngokusebenzisa umthetho wokushintshana kwe-polarity yesiginali. Uma kuyi-waveform ye-AMI-RZ, ngemva kokuyithola, inqobo nje uma ukulungiswa okugcwele kwegagasi, ingashintshwa ibe i-unipolar RZ waveform, okungakhishwa kuyo ingxenye yesikhathi esincane. Ngokubuka izinzuzo ezingenhla, ikhodi ye-AMI isiphenduke enye yamakhodi okudlulisela asetshenziswa kakhulu.
Ububi bekhodi ye-AMI: Uma ikhodi yoqobo ineyunithi yezinhlamvu “0″ ende, ileveli yesiginali ayigxumi isikhathi eside, okuholela ebunzimeni ekukhipheni isignali yesikhathi. Enye yezindlela ezisebenzayo zokuxazulula inkinga yekhodi ethi “0″ ukusebenzisa ikhodi ye-HDB3.
(2) Ikhodi ye-HDB3
Igama eligcwele lekhodi ye-HDB3 yikhodi yesithathu ye-high-density bipolar. Kuyinguqulo ethuthukisiwe yekhodi ye-AMI, inhloso yokuthuthukisa ukugcina izinzuzo zekhodi ye-AMI futhi unqobe ukushiyeka kwayo, ukuze inani elithi "0" lingeqi kokuthathu. Imithetho yayo yombhalo wekhodi imi kanje:
Hlola inombolo yoziro exhunywe kukhodi yomlayezo. Uma inombolo ethi “0” ingaphansi noma ilingana no-3, umthetho wokubhala ikhodi uyafana naleyo yekhodi ye-AMI. Uma inani loziro abalandelanayo lidlula kokuthathu, iqanda ngalinye kwamane alandelanayo liguqulwa libe isigatshana bese lithathelwa indawo ngu-000V. V(ukuthatha inani elingu-+1 noma -1) kufanele kube ne-polarity efanayo neyangaphambili eseduze okungeyona-” 0 “ishayela (ngoba lokhu kwephula umthetho wokushintshwa kwe-polarity, u-V ubizwa ngokuthi ishayela lokubhubhisa). Izimpawu ezisondelene zekhodi ye-V kufanele zishintshane. Uma inani lekhodi engu-V lingakwazi ukuhlangabezana nezimfuneko kokuthi (2) kodwa lingakwazi ukuhlangabezana nale mfuneko, elithi “0000″ lithathelwa indawo ngokuthi “B00V”. Inani lika-B lifana ne-V pulse elandelayo ukuxazulula le nkinga. Ngakho-ke, u-B ubizwa ngokuthi ishayela elilawulayo. I-polarity yokudluliswa kwenombolo ngemva kwekhodi engu-V nayo kufanele ishintshane.
Ngokungeziwe ezinhlelweni zekhodi ye-AMI, ikhodi ye-HDB3 iphinda ikhawulele inombolo yekhodi ethi “0″ ibe ngu-3, ukuze ulwazi lwesikhathi lukhishwe lapho lwamukelwa. Ngakho-ke, ikhodi ye-HDB3 iwuhlobo lwekhodi olusetshenziswa kakhulu e-China naseYurophu nakwamanye amazwe, futhi uhlobo lwekhodi yesixhumi esibonakalayo yomthetho A PCM ngezansi kwamaqembu amane kukhona ikhodi ye-HDB3.
Ekhodini ye-AMI engenhla kanye nekhodi ye-HDB3, ikhodi ngayinye yesignali kanambambili iguqulwa ibe ikhodi yeleveli emithathu yebhithi elilodwa (+1, 0,-1), ngakho lolu hlobo lwekhodi lubizwa nangokuthi ikhodi engu-1B1T. Ngaphezu kwalokho, ikhodi ye-HDBn ingaklanywa ngendlela yokuthi inombolo ethi “0″ ingeqi ku-n.
(3) ikhodi ye-biphase
Ikhodi ye-Biphasic yaziwa nangokuthi ikhodi yaseManchester. Isebenzisa amagagasi ayisikwele aqondile noma angalungile enkathi eyodwa ukuze amele u-“0” kanye nefomu layo eliguqukayo elimelela u-“1″. Omunye wemithetho yokufaka amakhodi ukuthi "0" ikhodi imelwe "01" ikhodi enamadijithi amabili, futhi "1" ikhodi imelwe "10" ikhodi enamadijithi amabili, isibonelo:
Inombolo yomlayezo: 1 1 0 0 0 1 0 1
Ikhodi ye-Biphase: 10 10 01 01 10 01 10
I-bipolar code waveform i-bipolar NRZ waveform enamazinga amabili kuphela e-polarity ephambene. Inokweqa izinga endaweni emaphakathi yesikhawu sophawu ngalunye, ngakho iqukethe ulwazi olucebile lwesikhathi, futhi ayikho ingxenye ye-DC, futhi inqubo yokubhala ikhodi ilula. Okubi ukuthi umkhawulokudonsa othathiwe uphindwe kabili, ukuze ukusetshenziswa kwebhendi yefrikhwensi kuncishiswe. Ikhodi ye-Biphase ilungele ukudluliswa kwebanga elifushane lemishini yedatha, futhi ivamise ukusetshenziswa njengohlobo lwekhodi yokudlulisela kunethiwekhi yendawo.
(4) Ikhodi ye-biphase ehlukile
Ukuze kuxazululwe amaphutha okukhipha amakhodi abangwe ukuhlehla kwe-polarity kumakhodi e-biphasic, umqondo wamakhodi wokuhlukanisa ungamukelwa. Amakhodi e-Biphasic ayavumelaniswa futhi amelelwa ukweqa kwezinga phakathi nesikhathi sophawu ngalunye (ukweqa ukusuka kokunegethivu kuye kokuphozithivu kumelela okubili “0” futhi ukweqa usuka kokuphozithivu ukuya kokunegethivu kumelela kanambambili “1″). Ekuhlukaniseni amakhodi e-biphase, ukweqa ileveli phakathi kwe-elementi ngayinye kusetshenziselwa ukuvumelanisa, nokuthi noma kukhona ukweqa okwengeziwe ekuqaleni kwento ngayinye kusetshenziswa ukunquma ikhodi yesiginali. Uma kukhona ukweqa, kukhombisa kanambambili “1″, futhi uma kungekho ukweqa, kukhombisa kanambambili “0”. Le khodi ivame ukusetshenziswa kumanethiwekhi endawo.
(5)Ikhodi ye-CMI
Ikhodi ye-CMI imfushane ngekhodi yokuhlehlisa uphawu, futhi ifana nekhodi ye-bipolar, futhi iyikhodi eyisicaba ye-bipolar bipolar. Imithetho yayo yokufaka amakhodi ithi: “1″ ikhodi imelwa ngokushintshana “ngamakhodi angu-11” kanye “no-00” namadijithi amabili; Ikhodi engu-0 imelwe ngu-01, futhi i-waveform yayo iboniswa kuMfanekiso 6-5(c).
Ikhodi ye-CMI kulula ukuyisebenzisa futhi iqukethe ulwazi olucebile lwesikhathi. Ngaphezu kwalokho, njengoba i-10 iyiqembu lekhodi ekhubazekile, amakhodi angaphezu kwamathathu ngeke avele, futhi lo mthetho ungasetshenziselwa ukutholwa kwamaphutha amakhulu. Le khodi inconywe yi-ITU-T njengohlobo lwekhodi ye-PCM ye-quad-group code, futhi ngezinye izikhathi isetshenziswa ezinhlelweni zokudlulisa ikhebula le-optical ngamanani angaphansi kuka-8.448Mb/s.
(6)Vimba ukubhala ikhodi
Ukuze kuthuthukiswe ukusebenza kombhalo wekhodi, uhlobo oluthile lokuphinda ludingeke ukuze kuqinisekiswe ukuvumelanisa nekhono lokuthola iphutha lamaphethini ekhodi. Ukwethulwa kwekhodi yebhulokhi kungafeza izinhloso zombili ngokwezinga elithile. Ifomu lekhodi yebhulokhi linekhodi ye-nBmB, ikhodi ye-nBmT nokunye.
Ikhodi ye-nBmB iwuhlobo lwekhodi yebhulokhi, ehlukanisa ikhodi kanambambili ye-n-bit yokusakaza kolwazi lwangempela ibe yiqembu, futhi ifake esikhundleni sayo iqembu lekhodi elisha lekhodi kanambambili ye-M-bit, lapho m>n. Ngoba m>n, isethi yekhodi entsha ingase ibe nezinhlanganisela ezingu-2^m, ngakho-ke kunezinhlanganisela ezengeziwe (2^m-2^n). Ku-2 "inhlanganisela, iqembu lekhodi elivunayo likhethwa njengeqembu lekhodi elivunyelwe ngandlela thize, kanti okunye kusetshenziswa njengeqembu lamakhodi akhubazekile ukuze kutholwe ukusebenza okuhle kokufakwa kwamakhodi. Isibonelo, ekubhalweni kwekhodi kwe-4B5B, esikhundleni sombhalo wekhodi we-4-bit ngombhalo wekhodi ongu-5-bit, kukhona izinhlanganisela ezihlukene ezingu-2^4=16 kuphela zeqoqo le-4-bit, kanye no-2^5=32 izinhlanganisela ezihlukene ze-5- ukuqoqa kancane. Ukuze sifinyelele ukuvumelanisa, singakhetha amaqembu ekhodi ngendlela engekho ngaphezu kweyodwa ehamba phambili ethi “0″ nezijobelelo ezimbili ezithi “0”, kanti ezinye zingamaqembu ekhodi akhutshaziwe. Ngale ndlela, uma kukhona ikhodi ekhubazekile ebekwe ekugcineni kokwamukela, kubonisa ukuthi kukhona iphutha lekhodi kunqubo yokudlulisela, ngaleyo ndlela ithuthukise ikhono lokubona iphutha lesistimu. Amakhodi e-biphase kanye namakhodi e-CMI achazwe ngaphambili angathathwa njengamakhodi angu-1B2B.
Ohlelweni lokuxhumana lwefiber optical, m=n+1 kuvame ukukhethwa, bese kuthathwa ikhodi ethi 1B2B, 2B3B code, 3B4B code kanye ne5B6B code. Phakathi kwazo, ikhodi ye-5B6B isetshenziswe ekusebenzeni njengekhodi yokudlulisa umugqa yamaqembu angama-cubic kanye namaqembu angaphezu kuka-quadruple.
Ikhodi ye-nBmB inikeza ukuvumelanisa okuhle nokutholwa kwamaphutha, kodwa iza ngezindleko, okungukuthi, ukukhuphuka komkhawulokudonsa odingekayo.
Umqondo wokuklama wekhodi ye-nBmT uwukuguqula amakhodi kanambambili angu-n abe amakhodi ama-m ternary, kanye ne-m
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