Sonke sazi kahle kamhlophe ukuthi umhlaba wobuchwepheshe osizungezile uyidijithali, noma uyawulwela. Ukusakaza ngedijithali akukusha kakhulu, kodwa uma ungazange ube nentshisekelo kukho, ubuchwepheshe obukhona bungase bukumangaze.
Okuqukethwe ochungechungeni lwezihloko
- Ingxenye 4: Ingxenye Yesiginali Yedijithali
- Ingxenye 5: Inethiwekhi yokusabalalisa i-coaxial
- Ingxenye 6: Izikhulisi Zesiginali ye-RF
- Ingxenye 7: Abamukeli be-Optical
- Ingxenye 8: Inethiwekhi ye-Optical backbone
- Ingxenye 9: Isihloko
- Ingxenye 10: Ukuxazulula inkinga inethiwekhi ye-CATV
Ukwakhiwa kwesiginali yethelevishini yedijithali
Isignali kamabonakude wedijithali wukusakazwa kokuthutha kwezinguqulo ezihlukene ze-MPEG (ngezinye izikhathi amanye ama-codec), asakazwa isignali yomsakazo kusetshenziswa i-QAM yamazinga ahlukahlukene. Lawa magama kufanele acace njengosuku kunoma yimuphi umuntu obonisa izimpawu, ngakho ngizovele nginikeze i-gif evela , engithemba ukuthi izonikeza ukuqonda ukuthi iyini kulabo abangakabi nesithakazelo:
Ukuguquguquka okunjalo ngendlela eyodwa noma enye akusetshenziselwa kuphela "i-anachronism yethelevishini", kodwa futhi kuzo zonke izinhlelo zokudlulisa idatha phezulu kwezobuchwepheshe. Isivinini sokugeleza kwedijithali kukhebula “ye-antenna” ngamakhulu ama-megabits!
Imingcele yesignali yedijithali
Sisebenzisa i-Deviser DS2400T kumodi yokubonisa imingcele yesiginali yedijithali, singabona ukuthi lokhu kwenzeka kanjani ngempela:
Inethiwekhi yethu iqukethe amasignali amazinga amathathu ngesikhathi esisodwa: DVB-T, DVB-T2 kanye DVB-C. Ake sibabheke ngamunye ngamunye.
I-DVB-T
Leli zinga alizange libe yilo eliyinhloko ezweni lakithi, linikeza inguqulo yesibili, kodwa lilungele ukusetshenziswa opharetha ngesizathu sokuthi abamukeli be-DVB-T2 babuyela emuva bayahambisana nezinga lesizukulwane sokuqala, okusho ukuthi obhalisile. ingathola isignali enjalo cishe kunoma iyiphi i-TV yedijithali ngaphandle kwama-consoles engeziwe. Ngaphezu kwalokho, izinga elihloselwe ukudluliselwa emoyeni (uhlamvu T lumele i-Terrestrial, ether) lunokuvikeleka okuhle komsindo nokuphindaphinda futhi ngezinye izikhathi kusebenza lapho, ngasizathu simbe, isignali ye-analog ingakwazi ukungena.
Esikrinini sedivayisi singabuka ukuthi umlaza we-64QAM wakhiwa kanjani (okujwayelekile kusekela i-QPSK, 16QAM, 64QAM). Kuyabonakala ukuthi ezimeni zangempela amaphuzu awahlangani abe munye, kodwa eza nokuhlakazeka okuthile. Lokhu kuvamile inqobo nje uma i-decoder ingakwazi ukunquma ukuthi isiphi isikwele indawo okufika kuyo, kodwa ngisho nasesithombeni esingenhla kunezindawo lapho zitholakala khona emngceleni noma eduze kwaso. Kusukela kulesi sithombe ungakwazi ukunquma ngokushesha ikhwalithi yesiginali "ngeso": uma i-amplifier ingasebenzi kahle, isibonelo, amachashazi atholakala ngesiphithiphithi, futhi i-TV ayikwazi ukuhlanganisa isithombe esivela kudatha etholiwe: "i-pixelates" , noma ngisho iqhwa ngokuphelele. Kunezikhathi lapho iphrosesa ye-amplifier "ikhohlwa" ukwengeza enye yezingxenye (i-amplitude noma isigaba) kusiginali. Ezimweni ezinjalo, esikrinini sedivayisi ungabona umbuthano noma ukhalise usayizi wenkundla yonke. Amaphuzu amabili angaphandle kwenkundla eyinhloko angamaphuzu okubhekisela kumamukeli futhi awaluphathi ulwazi.
Ngakwesokunxele kwesikrini, ngaphansi kwenombolo yesiteshi, sibona imingcele yobuningi:
Izinga lesiginali (P) ku-dBµV efanayo neye-analogue, nokho, kusignali yedijithali i-GOST ilawula kuphela u-50 dBµV kokokufaka kumamukeli. Okusho ukuthi, ezindaweni ezinokunciphisa okukhulu, "idijithali" izosebenza kangcono kune-analogue.
Inani lamaphutha wokumodulisa (Mer) ikhombisa ukuthi isignali esiyitholayo ihlanekezelwe kangakanani, okungukuthi, indawo yokufika ingaba kude kangakanani nendawo emaphakathi yesikwele. Le pharamitha iyafana nesilinganiso sesignali-kuya-nomsindo kusuka kusistimu ye-analog; inani elijwayelekile le-64QAM lisuka ku-28 dB. Kungabonakala ngokucacile ukuthi ukuchezuka okubalulekile esithombeni esingenhla kuhambisana nekhwalithi engaphezu kwejwayelekile: lokhu ukungavikeleki komsindo wesiginali yedijithali.
Inombolo yamaphutha kusiginali eyamukelwe (I-CBER) - inani lamaphutha kusiginali ngaphambi kokucutshungulwa nganoma yimaphi ama-algorithms okulungisa.
Inombolo yamaphutha ngemuva kokusebenza kwe-Viterbi decoder (I-VBER) kuwumphumela wedikhoda esebenzisa imininingwane engasasebenzi ukuze ithole amaphutha kusiginali. Yomibili le mingcele ikalwa “ngezingcezu ngenani elithathiwe.” Ukuze idivayisi ibonise inani lamaphutha ngaphansi kweyodwa ezinkulungwaneni eziyikhulu noma ezigidini eziyishumi (njengasesithombeni esingenhla), idinga ukwamukela lezi zingcezu eziyizigidi eziyishumi, okuthatha isikhathi esiteshini esisodwa, ngakho umphumela wokulinganisa. ayiveli ngokushesha, futhi ingase ibe yimbi ekuqaleni (E -03, isibonelo), kodwa ngemva kwemizuzwana embalwa ufinyelela ipharamitha enhle kakhulu.
I-DVB-T2
Izinga lokusakaza ngedijithali elamukelwa e-Russia lingasakazwa ngekhebula. Ukuma komlaza kungase kusimangaze kancane lapho uqala nje:
Lokhu kuzungezisa futhi kukhulisa ukungavikeleki komsindo, njengoba umamukeli azi ukuthi umlaza kufanele uzungeziswe nge-engeli enikeziwe, okusho ukuthi ingahlunga okuza ngaphandle kokushintsha okwakhelwe ngaphakathi. Kungabonakala ukuthi kuleli zinga izinga lezilinganiso zephutha elincane liwuhlelo lobukhulu obuphezulu futhi amaphutha esignali ngaphambi kokucubungula awaseqi umkhawulo wokulinganisa, kodwa afinyelela ku-8,6 wangempela ngesigidi. Ukuzilungisa, kusetshenziswa idekhoda I-LDPC, ngakho ipharamitha ibizwa nge-LBER.
Ngenxa yokwanda kokuvikeleka komsindo, leli zinga lisekela izinga lokuguquguquka elingu-256QAM, kodwa okwamanje kusetshenziswa ama-64QAM kuphela ekusakazeni.
I-DVB-C
Leli zinga ekuqaleni lalidalelwe ukudluliselwa ngekhebula (C - Cable) - eliphakathi nendawo elizinze kakhulu kunomoya, ngakho-ke livumela ukusetshenziswa kwezinga eliphakeme lokuguquguquka kune-DVB-T, ngakho-ke lidlulisela inani elikhulu lolwazi ngaphandle kokusebenzisa inkimbinkimbi. ukubhala amakhodi.
Lapha sibona umlaza 256QAM. Kunezikwele eziningi, ubukhulu bazo bube buncane. Amathuba ephutha anyukile, okusho ukuthi i-medium enokwethenjelwa kakhudlwana (noma ikhodi eyinkimbinkimbi kakhulu, njengaku-DVB-T2) iyadingeka ukuze kudluliselwe isignali enjalo. Isignali enjalo "ingahlakaza" lapho i-analog ne-DVB-T/T2 isebenza khona, kodwa futhi inomkhawulo wokungavikeleki komsindo kanye nama-algorithms okulungisa amaphutha.
Ngenxa yamathuba aphezulu ephutha, ipharamitha ye-MER ye-256-QAM ijwayeleke ibe ngu-32 dB.
I-counter of bits eyiphutha ikhuphuke enye i-oda lobukhulu futhi manje ibala ingxenye eyodwa eyiphutha ngebhiliyoni ngayinye, kodwa noma ngabe kukhona amakhulu ezigidi zazo (PRE-BER ~E-07-8), i-decoder Reed-Solomon esetshenziswe kulokhu. okujwayelekile kuzosusa wonke amaphutha.
Source: www.habr.com