Izisekelo Zokuxhumana Ngesathelayithi
Ukuxhumana ngesathelayithi kuyinsika ebalulekile yengqalasizinda yezokuxhumana yesimanje. Lobu buchwepheshe buvumela ukudluliswa kwezwi, idatha, kanye nevidiyo ebangeni elikhulu—ngisho namazwekazi—ngaphandle kokuthembela ngokuphelele ezintanjeni zomhlaba noma kumanethiwekhi omhlaba. Ngenxa yamasathelayithi, konke kusukela ekusakazweni kwethelevishini kanye nezinsizakalo ze-inthanethi ezindaweni ezikude, ukuxhumana kwasolwandle kanye nezindiza, ngisho nokuxhumanisa izinhlekelele kungaba okuthembekile kakhudlwana. Ukuze siqonde ukuthi zisebenza kanjani, sidinga ukuqonda imiqondo eyisisekelo yezindlela zokujikeleza kwesathelayithi, izingxenye zesistimu, izimiso zokudlulisa umsakazo, kanye nezinselele zobuchwepheshe ezihilelekile.
1. Kuyini ukuxhumana ngesathelayithi?
Ukuxhumana ngesathelayithi kuyinqubo yokushintshana ngolwazi kusetshenziswa amasathelayithi njenge-relay emkhathini. Ngokuvamile, isiteshi sasemhlabeni sithumela isignali yomsakazo esathelayithi (i-uplink). Isathelayithi bese siyamukela, sikhulise, noma sisicubungule, bese sidlulisela isignali kwesinye isiteshi sasemhlabeni noma umamukeli endaweni ethile yokumboza (i-downlink). Le ndlela inqoba izithiyo zendawo njengezintaba, izilwandle, kanye nengqalasizinda yomhlaba elinganiselwe ngoba indlela yokuxhumana idlula emkhathini.
Kalula nje, amasathelayithi asebenza njengemibhoshongo yokudlulisa ephezulu kakhulu. Ngenxa yokuthi abekwe phezulu ngaphezu kobuso boMhlaba, amasathelayithi angamboza indawo ebanzi, okwenza abe yindawo ekahle yokusakaza nokuxhumana ezindaweni ezinokufinyelela okulinganiselwe kwenethiwekhi.
2. Izingxenye eziyinhloko zesistimu yokuxhumana ngesathelayithi
Uhlelo lokuxhumana ngesathelayithi ngokuvamile luqukethe izingxenye ezintathu eziyinhloko:
1. Ingxenye yesikhala
Lokhu kufaka phakathi i-satellite uqobo kanye nomthwalo wayo, njenge-transponders, ama-antenna, kanye nezinhlelo zamandla. Ama-transponders ayizingxenye ezibalulekile ezithola izimpawu ngemvamisa ethile, ziwakhulise, bese ziwathumela kabusha ngemvamisa ethile.
2. Ingxenye yomhlabathi
Le ngxenye ihlanganisa iziteshi zomhlaba zokulawula isathelayithi, iziteshi zamasango, ama-VSAT (ama-Very Small Aperture Terminals), kanye nemishini yokwamukela njengezitsha zesathelayithi zasekhaya ze-TV yesathelayithi. Iziteshi zomhlaba ngokuvamile zinezinti ezinkulu, izinhlelo zokudlulisela/zokwamukela, kanye nemishini yokuguqula isandiso ukuze kucutshungulwe isignali.
3. Ingxenye yomsebenzisi
Le ngxenye ihlanganisa amadivayisi abasebenzisi bokugcina, njengemodemu yesathelayithi, amafoni esathelayithi, amadivayisi okuxhumana ngebhodi lemikhumbi, noma amatheminali e-inthanethi esathelayithi. Kweminye imisebenzi, ingxenye yomsebenzisi ingaxhumana ngqo nesathelayithi ngaphandle komlamuleli wesiteshi esikhulu sesango.
3. Imizila yesathelayithi kanye nomthelela wayo ezinsizeni
Imizila yesathelayithi inquma ububanzi bokumbozwa, ukubambezeleka, kanye nobunzima besistimu. Izinhlobo ezintathu zemizila evame ukusetshenziswa yilezi:
a. I-GEO (Umjikelezo Womhlaba We-Geostationary)
Amasathelayithi e-GEO atholakala cishe ngamakhilomitha angu-35.786 ngaphezu kwe-equator futhi abonakala "engashintshi" uma kuqhathaniswa noMhlaba. Lokhu kuvumela ama-antenna amukelayo ukuthi aqine (akhombe ngokugxilile) ngaphandle kwesidingo sokulandelela ukunyakaza kwesathelayithi. Amasathelayithi e-GEO athandwa kakhulu kumabonakude wesathelayithi kanye nokuxhumana kwendawo ebanzi.
Kodwa-ke, amabanga amade abangela ukubambezeleka okuphezulu. Amasignali kumele ahambe izinkulungwane zamakhilomitha phezulu naphansi kunethiwekhi, okuholela ekubambezelekeni okubonakalayo kohambo oluya nokubuya ezinsizakalweni ezisebenzisanayo njengezingcingo zevidiyo noma imidlalo eku-inthanethi.
b. I-MEO (Umjikelezo Womhlaba Ophakathi)
Amasathelayithi e-MEO atholakala ebangeni eliphakathi kwamakhilomitha angu-2.000–20.000. Amasathelayithi e-MEO avame ukusetshenziselwa izinhlelo zokuzulazula zomhlaba wonke njenge-GPS, i-Galileo, noma i-GLONASS. Ezokuxhumana, i-MEO inikeza ukubambezeleka okuphansi kune-GEO, kodwa amasathelayithi ahamba uma kuqhathaniswa noMhlaba, okudinga ukulandelela nokuphathwa kokudluliselwa.
c. I-LEO (Umjikelezo Womhlaba Ophansi)
Amasathelayithi e-LEO atholakala ezindaweni eziphakeme ezingaba ngu-160–2.000 km. Amasathelayithi e-LEO anikeza ukubambezeleka okuphansi kanye nezibonakaliso eziqinile ngenxa yokusondela kwawo eduze. Inkinga ukuthi indawo yokumbozwa kwesathelayithi eyodwa incane, edinga inqwaba enkulu (amashumi kuya ezinkulungwaneni zamasathelayithi) ukuze inikeze isevisi yomhlaba wonke. Izinhlelo ze-inthanethi zesathelayithi zanamuhla zisebenzisa i-LEO kakhulu ngoba ifanelekela ukufinyelela idatha ngesivinini esikhulu.
4. Isixhumanisi Esiphezulu, isixhumanisi Esiphansi, kanye ne-transponder
Ekuxhumaneni ngesathelayithi, izimpawu zivame ukuhamba ngezindlela ezimbili eziyinhloko:
– I-Uplink: ukuthumela izimpawu ezivela esiteshini sasemhlabeni ziye kwisathelayithi.
– I-Downlink: ukuthumela izimpawu ezivela ku-satellite ziye esiteshini/kumsebenzisi osemhlabeni.
Amaza okuxhumanisa phezulu kanye nawaphansi ahlukaniswe ukuze kuvinjelwe ukuphazamiseka. Amasathelayithi asebenzisa ama-transponder ukuthola isignali ye-uplink, bese ehumusha imvamisa, ayikhulise, bese eyithumela kabusha njengesignali ye-downlink.
Kunezindlela ezimbili eziyinhloko zokucubungula kuma-satellite:
– Ipayipi eligobile (elibonakalayo): isathelayithi iphinda isignali kuphela ngaphandle kokucubungula okuqukethwe kwedatha.
– Okuvuselelayo: isathelayithi yenza ukucubungula okwengeziwe, njengokususa i-demodulation kanye nokulungisa kabusha, ngaleyo ndlela ithuthukisa ikhwalithi kanye nokusebenza kahle, yize iyinkimbinkimbi kakhulu.
5. Amabhendi emvamisa asetshenziswa kakhulu
Ukuxhumana ngesathelayithi kusebenzisa amabhendi ahlukahlukene emvamisa, ngalinye linezici ezihlukile:
– Ibhendi ye-L (1–2 GHz): imelana nemvula; isetshenziselwa ukuxhumana kweselula njengezingcingo zesathelayithi kanye nokuzulazula.
– Ibhendi ye-C (4–8 GHz): imelana kakhulu nemvula kune-Ku/Ka; isetshenziswa kabanzi njengomgogodla kanye nokusakaza ezindaweni ezishisayo.
– I-Ku-band (12–18 GHz): ivame kakhulu kuma-TV e-satellite kanye ne-VSAT; ama-antenna amancane kodwa asengozini enkulu yokuphazamiseka yimvula.
– I-Ka-band (26–40 GHz): isekela i-bandwidth enkulu ye-inthanethi yesathelayithi; kodwa ithinteka kakhulu ukufiphala kwemvula.
Ukukhethwa kwebhendi yemvamisa kuncike ezidingweni zomthamo, usayizi we-antenna, imithethonqubo ye-spectrum, kanye nezimo zezulu.
6. Ukushintshashintsha, ukufinyelela okuningi, kanye nokusebenza kahle kwe-spectrum
Ukuze kudluliselwe idatha ngamagagasi omsakazo, isignali yolwazi iyaguqulwa. Ezinhlelweni zesimanje, ukuguqulwa kwedijithali njenge-QPSK, 8PSK, noma i-QAM kusetshenziselwa ukuthuthukisa ukusebenza kahle kwe-spectrum. Izindinganiso ezifana ne-DVB-S2/S2X zezinsizakalo zokusakaza kanye nedatha nazo zisebenzisa ikhodi yokulungisa amaphutha (i-FEC) ukuqinisekisa ukwamukelwa kwesignali naphezu komsindo noma ukuphazamiseka.
Ngaphezu kwalokho, ngenxa yokuthi abasebenzisi abaningi babelana ngesathelayithi efanayo, kudingeka izindlela eziningi zokufinyelela, okuhlanganisa:
– I-FDMA: ukuhlukaniswa kwemvamisa.
– I-TDMA: ukuhlukaniswa okusekelwe esikhathini.
– I-CDMA: ukuhlukaniswa kwekhodi.
– I-OFDMA (kwezinye izinhlelo zesimanje): ukuhlukaniswa okusekelwe ezithwalini ezincane.
Umgomo uwukwenza ngcono ukusetshenziswa kwamandla esathelayithi nokuvimbela ukuphazamiseka phakathi kwabasebenzisi.
7. Izinselele eziyinhloko: ukubambezeleka, imvula, kanye nokuphazamiseka
Ukuxhumana ngesathelayithi kubhekene nezinselele ezithile ezihlukile:
– Ukubambezeleka: ikakhulukazi ku-GEO, kudala ukubambezeleka okuthinta izinhlelo zokusebenza zesikhathi sangempela.
– Ukufiphala kwemvula: Ukuncishiswa kwesignali ngenxa yemvula, ikakhulukazi kuma-Ku-bands nase-Ka, kubalulekile ezindaweni ezishisayo. Izixazululo zifaka phakathi ukuguqulwa kwezwi kanye nokuguqulwa kwekhodi, amandla okudlulisa akhuphukile, kanye nomklamo wesabelomali sezixhumanisi ezilondolozayo.
– Ukuphazamiseka: kungavela kwezinye iziphuphutheki, imishini yomsakazo yasemhlabeni, noma ukungalungi kahle kwe-antenna. Ukuhlanganiswa kwe-spectrum kanye nokulungiswa kwe-antenna polarity kusiza ekunciphiseni ukuphazamiseka.
8. Izinhlelo zokuxhumana ngesathelayithi
Lobu buchwepheshe busetshenziswa emikhakheni eyahlukene:
– Ukusakazwa kwe-TV nomsakazo: ukusatshalaliswa kokuqukethwe kuzwelonke kuya kwamanye amazwe.
– I-inthanethi yesathelayithi: izixazululo zokuxhuma ezindaweni ezikude, imikhumbi, izindiza kanye nezindawo zenhlekelele.
– Ukuxhumana kwezasolwandle kanye nezindiza: ukuxhumana kokuphepha, ukusebenza kanye nokuqapha.
– Ezempi kanye nokuphepha: ukuxhumana okubethelwe nokungaphazanyiswa.
– Ukuphathwa kwezinhlekelele: lapho amanethiwekhi omhlaba onakele, amasathelayithi avame ukuba umgogodla wokuxhumanisa.
9. Isiphetho
Izisekelo zokuxhumana ngesathelayithi zigxile emcabangweni wokudluliselwa kwesignali kusuka esiteshini sasemhlabeni kuya esathelayithi bese kubuyela eMhlabeni. Ukukhetha i-orbit (GEO, MEO, LEO), ibhendi yemvamisa, kanye nokuguqulwa kwesimo kanye namasu amaningi okufinyelela kunquma kakhulu ukusebenza kwesevisi. Naphezu kwezinzuzo zokumbozwa okubanzi kanye nokuguquguquka, ukuxhumana ngesathelayithi nakho kubhekene nezinselele ezifana nokubambezeleka, ukuncishiswa kwesimo sezulu, kanye nokuphazamiseka. Kodwa-ke, ngokuthuthukiswa kwamaqoqo ezinkanyezi e-LEO, ubuchwepheshe be-antenna yesimanje, kanye nezindinganiso zokudlulisa ezisebenza kahle ngokwengeziwe, ukuxhumana ngesathelayithi kuyaqhubeka nokuba yisisombululo esibalulekile sokuxhumanisa umhlaba—ikakhulukazi ezindaweni lapho amanethiwekhi omhlaba kunzima ukufinyelela khona.
Uma ufisa, ngingangeza umfanekiso wokugeleza kwe-uplink-downlink, isibonelo esilula sokubala isabelomali sesixhumanisi, noma ngixoxe ngomehluko phakathi kwe-VSAT, i-HTS (i-High Throughput Satellite), kanye ne-LEO constellations ngamagama obuchwepheshe.
