Leli khasi lichaza izisekelo zokushabalala kanye nezinhlobo zokushabalala ekuxhumaneni okungenantambo. Izinhlobo zokushabalala zihlukaniswe ukushabalala okukhulu kanye nokushabalala okuncane (ukusabalala kokulibaziseka kwe-multipath kanye nokusabalala kwe-doppler).
Ukufiphala okuthe tyaba kanye nokufiphala kokukhetha imvamisa kuyingxenye yokufiphala kwezindlela eziningi lapho ukufiphala okusheshayo kanye nokufiphala okuhamba kancane kuyingxenye yokufiphala kokusabalala kwe-doppler. Lezi zinhlobo zokufiphala zisetshenziswa njengokusatshalaliswa noma amamodeli kaRayleigh, Rician, Nakagami kanye neWeibull.
Isingeniso:
Njengoba sazi, uhlelo lokuxhumana olungenantambo luqukethe umthumeli kanye nomukeli. Indlela esuka kumthumeli iye kumukeli ayibushelelezi futhi isignali edlulisiwe ingadlula ezinhlotsheni ezahlukene zokunciphisa okuhlanganisa ukulahleka kwendlela, ukunciphisa izindlela eziningi njll. Ukunciphisa isignali endleleni kuncike ezintweni ezahlukahlukene. Yisikhathi, imvamisa yomsakazo kanye nendlela noma isikhundla somthumeli/umamukeli. Isiteshi phakathi komthumeli kanye nomukeli singahluka noma siqine isikhathi kuye ngokuthi umthumeli/umamukeli uzinzile noma uyahamba ngokuqondene nomunye nomunye.
Kuyini ukushabalala?
Ukwehluka kwesikhathi kwamandla esignali atholakele ngenxa yezinguquko endaweni yokudlulisela noma ezindleleni kwaziwa ngokuthi ukufiphala. Ukufiphala kuncike ezintweni ezahlukahlukene njengoba kushiwo ngenhla. Esimweni esinqunyiwe, ukufiphala kuncike ezimweni zomkhathi ezifana nemvula, umbani njll. Esimweni esihambayo, ukufiphala kuncike ezinkingeni endleleni ezihlukahluka ngokwesikhathi. Lezi zithiyo zidala imiphumela eyinkimbinkimbi yokudlulisela esignalini edlulisiwe.
Isibalo-1 sibonisa ishadi le-amplitude vs. ibanga lezinhlobo zokuphela kancane kanye nokuphela okusheshayo esizoxoxa ngakho kamuva.
Izinhlobo zokushabalala
Uma ubheka izinkinga ezahlukahlukene ezihlobene nesiteshi kanye nendawo yomthumeli/umamukeli, okulandelayo yizinhlobo zokuphela kohlelo lokuxhumana olungenantambo.
➤Ukufiphala Kwesilinganiso Esikhulu: Kuhlanganisa imiphumela yokulahleka kwendlela kanye nomthunzi.
➤Ukufiphala Kwesilinganiso Esincane: Kuhlukaniswe ngezigaba ezimbili eziyinhloko okungukusabalala kokulibaziseka kwezindlela eziningi kanye nokusabalala kwe-doppler. Ukusabalala kokulibaziseka kwezindlela eziningi kuhlukaniswe ngokwengeziwe ukufiphala okuyisicaba kanye nokufiphala okukhethayo kwemvamisa. Ukusabalala kwe-Doppler kuhlukaniswe ukufiphala okusheshayo kanye nokufiphala kancane.
➤Amamodeli anyamalalayo: Izinhlobo ezinyamalalayo ezingenhla zisetshenziswa kumamodeli noma ukusatshalaliswa okuhlukahlukene okuhlanganisa uRayleigh, uRician, uNakagami, uWeibull njll.
Njengoba sazi, izimpawu zokufiphala zenzeka ngenxa yokukhanya okuvela phansi nasezindaweni ezizungezile kanye nezibonakaliso ezihlakazekile ezivela ezihlahleni, kubantu nasezindongeni ezikhona endaweni enkulu. Kunezinhlobo ezimbili zokufiphala okungukuthi, ukufiphala okukhulu kanye nokufiphala okuncane.
1.) Ukufiphala Kwezinga Elikhulu
Ukufiphala okukhulu kwenzeka lapho isithiyo singena phakathi komthumeli kanye nomamukeli. Lolu hlobo lokuphazamiseka lubangela ukwehla okukhulu kwamandla esignali. Lokhu kungenxa yokuthi igagasi le-EM lifihlwe noma livinjwe yisithiyo. Kuhlobene nokushintshashintsha okukhulu kwesignali ngokuhamba kwebanga.
1.a) Ukulahleka kwendlela
Ukulahleka kwendlela yesikhala samahhala kungachazwa kanje.
➤ Iphuzu/I-Pr = {(4 * π * d)2/ λ2} = (4*π*f*d)2/c2
Kuphi,
I-Pt = Amandla okudlulisa
Pr = Thola amandla
λ = ubude besikhathi
d = ibanga phakathi kwe-antenna yokudlulisa nokwamukela
c = isivinini sokukhanya okungukuthi 3 x 108
Kusukela ku-equation kusho ukuthi isignali edlulisiwe iyancipha ngebanga njengoba isignali isakazeka endaweni enkulu nenkulu kusukela ekugcineni kokudlulisela kuya ekugcineni kokwamukela.
1.b) Umphumela wokufihla
• Kuyabonakala ekuxhumaneni okungenantambo. Ukufiphaza kuwukuphambuka kwamandla atholiwe esignali ye-EM kusuka enanini elimaphakathi.
• Kungumphumela wezithiyo endleleni ephakathi komthumeli kanye nomemukeli.
• Kuncike endaweni kanye nemvamisa yomsakazo yamagagasi e-EM (ElectroMagnetic).
2. Ukufiphala Kwezinga Elincane
Ukufiphala okuncane kuhlobene nokushintshashintsha okusheshayo kwamandla esignali atholakele ngebanga elifushane kakhulu kanye nesikhathi esifushane.
Ngokusekelwe kuukusabalala kokubambezeleka kwezindlela eziningiKunezinhlobo ezimbili zokufiphala okuncane okungukuthi, ukufiphala okuyisicaba kanye nokufiphala okukhethwayo njalo. Lezi zinhlobo zokufiphala kwezindlela eziningi zincike endaweni yokusabalala.
2.a) Ukufiphala okuyisicaba
Kuthiwa isiteshi esingenantambo siyaphela uma sinempendulo yesigaba sokuzuza kanye nesomugqa eqhubekayo phezu komkhawulokudonsa omkhulu kunomkhawulokudonsa wesiginali esidlulisiwe.
Kulolu hlobo lokufiphala zonke izingxenye zemvamisa yesiginali etholakele ziyashintshashintsha ngezilinganiso ezifanayo ngasikhathi sinye. Kwaziwa nangokuthi ukufiphala okungakhethi.
• Isignali ye-BW << Isiteshi se-BW
• Isikhathi sezimpawu >> Ukusabalala Kokulibaziseka
Umphumela wokuphela okuyisicaba ubonakala njengokwehla kwe-SNR. Lezi ziteshi zokuphela eziyisicaba zaziwa ngokuthi iziteshi eziguquguqukayo ze-amplitude noma iziteshi ze-narrowband.
2.b) Ukufiphala kokukhetha okujwayelekile
Kuthinta izingxenye ezahlukene ze-spectral zesignali yomsakazo ene-amplitudes ehlukene. Yingakho igama lishintsha umbala.
• Isignali BW > Isiteshi BW
• Isikhathi sesimboli < Ukusabalala Kokulibaziseka
Ngokusekelwe kuukusabalala kwe-dopplerKunezinhlobo ezimbili zokuphela okungukuthi, ukuphela okusheshayo kanye nokuphela kancane. Lezi zinhlobo zokuphela kokusabalalisa kwe-doppler zincike esivinini seselula okungukuthi isivinini somamukeli maqondana nomthumeli.
2.c) Ukufiphala okusheshayo
Isenzakalo sokufiphala okusheshayo simelelwa ukushintshashintsha okusheshayo kwesiginali ezindaweni ezincane (okungukuthi i-bandwidth). Lapho izimpawu zifika zivela kuzo zonke izinkomba endizeni, ukufiphala okusheshayo kuzobonwa kuzo zonke izinkomba zokunyakaza.
Ukuphela okusheshayo kwenzeka lapho impendulo ye-channel impulse ishintsha ngokushesha kakhulu phakathi nesikhathi sophawu.
• Ukusabalala kwe-doppler ephezulu
• Isikhathi sezimpawu > Isikhathi sokuhambisana
• Ukwehluka kwesignali < Ukwehluka kwesiteshi
Lokhu kuholela ekusabalaleni kwemvamisa noma ekufiphaleni okukhetha isikhathi ngenxa yokusabalala kwe-doppler. Ukufiphala okusheshayo kuwumphumela wokubonakaliswa kwezinto zasendaweni kanye nokunyakaza kwezinto maqondana nalezo zinto.
Ekufiphaleni okusheshayo, isignali yokwamukela yisamba sezimpawu eziningi ezibonakala ezindaweni ezahlukene. Lesi signali siyisamba noma umehluko wezibonakaliso eziningi ezingakha noma zibhubhise ngokusekelwe ekushintsheni kwesigaba okuhlobene phakathi kwazo. Ubudlelwano besigaba buxhomeke esivinini sokunyakaza, imvamisa yokudlulisela kanye nobude bendlela ehlobene.
Ukufiphala okusheshayo kuhlanekezela ukuma kwe-baseband pulse. Lokhu kuhlanekezela kuqondile futhi kudalaI-ISI(Ukuphazamiseka Kwezimpawu Eziphakathi). Ukulingana okuguquguqukayo kunciphisa i-ISI ngokususa ukuphambuka okuqondile okubangelwa yisiteshi.
2.d) Ukufiphala kancane
Ukufiphala kancane kubangelwa ukufihlwa yizakhiwo, amagquma, izintaba nezinye izinto phezu kwendlela.
• Ukusabalala kwe-Doppler ephansi
• Isikhathi sesimboli <
• Ukwehluka Kwesignali >> Ukwehluka Kwesiteshi
Ukusetshenziswa kwamamodeli okufiphala noma ukusatshalaliswa kokufiphala
Ukusetshenziswa kwamamodeli okuphela noma ukusatshalaliswa kokuphela kufaka phakathi ukuncipha kukaRayleigh, ukuncipha kukaRician, ukuncipha kukaNakagami kanye nokuncipha kukaWeibull. Lokhu kusatshalaliswa kwesiteshi noma amamodeli aklanyelwe ukufaka ukuncipha kusignali yedatha ye-baseband ngokwezidingo zephrofayili yokuphela.
URayleigh uyaphela
• Kumodeli kaRayleigh, izingxenye ezingezona zomugqa wokubona (i-NLOS) kuphela ezilingiswa phakathi komthumeli kanye nomamukeli. Kucatshangwa ukuthi ayikho indlela ye-LOS ekhona phakathi komthumeli kanye nomamukeli.
• I-MATLAB inikeza umsebenzi "we-rayleighchan" wokulingisa imodeli yesiteshi se-rayleigh.
• Amandla asatshalaliswa ngokushesha.
• Isigaba sisatshalaliswa ngokulinganayo futhi asincikile ku-amplitude. Siyizinhlobo ezisetshenziswa kakhulu ze-Fading ekuxhumaneni okungenantambo.
Ukufiphala kukaRician
• Kumodeli kaRician, zombili izingxenye ze-Line of Sight (LOS) kanye ne-non Line of Sight (NLOS) zilingiswa phakathi kwe-transmitter kanye ne-receiver.
• I-MATLAB inikeza umsebenzi "we-ricianchan" wokulingisa imodeli yesiteshi se-rician.
Ukufiphala kweNakagami
Isiteshi sokufiphala seNakagami siyimodeli yezibalo esetshenziselwa ukuchaza iziteshi zokuxhumana ezingenantambo lapho i-sgnal etholiwe idlula khona ekufiphaleni kwezindlela eziningi. Simelela izindawo ezinokuphela okumaphakathi kuya kokubi njengezindawo zasemadolobheni noma zasemadolobheni. Isibalo esilandelayo singasetshenziswa ukulingisa imodeli yesiteshi sokufiphala seNakagami.
• Kulesi simo sisho u-h = r*ejΦfuthi i-engeli Φ isatshalaliswa ngokulinganayo ku-[-π, π]
• I-variable r kanye ne-Φ kucatshangwa ukuthi zizimele zombili.
• I-pdf ye-Nakagami ivezwe njengoba ingenhla.
• Ku-pdf ye-Nakagami, 2σ2= E{r2}, Γ(.) umsebenzi we-Gamma kanye no-k >= (1/2) yisibalo esinyamalalayo (amadigri enkululeko ahlobene nenani lezinguquko ezingahleliwe ze-Gaussion ezengeziwe).
• Ekuqaleni yathuthukiswa ngokwesayensi ngokusekelwe ezilinganisweni.
• Amandla okwamukela ngokushesha asakazwa yiGamma. • Nge-k = 1 Rayleigh = Nakagami
Ukufiphala kwe-Weibull
Lesi siteshi singenye imodeli yezibalo esetshenziselwa ukuchaza isiteshi sokuxhumana esingenantambo. Isiteshi sokuphela se-Weibull sivame ukusetshenziswa ukumelela izindawo ezinezinhlobo ezahlukene zezimo zokuphela okuhlanganisa kokubili ukuncipha okubuthakathaka nokukhulu.
Kuphi,
2σ2= E{r2}
• Ukusatshalaliswa kwe-Weibull kumelela okunye ukusatshalaliswa kwe-Rayleigh.
• Uma u-X no-Y beyi-iid zero mean gaussian variables, i-envelope ka-R = (X)2+ Y2)1/2iRayleigh isatshalaliswa. • Kodwa-ke imvilophu ichazwe R = (X)2+ Y2)1/2, futhi i-pdf ehambisanayo (iphrofayili yokusatshalaliswa kwamandla) i-Weibull esakazwayo.
• Lesi sibalo esilandelayo singasetshenziswa ukulingisa imodeli yokufiphala kwe-Weibull.
Kuleli khasi sidlule ezihlokweni ezahlukahlukene mayelana nokufiphala njengokuthi yini isiteshi esifiphalayo, izinhlobo zaso, amamodeli afiphalayo, izinhlelo zokusebenza zazo, imisebenzi nokunye. Umuntu angasebenzisa ulwazi olunikezwe kuleli khasi ukuze aqhathanise futhi athole umehluko phakathi kokufiphala okuncane kanye nokufiphala okukhulu, umehluko phakathi kokufiphala okuyisicaba kanye nokufiphala okukhethwayo okuvama, umehluko phakathi kokufiphala okusheshayo kanye nokufiphala kancane, umehluko phakathi kokufiphala kwe-rayleigh kanye nokufiphala kwe-rician nokunye.
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Isikhathi sokuthunyelwe: Agasti-14-2023
