Leli khasi lichaza okuyisisekelo Okufiphalayo nezinhlobo zokufiphala ekuxhumaneni okungenantambo. Izinhlobo zokufiphala zihlukaniswe zaba ukufiphala kwesikali esikhulu kanye nokufiphala kwesikali esincane (ukusabalala kokulibaziseka kwezindlela eziningi kanye nokusabalala kwe-doppler).
Ukufiphala okuyisicaba nokukhetha ukufiphala kwemvamisa kuyingxenye yokufiphala kwezindlela eziningi lapho ukufiphala okusheshayo nokufiphala kancane kuyingxenye yokufiphala kwe-doppler. Lezi zinhlobo ezifiphalayo zisetshenziswa njengokusatshalaliswa noma amamodeli e-Rayleigh, Rician, Nakagami kanye ne-Weibull.
Isingeniso:
Njengoba sazi ukuthi uhlelo lokuxhumana olungenantambo luqukethe isidlulisi nomamukeli. Umzila osuka kumthumeli uye kumamukeli awusheleli futhi isignali edlulisiwe ingase idlule ezinhlotsheni ezihlukahlukene zokuncipha okuhlanganisa ukulahleka kwendlela, ukuncipha kwezindlela eziningi njll. Ukuncishiswa kwesignali endleleni kuncike ezintweni ezihlukahlukene. Isikhathi, ifrikhwensi yomsakazo nendlela noma indawo yesithumeli/umamukeli. Isiteshi esiphakathi komthumeli nomamukeli singashintsha isikhathi noma simiswe kuye ngokuthi isidlulisi/umamukeli silungisiwe noma siyahamba ngokuhloniphana.
Kuyini ukufiphala?
Ukuhluka kwesikhathi samandla esignali atholiwe ngenxa yezinguquko ku-transmission medium noma imizila kwaziwa njengokufiphala. Ukufiphala kuncike ezintweni ezehlukene njengoba kushiwo ngenhla. Esimeni esingaguquki, ukufiphala kuncike ezimweni zomoya ezifana nemvula, ukukhanyisa njll. Esimeni seselula, ukufiphala kuncike kuzithiyo endleleni ezihlukayo ngokuphathelene nesikhathi. Lezi zithiyo zidala imiphumela eyinkimbinkimbi yokudlulisela esignali edlulisiwe.
Umfanekiso-1 ubonisa i-amplitude neshadi lebanga lezinhlobo ezishabalala kancane neziphela ngokushesha esizoxoxa ngazo kamuva.
Izinhlobo ezifiphalayo
Uma kucatshangelwa ukonakala okuhlukahlukene okuhlobene nesiteshi kanye nendawo yesithumeli/umamukeli okulandelayo izinhlobo zokufiphala ohlelweni lokuxhumana okungenantambo.
➤Ukufiphala Kwesilinganiso Esikhulu: Kuhlanganisa ukulahleka kwendlela kanye nemiphumela yomthunzi.
➤Ukufiphala Kwesikali Esincane: Kuhlukaniswe izigaba ezimbili eziyinhloko okungukuthi. ukusabalala kokulibaziseka kwe-multipath kanye nokusabalala kwe-doppler. Ukusabalala kokulibaziseka kwe-multipath kuphinde kuhlukaniswe ngokufiphala okuyisicaba kanye nokufiphala okukhetha imvamisa. Ukusabalala kwe-Doppler kuhlukaniswe ngokufiphala okusheshayo nokufiphala kancane.
➤Amamodeli afiphalayo: Izinhlobo ezifiphalayo ezingenhla zisetshenziswa kumamodeli ahlukahlukene noma ukusatshalaliswa okuhlanganisa uRayleigh, uRician, uNakagami, Weibull njll.
Njengoba sazi, izimpawu ezifiphalayo zenzeka ngenxa yokubonakala komhlabathi nezakhiwo ezizungezile kanye nezimpawu ezihlakazekile ezivela ezihlahleni, abantu nemibhoshongo ekhona endaweni enkulu. Kunezinhlobo ezimbili zokufiphala okuyizi. ukwehla okukhulu kanye nokwehla kwezinga elincane.
1.) Ukufiphala Kwesikali Esikhulu
Ukufiphala kwesikali esikhulu kwenzeka lapho isithiyo singena phakathi komthumeli nomamukeli. Lolu hlobo lokuphazamiseka ludala inani elibalulekile lokuncipha kwamandla esignali. Lokhu kungenxa yokuthi igagasi le-EM linethunzi noma livinjwe isithiyo. Ihlobene nokuguquguquka okukhulu kwesignali ebangeni.
1.a) Ukulahleka kwendlela
Ukulahlekelwa kwendlela yesikhala yamahhala kungavezwa kanje.
➤ Pt/Pr = {(4 * π * d)2/ λ2} = (4*π*f*d)2/c2
Lapho,
Pt = Dlulisa amandla
Pr = Thola amandla
λ = ubude begagasi
d = ibanga phakathi kokudlulisa nokwamukela uthi
c = isivinini sokukhanya okungukuthi 3 x 108
Kusukela kuzibalo kusho ukuthi isignali edlulisiwe incipha ngebanga njengoba isignali isatshalaliswa endaweni enkulu nenkulu ukusuka ekugcineni kokudlulisela kuye ekugcineni kokwamukela.
1.b) Umphumela wokwenza ithunzi
• Ibonakala ekuxhumaneni okungenantambo. Ukwenza ithunzi ukuchezuka kwamandla atholiwe esignali ye-EM ukusuka kunani eliyisilinganiso.
• Kuwumphumela wezithiyo endleleni phakathi komthumeli nomamukeli.
• Kuncike endaweni kanye nefrikhwensi yomsakazo wamagagasi e-EM (ElectroMagnetic).
2. Ukufiphala Kwezinga Elincane
Ukufiphala kwezinga elincane kuphathelene nokuguquguquka okusheshayo kwamandla esignali atholiwe ngebanga elifushane kakhulu nesikhathi esifushane.
Ngokusekelwe kuukusabalala kokulibaziseka kwe-multipathkunezinhlobo ezimbili zezikali ezincane ezifiphalayo okungukuthi. ukufiphala okuyisicaba kanye nokufiphala okukhethayo imvamisa. Lezi zinhlobo zokufiphala kwezindlela eziningi zincike endaweni yokusabalalisa.
2.a) Ukufiphala okuyisicaba
Isiteshi esingenantambo kuthiwa siba sicaba uma sinenzuzo eqhubekayo kanye nempendulo yesigaba esiqondile phezu komkhawulokudonsa omkhulu kunomkhawulokudonsa wesiginali edlulisiwe.
Kulolu hlobo lokufiphala zonke izingxenye zemvamisa yesiginali eyamukelwe zishintshashintsha ngezilinganiso ezifanayo ngesikhathi esisodwa. Kwaziwa nangokuthi ukufiphala okungakhethi.
• Isiginali BW << Isiteshi BW
• Inkathi yezimpawu >> Ukubambezeleka Ukusabalala
Umthelela wokufiphala okuyisicaba ubonakala njengokuncipha kwe-SNR. Lezi ziteshi ezifiphalayo eziyisicaba zaziwa ngokuthi amashaneli ahlukahlukene ama-amplitude noma amashaneli amabhande amancane.
2.b) Ukufiphala kokukhetha imvamisa
Kuthinta izingxenye ezahlukene ze-spectral zesignali yomsakazo enama-amplitude ahlukene. Ngakho-ke igama liyafiphala ngokukhethayo.
• Isiginali BW > Isiteshi BW
• Isikhathi sophawu < Ukubambezeleka Ukusabalala
Ngokusekelwe kuukusabalala kwe-dopplerkunezinhlobo ezimbili zokufiphala okuyizi. ukunyamalala okusheshayo nokufiphala kancane. Lezi zinhlobo ezifiphalayo ze-doppler zincike esivinini seselula okungukuthi isivinini somamukeli maqondana nesidlulisi.
2.c) Ukufiphala ngokushesha
Isimo sokufiphala ngokushesha simelelwa ukushintshashintsha kwesignali ngokushesha ezindaweni ezincane (okungukuthi umkhawulokudonsa). Lapho amasignali efika evela kuzo zonke izikhombisi-ndlela endizeni, ukufiphala okusheshayo kuzobonwa kuzo zonke izinkomba zokunyakaza.
Ukufiphala okusheshayo kwenzeka lapho impendulo yomfutho wesiteshi ishintsha ngokushesha kakhulu phakathi nesikhathi sophawu.
• Ukusabalala kwe-doppler ephezulu
• Isikhathi sophawu > Isikhathi sokuhambisana
• Ukuhluka Kwesiginali < Ukuhluka kwesiteshi
Lezi zinhlaka ziholela ekuhlakazweni kwemvamisa noma ekufiphaleni okukhetha isikhathi ngenxa yokusabalala kwe-doppler. Ukufiphala okusheshayo kuwumphumela wokuboniswa kwezinto zasendaweni nokunyakaza kwezinto ezihlobene nalezo zinto.
Ekufipheleni okusheshayo, isignali yokwamukela iyisamba samasignali amaningi avela ezindaweni ezihlukahlukene. Lesi siginali yisamba noma umehluko wamasignali amaningi angabakhayo noma acekele phansi ngokusekelwe ekushintsheni kwesigaba esihlobene phakathi kwawo. Ubudlelwano besigaba buncike esivinini sokunyakaza, imvamisa yokudlulisela kanye nobude bendlela obuhlobene.
Ukufiphala okusheshayo kuhlanekezela umumo we-baseband pulse. Lokhu kuhlanekezela kuqondile futhi kuyadalaISI(I-Inter Symbol Interference). Ukulinganisa okuguquguqukayo kunciphisa i-ISI ngokususa ukuhlanekezela komugqa okubangelwa isiteshi.
2.d) Ukufiphala kancane
Ukufiphala kancane kuwumphumela wokuthunjwa kwezakhiwo, amagquma, izintaba nezinye izinto endleleni.
• Ukusabalala kwe-Doppler ephansi
• Isikhathi sophawu <
• Ukushintshashintsha Kwesiginali >> Ukuhluka Kwesiteshi
Ukusetshenziswa kwamamodeli Afiphalayo noma ukusabalalisa okufiphalayo
Ukusetshenziswa kwamamodeli aphelayo noma ukusabalalisa okufiphalayo kufaka phakathi ukufiphala kwe-Rayleigh, ukufiphala kwe-Rician, ukufiphala kwe-Nakagami kanye nokufiphala kwe-Weibull. Lokhu kusatshalaliswa kweziteshi noma amamodeli aklanyelwe ukuhlanganisa ukufiphala kusiginali yedatha ye-baseband ngokwezidingo zephrofayela ephelayo.
I-Rayleigh iyancipha
• Kumodeli ye-Rayleigh, izingxenye ze-Non Line of Sight(NLOS) kuphela ezilingiswa phakathi komthumeli nomamukeli. Kucatshangwa ukuthi ayikho indlela ye-LOS ekhona phakathi komthumeli nomamukeli.
• I-MATLAB inikeza umsebenzi we-"rayleighchan" ukulingisa imodeli yesiteshi se-rayleigh.
• Amandla asatshalaliswa ngokuqhubekayo.
• Isigaba sisatshalaliswa ngokufanayo futhi sizimele ku-amplitude. Yizinhlobo ezisetshenziswa kakhulu zokufiphala ekuxhumaneni okungenantambo.
U-Rician uyafiphala
• Kumodeli ye-rician, kokubili izingxenye ze-Line of Sight (LOS) kanye ne-non Line of Sight(NLOS) zilingiswa phakathi komthumeli nomamukeli.
• I-MATLAB inikeza umsebenzi we-"ricianchan" ukuze ulingise imodeli yesiteshi.
I-Nakagami iyancipha
Isiteshi se-Nakagami fadding siyimodeli yezibalo esetshenziselwa ukuchaza iziteshi zokuxhumana ezingenazintambo lapho i-sgnal eyamukelwe iba nokufiphala kwe-multipath. Imele izindawo ezinokufiphala okumaphakathi kuya kokunzima njengezindawo zasemadolobheni noma ezisemadolobheni. Isibalo esilandelayo singasetshenziswa ukulingisa imodeli yesiteshi ephelayo ye-Nakagami.
• Kulokhu sichaza u-h = r*ejΦkanye ne-engeli Φ isatshalaliswa ngokulinganayo kokuthi [-π, π]
• Okuguquguqukayo r kanye no-Φ kucatshangwa ukuthi azimele.
• I-pdf ye-Nakagami ichazwe ngenhla.
• Ku-pdf ye-Nakagami, 2σ2= E{r2}, Γ(.) umsebenzi we-Gamma futhi u-k >= (1/2) uyisibalo esifiphalayo (amadigri enkululeko ahlobene nenani lokuhlukahluka okungahleliwe kwe-Gaussion eyengeziwe).
• Ekuqaleni yathuthukiswa ngokomlando ngokusekelwe ezilinganisweni.
• Amandla okwamukela ngokushesha asakazwa nge-Gamma. • Nge-k = 1 Rayleigh = Nakagami
I-Weibull iyafiphala
Lesi siteshi singesinye imodeli yezibalo esetshenziswa ukuchaza ishaneli yokuxhumana engenantambo. Isiteshi esifiphalayo se-Weibull sivame ukusetshenziselwa ukumela izindawo ezinezinhlobo ezahlukene zezimo ezifiphalayo ezihlanganisa kokubili ukufiphala okubuthakathaka nokuqinile.
Lapho,
2 σ2= E{r2}
• Ukusatshalaliswa kwe-Weibull kumelela okunye ukwenziwa okuvamile kokusatshalaliswa kwe-Rayleigh.
• Uma u-X kanye no-Y bethi iid zero kusho okuguquguqukayo kwe-gaussian, imvilophu ka-R = (X2+Y2)1/2i-Rayleigh isatshalaliswa. • Nokho imvilophu ichazwa ngokuthi R = (X2+Y2)1/2, kanye ne-pdf ehambisanayo (iphrofayili yokusabalalisa amandla) i-Weibull isatshalaliswa.
• Isibalo esilandelayo singasetshenziswa ukulingisa imodeli efiphalayo ye-Weibull.
Kuleli khasi sidlule ezihlokweni ezehlukene ezimayelana nokufiphala njengokuthi yini ephelayo ishaneli, izinhlobo zayo, amamodeli aphelayo, ukusetshenziswa kwawo, imisebenzi nokunye. Umuntu angasebenzisa ulwazi olunikezwe kuleli khasi ukuze aqhathanise futhi athole umehluko phakathi kokufiphala kwesilinganiso esincane nokufiphala okukhulu, umehluko phakathi kokufiphala okuyisicaba kanye nokufiphala okukhethayo, umehluko phakathi kokufiphala okusheshayo nokufiphala kancane, umehluko phakathi kokufiphala kwe-rayleigh nokufiphala kwe-rician kanye njalonjalo.
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Isikhathi sokuthumela: Aug-14-2023
