Eli phepha lichaza iziseko zokuFipha kunye neentlobo zokuFipha kunxibelelwano olungenazingcingo. Iintlobo zokuFipha zahlulwe zibe kuFipha okukhulu kunye nokuFipha okuncinci (ukusasazeka kokulibaziseka kwe-multipath kunye nokusasazeka kwe-doppler).
Ukufiphala okuthe tyaba kunye nokukhetha ukufiphala rhoqo kuyinxalenye yokufiphala kweendlela ezininzi apho ukufiphala okukhawulezayo kunye nokufiphala okucothayo kuyinxalenye yokufiphala kokusasazeka kwe-doppler. Ezi ntlobo zokufiphala zisetyenziswa ngokweemodeli okanye ukusasazwa kweRayleigh, Rician, Nakagami kunye neWeibull.
Intshayelelo:
Njengoko sisazi, inkqubo yonxibelelwano engenazingcingo ine-transmitter kunye ne-receiver. Indlela esuka kwi-transmitter ukuya kwi-receiver ayigudi kwaye i-transmission signal ingadlula kwiintlobo ezahlukeneyo ze-attenuations kuquka ukulahleka kwendlela, i-multipath attenuation njl. Ukuncitshiswa kwesignali endleleni kuxhomekeke kwizinto ezahlukeneyo. Zixesha, i-radio frequency kunye nendlela okanye indawo ye-transmitter/receiver. Itshaneli phakathi kwe-transmitter kunye ne-receiver inokwahluka okanye ihlale ixesha ngokuxhomekeke ekubeni i-transmitter/receiver izinzile okanye iyahamba ngokuhambelana.
Yintoni ephelayo?
Utshintsho lwexesha lamandla esignali afunyenweyo ngenxa yotshintsho kwindlela yokudlulisela okanye iindlela zaziwa ngokuba kukuphela. Ukunyamalala kuxhomekeke kwizinto ezahlukeneyo njengoko kukhankanyiwe apha ngasentla. Kwimeko emiselweyo, ukunyamalala kuxhomekeke kwiimeko zomoya ezifana nemvula, umbane njl. Kwimeko yokuhambahamba, ukunyamalala kuxhomekeke kwimiqobo edlula kwindlela eyahlukayo ngokwexesha. Le miqobo idala iziphumo ezintsonkothileyo zokudlulisela isignali edluliselweyo.
Umfanekiso-1 ubonisa itshathi ye-amplitude xa ithelekiswa nomgama weentlobo zokuphela kancinci kunye nokuphela ngokukhawuleza, nto leyo esiza kuyixoxa kamva.
Iintlobo zokunyamalala
Xa kujongwa iingxaki ezahlukeneyo ezinxulumene nesiteshi kunye nendawo yesixhobo sokudlulisa/sokwamkela, ezi zilandelayo ziintlobo zokuphela kwenkqubo yonxibelelwano olungenazingcingo.
➤Ukufiphala Kwesikali Esikhulu: Kubandakanya ukulahleka kwendlela kunye nemiphumo yokusibekela.
➤Ukuphela kweSmall Scale: Yahlulwe yangamacandelo amabini aphambili, ukusasazeka kokulibaziseka kweendlela ezininzi kunye nokusasazeka kwe-doppler. Ukusasazeka kokulibaziseka kweendlela ezininzi kwahlulwe ngakumbi kokufiphala okuthe tyaba kunye nokufiphala okukhethayo rhoqo. Ukusasazeka kwe-Doppler kwahlulwe kokufiphala okukhawulezayo kunye nokufiphala okucothayo.
➤Iimodeli eziphelayo: Iintlobo eziphelayo ezingentla zisetyenziswa kwiimodeli ezahlukeneyo okanye ukusasazwa okuquka uRayleigh, uRician, uNakagami, uWeibull njl.njl.
Njengoko sisazi, iimpawu eziphelayo zenzeka ngenxa yokukhanya okuvela emhlabeni nakwizakhiwo ezingqongileyo kunye neempawu ezisasazekileyo ezivela kwimithi, abantu kunye neenqaba ezikhoyo kwindawo enkulu. Kukho iintlobo ezimbini zokuphela, ezizezi: ukufiphala okukhulu kunye nokufiphala okuncinci.
1.) Ukunyamalala komlinganiselo omkhulu
Ukufiphala okukhulu kwenzeka xa kukho umqobo phakathi komthumeli kunye nomamkeli. Olu hlobo lokuphazamiseka lubangela ukuncipha okukhulu kwamandla esignali. Oku kungenxa yokuba i-EM wave igqunywe okanye ivalwe ngumqobo. Oku kunxulumene nokuguquguquka okukhulu kwesignali kumgama.
1.a) Ukulahleka kwendlela
Ukulahleka kwendlela ekhululekileyo kunokubonakaliswa ngolu hlobo lulandelayo.
➤ I-Pt/Pr = {(4 * π * d)2/ λ2} = (4*π*f*d)2/c2
Apho,
I-Pt = Amandla okudlulisa
Pr = Fumana amandla
λ = ubude bexesha
d = umgama phakathi kokudlulisela kunye nokufumana i-antenna
c = isantya sokukhanya oko kukuthi 3 x 108
Ukusuka kwi-equation kuthetha ukuba isignali edluliselweyo iyancipha kumgama njengoko isignali isasazeka kwindawo enkulu nangakumbi ukusuka kwisiphelo sokudlulisela ukuya kwisiphelo sokwamkela.
1.b) Isiphumo somthunzi
• Ibonwa kunxibelelwano olungenazingcingo. Umthunzi kukuphambuka kwamandla afunyenweyo esignali ye-EM ukusuka kwixabiso eliphakathi.
• Yimiphumo yemiqobo endleleni ephakathi komthumeli kunye nomamkeli.
• Kuxhomekeke kwindawo yejografi kunye nerediyo yamaza e-EM (ElectroMagnetic).
2. Ukunyamalala komlinganiselo omncinci
Ukufiphala okuncinci kunxulumene nokuguquguquka ngokukhawuleza kwamandla esignali efunyenweyo kumgama omfutshane kakhulu kunye nexesha elifutshane.
Ngenxa yeukusasazeka kokulibaziseka kweendlela ezininziKukho iintlobo ezimbini zokufiphala okuncinci, oko kukuthi, ukufiphala okuthe tyaba kunye nokufiphala okukhethwa rhoqo. Ezi ntlobo zokufiphala kweendlela ezininzi zixhomekeke kwindawo yokwanda.
2.a) Ukufiphala okuthe tyaba
Kuthiwa itshaneli engenazingcingo iyaphela ukuba inempendulo yesigaba sokufumana ulwazi rhoqo kunye ne-linear phase phezu kwe-bandwidth engaphezulu kune-bandwidth yesignali edlulisiweyo.
Kolu hlobo lokufiphala zonke iinxalenye zefrikhwensi zesignali efunyenweyo ziyatshintshatshintsha ngaxeshanye. Ikwaziwa nangokufiphala okungakhethiyo.
• I-BW yeSignali << Itshaneli ye-BW
• Ixesha leempawu >> Ukusasazeka kokulibaziseka
Isiphumo sokufiphala okuthe tyaba sibonwa njengokuncipha kwe-SNR. Ezi channels zifiphalayo ezithe tyaba zaziwa ngokuba zii-amplitude varying channels okanye ii-narrowband channels.
2.b) Ukuphindaphinda Ukuphela kokukhetha
Ichaphazela iindawo ezahlukeneyo ze-spectral zesignali yerediyo ene-amplitudes ezahlukeneyo. Yiyo loo nto igama litshintsha umbala.
• Isignali ye-BW > Itshaneli ye-BW
• Ixesha leempawu < Ukulibaziseka Ukusasazeka
Ngenxa yeukusasazeka kwe-dopplerKukho iintlobo ezimbini zokufiphala, ezithi, ukufiphala ngokukhawuleza kunye nokufiphala kancinci. Ezi ntlobo zokufiphala kwe-doppler spread zixhomekeke kwisantya seselula, oko kukuthi isantya sesamkeli ngokubhekiselele kwi-transmitter.
2.c) Ukunyamalala ngokukhawuleza
Ingxaki yokufiphala ngokukhawuleza ibonakaliswa kukutshintshatshintsha ngokukhawuleza kwesignali kwiindawo ezincinci (umz. i-bandwidth). Xa imiqondiso ifika kuzo zonke iindlela ezikwinqwelomoya, ukufiphala ngokukhawuleza kuya kubonwa kuzo zonke iindlela zokuhamba.
Ukuphela ngokukhawuleza kwenzeka xa impendulo ye-channel impulse itshintsha ngokukhawuleza kakhulu ngaphakathi kwexesha lophawu.
• Ukusasazeka kwe-doppler ephezulu
• Ixesha leempawu > Ixesha lokuvumelana
• Utshintsho lweSignali < Utshintsho lweSiteshi
Ezi parameters zikhokelela ekusasazekeni kwamaza okanye ekunyamalaleni okukhetha ixesha ngenxa yokusasazeka kwe-doppler. Ukunyamalala okukhawulezileyo kubangelwa kukubonakaliswa kwezinto zasekuhlaleni kunye nokuhamba kwezinto xa kuthelekiswa nezo zinto.
Kwi-fasting ekhawulezayo, i-receive signal yi-collection ye-signals ezininzi ezibonakala kwiindawo ezahlukeneyo. Le signal yi-collection okanye umahluko we-signals ezininzi ezinokuba zakha okanye zitshabalalise ngokusekelwe kutshintsho lwe-phase phakathi kwazo. Ubudlelwane be-phase buxhomekeke kwisantya se-motion, i-frequency yokudluliselwa kunye nobude bendlela ehambelanayo.
Ukuphela ngokukhawuleza kuphazamisa imo ye-baseband pulse. Oku kuphazamiseka kuqondile kwaye kudalaI-ISI(Ukuphazamiseka kweSimboli esiPhakathi). Ukulingana okuguquguqukayo kunciphisa i-ISI ngokususa ukuphambuka okuthe ngqo okubangelwa yitshaneli.
2.d) Ukunyamalala kancinci
Ukunyamalala kancinci kubangelwa kukusithwa zizakhiwo, iinduli, iintaba nezinye izinto phezu kwendlela.
• Ukusasazeka kweDoppler ephantsi
• Ixesha leesimboli <
• Utshintsho lweSignali >> Utshintsho lweSiteshi
Ukuphunyezwa kweemodeli zokuFipha okanye ukusasazwa kokuFipha
Ukuphunyezwa kweemodeli ezifiphalayo okanye ukusasazwa okufiphalayo kuquka uRayleigh fading, uRician fading, uNakagami fading kunye noWeibull fading. Olu sasazo lwetshaneli okanye iimodeli zenzelwe ukufaka ufiphala kwisignali yedatha yebaseband ngokweemfuno zeprofayili ezifiphalayo.
Ukunyamalala kukaRayleigh
• Kwimodeli kaRayleigh, kuphela izinto ezingezizo zoMgca wokubona (i-NLOS) ezilinganiswa phakathi komthumeli kunye nommkeli. Kucingelwa ukuba akukho ndlela ye-LOS ekhoyo phakathi komthumeli kunye nommkeli.
• I-MATLAB inika umsebenzi "we-rayleighchan" ukulinganisa imodeli yetshaneli ye-rayleigh.
• Amandla asasazwa ngokukhawuleza.
• Isigaba sisasazwe ngokulinganayo kwaye asixhomekekanga kwi-amplitude. Sihlobo olusetyenziswa kakhulu lwe-Fading kunxibelelwano olungenazingcingo.
Ukunyamalala kukaRician
• Kwimodeli kaRician, zombini izinto zeLine of Sight (LOS) kunye nezingezizo zeLine of Sight (NLOS) ziyalinganiswa phakathi kwetransmitter kunye nereceiver.
• I-MATLAB inika umsebenzi "we-ricianchan" ukulinganisa imodeli yetshaneli ye-rician.
Ukunyamalala kweNakagami
Itshaneli yokufiphala yeNakagami yimodeli yezibalo esetyenziselwa ukuchaza iziteshi zonxibelelwano ezingenazingcingo apho i-sgnal efunyenweyo idlula kwi-multipath fading. Imele iindawo ezinofiphala oluphakathi ukuya kolunzima njengeendawo zasezidolophini okanye zasezidolophini. Le equation ilandelayo ingasetyenziselwa ukulinganisa imodeli yetshaneli yokufiphala yeNakagami.
• Kule meko sibonisa u-h = r*ejΦkwaye i-engile Φ isasazwa ngokulinganayo kwi-[-π, π]
• I-variable r kunye ne-Φ zithathwa njengezizimeleyo.
• I-pdf yeNakagami ichazwe ngolu hlobo lungasentla.
• Kwi-pdf yeNakagami, 2σ2= E{r2}, Γ(.) ngumsebenzi weGamma kwaye u-k >= (1/2) ngumfanekiso onyamalalayo (iidigri zenkululeko ezinxulumene nenani lee-variables ze-Gaussion ezingacwangciswanga ezongeziweyo).
• Ekuqaleni yaphuhliswa ngokweempendulo ngokusekelwe kwiimilinganiselo.
• Amandla okufumana ngoko nangoko asasazwa yiGamma. • Nge-k = 1 Rayleigh = Nakagami
Ukunyamalala kweWeibull
Le tshaneli yenye imodeli yezibalo esetyenziselwa ukuchaza itshaneli yonxibelelwano engenazingcingo. Itshaneli yokuphela kweWeibull idla ngokusetyenziswa ukumela iindawo ezineentlobo ezahlukeneyo zeemeko zokuphela kuquka ubuthathaka kunye nokuphela okuqatha.
Apho,
2σ2= E{r2}
• Ukusasazwa kweWeibull kubonisa olunye uhlobo lokusasazwa kweRayleigh.
• Xa u-X no-Y bengabantu abaguquguqukayo be-gaussian abaphakathi be-iid zero, i-envelope ka-R = (X)2+ Y2)1/2iRayleigh isasazwe. • Nangona kunjalo, imvulophu ichazwe njenge-R = (X)2+ Y2)1/2, kwaye i-pdf ehambelanayo (iprofayili yosasazo lwamandla) yi-Weibull esasazwe.
• Le equation ilandelayo ingasetyenziselwa ukulinganisa imodeli yokufiphala kweWeibull.
Kule phepha sidlule kwizihloko ezahlukeneyo malunga nokufiphala ezifana nokuba yintoni itshaneli efiphalayo, iintlobo zayo, iimodeli ezifiphalayo, usetyenziso lwazo, imisebenzi yazo njalo njalo. Umntu angasebenzisa ulwazi olunikwe kweli phepha ukuze athelekise aze afumane umahluko phakathi kokufiphala okuncinci kunye nokufiphala okukhulu, umahluko phakathi kokufiphala okuthe tyaba kunye nokufiphala okukhethwayo rhoqo, umahluko phakathi kokufiphala okukhawulezayo kunye nokufiphala okucothayo, umahluko phakathi kokufiphala kwe-rayleigh kunye nokufiphala kwe-rician njalo njalo.
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Ixesha lokuthumela: Agasti-14-2023
