Tsambali likufotokoza Zoyamba Kuzimiririka ndi mitundu ya kuzimiririka mukulankhulana opanda zingwe. Mitundu Yozimiririka imagawidwa m'magulu akulu ndi kuzimiririka pang'ono (kuchuluka kwa kuchedwa kufalikira ndi kufalikira kwa doppler).
Kuzimiririka kwa lathyathyathya ndi kusankha kuzimiririka pafupipafupi ndi gawo limodzi la kuzirala kochulukira komwe kuzirala mwachangu ndi kufota pang'onopang'ono ndi gawo la kufalikira kwa ma doppler. Mitundu yozimiririka iyi imayendetsedwa molingana ndi magawo a Rayleigh, Rician, Nakagami ndi Weibull kapena mitundu.
Chiyambi:
Monga tikudziwira njira yolumikizirana opanda zingwe imakhala ndi ma transmitter ndi olandila. Njira yochokera ku transmitter kupita ku wolandila si yosalala ndipo chizindikiritso chopatsirana chimatha kudutsa mitundu yosiyanasiyana ya ma attenuation kuphatikiza kutayika kwa njira, kuchulukirachulukira etc. Ndi nthawi, ma frequency a wailesi ndi njira kapena malo a transmitter/receiver. Njira pakati pa ma transmitter ndi wolandila imatha kukhala yosiyana nthawi kapena kukhazikika kutengera ngati chopatsira / cholandila chakhazikika kapena kusuntha molemekezana.
Kodi kuzimiririka ndi chiyani?
Kusintha kwa nthawi kwa mphamvu yolandirira mphamvu chifukwa cha kusintha kwa sing'anga yopatsirana kapena njira kumadziwika kuti kuzimiririka. Kuzimiririka kumadalira pazifukwa zosiyanasiyana monga tafotokozera pamwambapa. Muzochitika zosasunthika, kuzimiririka kumadalira mikhalidwe ya mumlengalenga monga mvula, mphezi ndi zina. Muzochitika zoyendayenda, kuzimiririka kumadalira zopinga panjira zomwe zimasiyana malinga ndi nthawi. Zopinga izi zimapanga zotsatira zovuta zotumizira ku siginecha yopatsirana.
Chithunzi-1 chikuwonetsa matalikidwe ndi tchati cha mtunda wa mitundu yomwe ikuzirala pang'onopang'ono komanso kuzimiririka mwachangu zomwe tidzakambirana pambuyo pake.
Mitundu yozimiririka
Poganizira zovuta zosiyanasiyana zokhudzana ndi tchanelo ndi malo a transmitter/receiver zotsatirazi ndi mitundu yakuzirala mumayendedwe opanda zingwe.
➤Kuzimiririka Kwakukulu: Kumaphatikizapo kuwonongeka kwa njira ndi mthunzi.
➤Kuzimiririka Kwapang’ono: Imagawidwa m’magulu akulu awiri monga. multipath kuchedwa kufalikira ndi kufalikira kwa doppler. Kuchuluka kwa kuchedwa kufalikira kumagawikanso kukhala kuzirala kwa lathyathyathya ndi kuzimiririka kosankha pafupipafupi. Kufalikira kwa doppler kumagawika ndikuzimiririka mwachangu komanso pang'onopang'ono.
➤Zitsanzo zomwe zikuzimiririka: Mitundu yozimiririka pamwambayi imayikidwa m'mitundu kapena magawo osiyanasiyana monga Rayleigh, Rician, Nakagami, Weibull etc.
Monga tikudziwira, zizindikiro zowonongeka zimachitika chifukwa cha kuwonetsera kuchokera pansi ndi nyumba zozungulira komanso zizindikiro zobalalika zochokera kumitengo, anthu ndi nsanja zomwe zilipo m'dera lalikulu. Pali mitundu iwiri ya kuzimiririka ndiko kuti. kufooka kwakukulu komanso kuchepa kwa thupi.
1.) Kutha Kwambiri Kwambiri
Kutsika kwakukulu kumachitika pamene chopinga chimabwera pakati pa transmitter ndi receiver. Mtundu wosokonezawu umayambitsa kuchepetsedwa kwakukulu kwa mphamvu yazizindikiro. Izi ndichifukwa choti mafunde a EM amaphimbidwa kapena kutsekedwa ndi chopingacho. Zimakhudzana ndi kusinthasintha kwakukulu kwa chizindikiro pamtunda.
1.a) Kutaya njira
Kutayika kwa njira yaulere kumatha kuwonetsedwa motere.
➤ Pt/Pr = {(4 * π * d)2/ λ2} = (4*π*f*d)2/c2
Kumeneko,
Pt = Kutumiza mphamvu
Pr = Landirani mphamvu
λ = kutalika
d = mtunda pakati pa kutumiza ndi kulandira mlongoti
c = liwiro la kuwala ie 3 x 108
Kuchokera pa equation zikutanthawuza kuti chizindikiro chopatsirana chimacheperachepera patali pomwe chizindikirocho chikufalikira kudera lalikulu ndi lalikulu kuchokera kumalekezero otumizira kupita kumalo olandirira.
1.b) Zotsatira zazithunzi
• Zimawonedwa mukulankhulana opanda zingwe. Kujambula ndi kupatuka kwa mphamvu yolandilidwa ya siginecha ya EM kuchokera pamtengo wapakati.
• Ndi zotsatira za zopinga panjira pakati pa transmitter ndi wolandira.
• Zimatengera malo komanso mafunde a wailesi a EM (ElectroMagnetic).
2. Pang'ono Kuzimiririka
Kuzimiririka kwakung'ono kumakhudzana ndi kusinthasintha kofulumira kwa mphamvu zamasinthidwe omwe alandilidwa pakamtunda waufupi komanso kwakanthawi kochepa.
Kutengerakuchulukitsa kuchedwa kufalikirapali mitundu iwiri ya ang'onoang'ono kuzirala monga. lathyathyathya kuzimiririka ndi pafupipafupi kusankha kuzimiririka. Mitundu yambirimbiri yozimiririka iyi imadalira kufalikira kwa malo.
2.a) Kuzimiririka kwa lathyathyathya
Njira yopanda zingwe imanenedwa kuti imakhala yocheperapo ngati imakhala ndi kupindula kosalekeza komanso kuyankha kwa mzere wozungulira pa bandwidth yomwe ndi yayikulu kuposa bandwidth ya siginecha yotumizidwa.
Mu mtundu uwu wa kuzimiririka zigawo zonse zafupipafupi za chizindikiro cholandiridwa zimasinthasintha mofanana nthawi imodzi. Amadziwikanso kuti kuzirala kosasankha.
• Signal BW << Channel BW
• Chizindikiro nthawi >> Kuchedwa Kufalikira
Zotsatira za kufota kosalala zimawoneka ngati kuchepa kwa SNR. Njira zofolerazi zathyathyathyazi zimadziwika kuti matalikidwe osiyana siyana kapena ngalande zopapatiza.
2.b) Kuzimiririka kwa Frequency Selection
Zimakhudza magawo osiyanasiyana amtundu wa wailesi ndi ma amplitudes osiyanasiyana. Choncho dzina kusankha kuzimiririka.
• Signal BW > Channel BW
• Chizindikiro nthawi < Kuchedwa Kufalikira
Kutengerakufalikira kwa dopplerpali mitundu iwiri ya kuzimiririka ndiko kuti. kusowa kwachangu komanso kuchepa kwachangu. Mitundu yofalira ya ma doppler awa imadalira kuthamanga kwa m'manja mwachitsanzo, liwiro la wolandila potengera ma transmitter.
2.c) Kuzimiririka mwachangu
Chochitika cha kuzimiririka mwachangu chimayimiridwa ndi kusinthasintha kwachangu kwa siginecha m'malo ang'onoang'ono (ie bandwidth). Pamene zizindikiro zifika kuchokera kumbali zonse za ndege, kuzimiririka mofulumira kumawonekera kumbali zonse za kuyenda.
Kuzimiririka kofulumira kumachitika pamene kuyankha kwachannel kumasintha mwachangu kwambiri mkati mwa nthawi ya chizindikiro.
• Kufalikira kwakukulu kwa doppler
• Nthawi ya zizindikiro > Nthawi yolumikizana
• Kusintha kwa Signal < Kusintha kwa Channel
Izi zimabweretsa kufalikira kwafupipafupi kapena kutha kosankha nthawi chifukwa cha kufalikira kwa doppler. Kuzimiririka mwachangu kumachitika chifukwa cha mawonekedwe a zinthu zakumaloko komanso kuyenda kwa zinthu mogwirizana ndi zinthuzo.
Pakutha msanga, chizindikiro cholandirira ndi kuchuluka kwa ma siginecha ambiri omwe amawonekera kuchokera kumadera osiyanasiyana. Chizindikirochi ndi kuchuluka kapena kusiyana kwa ma sign angapo omwe amatha kukhala olimbikitsa kapena owononga kutengera kusintha kwa gawo pakati pawo. Ubale wa gawo umadalira liwiro la kuyenda, kuchuluka kwa kufalikira ndi kutalika kwa njira.
Kuzimiririka mwachangu kumasokoneza mawonekedwe a baseband pulse. Kupotoza uku ndikokhazikika komanso kumapangaISI(Kusokoneza Zizindikiro za Inter). Kufanana kosinthika kumachepetsa ISI pochotsa kupotoza kwa mzere komwe kumayambitsidwa ndi njira.
2.d) Kuchepa pang'onopang'ono
Kuchepa pang'onopang'ono kumachitika chifukwa cha mthunzi wa nyumba, mapiri, mapiri ndi zinthu zina zomwe zili m'njira.
• Low Doppler Kufalikira
• Chizindikiro cha nthawi <
• Kusintha kwa Signal >> Kusintha kwa Channel
Kukhazikitsa kwa zitsanzo Zozimiririka kapena magawo omwe amazimiririka
Kukhazikitsa kwa mitundu yozimiririka kapena magawo omwe akuzimiririka akuphatikizapo Rayleigh fading, Rician fading, Nakagami fading ndi Weibull fading. Kugawidwa kwa ma tchanelo kapena mafanizidwewa adapangidwa kuti aphatikize kuzimiririka mu siginecha ya data ya baseband malinga ndi zomwe zimafunikira mbiri.
Rayleigh akukula
• Muchitsanzo cha Rayleigh, zigawo za Non Line of Sight(NLOS) zokha ndizo zomwe zimafanizidwa pakati pa transmitter ndi receiver. Zimaganiziridwa kuti palibe njira ya LOS yomwe ilipo pakati pa transmitter ndi wolandila.
• MATLAB imapereka ntchito ya "rayleighchan" kutengera chitsanzo cha tchanelo cha rayleigh.
• Mphamvu zimagawidwa mochuluka.
• Gawoli limagawidwa mofanana komanso lodziimira patali. Ndiwo mitundu yogwiritsidwa ntchito kwambiri ya Kuzirala mukulankhulana opanda zingwe.
Rician akukula
• Muchitsanzo cha rician, zigawo zonse za Line of Sight (LOS) ndi zopanda Line of Sight(NLOS) zimayesedwera pakati pa transmitter ndi wolandira.
• MATLAB imapereka ntchito ya "ricianchan" kutengera mtundu wa tchanelo wa rician.
Nakagami kuzirala
Nakagami fadding channel ndi chitsanzo cha ziwerengero chomwe chimagwiritsidwa ntchito kufotokoza njira zoyankhulirana zopanda zingwe momwe sgnal yolandilidwa imadutsa munjira zambiri. Imayimira madera omwe akuzirala pang'ono mpaka koopsa monga madera akumidzi kapena akumidzi. Equation yotsatirayi itha kugwiritsidwa ntchito kutengera mtundu wa Nakagami fading channel.
• Pamenepa tikutanthauza h = r*ejΦ ndindi ngodya Φ imagawidwa mofanana pa [-π, π]
• Zosintha r ndi Φ zimaganiziridwa kuti zimagwirizana.
• Nakagami pdf yafotokozedwa monga pamwambapa.
• Mu Nakagami pdf, 2σ2= E{r2}, Γ(.) ndi ntchito ya Gamma ndipo k >= (1/2) ndi chiwerengero chomwe chikuzimiririka (madigiri a ufulu okhudzana ndi kuchuluka kwa zosintha zosasinthika za Gaussion).
• Idapangidwa poyambilira motengera miyeso.
• Mphamvu yolandila nthawi yomweyo imagawidwa ndi Gamma. • Ndi k = 1 Rayleigh = Nakagami
Weibull kuzimiririka
Njirayi ndi chitsanzo china cha ziwerengero chomwe chimagwiritsidwa ntchito pofotokoza njira yolumikizirana opanda zingwe. Weibull fading channel nthawi zambiri amagwiritsidwa ntchito kuimira malo omwe ali ndi mitundu yosiyanasiyana ya zinthu zomwe zimazimiririka, kuphatikizapo kufooka komanso kuzimiririka kwambiri.
Kumeneko,
2s2= E{r2}
• Kugawa kwa Weibull kumayimira kugawa kwina kwa Rayleigh.
• Pamene X ndi Y ali iid zero amatanthauza zosintha za gaussian, envelopu ya R = (X2+ Y2)1/2ndi Rayleigh kugawidwa. • Komabe envelopu imatanthauzidwa kuti R = (X2+ Y2)1/2, ndi pdf yofananira (mbiri yogawa mphamvu) imagawidwa ndi Weibull.
• Equation yotsatirayi ingagwiritsidwe ntchito kutsanzira Weibull fading model.
Patsambali tadutsa mitu yosiyanasiyana ya kuzimiririka monga njira yomwe ikuzirala, mitundu yake, mitundu yozimiririka, magwiritsidwe ake, magwiridwe antchito ndi zina zotero. Munthu atha kugwiritsa ntchito zomwe zaperekedwa patsamba lino kuti afananize ndi kupeza kusiyana pakati pa kuzimiririka kwakung'ono ndi kuzimiririka kwakukulu, kusiyana pakati pa kuzimiririka kwa lathyathyathya ndi kuzimiririka kosankha pafupipafupi, kusiyana pakati pa kuzimiririka mwachangu ndi kuzimiririka pang'onopang'ono, kusiyana pakati pa kuzimiririka kwa rayleigh ndi kutha kwa rician ndi zina zotero.
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Nthawi yotumiza: Aug-14-2023
