Leqephe lena le hlalosa lintho tsa motheo tse Feleng le mefuta ea ho fela ha puisano e se nang mohala.Mefuta ea Fading e arotsoe ka sekhahla se seholo se felang le se senyane se nyamelang (ho ata ha tieho e ngata le ho ata ha doppler).
Ho fela ha sephara le ho khetha khafetsa ho fifala ke karolo ea ho fifala ha li-multipath moo ho fela kapele le ho fela butle e leng karolo ea ho fela ha li-doppler.Mefuta ena e nyamelang e kengoa ts'ebetsong ho latela kabo kapa mehlala ea Rayleigh, Rician, Nakagami le Weibull.
Selelekela:
Joalo ka ha re tseba, sistimi ea puisano ea waelese e na le transmitter le receiver.Tsela e tsoang ho transmitter ho ea ho moamoheli ha e boreleli mme lets'oao le fetisoang le ka feta ka mefuta e fapaneng ea likhahla ho kenyelletsa tahlehelo ea tsela, ho fokotseha ha multipath joalo-joalo.Ke nako, maqhubu a seea-le-moea le tsela kapa boemo ba sefetisi/moamoheli.Seteishene pakeng tsa transmitter le receiver e ka ba nako e fapaneng kapa e tsitsitseng ho latela hore na transmitter/receiver e tsitsitse kapa e tsamaea ka tlhompho.
Ho nyamela ke eng?
Phapang ea nako ea matla a lets'oao a amohetsoeng ka lebaka la liphetoho tse lipakeng tsa phetiso kapa litselana li tsejoa e le ho fifala.Ho fela ho itšetlehile ka lintlha tse fapaneng tse boletsoeng ka holimo.Boemong bo tsitsitseng, ho fifala ho ipapisitse le maemo a sepakapaka joalo ka pula, ho khanya joalo-joalo. Boemong bo tsamaeang, ho putlama ho ipapisitse le litšitiso tse holim'a tsela tse fapaneng mabapi le nako.Litšitiso tsena li baka liphello tse rarahaneng tsa phetisetso ho letšoao le fetisitsoeng.
Setšoantšo sa 1 se bonts'a amplitude khahlano le chate ea sebaka bakeng sa mefuta e ntseng e fela butle le e felang ka potlako eo re tla e tšohla hamorao.
Mefuta e fokolang
Ha ho nahanoa ka mefokolo e fapaneng e amanang le likanale le boemo ba transmitter/receiver tse latelang ke mefuta ea ho putlama ka har'a sistimi ea puisano e se nang mohala.
➤Sekala se Seholo se Fetelang: E kenyelletsa tahlehelo ea tsela le litlamorao tsa moriti.
➤ Nyenyane e Feletseng: E arotsoe ka mekhahlelo e 'meli e meholo e leng.multipath ho lieha ho ata le ho ata ha doppler.Ho ata ha tieho ea litsela tse ngata ho arotsoe ka ho fifala ha sephara le ho fifala ho khethang khafetsa.Ho ata ha Doppler ho arotsoe ka ho fela kapele le ho fela butle.
➤Mefuta e ntseng e fela: Mefuta e kaholimo e fela e kengoa tšebetsong mefuteng e fapaneng kapa kabong e kenyelletsang Rayleigh, Rician, Nakagami, Weibull jj.
Joalo ka ha re tseba, matšoao a nyamelang a hlaha ka lebaka la menahano e tsoang mobung le meahong e potolohileng hammoho le matšoao a hasaneng a tsoang lifateng, bathong le litora tse teng sebakeng se seholo.Ho na le mefuta e 'meli ea ho fifala, e leng.ho putlama ha tekanyo e kgolo le ho fela ha tekanyo e nyane.
1.) Sekhahla se seholo se Fading
Ho nyamela ho hoholo ho etsahala ha tšitiso e kena lipakeng tsa transmitter le receiver.Mofuta ona oa tšitiso o baka palo e kholo ea phokotso ea matla a lets'oao.Sena ke hobane EM wave e koetsoe kapa e koetsoe ke tšitiso.E amana le ho feto-fetoha ho hoholo ha lets'oao le hole.
1.a) Ho lahleheloa ke tsela
Tahlehelo ea sebaka sa mahala e ka hlalosoa ka tsela e latelang.
➤ Pt/Pr = {(4 * π * d)2/ λ2} = (4*π*f*d)2/c2
Kae,
Pt = Fetisa matla
Pr = Fumana matla
λ = bolelele ba maqhubu
d = sebaka se pakeng tsa ho fetisa le ho amohela lenakana
c = lebelo la khanya ke hore 3 x 108
Ho tsoa ho equation ho bolela hore lets'oao le fetisoang le kokobela hole hole ha lets'oao le ntse le hasana sebakeng se seholo le se seholo ho tloha pheletsong ea phetiso ho ea pheletsong e amohelang.
1.b) Phello ea moriti
• E bonoa puisanong ea waelese.Moriti ke ho kheloha ha matla a amohetsoeng a lets'oao la EM ho tsoa ho boleng bo tloaelehileng.
• Ke phello ea litšitiso holim'a tsela pakeng tsa transmitter le receiver.
• E ipapisitse le boemo ba sebaka hammoho le maqhubu a seea-le-moea a EM (ElectroMagnetic).
2. Nyenyane Fading
Ho nyamela ho honyane ho amahanngoa le ho fetoha ho potlakileng ha matla a mats'oao a amohetsoeng nakong e khuts'oane haholo le nako e khuts'oane.
Ho ipapisitsoe leho ata ha tieho e ngataho na le mefuta e 'meli ea likhahla tse nyane tse fokolang, e leng.fading e bataletseng le ho fela ka makhetlo a mangata.Mefuta ena ea multipath fading e itšetlehile ka tikoloho ea ho ata.
2.a) Ho nyamela ka sephara
Ho boleloa hore mocha o se nang mohala o ntse o putlama haeba o na le phaello e sa khaotseng le karabelo ea mokhahlelo o lekanang holim'a bandwidth e kholo ho feta bandwidth ea lets'oao le fetisoang.
Mofuteng ona oa ho nyamela likarolo tsohle tsa maqhubu a lets'oao le amoheloang li fetoha ka tekanyo e ts'oanang ka nako e le 'ngoe.E boetse e tsejoa e le fading e sa khethoeng.
• Letšoao la BW << Channel BW
• Letšoao nako >> Ho lieha ho ata
Phello ea ho fifala ha sephara e bonoa e le ho fokotseha hoa SNR.Likanale tsena tse sephara tse fading li tsejoa e le likanale tse fapaneng tsa amplitude kapa likanale tse tšesaane.
2.b) Ho felloa ke nako ho khethang khafetsa
E ama likarolo tse fapaneng tsa spectral tsa lets'oao la seea-le-moea le li-amplitudes tse fapaneng.Kahoo lebitso le khethang le fela.
• Letshwao la BW > Channel BW
• Nako ea matšoao < Ho lieha ho ata
Ho ipapisitsoe leho ata ha dopplerho na le mefuta e 'meli ea ho nyahama e leng.ho fela kapele le ho fela butle.Mefuta ena ea li-doppler e ntseng e fela e ipapisitse le lebelo la mohala, ke hore, lebelo la moamoheli mabapi le transmitter.
2.c) Ho fela kapele
Ketsahalo ea ho fela ka potlako e emeloa ke ho fetoha ha lets'oao ka potlako libakeng tse nyane (ke hore, bandwidth).Ha mats'oao a fihla a tsoa mahlakoreng 'ohle a sefofane, ho fela kapele ho tla bonoa libakeng tsohle tsa motsamao.
Ho fela ka potlako ho etsahala ha karabelo ea tšusumetso ea mocha e fetoha ka potlako haholo nakong ea letšoao.
• Ho ata ha li-doppler tse phahameng
• Nako ya matshwao > Nako ya momahano
• Phapang ea Lipontšo < Phapang ea mocha
Mekhahlelo ena e fella ka ho hasana khafetsa kapa ho fifala ho khethang nako ka lebaka la ho ata ha li-doppler.Ho fela ka potlako ho bakoa ke ponahalo ea lintho tsa lehae le motsamao oa lintho tse amanang le lintho tseo.
Ka ho fela ka potlako, lets'oao la ho amohela ke kakaretso ea mats'oao a mangata a hlahang libakeng tse fapaneng.Letšoao lena ke kakaretso kapa phapang ea matšoao a mangata a ka hahang kapa a senya ho ipapisitse le phetoho ea mekhahlelo lipakeng tsa ona.Likamano tsa mekhahlelo li itšetlehile ka lebelo la ho sisinyeha, makhetlo a phetisetso le bolelele ba tsela e lekanyelitsoeng.
Ho fela ka potlako ho khopamisa sebopeho sa baseband pulse.Phapang ena e lekane ebile e ea bopaISI(Ho kena-kenana le Letšoao la Inter).Ho lekanngoa ha Adaptive ho fokotsa ISI ka ho tlosa ho sotha ha linear ho bakoang ke mocha.
2.d) Ho fela butle
Ho fifala butle ho bakoa ke meriti ea meaho, maralla, lithaba le lintho tse ling tseleng.
• Ho ata ha Doppler e tlase
• Nako ea matšoao <
• Phapang ea Lipontšo >> Phapang ea Channel
Ho kenya ts'ebetsong ea mefuta e Felletseng kapa kabo e felloang ke nako
Ts'ebetsong ea mefuta e ntseng e fela kapa kabo e ntseng e fela e kenyelletsa ho putlama ha Rayleigh, ho fela ha Rician, ho fela ha Nakagami le Weibull fading.Kabo ea liteishene kapa mefuta ena e etselitsoe ho kenyelletsa ho fifala ha lets'oao la data la baseband ho latela litlhoko tsa profil e ntseng e fela.
Rayleigh e felile
• Ka mohlala oa Rayleigh, ke likaroloana feela tsa Non Line of Sight(NLOS) tse etsisoang pakeng tsa transmitter le receiver.Ho nahanoa hore ha ho na tsela ea LOS e teng pakeng tsa transmitter le receiver.
• MATLAB e fana ka ts'ebetso ea "rayleighchan" ho etsisa mohlala oa mocha oa rayleigh.
• Matla a ajoa ka mokhoa o pharalletseng.
• Mokhahlelo o ajoa ka mokhoa o ts'oanang 'me o ikemetse ho tloha ho amplitude.Ke mefuta e sebelisoang haholo ea Fading puisanong ea waelese.
Rician e nyamela
• Ka mohlala oa rician, likarolo tse peli tsa Line of Sight (LOS) le tseo e seng tsa Line of Sight(NLOS) li etsisoa pakeng tsa transmitter le receiver.
• MATLAB e fana ka ts'ebetso ea "ricianchan" ho etsisa mohlala oa mocha oa rician.
Nakagami e nyamela
Nakagami fadding channel ke mohlala oa lipalo-palo o sebelisetsoang ho hlalosa liteishene tsa puisano tse se nang mohala tseo ho tsona sgnal e amoheloang e senyehang ka litsela tse ngata.E emetse libaka tse nang le maemo a mahareng ho isa ho a matla joalo ka libaka tsa litoropo kapa litoropo.Equation e latelang e ka sebelisoa ho etsisa mohlala oa mocha oa Nakagami.
• Tabeng ena re bolela h = r*ejΦle angle Φ e ajoa ka ho lekana ho [-π, π]
• Phapang r le Φ ho nahanoa hore li ikemetse ka bobeli.
• Nakagami pdf e hlalositsoe ka holimo.
• Ho Nakagami pdf, 2σ2= E{r2}, Γ(.) ke tshebetso ya Gamma mme k >= (1/2) ke palo e ntseng e fela (digree tsa tokoloho tse amanang le palo ya diphetoho tse ekeditsweng tsa Gaussion).
• E ne e ntshetswa pele empirically thehiloeng litekanyo.
• Matla a ho amohela hanghang a ajoa ka Gamma.• Ka k = 1 Rayleigh = Nakagami
Weibull e nyamela
Kanale ena ke mohlala o mong oa lipalo o sebelisoang ho hlalosa mocha oa puisano o se nang mohala.Seteishene sa Weibull fading hangata se sebelisoa ho emela libaka tse nang le mefuta e fapaneng ea maemo a fifalang ho kenyelletsa le ho putlama ho hoholo le ho matla.
Kae,
2 σ2= E{r2}
• Kabo ea Weibull e emetse kakaretso e 'ngoe ea kabo ea Rayleigh.
• Ha X le Y e le iid zero e bolela mefuta e fapaneng ya gaussian, enfelopo ya R = (X2+Y2)1/2ke Rayleigh e ajoa.• Leha ho le joalo enfelopo e hlalosoa R = (X2+Y2)1/2, le pdf e tsamaellanang (profaele ea kabo ea matla) e ajoa ke Weibull.
• Equation e latelang e ka sebelisoa ho etsisa mohlala oa Weibull fading.
Leqepheng lena re fetile lihloohong tse fapaneng mabapi le ho fifala joalo ka hore na kanale e felloang ke eng, mefuta ea eona, mefuta e nyamelang, ts'ebeliso ea eona, mesebetsi le tse ling.Motho a ka sebelisa boitsebiso bo fanoeng leqepheng lena ho bapisa le ho fumana phapang pakeng tsa ho fela ha tekanyo e nyenyane le ho fifala ho hoholo, phapang pakeng tsa ho fela ha sephara le ho fifala ha makhetlo a mangata, phapang pakeng tsa ho fela ka potlako le ho fela butle, phapang pakeng tsa ho fela ha rayleigh le ho fela ha rician. joalo-joalo.
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Nako ea poso: Aug-14-2023
