Hōʻike kēia ʻaoʻao i nā kumu kumu o ka Fading a me nā ʻano o ka fading i ke kamaʻilio uea ʻole. Ua māhele ʻia nā ʻano Fading i ka fading nui a me ka fading liʻiliʻi (multipath delay spread a me ka doppler spread).
ʻO ka fading pālahalaha a me ka fading koho alapine he ʻāpana ia o ka fading multipath kahi ʻo ka fading wikiwiki a me ka fading lohi he ʻāpana ia o ka fading hohola doppler. Hoʻokō ʻia kēia mau ʻano fading e like me nā hoʻolaha a i ʻole nā kumu hoʻohālike ʻo Rayleigh, Rician, Nakagami a me Weibull.
Hoʻolauna:
E like me kā mākou e ʻike nei, ʻo ka ʻōnaehana kamaʻilio uea ʻole he mea hoʻoili a me ka mea loaʻa. ʻAʻole maʻalahi ke ala mai ka mea hoʻoili a i ka mea loaʻa a hiki i ka hōʻailona i hoʻouna ʻia ke hele ma o nā ʻano attenuations like ʻole me ka nalowale o ke ala, ka attenuation multipath etc. ʻO ka attenuation hōʻailona ma o ke ala e pili ana i nā kumu like ʻole. ʻO lākou ka manawa, ka alapine lekiō a me ke ala a i ʻole ke kūlana o ka mea hoʻoili/mea loaʻa. Hiki ke hoʻololi manawa a paʻa paha ke kahawai ma waena o ka mea hoʻoili a me ka mea loaʻa ma muli o ka paʻa ʻana o ka mea hoʻoili/mea loaʻa a neʻe paha kekahi i kekahi.
He aha ka mae ʻana?
ʻO ka loli manawa o ka mana hōʻailona i loaʻa ma muli o nā loli i ka medium transmission a i ʻole nā ala i ʻike ʻia ʻo ka fading. Pili ka fading i nā kumu like ʻole e like me ka mea i ʻōlelo ʻia ma luna. I loko o ke kūlana paʻa, pili ka fading i nā kūlana lewa e like me ka ua, ka uila a pēlā aku. I loko o ke kūlana kelepona, pili ka fading i nā pilikia ma ke ala e loli ana me ka manawa. Hoʻokumu kēia mau pilikia i nā hopena hoʻoili paʻakikī i ka hōʻailona i hoʻouna ʻia.
Hōʻike ka kiʻi-1 i ka pakuhi amplitude vs mamao no nā ʻano mae lohi a me ka mae wikiwiki a mākou e kūkākūkā ai ma hope.
Nā ʻano mae
Ke noʻonoʻo nei i nā hemahema pili i ke kahawai a me ke kūlana o ka mea hoʻoili/mea loaʻa, a laila nā ʻano mae ʻana i ka ʻōnaehana kamaʻilio uea ʻole.
➤Fading Unahi Nui: Hoʻokomo pū ia i ka nalowale o ke ala a me nā hopena aka.
➤Fading Scale Liʻiliʻi: Ua māhele ʻia i ʻelua mau māhele nui ʻo ia hoʻi ka laha lohi multipath a me ka laha doppler. Ua māhele hou ʻia ka laha lohi multipath i ka fading pālahalaha a me ka fading koho alapine. Ua māhele ʻia ka laha Doppler i ka fading wikiwiki a me ka fading lohi.
➤Nā hiʻohiʻona mae: Hoʻokō ʻia nā ʻano mae ma luna nei i nā hiʻohiʻona a i ʻole nā hoʻolaha like ʻole e like me Rayleigh, Rician, Nakagami, Weibull etc.
E like me kā mākou e ʻike nei, loaʻa nā hōʻailona mae ma muli o nā ʻōlinolino mai ka lepo a me nā hale a puni a me nā hōʻailona i hoʻopuehu ʻia mai nā kumulāʻau, nā kānaka a me nā hale kiaʻi i loaʻa ma kahi ākea. Aia ʻelua ʻano o ka mae ʻana, ʻo ia hoʻi ka mae nui a me ka mae liʻiliʻi.
1.) Ka mae nui ʻana
ʻO ka mae nui ʻana o ka leo ke hele mai kahi mea keakea ma waena o ka mea hoʻoili a me ka mea loaʻa. ʻO kēia ʻano keakea ke kumu o ka emi nui ʻana o ka ikaika o ka hōʻailona. ʻO kēia no ka mea ua uhi ʻia a ālai ʻia paha ka nalu EM e ka mea keakea. Pili ia i nā loli nui o ka hōʻailona ma kahi mamao.
1.a) Ka nalowale o ke ala
Hiki ke hōʻike ʻia ka pohō o ke ala hakahaka penei.
➤ Pt/Pr = {(4 * π * d)2/ λ2} = (4*π*f*d)2/c2
Ma hea,
Pt = Mana hoʻoili
Pr = Loaʻa ka mana
λ = ka nalu
d = ka mamao ma waena o ka antenna hoʻouna a me ka antenna loaʻa
c = ka wikiwiki o ka mālamalama ie 3 x 108
Mai ke kaulike, ke manaʻo nei ia e hoʻēmi ana ka hōʻailona i hoʻouna ʻia ma kahi mamao aku i ka wā e hohola ʻia ana ka hōʻailona ma luna o kahi nui a ʻoi aku ka nui mai ka hopena hoʻouna a i ka hopena loaʻa.
1.b) Hopena aka
• ʻIke ʻia ia ma ke kamaʻilio uea ʻole. ʻO ke aka ʻana ka ʻokoʻa o ka mana i loaʻa o ka hōʻailona EM mai ka waiwai awelika.
• He hopena ia o nā mea keakea ma ke ala ma waena o ka mea hoʻoili a me ka mea loaʻa.
• Aia ia i ke kūlana honua a me ke alapine (frequency) lekiō o nā nalu EM (ElectroMagnetic).
2. Ka mae ʻana o ka unahi liʻiliʻi
Pili ka fading liʻiliʻi me nā loli wikiwiki o ka ikaika hōʻailona i loaʻa ma kahi mamao pōkole a me ka manawa pōkole.
Ma muli oka laha lohi multipathʻElua ʻano o ka fading liʻiliʻi, ʻo ia hoʻi ka fading pālahalaha a me ka fading koho alapine (frequency). Pili kēia mau ʻano fading multipath i ke kaiapuni hoʻolaha.
2.a) Ka mae palahalaha
Ua ʻōlelo ʻia ke kahawai uea ʻole he flat fading inā loaʻa iā ia ka loaʻa mau a me ka pane pae linear ma luna o kahi bandwidth i ʻoi aku ka nui ma mua o ka bandwidth o ka hōʻailona i hoʻouna ʻia.
Ma kēia ʻano mae ʻole, e loli like nā ʻāpana alapine (frequency) a pau o ka hōʻailona i loaʻa i ka manawa like. Ua kapa ʻia hoʻi ia he mae ʻole koho.
• Hōʻailona BW << Kahawai BW
• Ka wā hōʻailona >> Ka laha lohi
ʻIke ʻia ka hopena o ka mae pālahalaha ma ke ʻano he emi ʻana o SNR. Ua ʻike ʻia kēia mau kahawai mae pālahalaha he mau kahawai loli amplitude a i ʻole nā kahawai narrowband.
2.b) Ka mae ʻana o ke koho alapine (frequency)
Hoʻopilikia ia i nā ʻāpana spectral like ʻole o kahi hōʻailona lekiō me nā amplitudes like ʻole. No laila ka inoa selective fading.
• Hōʻailona BW > Kahawai BW
• Ka wā hōʻailona < Ka laha lohi
Ma muli oka hohola ʻana o ka dopplerʻElua ʻano o ka mae ʻana, ʻo ia hoʻi ka mae wikiwiki a me ka mae lohi. Pili kēia mau ʻano mae hoʻolaha doppler i ka wikiwiki o ke kelepona, ʻo ia hoʻi ka wikiwiki o ka mea hoʻokipa e pili ana i ka mea hoʻouna.
2.c) Māʻele wikiwiki
Hōʻike ʻia ka hanana o ka mae wikiwiki e nā loli wikiwiki o ka hōʻailona ma luna o nā wahi liʻiliʻi (ʻo ia hoʻi ka bandwidth). Ke hōʻea mai nā hōʻailona mai nā ʻaoʻao āpau o ka mokulele, e ʻike ʻia ka mae wikiwiki no nā ʻaoʻao āpau o ka neʻe ʻana.
Hiki mai ka mae wikiwiki ʻana ke loli koke ka pane impulse kahawai i loko o ka lōʻihi o ka hōʻailona.
• Hohola doppler kiʻekiʻe
• Ka wā hōʻailona > Ka manawa kūlike
• Ka loli ʻana o ka hōʻailona < Ka loli ʻana o ke kahawai
ʻO kēia mau palena e hopena i ka hoʻolaha pinepine ʻana a i ʻole ka mae ʻana o ke koho manawa ma muli o ka hoʻolaha ʻana o ka doppler. ʻO ka mae wikiwiki ka hopena o nā noʻonoʻo ʻana o nā mea kūloko a me ka neʻe ʻana o nā mea e pili ana i kēlā mau mea.
I ka fast fading, ʻo ka hōʻailona loaʻa ka huina o nā hōʻailona he nui i hōʻike ʻia mai nā ʻili like ʻole. ʻO kēia hōʻailona ka huina a i ʻole ka ʻokoʻa o nā hōʻailona he nui i hiki ke kūkulu a luku paha ma muli o ka neʻe ʻana o ka pae ma waena o lākou. Aia nā pilina pae i ka wikiwiki o ka neʻe ʻana, ka alapine o ka hoʻouna ʻana a me nā lōʻihi o ke ala pili.
Hoʻopilikia ka mae wikiwiki i ke ʻano o ka pulse baseband. He linear kēia distortion a hanaISI(Inter Symbol Interference). Hoʻemi ka hoʻohālikelike adaptive i ka ISI ma ka wehe ʻana i ka distortion linear i hoʻokumu ʻia e ke kahawai.
2.d) Mālie mālie
ʻO ka mae mālie ʻana ka hopena o ke aka ʻia ʻana e nā hale, nā puʻu, nā mauna a me nā mea ʻē aʻe ma luna o ke ala.
• Hohola Doppler Haʻahaʻa
• Ka wā hōʻailona <
• Ka loli ʻana o ka hōʻailona >> Ka loli ʻana o ke kahawai
Hoʻokō ʻana i nā hiʻohiʻona Fading a i ʻole nā hoʻolaha fading
ʻO nā hoʻokō ʻana o nā hiʻohiʻona fading a i ʻole nā hoʻolaha fading e komo pū me Rayleigh fading, Rician fading, Nakagami fading a me Weibull fading. Ua hoʻolālā ʻia kēia mau hoʻolaha kahawai a i ʻole nā hiʻohiʻona e hoʻokomo i ka fading i loko o ka hōʻailona ʻikepili baseband e like me nā koi o ka profile fading.
ʻO Rayleigh e mae ana
• Ma ke kumu hoʻohālike ʻo Rayleigh, ua hoʻohālikelike ʻia nā ʻāpana Non Line of Sight (NLOS) ma waena o ka mea hoʻoili a me ka mea loaʻa. Ua manaʻo ʻia ʻaʻohe ala LOS ma waena o ka mea hoʻoili a me ka mea loaʻa.
• Hāʻawi ʻo MATLAB i ka hana "rayleighchan" e hoʻohālike i ke kumu hoʻohālike o ke kahawai rayleigh.
• Ua puʻunaue ʻia ka mana me ka exponential.
• Ua hoʻolaha like ʻia ke ʻano a kūʻokoʻa mai ka amplitude. ʻO ia ke ʻano Fading i hoʻohana nui ʻia i ke kamaʻilio uea ʻole.
Ka mae ʻana o Rician
• Ma ke kumu hoʻohālike ʻo Rican, ua hoʻohālikelike ʻia nā ʻāpana Line of Sight (LOS) a me nā ʻāpana ʻaʻole Line of Sight (NLOS) ma waena o ka mea hoʻoili a me ka mea loaʻa.
• Hāʻawi ʻo MATLAB i ka hana "ricianchan" e hoʻohālike i ke kumu hoʻohālike kahawai rician.
Ka mae ʻana o Nakagami
ʻO ke kahawai fadding Nakagami kahi kumu hoʻohālike helu i hoʻohana ʻia e wehewehe i nā kahawai kamaʻilio uea ʻole kahi e hele ai ka sgnal i loaʻa i ka multipath fading. Hōʻike ia i nā wahi me ka fading waena a koʻikoʻi e like me nā wahi kūlanakauhale a i ʻole nā wahi suburban. Hiki ke hoʻohana ʻia ka hoʻohālikelike ma lalo nei e hoʻohālike i ke kumu hoʻohālike kahawai fading Nakagami.
• Ma kēia hihia, hōʻike mākou iā h = r*ejΦa ua hoʻolaha like ʻia ke kihi Φ ma [-π, π]
• Ua manaʻo ʻia ke kūʻokoʻa o ka loli r a me Φ.
• Ua hōʻike ʻia ka pdf Nakagami e like me luna.
• Ma ka pdf Nakagami, 2σ2= E{r2}, ʻo Γ(.) ka hana Gamma a ʻo k >= (1/2) ka helu mae (nā kekelē o ke kūʻokoʻa e pili ana i ka helu o nā loli Gaussion i hoʻohui ʻia).
• Ua hoʻomohala mua ʻia ma ke ʻano empirika ma muli o nā ana.
• Ua puʻunaue ʻia ka mana loaʻa koke ʻo Gamma. • Me k = 1 Rayleigh = Nakagami
Weibull mae
ʻO kēia kahawai kekahi kumu hoʻohālike helu i hoʻohana ʻia e wehewehe i ke kahawai kamaʻilio uea ʻole. Hoʻohana pinepine ʻia ke kahawai mae ʻo Weibull e hōʻike i nā wahi me nā ʻano ʻano mae like ʻole e pili ana i ka mae nāwaliwali a me ka mae koʻikoʻi.
Ma hea,
2σ2= E{r2}
• Hōʻike ka hoʻolaha ʻana o Weibull i kahi hoʻolaha laulā ʻē aʻe o ka hoʻolaha ʻana o Rayleigh.
• Ke ʻole ʻo X a me Y i nā loli gaussian awelika, ʻo ka envelope o R = (X2+ Y2)1/2ua hoʻolaha ʻia ʻo Rayleigh. • Eia naʻe ua wehewehe ʻia ka envelope R = (X2+ Y2)1/2, a ʻo ka pdf pili (ʻikepili hoʻolaha mana) ʻo Weibull i hoʻolaha ʻia.
• Hiki ke hoʻohana ʻia ke kaulike ma lalo nei e hoʻohālike i ke kumu hoʻohālike mae ʻo Weibull.
Ma kēia ʻaoʻao ua nānā mākou i nā kumuhana like ʻole e pili ana i ka fading e like me ke ʻano o ka fading channel, kona mau ʻano, nā hiʻohiʻona fading, kā lākou noi, nā hana a pēlā aku. Hiki i kekahi ke hoʻohana i ka ʻike i hāʻawi ʻia ma kēia ʻaoʻao i mea e hoʻohālikelike ai a loaʻa ai ka ʻokoʻa ma waena o ka fading liʻiliʻi a me ka fading nui, ka ʻokoʻa ma waena o ka fading pālahalaha a me ka fading koho alapine, ka ʻokoʻa ma waena o ka fading wikiwiki a me ka fading lohi, ka ʻokoʻa ma waena o ka fading rayleigh a me ka fading rician a pēlā aku.
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Ka manawa hoʻouna: ʻAukake-14-2023
