1 li^n 1 wAN VUNG PHU SONG
VOX P H A N M E M W I R E L E S S I N S I T E Trdn Dire Tdn
Trudng Dgi hgc Cdng Nghe, DHQGHN Tom tdt:
Hien nay cdng nghe WIMAX dugc xem nhu la cdng nghe se gdp phdn thuc ddy Internet tai cac viing ngoai d, ndng thdn. Viec truyen thdng giiia tam phdt vd cac may thu phu thudc vao muc tfn hieu tai cac anten thu. Bai bao nay trinh bay ve vdn de tfnh toan vung phii sdng dua tren viec md phdng truyen sdng tai cdc tdn so tieu chudn danh cho WIMAX Id 2.5 vd 3.5 GHz. Nhiing ket qud md phdng rdt hiru fch cho viec lap ke hoach vd ddnh gia chi phf thyc hien.
Tir khod: md phdng truyen sdng, suy hao dudng truyen, he thdng khdng day.
Abstract:
To foster Internet usage in rural areas, WiMAX (Woridwide Interoperability for Microwave Access) was considered to enable the delivery of last-mile access to many end- users. Communication from a transmitter to receivers depends on the strength of the signal at the receiver antennas. This paper presents a case study simulation of wireless propagation at standard WIMAX frequencies of 2.5 and 3.5 GHz in order to calculate the coverage area. The result is needed for evaluating the budget and planning.
Keywords: propagation simulation, path loss, wireless systems.
L G I 6 I THIEU
Ngdy nay, cdng nghe Internet da dugc sii dung rdt phd bien tai nhirng thanh phd. Tuy nhien, tai nhimg vung ngoai d, ndng thdn thi viec sir dung Internet cdn rdt ban che. Co rat nhieu nguyen nhdn cd the dugc ke den nhu chi phf ban ddu cao, nhu cdu sir dung chua dii Idn...Cdng nghe WIMAX [1] da dugc coi Id mgt trong nhung gidi phdp de cd the dua Internet vdo nhimg khu vuec ndng thdn hay ddi nui. Truyen sdng Id ITnh vyc rat quan trgng ke tir khi Marconi kham phd ra viec truyen thdng dung sdng dien tir. Viec truyen tfn hieu se phu thudc vao do Idn cua tin hieu thu dugc tai anten thu. De cd the trien khai thdnh cdng thi khdu nghien ciru va md phdng truyin sdng khdng ddy Id rdt quan trgng. Viec md phdng nay phdi dugc tien hanh dya tren cdc thdng tin thyc te (dja hinh, cdc cdng trinh xdy dyng, cay cdi vd thdi tiet) moi cd the cho ket qud ddng tin cay.
Bdi bao nay tap trung vdo vdn de truyen sdng vd tuyen tai cdc tdn so chudn ciia WIMAX, tir dd tfnh todn vung phii sdng. nhdm tirng budc ddnh gid cdc chi phf cho viec trien khai WIMAX tai mdt viing ngoai thdnh cu thi (Bdc ninh). Chiing tdi kit hgp cdc thdng sd dja ly (dja hinh, cdng trinh xdy dyng, rirng niii,...) vd cdc thdng sd ky thuat (cdu hinh anten phdt - thu. do cao ldp ddt anten,...) vdo phdn mIm Remcom Wireless InSite (phan nriem md phdng dien-tir trudng). Phdn mIm se cho phep md phdng viec truyin tfn hieu vd tuyen vdi cdc dieu kien khac nhau ( thdi tilt, kenh truyen....).
II. M 6 HINH TRUYEN S 6 N G
Nhu chung ta se thdy. hien tugng lan truyen sdng tren cdc dudng ddy cd the dugc tiep can tir viec md rgng ly thuylt mach, hodc tir sy biln dii ddc biet cdc phuang trinh Maxwell.
Khi khodng cdch tir ngudn din tdi ciia mdt mach dien cd chilu dai so sdnh dugc vdi budc sdng hodc Idn ban nhilu Idn so vdi budc sdng thi tfn hieu dugc phdt di tir nguon phdi rpat mdt khodng thdi gian (mdt vdi chu ky) dk lan truyin din tdi. Ta ggi dd la hien tugng truyin/sdng tren dudng day.
Truyin sdng sieu cao tdn tren dudng day cd cdc he qud sau:
• Cd sy tri pha cua tfn hieu tai dilm thu so vdi tfn hieu tai diem phdt.
• Cd sy suy hao bien do tfn hieu khi lan truyen
599
• Co su phan xa song Ircn tai va tren ngudn. Dieu nay dan den hien tugng song ouug m^i, dudng day.
Do dae diem uiiyen S()ng khong on djnh. nen eac mo hinh truyen sdng deu mangtinli ihirc nghiem. Dudi day la xet mo hinh iruycn sdng dirge sir dung rdng rdi la md hinh Hata- Okumura [2,4].
Cae bilu ihiie lOcln hgc dugc sir dung Irong mo hinh Hata-Okumura de xac djnh ton
hao trung binh L: j L,= 69,55 + 26,161^/;. - 13,82lg///, - a(h,n) + (44,9 - 6,55lg///,)lgA- dB i
trong dd: f,-: tdn so hoat dgng (MHz); Lib: tdn hao trung binh
hb! dg cao anten tram gdc (m); hmi dgcao anten tram di dgng (m) r: ban kfnh cell (khodng each tir tram gdc) (km)
a(hn,): h? so hieu chinh cho dg cao anten di dgng (dB) [3]
III. M O HINH HOA DUNG WIRELESS INSITE I Wireless Insite la phdn mem md phdng truyen sdng di?n tir nhdm dy dodn tac don
ciia cac toa nhd hay dia hinh. Tai may phdt tfn hieu truyen dang tia dugc phdt ra, truyen tron mdt mdi tiirdng xac djnh trudc. Tfn hi?u cd the luong tdc vdi mdi trudng truyin thong qa viec phdn xa, tdn xa, truyin qua tudng,,..Tan so tfn hieu cd thi dugc md phdng chfnh xa trong dai 50 MHz tdi 40 GHz.
Trong bdi bdo ndy, chiing ta chgn ddi tugng Id khu vyc giap Hd ngi (Bdc Ninh). Bai todn md phong dugc thyc hien khi chung ta cd:
///. ILdrpl: Bdn dd dia hinh
Hinh I mo ta bdn do dja hinh khu vyc, cd thi thdy cdc vj trf cd dg cao ban cdc dilm khac traii ban dd. Chiing ta cd thi xdc djnh do cao tai vj tri bat ki bdng each trd chugt tdi vi tri ddtronj Wireless Insite.
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Hinh 1. Ban do dia hinh 111.2 Ldp 2: Mo hinh nhd cim
N t ^ u n l t r n h r - ' ? '"^ l ^ ' ^ . t ' "^° '^ "^^ '^ "^^ ^^° ^^"g ("^"^ ^hua that) trong khu.
Nhung toa nha co dg cao thap khdng dugc nap vdo trong chuang trinh
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H i n h 2 . M o h i n h n h a c d a
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111.3 Anten
Hinh 3 md td 2 mdu anten djnh hudng phat va thu dugc sir dung trong bdi todn nay. Anten phdt ddt d do cao 60m cdn anten thu ddt d 4d cao 1 Im.
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Hinh 3. Anten dinh huong: phat (trai) va thu (phai)
111.4 Mo hinh truyen song: Hata
Chuang trinh sir dung md hinh truyen sdng Hata - Okumura vdi may phdt la cdc may tram (BS) va may thu cd the di ddng.
Hinh 4 Id ket qud phdn bd cdng sudt nhdn tren khu vyc phii song. Do manh yeu the hien qua mdu sac thay ddi theo khodng each.
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tireless insite
K^ir r U.'i/La
Hinh 4. Phan bo coiig .suat
