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TI : H THNG DNG OFDM QUA KNH TRUYN AWGNGVHD: Th.S ng L KhoaNhm thc hin :Nng Vit BnhH Quc DngL Hoi NamTrn Hong Tun

PHN M PHNGS khiM phng trn Matlab/SimulinkPHN L THUYTTng quan v OFDMNguyn l hot ng ca OFDMu im v hn ch OFDMNI DUNG

Tng quan v OFDMK thut OFDM c pht minh bi R.W Chang nm 1966 M.OFDM (Orthogonal Frequency Division Multiplexing ) l k thut ghp knh phn chia theo tn s trc giao.L mt k thut iu ch a sng mang, s dng cc sng mang con trc giao v tn s.S chng ln ph tn hiu lm cho h thng OFDM c hiu sut s dng ph ln hn nhiu so vi cc k thut iu ch thng thng.

Tng quan v OFDM OFDM s dng php bin i nhanh IFFT b pht v s dng php bin i FFT b nhn . Ngy nay OFDM khng ngng c nghin cu v m rng phm vi ng dng. (nh : DVB, wifi, wimax, h thng LTE.)

Nguyn l ca OFDM u pht: H thng OFDM s phn chia dng d liu ni tip tc cao thnh N lung d liu song song tc thp(c mang trn cc sng mang con trc giao v tn s) thng qua b bin i S/P.Tip tn hiu c tng hp li v a ti b bin i IFFT chuyn i tn hiu thnh cc mu ri rc thi gian sau c chn thm khong bo v v c truyn i.

Nguyn l ca OFDM S b pht OFDM c bn

u thu: Khong bo v c loi b. Tn hiu c bin i ngc li t min thi gian sang min tn s thng qua b bin i FFT sau c loi b pilot v c sp xp li cui cng nhn c chui d liu ban u c truyn i.Nguyn l ca OFDM S b thu OFDM c bn

Ph ca cc sng mang con trc giao trong OFDMNguyn l ca OFDM Tnh trc giao ca song mang conPh ca sng mang trong FDM

Ph ca cc sng mang con trc giaoNguyn l ca OFDM

Ph ca tn hiu OFDM trn Matlab Nguyn l ca OFDM

chng nhiu ISI trn knh truyn cc symbol OFDM c gn thm mt khong bo v (Cyclic Prefix) trc khi truyn i.

Nguyn l ca OFDM Cyclic Prefix

Nguyn l ca OFDM S tn s v thi gian ca tin hiu OFDM

u im ca h thng OFDM OFDM tng hiu sut s dng bng thng bng cch cho php chng lp nhng sng mang con. OFDM chu ng fading la chn tn s tt hn nhng h thng sng mang n.Hn ch c xuyn nhiu gia cc sng mang (ICI) v giao thoa gia cc k hiu (ISI) nh khong CP .S phc tp ca my pht v my thu gim ng k nh s dng FFT v IFFT.C th truyn d liu tc cao.

Nhc im ca h thng OFDMNhy vi offset tn s. V d nh hiu ng dch tn dopler. H thng ng b tn s trong OFDM phc tp hn nhiu so vi h thng khc.Ti my thu, s rt kh khn trong vic quyt nh v tr nh thi ti u gim nh hng ca ICI v ISI.T s cng sut nh trn cng sut trung bnh PAPR (Peak to Average Power Ratio) ln.

S khi :

S khi h thng OFDMPhn m phng

Phn m phngS h thng s dng OFDM qua knh AWGNM phng trn Matlab/Similink

Phn m phngPh tn hiu OFDM