I Prees ►i s FCS 4 04 Yeats j COL Munn *0 E la ann e n
a.Co s8 vi OFDMA
OFDM 111 met c8ng nghe ghdp kenh Olen chia theo tin sO tnrc giao, n6 chia nhe bang tin thanh nhQng sting mang con c6 tin se khac biet. Trong mOt he thong OFDM,
chu6i dit lieu diu vao dirge chia thanh nheng chuai con song song c45 tee dO thip va
m6i chuOi con nay doge dieu chi va phut di tren mOt sting mang con tnrc giao rieng.
OFDM khai thac su da dung tin se cua kenh truyen da dubng bring each ma h6a va
xen ke th8ng tin dirge mang bed song mang con fru& khi truyen. Dieu chi OFDM c6
the dirge 'than dung bing phdp bien del Fourier (nhanh) ngugc 1FFT, cho phep met sO
luting km song mang con (len toi 2048) vei dO phtic tap khung clang ke. Trong he
thong OFDM, tai nguyen sin c6 trong mien thbi gian the hien qua symbol OFDM va trong mien tin s6 the hien 6 song mang con. TM nguyen thbi gian vi tin se c6 the dirge t6 chirc titbit nhang kenh con (sub-channel) cep cho nhitng ngtrai dung rieng. CEng nghe da truy cap OFDMA la mOt ca the ghep kenh/da truy nh$p cung cap sir ghep 'then luting dit lieu tir nhieu ngubi sur chmg vac) nhemg kenh con tren clueing
xuOng va stir da truy nhip vao m6i kenh con 6 dubng len.
➢ C>iu frac kJ Neu OFDMA va kink con boa
Nhu da not t chucmg 11 ceu true kf hieu OFDMA bao gam 3 loci sting mang con: song mang con do lieu (data sub-carrier) cho viec truyen de lieu; sting mang con din throng (pilot sub-carrier) cho nhang muc dich u6c luting kenh vi clang 1:0; sting mang
con rang (null sub-carrier) kh8ng mang die lieu ma dupe se dung lam did bao ve va
sting mang met chat' DC.
Nheng song mang con die lieu vi din dubng dirge nhOm thanh No Group. Mid Group c6 NE sting mang con, to thanh NE kenh con, m8i kenh con c6 mOt sting mang