10 9 8 7 58 3 6 T ap 210 100-80 60-40 200 100 Frequency (Hz) Scattering function of a medium-range tropospheric scatter channel
Example of OFDM signals data Real part: cos(2Ifit) Imaginary part: sing (2IfiO) OFDM
Example of OFDM signals data Real part: cos(2fk t) Imaginary part: sing(2fk t) 1 -1 -1 1 1 OFDM
Comparison with FDMA 0.6 chI ch2 ch3 s04 802 Frequency guar -0.2 Subcarrier number k
0 1 2 3 4 5 6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 Subcarrier Number k Spectra Comparison with FDMA ch1 ch2 ch3 Frequency guard
Assume the information data sequence be X(), k=0, I. N-1, then the transmitted signal s(t) can be expressed as )=∑X(D)p(27) =∑X(plep(12m△)0≤1<7,0≤p≤N and T OFDM Symbol period △f The received signal r(t) is ()=s()*()+() h(t: Channel response; w(O:AWGN signal
Assume the information data sequence be X(k), k=0,1…N-1, then the transmitted signal s(t) can be expressed as ( ) ( ) ( ) ( )exp( 2 ), 0 ; 0 1. exp 2 1 0 1 0 = − = − = − = X p j p f t t T p N s t X p j f t N p p N p f T = 1 and The received signal r(t) is r(t) = s(t)*h(t)+w(t) h(t):Channel response; w(t):AWGN signal OFDM symbol period
The received on subcarrier ko is y()=7(Oxp(12△f Assume h(=l, w(t=0 (ideal channel), then y() becomes Y()=J 2X(p) 2 rpaf exp(= Afn)
The received on subcarrier k0 is ( ) r(t) ( j k f t)dt T Y k T = − 0 exp 2 1 Assume h(t)=1, w(t)=0 (ideal channel), then Y(k) becomes ( ) ( ) ( ) ( ) − = = − T N p X p j p f t j k f t T Y k 0 1 0 exp 2 exp 2 1