Single carrier system Bandwidth= B Frequency Symbol duration t=1/B Whenτmax>T >Intersymbol interference(sl) (IMHZ Time T=1/B(1μs) Equaliser is needed to reduce si
Time Single Carrier System T=1/B (1s) Frequency B (1MHz) When _max>T →Intersymbol interference (ISI) Bandwidth = B Symbol Duration T=1/B Equaliser is needed to reduce ISI
OFDM Systems(N subcarriers) frequency · Available bandwidth is divided into n subband B Each symbol △f occupies a narrow (kHz) band but longer time lme period T(Ims) For each subcarriers Bandwidth△f=B/N ymbol duration T=NB
Frequency Time T (1ms) B OFDM Systems (N subcarriers) f (1kHz) •Available bandwidth is divided into N subband •Each symbol occupies a narrow band but longer time period For each subcarriers Bandwidth f=B/N Symbol duration T=N/B
已 Source Serial >Encoding>如 Lowpass 个⑧个 Filiter Parallel 2πfN-1 Channel Binary Data Parallel T Decoding to Filter Seria JafAr j2IfN-lt Baseband model of an oFdM communication system For the uniform subcarrier spacing fk=k△k=0,1,…,N-1
e j2 f0t e j 2 fN− 1t e j2 fN− 1t e j2 f0t e j2 fk t e j2 fk t Baseband model of an OFDM communication system f k f k = k = 0,1, ,N −1. - - - For the uniform subcarrier spacing
The basic orthogonal function for the kth subcarrier is defined as (,k)=exp(2n/)0≤t<T, Ig(t, k)=O, otherwise The basic functions satisfies the condition of orthogonality g(t,k)·g(t,p)dt=0,k≠p, T (t,k).g(t, p)dt=lg(t, k) dt=T, k=p
( ) = = ( , ) 0, . ( , ) exp 2 , 0 , g t k otherwise g t k j f k t t T = = = = T T T g t k g t p dt g t k dt T k p g t k g t p dt k p 0 2 0 * 0 * ( , ) ( , ) ( , ) , . ( , ) ( , ) 0, , The basic orthogonal function for the kth subcarrier is defined as The basic functions satisfies the condition of orthogonality
Structure of oFDM systems using FFT X(h) x(n) S(1) binary data encoding Guard Lowpass arrier (BPSK IFFT Insertion filtering modulation nanne y(k) y(n y'(n Binary data decoding lowpass (BPSK.) FFT Guard filtering Carrier deleting demodulation converting Channel OFDM symbol estimation synchronisation
Structure of OFDM systems using FFT Encoding (BPSK…) IFFT Guard insertion Lowpass filtering Carrier modulation Binary data Channel Carrier demodulation Lowpass filtering A/D converting Guard FFT deleting decoding (BPSK…) Binary data OFDM symbol synchronisation Channel estimation X(k) x(n) x’(n) s(t) y’(k) y(n) y’(n) r(t)