(a) (b) OFDM中的一个载波的频谱 OFDM中的多个载波的频谱
OFDM中的一个载波的频谱 OFDM中的多个载波的频谱
10 spectrum of 1st sub-channel OFDM spectrum 0 : -10 -20 : -30 1 0.5 0 0.5 1
。MCM的基本思想 Channel bandwidth is divided into multiple subchannels to reduce ISI and frequency-selective fading. Multicarrier transmission Subcarriers are orthogonal each other in frequency domain. ofjaueo-qns serial data symbols 1-Nfaweqns parallel data symbols ser parallel converter ☒ T
MCM的基本思想 Channel bandwidth is divided into multiple subchannels to reduce ISI and frequency-selective fading. Multicarrier transmission : Subcarriers are orthogonal each other in frequency domain
For a large number of subchannels,the arrays of sinusoidal generators and coherent demodulators required in a parallel system become unreasonably expensive and complex.The receiver needs precise phasing of the demodulating carriers and sampling times.Weinstein and Ebert applied the discrete Fourier transform (DFT)to parallel data transmission system as part of the modulation and demodulation process
For a large number of subchannels, the arrays of sinusoidal generators and coherent demodulators required in a parallel system become unreasonably expensive and complex. The receiver needs precise phasing of the demodulating carriers and sampling times. Weinstein and Ebert applied the discrete Fourier transform (DFT) to parallel data transmission system as part of the modulation and demodulation process
OFDM Modem N subchannels Ncomplex samples quadrature Bits I amplitude add D/A+ 十 S/P modulation ● W-IFFT ● ● cyclic ● P/S transmit 001101 ● QAM) ● prefix ● filter encoder TRANSMITTER RECEIVE multipath channel R Ncomplex N subchannels samples nvert channel Receive remove QAM ● filter decoder ● ● W-FFT ● S/P cyclic + ● ● frequency ● ● prefix domain A/D equalizer
OFDM Modem P/S QAM decoder invert channel = frequency domain equalizer S/P quadrature amplitude modulation (QAM) encoder N-IFFT add cyclic prefix P/S D/A + transmit filter N-FFT S/P remove cyclic prefix TRANSMITTER RECEIVE R N subchannels N complex samples N complex samples N subchannels Receive filter + A/D multipath channel Bits 00110