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先求了一个OFDM信号再接下来就功率谱密度时候图形好像不对请明白人指点整个程序如下：（附件里也是这个程序） numbits = 4096; % number of bits to be transmitted fp = 3.432e9; % central frequency fc = 50e9; % sampling frequency T0 = 242.4e-9; % information length TP = 60.6e-9; % cyclic prefix TG = 70.1e-9; % total guard time A = 1; % amplitude of the rectangular impulse % response N = 128; % number of carriers of the OFDM % system % ------------------------- % Step One - OFDM modulator % ------------------------- tc = T0 / N; % chip time ntcp = floor(TP/tc); % number of tones of the cyclic % prefix n = (-ntcp+1:1:N); % tone counter NT = length(n); % total number of tones per symbol % Bit generation ([bits] = cp0201_bits(numbits);) bits=rand(1,numbits)>0.5; % QPSK modulator ([S,Sc,Ss] = cp0203_qpsk_mod(bits);) nb = length(bits); % number of bits ns = ceil(nb/2); % number of symbols b0 = zeros(1,ns*2); % zero padding b0(1:nb) = bits; j = sqrt(-1); for s = 1 : ns ba = b0(((s-1)*2)+1); bb = b0(((s-1)*2)+2); k = bb + ba*2; p = ((pi/4)*(2*k-1))-pi; Sc(s) = cos(p); Ss(s) = sin(p); S(s) = Sc(s) + j*Ss(s); end % OFDM modulator nb = ceil(length(S)/N); % number of OFDM blocks to be % transmitted S0 = zeros(1,nb*N); % zero padding S0(1:length(S))=S; dt = 1 / fc; % sampling period if ntcp>0 tc = (T0+TP)/NT; % tone duration end tonesamples = floor(tc/dt); % samples per tone toneres = floor((TG-TP)/dt); % samples for the residual % part symsamp = (tonesamples*NT)+toneres; % number of samples representing one OFDM symbol totsamp = symsamp * nb; % number of samples representing the transmitted signal X = [zeros(1,totsamp)']; for b = 1 : nb c = S0((1+(b-1)*N):(N+(b-1)*N)); % block extraction % S/P conversion and zero padding A = length(c); a1 = floor(A/2); a2 = A - a1; FS = 2*A; Czp=zeros(FS,1); Czp(1:a1)=[c(1:a1).']; Czp(FS-a2+1:FS)=[c(A-a2+1:A).']; C = ifft(Czp); % IFFT of the zero-padded input if ntcp>0 % Insertion of the cyclic prefix C1=zeros(length(C)+2*ntcp,1); C1(1:(2*ntcp))=C(2*N+1-(2*ntcp):2*N); C1(2*ntcp+1:length(C1))=C; else C1=C; end zp = floor(tonesamples/2); C2 = [C1.';zeros((zp-1),length(C1))]; C3 = C2(:); g = ones(1,zp); C4 = conv(g,C3); C4 = C4(1:(zp*NT*2)); ics = 1 + (b-1)*symsamp + toneres; X(ics:ics+length(C4)-1)=C4; end % for b = 1 : nb XM = X'; % P/S conversion XM = XM(1:totsamp); I = real(XM); Q = imag(XM); % Carrier modulation time = linspace(0,totsamp*dt,length(I)); SI = I.*(cos((2*pi*fp).*time)); SQ = Q.*(sin((2*pi*fp).*time)); Stx = SI - SQ; %************************************下面求功率谱密度************************* dt=1/fc; N=length(Stx); T=N*dt; df=1/T; X = fft(Stx); X = X / N; mPSD=abs(X).^2/(df^2); PSD = fftshift(mPSD); PSD = (1/T).*PSD; % ----------------------------------- % Step Two - Graphical representation % ----------------------------------- frequency = linspace(-fc/2,fc/2,length(PSD)); PF=plot(frequency,PSD); set(PF,'LineWidth',[2]); AX=gca; set(AX,'FontSize',12); X=xlabel('Frequency [Hz]'); set(X,'FontSize',14); Y=ylabel('Power Spectral Density [V^2/Hz]'); set(Y,'FontSize',14);

[求助]关于求OFDM信号的功率谱问题 感激不尽！

[求助]关于求OFDM信号的功率谱问题感激不尽！