Hermitian symmetry for IFFT

Started by s22139584 in comp.dsp14 years ago 1 reply

Hi all I am strugling to get real valued output from a IFFT from a complex valued input. I know if the complex input is aligned using hermitian...

Hi all I am strugling to get real valued output from a IFFT from a complex valued input. I know if the complex input is aligned using hermitian symmetry, the output must be only real valued. My question is how to align the values hermitially. For example: If my input is: 1+2j; 2+3j; 5+j; 7+2j How do one align this hermitally? I have tried the following two approaches but neither seem...


What is the difference between FFT and IFFT?

Started by Sea Squid in comp.dsp14 years ago 15 replies

I used to think the operations are the same? Thank you.

I used to think the operations are the same? Thank you.


Channel Estimation in the frequency domain

Started by JAlbertoDJ in comp.dsp3 years ago 4 replies

Hello, I am using the ifft for the typical channel estimation in the frequency domain, in this case using 64 carriers: ChannelEst= ifft(...

Hello, I am using the ifft for the typical channel estimation in the frequency domain, in this case using 64 carriers: ChannelEst= ifft( Y./X , 64); Y is the FFT of RX signal X is the FFT of TX signal When all the 64 FFT points are filled, the channel estimation is perfect. But if i only TX some carriers: [12:50] and the rest of carriers are zero, then the estimation channel ha...


OFDM transmitter

Started by Zeph80 in comp.dsp9 years ago 8 replies

I'm simulating a DVB-T OFDM 8 Mhz BW transmitter with 2K tones, DVB-T sample rate is 9MHz. I'm doing this by using a 4K IFFT and 18 MHz...

I'm simulating a DVB-T OFDM 8 Mhz BW transmitter with 2K tones, DVB-T sample rate is 9MHz. I'm doing this by using a 4K IFFT and 18 MHz sample rate (I arrange the IFFT input with 1K tones (worth 4 MHz) having QPSK data, then zero out all the central tones, and put remaining QPSK data on the last 1 K tones ( worth the remaining 4 MHz BW).So I get a base-band OFDM spectrum to begin with. I'm then ...


ifft in C/C++

Started by Parlous in comp.dsp16 years ago 6 replies

I have used FFTW for my fourier operations in the past, but is there a inverse fourier transform library of some sort out there that is just...

I have used FFTW for my fourier operations in the past, but is there a inverse fourier transform library of some sort out there that is just as fast?


Re: fftw and derivative. once again

Started by Jerry Avins in comp.dsp8 years ago

On Sunday, January 9, 2011 6:52:09 PM UTC-5, Tim Wescott wrote: ... > You're not using any frequency limiting -- are you sure you're not...

On Sunday, January 9, 2011 6:52:09 PM UTC-5, Tim Wescott wrote: ... > You're not using any frequency limiting -- are you sure you're not just > amplifying the heck out of your noise? > > In Scilab: > > --> N = 4096; n = 0:N-1; > > --> nn = pmodulo(n + N/2, N) - N/2; > > --> x = exp(-nn.^2 / 100000); xd = ifft(fft(x) .* (-nn .^ 2)); > > --> clf; plot2d(n, [x' xd']) > > gives


how to derive that the IFFT when x(k) = 1 is an impulse

Started by bharat pathak in comp.dsp11 years ago 1 reply

Hello All, The IDFT equation is x(n) = 1/N * {summation(k=0:N-1) (X(k) * exp(j*2*pi*k*n/N))} My question is if ...

Hello All, The IDFT equation is x(n) = 1/N * {summation(k=0:N-1) (X(k) * exp(j*2*pi*k*n/N))} My question is if X(k) = [1 1 1 1]; example case of N=4 Using the IDFT equation how to prove that x(n) = [1 0 0 0]; Regards Bharat


needed help in radix 4 algorithm

Started by senthil in comp.dsp15 years ago 1 reply

hello friends, here i do my ifft coding with the help of the radix 4 algorithm formulae is y(l) = x(l) + x(l+N/2) + x(l+N/4) +...

hello friends, here i do my ifft coding with the help of the radix 4 algorithm formulae is y(l) = x(l) + x(l+N/2) + x(l+N/4) + x(l+3N/4); z(l) = x(l) - x(l+N/2)+j(x(l+N/4) - x(l+3N/4); g(l) = x(l) + x(l+N/2) - x(l+N/4) - x(l+3N/4); h(l) = x(l) - x(l+N/2)-j(x(l+N/4) - x(l+3N/4); with respect to above if i design for the 64 point i put N = 64.AND I first i calculate the first stage o...


Re: How to zoom into a certain part of FFT?

Started by Vista in comp.dsp12 years ago 13 replies

Hi folks, This is not a joke post. I really have this question in my mind for long time. When I truncate/extract out F(w) for w in [-B, B]...

Hi folks, This is not a joke post. I really have this question in my mind for long time. When I truncate/extract out F(w) for w in [-B, B] and use step size deltaB to sample it and then do IFFT, what is the portion of f(t) I see? Say f(t) for t in [a, b]. What are a and b? Now suppose I find there is some fine structure in [c, d], which is shown from the visual display of f_hat(t)...


kindly help me in understanding this

Started by vividreddy in comp.dsp11 years ago 1 reply

hi all, i am new to OFDM concept, i took a sequence of +1 and -1 levels for FFT and before that i ensured that i have to keep 0 at DC...

hi all, i am new to OFDM concept, i took a sequence of +1 and -1 levels for FFT and before that i ensured that i have to keep 0 at DC CARRIER and guard carriers in between. and i have ensured a cyclic prefix of 4 samples the FFT is of 16- point and IFFT is taken and then i am doing FFTSHIFT again but my answer is not same as (all along, i took it for granted, but now i see that ...


2D image processing with FFTW

Started by Johannes Bauer in comp.dsp10 years ago 4 replies

Hello group, I'm having some trouble getting my code to work correctly using C++ and libfftw (which is, may I remark, absolutely marvellous)....

Hello group, I'm having some trouble getting my code to work correctly using C++ and libfftw (which is, may I remark, absolutely marvellous). Basically I'm FFTing a picture (real to complex) and then performing and IFFT (just to see if everything works as expected). Well, it does not - I'm having some really stupid problem with which I now spent half a day. Can't figure out what I'm doing ...


efficient inverse fft of a band-pass function

Started by anando in comp.dsp11 years ago 13 replies

Hi I'd be grateful if somebody could point me to the right literature for the following problem: I have a function r(t) which is known as...

Hi I'd be grateful if somebody could point me to the right literature for the following problem: I have a function r(t) which is known as well as its Fourier transform R(f). Thus R(f) --> IFFT --> r(t). Both of them are known. Now suppose I have a bandpass version of R(f) [let us call it R_b(f)] such that R_b(f) = R(f) for f_1


Problem with IFFT, any idea?

Started by rapidiablo in comp.dsp11 years ago 10 replies

Hi everybody... i am new in signal processing. something about me... i am a student of software Engineering, My name is Juan and i live in...

Hi everybody... i am new in signal processing. something about me... i am a student of software Engineering, My name is Juan and i live in Argentina. I am migrating one application developed in VEE (Agilent) to c++. This is my new task in my work. This application analyzes signals and then... use that info to set some alarms.. Nothing complicated... so far.. everything goes fine.. until...


Zero Padding a DFT

Started by quick one in comp.dsp14 years ago 5 replies

What I meant to ask about crosscorrelation: Suppose I have 2 signals r[n] and y[n] each of length N, and zero pad them to double their lengths...

What I meant to ask about crosscorrelation: Suppose I have 2 signals r[n] and y[n] each of length N, and zero pad them to double their lengths and compute Y[k]R[k]* using FFTs in matlab. And then I zero pad that product with 8N zeros BEFORE taking the 10N-IFFT to get the crosscorrelation. It seems my correlation results are worse, but I cant understand exactly why. any help is appr...


Is "brick wall" filter realizable?

Started by Richard Owlett in comp.dsp15 years ago 12 replies

This is intentionally "dumb" question. I suspect a good answer will illuminate a fallacy in my thinking. assume a real input perform FFT set...

This is intentionally "dumb" question. I suspect a good answer will illuminate a fallacy in my thinking. assume a real input perform FFT set all bins to 0 that are outside pass band perform suitably scaled IFFT What's wrong with this picture?


OFDM Spectrum

Started by Shahin in comp.dsp13 years ago 2 replies

Hi, I'm trying to visualize the sub-carriers in my ofdm model. What I do is I generate a BPSK OFDM symbol and after IFFT I...

Hi, I'm trying to visualize the sub-carriers in my ofdm model. What I do is I generate a BPSK OFDM symbol and after IFFT I plot the FFT of transmitter output. I only get one Sinc graph not the overlapping sub-channels. Could you please correct me to get a proper view of sub-carriers? Best regards Shahin


issues from ifft from real in only

Started by akoties in comp.dsp12 years ago 4 replies

Can someone please help me out here. I'm trying to create a audio file from a picture for an art project. I know that its been done before...

Can someone please help me out here. I'm trying to create a audio file from a picture for an art project. I know that its been done before from dsp guys but I'm not very adept when it comes to implementing DSP stuff. As I'm doing it from a picture the input data only has positive values, so I've assumed that the source at s(x) in grey scale s(x) = s(x) - 128 then to get the complex ...


Newbie question

Started by Skice in comp.dsp13 years ago 1 reply

I have a 2d signal (an image, actually) of which I want to calculate ACF. I tried to use the IFFT/FFT approach, but when I rotate the image...

I have a 2d signal (an image, actually) of which I want to calculate ACF. I tried to use the IFFT/FFT approach, but when I rotate the image I notice some strange effects (something aliasing-like). So I tried to pad my image both vertically and horizontally with zeros, doubling its dimension before calculating the FFT. Am I doing right? Someone can help me? Thank you Lorenzo


Log Scale FFT ?

Started by edwardehopkins in comp.dsp14 years ago 2 replies

Does anyone know if there is a way to compute an IFFT over a log scale of sampled frequencies? In other words if I have a frequency response...

Does anyone know if there is a way to compute an IFFT over a log scale of sampled frequencies? In other words if I have a frequency response that is on a log scale (base 10) what does this mean in the time domain? This message was sent using the Comp.DSP web interface on www.DSPRelated.com


IFFT

Started by Sam Harman in comp.dsp8 years ago 2 replies

Hi All, I am trying to implement a Fast Fourier Transform, followed by an Inverse FFT on the iPhone in Objective-C. To do this I am using...

Hi All, I am trying to implement a Fast Fourier Transform, followed by an Inverse FFT on the iPhone in Objective-C. To do this I am using the functions within the 'rvfft.cpp' file available here: http://www.musicdsp.org/archive.php?classid=2#79 I am trying to perform the operation on an array of doubles of length 131072 (padded with zeros to ensure it is divisible by 2). My code is belo...