## Hermitian symmetry for IFFT

Started by in comp.dsp16 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 in comp.dsp17 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 in comp.dsp6 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 in comp.dsp11 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 in comp.dsp18 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 in comp.dsp11 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 in comp.dsp14 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 in comp.dsp18 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 in comp.dsp14 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 in comp.dsp14 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 in comp.dsp13 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 in comp.dsp14 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 in comp.dsp13 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...

## non-recursive fft

Started by in comp.dsp2 years ago 14 replies

Is there any info on how to implement fft and ifft algorithms that aren't recursive? I'd like to possibly calculate a really long on inside a...

Is there any info on how to implement fft and ifft algorithms that aren't recursive? I'd like to possibly calculate a really long on inside a signal chain so attempting to compute a 2 second fft in one function call would probably be disastrous. -Matt

Started by in comp.dsp17 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 in comp.dsp17 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 in comp.dsp15 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 in comp.dsp15 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 in comp.dsp16 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 in comp.dsp17 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