## Forums Search for: IFFT

## Sampling Frequency effect on OFDM

inHi, I am doing a baseband simulation for IEEE 802.11 g. The standard uses 64 IFFT length (3.2?s) and 20 Msamples per second. I think this result...

Hi, I am doing a baseband simulation for IEEE 802.11 g. The standard uses 64 IFFT length (3.2?s) and 20 Msamples per second. I think this result in one sample per symbol. I am wondering what the structure will be if I use 40 Msample per second, i.e will the IFFT size change, or interpolation will be used? or what is the effect of sampling frequency on the baseband simulation? Best Regards,

## pruned FFT/IFFT

inHi folks, Im working on developing a Matlab version of pruned FFT/IFFT algorithm. But although i think that the implementation is correct, the...

Hi folks, Im working on developing a Matlab version of pruned FFT/IFFT algorithm. But although i think that the implementation is correct, the reults are not equal to full FFT. So, in a fast x-correlation problem this mismatch arises out of the maximum (the time delay) is somtimes shifted. I am at pains to search about this accuracy/mismatch but i have not found the point. I need your knowle...

## FFTW: FFT and IFFT of real data - wrong data after IFFT

inHi, I use the FFTW lib to do a FFT and a IFFT of real data. So I declare int len = 32; out1 = (fftw_complex*)...

Hi, I use the FFTW lib to do a FFT and a IFFT of real data. So I declare int len = 32; out1 = (fftw_complex*) fftw_malloc(sizeof(fftw_complex) * len); in1 = (double*) malloc(sizeof(double) * len); I initialize the in1 field with 0,1,2,3...len-1 I do the FFT due to the documentation: p_for = fftw_plan_dft_r2c_1d(len, in1, out1, FFTW_FORWARD); fftw_execute(p_for); And now the ...

## Accuracy of FFT/iFFT on the C55x?

inHello all, I'm trying to implement a frequency-domain filter on the TI C55x and encountered some problems with accuracy. My code takes the...

Hello all, I'm trying to implement a frequency-domain filter on the TI C55x and encountered some problems with accuracy. My code takes the FFT of the input and the coefficients, multiply them, and applies iFFT to get the time-domain output back. However, when I tested the algorithm with random data, the error (compared to Matlab convolution) is not centered at zero for the last few sampl...

## Why Padding Zeros before OFDM IFFT?

inHi all, In many OFDM system(like 802.11a and DVB-T), they always padding zeros to data before go to the IFFT module. Why use padding...

Hi all, In many OFDM system(like 802.11a and DVB-T), they always padding zeros to data before go to the IFFT module. Why use padding zeros? Best regards, Davy

## Signal orthogonality.

inI am trying to generate orthogonal signals using the IFFT routine of dsPIC and DAC. My setup is: - 256 point IFFT. Sampling rate =...

I am trying to generate orthogonal signals using the IFFT routine of dsPIC and DAC. My setup is: - 256 point IFFT. Sampling rate = 200KHz. Hence, each bin resolution = 781Hz. Frequency of interest = from 10KHz to 95KHz. Literature says that for signals to be orthogonal, the integral of dot product should be zero. That way, if my starting freq is 10KHz, I can have 10KHz, 15KHz, 20KHz, 25KH...

## OFDM PSD

hi all, i'm trying to plot ofdm normalized (dBr) psd after ifft function. i.e: carriers=NFFT.*ifft(tx); %plot normalized PSD i've tried...

hi all, i'm trying to plot ofdm normalized (dBr) psd after ifft function. i.e: carriers=NFFT.*ifft(tx); %plot normalized PSD i've tried pwelch(), psd() and their varients but my results do not match the theory. i'll appreciate some help on the subject. thanks.

## FIR Filters using frequency Sampling

inHello All Our application is channel embed/de-embedding. The frequency characteristics of the channel are specified in a ...

Hello All Our application is channel embed/de-embedding. The frequency characteristics of the channel are specified in a (S-parameters file). To generate an FIR filter, matching the specified frequency response, Frequecny sampling method using IFFT is used. We have been able to use this with limited success. I am looking for the limitation's of this IFFT method - ...

## Super-resolution technique

inHi! I have performed some propagation channel measurements in frequency domain i.e. I stored the measurement data as complex...

Hi! I have performed some propagation channel measurements in frequency domain i.e. I stored the measurement data as complex transfer function. I know I can obtain the channel impulse response by taking the IFFT. My question is, instead of taking IFFT. Can I employ other techniques (usually called super-resolution techniques in radar/wireless communications) such as ESPRIT, EM, SAGE, et...

## fft / ifft implementation

Dear, I have decided to use dspic 30f4012 with 48k rom and 2k ram for implementing fft/ifft. My aim is to sample the incoming voice from a mic...

Dear, I have decided to use dspic 30f4012 with 48k rom and 2k ram for implementing fft/ifft. My aim is to sample the incoming voice from a mic to the adc module for 5sec and then perform fft. I also wanted to inverse the process to play back the voice, just to check the process. So please help me regarding the SAMPLING RATE, HOW TO USE THE LIBRARY FUNCTION IN DSPIC FOR MY DEVICE, WHAT SHOULD B...

## Inverse of Non Minimum Phase System

inSuppose one takes a simple non minimum phase system with the z transform H(z) = 1 - 2*z. This system can obviously not be inverted as the pole...

Suppose one takes a simple non minimum phase system with the z transform H(z) = 1 - 2*z. This system can obviously not be inverted as the pole will lie outside the unit circle (inversion will lead to unstable impulse response). However if one tries to invert this system using Y(w) = 1/H(w) and then take the IFFT I do end up with a time domain impulse response y(t) (y(t) = IFFT(Y(w))) which i...

## fast convolution and normalization

inHi, i searched the web for quite some time now and just don't grok how to normalize when doing partitioned frequency domain...

Hi, i searched the web for quite some time now and just don't grok how to normalize when doing partitioned frequency domain convolution. Basically for an unnormalized FFT/IFFT pair (i use fftw, so all the FFT/IFFT i use is unnormalized), the necessary normalization factor would be 1/N applied once or 1/sqrt(N) applied twice. But now i have IFF(FFT(signal)*FFT(response)) and i wonder wh...

## Help with OFDM transmitted over multipath channel

inHi I want to simulate the transmission of a set of OFDM symbols over a multipath channel. The steps I intend to implement are 1) Generate a...

Hi I want to simulate the transmission of a set of OFDM symbols over a multipath channel. The steps I intend to implement are 1) Generate a 64 subcarrier OFDM system as follows. Take binary data and modulate it using a standard modulation scheme, say 64 QAM. Pass these modulated symbols through a 64 IFFT block. Before passing it through the IFFT block insert 16 pilots at 16 subcarriers. The ...

## IFFT in dvb-t

inHi all, I'm working on the Matlab Simulink DVB-T demos (2k). I'd like to understand: After the IFFT block, the frames composed by 2048 data...

Hi all, I'm working on the Matlab Simulink DVB-T demos (2k). I'd like to understand: After the IFFT block, the frames composed by 2048 data samples ( or elementary symbols of 7/64us duration) are sent to the AWGN channel. But, according the standard ETSI EN 300 744 v.1.12 (1997-08) on which the model is based, an OFDM symbol should be composed by 2176 elementary symbols (2048+128 of Guard Int...

## 56 bits out of Binary Input Reed Solomon Encoder

inHello, I am trying to implement a COFDM System which has an IFFT/FFT length of 64. Out of 64 carriers, 8 are set aside for nulls and pilots...

Hello, I am trying to implement a COFDM System which has an IFFT/FFT length of 64. Out of 64 carriers, 8 are set aside for nulls and pilots (56 remaining). So, out of Reed Solomon encoder I want to get 56 bits which will then be convolutionally encoded and modulated using QPSK before presenting them as inputs to the IFFT. So, in order to 56 bits out of the Reed Solomon Encoder, I w...

## FFT / IFFT sample rate converter

I am currently writing a FFT / IFFT based sample rate converter. However, after finding some code to do the transform (both fast and accurately),...

I am currently writing a FFT / IFFT based sample rate converter. However, after finding some code to do the transform (both fast and accurately), I am stuck.... the code I am using for the transform is from http://local.wasp.uwa.edu.au/~pbourke/miscellaneous/dft/. When I try and enlarge my buffers up to their final size, I hit the problem of the output is not the same as the input (in the way of t...

## 48 data carriers or 24 in 802.11 OFDM transmission?

inI understand to obtain a real output from IFFT, its input has to be conjugate symmetric. In 802.11a, 64-point IFFT is used with 48 data carriers...

I understand to obtain a real output from IFFT, its input has to be conjugate symmetric. In 802.11a, 64-point IFFT is used with 48 data carriers and 4 pilot carriers. If all the 48 data carriers are carrying data then where are its conjugate carriers?

## Minimum phase filter design using cepstrum methods?

inI've run across a few web pages describing how to convert an arbitrary FIR filter to a minimum phase variant by the use of cepstral...

I've run across a few web pages describing how to convert an arbitrary FIR filter to a minimum phase variant by the use of cepstral methods: e.g. > wn = [ones(1,m); 2*ones((n+odd)/2-1,m) ; ones(1-rem(n,2),m); > zeros((n+od d)/2-1,m)]; > y = real(ifft(exp(fft(wn.*real(ifft(log(abs(fft(x))))))))); etc. I've tried this algorithm on a few windowed-sinc filters and it seems to work...

## Re: Xilinx FFT core's IFFT function not working? Dun Xilinx TEST their cores before releasing them?

Hi, I have checked. the first input sample is fed in when index for xn is 3. I have followed the timing. But i found something further....

Hi, I have checked. the first input sample is fed in when index for xn is 3. I have followed the timing. But i found something further. The problem is due to the FFT result. Did you do this the last time? 1) generate 24 bit number 2) feed into the FFT 3) the 34 bit result which you obtain in VHDL testbench is piped into a text file. afterward, you IFFT the result in matlab the...

## IFFT in OFDM

inHi all, I'm trying to perform the OFDM modulation of a DVB-T system. So far, I have the complex valued carriers ck, 1705 altogether (for the...

Hi all, I'm trying to perform the OFDM modulation of a DVB-T system. So far, I have the complex valued carriers ck, 1705 altogether (for the 2k mode). To perform the 2048 point IFFT, somehow I have to map this 1705 carriers into 2048 values, xq. My question is, how should I perform this mapping? It seems to me that the solution would be symply padding with 2048-1705 zeros at the end of th...