## orthogonality not acheived after IFFT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Started by in comp.dsp15 years ago 5 replies

Guys i am working on ofdm simulation.after taking the ifft of my crriers (having baseband data in the form of matrix) mycarriers are not...

Guys i am working on ofdm simulation.after taking the ifft of my crriers (having baseband data in the form of matrix) mycarriers are not orthogonal. As the ifft is responsible for making carriers orthogonal in order to acheive OFDM. I am using built in command of ifft in matlab. For eg x=ifft (carrier_matrix,128) then when i take dot product of my vectors the result is a non-zero number or...

## DVB-T Pre-IFFT on OFDM Symbol ...

Started by in comp.dsp16 years ago

I to write a simulator DVB-T (ex: http://dante.diei.unipg.it/~baruffa/dvbt/cdevelop.php). I am successful to implement the simulator until the...

I to write a simulator DVB-T (ex: http://dante.diei.unipg.it/~baruffa/dvbt/cdevelop.php). I am successful to implement the simulator until the Pre-IFFT phase (Data + Pilot + TPS) but now I am blocked to the preparation of the data before the IFFT (Pre-IFFT). In that way the data must be prepare before entering in block IFFT ? There is need to implement Hermitian Matrix ? But like ? Fo...

## Calculating a "partial" IFFT

Started by in comp.dsp16 years ago 8 replies

Hi All, I?m wondering if there is some way to save processing time when you want only a subset of the data from an IFFT. To be more...

Hi All, I?m wondering if there is some way to save processing time when you want only a subset of the data from an IFFT. To be more concrete, suppose you perform an N point IFFT on some frequency data, but you are interested in only a subset of the resulting time domain values. Is there a way to perform a smaller IFFT that will let you recover those values of interest? I am not speaking ...

## how to use IFFT to reconstruct signal in a specific region t in [a, b]?

Started by in comp.dsp15 years ago 9 replies

Hi all, Let's say by doing IFFT on F(v), which is the spectrum of signal f(t), I was able to reconstruct f(t), for t in [0, T]. Now I want...

Hi all, Let's say by doing IFFT on F(v), which is the spectrum of signal f(t), I was able to reconstruct f(t), for t in [0, T]. Now I want to ask is there a way to do another IFFT to reconstruct the specific part f(t) for t in [T, 2T], without any waste of previous calculations? Basically, I want to ask, if it is possible to use IFFT to reconstruct to any slot t in [a, b] in the t...

## IFFT & DAC in IFFT

Started by in comp.dsp16 years ago 1 reply

Hi, I am doing project in OFDM .I have doubts regarding the functionality of IFFT & DAC in OFDM TX. In OFDM block Where the carrier comes...

Hi, I am doing project in OFDM .I have doubts regarding the functionality of IFFT & DAC in OFDM TX. In OFDM block Where the carrier comes into picture?. After IFFT what is exactly done in DAC block?. There we are using any carrier suppliers?. IF possible anybody can explain the flow of data in OFDM Tx. can anybody help me out regarding the above queries. Thanks & Regards Lakku Raji...

## DCT-IV using IFFT

Started by in comp.dsp18 years ago 7 replies

Hello, I am trying to use IFFT to calculate the IDCT(Type 4). Can any one please explain how I am supposed to go about it. I am familiar...

Hello, I am trying to use IFFT to calculate the IDCT(Type 4). Can any one please explain how I am supposed to go about it. I am familiar with the procedure required to evaluate IDCT (Type I ) using IFFT but cannot seem to figure out how it is going to work for IDCT Type - 4. Thanks, -Mugdha

## FFT / IFFT

Started by in comp.dsp16 years ago 5 replies

Hello everybody, I'm a DSP newbie and have some basic questions. I want to process a signal with a FFT, a filter and then with an IFFT...

Hello everybody, I'm a DSP newbie and have some basic questions. I want to process a signal with a FFT, a filter and then with an IFFT back in a time-domain signal The test system has the following setup. 1.) FFT of the time-domain signal 2.) IFFT of the freq-domain signal Both transformation are with complex values. The ifft is implemented as fft with confugated input values. As t...

## IFFT feeding order in DVB-T

Started by in comp.dsp15 years ago 3 replies

Hi everyone! It's my first post here, so please be patient if I'm too newbie ;) I've tried a search in the newsgroup but no valid...

Hi everyone! It's my first post here, so please be patient if I'm too newbie ;) I've tried a search in the newsgroup but no valid results. I'm trying to make a DVB-T transmitter in VHDL, but I find some problems when feeding the IFFT. For example, I'm using the 2k mode. After insertion of TPS and pilots, I have 1705 (sub)carriers. The IFFT accepts 2048 couples-data of real and imaginar...

## In OFDM, do we need to send all the outputs of the IFFt block?

Started by in comp.dsp8 years ago 5 replies

In OFDM Transmitter, when you do the IFFT of input samples x(0),x(1),x(2)....x(N-1), then at the output of the IFFT block you get a sequence...

In OFDM Transmitter, when you do the IFFT of input samples x(0),x(1),x(2)....x(N-1), then at the output of the IFFT block you get a sequence X,X,....X[N-1]. My question is, that do we then transmit X,X,....X[N-1] one by one over the channel (and hence the need for parallel to serial blockafter IFF block)? If that is so, don't you think we only need to transmit only one element fr...

## Efficient Calculation of Complex Analytic IFFT

Started by in comp.dsp17 years ago 1 reply

Hi All, My question is as follows. When calculating an N-point IFFT with the inputs conjugate symmetric (real output), this can be performed...

Hi All, My question is as follows. When calculating an N-point IFFT with the inputs conjugate symmetric (real output), this can be performed using a single N/2-point IFFT and some pre and post processing. Is there any method to do this (use a single N/2-point IFFT) with half the inputs set to zero instead of the complex conjugate? (and thus getting the complex analytic output instead of the ...

## how to derive IFFT of boxcar filter

Started by in comp.dsp14 years ago 34 replies

Hi, We can very well represent brickwall filter in FFT domain. Also we know that IFFT of brickwall will look like sin(x)/x function...

Hi, We can very well represent brickwall filter in FFT domain. Also we know that IFFT of brickwall will look like sin(x)/x function extending towards +/- infinity. How to derive this using IFFT equation?? Regards Bharat Pathak Arithos Designs www.Arithos.com

## how to do IFFT using only FFT?

Started by in comp.dsp18 years ago 9 replies

Hi all, Suppose we are only given the function for FFT, but we don't have IFFT routine... and we have a real input data squence...

Hi all, Suppose we are only given the function for FFT, but we don't have IFFT routine... and we have a real input data squence x, y=fft(x), now how to use FFT only to obtain the x=ifft(y)? -------------------------------------- What if the input data sequence x is complex-valued? Thanks alot

## ifft and fft in matlab

Started by in comp.dsp13 years ago 4 replies

hi i want to ask whether there is any difference between taking n-point ifft and then fft for OFDM Vs taking ifft and then n-point fft in...

hi i want to ask whether there is any difference between taking n-point ifft and then fft for OFDM Vs taking ifft and then n-point fft in matlab. the difference i get is the signal with n-point ifft and then fft has a spectrum which do not have good resolution can anyone help me in this regard. Regards

## FFT/IFFT on real signals

Started by in comp.dsp12 years ago 2 replies

Dear all, I have a question about the FFT and IFFT on real signals. For example, I want to perform 512-point FFT/IFFT pair on real...

Dear all, I have a question about the FFT and IFFT on real signals. For example, I want to perform 512-point FFT/IFFT pair on real signals, x, x, ... , x. There is a well-known method that 512-point FFT on real signals can be simplified to 256-point FFT. However, how about the IFFT? The spectrum of real signals is conjugate symmetric about N/2. I need to perform 512-point IFFT or ...

## OFDM modulator

Started by in comp.dsp14 years ago 2 replies

Hi, I have problem concerning process of generating OFDM signal. From what I know, the real part of IFFT is sampled OFDM signal. So why after...

Hi, I have problem concerning process of generating OFDM signal. From what I know, the real part of IFFT is sampled OFDM signal. So why after IFFT block is IQ modulator that uses real and imaginalis part of IFFT? Why we do not take the real part of IFFT and then convert it to analog signal and then upconvert to the IF frequency? And what about real part of OFDM signal at the output of IQ modula...

## Use of FFT and IFFT in OFDM

Started by in comp.dsp16 years ago 1 reply

Looking at the discrete equation for DFT and its inverse(algorithm wise FFT and IFFT), it is evident that the results are the same, especially if...

Looking at the discrete equation for DFT and its inverse(algorithm wise FFT and IFFT), it is evident that the results are the same, especially if you consider the magnitude. After the base band symbol mapping, the result looks to be in the frequency domain already. Why go through a conversion to time domain through IFFT and again mapping this onto a frequency up conversion.

## IFFT and FFT of a real signal in OFDM

Started by in comp.dsp9 years ago 2 replies

Hi, I'm developing an OFDM system. In the transmitter I have taken 4 transmission symbols. Then zero padding is done according to IFFT size...

Hi, I'm developing an OFDM system. In the transmitter I have taken 4 transmission symbols. Then zero padding is done according to IFFT size and to get a real signal after IFFT, I have taken the symmetry of that. The problem is I'm not receiving the same transmitted symbol stream after doing FFT at the receiver (transmission channel is not included yet). Please correct my MATLAB code. ...

## FFT and IFFT

Started by in comp.dsp16 years ago

i am doing a project on audio watermarking. in this after shaping the moise spectrum according to the frequency mask of the human auditory system,...

i am doing a project on audio watermarking. in this after shaping the moise spectrum according to the frequency mask of the human auditory system, i am taking IFFT of the noise samples. the thing is that the number of frequency bins for the unfiltered noise and the mask are both 512. so i will get 512 points as the product of the above two . now i need to take ifft of 384 samples as per MPEG Audi...

## overlap in the frequency domain

Started by in comp.dsp15 years ago 7 replies

Hi, Anyone know a way to overlap successive blocks of FFT data in the frequency domain as opposed to having to IFFT then overlap in the...

Hi, Anyone know a way to overlap successive blocks of FFT data in the frequency domain as opposed to having to IFFT then overlap in the time domain, as part of a partioned convolution process im doing: loop x { FFT > Multiply > IFFT } overlap/accumulate > output (and so x IFFTs) when ide like to do: loop x { FFT > Multiply > overlap/accumulate } IFFT > output (just 1 IFFT) but im n

## Iterative IFFT

Started by in comp.dsp8 years ago 2 replies

Hello. I have an application where I am using IFFT to generate a number of precomputed tables each table[n] containing pow(2, n)...

Hello. I have an application where I am using IFFT to generate a number of precomputed tables each table[n] containing pow(2, n) frequency components/bins. The way this is done is by regular IFFT: synthesize(fdomain) for each(table:n) table[n] = IFFTreal(data:=fdomain, size:=pow(2, n) As such, each table[n] is half the size of the next one, and also contains only half the frequencies....