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

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 prepa...

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

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 (...

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

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? Basic...

IFFT & DAC in IFFT

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...

DCT-IV using IFFT

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, -...

Scale data before or after IFFT?

Hello, I am working on a self-study project and try to implement a DMT transmitter in VHDL. This is the first time I am dealing with fixed-point implementation of a DSP algorithm. One of the blocks is an IFFT which outputs the time domain signal. At the end this signal is passed to an ADC, wh...

how to derive IFFT of boxcar filter

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 ...

Problems with IFFT

Hi, I'm kind of newbie in Matlab so I want to excuse wether the q=FCestion is too simple... I'm working with a link of two antennas and I want to obtain the ifft of a parameter. With an antenna design software I obtain the amplitude and phase in the frequency domain of such parameter. Then ...

how to do IFFT using only FFT?

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-value...

FFT and IFFT

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 5...

IFFT feeding order in DVB-T

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 T...

Efficient Calculation of Complex Analytic IFFT

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 ...

Use of FFT and IFFT in OFDM

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 ti...

Questions about IFFT!

Hi, I am a newbie in DSP. I am trying to get the impulse response of a Channel model, the channel model is in frequency domain(please see below) k_z(m)=(m-1/2)*pi/D;% k sub z k_r(m)=sqrt((2*pi*F(f)/c)^2-(k_z(m))^2); H=besselj(0,k_r(m)*r)+j*bessely(0,k_r(m)*r); Channel(f)=Channel(f)+(i/(2*D))*...

IFFT fixed point and AWGN channel

Hi, I am building an fixed point OFDM for 802.16,using 2^10 quantisation(ie the floating point values are multiplied by 1024). The system was working fine, so I decided to test with AWGN channel. The problem is that the code for AWGN that I have is for Floating point. I normalised the output o...

ifft problem!

I am learning DSP, I am trying to transform frequency domain function to time domain to get the time domain signal. Follwing is the code I used, The signal x(t) can be written as x(t)=2∧(t/2)-∧(t), and therefore its fourier transform is X(f)=4sinc^2(2f)-sinc^2(f). % MATLAB script f...

IFFT conversion using FFTW libraries

Hi, I am trying to convert a FFT and IFFT Matlab code to C using the fftw libraries. Hoiwever, I am stuck at a particular step: The Matlab command is: G = ifftn(P21,'symmetric'); ow do I convert this statement to C using the fftw library. I have tried the following steps: 1.I used fftw_plan_dft_...

needed help in radix 4 algorithm

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 r...

Calculating a "partial" IFFT

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 w...

overlap in the frequency domain

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 id...

FFT / 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 transfor...

IDCT

Hi! I just implemented an IFFT on a DSP and now I=B4d like to know, what has = to be done, so that I can use that IFFT as an IDCT. Thanks, Matthias ...

Oversampling in OFDM

Hi, I have a question related with the OFDM transmitter. What is the commonly method to increase the sampling rate ? - Increasing the IFFT size and insert zero in the inpput ? or - Insert zero in the IFFT output and followed by interpolation filter ? What is the trade-off ? anyone can h...

issues from ifft from real in only

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,...

IFFT in OFDM

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 mappin...

Re: fast convolution and normalization

Florian Schmidt wrote: > 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 neces...

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

Micha80 wrote: > The problem is, that values in in1 are all zero now. But there must be the > values 0...len-1 again. FFTW FAQ, Q3.16. ...

How to calculate IFFT based on FFT result?

Dear All, I just wonder if there is a simple way to calculate IFFT based on FFT results? Cheers, Yao ...

Fast Convolution: does it matter whether I normalize to block length (N) in the FFT versus in the iFFT?

Hi all, I have recently implemented a fast convolution algorithm using the FFT/iFFT to convert input signal and filter into the frequency domain, multiply them out, and iFFT them back to the time domain to get my result. It all seems to work fine, however, I recently got a little confused on one ...

Efficient implementation avoiding ifft

I have two pairs of variables x and y ,a and b,all of same length.I want to convolve a and b and save result as term1 and convolve x and y and save result in term2.then i cross correlate term1 and term2 to get the correlation coefficient. Because,time domain implementation takes much time,i tried t...

how to use ifwt instead of ifft in dmt modulator

dear all i am new to comp.dsp. i have just finished simulation of dmt using matlab. now i want to simulate dwmt.can i use my existing code? how to use ifwt instead of ifft.in matlab dwt and idwt function is available. but not ifwt or fwt which is suggested by many authers. need ur help for dir...

Baseband OFDM matlab simulation question

I am attempting to simulate a baseband OFDM communication system in MATLAB. I have the parallelized QAM symbols feeding into an IFFT, but this produces a vector of complex numbers. I found much information about taking the real and imaginary parts and modulating them with an In-phase and Quad...

OFDM Code---Not acheiving orthogonality after IFFT

seldata=rand(1,25)> 0.5; seldata2=2*seldata-1; %serial data in the form of -1 and 1 complex=complex(seldata2) %Mapping of data in complex nos aparadata=reshape(seldata2,5,5) %S to P in a 5x5 matrix sym=fliplr(aparadata) %Flipping ...

OFDM Code---Not acheiving orthogonality after IFFT

seldata=rand(1,25)> 0.5; seldata2=2*seldata-1; %serial data in the form of -1 and 1 complex=complex(seldata2) %Mapping of data in complex nos aparadata=reshape(seldata2,5,5) %S to P in a 5x5 matrix sym=fliplr(aparadata) %Flipping ...

TI dsp library

Hello, I want to use TI DSP library (more specifically its FFT and IFFT routines) on a 6414 processor. I heard that there is a bug in these routines that they disable interrupts and doesn't enable them on return. Is it true? Does anybody has any experience with these library funct...

Why Padding Zeros before OFDM IFFT?

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 ...

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 pwelch(), psd() and their varients but my results do not match the theory. i'll appreciate some help on the subject. thanks. ...

Re: Inverse FFT, Please Help!

Try the following octave (a Matlab clone) code #!/usr/bin/octave -qf t = 1:10; y1 = sin(t); Y = fft(y1); y2 = ifft(Y); diff = y1-y2; for i = 1:10 printf("%g\n", abs(diff(i))); end and you will get result similar to what I got below: 7.53521e-19 7.01452e-16 2.1673e-16 4.15459e...

Re: first post - first trick

I believe that's how the optimized mixed radix ifft works on c67. It uses a single precision, single cycle, approximate inverse (rcpsp?) instruction. It's supposed to be correct for powers of two. Since the ifft has to be a power of two, this is all you need for the division. I just multipli...

Re: OFDM and oversampling

If i well understand your answer : The Raised cosine Filter is not usefull in OFDM systems if I don't use all the IFFT bins ? > To go back to your original question, if you do not have sufficient > guard bands, i.e., if you are using almost all of your IFFT bins, then > oversampling may be req...