IFFT is not working

Started by Il Totem in comp.dsp10 years ago 11 replies

I am struggling to make IFFT work, but I have had a few problems. I have read over the Internet that it is relatively simple to compute an IFFT of...

I am struggling to make IFFT work, but I have had a few problems. I have read over the Internet that it is relatively simple to compute an IFFT of a frequency domain: conjugate the frequency domain's samples, than compute a direct FFT on them, and therefore take the conjugate of the output. I have tried with a 4-points FFT with a simple sinusoid time domain signal (only real parts set: 1, 0, -1, ...


How many samples are there in one period of a subcarrier which is produced after IFFT in OFDM systems?

Started by runinrainy in comp.dsp4 years ago 4 replies

Hello, In an OFDM system, by using N subcarriers we get one OFDM symbol. But before that the data is first mapped into frequency domain by...

Hello, In an OFDM system, by using N subcarriers we get one OFDM symbol. But before that the data is first mapped into frequency domain by the constellation mapper and we get N-parallel streams as an input to the IFFT process. The IFFT takes these N-parallel streams and produces N-parallel subcarriers in time domain, all these subcarriers are in digital form and has different frequencies. Let?...


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

Started by Ron Gerhards in comp.dsp14 years ago 24 replies

Hi all, I have recently implemented a fast convolution algorithm using the FFT/iFFT to convert input signal and filter into the frequency...

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 point. I need to determine the gain that my filter will be applying to the signal. I've done thi...


IDCT

Started by Matthias Alles in comp.dsp15 years ago 2 replies

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...

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


After IFFT, Real and Imaginary have the Same PDF(Gaussain )

Started by tmnhuda09 in comp.dsp9 years ago 1 reply

The real and imaginary have the same PDF(Gaussain PDF)after IFFT of complex signal. But in my matlab code it looks different. why? can anybody...

The real and imaginary have the same PDF(Gaussain PDF)after IFFT of complex signal. But in my matlab code it looks different. why? can anybody explain it please? here is my code N=10; ml=2; for p=0:1000-1 x=randint(N*ml,1)*2-1; ich = x((1:N),1); qch = x((N+1:ml*N),1); x1=ich+qch*i; y=ifft(x1,10); yr=real(y); yi=imag(y); env=sqrt(yr.^2+yi.^2); for i=1:10 real_p(p*10+i)=yr(i...


Basic IFFT Question - Please tell me if this is correct ...

Started by Lord Labakudas in comp.dsp15 years ago 4 replies

Hi, I have collected the complex transfer function H(f) of a device using a network analyzer. The data is between frequencies f1 and f2...

Hi, I have collected the complex transfer function H(f) of a device using a network analyzer. The data is between frequencies f1 and f2 and there are N available points (N is usually odd). I wish to use IFFT to study the time-domain response of the system. Now, my frequency resolution, fR = (f2 - f1)/(N-1). Hence, my sampling time would be tS = 1/(N*fR) which gives, tS = (N-1)/(N*(f2 - f...


Care to give me the IFFT of this 64 lines of data?

Started by Confused Frank in comp.dsp14 years ago 4 replies

First column is line number, I need the IFFT if Second (b) and third column (c). I used this function, but the result I got was different...

First column is line number, I need the IFFT if Second (b) and third column (c). I used this function, but the result I got was different from another source. -------------------------------------------- [a,b,c] = textread(...blah blah...); f = b + i * c; t = zeros(size(t1)); for j = 1:1:N t(j) = 1/N * sum( f' .* exp( i * 2 * pi * (0:1:(N-1)) * (j-1)/N) ); end --------------...


Oversampling in OFDM

Started by Mas Bas in comp.dsp14 years ago 1 reply

Hi, I have a question related with the OFDM transmitter. What is the commonly method to increase the sampling rate ? - Increasing the IFFT...

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 help ? Thanks. Buzz


IFFT fixed point and AWGN channel

Started by shan_100 in comp.dsp13 years ago 2 replies

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...

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 of the IFFT by- IFFt symbol = Symbol / sqrt(real*real+imag*imag), and converted this to float. Th...


OFDM symbol

Started by harishm in comp.dsp5 years ago 1 reply

Hi, I have a question on IFFT input in OFDM systems. Why center tone is always set to ZERO for IFFT input ? is it one method to reduce...

Hi, I have a question on IFFT input in OFDM systems. Why center tone is always set to ZERO for IFFT input ? is it one method to reduce PAPR in OFDM systems ? _____________________________ Posted through www.DSPRelated.com


How to calculate IFFT based on FFT result?

Started by Yao Sics in comp.dsp12 years ago 7 replies

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

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


IFFT in OFDM

Started by velan in comp.dsp10 years ago 3 replies

Dear sir / Madam, I am doing M.E in Communication system, i have gone through the concept and fundamentals of OFDM first time , but i could...

Dear sir / Madam, I am doing M.E in Communication system, i have gone through the concept and fundamentals of OFDM first time , but i could not understand the process of IFFT in OFDM modulation, why FFT is not taken at the first stage? if any kind personality explains the concepts behind the IIFT in OFDM, which will helpful for me to understand better. How can i get e-version of any OFDM text...


how to use ifwt instead of ifft in dmt modulator

Started by pradip.varade in comp.dsp13 years ago

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...

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 direction . thanks in advance. pradip


IFFT wrapping?

Started by Pawel in comp.dsp11 years ago 9 replies

Hello All, I did some very simple ifft of real valued vector representing frequency domain samples ie. X[n]=[1 2 3 3 2]; imaginary part is 0...

Hello All, I did some very simple ifft of real valued vector representing frequency domain samples ie. X[n]=[1 2 3 3 2]; imaginary part is 0 for all samples, to my surprise recreated time domain signal is h[n]=[2.2 -0.52 -0.076 -0.076 -0.52].Those two last samples in h[n] look like they are just symmetry around first sample. According to my knowledge this should represent noncausal filter...


real values of time domain after IFFT

Started by kengkc in comp.dsp11 years ago 3 replies

Hi, I have some problems regarding IFFT used in Matlab. I have a frequency range from 2M to 4M Hz where I have obtained the datas into 1601...

Hi, I have some problems regarding IFFT used in Matlab. I have a frequency range from 2M to 4M Hz where I have obtained the datas into 1601 data points. Currently, I am trying to get the real values of time domain. Currently, I have IFFT the data obtained (1601 points) and plotted out the time domain waveform. Currently, I am having problem in determine the real time axis of waveform for 1...


OFDM Modulator

Started by vanessa_lima in comp.dsp13 years ago

Hi Everybody... Good Afternoon. My name is Vanessa. I?m an engineer and I?m developing a prototype of an OFDM Modulator. The configuration I...

Hi Everybody... Good Afternoon. My name is Vanessa. I?m an engineer and I?m developing a prototype of an OFDM Modulator. The configuration I choosed was: 2K IFFT, 64QAM and 1/16 for the cyclic prefix.The sampling frequency used in the IFFT was 12.5MHz. When I did the cyclic extention, the output spectrum became filled with running spurious tones, overlaping the correct base band signal. My q...


Scale data before or after IFFT?

Started by Guenter Dannoritzer in comp.dsp15 years ago 2 replies

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...

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, which has at the most a precision of 16-bit. My question is now whether I should scale my data at t...


TI dsp library

Started by mans in comp.dsp12 years ago 2 replies

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...

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 functions? Is there any other fixed point FFT (IFFT) library that I can use? Regards ...


Problems with IFFT

Started by Anonymous in comp.dsp12 years ago

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...

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 I have to construct the complex parameter with the amplitude and phase and finally I have to apply...


OFDM Question

Started by Crisanquito in comp.dsp10 years ago 2 replies

Hello I have got a simple question about the OFDM transmitter and the spectrum we obtain after IFFT processing-DAC-IQ modulator. It must be...

Hello I have got a simple question about the OFDM transmitter and the spectrum we obtain after IFFT processing-DAC-IQ modulator. It must be very simple because I have not found anything to clear my mind. I just do not understand how we can obtain a symmetric location of all the subcarriers after a N-IFFT processing, with N even, if one of the subcarries is located at 0 frequency: even numbe...