## Forums Search for: complex

## Real and Complex value for AWGN & multipath channel

inHi, I noticed that the value for AWGN & multipath channel could be real & complex value. Thus, in a practical wireless system, these values...

Hi, I noticed that the value for AWGN & multipath channel could be real & complex value. Thus, in a practical wireless system, these values should be real or complex? For simulation purpose, when should I apply the real value and when should I apply the complex value? Or it is dependent on the transmitted signal? Many thanks. Richard

## complex output from matlab IFFT

inWhy am i getting complex output when i compute the inverse fft of a vector of complex numbers? This does not happen always and the imaginary...

Why am i getting complex output when i compute the inverse fft of a vector of complex numbers? This does not happen always and the imaginary part of the output is very small compared to the real part. thanks for any insight jeremy

## complex matrix inversion

inHello I need to invert square complex matrixes of sizes 52x52,64x64 and 128x128 in MS VC++6.I need to implement it as fast as possible....

Hello I need to invert square complex matrixes of sizes 52x52,64x64 and 128x128 in MS VC++6.I need to implement it as fast as possible. I have written a code for complex matrix inversion but it takes lot of time. (e.g. a complex matrix inversion of 52x52 matrix takes more than 2ms) Can any one tell me free intel library or any other related library to do my task more fastly? ...

## Converting complex signals to real

inHello: I'm trying to figure out how best to convert a complex signal to a real. I've heard of one approach that says to take the magnitude...

Hello: I'm trying to figure out how best to convert a complex signal to a real. I've heard of one approach that says to take the magnitude of the complex sample and use that as the real sample. And another approach where you just drop the imaginary part. Are there other techniques? If I'm looking to convert the complex signal to an audio format, is one approach better than the other?...

## complex convolution

inDear All, I would like to convolve two complex sequences. Could anybody help me how to define the convolution of two complex sequences...

Dear All, I would like to convolve two complex sequences. Could anybody help me how to define the convolution of two complex sequences please? Thanks in advanced. Regard, estdev

## Complex baseband

inHowdy, For FM/AM demod, you require a complex baseband. I am downconverting the IF from 1MHz to baseband by multiplying the input stream (12...

Howdy, For FM/AM demod, you require a complex baseband. I am downconverting the IF from 1MHz to baseband by multiplying the input stream (12 bits) from the ADC with Sin and Cosine outputs of a DDS and therefore, generating I, Q I am using standard 18x18 signed multipliers in Xilinx to do the mixing. Is this right or should I use a complex multiplier? The reason why I am asking this question...

## What is the meaning of complex values in results from an IFFT?

inOK, I understand that when you do an FFT on an array of real values you get an array of complex numbers. Where each complex number represents a...

OK, I understand that when you do an FFT on an array of real values you get an array of complex numbers. Where each complex number represents a frequency wave (sine), the magnitude representing amplitude of the wave and the argument (angle) representing the phase. But when you do an IFFT, what does a complex number represent in the output array? When you are working with IFFTs an

## Hilbert Transform Problem

inDear All, I have a question regarding hilbert transformer. If i take the bandpass signal and sample it it would be real. Now when i multiply...

Dear All, I have a question regarding hilbert transformer. If i take the bandpass signal and sample it it would be real. Now when i multiply it with a complex exponential to downconvert it I get a complex baseband signal. On the other hand, if i take the bandpass signal, pass it through a hilbert transformer and get a complex signal, and then downconvert using complex multiplication i get di...

## Re: Possibly unrelated questions

inHi Richard, One of your comments gave me a little laugh-- "I don't have too much problem with complex notation and its advantages per...

Hi Richard, One of your comments gave me a little laugh-- "I don't have too much problem with complex notation and its advantages per se." In contrast, I have a terrible problem with complex notation. I'd even go so far at to call it the "scourge of DSP." Let me stand on my soap box a bit. There is no question that complex numbers are elegant and enable some techniques that could not ...

## Thinking about complex numbers

inGreetings Earthlings, It's been a bit quiet here on comp.dsp for the last few days, so I thought I'd post something with the sole...

Greetings Earthlings, It's been a bit quiet here on comp.dsp for the last few days, so I thought I'd post something with the sole purpose of rattling your cages. Regarding the complex-valued j-operator, where j = sqrt(-1), I was thinking about the interesting notion that j raised to the j-th power, j^j, is a real-valued number. To increase my limited knowledge of complex nu...

## Interpolation of a complex transfer function.

inHello all I have a complex transfer function e.g. like this: Y=[0.1+0.2i, 0.3+0.77i, 0.11+0.22i] corresponding to a frequency vector e.g....

Hello all I have a complex transfer function e.g. like this: Y=[0.1+0.2i, 0.3+0.77i, 0.11+0.22i] corresponding to a frequency vector e.g. X = [1, 3, 5] Now I want to have the frequencies between the points of my oryginal vector e.g. X1=[1.2, 2.5, 4.2, 4.8, 4.9] And I want to find a corresponding vector Y1 of complex values. The question is whether I can perform an interpolati...

## Complex Filter bandwidth - newbie question

inA DDC requires an output bandwidth of 80% of the output sample rate. A complex mixer generates I and Q signals from the real input, I and...

A DDC requires an output bandwidth of 80% of the output sample rate. A complex mixer generates I and Q signals from the real input, I and Q are decimated and filtered. To achieve the 80% complex bandwidth requirement are the individual I and Q the filter passbands at Fs-out * 0.8 or 0.4? Thanks!

## Is there a way to reduce the number of operations in this FFT procedure?

Hi all, Suppose my signal is a complex valued signal, and it is complex conjugated with respect to the center t=0. That's to say...

Hi all, Suppose my signal is a complex valued signal, and it is complex conjugated with respect to the center t=0. That's to say f(-t)=f(t)*, where "*" denotes the complex conjugate. Suppose now I do the truncation of above signal into between [-B, B), and I sample it using stepsize dB, then in Matlab, the sampling points are cfs=[-B:dB:B-dB], which has 2B/dB data points, e.g. ...

## real input FFT for SDF architecture

inHi forum, I have a complex input FFT core implementation for FPGA. Now I want redesign the core to reduce the logic for real input...

Hi forum, I have a complex input FFT core implementation for FPGA. Now I want redesign the core to reduce the logic for real input sequences. I use SDF (single delay feedback) architecture. Output is 1 complex sample per clock. The standard 2N real FFT with N complex FFT doesn't work for me. The difference between 2N and N point FFTs is only one butterfly stage (one complex multiplication a...

## Computing complex phase rotation in fixed-point

inGreetings, I'm looking for a quick way to computing complex phase rotation in fixed-point, basically for a given complex number X and phase...

Greetings, I'm looking for a quick way to computing complex phase rotation in fixed-point, basically for a given complex number X and phase theta, I'd like to compute: Y = X exp(j theta). I know that I can use CORDIC to first find Z = exp(j theta), and then do a complex multiply, but I'm hoping for a shortcut given that I am only rotating, and not scaling. If it makes a differe...

## LMS Pseudo Inverses of Complex Matrices

inI have an overconstrained system of equations (m equations in n variables with m> n) where the variables are complex. Using the...

I have an overconstrained system of equations (m equations in n variables with m> n) where the variables are complex. Using the Moore-Penrose pseudoinverse method of solution is giving me results that are terribly counterintuitive. Does anyone know what exactly is minimized in the least squares sense when the variables and solution coeficients are complex? Thanks, Bob -- "

## FFTW_BACKWARD: Every other element looks bad

I use the following code to get an RFT of an 8 byte complex data array. sPadding=1 in this case. typedef struct...

I use the following code to get an RFT of an 8 byte complex data array. sPadding=1 in this case. typedef struct Complex_Struct { float fReal; float fImaginary; } Complex; ERROR_NUMBER CMyLib::FFTWMake1DInverseFourierTransform(Complex *cpInputVector, float **fppOutputVector, DWORD dwVectorLength, short sPadding) { fftw_complex *in, *out; fftw_plan p; size_t stNumElem...

## Using FFTW with blocks of Complex input...

inI am using FFTW 3.0.1 with a C-program I'm developing. My input data consists of a block of complex data for M channels ordered in the following...

I am using FFTW 3.0.1 with a C-program I'm developing. My input data consists of a block of complex data for M channels ordered in the following fashion: input = [ chan1_sample0, chan1_sample1,...,chan1_sampleN-1, chan2_sample0,...,chan2_sampleN-1,...,...,chanM_sample0,...,chanM_sampleN-1] I would like to take advantage of the "Advanced Complex DFT" capability (e.g.-fftw_plan_many_dft()) to...

## complex baseband

inHello all, I am currently working on analysing a VHDL code of a FM baseband receiver. I have a block in VHDL which accepts 2 inputs 1)one...

Hello all, I am currently working on analysing a VHDL code of a FM baseband receiver. I have a block in VHDL which accepts 2 inputs 1)one from the AD converter and 2)other a sawtooth wave this block produces 2 outputs 1)complex baseband I 2)complex baseband Q There is a lookuptable within this module.I hope he has used CORDIC in his design.But iam not sure what this does to ...

## Convolution using real-valued FFT

inI have implemented the basic overlap-add convolution using a standard complex FFT routine. This has lots of zeroes, first from padding data and...

I have implemented the basic overlap-add convolution using a standard complex FFT routine. This has lots of zeroes, first from padding data and IR (impulse response) to FFT size, then I have to copy data and IR to complex numbers (with zero imaginary part). Now I tried instead to replace the complex FFT routine with a real-valued FFT so I can skip copying all data and IR to complex numbers. ...