Questions tagged [modulation]
Modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with the amplitude of low-frequence modulating signal which typically contains information to be transmitted.
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Why does the frequency in fft plot of the baseband modulated signal isn't changing at the receiver
I have designed a transceiver system for cellular frequencies(800MHz). On the receiver side, I have converted the band signal to baseband signal through digital mixing. I have added the Inphase and Q ...
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Pre-envelope of an FM signal $s(t) = A\cos[\omega_ct + B\sin(\omega_xt)]$ [duplicate]
I want to ask a question about pre-envelope of an FM wave:
$$s(t) = A\cos[\omega_ct + B\sin(\omega_xt)]$$
Can someone explain briefly how we calculate the pre-envelope of this signal?
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Can someone explain the Walsh modulation sequence of “0” and “4”? [closed]
can someone explain the tribit sequence generation please ? and the meaning of "0" and "4" ?
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What is difference between Phase shift keying (PSK) and Quadrature Amplitude Modulation (QAM) mathematical equation
I went through a literature and found the following expression for PSK signal. On this basis, what will be the equation for **QAM signal **. Also from where i would be able to read about this equation ...
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BFSK modulation coding on MATLAB
Like for BPSK we generate random bits and then
data= round(rand(1,num_bit));
%Generate binary data
bpskModulated = 2*data-1 % mapping to -1 and +1
Can we do ...
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Non coherent detection BFSK demodulation?
I am simulating BER performance of BFSK under AWGN and Rayleigh fading, BFSK has two symbols one entirely on the real plane while other on the complex plane for representing let's say zero and one, ...
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1answer
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Next steps for analyzing this PWM algorithm and choosing a low pass filtering technique?
The Broadcom BCM2711 GPIO controller used by the Raspberry Pi has a hardware PWM implementation option using an algorithm that provides an average value defined by a rational fraction $N/M$ defined as ...
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How to find the noise power in my simulation
I am currently working a tricky communication chain that I want to simulate into Matlab.
The chain is like a classic BPSK modulator/demodulator chain, but where the BPSK modulated signal has been ...
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1answer
35 views
Channel encoding after digital modulation
Generally, when using channel encoding followed by interleaving, that process should be performed before the modulator and the system structure should be like that :
For me, I only use the ...
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1answer
17 views
How to demodulate PM modulation
I'm using a sin wave $s_{sc}(t) = d(t)\cos(\omega_{sc}t + \varphi_{sc})$ to modulate a carrier using phase modulation. I'm working on Matlab so I use the pmmod function to do so. It is not too ...
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1answer
31 views
Is there use of $\pi/8$-DQPSK as shown in MATLAB's documentation?
I was reading MATLAB's documentation on dpskmod. They gave an example of an $\pi/8$-DQPSK. I felt that this is strange as I have seen $\pi/4$-DQSPK and $\pi/8$-...
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Nyquist Rate of cosine modulated function
Here's my understanding:
$$y(t) = x(t)~ \cos(\Omega_0 t)$$
I take the Fourier transform of y(t) and I get this result:
$$Y(\Omega) = \frac{1}{2}X(\Omega - \Omega_0) + \frac{1}{2}X(\Omega + \...
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Representing the signal $ u(t)=A_c \cos (2 \pi f_c t + \beta \cos 2 \pi f_m t) $ in terms of Bessel function
I want to represent the signal $ u(t)=A_c \cos (2 \pi f_c t + \beta \cos 2 \pi f_m t) $ in terms of Bessel function. I have done the exercise. I want someone to check whether what I have done is ...
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Model of modulator and demodulator in Simulink. Why is MER so lowest?
I created a simple model in Simulink of a quadrature modulator, amplifier and quadrature demodulator. On the oscilloscope(scope in Simulink) and spectrum analyzer the displayed results look normal (at ...
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1answer
36 views
Conditions for analytical signal reconstruction with the Hilbert Transform (HT)
I'm new to the Hilbert Transform, I was reading the paper: "SISAR Imaging - Radio Holography Signal Reconstruction Based on Receiver-Transmitter Motion", and the next sentence was written in the paper:...
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CDMA scheme that preserves constant envelope (NRZ/ASK shape)
(This is a followup question to Is this a "valid" CDMA modulation?)
Is it possible to find a CDMA scheme in which the receiver can only have a simple slicer?
In other words, for the ...
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Is this a “valid” CDMA modulation?
I am banging my head against (specific aspects of) CDMA for a few days. At the basic level I am confused about the interrelation between implementations that are modeled as mixing and fully digital ...
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MATLAB: Issue with passing data through AWGN Channel [closed]
I am trying to send QAM data through AWGN channel and I have 256 samples/symbol, I have the following code:
...
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1answer
28 views
Phase Noise in Constellation Plot
I have the following phase noise plot (-100dBc/Hz @ 1MHz offset and -130dBc/Hz noise floor):
The integrated phase jitter for this phase noise is around $4.6^\circ$. According to my understanding the ...
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2answers
38 views
What is symbol in signal processing?
I am new to signal processing and have been trying to understand the terminology. I came across this statement: "Assuming the signal modulation $\mathfrak{M}$ has an alphabet A of M symbols and the ...
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1answer
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Please clarify the mandatory condition on Vestigial Sideband Modulation filter?
In VSB filter we have the Transfer function condition as $H(F-F_c)+H(F+F_c)=1$
So can we accept that for the range of $F$ in $(F-df,F_c)$ we have $H(F)$ and for $(F_c,F+dF)$ we have $A-H(-F)$ where $...
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Why does my digital upconversion result in two tones?
I am using Xilinx's RFSoC in I/Q mode. The important point is that in the digital space I have real and complex samples. I take the incoming data and multiply it by a complex sinusoid.
In my test ...
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How do you determine the power required for a phase shift keying modulation scheme?
This wiki article has a diagram :
which shows how the message "11000110" is conveyed as a waveform.
I'm trying to understand how the power to transmit this message can be determined.
Do I need ...
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Please, help me interpret my Simulink simulation of AM. Why does carrier not appear in the spectogram?
Carrier is 2 * pi * 25, modulating signal is 2 * pi, all the amplitudes are 1s and zero phase.
I realized that I could add a sine wave right at the end. I get a carrier in frequency domain, but my ...
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58 views
I/Q Signal Power Calculation
I am trying to understand the basics of IQ modulation. The amplitude of a demodulated IQ signal is given as $\sqrt{I^2 + Q^2}$ which is easy to understand from the phasor diagram.
Yet, I don't ...
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1answer
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Serial to Parallel Converter
in many texts about modulators I have seen there is a component called "Serial to Parallel Converter". For instance, let's consider this scheme and let's focus on the second block (reference):
The ...
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1answer
45 views
Confusion about collection of bits and symbols
I'm taking an intro communications module and I'm quite confused on what the term "symbol" really means?
Consider this setup:
My understanding is as folllows
After the information source, we have ...
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34 views
Is this PSK or FSK
I am analysing a captured 433.92MHz signal sampled at 2MHz:
If we zoom in:
I am thinking this is PSK? Am I wrong?
Thanks
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Can you help me to understand Multi-tone FSK, and how I can implement it?
Any paper, book, Matlab file... that you would recommend.
Thanks.
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1answer
29 views
FM: Do rational ratios of carrier to modulator signals really produce harmonic spectra?
I've read that in FM, all rational ratios of the carrier frequency to the modulator frequency produce harmonic spectrum in the FM signal. Link to what I read.
I don't understand why this is. If for ...
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Getting hilbert transform of IQ signal
Im new to communications so this may be a stupid question, but I am somewhat confused. I am trying to train an automatic modulation classification (AMC) algorithm on IQ data from the RadioML dataset. ...
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1answer
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Modulation classification via demodulation confidence?
I'm not sure if this is the right place to post this question, but will try anyway :-)
I recently started reading up on the field of automated modulation classification (AMC) where an algorithm ...
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1answer
58 views
Phase response distortion due to IQ demodulation
I have a bandpass signal, I do IQ demodulation meaning:
first step:
$IQ(t) = x(t)*exp(-2\pi f_ct)$
second step:
low pass using $filtfilt$ function in MATLAB. (in order to avoid phase ...
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1answer
26 views
inter symbol interference vs digital modulation
I am a little confused after my lecture today. My professor started off with explaining what inter symbol interference (ISI) is and he ended the lecture talking about the different types of digital ...
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What is the range for a demodulated AM signal?
Lets say I perform amplitude modulation (modulation index = 1) of a signal that has a range of [0, 1]. If I demodulate by taking the absolute value of this signal and then low-pass filter it, what ...
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Why do we integrate the modulating function in FM?
I've been reading about FM and I keep coming to an expression, where the instantaneous phase
$$\Theta=2\pi f_it+\phi\text, \tag1$$ where
$$f_i=f_c+k_fm(t)\text,\tag2$$
($f_c$ being the base carrier ...
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2answers
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Why is the carrier suppressed by AM-DSB-SC modulation?
Lets say I have a message that is a sine wave at 1KHz. As I understand it, I can perform amplitude modulation by multiplying this signal with a carrier, lets say 10KHz, and this process is essentially ...
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2answers
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Could modulation/coding schemes be generated from an AI?
Warning: I'm a bit of a noob with respect to this entire field, but I took some classes on it (a few years ago) and found it fascinating.
Anyhow, as far as I understand it, modulation is the process ...
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QAM and APSK error comparision [closed]
Due to the 16QAM and 16APSK characteristic, is there exact comparison between 16QAM and 16APSK BER?
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1answer
49 views
The sound of modulated audio signal
As I was learned in signal processing, modulation took the signal spectrum to higher frequency range, so I made an experiment for audio file. The audio file "handel.ogg" plays a small part of music "...
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Length of CDMA code and message length vs. number of participants
What is the minimum code size for CDMA codes for synchronuous CDMA (not asynchronous CDMA!) with N number of participants?
Furthermore, suppose N parties want to uniquely transmit a message of length ...
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Learning PSK Modulation and Demodulation - Good Text to Read?
Title sums it up. I am curious to see what you all suggest. I'm a newbie and just need some beginner/intermediate material.
Thanks!
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What is DAB modulation in signal generators?
I am using R&S signal generator and for generating a DAB signal there is an option for mentioning the modulation level in %. For example, we can generate DAB modulation 50% . I can understand that ...
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OQPSK - GNU Radio Companion
I was wondering if anyone has had any success in implementing OQPSK in gnuradio.
I have a working theory of expanding on the Constellation Modulator to include a custom OQPSK function.
I have ...
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What's wrong with my M-ary ASK modulation demodulation MATLAB code?
My MATLAB code linked below implements ASK modulation of an M-ary signal, impresses it on a carrier, adds AWG noise of various SNRs. Then, for each SNR, demodulates the signal and calculates the ...
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GNU Radio - Bandwidth and Band Reject Filter
I am currently trying to generate a psk modulated carrier with gnu radio.
Attach is an image of my flow graph.
As can be seen I am generating a bit stream using the Random Source module and ...
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Pulse shape estimation
Given a captured noisy BPSK signal, how do I formulate the maximum-likelihood problem so as to estimate the matched filter? The model of interest would be baseband BPSK with AWGN:
$$c(t) = \sum_{\ell=...
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1answer
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Mapping soft symbols in DQPSK
I'm trying to soft decode DQPSK. According to this paper the bits are:
$b_1 = \mathrm{Re}\{s_n s^*_{n-1}\}, b_2 = \mathrm{Im}\{s_n s^*_{n-1}\}$
If I put 0.707 as a 100% probability of 0:
$\begin{...
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1answer
27 views
Modulation with Maximum Likelihood decoder and capacity
My question comes from the high spectrum efficiency claim of OFDM. This seems not correct IMHO, at least theoretically.
For me, we lose energy in using cyclic prefix, hence OFDM should be a waste of ...
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1answer
137 views
Binary and Quadrature Phase Shift Keying [duplicate]
I was learning Modulation Techniques and was on the topic Phase Shift Keying (PSK). As far as I have understood,
In Binary PSK we encode a single bit on a one signal element and we differentiate ...
