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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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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20 views
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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41 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
23 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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22 views
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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416 views
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
53 views
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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34 views
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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38 views
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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33 views
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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40 views
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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72 views
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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55 views
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
41 views
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
24 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
110 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 ...
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26 views
How to make SL to RF inport in simulink work real time?
I am using qam in the simulink and need to upconvert the complex baseband data and obtain the time domain passband signal.
I pass the complex baseband data to SL to RF inport and then do the ...
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1answer
47 views
Demodulation of OFDM symbol in LTE for multi-user case
I was trying to understand what exactly happens when you try to modulate an ofdm symbol in the downlink in LTE for multi-user case.
When we modulate, usually we allocate different sets of RBs for ...
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40 views
Explanation for the following code in python [closed]
x=2 *(rand(N) >= 0.5) - 1
Can someone please explain how the above expression corresponds to BPSK signal please?
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Why bit rate is same in a lower frequency spectrum and higher spectrum?
If there is a spectrum between 0 Mhz - 1 Mhz, bandwidth would be 1 Mhz here and for example with baseband we can send 2000 bps. What I can't understand is if spectrum is 5-6 Mhz instead of 0 - 1 Mhz, ...
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1answer
53 views
Is there any relation between QAM and streaming?
I am trying to determine whether there is any relation between QAM and streaming (e.g., video streaming).
I know that QAM can be used for broadcast TV. I'm not sure if QAM is used for WiFi bit ...
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1answer
33 views
Diode demodulation for AM
What is the capacitor and resistance at output of LPF meant for in the document it was mentioned that it is DC blocker I don't get it can't message contain DC value.
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60 views
Envelope detector for AM signals
How or what are the constraints for deciding factors of envelope detector for AM As far as I know that charging time of capacitor should be below 20T where T is periodic time of carrier and ...
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0answers
70 views
Channel state information from non-HT packets: is that possible?
I read several papers about CSI data, but one thing is not clear.
I would like to extract csi from legacy rate packets. I read some forums related to existing CSI tools and they only state that CSI ...
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24 views
How to find index of FM modulation
In text I know that frequency of amplitude signal is 10KHz and carrier frequency is 80 MHz. And I need to write code for FM modulation in matlab, I know how to calculate index but here I do not know ...
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2answers
129 views
Getting the bitstream of an unknown RF signal
I am trying to get the bitstream of a signal sent over 433MHz. I have installed SDR# (I'm on Windows), connected my NESDR SMART, and I identified the signal here:
I can see there is only one peak ...
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3answers
70 views
Why only odd harmonics after non-linear amplification?
Why do I get only odd harmonics appearing? This not only happens at saturation of the transfer curve, but also in the linear portion of the curve.
I make a input signal that has too high power that ...
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1answer
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What does this spectrogram mean?This is spectrogram of a multitone FM signal
! The spectrogram of FM signal has been generated by using Matlab.Now I want to what does these scratch like lined represent, though I have only two frequency components in my message signal(https://i....
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What determines the maximum/minimum values in I/Q constellation diagram?
I need to do some data analysis on I/Q samples and was trying to know what are the parameters that determine the maximum/minimum values of these samples. In other words, what determines the maximum/...
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Generating a phase modulation frequency spectrum with jitter
I would like to produce a frequency spectrum plot like this:
(from All About Circuits)
I know that one can take the modulation frequency and multiply it by a given order and scale by the modulation ...
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1answer
200 views
Relation between constellation SNR and baseband SNR
Let's say I have an I/Q modulation, ie. QPSK.
I can simulate an the effects of an AWGN channel by adding to my QPSK symbols the realizations of a complex normal.
$\mathcal{CN}(0,\frac{1}{\mathrm{SNR}...
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How to compare two 802.15.4 O-QPSK modulated digitals signals?
I am working on wireless sensors project and I am trying to simulate a transmission between two nodes.
So let's say I have two nodes which transmit the message to each other, i.e. node 1 transmits ...
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198 views
Does gray coding bring improvement to SER of QPSK, compared with natural coding?
I understand gray coding contributes to BER of QPSK, yet really don't understand why it brings improvement to SER. According to the relationship of SER and BER, it should be improved. Actually, when ...
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33 views
IT++ and Alternatives DSP Libraries
I want to implement some signal processing blocks in C++ so I did a bit of search on the available libraries for signal processing in C++ and I found that IT++ provides comprehensive set of functions, ...
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1answer
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Differential Pulse Code Modulation (DPCM)
In the following figure we see an encoder and a decoder of a Delta Modulation System, which is a simple DPCM System with a 1-bit quantizer:
We assume that signal $x(n)$ is known, that $\hat{x}(-1)=0$ ...
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Continuous Phase Modulation
The wikipedia article on continuous-phase modulation states the following:
For instance, with QPSK the carrier instantaneously jumps from a sine to a cosine (i.e. a 90 degree phase shift) whenever ...
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1answer
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confused in using modulation technique
I am given a question in which I have to draw the spectrum of the signal $m(t)$ and then draw the spectrum of this modulated signal. The signal is
$$m(t)=\cos(1000\pi t)$$
Now in solution manual ...
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1answer
36 views
Synchronization Accuracy Required For Communications
One of the biggest problems in phase modulated communication is discovering when your signal has arrived. High accuracy in this area is important, as even a quarter wavelength error can cause the ...
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1answer
73 views
Multiply signal $x[k]$ with $\cos(2\pi\nu_0k)$, then given $X(\nu)$ draw resulting function in frequency domain?
Let
$$y[k]=x[k]\cdot \cos(2\pi\nu_0k) .\tag{1}$$
Then, given a signal $x[k]$ with the DTFT $X(\nu)$ according to the following figure
what will the frequency domain for $Y(\nu)$ look like for a ...
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30 views
BER vs Eb/N0 for BPSK signal with depth of modulation 120 degrees (+-60 degrees)
I want to draw graph of function BER vs Eb/N0 for BPSK modulation with depth of modulation is from –60 to 60 degrees (or from 0 to 120 degrees). Can I use for that MatLab's tool 'bertool', or I need ...
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magnitude spectrum of a signal xc(t), where xc(t) = square function * cosine function
im currently learning about signal processing in school. The objective i want to achieve is to modulate the square wave to a certain frequency for transmission and apply a LPF and demodulate at the ...
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Why do IQ Impairements, Quadrature Skew and DC offset have these geometric effects on the constellation?
I'm studying telecommunications, and would like to be sure to understand the maths behind these effects.
For IQ Imbalance and DC offset, it seems pretty clear why we observe a rectangle shape or a ...
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214 views
What does the phase discriminator portion of the Costas Receiver do mathematically?
What does the phase discriminator portion of the Costas Receiver do mathematically?
The output of the I-channel is $ \frac{1}{2}A_C \cos \phi \, m(t) $. Which means for small deviation of phase $ \...
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1answer
133 views
How is frequency related to data rate?
How does (if it does) frequency affect/relates to Data Rate.
Why for example using the same modulation, LoRa (in the physical layer),
you get somewhere around 250kbps at 2.4Ghz and only 20kbps at ...
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1answer
65 views
How to correct a QAM time delay
How can you correct the anticlockwise rotation that occurs in the received constellation of a QAM system?
My only idea is to compensate the delay with an advance but this is impossible since you ...
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1answer
55 views
Is there a relationship between Average energy of transmission and power saving
As mentioned in many books, the average energy of transmitted symbol is given by:
$E_s = (2/3)(M - 1) $
where $M$ indicated the modulation order.
Suppose that we are using in the first scenario $...
