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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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 ...
0 votes
1 answer
53 views

Spectrum of a baseband digital signal

I'm building a Continuous-Phase BFSK Transmitter using Python and PlutoSDR. Something that I don't understand is the spectrum of the up-sampled baseband signal - the digital 0's and 1's over-sampled ...
1 vote
2 answers
98 views

How do audio readers interpolate?

$124$ Hz sampled at $256$ Hz has "beats", but $128$ doesn't - a phenomenon of this question: Whether these are "legitimate" beats is up to interpretation, but suppose the goal is ...
1 vote
1 answer
29 views

Why is 16 APSK arrangement 4 + 12?

Why does constellation arrangement affect the BER ? For example 4 + 12 vs 6 + 10 ? Is it because the correlation coefficient ?
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55 views

How composite signal in CDMA is normalise in general?

I had CDMA composite signal with 3 users. I assume that the signals are linearly sum together so for my maximum and minimum amplitude of composite signal are +3 and -3 respectively. Reference: ...
5 votes
2 answers
7k views

Conversion between Eb/N0 and SNR in spread-spectrum modulation like LoRa CSS?

This question is somewhat related to the one asked here: How is multiplexing achieved in spread-spectrum modulations like CSS? I am looking at the bit error rate (BER) performance of communication ...
0 votes
1 answer
612 views

What are and why are sine and cosine modulated integrals used?

I have found the definition of the following formulas in a paper regarding active vibration control, where they are called sine and cosine modulated integrals. $y$ is measurement signal with a strong ...
1 vote
1 answer
32 views

Power of signal in specific frequency in FM and AM modulation

My professor gave us the following problem: Given a sinusoidal signal with $f_m = 1KHz$ which is put into an AM and FM modulation find the modulation index of FM and AM if you know that (amongst ...
0 votes
1 answer
32 views

Real parameters design and computation for a filter, modulator

I design in Gaussian filter for a modulator in MATLAB, which should be later implemented in FPGA. I have an implemented design of the filter and the modulator as well and now I have to determine some ...
1 vote
1 answer
387 views

Difference between MSK and GMSK?

I try to understand differencies between MSK and GMSK on transmitter side. Is GMSK the same than MSK except that a gaussian filter is applied on bits before modulating them? Is the half symbol delay ...
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0 answers
42 views

Difference between MSK and CPSK

I'm trying to understand the differences between the MSK and CPSK transmission, but I am not understanding some things about it. I understood that they are two signals without discontinuity, but what ...
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0 answers
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S/P conversion in IQ modulator

"serial to parallel" separats/switchs a signal into the real and imaginary. Even samples are entering the real branch I (imaginary is 0) Odd samples are entering the imaginary branch Q (...
-1 votes
1 answer
159 views

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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0 answers
49 views

Seamless Filter Transition for Sawtooth Waveform?

I have an old digital hardware device that tracks a sawtooth waveform's frequency with a high pass filter (to remove aliases) seamlessly - even jumps of multiple octaves retain the converged waveform ...
-1 votes
1 answer
40 views

Phase of PM signal

Given two signals: s1 is a baseband frequency modulated signal (output of a frequency modulator, FM) and s2 is a baseband phase ...
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1 answer
890 views

modulate/demodulate audio file as FSK signal mixed with music signal

What I want to do: I want to encode an audio message inside a regular music file; this shall be decoded by an audio analyzer running on another machine (by listening to the audio playback from the ...
-1 votes
1 answer
3k views

Ratio of the power in the sidebands to the total power in conventional AM

Message signal and carrier signal are given as $m=\cos(2 \pi \cdot f_{m} \cdot t) $ $c=A_{c}\cdot \cos(2 \pi \cdot f_{c} \cdot t) $ I was asked to find modulation index $a$ so that ratio of the ...
0 votes
1 answer
388 views

How to find a know signal in another signal which contains other signals along with the signal i need in python

I am working on BPSK with sound waves a carrier waves. Actually I am modulating my data with some known sync bits along with the information I need to send. So the things I will be having at ...
-1 votes
1 answer
56 views

Filtering a sum of cosines

The block diagram below represents a linear modulation system operating at the frequency of $1000 Hz$, $f_C = 1000 Hz$, transmitting the message $m(t) = 2\cos(400πt)$ At point B, i got the signal: $$...
0 votes
1 answer
27 views

Writing an OFDM modem - subcarriers are interferring

I am trying to write an OFDM modem. I've already written a QAM modem, which I'm using as a basis for this project. The way I'm doing this currently is by spinning up several QAM modulators, each with ...
0 votes
1 answer
17 views

Message signal and the Envelope of AM wave

Amplitude modulated signal is represented by $$ x(t) = (E_c + E_m \cdot \cos(2\pi f_m t)) \cdot \cos(2\pi f_c t). $$ At t=0, we have max. amplitude i.e, Ec + Em. Since the envelope is periodic, I ...
1 vote
1 answer
680 views

Recover IQ samples from signal

I have a data acquisition device that provides me with an array of integers that represents a modulated signal (let's say QAM16). I would like to recover the I and Q samples from the raw time-domain ...
1 vote
1 answer
87 views

Bandwidth of a modulated signal in analog domain

If i am using QPSK modulation with data rate 4 Mbps with rolloff factor $0.5$, then the bandwidth will be symbol $\rm rate\times (1 + rolloff\ factor)$. So here it will be $\rm 2\ MHz\times 1.5 = 3\ ...
-1 votes
2 answers
2k views

GNU Radio QPSK 4 Symbols

I'd like to generate a simple QPSK signal in GNU radio, but so far I haven't been able to get it to perform the way I'd like and I'm not sure if this has to do with some misunderstanding I have about ...
-1 votes
1 answer
500 views

How to set a Carrier Wave for DBPSK Modulators in gnuradio?

for a Project I need to build an Audio Modem in GNU Radio. I decided, that it would be the best to use DBPSK Modulation, because that is fast and relatively noise resistant. But as it seems, the ...
2 votes
1 answer
92 views

How to Modulate down a hidden message after filtering base signal from audio file

I have an audio file that is 6 seconds long. The file has a message hidden into it in the ultra high frequency range. I plot the Mel Spectrogram with a sample rate of 44100 and use a high-pass filter ...
0 votes
2 answers
442 views

Adding a constant to a bandpass-signal in transmission

I do understand AM-DSB-SC and AM-DSB-TC, but can't see the point in adding a constant DC-offset of 2 in the upper part of this Simulink-model? Source
2 votes
1 answer
70 views

Do PSK/QAM modulators (e.g. 4G/5G) fundamentally use more energy per packet than CSS modulators (e.g. LoRa)?

Not sure if this is the right place or even the right question to ask, but googling did not get me much further, so here goes: I'm trying to assess whether the power consumed by an IoT device, based ...
0 votes
0 answers
36 views

Understanding FSK and FHSS combination

I am having trouble to understand how to combine Frequency Shift Keying (FSK) with Frequency Hopping Spread Spectrum (FHSS). As far as I understand, A IQ FSK-modulated signal $s(t)$ can be written as $...
3 votes
2 answers
4k views

What is a constant envelope modulation?

The Book "Digital Modulation Techniques" by Fuqin Xiong groups digital modulation schemes into two classes: "constant envelope" and "nonconstant envelope." However, I was surprised by the inclusion ...
0 votes
1 answer
137 views

Why do I see a frequency shift from center when transmitting a QPSK via USRP with GNU Radio?

I am transmitting a QPSK signal via GRC and when I look at it on the spectrum analyzer, the signal is shifted away from my center frequency. This shift increases the higher the center frequency (i.e. ...
0 votes
2 answers
39 views

How can an UWB signal (pulse) radiate from an antenna?

This picture compares an uwb- and narrowband-signal: https://cdn.sewio.net/wp-content/uploads/2017/02/UWB-e1486395802254.jpg Like I understand UWB, the signal("pulse") is directly put into ...
-1 votes
1 answer
706 views

Finding the maximum phase and the maximum frequency deviation of an angle-modulated signal

I have an angle-modulated signal: $$ s(t)=10\left[\cos\left(10^8\pi · t + 5\sin\left(2\pi\cdot10^3·t\right)\right)\right] $$ How would I go about finding the maximum phase and the maximum frequency ...
1 vote
1 answer
482 views

Coding an LFO in C

I want to know how I could implement a Low Frequency Oscilator on a simple synth I've coded in C. First in order to understand how to make this happen I would like just to modulate a sine wave by a ...
1 vote
0 answers
64 views

What is the difference between sending pulses and modulating waves?

If you look for amplitude, frequency, phase modulation, you typically get some picture saying you have a wave and you modulate the corresponding parameter (amplitude, frequency, phase). On the other ...
0 votes
1 answer
39 views

Implementing triangular modulation in Matlab

I am trying to implement a triangular modulation in Matlab, however I am having issues implementing the resulting frequency ramps. I have the following input signal (in reality, this signal is the ...
0 votes
1 answer
41 views

Phase of AM Signal After Mixer

Let's assume we have a carrier at $f_{c}$, and a message at $f_{m}$ ($f_{c} \gg f_{m}$). Amplitude modulation is used to modulate the message on the carrier. Let's call the modulated carrier $\text{rf}...
3 votes
1 answer
61 views

Time warping / frequency modulation natural examples?

"Time warping" defined as $$ x(t) \rightarrow x(t - \tau(t)) $$ where $|\tau'(t)| < 1$ ($=1$ is time stopping, $=0$ is time shift, $>1$ is time reversal). Where can this occur? A ...
0 votes
1 answer
66 views

Calculate moving RMS with exponential averaging

This is moving RMS, now how to add exponential averaging in this df['signal'].rolling(21*24*60).apply(lambda x: np.sqrt(x.mean()))
2 votes
2 answers
756 views

I'm missing something when it comes to understanding FM

I understand why FM is preferred for music: noise is mostly amplitude modulated, FM yields much higher fidelity. I also understand why commercial FM signals have a much larger bandwidth than ...
2 votes
1 answer
45 views

Is it possible to obtain a complex lowpass signal directly from its equivalent bandpass signal?

Given the complex lowpass signal $x_l(t)$, its real bandpass equivalent signal with center frequency $f_c$ is \begin{align} x_b(t) &= \text{Re}\{x_l(t) \cdot e^{j2\pi f_c t}\} \\ &= \frac{1}{2}...
1 vote
1 answer
74 views

How does analog television chroma signal work with QAM and vestigial sideband?

In NTSC analog television (presumably PAL is similar) the chroma (color) signal is included through a subcarrier which is QAM modulated. This particular QAM modulation is a bit unusual in that besides ...
1 vote
1 answer
91 views

Why is Line coding called "Line coding"?

Guys do you now why line coding also called digital base band modulation named "line coding" where does it come? and how is the name related to modulation
1 vote
1 answer
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What is the result of taking the real part and imaginary part of a complex signal in the frequency domain?

Suppose that $g(t)$ is a lowpass complex signal with magnitude (solid line) and phase (dashed line) To modulate $g(t)$ into a bandpass equivalent signal $f(t)$ with center frequency $f_c$, we compute ...
4 votes
3 answers
276 views

Do BPSK vs QPSK have the same performance?

I'm trying to re-learn digital communication theory again and am creating a bit error probability simulation for various modulations. So far I've added BPSK, QPSK, and 8PSK and below is a plot that ...
1 vote
2 answers
72 views

Is digital (discrete) SSB plausible?

Do any examples of digital SSB modulation exist? If not, is it implausible for some reason? The closest thing I can find is something like 8VSB which comes very close to being single sideband. I read ...
0 votes
1 answer
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Using SSB modulation to frequnecy shift an arbitary signal downwards

I've managed to use SSB digitally to create frequency envelopes such that I can increase frequencies at any arbitrary rate given by my envelop. But I am unable to manage a downward frequency shift. ...
0 votes
0 answers
113 views

GNURadio GFSK demod missing data

we are trying to develop a flowgraph for cubesat operation. Our flowgraph for includes both downlink and uplink parts in one flowgraph. It uses SoapySDR as a driver of an SDR. Most of the used blocks ...
7 votes
3 answers
1k 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 ...
1 vote
1 answer
40 views

On-Off keying for wireless communication channel estimation

Let us assume I have $k$ (a fixed number) sensors in a wireless sensor network with unknown channel statistics $\{h_1,h_2 \ldots, h_k\}$. In my system model, each of these $k$ sensors has an ...

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