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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Demodulation + LPF gives derivative of modulated signal
I'm new in this community and I hope it is the right place to post my question. Unfortunately, signal processing and electronics in general are not my fields, so I'm sorry if the question is trivial.
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Does phase shift introduce high frequencies?
In PSK phase modulation scheme, the signal phase is shifted, hence it looks something like this:
I cannot understand why this doesn't introduce a set of unwanted high-frequencies, as the steep ...
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Why does NB-IoT use standard QPSK in multi-tone transmission, when pi/4 QPSK is implemented for single-tone?
I've been studying the modulation schemes used in NB-IoT communication, with a particular focus on energy efficiency. I've noticed that QPSK (Quadrature Phase Shift Keying) is used in multi-tone ...
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Clarification on video about frequency deviation in phase modulation bandwidth
I am watching this video and at 7:12 he calculates the frequency deviation $\Delta f = f_{c}f_{m}A_{m} $ where the $c$ underscript is for "carrier" and the $m$ underscript is for "...
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modulation transfer function and ground resolved distance
I am trying to understand something in remote sensing but lack a background in science and technology so it is difficult. Hopefully this is a reasonable question to ask.
In sensing there are different ...
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Why for bandpass signals complex envelope and pre-envelope signal representations are used in digital communications/analog communications (FM)?
When we need to analyse band pass signals we use complex envelope and preenvelope representations, wherein a signal is given an equivalent low pass representation.
My issue is why it is done, though I ...
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Meaning of roll-off factor 0.5 and bandwidth
We currently have a radio that is transmitting at the following RF params:
Modulation: OQPSK
Data rate: 500Kbps
Uplink coding: BCH
I am interested in understanding what is the associated uplink ...
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I don't understand which signal I should use as a carrier in my excersise
$\DeclareMathOperator{\sinc}{sinc}$ Given 3 signals
$x_1(t) = \sinc(t) , x_2(t) = 10\cos(2\pi f_2t)$ and $x_3(t) = 5\cos(2\pi f_1t)$,
where $f_2 = 100\text{ kHz}$ and $f_1 = 1\text{ kHz}$.
I must ...
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DS-CDMA Spreading Code Length Selection
I'm trying to wrap my head around the process of selecting DS-CDMA spreading codes, and I'm having trouble understanding the tradeoffs of longer codes. For all scenarios described below, I'm using a ...
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Understanding homework solution - why are $\{X_t\}$ and $\{Y_t\}$ joint WSS, and finding Wiener filter + error
I'm walking through the published solutions of my homework and I'm struggling interpreting them. In them I was given a random Gaussian process $\{X_t\}$ and a random variable
$$\{Y_t\} = X_t\cos(2\pi ...
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Recognizing different pulse shaping forms (16-QAM modulation)
I have three versions of a 16-QAM modulated signal, each showing the time curve of the real and imaginary parts, the spectrum and the symbol constellation. These three versions differ by the ...
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Testing a Hilbert transform on a real signal to transmit it as Single SideBand
I am testing some Hilbert transform theory in practice. On the practical side I use Python and a soundcard to generate baseband I and Q signals. And an IQ modulator to upconvert with 250kHz. Lastly a ...
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How to modulate a signal to a certain frequency in time domain
I have a root-raised cosine pulse signal of bandwidth $500$ MHz.
If the signal is modulated at the frequency $6$ GHz, the result should apparently look like this :
If I understand well, to modulate ...
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Modeling an OFDM signal and comparing it with QPSK
I am trying to model an OFDM signal based on original QPSK stream and compare their baseband spectrums.
I've used this article as a reference for plotting spectrum and this as a MATLAB OFDM reference
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Block Diagram 2nd Butterworth Low-pass
I would like to represent a second-order butterworth low-pass filter in a block diagram, how can I get started?
As per the attached image
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Which type of modulation is used in this RF Signal?
I am working on reverse-engineering a few devices, I got some using ASK and FSK but I could not grasp this other one. I am attaching some photos from its captured signal took from URH (Universal Radio ...
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Modulating and transmitting three different voice signals (in MATLAB)
I want to record, modulate and transmit three different voice signals. I will be doing this in MATLAB.
Please can you help me figure out how can I do this?
Or give me a block diagram that can show ...
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How to correctly accept Polar/LDPC encoded bits with PSK modulation?
I have implemented a packet reception and transmission scheme using QPSK. Next I decided to add Polar/LDPC encoding. As a result, nothing is written to the received file.
I think the thing is that I'm ...
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OFDM does not work with USRP
I found the ofdm flowchart in the Gnu radio examples.(ofdm_loopback)
Scheme:
The spectrum and the received data of the received signal:
After that, I connect the USRP Sink and the USRP Source.
The ...
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8PSK modulation does not work
I implemented a data transfer system using two tutorials: Guided Tutorial PSK Demodulation and Packet Communications. After that, I decided to change QPSK to 8PSK.
My scheme:
Constellation Sink:
For ...
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Can frequency multiplier (e.g. doubler) impact signal bandwidth?
My understanding is that if a single tone at frequency F is inputted to the frequency doubler, one should observe at its output in the spectrum the same tone but now at a frequency 2F.
However, what ...
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Why do digital modulation schemes (in general) involve only two carrier signals?
In my digital communication, class we have covered the various modulation schemes, namely QAM and its derivatives (B(A/P)SK, PAM and (Q/M)PSK) as well as BFSK. These two schemes have one or at most ...
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Why is the symbol duration in QPSK twice the bit duration?
I saw many answers for such questions by writing down equations such that the symbol is formed of n bits so the duration of the symbol in QPSK must be n multiple of the bit duration.
I am not ...
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Plotting Constellation Diagrams
I'm working with some IQ data from the paper A Wideband Signal Recognition Dataset. Specifcally I've been trying to plot the constellation diagram for some the modulations within the dataset, however, ...
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Expectation and autocorrelation for modulated sinusoid
Given
$$ Y(t) = A X(t) \cos(\omega t + \phi) $$
with $X(t)$ is zero-mean WSS (wide-sense stationary) process, $\phi$ ~ Unif$(0,2\pi)$. Suppose $X(t)$ and $\phi$ are independent random variables. I ...
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FSK: Selecting center frequencies and Carson's Rule
I'm implementing 2FSK and 4FSK modulation schemes for an experimental system. I'm using GNURadio, although that shouldn't affect the question.
I'm trying to figure out how the center frequency should ...
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Converting real samples to IQ
I have real-valued samples of a signal at a negative frequency (was mixed with a cosine of a higher frequency than itself). I want to quadrature modulate it up from $-\omega_c$ to 0. There seem to be ...
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What process could generate this kind of noise in the multitaper spectrum?
I am recording some data for scientific purposes (it is neurological data), and the data is corrupted by some very strange noise. At multiples of about 700 Hz (slightly differing on different days) ...
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In Bluetooth Low Energy, why are Enhanced Data Rate packets only 3 Mb/s?
In the "Introduction tu Bluetooth Device Testing" document ( https://download.ni.com/evaluation/rf/intro_to_bluetooth_test.pdf ), the modulations for Bluetooth Classic are said to be a ...
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Why does QAM modulation produce asymmetric sidebands?
With amplitude modulation the signal only has a real component and the modulated signal has two sidebands that are symmetric around the carrier frequency. My understanding is that in QAM the sidebands ...
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What is the spectral efficiency of OQPSK modulation?
Offset Quadrature Phase Shift Keying (OQPSK) like QPSK transmits two bits per symbol. However, because of the offset on the quadrature component there are two transitions per symbol. Does this not ...
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Do amplitude shift keying modulation occupies a large portion of the spectrum?
In the PySDR online course, to the question "Why can’t we directly transmit the ethernet signal [directly in the antenna]", one answer is the following :
Square waves take an excessive ...
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IQ Constelation Diagram of FSK signal
I'm want to generate the IQ components of a FSK signal using numpy and then try to demodulate the resulting IQ samples by looking at the derivative of its phase in time.
This is the script I have:
<...
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Choosing the scaling parameters for a modem implementation
I have succesfully modeled a modem using floating-point data and with the following scheme, where the SRRC filter has gain G=6dB.
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What tricks can one play on a bandwidth-limited IQ modulator?
I would like to create a pulsed RF signal that has a carrier frequency of 2 GHz by IQ up-conversion. The pulse should be 2-4 ns long. The carrier phase has to jump by 90° in the centre of the pulse. ...
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Deriving the IF phase equation of FMCW
My understanding of the FMCW was limited to one chirp and was mostly focused on frequency analysis. (Mostly built upon this answer)
I wanted to expand my understanding to multiple chirps and was ...
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Range-Doppler Coupling in FMCW
I did some derivation of the IF signal of the FMCW using sawtooth LFM.
A chirp with sawtooth LFM is expressed like below
$$x_T (t)=\cos\left(2\pi f_c t + \frac{\pi}{T}B (t-mT)^2 \right)$$
Where, $f_c$ ...
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Omission of 8-PSK and 32-QAM in LTE/5GNR
In 4G LTE/5G NR, the modulation schemes 8-PSK (which is an intermediate scheme between QPSK and 16 QAM) ,32-QAM (which is in between 16 and 64 QAM) are omitted. If the channel is bad , or the distance ...
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How to get trellis-coded modulation trellis after set partitioning?
Given a 4-PAM modulation and after doing the set partitioning for it,
I'm unsure how to arrive at the trellis with the edge labels and the trellis structure as shown below,
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How to achieve 3 Gbps with 210 MHz bandwidth in 5G?
I read an article from T-Mobile link where they claimed a 3Gbps speedtest with the aggregation of 3 three bands in 5G.
How it is possible to make 3 Gbps with a 210 MHz bandwidth and using 256QAM in 5G?...
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Selecting convolutional code for a M-QAM transmitter
I am tasked in an assignement to select an appropriate rate 1/2 convolution code for a QAM modulated transmitter with the following setup,
However, from my understanding of codes and modulation they ...
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Matlab Filter-Span-In-Symbols property for RRC: source bits lost
I am using the matlab online simulator and taking the course "Wireless communications Onramp" where I need to use a Raised Cosine Transmit Filter to filter the data both in the transmitter ...
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Can humans hear Hilbert transform in audio?
I stumbled upon Hilbert transform when researching single sideband modulation. Apparently when the demodulator frequency is bit off by $\Delta f$, the signal after demodulation and low-pass filtering ...
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QAM modulation problem with python
I have a IQ signal with a bandwidth of $200\,\text{MHz}$.
I do I*cos(2*pi*1000e6*t)-Q*sin(2*pi*1000e6*t), but my signal doesn't shift to carrier frequency ...
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How are discontinuities in quadrature modulated signal QAM physically produced?
In quadrature modulated signals, for instance:
I am unclear how the "discontinuities" in the waveform at the junction of each data point can be physically produced?
Taking a speaker as an ...
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Effect of Passband Slope on a BPSK Constellation
What is the effect of a passband slope on a BPSK constellation? (This is a companion question to the related "DSP Puzzle" for QPSK)
Specifically given a linear slope (in magnitude, not dB), ...
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Effect of Passband Slope on QPSK Constellation
What is the effect of a passband slope on a QPSK (or any QAM) constellation? Specifically given a linear slope (in magnitude, not dB), and no phase distortion (linear phase or even zero-phase) how ...
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BER result in MATLAB
I build a pam-2 modulation, then I make a pulse shaping with half sine (matched filter). Then I send it through the AWGN channel. At the end I do down sampling and demodulation. But i have problem ...
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Higher order M-FSK modem implementation
I am looking for the optimum modulation scheme to build a half-duplex modem minimizing the required SNR at the expense of bandwidth efficiency. The key system parameters are described below:
Target ...
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Answered-Question About Radar Pulse Modulation
I am trying to simulate a radar-transmitted signal with a 4.5 Hz clock frequency and 1.8 GHz carrier frequency. I generated the carrier signal and a rectangle shape pulse signal, then multiplied in ...
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