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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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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Output spectrum of Weaver SSB modulator modelled in GNURadio does not meet expectation
I'm trying for quite some time now to model a Weaver SSB modular using GNURadio. The base for my work is Derek Rowell's "Weaver SSB Modulation / Demodulation - A Tutorial", which can be ...
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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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Issues with playing and recording a square wave sound on the same PC
I am learning signal processing. For a hobby project I wanted to transmit and record a simple ASK signal via my soundcard, to see if I can write code to recover the sent data. After playback and ...
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$S/N_0$ of a PM Modulated tone
I have been looking into a Satellite tone ranging system.
Phase error Performance criteria has been given as a function of $S/N_0=40 dB.Hz$ of the Major tone.
The major tone is 100 kHz away from the ...
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BER formula for chirp spread spectrum BPSK modulation scheme
May I know how to derive the BER formula for chirp spread spectrum BPSK modulation scheme ?
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QAM Bit rate and how it is applied in analogue
For QAM modulations how to obtain the bitrates with the used channel spacing, i have been searching but mathematically couldn`t find an equation that gives me the exact bitrate
for example how to find ...
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Why is automatic modulation classification hard?
There is a huge amount of research into automatic modulation classification (AMC) using machine learning.. Why is AMC a hard/difficult problem that we need to use machine learning or even deep ...
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A question regarding using analog PLL circuit with QAM modulation for phase sync
I was wondering if you can implement analog PLL circuits for phase synchronization in communication systems that transmit MQAM modulation signals?
I heard that you can't use analog PLL because QAM ...
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Autocorrelation & Cross-Correlation -> Main uses in DSP??
Please help understanding the DSP usage of Autocorrelation & Cross-correlation
It seems this is strongly linked to calculating phase offsets, frequency offset for carrier recovery, symbol timing ...
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Block diagram of a demodulator with a low-pass filter
I am having some difficulty designing a block diagram of a demodulator with a low pass filter - I don't know how to add it to the schematic(apply the LP filter to the diagram). I have an input signal ...
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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 ...
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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 ...
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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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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 ...
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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 ...
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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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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 ...
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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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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 ...
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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 ...
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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 ...
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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
$...
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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 ...
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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 ...
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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}...
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