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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Use of I/Q representation for unmodulated Rx Signal

it may be a stupid question but while learning about DSP and Modulation I was wondering, if the I/Q representation of an RF Signal is of any use, when the received signal does not contain any ...
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33 views

Max frequency of cosine in SDR

I would like to transmit a 56 MHz real cosine and receive it using SDR with max complex sample rate equals 61.44MSPS and an analog filter with BW = 56MHz (the transceiver is AD9361). Can I do it? How ...
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What causes this type of distortion in a constellation I/Q plot?

I'm transmitting QPSK through a digital pulse shaping filter (RRC, 35% excess BW, 2 samples per symbol, 64 taps) at a rate of 56Msym/sec. Receiving it on standard lab equipment (Vector signal ...
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34 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\ ...
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Which type of modulation should I use ?? QPSK or QAM? [closed]

Which type of modulation should I use ?? QPSK or QAM ?
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How are the constellation point coordinates determined in digital modulation

I need to understand where the concept of the distance comes from. What I mean is, how do we know what coordinates are to assign to points in the constellation. For example here for QPSK the points ...
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35 views

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 same for BFSK like ...
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modulation depth

When a value for the power dissipated by an AM signal is given, and the depth of modulation is also given. Then you are told to find the modulation depth required to increase the power to a higher ...
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Sharp EL-5500III (PC-1403) cassette tape encoding

I have an old audio cassette tape of digital data I converted to .wav and am hacking to recover the original data. I demodulated the 4K/2K FSK modulation with minimodem. Then I get stuck with ...
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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 ...
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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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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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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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Numerically Controlled Oscillator (NCO) for phasor implementation?

If I want to simulate a digital oscillator (or phasor) to modulate an arbitrarily length signal: $$y(t) = \cos(2\pi f_ct)\quad\text{where}\quad t = \frac{n}{f_s}\quad\text{for sample}\quad n$$ What ...
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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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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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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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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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36 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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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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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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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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994 views

How to implement a $1$-bit quantizer in Simulink?

I am trying to implement a delta-sigma modulator block diagram in Matlab Simulink but can't find a $1$-bit quantizer (which is required in the modulator) anywhere. Could anyone please tell me how to ...
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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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Modulation and Noise

I am fairly new to studying communication systems. When it comes to different digital modulation techniques, does the effect of an additive complex noise (a) introduced by the system, and (b) by the ...
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How would sigma-delta modulation work in software?

I've recently come across this YouTube video that shows a PCM stream being played back via the 1-bit internal "PC Speaker", and after hours of googling I've come to think this is done via Sigma-Delta ...
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401 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 ...
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715 views

What are thoughts on best modulation to use for underwater acoustic communications at low frequencies?

I wanted to ping the DSP hivemind for general thoughts on what would be the best modulation type to use for low frequency underwater communications. I have chosen this project since I can learn a lot ...
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2k 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 ...
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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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37 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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268 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 ...
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651 views

How to generate IQ component for transmitting 2FSK

I am trying to generate IQ components for 2FSK modulation. I have started off from this thread FSK and IQ modulation , but I don't quite understand the IQ TX components plotted in the example there by ...
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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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Why do SDR receivers emit I/Q samples?

To my understanding hardware receivers for software-defined radio applications basically take the input signal, mix it with the tuning frequency to remove the carrier frequency and then sample the ...
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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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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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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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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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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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409 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 ...
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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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Relation between Normal Phase Shift of a wave and Phase Modulation

I am little confused with the Phase Modulation and the phase of a sine wave. I get the phase modulated wave from the google images as below: Phase modulation has the form: $$PM(t)=A_c \cos\big(2\pi ...
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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 ...
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concurrent multiple sound sources seperation for TDoA estimation

consider a room with some sound resources and several mics, these sound resources almost concurrently emit sound signals. As for one mic, it may pick up sound signals from different sound sources ...
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442 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 ...
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Up-converting a sinusoidal signal

I want to up-convert a baseband sinusoidal signal of frequency $4000 \, \rm{Hz}$ using a carrier frequency of $20\, \rm{KHz}$. I read that one can up-convert a baseband signal to a passband signal ...
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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
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Cyclic prefix length in baseband OFDM with ZF equalizer

My question is about baseband OFDM. I try to plot the BER according to the SNR. I noticed that changing cyclic prefix length does not affect the performances. I.e., following the code below, ...

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