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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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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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 ...
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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}...
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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 ...
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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
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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 ...
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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 ...
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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. ...
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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 ...
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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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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 ...
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How is IQ-modulation done on the digital side rather than the analog side?

The original way of doing In-phase Quadrature (IQ) modulation is by modulating and mixing on the analog side. I have read that as the digital processing have gotten better, the modulation and mixing ...
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Exact formula for 8-PSK BER

Is there an exact formula for the probability of bit error (or bit error rate, BER) for 8-PSK (in the literature, course slides, etc.)? I am not referring to SEP (Symbol Error Probability) but BER. ...
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Why does the Superheterodyne AM Receiver use an envelope detector?

I'm currently learning about the Superheterodyne AM Receiver and I don't understand why does it use an envelope detector (as suggested here) rather than taking the signal back to its baseband ...
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Why does my output signal look like this?

This is a coherent demodulation of a BPSK signal. I'm using this link as a reference However my demodulated output comes out with too many redundant values compared to the transmitter. This only ...
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Send complex signal and receive the same complex signal, GNU radio

I’m working on a project where I want to send complex symbols like 4-QAM, 8-QAM or 16-QAM for example and demodulate those symbols, the idea is to use the signals as points (like in the constellation ...
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In wireless communications, is it true to say: The more the range, the more the delay spread?

The general idea which can be drawn by reviewing wireless channel models says that the longer the range/distance, the more the delay spread, even in LOS microwave links. But I really wonder why it is ...
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802.11a OFDM Long Preamble Cyclic Prefix

im currently looking at an implementation of the preamble for OFDM in the 802.11a standard, as shown in the pic below What I dont understand is the cyclic prefix (labelled GI2). Based on this picture ...
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What is the difference between a guard band and a cyclic prefix in OFDM?

im trying to understand the difference between a guard band, and the cyclic prefix, or at least the relationship between the two. Prior to now, I was under the interpretation that the cyclic prefix ...
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FM and PM waves

I have to find the FM and PM waves corresponding to this sawtooth signal: I have found out the PM wave as: I am getting the FM wave as this : I have plotted this using Python. Can anyone please ...
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How to implement GMSK model by Thierry Turletti

I'm kind of new to signal processing and trying to implement a GMSK modulator using GMSK in a nutshell by Thierry Turletti to modulate a bunch of binary data and send them over RF antennas. I'm very ...
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Can a cosine modulated complex valued baseband signal be transmitted over physical channels?

I am reading Digital Communication by Lee and Messerschmitt. In Chapter 6 on modulation, the authors say: "Modulating a complex-valued baseband signal with a cosine wave yields complex-valued ...
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What is Homodyne BPSK? [duplicate]

Could someone explain what Homodyne BPSK is? What is a difference between BPSK and Homodyne BPSK? I have read about this type of modulation in researches in optic communication. I surprised how phase ...
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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 ...
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