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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Modulation of Analytic Signal

Given a signal of the for $x(t) = p(t) + j\hat{p}(t)$ where $\hat{p}(t)$ is the hilbert transform of $p(t)$. The information signal ( message signal) here is $x(t)$. I have to transmit this signal ...
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is there a single process/term to describe dissipation and amplification of a signal?

I am writing a paper, and the topic is about a signal that could be either amplified or dissipated while traveling through a medium. Since I don't wanna write everywhere "amplified or dissipated &...
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49 views

Clarification Regarding Changing the Variable

Assume I have that : $$ X(j\omega)=\begin{cases}e^{-2\omega}&\text{if $|\omega|<2\pi$}\\0&\text{if otherwise}\end{cases} $$ Say, I want to make this change substitution $X(j(\omega-\Omega))$...
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Spectral efficiency of with OFDM vs without OFDM?

OFDM has advantage over frequency selective channel with addition of cyclic prefix after IFFT of MPSK or MQAM symbol. but I wonder that the spectral efficiency of with OFDM vs without OFDM.
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32 views

Direct downconversion (IQ downconverter) with ASK modulation— what kind of Balun do you need?

I have a simple but confused question. I am trying demodulate a 915MHz ASK modulated signal with direct downconversion. So what I am building up is: Antenna --> SAW bandpass filter @915MHz --> ...
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Does direct-digital RF signal generation have a “baseband?”

Semiconductor technology has advanced to the point that the digital representation of a modulated RF signal can be applied directly to a DAC for transmission. Is there, then, any distinction between a ...
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72 views

Energy per symbol calculation

I am having trouble calculating my Energy per symbol and Es/No. Using these parameters and equation $N_s = $Number Symbols $R_s = $Symbol Rate $T_s = $Symbol Time $sps = $samples per symbol x = signal ...
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43 views

Using DFT Rotation for Frequency Down-Mixing

Is it possible to perform Frequency Down-Mixing (sometimes referred to as Down-Conversion) by simply rotating the DFT sequence? If so what are the Advantages and Disadvantages of this method?
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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. ...
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42 views

Time domain representation of a modulated signal when symbol rate >> carrier frequency?

I need to understand the relationship between carrier vs. bits with PSK modulation, and what the signal in the time domain would look like if my symbol rate is far greater than my carrier frequency. ...
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54 views

Why Does ASK Modulation Create Fourier Sidebands?

I know why analog amplitude modulation has side bands, it is related to (fc+fd) and (fc-fd). But what about DAM? ASK(DAM) is a type of digital modulation, and there are only two state: carrier signal ...
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Do we assume modulating and carrier signal uncorrelated in AM modulation?

I am new to communication and studying amplitude modulation. Let us assume an amplitude modulated wave given by $$\big(m(t)+ A\big) \cos(2\pi f_c t)$$ Now we have formula for efficiency as $$ \eta=\...
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What modulation is done when I connect a signal source to a USRP block in GNURadio?

When I connect a sinusoidal signal source to a USRP sink and upconvert the frequency, what modulation is done to convert the baseband signal to a passband signal?
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47 views

Error probability for 8-PSK

How can I calculate bit error rate for 8-PSK modulation when I have $E_b/N_0$ given? I know that for QPSK/BPSK the matter is quite simple, but I cannot cope with 8-PSK. Let's say that my $E_b/N_0$ = ...
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SPL dB to voltage conversion misunderstanding

base on these links: https://electronics.stackexchange.com/questions/96205/how-to-convert-volts-to-db-spl https://electronics.stackexchange.com/questions/302833/convert-digital-and-analog-values-to-...
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49 views

how to find frequency response of microphone

hello I want to find the frequency response of a microphone. I give the input signal to my speaker and it produces a specific SPL with specific frequency. on the other side, I read the microphone ...
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57 views

Demodulating unknown signals - unmatched frequency sampling

My goal is to make an approach to recognize modulation type of unknown signals. I have energy detector which monitors spectrum and it provides information about center frequency and bandwidth of ...
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174 views

Block diagram of M-PSK modulation and demodulation

I have come across this quadrature modulator block diagram in many books and websites: I've read that the quadrature modulator allows to realize many different digital modulations, including ...
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66 views

Why in FSK the phase shift is allowed?

FSK modulation encodes information into the frequency of the signals. But when I checked the reference books, the formal expression for a frequency modulated signal is: $x_i(t) = \alpha cos(2\pi f_it +...
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47 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 ...
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94 views

Bandwidth of PSK modulated signal

What does it mean that the bandwidth of PSK modulated signal without applying any filtering or shaping of the pulse, is equal to the sampling rate with "1st lobe" equal to two times of ...
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24 views

Is there a way to describe the pattern of a signal as a numeric value?

I've been digging a little into signal processing and I just started a networks and telecommunications class at college. We saw there are different encode techniques Amplitude, Frequency and Phase ...
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80 views

Filtering a QPSK signal

Envelope variation due to filtering of a QPSK signal becomes more pronounced at greater phase steps. Why is that? Why do greater phase steps (180 vs 90 degrees for example) lead to more pronounced ...
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21 views

Issue with demonstrating amplitude modulation of sinusoid using MatLab

I am trying to demonstrate Conventional and DSB-SC modulation of a signal $ \sin(2\pi1000t) $ using MatLab. My carrier signal is $ \sin(2\pi f_ct)$ where $f_c = 100\text{ MHz}$. Now according to ...
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Does baseband signal has negative frequency?

Does baseband signal has negative frequency? In wiki baseband signal means that can include frequencies that are very near zero. I wonder whether baseband signal has negative frequency. Thank your ...
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27 views

What is the correct block diagram of CDMA communication system?

I was reading someone's thesis and now i am more confused about CDMA system. From what i understood is CDMA is multiplexing which allows multiple signals to transmit over single channel. so general ...
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FM modulation - recovering bits

I'm trying to complete one task: Download some FM modulated signals from page http://www.w1hkj.com/modes/index.htm. Calculate their spectrograms, i.e. short-time Fourier transform. Observe different ...
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Questionable Eb/N0 results for different modulations - measurements for 8-PSK do not match the theory

I would like to warn you that this post will be long, so thank you in advance to everyone who reads it and is able to help. I am running a certain simulation. I created a measurement environment (...
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88 views

Why 8-PSK modulation has higher Eb/N0 than QPSK or BPSK?

I run a transmitter/receiver simulation using QPSK, BPSK, and 8-PSK modulations. As far as I have noticed, the best SNR per bit results are obtained when simulating with 8-PSK modulation (and also at ...
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Simulating Rayleigh channel - Problem with adding channel coefficents

I am currently trying to simulate a Rayleigh channel using python (numpy). Full Jupyter Notebook on GitHub: Jupyter Notebook I assume that the channel changes with each new symbol. So I create myself ...
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Which modulation technique is better for long distance transmission, if I'm using the CC1101?

I'm using the Texas Instrument transceiver cc1101 at 430-440 [MHz] and I'm wondering what the best modulation technique is for long distance transmission. This transceiver offers several modulation ...
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35 views

What is conceptually happening in this modulation function?

I know this is a programming question but i am trying to understand the logic of this. I have come across below function which is basically written in the groovy, ...
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40 views

Find which signal was transferred in 32QAM

I've been assigned to solve a problem for 32QAM signals. The thing is, there are little to none sources in my native language to get any decent information on the topic. The problem is (in its ...
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31 views

If a function has slowly varying amplitude and phase what is the bandwidth of the amplitude and phase individually?

I am dealing with time histories that are narrow band with slowly varying amplitude and phase. I wish to extract the amplitude and phase but there is noise on the time history. An example of the type ...
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39 views

SNR measurement

I am using QPSK modulation for a BER of $10^{-6}$ at $\text{SNR}=E_b/N_0=10 \ \rm dB$. If my data rate is $5 \ \rm kbps$ then $$S/N_0 = 10\log_{10}(5000)+10 = 47\ \rm dB$$ And if my RF section has a ...
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69 views

Difference between delta modulation and differential PCM

Delta modulation encodes the difference between a sample and the previous sample in only one bit. Differential PCM encodes the difference between a sample and its predicted value. Is this difference ...
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206 views

How do I generate a QAM signal using Python?

I have created a 16-QAM Constellation diagram ranging from {-3-3j ... +1+1j}. I then transform a given input string into symbols ...
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141 views

Wideband FM bandwidth estimation

In the book Modern Digital and Analog Communication Systems by B. P Lathi, there is a section for the estimation of WBFM bandwidth. First, the staircase approximation of $m(t)$ is constructed by the ...
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106 views

Power of an angle-modulated wave

Let $$\phi(t) = A\cos(\omega_c t + km(t)) \tag{1}$$ be an angle-modulated wave(FM or PM). What's the power of $\phi(t)$? Intuitively, it seems that the answer is $$P = \frac{A^2}{2} \tag{2}$$ since ...
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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. How can i ...
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63 views

How to remove the modulation before doing frequency offset estimation?

To use DFT/FFT (or maximum likelihood) method to estimate the frequency offset introduced by the channel, we need to remove the modulation on the received data samples in the front. If the unknown ...
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25 views

Mathematical relationship between phase modulated (PM) signal and the complex phase/magnitude of the frequency component at the carrier frequency?

What is the mathematical relationship between phase modulated (PM) signal and the complex phase/magnitude of the frequency component at the carrier frequency used? This is partially related to the ...
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41 views

Digital Phase Modulation baseband or passband?

Say I want to transmit messages using PSK: I send the message $$s_m(t) = \text{Re} \left [g(t) e^{\frac{j 2 \pi (m-1)}{M}}e^{j 2 \pi f_c t} \right]$$ where $f_c$ is the carrier frequency. Now my ...
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27 views

PSD of linearly modulated signal using autocorrelation?

Consider a signal $v(t)$ given by $$v(t)=\sum_{n=-\infty}^{\infty} b[n]p(t-nT).$$ Assume that $b[n]$ is uncorrelated with zero mean, i.e. $\mathbb{E}[b[n]b^*[m]]=\mathbb{E}[|b[n]|^2]\delta[n-m]$ and $\...
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78 views

How to separate Even and odd part (in-phase bit streams I and quadrature-bit streams Q) of the signal?

I am working on communication system in simulink and wondering, how can i separate the Even and odd part of the signal. In my Transmitter block, I have : $$ \boxed{\text{Binary Data signal}}{\...
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Non-coherent FSK and Orthogonality and square-law detectors

This is a basic figure that explains how Non-Coherent FSK actually works. The incoming signal $ r (t)=\sqrt{2 P}{Cos}(2 \pi t (\text{fc}+\text{fi})+\text{n(t)}$ where P denotes the signal power in ...
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114 views

How does modulation frequency appear in the modulation spectra?

I'm trying to familiarise myself with the concept of modulation spectra that I met in this work. My main question appears in the title: how does the modulation frequency appear in the modulation ...
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4answers
332 views

What can be done with I/Q data which would otherwise be impossible?

As I understand it, I/Q data is the complex representation of any waveform. It enables us to understand two things at any arbitrary point in time: The projected amplitude of the waveform. The ...
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40 views

Modulate Bipolar(?) signal

I want to modulate this signal if possible with an Arduino, but have no idea what circuit can help me here. Let's ignore the timing and the measurements from the image for a moment, my problem is more ...
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Why can so little digital information be stored on a cassette tape?

I had heard that tape is still the best medium for storing large amounts of data. So I figured I can store a relatively large amount of data on a cassette tape. I was thinking of a little project to ...

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