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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Time warping / frequency modulation natural examples?

"Time warping" defined as $$ x(t) \rightarrow x(t - \tau(t)) $$ where $|\tau'(t)| < 1$ ($=1$ is time stopping, $=0$ is time shift, $>1$ is time reversal). Where can this occur? A ...
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Implementing OQPSK in Gnu Radio Companion

I am currently trying to realize this block diagram in Gnu Radio Companion: Before using a file source block with the binary I want to send, I plan on just using a vector with an alternating 1,0 ...
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52 views

Meaning of complex envelope in simple terms?

I tried to find a simple explanation of what a complex envelope of a signal is, with no luck. I'm looking for an explanation with simple terms, and possibly that is easy to visualize or imagine, so ...
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28 views

MSK receiver for ultra-low SNR

I am designing a low-rate DSSS communication system (~1ms chip period, Spreading Factor 128/256 bits long) for using at ultra low SNR scenarios (~0dB SNR). Due to the problems related to clock ...
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Limiting Bandwidth for QAM and OFDM signal in MATLAB Simulink

currently im creating an application capable of generating QAM and OFDM signal to be transmitted using SDR. The whole application is implemented in MATLAB Simulink using only code generateable ...
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weird Demodulated BPSK waveform

I am using an acoustic wave of 3khz(audio BPSK) as my carrier frequency with a sampling rate of 10k samples per bit. at the receiver end, I play the audio from my phone to my computer, record it ...
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52 views

Difference between FFSK and FSK modulation schemes

Can somebody explain to me what is the difference between FFSK (Fast Frequency Shift Keying) and FSK (Frequency Shift Keying) modulation schemes?
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How is it that a dial-up modem can achieve 33.6Kbit/s with only 3100Hz of bandwidth?

My understanding is that plain old telephone service passes frequencies between 300Hz and 3400Hz. How is it that a V.34 modem in the late 90s would be able to achieve data rates of 33,600bits/s with ...
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BPSK(10) and chip rate

I am doing some research have come across signals listed as having the in-phase channels modulated with BPSK(10), etc. I understand the concept of BPSK - Binary Phase Shift Keying, and know the 10 is ...
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46 views

Filtering a sum of cosines

The block diagram below represents a linear modulation system operating at the frequency of $1000 Hz$, $f_C = 1000 Hz$, transmitting the message $m(t) = 2\cos(400πt)$ At point B, i got the signal: $$...
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In practice, why is there any overlap in frequency-division multiplexing?

Okay, so I am aware of the math behind perfect reconstruction in filterbank and wavelet theory when there is half-band symmetry. But I don't understand, when we have the computational power to do ...
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Shannon capacity limit & FEC comparisons

In this figure from Fundamentals of Digital Communications by Madhow , pp 328 there is a comparison of a rate 1/3 turbo code with the shannon limit for rate 1/3 BPSK: Trying to understand the limit ...
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Difference between MSK and GMSK?

I try to understand differencies between MSK and GMSK on transmitter side. Is GMSK the same than MSK except that a gaussian filter is applied on bits before modulating them? Is the half symbol delay ...
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Nyquist frequency isn't working

The situation is that I have a signal with linearly increasing frequency, $$\text{sin}(2\pi\omega(t)t),$$ where $\omega(t)=a+bt$ for some $a$ and $b$, and we constantly sample at one point per second ...
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Determination of Variance from Symbol Error Probability Equation

For a M-ary QAM receiver, the symbol with AWGN noise is received and detected with Maximum–Likelihood (ML) Decision algorithm. The symbol error probability (SEP)is approximated as : here, Eb is the ...
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How to Modulate down a hidden message after filtering base signal from audio file

I have an audio file that is 6 seconds long. The file has a message hidden into it in the ultra high frequency range. I plot the Mel Spectrogram with a sample rate of 44100 and use a high-pass filter ...
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Modulation order in real signal and complex signal modulation

In real signal modulation, e.g. ofdm based on DCT transform, the modulation order $m$ should be $\sqrt{M}$ where $M$ is the modulation order of the complex signal. for example, if we are using QPSK ...
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Why Bluetooth 2 use pi/4-DQPSK instead of OQPSK?

From the peak to average power ratio point of view OQPSK is better than pi/4-DQPSK. What is the advantage of pi/4-DQPSK compare to OQPSK? Why Bluetooth 2 use pi/4-DQPSK instead of OQPSK?
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Find the total amount of frequency multiplication needed for an Armstrong indirect FM modulator, when frequency deviation is adjustable in a range

I am currently practicing for my college exams and in this question, they are asking us to find the total multiplication needed in the system. But I am stuck because I have no idea of how to make use ...
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AM and FM frequency range

I don't know what I misunderstood or what but I thought in FM and AM you can transfer your frequency characteristics of modulating signal anywhere you want but I find out that there is a range for ...
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24 views

Transmitting an approximate CW with an FM modulator

Imagine we had an FM modulator with carrier frecuency $f_c$. My doubt is about the optimal approach to use it for transmitting a tone (CW) of a frequency $f_c+\Delta f$. Let $x(t)$ a and $y(t)$ be the ...
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I/Q Imbalance Correction using S.W. Ellingson Algorithm

Correcting I/Q phase and amplitude imbalance using S.W. Ellingson method. https://www.faculty.ece.vt.edu/swe/argus/iqbal.pdf -- S.W. Ellingson Algorithm When I try to use the set of equations to ...
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2FSK implementation with VCO GNURadio

I am fairly new to GNURadio. I am trying to generate a 2FSK with minimum frequency shift. Instead of multiplying with a 8MHz complex carrier, I directly use VCO to generate two frequencies. One at 7....
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102 views

Audio signal arrival timing, impulse response, and reverberation

I'm building an application that requires determining the arrival time of an audio signal with a very high degree of accuracy (within 1ms would be ideal) using commodity smartphone hardware. I found ...
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70 views

Why symbols have to be upsampling, if the symbol rate and sample rate is same what happen?

In digital modulation process, after constellation mapping and before pulse shaping, the symbols are upsampled with the number L(samples per symbol). At this moment, why symbol have to be upsampled, ...
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Clock recovery using Mueller and Muller adds noise affecting EVM or SNR (Two cases - GNU Radio & Python code)

The implementation of the Mueller and Muller clock recovery that I am seeing adds a large amount of 'noise' or degradation to the Error Vector Magnitude (EVM) to the symbols on the constellation. This ...
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44 views

SDR and amplitude modulated signals

Can I view every signal that has been transmitted using software defined radio as a amplitude modulated signal? For example I could make a frequency modulated baseband signal in GNU Radio and connect ...
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38 views

Calculate moving RMS with exponential averaging

This is moving RMS, now how to add exponential averaging in this df['signal'].rolling(21*24*60).apply(lambda x: np.sqrt(x.mean()))
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80 views

Adding phase noise to a signal results in amplitude variation on a constellation - whats the mistake? *plots inside*

I am attempting to add phase noise to a modulated signal. I am doing this by taking a phase noise mask (single sided 0 Hz to 1 MHz), which shows dBc values away from central value or reference value. ...
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85 views

Error probability for orthogonal signaling with unequal symbol probabilities

I'm trying to derive the equation of error probability in orthogonal signaling. Here what I've tried: Let $\vec{s_1} = (\sqrt{E_b} , 0)$ and $\vec{s_2} = (0, \sqrt{E_b} )$ be vector representation of $...
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How to solve this question on communication lines?

The Question asked is as follows: A communication link operates at a bitrate of 20 Mbps. The receiver is expected to perform at a $BER$ of $10^{-6}$ or better using $QPSK$ modulation scheme. [Note: $...
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Why we only can transmit a real signal? [duplicate]

i just wondering, why we always transmit a real signal but when we deal with a baseband signal we use a complex signal ? are this is related to up and down conversion of the signal (Because complex ...
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Is the modulation on my WiFi different to the modulation on cellular?

Is the modulation method, or nature of modulation otherwise, between my phone and my WiFi modem, versus my phone and a cellular mast, different?
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Adaptive Delta Modulation: Logic for step size control at receiver

I read that in adaptive delta modulation, we have a block for step size control (diagram below) which takes into account the one bit quantizer output in a feedback loop and modulates it, the intent ...
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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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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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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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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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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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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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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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152 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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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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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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