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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Can someone help me do this MATLAB code, Please tell me what should be the parameters of sin and pulse signals [closed]

Write MATLAB Code for the following problem A sinusoidal signal of frequency 𝑓0 = 10^4 /2𝜋 Hz is sampled at the rate of 8 kHz and then applied to a sample-and-hold circuit to produce a flat-topped ...
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How to understand haw many matched filters to use?

I have a question that i can not find a concrete answer. Haw many matched filters should be used for 8-PAM/16-QAM/64-QAM/BPSK? Can somebody shortly explain the logic we should follow? Thank you.
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Frequency Modulation - Demodulation - Distorted frequency shape

I am interested in the effect frequency modulation has on the signal. I am using an acousto-optic deflector to steer a laser beam. The deflector receives a Radio-frequency (RF) signal (~100 MHz, sine-...
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How to derive the error probability for pulse position modulation in digital communication?

I am trying to build a simulation on MATLAB for PPM transmission through AWGN channel. I have a function wrapping the transmitter, channel and receiver that takes a SNR value as input. My simulation ...
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delta modulation

I need to implement some sort of simple delta modulation for my homework. The test signal is $x(t)=10\sin(20\pi t)+\cos(100\pi t)$, sampled at $f_s=40f_{\tt{max}}$ Block scheme of delta modulator is ...
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Why do I find a low frequency oscillation when I add a carrier frequency to my baseband signal ? And Why is my demodulation step not working?

I am trying to build a simulation for a 2PPM signal, modulate it at high frequency and then retrieve my baseband signal. Here is my full code (minus the plots) before explaining more. ...
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How should I decode Pulse Density Modulation signal?

I'm trying to learn the concept of Pulse-density Modulation. The wiki page gives a good overview and pseudocode of encoding procedure, but it lacks the decoding part: The process of decoding a PDM ...
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Choosing a suitable modulation format

I'm trying to deal with this question about multiplexing and choosing an appropriate modulation format. It's in two parts. (i) You need to design a system for the transmission of surround audio ...
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Sending and receiving an image

After studying digital communication courses, I wanted to implement these theories and create an application for sending and receiving a gray image via WiFi between two Raspberry Pi devices. The ...
Mouh Kramo's user avatar
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Convolution with an impulse train in time, what happens in frequency domain

Following figure is drawn as the block diagram of the digital modulator: The output of the filter block (with the impulse response p(t)) is the convolution of the weighted impulse train with the ...
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Does MSK modulation maintain continous phase after spectrum spread?

I need to check if MSK modulation keeps the phase continuous after DS spectrum spread. My thinking is that since we're expanding the bandwidth, it likely involves abrupt frequency changes so it won't ...
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Continuous Phase Modulation - Phase trajectory expansion

For continuous phase modulation (CPM), the circular phase trajectory is expressed as follows: $$\phi(t) = 2\pi h\int_0^t\sum_k \xi_k g(\tau - kT_s)d\tau + \Phi_0\tag{1.1}$$ Where: $h$ is the ...
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spectral density of Modulated ofdm signal

I have formed my OFDM symbol his length is 88 (Nsubcarrier=72,Ncp=16) with Fs=1080000 Hz we call this symbol as Signal_from_baseband I want to modulate the OFDM symbol with Fc carrier=2.1 GHz and plot ...
ahmed bennani's user avatar
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Help me understand the concept of IQ signals

I am a computer science student working on a school project involving RTL-SDR receivers, and I have a hard time grasping the concept of IQ data. Basically what I think I have learned from all of the ...
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What is the relationship between Symbol Duration and Sampling Frequency in a 256 MPSK radio link

I'm struggling to work out the relationship between Symbol Duration and Sampling Frequency in an MPSK link. For instance, if the Sampling Frequency is 10MHz this means that a sample is taken every ...
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How is the normalized power required for unipolar NRZ twice that of polar NRZ?

So, the normalized power for unipolar NRZ scheme is $\frac{1}{2}V^2$. According to my book, the normalized power required for polar NRZ is half that of unipolar NRZ. So, the power should be $\frac{V^2}...
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Oqpsk pll delay axis ambiguity

I don’t understand how this phenomenon appear in OQPSK carrier recovery loop. I found nothing on google. Is it a normal phenomenon in OQPSK loop or specific? Why does it get reversed I and Q? In the ...
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What are different encoding schemes used in gigabit ethernet?

I was reading about digital transmission, there are many steps namely Analog to Digital conversion Source coding Channel coding Line coding Pulse shaping Modulation Multiple access techniques Out of ...
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Is there an open source "Data over Voice" library?

I need to transfer data from A to B using audio as the medium, with a speaker at one end and a microphone at the other. Sometimes simply through the air, but it must also work through legacy phone ...
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Pulse amplitude modulation

I am reading from the internet and my professor's course on PAM. This course is not well-organized, and I would like to ask for book recommendations. I know that this modulation is divided into two ...
Mouh Kramo's user avatar
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Is BPSK relevant, or does it even exist, in wireless data transmission?

I ask this question because it seems to me that if pulse shaping has been applied in the transmitter, the signal that is actually transmitted is not phase modulated at all, rather, it is amplitude ...
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How does PAM-4 encoding of a digital signal relate to theoretical *pulse* amplitude modulation?

Pulse amplitude modulation in general is often explained using plots like this one from wikipedia: There is a sinusoid analog signal (red) to be "imprinted" on a train of pulses. The result ...
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Exactly when is pulse shaping applied in the radio transmitter, before or after modulation, and is it applied differently in BPSK, QPSK and 16QAM? [duplicate]

I previously asked at which stage pulse shaping is applied in a WiFI transmitter and my question was closed due to duplication. The answers I was directed to have only served to confuse the issue for ...
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What is the phase of $Y(\omega)$ in relation to the phase of $X(\omega)$ where $x(t)$ modulated with an exponential carrier that has no phase shift?

A homework problem of a free online course I am taking, asked to draw the magnitude and phase of $Y(\omega)$ where $y(t) = x(t) c(t)$ where $c(t)$ is $e^{j 3 \omega_{c} t}$ and where $X(\omega)$ is: ...
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Preparing data for modulation classification based on RML2016

I would like to validate a trained model based on RML2016.10a. My idea is to capture a certain amount of data (20 Msps) for approximately 0.3 seconds. Then, I identify all the signals in this ...
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Comparing communication systems with different modulation orders and code rates

I propose an end-to-end communication method in my research. The key part of the method is not the channel coding and modulation but we use them anyway. I am using 1/3 rate Turbo codes with QPSK and ...
tuna's user avatar
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Raised cosine filter and root raised cosine filter IQ for modulated signal QAM/QPSK

If I am passing a QAM signal through Root raised cosine Tx filter and measure the constellation at output, it seems very bad. If this bad output again pass with other another root raised cosine Rx ...
kecbackbencher's user avatar
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Demodulation + LPF gives derivative of modulated signal

I'm new in this community and I hope it is the right place to post my question. Unfortunately, signal processing and electronics in general are not my fields, so I'm sorry if the question is trivial. ...
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Does phase shift introduce high frequencies?

In PSK phase modulation scheme, the signal phase is shifted, hence it looks something like this: I cannot understand why this doesn't introduce a set of unwanted high-frequencies, as the steep ...
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Why does NB-IoT use standard QPSK in multi-tone transmission, when pi/4 QPSK is implemented for single-tone?

I've been studying the modulation schemes used in NB-IoT communication, with a particular focus on energy efficiency. I've noticed that QPSK (Quadrature Phase Shift Keying) is used in multi-tone ...
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Clarification on video about frequency deviation in phase modulation bandwidth

I am watching this video and at 7:12 he calculates the frequency deviation $\Delta f = f_{c}f_{m}A_{m} $ where the $c$ underscript is for "carrier" and the $m$ underscript is for "...
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modulation transfer function and ground resolved distance

I am trying to understand something in remote sensing but lack a background in science and technology so it is difficult. Hopefully this is a reasonable question to ask. In sensing there are different ...
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Why for bandpass signals complex envelope and pre-envelope signal representations are used in digital communications/analog communications (FM)?

When we need to analyse band pass signals we use complex envelope and preenvelope representations, wherein a signal is given an equivalent low pass representation. My issue is why it is done, though I ...
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Meaning of roll-off factor 0.5 and bandwidth

We currently have a radio that is transmitting at the following RF params: Modulation: OQPSK Data rate: 500Kbps Uplink coding: BCH I am interested in understanding what is the associated uplink ...
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I don't understand which signal I should use as a carrier in my excersise

$\DeclareMathOperator{\sinc}{sinc}$ Given 3 signals $x_1(t) = \sinc(t) , x_2(t) = 10\cos(2\pi f_2t)$ and $x_3(t) = 5\cos(2\pi f_1t)$, where $f_2 = 100\text{ kHz}$ and $f_1 = 1\text{ kHz}$. I must ...
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DS-CDMA Spreading Code Length Selection

I'm trying to wrap my head around the process of selecting DS-CDMA spreading codes, and I'm having trouble understanding the tradeoffs of longer codes. For all scenarios described below, I'm using a ...
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Understanding homework solution - why are $\{X_t\}$ and $\{Y_t\}$ joint WSS, and finding Wiener filter + error

I'm walking through the published solutions of my homework and I'm struggling interpreting them. In them I was given a random Gaussian process $\{X_t\}$ and a random variable $$\{Y_t\} = X_t\cos(2\pi ...
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Recognizing different pulse shaping forms (16-QAM modulation)

I have three versions of a 16-QAM modulated signal, each showing the time curve of the real and imaginary parts, the spectrum and the symbol constellation. These three versions differ by the ...
lyx's user avatar
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Testing a Hilbert transform on a real signal to transmit it as Single SideBand

I am testing some Hilbert transform theory in practice. On the practical side I use Python and a soundcard to generate baseband I and Q signals. And an IQ modulator to upconvert with 250kHz. Lastly a ...
JeromeBu1982's user avatar
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How to modulate a signal to a certain frequency in time domain

I have a root-raised cosine pulse signal of bandwidth $500$ MHz. If the signal is modulated at the frequency $6$ GHz, the result should apparently look like this : If I understand well, to modulate ...
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Modeling an OFDM signal and comparing it with QPSK

I am trying to model an OFDM signal based on original QPSK stream and compare their baseband spectrums. I've used this article as a reference for plotting spectrum and this as a MATLAB OFDM reference ...
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Block Diagram 2nd Butterworth Low-pass

I would like to represent a second-order butterworth low-pass filter in a block diagram, how can I get started? As per the attached image
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Which type of modulation is used in this RF Signal?

I am working on reverse-engineering a few devices, I got some using ASK and FSK but I could not grasp this other one. I am attaching some photos from its captured signal took from URH (Universal Radio ...
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Modulating and transmitting three different voice signals (in MATLAB)

I want to record, modulate and transmit three different voice signals. I will be doing this in MATLAB. Please can you help me figure out how can I do this? Or give me a block diagram that can show ...
Sajjad Ali's user avatar
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How to correctly accept Polar/LDPC encoded bits with PSK modulation?

I have implemented a packet reception and transmission scheme using QPSK. Next I decided to add Polar/LDPC encoding. As a result, nothing is written to the received file. I think the thing is that I'm ...
Ice Cool's user avatar
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OFDM does not work with USRP

I found the ofdm flowchart in the Gnu radio examples.(ofdm_loopback) Scheme: The spectrum and the received data of the received signal: After that, I connect the USRP Sink and the USRP Source. The ...
Ice Cool's user avatar
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8PSK modulation does not work

I implemented a data transfer system using two tutorials: Guided Tutorial PSK Demodulation and Packet Communications. After that, I decided to change QPSK to 8PSK. My scheme: Constellation Sink: For ...
Ice Cool's user avatar
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Can frequency multiplier (e.g. doubler) impact signal bandwidth?

My understanding is that if a single tone at frequency F is inputted to the frequency doubler, one should observe at its output in the spectrum the same tone but now at a frequency 2F. However, what ...
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Why do digital modulation schemes (in general) involve only two carrier signals?

In my digital communication, class we have covered the various modulation schemes, namely QAM and its derivatives (B(A/P)SK, PAM and (Q/M)PSK) as well as BFSK. These two schemes have one or at most ...
LuckyPants's user avatar
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Why is the symbol duration in QPSK twice the bit duration?

I saw many answers for such questions by writing down equations such that the symbol is formed of n bits so the duration of the symbol in QPSK must be n multiple of the bit duration. I am not ...
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