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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1answer
287 views

Are IQ-samples independent from the carrier frequency?

Since i am not sure if i have understood IQ samples correctly, i want to ask the following question: If i look at inphase and quadrature in an IQ diagramme, the length of the arrow describes the ...
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1answer
593 views

Power Spectral Density of Digital Modulations

I want to simulate the power spectral densities of different modulations in MATLAB (without Simulink). Unfortunately I have only very basic understanding of signal processing, hence I struggle with ...
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2k views

The error probability of 16QAM

The signal constellation for a communication system with 16 equiprobable symbols is shown as below. The channel is AWGN with noise power spectral density of $N_ 0/2.$Using the union bound, find a bound ...
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2answers
494 views

What is the meaning of channel capacity?

If the transmitted information signal takes values from a modulation constellation, then is there a way to know what the channel capacity is? Is there a connection between the modulation kind and ...
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45 views

Some problem with the expression of QAM basis and signal

The expression of QAM basis is \begin{align} \psi_1&= \sqrt{\frac{2}{E_g}}g(t)\cos(2\pi ft)\\ \psi_2&= -\sqrt{\frac{2}{E_g}}g(t)\sin(2\pi ft) \end{align} I want to ask why is $\psi_2= -\sqrt{\...
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Transmit data through sound between 2 computers (very close distance)

I'm writing an example on transmitting data through sound betwwen 2 computers. Some requirements: The distance is very close , i.e the 2 computers are basically adjacent to each other Very little ...
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1answer
629 views

Typical number of samples per symbol

Assuming a pulse shaping of a source of symbols (like $s=\{3,-i,2+5i\}$), and a SRRC waveform (or any other waveform). I know that it depends on many factors like modulation scheme, but, in practice, ...
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1answer
139 views

AM modulated signal not centered at carrier frequency [closed]

I am trying to modulate the signal bl_msg_time (this is a speech signal) using DSB-SC modulation however the signal doesn't appear centered at the carrier frequency....
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2answers
204 views

Relation between erfc and the BER

Antipodal Signalling has a bit error probability of $P_b = \frac{1}{2} \mathrm{erfc}\big(\sqrt{\frac{E_s}{N_0}}\big)$ and on-off-signalling has a bit error probability of $\frac{1}{2} \mathrm{erfc}\...
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1answer
166 views

FM modulation audio 50 Hz – 16 kHz MATLAB

I'm trying to modulate in FM an audio signal $x(t)$ coming from a microphone which works from 50 Hz to 16 kHz in MATLAB. But the problem is that I want a FM Bandwidth of 25 kHz at the output of ...
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541 views

Information in GFSK signal

I was measuring a Bluetooth LE Signal, particullary a Channel with center frequency 2402 MHz and Bandwidth of 2 MHz, 2401 - 2403 MHz. Those measurement points are just the highest peaks. In the ...
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1answer
895 views

Modulation Index of Conventional AM Signal

An AM signal has the form $$u(t)=100\left[1+\sin(2000 \pi t)+5\cos(4000\pi t)\right]\cos(2\pi f_ct)$$ Where $f_c$ is 800 kHz. What is the modulation index? (We can define modulation index as the ...
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711 views

How can I generate offset QPSK symbols from QPSK symbols

I am trying to generate Offset-QPSK modulated symbols. But I am facing some difficulties. I know how to make QPSK symbols but I am unable to figure out at what stage I have to bring in changes to make ...
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2answers
133 views

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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2answers
64 views

Meaning of 'angle' in angle modulation

I know what is angle modulation. I want to know why is named as 'Angle'. Is it because in the vector plot of sidebands are described by various angles? or what?
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1answer
45 views

Modulation and filtering

When I modulate a signal $x(t)$ with $\cos(2 \pi f t)$ and the modulated signal passes through a HPF, what output do i get in the frequency domain?
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4answers
811 views

How can the I and Q components of a quatrature signal be different from each other (apart from the 90º phase shift)

I've spent many hours reading and doing research about this. I don't attend any university classes or any type of classes that may approach such a topic. I am trying to learn this by my own without ...
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1answer
234 views

Why do signal have mirror signal after pure frequency shift?

In my Matlab code I have a simple simulation of FPGA with the ability to simulate doppler shift, and after I and Q components plugged into IQmod with some carrier freq. In my Matlab code when I ...
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1answer
276 views

Why is one of the modulated frequency spikes smaller?

This is a simple amplitude modulation experiment. Both waves are sinusoids of the type cos(2 x pi x f x t). The base signal has a frequency 100Hz, and the ...
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0answers
55 views

Is an extra symbol at the origin of a QAM constellation ok?

This question is specifically directed at Maximilian Matthé (as you work with 5G systems), and to anyone who can shed some light. I am trying to implement a GFDM system with a total of N = K*M ...
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1answer
123 views

Changing the number of cycles of an sinusoidal input signal

Imagine we have an ultrasonic sensor that transmits a multiple cycles of sinusoidal signal/waveform that can travel up to a specific distance/range. Can we achieve more distance coverage using more ...
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1answer
735 views

how to implement a one 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 go ...
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1answer
2k views

why is the z transform transfer function 1/(z-1) called an integrator?

I am reading up on delta sigma modulators and there this term $\frac{1}{z-1}$ that appears repeatedly and is referred to as an "integrator". Why is this so ?
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How does bandwidth affect a modulated digital signal? [duplicate]

I'm currently reading up on how the lower layers of the ISO/OSI model work and I don't quite understand how broadband communication works yet. Suppose I want to send some data from point A to point B ...
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2answers
2k views

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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1answer
319 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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1answer
432 views

How is the number of amplitude levels decided in modulation techniques?

For M-QAM modulation, where e.g. $M = 64$ there are 8 amplitude levels. Each level is represented by a symbol that is further represented by bits through the relation: $$b=\log_2(M)$$ This means ...
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Mathematics in selection of RC time constant for an envelope detector for AM

Let the capacitor be charged to voltage $ V(t_0) $ at $ t=t_0 $ and then start discharging. At time $ t \, (>t_0)$, the delayed capacitor voltage is $$ v(t)=V(t_0)\operatorname{exp}(- \frac{t-t_0}{...
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1answer
253 views

Distortion in demodulation signal

I'm doing amplitude modulation and demodulation for DSB. the maximum amplitude of my original signal is $1$. After demodulating the signal, I should be getting the original signal which is $1$ but ...
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106 views

How to find and fix the delay of a modulation

I am creating a model in MATLAB to simulate power line communication, but I found a problem. I'm very new to the DSP area, I get my code below from a MATLAB example. ...
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1answer
628 views

QAM Constellation Construction - Basic 4/8 QAM

I wanted to know how to construct the set of amplitudes/phase for QAM modulation. I saw that a QAM signal can be represented as: $$ s_m(t)=A_{mi}g(t)\cos(2\pi f_c t)-A_{mq}g(t)\sin(2\pi f_c t) $$ ...
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1answer
735 views

Confusion between PSK and QPSK

What is the difference between PSK (Phase Shift Keying) and QPSK (Quadrature Phase Shift Keying)? Doesn't PSK need quadrature component for its working?
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393 views

Demodulation distortion in single-sideband and double-sideband

I am trying to compare the demodulation for single sideband (SSB) and dual sideband modulation formats (DSB) when the reconstructed carrier is not perfect (i.e. shifted in both frequency and phase). I ...
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2answers
6k views

Envelope behavior dIfference between QPSK, OQPSK and $\pi/4$-QPSK

I am trying to analyze whats the major difference between these three variants of 4PSK. I know that QPSK - signal points are at 0,90,180,270 OQPSK - The bit period of Quadrature component is ...
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1answer
436 views

Zigbee Transceiver Using OQPSK Modulation under Fading Channels

I am working on transmitting ECG signal over wireless body area networks. According to IEEE802.15.4 standards , I am using ZigBee transceiver at 2.4 GHZ . Complex baseband equivalent channel model is ...
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1answer
1k views

difference between GMSK (Gaussian Minimum shift keying) and GFSK (Gaussain frequency shift keying) [closed]

I am unable to differentiate GMSK and GFSK. How do the modulation techniques differ in Tx? How do their receiving techniques differ..?
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1answer
217 views

Why do digital modulation when the signal entering the channel is analog?

I am learning about digital filters and came across the link Why do digital filters work? In real world communications, I think the input to the channel is in analog after being modulated by digital ...
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1answer
102 views

Brief introduction to wireless communication and communication terminologies [closed]

In the Question Design of equalizer for wireless communication the diagram of a basic communication system is presented with informative points and discussions. My Questions are: Considering the ...
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348 views

GMSK Big error in demodulation MatLAB Simulink

I am trying to do a PLC simulation system, but my problem is in GMSK demodulator, in my simulation in Simulink MatLAB my output signal is very different from the input signal, below the model: Below ...
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1answer
302 views

A query on Power spectral density (PSD)

Say a narrow band signal $n(t)$ has Power Spectral Density (PSD) $S(f)$. If the signal $n(t)$ got multiplied by $\cos(2\pi Ft)$, then what will the PSD of resulting signal in terms of $S(f)$ be? Will ...
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39 views

What is full AM used for?

What are some applications where full AM is used nowadays? Is it used at all considering the fact that it is less power-efficient than, say, AM with suppressed carrier?
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375 views

Simplest All Digital GMSK Modulator

What is the simplest way to implement an all digital GMSK modulator with no multipliers? The implementation approach should be applicable to GMSK modulation with BT=0.5 or less (where intentional ISI ...
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1answer
146 views

Quadrature Amplitude Modulation: I and Q Same

I am trying to understand a previous design that uses Amplitude Modulation. Instead of just using the real part of the signal, the designers put the voice signal on both I and Q. Both I and Q have ...
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1answer
435 views

PSK Bandwidth for SNR

I'm conducting experiments on several n-ary Psk signals of differing symbol rates. I'm comparing detection levels of different signal detection approaches on sets of PSK signals. I'm using a cosine-...
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1answer
2k views

Why DFT-SPREAD OFDM has lower PAPR than OFDM?

I just read 4G LTE/LTE-Advanced for Mobile Broadband, and found the content as below, If the DFT size M equals the IDFT size N, the cascaded DFT/IDFT processing would obviously completely cancel ...
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2answers
1k views

Average bit error and symbol energy

How do you draw decision boundaries given this type of 16-qam constellation diagram, I know that there should be no vacant decision boundary but I can't seem to get it.Also, assuming that the correct ...
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2answers
684 views

Impact of modulation index in FM

If I have the spectrum of a FM modulation, does the frequency of the carrier disappear when the modulation index is too big? Does the amplitude of any side band depend from the modulation index? And ...
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1answer
237 views

FSK: non-integer vs integer rmodulation index, peculiar peaks

I've been experimenting with frequency shift keying (FSK) and found a peculiar pattern I cannot explain. I noticed that there is a significant change to the shape of the power spectral density of the ...
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2answers
2k views

Analyzing a 16-QAM modulated waveform?

Okay I'm really confused about analyzing the waveform I generated using 16-QAM on MATLAB... I transmitted a $y = [0 \ 1 \ 2 \ 3 \ 4 \ldots \ 15]$ discrete signal (in order) to ...