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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300 views

QAM-spectrum with uneven real & non-odd imaginary part

Despite the signal being real, as is seen in the last line of the first picture: , the exemplary spectrum of the signal shows neither an even real nor an odd imaginary part: But from my theorems I ...
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1answer
3k views

Numerically Controlled Oscillator (NCO) for phasor implementation?

If I want to simulate a digital oscillator (or phasor) to modulate an arbitrarily length signal: $$y(t) = \cos(2\pi f_ct)\quad\text{where}\quad t = \frac{n}{f_s}\quad\text{for sample}\quad n$$ What ...
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Resources for modulation/demodulation techniques with example code

So I remember seeing someone recommending a DSP book that had actual code for modulation and demodulation of a communication signal. Does anyone have any recommended resources they could point me ...
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132 views

Are there amplitude and phase characteristics of harmonic signal components?

Nonlinear amplifiers are characterized by their AM/AM and AM/PM. That's what I thought. But now I have a question: The amplitude and phase distortion characteristics, do they only belong to the ...
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113 views

Beginner level confusion regarding symbols used in modulation

For 4-QAM symbol sequence, each symbol can be represented by $k=\log_2(4) = 2$ bits. 4-QAM constellation can be generated using s = round(rand(1,T)*2 -1) For 16-QAM,...
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Why do SDR receivers emit I/Q samples?

To my understanding hardware receivers for software-defined radio applications basically take the input signal, mix it with the tuning frequency to remove the carrier frequency and then sample the ...
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1answer
379 views

Rayleigh fading in simulink

I have a simulink model of zigbee over a Rayleigh fading channel. The modulation in the transmitter part is O-QPSK modulated baseband. Most of the examples didn't add the RF frequency after the ...
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1answer
264 views

How to detect Frequency Sweep Direction when Channel is unknown

So I would like to try to modulate data using the direction of frequency sweep (a data bit of 1 would be an up sweep, and 0 a down sweep). Encoding my transmit signal is fairly easy, but i'm not sure ...
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399 views

Eye Diagram of QPSK Modulated Signal

I need to plot eye diagram for RRC filtered QPSK modulated signal. The specifications are given as follows Sampling frequency : $1.024$ MHz Symbol Rate : $256$ Kbps (Hence, Upsampling rate = $4$) ...
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2answers
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Help me understand how Pulse-Amplitude Modulation (PAM) works

Reading on the Internet i learned that PAM is basically a sampling technique which converts an analog signal into a discrete signal. It modulates a train of pulses by varying the amplitudes of the ...
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101 views

How does a Huffman encoded message gets unified before channel encoding?

I aim to understand the signal entire transmission pipeline. Currenlty, I am facing a problem regarding the handling of a Huffman encoded message. Example: Message $X$ contains symbols $a(50\%)$, $...
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Why is the bandwidth doubled with AM?

Let's say I have an arbitrary signal which has the following frequency spectrum and a bandwidth of BNF: Now I use Amplitude Modulation to transport the signal. The frequency spectrum will change ...
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591 views

How is multiplexing achieved in spread-spectrum modulations like CSS?

I understand why it doesn't interfere with narrowband communication systems but how do different clients communicate in a system like LoRa. Is it time orthogonality like TDM?
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1answer
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what is the difference between QPSK and 4QAM? [duplicate]

i need to know the main difference between QPSK and 4QAM, i have searched over the internet and still i have not found a good explenation.
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595 views

8-PSK baseband signal with real and imaginary part

I want to draw the complex-valued baseband signal with real $S_{BB,I}(t)$ and imaginary part $S_{BB,Q}(t)$ for the following bit sequence: 011111001000 I have ...
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57 views

Spreading sequence and equalization based on a paper

I am having difficulty in understanding how the Authors in this paper, An EM based method for semi blind identification of linear systems driven by Chaotic signals have used the expressions derived ...
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1answer
237 views

How can I describe a sum of sinusoids by an equivalent lowpass signal?

I consider a sinusoidal signal with fixed amplitude $A_{\rm in}$ and frequency $f_c$. This signal is sent into a nonlinear amplifier, whose AM/AM and AM/PM characteristics are known. Using these ...
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2answers
103 views

Direct sequence spread spectrum modulation

When the receiver gets the signal $m_t$ sent by the transmitter, the signal will have an additive interference $i_t$. Thereby signal received will be : $$r_t = m_t + i_t$$ I know that to get back the ...
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Why the correct probability for a square M-QAM is equal to the square of correct probability of ($\sqrt M$)-PAM?

The question is why: $P_c (\text{square} $ $M-QAM) = (1 - P_{\sqrt M})^2$ where: $P_{\sqrt M}$ is the error probability for $\sqrt M$-PAM signal. Thanks.
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1answer
288 views

Why LFO should be alias-free?

I'm really tripping about this point! I try to reason with you and explain what's my trouble. Consider a scenario with Sample Rate 44100hz and a LFO square wave that will modulate some internal ...
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208 views

Does 4D-PAM5 has DC component?

Because of redundancy( 4^5>2^8 ) 4D-PAM5 has, I think there is no DC component and synchronization problem but I can't sure. What is the truth?
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Please help me understand this FM carrier frequency inequality

The link of the statement is evidenced in this book: I don't understand how equation 85 come? I try to use Carson rule to see this inequality but turns out I have $2 \Delta f$ instead of $3 \Delta f$....
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1k views

Power spectral density of a PAM signal

Say I have a PAM signal as $x(t) = \sum_n a_n h(t-nT)$ where $\{a_n\} \in \{\pm 1\}$ are equiprobable random binary bits and $h(t)$ is bandlimited to $[-1/(2T),1/(2T)]$. ($x(t)$ is random process and ...
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525 views

Amplitude Modulation with large carrier and suppressed carrier

From what I have read so far Amplitude modulation with large carrier is favaroble because envelope detector can be used at the receiver to derive the message signal and therefore another mixer is not ...
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5k views

FSK and IQ modulation

I am having trouble understanding the FSK modulation process. There are many ways of demodulating the FSK signal. What is the advantage of performing the FSK using IQ modulation? How to demodulate ...
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2answers
771 views

Frequency shifting property

Usually in radio systems in order to move the frequency response of the message signal to a new frequency band centered at f, the message signal is mixed with $\cos(2\pi ft)$. What would change in ...
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1answer
2k views

Energy per bit ($E_b$) in BPSK with non-unity channel gain

I would like to know what is exact and correct definition of $E_b$ (energy per bit) in digital communication. Consider I have a model such as r=a*x+n where <...
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1answer
2k views

The difference between MSK as CPFSK and OQPSK

I am working on MSK simulation. I have read the Chapter 5 of book entitled Digital Modulation Techniques by Fuqin Xiong. It is said that MSK can be viewed as a Sinusoidal Weighted OQPSK or CPFSK. If ...
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1answer
2k views

Adding AWGN noise with a correct noise power to the signal

I would like to add AWGN noise to my BPSK and QPSK signal. So assume the BPSK signal is x1 and QPSK signal is x2. The ...
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1answer
290 views

Finding $E_b/N_0$ when coding rate is $R_c$

I would like to calculate $E_b/N_0$ when the code rate is $R_c$ for BPSK signal. What I got this $$ E_b/N_0= \frac{1}{2R_mR_c \sigma^2} $$ and that is the case also according to this page. $R_m=1$ ...
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2answers
650 views

Relationship between $E_b/N_0$ and $\rm SNR$ with channel coding

I would like to know what would be the relationship between $E_b/N_0$ and $\rm SNR$ when there is a coding rate of $R_c=K/N$. Normally when there is no channel coding according to this link. $$\...
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2answers
2k views

Quadrature modulation for FM and AM

This might be a naïve question, are these correct statements? Both amplitude and frequency modulated radio signals nowadays use quadrature modulation and demodulation as a mean to transfer and ...
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7k views

How to reconstruct RF signal using IQ data

I have a complex IQ signal: $s = X + Yi$. I know my original $f_0$ was $5\textrm{ MHz}$. I can calculate the magnitude/amplitude of $s$: $A = \sqrt{X^2 + Y^2}$ and phase, $\phi = \arctan\left(\frac ...
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141 views

Receiving frequency modulated signal

I have two questions: If the FM radio at the receiver mixes with a another frequency to bring down the carrier frequency, wouldn't that affect the message signal? In today's digital world, why the ...
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1answer
57 views

Canonical Rectangular Modulation

http://zone.ni.com/images/reference/en-XX/help/371025N-01/loc_eps_rectangular_modulation.gif I just wanted to make sure that my assumption that in this figure $\phi(t)$ is representing $m(t)$, and $R(...
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3answers
602 views

Understanding I and Q modulation

As a newbie I am trying to understand I and Q modulation and demodulation. So from what I read the I and Q components of a signal separately mix with RF signals that are 90 degrees out of phase with ...
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1answer
399 views

Simplified equations for FM (frequency modulation) synthesis and PM (phase modulation)?

Clicking on the links I find on the web it seems many authors don't express them neatly enough for me or they're even confusing the two. Can someone please clear this up? Is frequency modulation \...
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1answer
826 views

Modulation of voice

I apologize in advance if the question is very basic. When I google modulation all I read are the techniques that are used to modulate a signal. I start from basic. Let's say I am a reporter and the ...
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ssbmod single sideband modulation artifacts

clc; clear all; close all; [c,fs]=audioread('60hz.wav') r=ssbmod(c,160, fs) r=r/max(max(abs(r))) audiowrite('artifacts.wav',r,fs,'BitsPerSample',24) I am trying ...
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279 views

Why does QAM use two cycles instead of one per byte?

If you look at this image, you can see that you have 256 possible binary values by modulating the amplitude (the radius of the trigonometric circle) and the phase (the degrees) of the carrier. ...
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1answer
2k views

Gardner Timing Recovery for Repeated Symbols

I am implementing the Gardner Timing Error Detection algorithm for a QPSK signal. I understand the concepts behind it but I am curious as to what effect repeated signals can have on the phase lock. ...
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2answers
410 views

Visible light communication and LED modulation

I work on a VLC system in which 16-PAM symbols with complex pilot symbols are as ifft input. I made the ifft output real and positive. Now how should i use these ofdm symbols to modulate LED? Their ...
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267 views

How to find a know signal in another signal which contains other signals along with the signal i need in python

I am working on BPSK with sound waves a carrier waves. Actually I am modulating my data with some known sync bits along with the information I need to send. So the things I will be having at ...
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1answer
293 views

why does the decision boundary change in BPSK? is it true?

I am working on modulation and demodulation of BPSK using python. i made a code for modulation and demodulation,while demodulate i tried to compare my actual data bit stream with demodulated bit ...
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1answer
406 views

How to derive the transmitted signal from a constellation diagram

Let us assume we have $16$ symbols to transmit. We can represent these $16$ symbols by $16$ unique signals and transmit. If at the receiver we can identify these $16$ signals correctly, we have ...
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1answer
5k views

FSK Demodulation, Bit Timing Recovery

I am currently implementing acoustic FSK modulation and demodulation. I am not a signal processing guy so any help about the bit timing recovery would be very appreciated. Currently I implemented the ...
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2answers
9k views

What is a $BT$ (Bandwidth-Time) product with reference to modulation?

I would like to know what does Bandwidth-Time product mean. I understand that Bandwidth ($B$) = 1/Symbol Time ($T$), hence $BT = 1$. But how can it vary? What is its significance? e.g. When we say ...
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1answer
439 views

How to set a Carrier Wave for DBPSK Modulators in gnuradio?

for a Project I need to build an Audio Modem in GNU Radio. I decided, that it would be the best to use DBPSK Modulation, because that is fast and relatively noise resistant. But as it seems, the ...
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2answers
867 views

M-Array DPSK decoding and encoding

So i'm trying to figure how how to do the encoding and decoding of an M-array Differential Phase Shift Keying (DPSK) signal. I understand how to do it for binary DPSK, but on higher ordered signals I'...
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1answer
84 views

Reasoning Behind Additional Phase Shift in DPSK

In MATLAB's Comm System Toolbox there is an option for 'Phase Rotation', defined as the phase difference between previous and current modulated symbols when the input is zero. This is the first time I'...

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