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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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19 views

How range of the signal increases when modulation is done?

I am very confused because we know by increasing frequency we decrease the wavelength hence the distance covered will be very less but when we modulate a signal we are basically increasing the signal ...
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4answers
28 views

Bandlimiting and OFDM spectrum - what is considered “bandlimited”?

I have been reading about OFDM modulation, it's not clear to me how you can have band-limited OFDM but given its prevalence in wireless communication there must be some designation of approximately ...
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2answers
53 views

What is a constant envelope modulation?

The Book "Digital Modulation Techniques" by Fuqin Xiong groups digital modulation schemes into two classes: "constant envelope" and "nonconstant envelope." However, I was surprised by the inclusion ...
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0answers
41 views

What is the relationship between FFT size and demodulation in OFDM

As I mentioned in the title of the question, how can we demodulate the data in order to get the same number of subcarriers with different FFT size. For example, 10 MHz LTE can be sampled with 15.36 ...
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1answer
25 views

How can I do QPSK in MATLAB [closed]

Could you please explain the step below, what is the benefit of it and how does it work. . I do qpsk demodulation, do I started doing the meshgrid, ...
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1answer
33 views

ISI/Equalization in digital signal processing

I am studying the OFDM system and before to start I have decided to study the main concepts of modulation. And I have spent yet a lot of time to understand the concept of an equalization to reduce ISI....
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2answers
54 views

IQ modulation: baseband to bandpass transformation

can someone explain me these doubts? it is a baseband signal representation. A- complex signal, R- real. If I multiply baseband signal with FT( cos) then the signal will look like this ( on the ...
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1answer
24 views

Modulation of real-valued signal

I have one doubt according to modulation of a real signal. there are so many examples where the real signal was modulated with frequency bigger then 0. Why the signal could not be putted in f=0? is ...
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0answers
33 views

Space-time trellis coding

Can someone explain to me how to calculate the branch metric of a Viterbi algorithm for a MIMO communications system? In an example, I came across they vaguely show the calculations and I have no ...
2
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1answer
132 views

Calculating SNR from Frequency Domain

As I am newbie to signals, I have collected an appliance signal in frequency domain as follows: (PSD- Power Spectral Density). So, I need to calculate the SNR (Signal to Noise Ratio) and BER (Bit ...
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1answer
38 views

The code explanation about QPSK modulation

This is the code about the QPSK modulation, and I don't understand the real part and the imaginary part code. Can anyone explain it to me if you know? Why is ...
0
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1answer
38 views

Homodyne concept of receiver

I would like to understand a concept of homodyne architecture of I-Q demodulator and how the wave looks like at each step. It is a bandpass Signal: Step 1: multiplication with cos and sin wave. I ...
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1answer
29 views

Don't understand the relation about the wireless communication flow chart and TDMA illustration diagram

The first picture is the wireless communication flow chart,and the second is the TDMA illustration diagram,Which part of first picture is TDMA ? or if first picture is the standard process for TDMA,...
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0answers
26 views

Modulation to achieve Shannon capacity in AWGN channels

If my understanding is correct, to achieve the Shannon capacity in AWGN channels, we need a modulation that codewords follow Normal distribution, or uniform on surface of a sphere (sphere hardening ...
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0answers
74 views

Why does my OFDM demod in GNU Radio not return anything?

This is the flowgraph I used: Output after mod: Output after demod: I've read that it might be a synchronization problem but since I'm not actually transmitting anything over a medium, that shouldn'...
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0answers
30 views

What are the pros and cons of common modulation techniques? [closed]

What are the pros and cons of commonly used modulation techniques? Why is one preferred over another in a given situation? Why do so many exist? Are some better at resisting noise, travelling long ...
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1answer
43 views

IQ modulation principle

I am new in the signal processing. I hope I can get help. I want to ask a question regarding IQ modulation work . Why can’t I simply multiply a complex base-band signal with a cosine to modulate it?
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1answer
25 views

Synchronization with a specified sequence

I'm currently creating a project in Matlab where I'm simulating a communication, based on the SSB modulation, between a transmitter and a receiver. I've added a Barker sequence in the trasmitted ...
2
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2answers
84 views

Audio Steganography: Inaudible Audio Watermarking for Source Identification

What is a relatively inaudible audio watermarking technique to overlay a broadband audio signal on top of playing music without analysing the music for low-bitrate source identification? Ideally ...
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2answers
107 views

GNU Radio QPSK 4 Symbols

I'd like to generate a simple QPSK signal in GNU radio, but so far I haven't been able to get it to perform the way I'd like and I'm not sure if this has to do with some misunderstanding I have about ...
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1answer
43 views

Is Oversampling a Signal Same as Discretizing the Signal?

I am confused about the new terminology 'oversampling' I have encountered very recently. To explain it better, I am going to use numerical examples. Now let's assume I am using a BPSK modulator and my ...
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1answer
41 views

modulate/demodulate audio file as FSK signal mixed with music signal

What I want to do: I want to encode an audio message inside a regular music file; this shall be decoded by an audio analyzer running on another machine (by listening to the audio playback from the ...
0
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1answer
49 views

Ratio of the power in the sidebands to the total power in conventional AM

Message signal and carrier signal are given as $m=\cos(2 \pi \cdot f_{m} \cdot t) $ $c=A_{c}\cdot \cos(2 \pi \cdot f_{c} \cdot t) $ I was asked to find modulation index $a$ so that ratio of the ...
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1answer
94 views

Cyclic prefix length in baseband OFDM with ZF equalizer

My question is about baseband OFDM. I try to plot the BER according to the SNR. I noticed that changing cyclic prefix length does not affect the performances. I.e., following the code below, ...
3
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1answer
84 views

FFT based symbol synchronization for digital demodulation

Where can I read more about "slow search" methods for symbol synchronization based on FFT for extracting a clock signal from the modulated signal? I have read here (8.7 Symbol synchronization) One ...
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0answers
23 views

Modulation Index in Case of Quadrature Modulation (IQ-modulation)

It says that in case of quadrature modulation, the modulation index can be maintained at exactly 0.5 without any settings or adjustments. I don't get it why. What is it which is making it sure that ...
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1answer
46 views

concurrent multiple sound sources seperation for TDoA estimation

consider a room with some sound resources and several mics, these sound resources almost concurrently emit sound signals. As for one mic, it may pick up sound signals from different sound sources ...
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0answers
54 views

QPSK modulation validation

I tried to replicate a Matlab code in python (for testing reasons) to do a QPSK modulation. So this is the original code(source Gaussian waves website): ...
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0answers
36 views

Relationships between $f(t)$ signal and $f(t) \times \sin(\omega t)$ signal

Let's assume that there is a signal $f(t)$, $0\le t \le T$. Then, is there any special meaning of the signal $g(t) =f(t) \times \sin(\omega t)$? Like AM transmission. What is shown/heard when we play ...
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0answers
87 views

Spectra of a basic OFDM transmitter

I try to simulate a primary (or very basic) OFDM transmitter. The goal is to have spectra exactly like these: But through my Matlab code: ...
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2answers
49 views

Relationship between the carrier frequency and the propagation distance? [duplicate]

For electromagnetic waves, Is there a relationship between the carrier frequency and the propagation distance? When transmission distance increases the signal tends to lose power, so carrier signal ...
2
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0answers
77 views

Does anyone recognize this modulation?

I'm trying to extract the code of my garage remote, but i have some difficulty to find witch modulation has been used. At first I thought it was a simple digital modulation, but there is some strange ...
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0answers
11 views

Vestigial Side Band Demodulation: Which components are to be retained and which are to be filtered out?

This article shows the analysis of Vestigial Side Band Suppressed Carrier demodulation. I have understood the mathematical derivation up to eq (1). However, I am unable to understand which components ...
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1answer
53 views

Square law demodulator. How can we eliminate the term containing $m^2(t)$?

We are trying to extract the message signal from the AM signal using square law demodulator. In the final expression, $V_2(t)$, the term encircled in blue has to be retained, and the others have to ...
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2answers
80 views

Bandwidth of product of two signals

POINT 1: According to convolution theorem, if g1(t) has a bandwidth B1 and g2(t) has a bandwidth B2, then product g1(t)g2(t) has a bandwidth = B1 + B2. POINT 2: Now, consider an AM waveform s(t)=g(t)...
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1answer
82 views

Frequency modulation of $m(t)$ in MATLAB

I have a message signal defined in the below interval $$ m(t)=\begin{cases}1&, 0\leq t < \frac{t_0}{3}\\[2ex] -2&, \frac{t_0}{3}\leq t <\frac{2t_0}{3}\\[2ex] 0&, \frac{2t_0}{3}\leq t ...
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1answer
88 views

Real-time modulated IIR filter

I've been learning to implement an IIR filter for a synthesizer project. It is now more or less stable when the parameters are constant, but ultimately I want the parameters to be arbitrarily ...
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2answers
102 views

How exactly does 8PSK work on each I and Q leg?

I am working on making a modulator in VHDL and am implementing 8PSK. Currently, I have BPSK and QPSK looking good, and I have verified the spectrums. However, now that I am moving to 8PSK, I am stuck ...
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1answer
49 views

Recommended literature to learn essential aspects of signals and its propagation [closed]

Where can I learn about signal's features. For instance mean, power, amplitude, frequency, energy, how they propagate in space or any other medium?. What power means its amplitude increases and ...
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0answers
390 views

AM Modulator-Demodulator in Python

I am trying to make a AM modem using Python Numpy and Matplotlib. I am successful in generating the AM Signal but I cannot demodulate it using a lowpass filter function that I made. The demodulation ...
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0answers
60 views

How is this signal being modulated?

I have a small device that transmits commands in bursts. Looking on the FCC website for the device, the encoding is supposed to be ASK. Previous examples of ASK encoding that I have seen look like ...
3
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1answer
116 views

Difference between Line Code and Keying

The following statements are from Wikipedia page of Keying Keying or digital modulation applies to transmitting a digital signal over an analogue passband channel. When a digital signal is ...
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2answers
70 views

Don't understand what is meant by signal dimension

I don't understand the concept of dimension of a signal. I ran into it in an explanation of Shannon Capacity, and in a paper on spread spectrum. I was hoping somebody could explain with an example. ...
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1answer
263 views

Confused in Bit rate, Symbol rate, Sample rate and Data rate

I'm using GMSK modulation to send $300 \ \rm bits$ and assuming $1 \ \rm bit/symbol$. $BT$ product is $0.5$. Sampling frequency is $100\ \rm kHz$ and bandwidth of the signal is $28 \ \rm kHz$. (a) ...
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0answers
33 views

low-frequency amplitude with phase modulation of low Hz carrier

I am writing an FM/PM synthesizer, using Java. For the most part it works pretty well. What I am curious about is an attempt to use a low frequency tone as a carrier. By low frequency, I mean in the ...
1
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1answer
242 views

Symbol rate and bit rate

Nyquist's formula for maximum channel capacity (noiseless channel): $C=2B \log_2(M)$ Shannon's formula (noisy channel): $C=B \log(1+S/N)$. I need to distinguish between the symbol rate and the bit ...
1
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1answer
96 views

Why would amplitude modulation result in change of frequency?

Question: (single choice correct; source: JEE Main 2015) A signal of $5 kHz$ frequency is amplitude modulated on a carrier wave of frequency $2 MHz$. The frequencies of the resultant signal is/are: ...
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1answer
89 views

How does modulation work in simple language?

I am reading modulation from this site (am a beginner). In the end, they've given this example: I am having trouble understanding how exactly they arrived at the two modulated results for AM and FM. ...
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1answer
36 views

Transmission frquency in MIMO-OFDM system

What I understand in MIMO system, the user data is broken down into several chunks and transmitted over the antennas (say 3 Tx antennas) by using same frequency Fc. In order to use the interference as ...
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1answer
267 views

Extracting the carrier signal from AM

I am new to DSP and leaning about amplitude modulation. I am trying to demodulate a 5 Hz signal that is modulated by a 50 Hz carrier. I am trying to extract the carrier, not the the 5 Hz signal. A ...