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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
327 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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1answer
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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401 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
151 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
464 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
789 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
255 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 ...
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2answers
349 views

Adding a constant to a bandpass-signal in transmission

I do understand AM-DSB-SC and AM-DSB-TC, but can't see the point in adding a constant DC-offset of 2 in the upper part of this Simulink-model? Source
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1answer
190 views

Frequency-ratio at baseband IQ-mixing

I was wondering by what logic or mathematics the frequency-ration $$ \frac{f_{lo}}{f_s} $$ in the sine-functions comes into existence? Source
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1answer
663 views

Maximum Throughput of QAM system

Consider a QAM system designed to transmit over a bandwidth of $3 \ \mathrm{kHz}$. The channel's power constraint imposes a maximum $\mathrm{SNR}$ of $30 \ \mathrm{dB}$. The system can tolerate a ...
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1answer
91 views

Basic OFDM spectrum question

As novice to OFDM, I have a question, related to modulator. Here, I present modulator block diagram, I found somewhere. OFDM modulator AFAIK, final output signal has to have frequency spectrum ...
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2answers
553 views

Non coherent Symbol Error Rate vs Es/N0

Purpose: Implementing a noncoherent M-ASK modulation ($M=2$) and comparing the results, $\mathrm{SER}$ vs. $E_s/N_0$, to the theoretical formula. The theoretical formula is not based on differential. ...
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1answer
229 views

Unipolar Transmission Spectrum

I am currently trying to understand mathematically the amplitude shift keying modulation technique. My question is, say I wanted to compute the Fourier series of a basic pulse train, it is quite ...
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2answers
2k views

baseband and passband modulation

I have a simulink model over 2.4GHz. In the transmitter part, the modulation is O-QPSK modulated baseband instead of passband modulation. In Matlab Help this is the reason of using baseband ...
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1answer
273 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
2k 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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0answers
124 views

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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1answer
124 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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1answer
102 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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2answers
3k views

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
337 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
246 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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1answer
387 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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1answer
2k views

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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1answer
96 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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2answers
2k views

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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2answers
544 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
12k views

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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2answers
522 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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1answer
55 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
183 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
98 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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2answers
71 views

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
250 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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1answer
192 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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1answer
47 views

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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1answer
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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1answer
452 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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2answers
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
451 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
1k 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
1k 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
1k 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
214 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
564 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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2answers
5k 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 ...