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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655 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, ...
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403 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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1answer
71 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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39 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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2answers
374 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 ...
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94 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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1answer
892 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
700 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
219 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
204 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
977 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
56 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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5k 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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1answer
728 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
340 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
2k 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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119 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 ...
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1answer
2k 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 ...
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1answer
878 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
1k 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
74 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
743 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 ...
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6answers
987 views

Use of the Dirac delta as a sampling operator

As we are all taught in signal processing classes, the Dirac delta is not a normal function but a generalized function. It is sometimes defined as either the limit of some normal function whose ...
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1answer
426 views

What is the phase coded modulation?

I'm trying to understand what is the "phase coded modulation" and how does it work. As far as I know, Although the linear frequency modulated (LFM) waveform continues to be the workhorse of modern ...
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1answer
3k views

Conversion between Eb/N0 and SNR in spread-spectrum modulation like LoRa CSS?

This question is somewhat related to the one asked here: How is multiplexing achieved in spread-spectrum modulations like CSS? I am looking at the bit error rate (BER) performance of communication ...
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1answer
399 views

QPSK on baseband question

Given a signal you are asked to perform baseband QPSK (not on a carrier). Does this mean the following? In baseband QPSK the (possible) constellation points are $$\sqrt {E_s} e^{jn \pi / 2} \...
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Bits - symbols mapping in M-PAM beginner question

I am trying to implement a M-PAM modulator in Matlab without using the built-in functions. I am confused when it comes to the symbols-bits mapping. Say I have a sequence of bits: ...
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1answer
342 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
845 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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1answer
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
654 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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3answers
46 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
933 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
183 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
305 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
210 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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735 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
1k 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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3answers
920 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
150 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
81 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
82 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
1k 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
282 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
330 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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60 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
128 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
933 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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2answers
4k 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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