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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Relationship between Carrier Frequency Offset and the Constellation Diagram
As part of a project I am doing, I have to investigate how having a carrier frequency offset would affect the constellation pattern of the received signal.This question has got me baffled because to ...
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Are there modulation schemes that use more bandwith than they need to, but don't require a spread-spectrum code to decode? (besides AM)
In this answer to Have deep-space spacecraft always used some form of spread-spectrum for data downlink? space scientist Mark Adler explains that while spread-spectrum proper (using specific codes in ...
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Confusion about collection of bits and symbols
I'm taking an intro communications module and I'm quite confused on what the term "symbol" really means?
Consider this setup:
My understanding is as folllows
After the information source, we have ...
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What is the mixed numerology in OFDM
In order to meet the user requirements in the next
generation radio access technology, the ongoing standardization within 3rd Generation Partnership Project (3GPP) offers flexibility in terms of ...
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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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Processing OBPSK as OQPSK
I'm trying to create and process an OBPSK signal, which, as I understand it, transmits even bits on one axis and the odd bits on the opposite axis, resulting in a constellation with 4 unique points. ...
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2-PAM or 4-PAM if I want to send data as fast as possible?
I would like to ask if I should use 2-PAM modulation or 4-PAM modulationif I want to send data as fast as possible given that in each case I have the same frequency spectrum available.
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AM and FM frequency range
I don't know what I misunderstood or what but I thought in FM and AM you can transfer your frequency characteristics of modulating signal anywhere you want but I find out that there is a range for ...
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Spectral efficiency of with OFDM vs without OFDM?
OFDM has advantage over frequency selective channel with addition of cyclic prefix after IFFT of MPSK or MQAM symbol. but I wonder that the spectral efficiency of with OFDM vs without OFDM.
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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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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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I can't figure out why spectral features are "displaced" on a spectrogram
I'm trying to create a spectrogram of a complex signal 'y', but I'm running into a problem where the spectrogram that I create appears to have its spectral features "displaced" in frequency space, and ...
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Barker Sequence for QPSK
I'm trying to implement a QPSK burst modulation and demodulation through a channel and I'm now considering the synchronization part.
I've read that Barker sequence were excellent option for this as ...
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Why the carrier frequency does not appear after AM modulation?
Okay, this might be a very basic question, but I'm completely new to the field.
I have a $40$ Hz sine wave ($1000$ samples, $fs = 1$ kHz), which I have amplitude modulated to a $4$ Hz sine wave ($...
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Raised cosine filter and root raised cosine filter IQ for modulated signal QAM/QPSK
If I am passing a QAM signal through Root raised cosine Tx filter and measure the constellation at output, it seems very bad. If this bad output again pass with other another root raised cosine Rx ...
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Difference between delta modulation and differential PCM
Delta modulation encodes the difference between a sample and the previous sample in only one bit.
Differential PCM encodes the difference between a sample and its predicted value. Is this difference ...
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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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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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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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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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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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Is this waterfall characteristic of QAM or OFDM (or something other) modulation?
I recorded this signal at 2.45GHz, it is coming from a camera.
Is this QAM or OFDM ?
Based on those side-lobes I would guess OFDM but I am not sure.
Also there seems to be an interesting preamble ...
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Why does DPSK constellation shrink when noise is added?
I am generating a DQPSK waveform at complex base band with constellation points on the unit circle and when I add AWG noise the constellation shrinks. The noisy constellation "blob" migrate inside ...
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what are the applications of fourier transform in modulation
what are the applications of Fourier transform in modulation ? What are modulation schemes that use Fourier transform? I guess, FSK & PSK are related to Fourier transform since it both have ...
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Double sideband AM
In A3E transmission, I wonder how a single antenna is used to transmit a carrier wave, upper sideband and lower sideband altogether at the same time?
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How should I modulate a $16$ bit input using FSK?
I need to graph a $16$ bits binary sequence, assuming that it'll be a FM analog signal I need to apply FSK to it.
So, I think I should use the formula
$A \cos(2\pi f_1 t)$ for binary $1$'s
$A \cos(...
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General question on where to learn modulation and radio theory
Does anyone have any good books/videos or courses to learn about radio waves,frequencys,phase spread spectrum and modulation?
I need a something that goes through the basics until advanced.
Thank you ...
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What is the most used signal for basic pulse?
My professor said that: in order to avoid interferences/harmonics caused by the nature of the square wave g(t) (sinc will have these secondary lobes), it's better to change the basic pulse g(t) to ...
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How to achieve 3 Gbps with 210 MHz bandwidth in 5G?
I read an article from T-Mobile link where they claimed a 3Gbps speedtest with the aggregation of 3 three bands in 5G.
How it is possible to make 3 Gbps with a 210 MHz bandwidth and using 256QAM in 5G?...
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Issues with playing and recording a square wave sound on the same PC
I am learning signal processing. For a hobby project I wanted to transmit and record a simple ASK signal via my soundcard, to see if I can write code to recover the sent data. After playback and ...
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How can an UWB signal (pulse) radiate from an antenna?
This picture compares an uwb- and narrowband-signal:
https://cdn.sewio.net/wp-content/uploads/2017/02/UWB-e1486395802254.jpg
Like I understand UWB, the signal("pulse") is directly put into ...
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Exact formula for 8-PSK BER
Is there an exact formula for the probability of bit error (or bit error rate, BER) for 8-PSK (in the literature, course slides, etc.)? I am not referring to SEP (Symbol Error Probability) but BER.
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Why does the Superheterodyne AM Receiver use an envelope detector?
I'm currently learning about the Superheterodyne AM Receiver and I don't understand why does it use an envelope detector (as suggested here) rather than taking the signal back to its baseband ...
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What is Homodyne BPSK? [duplicate]
Could someone explain what Homodyne BPSK is? What is a difference between BPSK and Homodyne BPSK?
I have read about this type of modulation in researches in optic communication. I surprised how phase ...
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Why Bluetooth 2 use pi/4-DQPSK instead of OQPSK?
From the peak to average power ratio point of view OQPSK is better than pi/4-DQPSK. What is the advantage of pi/4-DQPSK compare to OQPSK? Why Bluetooth 2 use pi/4-DQPSK instead of OQPSK?
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Audio signal arrival timing, impulse response, and reverberation
I'm building an application that requires determining the arrival time of an audio signal with a very high degree of accuracy (within 1ms would be ideal) using commodity smartphone hardware. I found ...
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Time domain representation of a modulated signal when symbol rate >> carrier frequency?
I need to understand the relationship between carrier vs. bits with PSK modulation, and what the signal in the time domain would look like if my symbol rate is far greater than my carrier frequency. ...
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Digital Phase Modulation baseband or passband?
Say I want to transmit messages using PSK:
I send the message
$$s_m(t) = \text{Re} \left [g(t) e^{\frac{j 2 \pi (m-1)}{M}}e^{j 2 \pi f_c t} \right]$$
where $f_c$ is the carrier frequency. Now my ...
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What is symbol in signal processing?
I am new to signal processing and have been trying to understand the terminology. I came across this statement: "Assuming the signal modulation $\mathfrak{M}$ has an alphabet A of M symbols and the ...
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Serial to Parallel Converter
in many texts about modulators I have seen there is a component called "Serial to Parallel Converter". For instance, let's consider this scheme and let's focus on the second block (reference):
The ...
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Diode demodulation for AM
What is the capacitor and resistance at output of LPF meant for in the document it was mentioned that it is DC blocker I don't get it can't message contain DC value.
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Question about QAM
I'm trying to understand QAM transmission and I'm struggling to understand this sentence, 'The advantage of using QAM is that it is a higher order form of modulation and as a result it is able to ...
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Converting complex baseband signal to passband signal
I have to convert baseband signal (BW-20MHz) to passband signal centred at 20MHz.
I am implementing this in matlab. so, this is how I tried it.
I have already generated LTE Waveform BW- 20MHz , fs =30....
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Relationship between Bandwidth and Bit Rate
In one of my classes I have learned that if we look at transmitting a binary signal with ASK, we can get the bandwidth (i.e. the width of the main lobe in the frequency domain) with BW = 2 * Fb, where ...
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Why is carrier wave affected by percentage modulation?
In amplitude modulation, Power of a carrier wave is represented by : $$P_c = \frac{A_c ^2}{2R}$$
Which is independent of modulation index!
Question: At what factor is the power of carrier wave ...
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How to calculate $E_b/N_0$ for a 8-PSK?
How to calculate $E_b/N_0$ for a 8PSK? My BER is given. But I don't understand how to calculate $E_b/N_0$ as it is inside a Q function.
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What is the index modulation in OFDM and Subcarrier Index modulation?
I'm new here, I'd like to ask about the OFDM-IM (OFDM - Index modulation), what is it and how it works? Is it the same as SIM-OFDM?
I checked white papers, I see it's using the index of sub-...
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How range of the signal increases when modulation is done? [closed]
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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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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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 ...
