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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OQPSK - GNU Radio Companion
I was wondering if anyone has had any success in implementing OQPSK in gnuradio.
I have a working theory of expanding on the Constellation Modulator to include a custom OQPSK function.
I have ...
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Help me understand the concept of IQ signals
I am a computer science student working on a school project involving RTL-SDR receivers, and I have a hard time grasping the concept of IQ data. Basically what I think I have learned from all of the ...
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Preparing data for modulation classification based on RML2016
I would like to validate a trained model based on RML2016.10a. My idea is to capture a certain amount of data (20 Msps) for approximately 0.3 seconds. Then, I identify all the signals in this ...
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How to calculate the accurate BER expression of circular 8-QAM constellation modulation?
It is easy to understand the BER derivation of square QAM, but the circular 8-QAM? I'm quite confused. The decision region is not in a rectangular shape anymore, meaning regular way does not work here....
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What is the relationship between Symbol Duration and Sampling Frequency in a 256 MPSK radio link
I'm struggling to work out the relationship between Symbol Duration and Sampling Frequency in an MPSK link.
For instance, if the Sampling Frequency is 10MHz this means that a sample is taken every ...
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QAM modulation problem with python
I have a IQ signal with a bandwidth of $200\,\text{MHz}$.
I do I*cos(2*pi*1000e6*t)-Q*sin(2*pi*1000e6*t), but my signal doesn't shift to carrier frequency ...
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How is the normalized power required for unipolar NRZ twice that of polar NRZ?
So, the normalized power for unipolar NRZ scheme is $\frac{1}{2}V^2$. According to my book, the normalized power required for polar NRZ is half that of unipolar NRZ. So, the power should be $\frac{V^2}...
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Oqpsk pll delay axis ambiguity
I don’t understand how this phenomenon appear in OQPSK carrier recovery loop. I found nothing on google. Is it a normal phenomenon in OQPSK loop or specific? Why does it get reversed I and Q? In the ...
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What are different encoding schemes used in gigabit ethernet?
I was reading about digital transmission, there are many steps namely
Analog to Digital conversion
Source coding
Channel coding
Line coding
Pulse shaping
Modulation
Multiple access techniques
Out of ...
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Is there an open source "Data over Voice" library?
I need to transfer data from A to B using audio as the medium, with a speaker at one end and a microphone at the other. Sometimes simply through the air, but it must also work through legacy phone ...
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Pulse amplitude modulation
I am reading from the internet and my professor's course on PAM. This course is not well-organized, and I would like to ask for book recommendations. I know that this modulation is divided into two ...
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Is BPSK relevant, or does it even exist, in wireless data transmission?
I ask this question because it seems to me that if pulse shaping has been applied in the transmitter, the signal that is actually transmitted is not phase modulated at all, rather, it is amplitude ...
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How does PAM-4 encoding of a digital signal relate to theoretical *pulse* amplitude modulation?
Pulse amplitude modulation in general is often explained using plots like this one from wikipedia:
There is a sinusoid analog signal (red) to be "imprinted" on a train of pulses. The result ...
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Exactly when is pulse shaping applied in the radio transmitter, before or after modulation, and is it applied differently in BPSK, QPSK and 16QAM? [duplicate]
I previously asked at which stage pulse shaping is applied in a WiFI transmitter and my question was closed due to duplication. The answers I was directed to have only served to confuse the issue for ...
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What is the phase of $Y(\omega)$ in relation to the phase of $X(\omega)$ where $x(t)$ modulated with an exponential carrier that has no phase shift?
A homework problem of a free online course I am taking, asked to draw the magnitude and phase of $Y(\omega)$ where $y(t) = x(t) c(t)$ where $c(t)$ is $e^{j 3 \omega_{c} t}$ and where $X(\omega)$ is:
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Comparing communication systems with different modulation orders and code rates
I propose an end-to-end communication method in my research. The key part of the method is not the channel coding and modulation but we use them anyway. I am using 1/3 rate Turbo codes with QPSK and ...
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Block diagram of a demodulator with a low-pass filter
I am having some difficulty designing a block diagram of a demodulator with a low pass filter - I don't know how to add it to the schematic(apply the LP filter to the diagram). I have an input signal ...
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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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802.11a OFDM Long Preamble Cyclic Prefix
im currently looking at an implementation of the preamble for OFDM in the 802.11a standard, as shown in the pic below
What I dont understand is the cyclic prefix (labelled GI2). Based on this picture ...
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Why do IQ Impairements, Quadrature Skew and DC offset have these geometric effects on the constellation?
I'm studying telecommunications, and would like to be sure to understand the maths behind these effects.
For IQ Imbalance and DC offset, it seems pretty clear why we observe a rectangle shape or a ...
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Demodulation + LPF gives derivative of modulated signal
I'm new in this community and I hope it is the right place to post my question. Unfortunately, signal processing and electronics in general are not my fields, so I'm sorry if the question is trivial.
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Does phase shift introduce high frequencies?
In PSK phase modulation scheme, the signal phase is shifted, hence it looks something like this:
I cannot understand why this doesn't introduce a set of unwanted high-frequencies, as the steep ...
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Why does NB-IoT use standard QPSK in multi-tone transmission, when pi/4 QPSK is implemented for single-tone?
I've been studying the modulation schemes used in NB-IoT communication, with a particular focus on energy efficiency. I've noticed that QPSK (Quadrature Phase Shift Keying) is used in multi-tone ...
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Clarification on video about frequency deviation in phase modulation bandwidth
I am watching this video and at 7:12 he calculates the frequency deviation $\Delta f = f_{c}f_{m}A_{m} $ where the $c$ underscript is for "carrier" and the $m$ underscript is for "...
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modulation transfer function and ground resolved distance
I am trying to understand something in remote sensing but lack a background in science and technology so it is difficult. Hopefully this is a reasonable question to ask.
In sensing there are different ...
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Meaning of roll-off factor 0.5 and bandwidth
We currently have a radio that is transmitting at the following RF params:
Modulation: OQPSK
Data rate: 500Kbps
Uplink coding: BCH
I am interested in understanding what is the associated uplink ...
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What can be done with I/Q data which would otherwise be impossible?
As I understand it, I/Q data is the complex representation of any waveform. It enables us to understand two things at any arbitrary point in time:
The projected amplitude of the waveform.
The ...
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Why for bandpass signals complex envelope and pre-envelope signal representations are used in digital communications/analog communications (FM)?
When we need to analyse band pass signals we use complex envelope and preenvelope representations, wherein a signal is given an equivalent low pass representation.
My issue is why it is done, though I ...
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Effect of Passband Slope on QPSK Constellation
What is the effect of a passband slope on a QPSK (or any QAM) constellation? Specifically given a linear slope (in magnitude, not dB), and no phase distortion (linear phase or even zero-phase) how ...
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I don't understand which signal I should use as a carrier in my excersise
$\DeclareMathOperator{\sinc}{sinc}$ Given 3 signals
$x_1(t) = \sinc(t) , x_2(t) = 10\cos(2\pi f_2t)$ and $x_3(t) = 5\cos(2\pi f_1t)$,
where $f_2 = 100\text{ kHz}$ and $f_1 = 1\text{ kHz}$.
I must ...
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Matlab Filter-Span-In-Symbols property for RRC: source bits lost
I am using the matlab online simulator and taking the course "Wireless communications Onramp" where I need to use a Raised Cosine Transmit Filter to filter the data both in the transmitter ...
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How is the symbol error rate for M-QAM, 4QAM,16QAM and 32QAM derived?
How do you derive the theoretical symbol error rate as a function of $E_\mathrm{b}/N_0$ for 4QAM? I know that the result should be $Q\left(\sqrt{2E_\mathrm{b}/N_0}\right)$ but I am ĺooking for the ...
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DS-CDMA Spreading Code Length Selection
I'm trying to wrap my head around the process of selecting DS-CDMA spreading codes, and I'm having trouble understanding the tradeoffs of longer codes. For all scenarios described below, I'm using a ...
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Recognizing different pulse shaping forms (16-QAM modulation)
I have three versions of a 16-QAM modulated signal, each showing the time curve of the real and imaginary parts, the spectrum and the symbol constellation. These three versions differ by the ...
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What process could generate this kind of noise in the multitaper spectrum?
I am recording some data for scientific purposes (it is neurological data), and the data is corrupted by some very strange noise. At multiples of about 700 Hz (slightly differing on different days) ...
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Understanding homework solution - why are $\{X_t\}$ and $\{Y_t\}$ joint WSS, and finding Wiener filter + error
I'm walking through the published solutions of my homework and I'm struggling interpreting them. In them I was given a random Gaussian process $\{X_t\}$ and a random variable
$$\{Y_t\} = X_t\cos(2\pi ...
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What is the difference between a guard band and a cyclic prefix in OFDM?
im trying to understand the difference between a guard band, and the cyclic prefix, or at least the relationship between the two.
Prior to now, I was under the interpretation that the cyclic prefix ...
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Testing a Hilbert transform on a real signal to transmit it as Single SideBand
I am testing some Hilbert transform theory in practice. On the practical side I use Python and a soundcard to generate baseband I and Q signals. And an IQ modulator to upconvert with 250kHz. Lastly a ...
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How to modulate a signal to a certain frequency in time domain
I have a root-raised cosine pulse signal of bandwidth $500$ MHz.
If the signal is modulated at the frequency $6$ GHz, the result should apparently look like this :
If I understand well, to modulate ...
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How to correctly accept Polar/LDPC encoded bits with PSK modulation?
I have implemented a packet reception and transmission scheme using QPSK. Next I decided to add Polar/LDPC encoding. As a result, nothing is written to the received file.
I think the thing is that I'm ...
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Modeling an OFDM signal and comparing it with QPSK
I am trying to model an OFDM signal based on original QPSK stream and compare their baseband spectrums.
I've used this article as a reference for plotting spectrum and this as a MATLAB OFDM reference
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Block Diagram 2nd Butterworth Low-pass
I would like to represent a second-order butterworth low-pass filter in a block diagram, how can I get started?
As per the attached image
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Which type of modulation is used in this RF Signal?
I am working on reverse-engineering a few devices, I got some using ASK and FSK but I could not grasp this other one. I am attaching some photos from its captured signal took from URH (Universal Radio ...
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Modulating and transmitting three different voice signals (in MATLAB)
I want to record, modulate and transmit three different voice signals. I will be doing this in MATLAB.
Please can you help me figure out how can I do this?
Or give me a block diagram that can show ...
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GNURadio GFSK demod missing data
we are trying to develop a flowgraph for cubesat operation. Our flowgraph for includes both downlink and uplink parts in one flowgraph. It uses SoapySDR as a driver of an SDR. Most of the used blocks ...
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OFDM does not work with USRP
I found the ofdm flowchart in the Gnu radio examples.(ofdm_loopback)
Scheme:
The spectrum and the received data of the received signal:
After that, I connect the USRP Sink and the USRP Source.
The ...
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8PSK modulation does not work
I implemented a data transfer system using two tutorials: Guided Tutorial PSK Demodulation and Packet Communications. After that, I decided to change QPSK to 8PSK.
My scheme:
Constellation Sink:
For ...
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Can frequency multiplier (e.g. doubler) impact signal bandwidth?
My understanding is that if a single tone at frequency F is inputted to the frequency doubler, one should observe at its output in the spectrum the same tone but now at a frequency 2F.
However, what ...
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Effect of Passband Slope on a BPSK Constellation
What is the effect of a passband slope on a BPSK constellation? (This is a companion question to the related "DSP Puzzle" for QPSK)
Specifically given a linear slope (in magnitude, not dB), ...
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Why is the symbol duration in QPSK twice the bit duration?
I saw many answers for such questions by writing down equations such that the symbol is formed of n bits so the duration of the symbol in QPSK must be n multiple of the bit duration.
I am not ...
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