Questions tagged [demodulation]
Demodulation is the act of extracting the original information-bearing signal from a modulated carrier wave.
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53 views
What is the minimum sampling rate for QPSK or what is the bandwidth of QPSK signal?
Consider we have created a QPSK signal with a carrier frequency 100kHz. Before applying matched filter or demodulation we need to take samples from the received signal. So what is the minimum ...
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1answer
82 views
Amplitude demodulation of sinusidal signal in matlab
AM-demodulation task and I was asked to demodulate the signal in MATLAB and the result should contain three pictures.
plotting the $fft$ the (frequency spectrum)of the signal i was able to determine ...
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10 views
Derive the LFSR sequence from demodulated bitstream
I'm new here and hope to have good feedback from you.
I'm trying to blindly demodulate an RF signal and managed to get a sequence of bits for a preamble. After some research, I'm in fact exactly in ...
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2answers
83 views
Getting the bitstream of an unknown RF signal
I am trying to get the bitstream of a signal sent over 433MHz. I have installed SDR# (I'm on Windows), connected my NESDR SMART, and I identified the signal here:
I can see there is only one peak ...
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1answer
71 views
How can an SDR recover a high-frequency signal?
How can software-defined radios operate at high frequency?
The Nyquist rate dictates that you need to sample at twice the frequency to fully recover the signal. If my signal of interest is modulated ...
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20 views
What determines the maximum/minimum values in I/Q constellation diagram?
I need to do some data analysis on I/Q samples and was trying to know what are the parameters that determine the maximum/minimum values of these samples. In other words, what determines the maximum/...
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20 views
IT++ and Alternatives DSP Libraries
I want to implement some signal processing blocks in C++ so I did a bit of search on the available libraries for signal processing in C++ and I found that IT++ provides comprehensive set of functions, ...
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1answer
13 views
qam demapper why are soft-outputs used?
I'm starting to learn about OFDM QAM demapping, and a lot of documentation points to using "soft-output" algorithms that calculate Log-Likelihood Ratios (LLRs).
Why is this method advantageous?
My ...
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22 views
Effect of down mixing on complex demodulation method
As I know, IQ demodulation (complex demodulation) consists of three steps:
Down mixing
X(complex demodulation)(t)=X(real signal)(t).{exp[(-i2π(f_demodulation).t)]}
low pass filtering
decimation
...
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1answer
12 views
Term for signal waveform correction or demodulation
Let say a periodic signal waveform $v(t)$ can be modeled as:
$v(t) = f(\phi) A \sin(2\pi ft + \psi)$
where $A$ is a constant amplitude, $f$ is signal frequency, $t$ is time and $\psi$ is a constant ...
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32 views
Help in identifying low speed image transmission protocol over RF
In the seventies I worked for Muirhead on press fax machines that used to transmit pictures over radio and landline as I recall two FM systems were used a carrier 800 Hz modulated +- 150 Hz and 1900Hz ...
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34 views
Signal acquisition equipment phase noise
I would like to check if there is a way to enhance an RF equipment's phase noise figure.
The considered RF acquisition homodyne system includes a mixer for carrier demodulation, amplifier and filter ...
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31 views
Changes in amplitude after Quadrature Demodulation
I'm getting the FSK signal from the satellite in I/Q format (see the last 2 waves at the bottom of the picture).
After applying Quadrature Demodulation, I'm getting the top wave.
The questions are:...
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1answer
112 views
From IQ to pi/4 DQPSK
I need to decode $\frac\pi4$-DQPSK packets from an SDR, preferably in C#.
I have the SDR receiver part done. Now I'm trying to learn how to take the IQ stream and get the packet info from it.
I've ...
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1answer
43 views
Symbol synchronization with M-QAM. M < 16
I working on M-QAM system using a Cortex-M4 processor. Using a alternating symbol as a preamble, I am able to get carrier lock. Symbol synchronization is then achieved by finding the peak. An early ...
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2answers
165 views
In case of using a Doppler radar, do we have to use IQ demodulation to find the direction of a target?
I want to know the way to find the velocity of a target by using a doppler radar.
I read some paper about it,
In summary,
send rf signal to a target
receive the reflected signal from the target.
...
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1answer
85 views
What does the phase discriminator portion of the Costas Receiver do mathematically?
What does the phase discriminator portion of the Costas Receiver do mathematically?
The output of the I-channel is $ \frac{1}{2}A_C \cos \phi \, m(t) $. Which means for small deviation of phase $ \...
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72 views
How does a Costas Loop lock to one of multiple BPSK signals
I've been looking into how GPS receivers work in terms of signal processing. When a GPS receiver tracks the received signal, it often uses a Costas loop to synchronize the carrier.
How that works ...
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90 views
CDMA-DSSS with orthogonal codes and BPSK modulation: proper way to demodulate
I am having problems when demodulating the signal: If I demodulate the sequence chip by chip and then operate only with binary information the "integrate and dump" (correlator) sometimes will provide ...
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0answers
20 views
Filtering of an AM signal at the reciever
Transfer function of a filter at the input of a receiver (synchronous demodulator of AM signal) is given with equation:
$$H(f)=e^\frac{-(f-f_0)^2}{B^2}+e^\frac{-(f+f_0)^2}{B^2}$$
$B=10kHz$
It is ...
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1answer
41 views
How to correct a QAM time delay
How can you correct the anticlockwise rotation that occurs in the received constellation of a QAM system?
My only idea is to compensate the delay with an advance but this is impossible since you ...
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1answer
131 views
RF demodulation for dummies
Given a signal that's been FM encoded on a carrier wave, what are the individual steps I need to take to demodulate it, and recover the original signal?
I don't have a background in signal processing,...
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3answers
79 views
Representing data in combination of QAM and BPSK
I have a question regarding the data representation in different modulations. Assuming we are using MIMO system whith $4$ $T_x$ x $4$ $R_x$ which means four transmission antennas by four receiving ...
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1answer
48 views
About combination between QAM and PAM
I have confused question regarding the possibility of combination between QAM modulation and PAM in order to improve the spectral efficiency. Is that possible?
As you see in the below Figure, it's ...
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2answers
129 views
Why would we simulate baseband rather than passband
My question is, Why do we usually use baseband in simulation rather than passband? however, if we want to test our simulated idea in real environment, it must be sometimes in passband !!
So, should ...
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0answers
125 views
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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2answers
74 views
Contradiction between complex baseband and real-valued baseband
Suppose a direct-conversion transmitter+receiver (ideal transmitter) along with its filters. In complex baseband, the filters in the signal chain can be modeled as a complex-valued FIR filter ($y$, $c$...
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1answer
131 views
QPSK constellation from baseband signal
My IQ sampler is measuring a QPSK carrier at a set frequency/bandwidth (40MSamp/s), but shifts the signal spectrum to baseband. My signal is 1.5Msym/s, but sampling at 1.5Msym/s gives me a ...
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1answer
130 views
Quadrature demodulation, homodyne detection, lock-in detection - what's the difference?
Quadrature demodulation
Homodyne detection
Lock-in detection
What is the difference between these terms? Are they all synonomous? In my mind they kind of are, so I'm never sure which to use.
I ...
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0answers
90 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
180 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
56 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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0answers
82 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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0answers
87 views
Synchronization of BPSK with variable-length symbols (ISO 14443)
Does anyone have an idea how one would perform BPSK symbol synchronization if symbol length is allowed to vary?
As dumb as that sounds, this is not a theretical question.The "Proximity" Type B NFC ...
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1answer
123 views
Bpsk demodulator implementation
For a project I'm trying to implement a BPSK demodulator on some random wave files, I'm getting a few difficulties:
How do I know my bit rate, i.e. how many bits each 'real data bit' I'm having.
How ...
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1answer
170 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 ...
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1answer
239 views
Carrier Recovery, Frequency and Phase offset in (CP)FSK
I wanted to ask what exactly is meant for phase recovery of signal (at least intuitively). I have a working example of an acoustic fsk modulation and demodulation software but i don't know how to ...
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2answers
525 views
QAM constellation slicer with unknown carrier phase
As shown in the image, I have a 16QAM constellation that is misaligned due to a phase rotation. In this case you can see that rotation amount is approximately $\theta = \pi/4$, but this won't be the ...
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2answers
111 views
Demodulation in Rayleigh Flat Fading Channels
A core part of demodulation in Flat-Fading channels is (assuming) the channel as a(random) constant complex number multiplied with your signal. This is done in order to de-rotate the symbol for ...
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1answer
80 views
Detecting I/Q imbalance
Are there any methods of detecting, measuring, and/or estimating I/Q imbalance (from, say, an upstream quadrature mixer and/or ADC), without using or having a controlled test signal (other than ...
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46 views
BPSK demodulation [duplicate]
For experimental reasons i created a function that helps me to modulate a signal using BPSK, the input signal is {1,1,0,1,0} and it works fine
...
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267 views
Removing I/Q phase rotation
What is the most reliable and agnostic way to correct for a phase rotation of I/Q downconversion - without time alignment of the signal and support different lengths of transmitted and received data?
...
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0answers
89 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
298 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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1answer
234 views
AM demodulation from a real RF signal
I'm capturing an RF signal transmitted at 433.8MHz, with a bandwidth of about 50KHz. My goal is to be able to save it as a .wav file.
I'm using an RTL-SDR dongle and a software named HDSDR, where I ...
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0answers
3k 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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2answers
309 views
Mystery signal - FSK, BPSK?
I have a mystery audio signal that I need to decode, it's from a discontinued product. Inspecting the object code shows a module called decodeFSK so that suggests ...
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1answer
393 views
Prepare IQ Data for Goertzel Algorithm
I have a quadrature (IQ - 0..255) data byte stream that I receive from an rtl-sdr dongle as IQIQIQIQ.....
That means that negative values are < 128 and positive values >= 128
I am attempting to ...
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1answer
563 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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1answer
29 views
How to model airborne sound channel
I'm making a soft demodulation/decoding to communicate a microphone and a speaker in short range. I have to calculate the LLR using my constellation and the airborne sound channel probability density ...
