Questions tagged [demodulation]
Demodulation is the act of extracting the original information-bearing signal from a modulated carrier wave.
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How to recover bits coded by different frequency values (states)?
I'm looking for help with one exercise. Firstly I was supposed to download a FM modulated signal.
[y,fs] = audioread('signal.wav');
And then I have to recover bits ...
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40 views
FM modulation - recovering bits
I'm trying to complete one task:
Download some FM modulated signals from page http://www.w1hkj.com/modes/index.htm. Calculate their spectrograms, i.e. short-time Fourier transform. Observe different
...
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26 views
Bit error rate transient
I see often people here posting about GNU Radio, I hope mine is not in the wrong place.
I try to implement a demodulation chain and would like to measure its performance.
I added a BER block and it ...
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23 views
Decoding images from NOAA satellite APT signals
I've been working on a decoder for these APT images for a while now. I started years ago, in Python, and was able to implement a working decoder quickly. A few months ago, I came back to the project ...
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Trade-off in sample-rate & FFT-size & Doppler
I've got a stream of digital IQ samples let's say at $F_s = 1 MSPS$ that consist of a narrowband signal, in awgn. Let's say the signal BW is ~ 100Hz. The narrowband signal's center (or base) frequency ...
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1answer
52 views
Dealing with bias in an FFT for frequency correction
I'm working on using an FFT for frequency correction of a generic modulation signal. My algorithm basically attempts to balance the energy in the positive and negative frequencies of the FFT to be ...
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14 views
How to make 2 finger rake receiver to counter intersymbol inferference?
I have to transmit Walsh sequence (spreading codes) modulated with 8 psk with a channel impaired by intersymbol interferences, fast fading .
Suppose i have a stream of data for instance 1 0 1 1, 0 0 0 ...
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1answer
37 views
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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38 views
Non-coherent FSK and Orthogonality and square-law detectors
This is a basic figure that explains how Non-Coherent FSK actually works. The incoming signal
$ r (t)=\sqrt{2 P}{Cos}(2 \pi t (\text{fc}+\text{fi})+\text{n(t)}$
where P denotes the signal power in ...
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3answers
107 views
How a diode-detector affects to Frequency Response?
I have a question related to crystal radio. I can't understand how a crystal detector (diode) shifts the spectrum from the carrier frequency to zero.
The antenna receives bunch of signals and the LC ...
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3answers
81 views
QAM Amplitude Levels
I'm working on a project to stream video between 2fpgas by using QAM. While mapping symbols with different amplitude pulses(PAM) a question popped up in my mind. In real life how does communicating ...
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34 views
Determining the right order of time-domain low pass filter for desired cutoff frequency
I've been stuck on a problem regarding complex demodulation of a signal for a while and wondered if anyone could help.
Suppose I have a signal $X(t)$ such that
\begin{align}
X(t) &= A(t)\cos(\...
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23 views
How LTE/5g receiver align phase?
I am trying to demodulate a captured 5g signal using matlab.
But it is likely that the 0-phase time point for each symbol lays between two samples,
which results in a minor phase shift, and such phase ...
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2answers
50 views
BPSK and QPSK demodulation computational complexity
I wanted to ask about the real operations of BPSK and QPSK demodulation. How can we calculate it?
I mean for example if I have a received symbol +0.6, then I need to demodulate it to be 0 or 1. what's ...
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1answer
41 views
Non Coherent BPSK with no Channel State Information at the receiver
Where or what is the proof for the failure of BPSK in fading channel when we have no knowledge of the fading coefficient $h$ at the receiver in the equation $y=hx+w$, where $x$ is BPSK symbol equally ...
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1answer
72 views
What is the functional difference between DSB and 2SB mixers, and why exactly would 2SB be better for radio astronomy?
The Astronomy SE question 2SB mixer in radio astronomy? asked in 2014 in its entirety:
In literature about the instrumentation of radio astronomy, I frequently come across a type of mixer described ...
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36 views
How to implement Walsh demodulation in matlab?
1 1 1 1 ==> 0
1 -1 1 -1 ==> 1
1 1 -1 -1
1 -1 -1 1
I have this sequence of walsh spreading ...
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1answer
58 views
Does the FFT size matter in OFDM demodulation?
The DFT size in OFDM demodulation is usually matched to the DFT size in the modulation process. This makes modulation/demodulation simple where each FFT bin (i.e., sample) represents one symbol. What ...
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1answer
64 views
Demodulating a LoRa data symbol
LoRa integrate data into symbols by selecting the starting frequency of an up chirp. The resulting up chirp traverses across BW and arrives at the same place it started. At the demodulator, this chirp ...
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1answer
37 views
A communication system
I am solving the following problem as an exercise.
I have a signal
$$z(t) = x(t)\cos(wt) + y(t)\cos(ut)$$
and we assume $x,y$ to be band-limited continuous time signals. In the frequency domain we ...
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52 views
How to demodulate DominoEx-like signal with liquid dsp?
I found a proprietary protocol that is used on ham radio bands. The author have published details,claiming that it's a version of DominoEX with slightly different baud rate and FEC.
I want to try to ...
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1answer
35 views
Cross-correlation with SDPSK modulation
I'm trying to detect a sync word in a signal using Symmetrical Differential PSK (bit 0 = +90° phase, bit 1 = -90° phase).
Given the signal is encoded in the phase difference between two symbols, the ...
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44 views
symbol synchronization
PLL is typically used in carrier synchronization and its diagram is well known, consisting of a multiplier, a low pass filter, and a VCO.
In "Phase-locked Loop" at wiki (https://en.wikipedia.org/wiki/...
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50 views
Non coherent detection BFSK demodulation?
I am simulating BER performance of BFSK under AWGN and Rayleigh fading, BFSK has two symbols one entirely on the real plane while other on the complex plane for representing let's say zero and one, ...
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1answer
41 views
Recover frequencies from IQ samples
I have a set of IQ data. From those data I'm trying to get the amplitudes and the frequencies of my signal as I then want to plot them vs. time.
I am able to obtain the amplitudes by squaring both ...
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2answers
49 views
What is the BER for multilevel modulated signal
Assume I want to transmit a low or high symbol which can be BPSK modulated. For ordinary BPSK, bit 0 can be mapped to 1+i0 and bit 1 mapped to ...
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1answer
72 views
How to demodulate PM modulation
I'm using a sin wave $s_{sc}(t) = d(t)\cos(\omega_{sc}t + \varphi_{sc})$ to modulate a carrier using phase modulation. I'm working on Matlab so I use the pmmod function to do so. It is not too ...
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Demodulating FM Signals. Understanding text from “Communication Systems Engineering” by Proakis
Please help me understand the following text from "Communication Systems Engineering" by Proakis.
Text:
What I was not able to understand:
1) Why is the transfer function of the FM demodulator ...
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12 views
Model of modulator and demodulator in Simulink. Why is MER so lowest?
I created a simple model in Simulink of a quadrature modulator, amplifier and quadrature demodulator. On the oscilloscope(scope in Simulink) and spectrum analyzer the displayed results look normal (at ...
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2answers
108 views
Demodulation of 4-QAM
Any help to get me started is appreciated. I have an array of values for the 4-QAM where attach is a copy of part of the values of the array. I want to know how do I get the bits 0 and 1s from those ...
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34 views
CDMA scheme that preserves constant envelope (NRZ/ASK shape)
(This is a followup question to Is this a "valid" CDMA modulation?)
Is it possible to find a CDMA scheme in which the receiver can only have a simple slicer?
In other words, for the ...
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1answer
46 views
Is this a “valid” CDMA modulation?
I am banging my head against (specific aspects of) CDMA for a few days. At the basic level I am confused about the interrelation between implementations that are modeled as mixing and fully digital ...
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Any DVB-S2 sample streams publicly available on-line?
I'm working on a DVB-S2 receiver and I'd like to be able to test a part of the DSP chain with real-world signals, but getting good sample streams from a digitizer is not terribly easy.
Can anyone ...
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1answer
29 views
Possibilities to get the amplitude of a signal at specific frequency from IQ
I'm newbie to the dsp topic and my understanding of math symbols is limited.
So at the moment I'm little bit lost to find the right resources.
I receive an IQ stream from a SDR.
Sample rate: 250k/s
...
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1answer
65 views
Loop Bandwidth for Carrier Demodulation loop
I am trying to implement a simple MATLAB model for the demodulators for phase modulated signals (PSK) used in communication systems.
For the detection of the phase modulated output (PM out in the ...
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1answer
63 views
I/Q Signal Power Calculation
I am trying to understand the basics of IQ modulation. The amplitude of a demodulated IQ signal is given as $\sqrt{I^2 + Q^2}$ which is easy to understand from the phasor diagram.
Yet, I don't ...
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1answer
36 views
Wrong output for phase demodulation
I tried to plot phase demodulated signal and original message signal but there is a significant difference between magnitudes of the message and demodulated signal. I have attached the code and the ...
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Designing a PI filter for a Costas Loop
I am currently trying to implement a Costas Loop in order to demodulate a BPSK signal. Here is the reference block diagram I have been using to design the loop:Costas Loop Block Diagram
I originally ...
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1answer
369 views
Getting hilbert transform of IQ signal
Im new to communications so this may be a stupid question, but I am somewhat confused. I am trying to train an automatic modulation classification (AMC) algorithm on IQ data from the RadioML dataset. ...
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1answer
45 views
Using I/Q demodulation/LIA for a fixed-frequency application of several signals - do the phases of the input signals affect the result?
My input is a single signal composed of the sum of four periodic signals, each 4 Hz apart, centered around some resonant f0 typically between 1200 - 1300 Hz; the actual frequencies will change ...
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71 views
GPS CDMA signal acquisition (BPSK modulation)
Sorry, this may be a rookie question: I have a CDMA gps communication in BPSK. Codes have a duration equal to $1\ \text{ms}$ and their length is 1023. At the carrier frequency ($f_c = 1.57524\ \text{...
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2answers
152 views
IQ signal FM descrimination using phase derivative
I'm trying to demodulate an FM signal recorded as IQ samples from RTL-SDR at 2.4Msps with RTL-SDR centered on an FM station's frequency.
So the input signal is 8 bit IQ baseband at 2.4MSps.
The data ...
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1answer
237 views
Demodulating wideband FM signal in Octave from recorded baseband IQ samples
Assuming I have a baseband recording of 8 bit IQ samples at 2.4MSps centered on an FM station is it correct to say that after low pass-filtering the complex signal to 240KHz, taking discrete ...
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1answer
83 views
Positive slope of BER with a greater frequency deviation?
I am trying to implement a frequency-modulated communication channel on MatLab. However, there is something I don't understand about the sensitivity of the frequency modulator (or the frequency ...
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1answer
83 views
Burst QPSK demodulator
I am working in burst QPSK demodulator. I just want to double check if what I am doing is right.
Large frequency feedforward recovery by FFT
Carrier recovery Costas with 4 samples/symbol
Timing ...
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QAM and APSK error comparision [closed]
Due to the 16QAM and 16APSK characteristic, is there exact comparison between 16QAM and 16APSK BER?
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1answer
966 views
DPSK vs PSK Error Probability
BACKGROUND
The bit error probability for BPSK under AWGN is easily derived from tail probabilities of Gaussian distributions and results in
$$P_e = Q\biggr(\sqrt{\frac{2E_b}{N_o}}\biggl)$$
The ...
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1answer
457 views
Demodulation of FSK signal
What kind of FSK signal is this and what demodulation technique can I use to demodulate it. Why is the phase of the 1's changing like that and how does that effect how it needs to be demodulated. I ...
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56 views
RF direct conversion down to DC and signal recovery from IQ
I've previously worked with super-heterodyne receivers where the IF spectral content has been above DC.
Reading the below tutorial; direct down conversion receivers are used to mix a signal of ...
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205 views
What's wrong with my M-ary ASK modulation demodulation MATLAB code?
My MATLAB code linked below implements ASK modulation of an M-ary signal, impresses it on a carrier, adds AWG noise of various SNRs. Then, for each SNR, demodulates the signal and calculates the ...
