Demodulation is the act of extracting the original information-bearing signal from a modulated carrier wave.

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Filtering and Differentiating phase-modulated signals

For a project work, I need to demodulate data from a Laser Doppler Vibrometer. The distance information is phase-modulated, therefore the velocity information is frequency-modulated: $$x \propto \...
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23 views

Is carrier recovery needed when preamble used?

I don't know if this is a good place to ask my question; if not, please let me know your suggestions. I want to simulate a digital transmitter and receiver. To demodulate coherently in the receiver, ...
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1answer
51 views

How to correct the phase offset for QPSK I-Q data

I have an I-Q data of QPSK modulation, the data is is smeared and I have to correct the phase offset that causes the smearing problem, how can I apply the Phased-locked loop or the Costas loop on this ...
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1answer
143 views

FSK analysis: only ever find one frequency

I've trying to write this software as part of my amateur radio and SDR hobby for analyzing various two-level FSK signals. I'm very new to DSP but have been having a lot of fun so far learning more ...
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1answer
37 views

How to find a know signal in another signal which contains other signals along with the signal i need in python

I am working on BPSK with sound waves a carrier waves. Actually I am modulating my data with some known sync bits along with the information I need to send. So the things I will be having at ...
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1answer
19 views

Demodulating upper sideband (USB) signals

A modulating signal $m(t)= \sin(2 \pi \nu_m t)$ is transmitted via a carrier of frequency $\nu_c$ using upper sideband (USB) modulation. Show that the USB modulated signal can be demodulated using a ...
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1answer
21 views

why does the decision boundary change in BPSK? is it true?

I am working on modulation and demodulation of BPSK using python. i made a code for modulation and demodulation,while demodulate i tried to compare my actual data bit stream with demodulated bit ...
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1answer
25 views

Difference between demodulation and band-stop Filter

I was wondering what is the difference between demodulating a signal that is carried with a frequency $F_{\rm carrier}$ and applying a band-stop on a band around $F_{\rm carrier}$ ?
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51 views

OFDM sensitivity to sampling time offset (with half of time interval between samples)

In simple QAM modulation symbol synchronization is crucial: the samples need to be taken (or interpolated and resampled to ) exactly corresponding to the time when the symbol was emitted. This is ...
3
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1answer
124 views

FSK Demodulation, Bit Timing Recovery

I am currently implementing acoustic FSK modulation and demodulation. I am not a signal processing guy so any help about the bit timing recovery would be very appreciated. Currently I implemented the ...
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1answer
56 views

OFDM symbol acquisition block in GNU Radio gives rotating constellation even if there is no carrier offset. How is this possible?

Why does the constellation rotate when using OFDM Symbol Acquisition block in this flow graph below ? The only explanation I could think of would be carrier frequency offset but in this flowgraph ...
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1answer
32 views

Denoising effect in GnuRadio OFDM Serializer block

Why does the OFDM serializer has such a strong denoising effect in the flow graph below ? Is that normal ? The upper constellation is AFTER the OFDM serializer block and the lower is BEFORE the OFDM ...
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1answer
19 views

How does carrier frequency offset effect the constellation diagram in OFDM?

In the case of OFDM modulation, if the carrier frequency is slightly off then how does that effect the constellation diagram ? Is there some general rule how it will change (such as rotate) ? Or ...
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1answer
34 views

OFDM demodulation, how to set the sampling rate?

I have a signal for which I know the OFDM burst length (from the autocorrelation function of the signal) T_burst and the FFT size 1024 (by measuring the channel ...
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1answer
40 views

How to set a Carrier Wave for DBPSK Modulators in gnuradio?

for a Project I need to build an Audio Modem in GNU Radio. I decided, that it would be the best to use DBPSK Modulation, because that is fast and relatively noise resistant. But as it seems, the ...
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2answers
45 views

M-Array DPSK decoding and encoding

So i'm trying to figure how how to do the encoding and decoding of an M-array Differential Phase Shift Keying (DPSK) signal. I understand how to do it for binary DPSK, but on higher ordered signals I'...
2
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1answer
158 views

Demodulating FSK audio in Python

I am trying to write a Python script that can demodulate an FSK modulated audio file and return the data encoded in the audio. The data being transmitted is GPS NMEA strings which are embedded as the ...
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37 views

Amplitude/phase recovery on noisy signal

I have a noisy signal that has an ac component of fixed frequency but variable amplitude and phase. I'd like to recover the ac component. The signal (blue trace) is mostly smooth, but has a few ...
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1answer
37 views

ASK demodulation using DSP

I need to implement an ASK (ampliltude shift keying) demodulation using a DSP ( a dsPIC ) and programming in C. Especifically talking, I need to demodulate a signal from a car's key transponder. I ...
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18 views

Car engine audible through AM radio — what is this called?

A car's engine rotates in the range of 500 RPM to 6000 RPM. This is in the audible range. The car's engine is activated using spark plugs which are an electrical system at the same frequency (or some ...
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1answer
68 views

Question about ASK, correlation, and frequency domain

So I'm currently studying ASK (amplitude shift keying) and how it is modulated and demodulated. The modulation take out data signal, $M(t)$, and multiplies it with our carrier frequency, lets say $\...
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67 views

FSK audio spectrum for demodulation

I am working on Python script to demodulate FSK audio signals. The audio signal contains GPS NMEA strings. I am a beginner in DSP, but trying to work my way through this problem. I think this is a ...
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181 views

FSK Demodulation in Python

I'm trying to demodulate an FSK audio file. The data are from geospatially encoded media where NMEA GPS strings were encoded to audio with 4800 baud and embedded in video. My goal is to use Python to ...
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1answer
29 views

Signal encoding identification

I've read this signal from a radio remote that opens a gate. This signal is already after AM demodulation, read by using a Saleae logic analyzer: I don't know much about signal processing, but I ...
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57 views

FSK demodulator by integration if the samples per symbols is 2

Say I have a binary FSK with +f and -f frequencies and I have two samples per symbol. Let's consider the "1) multiply with <...
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2answers
132 views

Minimum Sampling Rate of Bandpass signal

Consider a DSBSC signal s(t) = m(t).cos(2.pi.20k.t) where say m(t) is multi-tone signal with frequencies less than 5 kHz. The ...
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1answer
33 views

How to do base-band simulation of coherent detection of M-ary orthogonal signals?

I currently have a complex base-band simulator for non-coherent detection of M-ary orthogonal waveforms (such as M-FSK). I run the noisy signal through M correlators at lag=0, compute the magnitude ...
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9 views

Recommendation for type of analysis

I'm trying to figure out if there is a better way to do an analysis. I have a signal from a physics experiment. In this signal, there contains a signal around 20 Hz, but oscillates within maybe 0.1 Hz ...
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181 views

Doing analysis using IQ demodulation in Python

I'm trying to doing an analysis using IQ demodulation. I'm doing this by taking a noisy signal which has a desired signal in it. The desired signal has a frequency that is almost stable, which I'm ...
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1answer
117 views

Matlab : Help in getting the correct constellation diagram for QAM modulation

I would like to see the constellation diagram after equalization as shown in the website Correct constellation for QAM. But I am getting a different plot. Can somebody please tell me where I am going ...
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53 views

Matlab: Help in simulating the symbol error rate for higher order QAM modulation

I am trying to calculate the Bit Error rate (BER) for 16 and 64QAM modulation for channel equalization using Subspace algorithm. The algorithm / code works fine without the BER calculation. Question:...
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95 views

Matlab : Doubt in implementing MMSE equalizer - problem in decoding

I am trying to implement a Minimum Mean Square Error Equalizer for training based channel equalization using 64 QAM modulation technique. The code below works for 4 QAM but when I try to generate 64 ...
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37 views

Matlab: Unable to perform equalization by higher order cumulant

I need to apply Higher order cumulant -the 4th cumulant algorithm as an equalizer for blind equalization. The code returns only 5 samples for each signal-to-noise ratio and as a result, when ...
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1answer
229 views

Matlab: What should be the BER performance for BPSK using Constant Modulus Algorithm equalizer

I need help in plotting the Bit error curve or the symbol error curve for BPSK modulation scheme for varying Signal to Noise ratios or Eb/N0. The plot should show the simulated versus the theoretical ...
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2answers
59 views

Given a real signal, increase modulation frequency

Lets say I receive the signal $$x(t)\cos(\omega_c t)$$ and I want to change the the carrier frequency $x(t)\cos(1.001\omega_c t)$ How can this be done? If I modulated it with a complex exponential, ...
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68 views

Binary FSK optimal detection rule

Let us consider BFSK modulation with symbols $\in {{1,2}}$. For symbol m the transmitter sends $s_m(t)=\sqrt{P\over T} e^{j2\pi f_mt}$ where $m=1,2$ and $f_m$ is symbol's $m$ carrier frequency. The ...
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2answers
995 views

Frequency Shifting in MATLAB

I am currently attempting to demodulate an audio file using MATLAB. After taking the fft of the signal, I receive this: After some more coding, I found the following values: Fs = 44100; Window ...
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1answer
51 views

Maximum Likelihood carrier phase estimation of $A\cos(2\pi f_ct)$

This question refers to the example 5.2-1 of the book "Digital Communications, 5th Edition by John Proakis, Masoud Salehi" (example 6.2-1 in the 4th edition of the book) which asks for the estimate ...
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1answer
130 views

How to compute bit level soft decisions from an M-ary symbol?

When working with a decoder such as LDPC that can take in soft-decision inputs (or channel posterior probabilities as I've seen them called as well), how are these soft-decision values calculated for ...
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135 views

Very high SNR BPSK modulation

I am using BPSK modulation to modulate a signal in continuous time (making rectangular waveform, multiplying by a carrier). The channel is band-limited and frequency-selective, and has the following ...
4
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1answer
278 views

What is the connection between analog signal to noise ratio and signal to noise ratio in the IQ plane in a quadrature demodulation system?

We would like to compute the quantitative relation between analog noise near the LO frequency and the statistics of points found in the IQ plane after IQ demodulation. In order to completely ...
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1answer
575 views

Why isn't this AM Demod GNU Radio flow graph working with different sampling rates?

I am trying to demodulate an AM signal in GNU Radio, and I am having problems with the sampling rates. I will start off with an example where the flow graph was working. The sampling rate is 256kHz, ...
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130 views

In-phase and Quadrature demodulation

I'm new with signal processing and have started to learn it for physics research I am involved in. I have a signal which I want to process to find the amplitude of one frequency of. To do this, I'm ...
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38 views

How do you find the position of when a signal changes frequency?

Suppose I have a signal which varies between two frequencies (which represent a stream of binary data). I think this is called BFSK. I have the entire signal already sampled. Let's say each 'bit' ...
0
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1answer
114 views

Where do I start in learning how to demodulate a BPSK31 signal in software?

I'm a software developer and a Amateur Radio operator. Everything I know about audio (which isn't saying much) is self taught. I've learned how to generate audio samples and build wav files, send ...
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3answers
140 views

Can OFDM modulate analog signal?

I suppose that OFDM can't modulate analog signal. The basic mathematical description for OFDM is $$ v(t)=\sum_{k=0}^{N-1}X_{k}\exp(j2\pi k t /T),\quad 0<t<T$$ In this equation, $X_k$ is a ...
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1answer
40 views

Must OFDM signal be time-division in a multiple-transmitter and SFN system when the signal is free of spread-spectrum?

The OFDM baseband signal can be demodulated since each subcarrier is orthogonal to another. But In SFN system, i.e., Single Frequency Network, all OFDM signals from several transmitters are in the ...
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1answer
247 views

I/Q Sampling and Demodulation

A bit stream is mapped to symbols during baseband modulation, each symbol (say for QPSK) represents two bits. Each symbol has a corresponding I & Q value, which in QPSK, are used as the amplitude ...
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31 views

Recover signal from sum of AM and FM

I have samples of a signal that contains an AM signal added to an FM signal with the same carrier frequency $f_c$. The AM signal is a sinusoid with frequency $f_{AM}$ and the FM signal is a sinusoid ...
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1answer
49 views

dvb-s to dvb-c direct transmodulation

Is this possible to direct trans modulate DVB-S/S2 -> QI into -> DVB-C/C2 signals without doing it the way DVB-S/S2->Demodulator.ic-Transport Stream -> Modulator.ic-Transport Stream -> DVB-C/C2 ? Qpsk ...