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

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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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46 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
20 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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26 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
80 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
27 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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8 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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64 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
56 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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30 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. ...
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41 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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31 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
177 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
56 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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43 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
465 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
38 views

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

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
92 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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82 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 ...
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1answer
195 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
313 views

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

Please forgive me if this turns out to be a super newb question; I have spent some time (and also searched), and cannot find a solution. I am trying to demodulate an AM signal in GNU Radio, and I am ...
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0answers
92 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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27 views

How to do carrier recovery from base band data

Hi I am developing the carrier recovery model for QPSk demodulation. I am planning to use a IQ demodulator IC and bringing the 720MHz IF signal to baseband data of 320 Mbps each channel 160 Mbps. Now, ...
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32 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' ...
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44 views

Fractal Modulation Implementation

I would like to get help/assistance from whom could support me. I am trying to simulate the Fractal Modulation where the modulation and demodulation equations defined as: Modulation Equation ...
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1answer
100 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
104 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
36 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
186 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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30 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
40 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 ...
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2answers
80 views

FM demodulation amplifier with saturation

I'm trying to understand how FM demodulation works. I read a lot on the internet and as far as I understand, the main process is to extract the phase difference (that is also the output) between a ...
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1answer
58 views

Calculate properties of a given Modulated Signal

I'm having a hard time trying to understand signal modulation graphics and how can I calculate/find the properties of the signal. The properties I'm talking are: Max. amplitude Carrier frequency ...
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2answers
111 views

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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1answer
593 views

How to improve an FFT AM demodulator for NOAA APT satellite imagery?

My question involves proper FFT Technique for AM demodulation, in the special case where the modulation rate exceeds the carrier frequency. This question has a specific hobbyist application, the ...
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2answers
148 views

OFDM violates sampling theorem

The "textbook" OFDM block diagram is as the below figure. But I wonder if it satisfies the sampling theorem. Here, we have N points $X[k]$ before IFFT, and $$x[n]=\frac{1}{\sqrt{N}}\sum_{k=0}^{N-1} ...
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39 views

What is the complex-envelope notation?

In reading a paper on demodulation there was this sentence: "Using complex-envelope notation, the noise corrupted waveform at the IF filter output can be written as...". I've not heard this ...
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143 views

Detect FSK high/low bits in presence of noise with only simple processing

I'm currently in the process of writing DSP code, based on the amazing RTLSDR project, and using this as a vehicle to teach myself the basics of DSP (I have an extensive background in software ...
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1answer
212 views

Spectral effects of multiplying a signal by itself?

This has to do with creating the synchronization circuit for MSK in a DSP as described in "Minimum Shift Keying" by Subbarayan Pasupathy published in IEEE Communications Magazine. At the beginning of ...
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1answer
881 views

How to recover complex values (downconvert) from FM modulation (composite signal)?

How does one recover the complex IQ data from the output of a FM modulator. I have combined my signals correctly and performed FM modulation on them, now I'm looking for a way to find the IQ values ...
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2answers
131 views

Is there an efficient algorithm to extract low frequency signal from audio with high frequency carrier?

I need to process an audio signal in an Android app. As shown in the two examples below, there is a 16kHz carrier signal and a lower frequency signal of varying frequency (0-4kHz). Does anyone know of ...
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0answers
93 views

Extracing IQ samples from a composite signal?

I'm writing a modulator in matlab to simulate IQ data that I would get from my radio to test my demodulator. I've read that $I = x(t) cos(\omega t)$ and $Q = x(t) sin(\omega t)$. What is the ...
2
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1answer
747 views

why LTE doesn't use DC subcarrier in the downlink?

I know LTE doesn't use the DC subcarrier for OFDM/OFDMA modulation for the downlink, but no author gives a detailed explanation to this stuff. Can you tell me the reason behind it? Thank you!
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1answer
188 views

Demodulation with matlab

I am trying to listen VLF radio signals. I have a recorded wave file (download) and here is the frequency spectrum: I have produced this spectrum using this matlab code: ...
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2answers
84 views

What is wrong with this method of detecting the presence of a signal?

I am trying to decode Morse code from an audio (wav) file. Here is the technique I am using to detect the presence of the signal: I have a window of size (sampling_freq/tone), where tone is the ...
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1answer
229 views

how to get the phasor(frequency domain) representation of a digitalized signal?

I know that we can get the phasor representation(frequency domain) of a signal through Fourier transform, but the picture above gives a method that can get the phasor representation of a signal in a ...
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99 views

DSP Demodulation advice sought - please help

my field of engineering is condition monitoring. I use vibration analysis to determine the current state of health of a machine and then recommend any course of action required to ensure it does not ...
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50 views

Does this technique have a name?

It is possible to do IQ demodulation by using a zero crossing detector and a timer to take 4 samples of a sine wave if a reference signal is present. When there is no phase difference between the ...
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1answer
327 views

How to transmit the real+imaginary output of an IFFT over a transmission channel?

I'm working on a modem system using a 16-QAM scheme. The transmitter runs an IFFT to modulate the signal, and has a 12-bit DAC. The receiver runs an FFT to demodulate the signal, and has a 12-bit ADC. ...
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1answer
63 views

best meathod to lock onto a cdma signal?

I've been looking at 2 different methods to acquire a known prn code in a CDMA signal. The first trys Xor prn code chip to I sign data. Then average the result over a time period to determine the data ...