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

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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
70 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
51 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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0answers
55 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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45 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
51 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
52 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 ...
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1answer
38 views

resonance demodulation for bearing faults [closed]

Can someone explain me how are the different frequency bands useful for detecting bearing faults using resonance demodulation?
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59 views

Really basic question about OFDM

I am new to signal processing and am currently doing research into the subject. I am learning about Orthogonal Frequency Division Multiplexing and have a question. Most definitions of OFDM mention its ...
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108 views

Implementing QPSK Demodulation

I conducted a research on how to implement a QPSK demodulator. I found out the Quadrature QPSK demodulation technique which seems very straight forward. Here is what i understood from the explanation ...
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34 views

How to extract a strongest signal and subtract it from a composite signal at a wireless receiver

updated: It seems I made a naive mistake to over consider the question. Is it the answer like the following: first, analog signal to ADC and turn to digital, then store it to the memory(buffer), then ...
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40 views

TDOA using demodulated signal

Is it possible to find time delay of arrival using demodulated signals (of bandwidth ~200hz)? I have a setup in which I receive (multiple receivers, of course) modulated signal from a source. I want ...
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96 views

How to implement GMSK demodulation

I am currently trying to implement a GMSK demodulator, using Java. I am actualy trying to use the model of this block diagram. However, I really do not know what goes on within the mode selector and ...
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1answer
86 views

QAM for analog and digital waves [closed]

I tried the following code for modulation of two analog waves. Can anyone point to how to modulate and demodulate for an analog and a digital wave? I tried by replacing the second signal (x2) with a ...
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0answers
23 views

IQ sampling vs 2X f0 sampling for SDR

Are there any modulation schemes (or other situations) where sampling at or very near twice the carrier frequency would be better than IQ or quadrature sampling using a local oscillator at or near the ...
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1answer
146 views

ASK and Manchester Encoding

Firstly, the context: I've been given a signal in a wav file, the sampling rate and carrier frequency along with the fact it is Manchester encoded and has been ASK Modulated. Five periods of a ...
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5answers
151 views

Angle Averaging

I am working on an 802.11a demod that works, for the most part, but has a bug that causes intermittent errors. I haven't finished characterizing it, but it appears that the problem is in my ...
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2answers
167 views

Doppler effect on Baud Rate

I'm having a hard time wrapping my head around doppler and how it affects a digital communications signal's baud rate. The examples that I've seen explain that the center frequency of a signal is ...
3
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1answer
2k views

QPSK Modulation/Demodulation in C++

I'm trying to implement a QPSK Mod/DeMod system in C++. So far i have a bit generator that generates N bits and stores it into an array: ...
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1answer
133 views

Find beginning of signal for BPSK Demodulation

I want to store a small amount of data in a sound file recorded by a microphone but I know nearly nothing about signal processing. I managed to demodulate my data encoded using binary phase shift ...
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2answers
167 views

16 psk demodulation

I have to implement a complete receiver in digital communications. The transmitter gives me an output vector which has real and imaginary values. It uses 16psk for modulation. How would I ...
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95 views

PPM Variant - Analytic symbol error probability

I'm trying to calculate symbol error probability of variant of pulse position modulation considering only AWGN channel. The decoder is maximum likelihood so the implementation of the detector is by ...
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1answer
87 views

I can't figure out why spectral features are “displaced” on a spectrogram

I'm trying to create a spectrogram of a complex signal 'y', but I'm running into a problem where the spectrogram that I create appears to have its spectral features "displaced" in frequency space, and ...
3
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1answer
233 views

Improving the communication speed on a 10km cable (with high capacitance)

I'm working on improving the modem communication speed that can be achieved over a 10km cable. The current modem achieves a speed of 9600 bps via hardware (phase locked loop) and I'm looking for ways ...
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1answer
128 views

Pulse detection against various noise floors

I'm decoding a pulse amplitude modulation encoded digital signal. The goal is to detect the individual pulse against a background noise floor. The amplitude of the pulses varies depending on the ...
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1answer
255 views

Practical Gardner timing error implementation

I'm trying to demodulate a QPSK communication. For the moment I do: Signal detection by computing the ratio between the power of the carrier wave compared to the signal power. Initial clock ...
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0answers
174 views

How to correct for inperfect 90 degree phase shift before doing IQ demodulation?

I want to sample two signals, S and R and later do IQ demodulation on these. I am multiplying S with R and I also want to multiply S with a 90 degree phase shifted version of R by shifting the ...
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1answer
84 views

What are the options for turning a bit stream into a byte stream?

I am creating a system (modulator and demodulator) for broadcasting binary data through an analog signal. I'm using BPSK with great success – at least, I'm generating great graphs. Green is input ...
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2answers
237 views

Possible to break out complex WiFi signal?

Is it possible to break out the i and q of a complex WiFi signal? If I have a laptop with a standard WiFi card in it, could I break out the i and q in analog, or upon sampling in an FPGA via digital ...
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1answer
210 views

Integrator and the multiplier in the Optimal Binary Detector

The optimal binary detector for asymmetric, equiprobable PAM pulse normally have structure as shown below, But I cannot understand what is the multiplier and the integrator using for. Why the ...
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1answer
280 views

DC to phase relationship with Low pass filtered sine and square wave multiplication and it's pitfalls. IQ Demodulation

From what I have read about signal (de)modulation I understand that multiplying two sine waves, both with the same frequency, gives a two frequency component sine wave. One at DC and one at $2\omega$. ...
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2answers
1k views

How to normalize the power of a QAM signal?

If I have, for example a 16-QAM signal, and the constellation points are (3,3),(3,1),(1,3),(1,1),...(-3,-3). Now I have a simulated in coming signal with arbitrary ...
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1answer
2k views

How to perform carrier phase recovery in software?

What are the options for recovering the phase of a BPSK signal in software? The only resources I can find online contain circuit diagrams – there seems to be no one willing to explain this to people ...
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1answer
233 views

Why is a precoder necessary for DQPSK and what does it accomplish?

I've implemented a soft-decoder for DQPSK using the wonderful answers I received here: How to soft decode DQPSK? To get the soft-decoder working properly I needed to precode the data I was sending ...
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699 views

How to soft decode DQPSK?

I'm successfully soft-decoding D-BPSK by taking the dot-product of the constellation-position of the symbol and of the previous symbol. If the result is >= 1, then the symbol phase hasn't changed and ...
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89 views

A Laymans Fourier transform and harmonics explanation?

Please bear with me, I know some of you will scoff but I have looked on Wiki and in various literature (see below) and can't quite get a handle on a few things. I am a general business programmer, ...
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3answers
421 views

Common methods of transmitting digital data through an extremely noisy audio signal?

I am developing software for transmitting data from a computer to a mobile device using audio. Specifically, from the computer's speaker to the device's microphone. (I am developing both the sender ...
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2answers
957 views

Need help understanding 16QAM constellation diagram

Is the identification of each point on the constellation diagram arbitrary as long as the sender and receiver know the mapping? I have seen some diagrams which order in an outward spiral, while ...
3
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1answer
404 views

Estimating optimum sampling point for 16-QAM in MATLAB

I need to write a MATLAB function to estimate the best initial sampling point for demodulation of a 16-QAM. I can do it by looking at the eye diagram, the point which at which the eye is "open", but ...
5
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1answer
229 views

Which digital modulation scheme would be suitable for transmitting digital data through the output of a PC soundcard

I need to output a data stream at 40 kbit/s or faster out of a computer system whose only accessible output peripheral is the audio interface. This interface has reasonable specs, 96 kHz sample rate, ...
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191 views

how to demodulate the following signal except by fourier transform [closed]

We have a signal of the following form $$I\left(k\right)=\int_{0}^{\infty}R\left(z\right)\cos\left(2kz\right) dz$$ by CCD. $I\left(k\right)$ is the signal we get and $R\left(z\right)$ is signal we ...
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863 views

Demodulation of noisy AFSK signal

I'm trying to implement a software audio modem with fsk to transmit and receive short digital data between two devices (ex a PC and an iPhone) so I'm simulating simple cases study using Scilab/Matlab. ...
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1answer
501 views

How bandwidth is used in modulation

In a typical Digital cable environment in the US, the spectrum is divided into 6MHz bands. When a tuner locks to a signal at say 800MHz, I would assume that the band for that signal is 797 - 803 MHz. ...
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129 views

AFSK clock recovery in noise

What algorithms are available for optimizing estimated bit clock recovery of an audio FSK modulated signal over an extremely low S/N ratio channel? (e.g. barely audible due to high ambient noise and ...
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3answers
4k views

How to demodulate an AFSK signal in software

I am trying to transmit binary data from one device to another over an audio channel (speaker/mic). I use AFSK (Audio Frequency Shift Keying) as in Packet Radio, with $1200 \text{ Baud}$ and two ...
3
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3answers
680 views

Demodulation of a BFSK frequency hopping signal using FFT

I am not very familiar with DSP techniques, and I am currently working on my research project to develop the firmware of a DSP processor, using C/Linux. It involves the modulation and demodulation of ...
2
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1answer
290 views

How to Shift Carrier Frequency in QAM Signal?

If I wanted to apply a 100Hz frequency shift to a QAM signal with a 500MHz carrier frequency, I would Demodulate it at the carrier frequency Apply a frequency shift to the original signal Modulate ...
4
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1answer
703 views

Why can Quadrature Demodulation demod a Frequency Modulated Signal?

I use a Quadrature Demodulator in my SDR application, which is defined as: $\angle (S_n, S_{n+1})=arctan(S_{n+1}*\overline{S_{n}})$ So practically its amplitude is the angle between two Samples ...
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1k views

Improving SNR using DSP techniques

I am building an optical OOK (On off Key Ring) system without a carrier frequency. [However I have a guard time in between symbols, so a consecutive "1" messages will result in a pulse train as ...
2
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1answer
157 views

OFDM Phase compensation

I need to compensate a OFDM-16_qam constelation rotation but I could not find out how to implement it with MATLAB I have a Matrix [48 x 25] where each colum is a OFDMsymbol without CP , pad and ...