Demodulation is the act of extracting the original information-bearing signal from a modulated carrier wave.
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1answer
49 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 ...
2
votes
2answers
51 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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vote
1answer
42 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 ...
2
votes
1answer
66 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 $2\omega$. ...
2
votes
2answers
71 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 ...
3
votes
1answer
202 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
71 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 ...
4
votes
2answers
143 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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0answers
52 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, ...
5
votes
3answers
243 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 ...
1
vote
2answers
400 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
votes
1answer
229 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
votes
1answer
136 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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0answers
175 views
how to demodulate the following signal except by fourier transform
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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votes
0answers
402 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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votes
1answer
196 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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0answers
86 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 ...
3
votes
3answers
732 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
votes
3answers
292 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
votes
1answer
175 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
votes
1answer
345 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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votes
2answers
640 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
votes
1answer
122 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 ...
3
votes
1answer
143 views
Implementing a basic demodulator
I'm trying to implement a simple demodulator as an evening project (to understand how this works - my background is in physics not engineering) and was wondering if anyone has any advice.
To make a ...
5
votes
1answer
324 views
FFT window phase syncronising
I'm currently devising a solution for demodulating a DPSK signal in C#. So far I've got a working FFT with phase detection, BUT:
I now have an issue of aligning the window of the FFT to synchronise ...
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2answers
2k views
Extracting Binary Magnetic-Strip Card Data from raw WAV
I am faced with a tricky challenge: To extract binary data from an iPhone magnetic strip card reader. This is what the magnetisation on the card looks like:
Source
Here is the .WAV the iPhone ...
5
votes
1answer
193 views
How exactly to implement the fractional part of a 'fractional equalizer'?
I have written my own LSE equalizer (that works on the bit level), and literature I have read says that 'fractional' based ones are much better. So how exactly does one get 'fractional' bits? Is it as ...
2
votes
0answers
54 views
What effect does mutipath have on estimating optimal sampling time using the averaging method described therein
This question takes off from this question regarding syncronization of BPSK signals. For the sake of argument let us assume 10 samples make up 1 bit.
One method currently suggested is break up the ...
4
votes
1answer
703 views
How to determine where to sample for demodulation of BPSK signals?
I have a simple BPSK demodulator. Very simply, the signal comes in and is split into two branches, one for I and one for Q.
The I branch is mixed with a sin wave of the carrier, and the Q branch ...
8
votes
2answers
1k views
How to demodulate an OFDM signal
I'm looking at decoding an OFDM signal which consists of 6 carriers (or tones) which are BPSK modulated and a pilot tone which aids tuning. This is the first time I have worked with OFDM so I need to ...
