Demodulation is the act of extracting the original information-bearing signal from a modulated carrier wave.
3
votes
2answers
80 views
Why would we simulate baseband rather than passband
My question is, Why do we usually use baseband in simulation rather than passband? however, if we want to test our simulated idea in real environment, it must be sometimes in passband !!
So, should ...
0
votes
0answers
15 views
FSK receiver design - AGC placement in the chain
I am designing an AFSK (Bell 202) receiver/decoder that will be implemented in a microcontroller (Cortex-M, fixed-point). I have come up with such a processing chain:
90 degree shift frequency ...
0
votes
0answers
22 views
Peculiar OFDM Constellation
Currently testing blind demodulation methods on recorded OFDM signal.
The recordings were done with coax cables.
While the estimated Frequency and Time shifts were not accurate enough for ...
2
votes
0answers
32 views
How to calculate the accurate BER expression of circular 8-QAM constellation modulation?
It is easy to understand the BER derivation of square QAM, but the circular 8-QAM? I'm quite confused. The decision region is not in a rectangular shape anymore, meaning regular way does not work here....
1
vote
2answers
54 views
Contradiction between complex baseband and real-valued baseband
Suppose a direct-conversion transmitter+receiver (ideal transmitter) along with its filters. In complex baseband, the filters in the signal chain can be modeled as a complex-valued FIR filter ($y$, $c$...
0
votes
1answer
51 views
QPSK constellation from baseband signal
My IQ sampler is measuring a QPSK carrier at a set frequency/bandwidth (40MSamp/s), but shifts the signal spectrum to baseband. My signal is 1.5Msym/s, but sampling at 1.5Msym/s gives me a ...
2
votes
1answer
40 views
Quadrature demodulation, homodyne detection, lock-in detection - what's the difference?
Quadrature demodulation
Homodyne detection
Lock-in detection
What is the difference between these terms? Are they all synonomous? In my mind they kind of are, so I'm never sure which to use.
I ...
0
votes
0answers
51 views
What is the relationship between FFT size and demodulation in OFDM
As I mentioned in the title of the question, how can we demodulate the data in order to get the same number of subcarriers with different FFT size.
For example,
10 MHz LTE can be sampled with 15.36 ...
0
votes
1answer
31 views
How can I do QPSK in MATLAB [closed]
Could you please explain the step below, what is the benefit of it and how does it work. .
I do qpsk demodulation, do I started doing the meshgrid,
...
0
votes
0answers
50 views
Converting IQ value to distance in FMCW radar
I'm working with a FMCW radar to measure the distance. I'm receiving IQ as the output. I wonder, how to translate this data to millimeter?I have s parameters (<...
0
votes
1answer
42 views
Homodyne concept of receiver
I would like to understand a concept of homodyne architecture of I-Q demodulator and how the wave looks like at each step.
It is a bandpass Signal:
Step 1: multiplication with cos and sin wave. I ...
0
votes
0answers
132 views
Why does my OFDM demod in GNU Radio not return anything?
This is the flowgraph I used:
Output after mod:
Output after demod:
I've read that it might be a synchronization problem but since I'm not actually transmitting anything over a medium, that shouldn'...
1
vote
0answers
35 views
What are the pros and cons of common modulation techniques? [closed]
What are the pros and cons of commonly used modulation techniques? Why is one preferred over another in a given situation? Why do so many exist? Are some better at resisting noise, travelling long ...
3
votes
0answers
50 views
Synchronization of BPSK with variable-length symbols (ISO 14443)
Does anyone have an idea how one would perform BPSK symbol synchronization if symbol length is allowed to vary?
As dumb as that sounds, this is not a theretical question.The "Proximity" Type B NFC ...
0
votes
1answer
57 views
Bpsk demodulator implementation
For a project I'm trying to implement a BPSK demodulator on some random wave files, I'm getting a few difficulties:
How do I know my bit rate, i.e. how many bits each 'real data bit' I'm having.
How ...
0
votes
1answer
57 views
modulate/demodulate audio file as FSK signal mixed with music signal
What I want to do:
I want to encode an audio message inside a regular music file; this shall be decoded by an audio analyzer running on another machine (by listening to the audio playback from the ...
0
votes
1answer
111 views
Carrier Recovery, Frequency and Phase offset in (CP)FSK
I wanted to ask what exactly is meant for phase recovery of signal (at least intuitively). I have a working example of an acoustic fsk modulation and demodulation software but i don't know how to ...
7
votes
2answers
409 views
QAM constellation slicer with unknown carrier phase
As shown in the image, I have a 16QAM constellation that is misaligned due to a phase rotation. In this case you can see that rotation amount is approximately $\theta = \pi/4$, but this won't be the ...
0
votes
2answers
58 views
Demodulation in Rayleigh Flat Fading Channels
A core part of demodulation in Flat-Fading channels is (assuming) the channel as a(random) constant complex number multiplied with your signal. This is done in order to de-rotate the symbol for ...
0
votes
1answer
35 views
Detecting I/Q imbalance
Are there any methods of detecting, measuring, and/or estimating I/Q imbalance (from, say, an upstream quadrature mixer and/or ADC), without using or having a controlled test signal (other than ...
0
votes
0answers
39 views
BPSK demodulation [duplicate]
For experimental reasons i created a function that helps me to modulate a signal using BPSK, the input signal is {1,1,0,1,0} and it works fine
...
0
votes
0answers
95 views
Removing I/Q phase rotation
What is the most reliable and agnostic way to correct for a phase rotation of I/Q downconversion - without time alignment of the signal and support different lengths of transmitted and received data?
...
2
votes
0answers
81 views
Does anyone recognize this modulation?
I'm trying to extract the code of my garage remote, but i have some difficulty to find witch modulation has been used.
At first I thought it was a simple digital modulation, but there is some strange ...
0
votes
0answers
23 views
Vestigial Side Band Demodulation: Which components are to be retained and which are to be filtered out?
This article shows the analysis of Vestigial Side Band Suppressed Carrier demodulation.
I have understood the mathematical derivation up to eq (1). However, I am unable to understand which components ...
0
votes
1answer
92 views
Square law demodulator. How can we eliminate the term containing $m^2(t)$?
We are trying to extract the message signal from the AM signal using square law demodulator.
In the final expression, $V_2(t)$, the term encircled in blue has to be retained, and the others have to ...
-1
votes
1answer
75 views
AM demodulation from a real RF signal
I'm capturing an RF signal transmitted at 433.8MHz, with a bandwidth of about 50KHz. My goal is to be able to save it as a .wav file.
I'm using an RTL-SDR dongle and a software named HDSDR, where I ...
0
votes
0answers
60 views
Wrap Around Viterbi Algorithm for tail biting decoding “WAVA”
Tail-biting where the initial and final states of the encoder are identical.
Tail biting is done by initializing the shift register contents with the last m
information bits in the input block to ...
0
votes
0answers
23 views
Single sideband demodulation via phasing method
Math. I need the math! None of the articles show the math! Need help with demodulation part about "selecting either uppersideband or lowersideband".
Modulation.
Let's say I will get Lower sideband ...
0
votes
0answers
756 views
AM Modulator-Demodulator in Python
I am trying to make a AM modem using Python Numpy and Matplotlib. I am successful in generating the AM Signal but I cannot demodulate it using a lowpass filter function that I made. The demodulation ...
0
votes
0answers
61 views
How is this signal being modulated?
I have a small device that transmits commands in bursts. Looking on the FCC website for the device, the encoding is supposed to be ASK. Previous examples of ASK encoding that I have seen look like ...
0
votes
0answers
340 views
Help with OQPSK Demodulation with GNU Radio
I am working on demodulating/decoding the GOES-15 satellite EMWIN signal @1692.7MHz, BW: 50KHz Mod: OQPSK. I have minimal experience in signal processing and some experience in using GNU Radio. I have ...
2
votes
2answers
194 views
Mystery signal - FSK, BPSK?
I have a mystery audio signal that I need to decode, it's from a discontinued product. Inspecting the object code shows a module called decodeFSK so that suggests ...
1
vote
1answer
211 views
Prepare IQ Data for Goertzel Algorithm
I have a quadrature (IQ - 0..255) data byte stream that I receive from an rtl-sdr dongle as IQIQIQIQ.....
That means that negative values are < 128 and positive values >= 128
I am attempting to ...
0
votes
1answer
316 views
Extracting the carrier signal from AM
I am new to DSP and leaning about amplitude modulation.
I am trying to demodulate a 5 Hz signal that is modulated by a 50 Hz carrier. I am trying to extract the carrier, not the the 5 Hz signal.
A ...
0
votes
0answers
55 views
Autocorrelation BPSK Transmit with Binary Sequence (PRN Code)
I am working to design the Transceiver using a SDR hardware. In the transmitter side, the BPSK modulation was used to modulate a binary sequence number which has good autocorrelation properties. The ...
0
votes
1answer
25 views
How to model airborne sound channel
I'm making a soft demodulation/decoding to communicate a microphone and a speaker in short range. I have to calculate the LLR using my constellation and the airborne sound channel probability density ...
0
votes
1answer
213 views
FM demodulation
I have a frequency modulated signal. My problem is the following:
The sidebands are asymmetric. Meaning that the amplitudes of the sidebands left and right are not equal. Does anyone know what this ...
0
votes
1answer
83 views
How to calculate baudrate?
I'm going through this article https://www.elttam.com.au/blog/intro-sdr-and-rf-analysis/ and I find it hard to understand the following part:
However, in our case we might want to transmit this ...
0
votes
2answers
73 views
mpsk demodulation using digital sample
I am trying to receive and demodulate a 8PSK modulated sinusoidal waveform (real not complex) which is constant envelop and changing only in phase of the continuous sinusoid carrier every Symbol ...
0
votes
0answers
44 views
A Homework Question About Delta Modulation
I have to simulate a communication scheme with delta modulation and 8-pam modulation. Here is what I understand and what I have done so far.
Delta modulation is appeared a quite like quantization. ...
-1
votes
1answer
86 views
Recovering DSSS signal from below noise Floor
I want to understand what actually happens in the direct sequence spread spectrum demodulator ? Why is it said that the signal is recovered from below the noise floor ? Can someone please explain the ...
3
votes
2answers
297 views
Demodulating AM signal from carrier signal on Matlab
I'm trying to demodulate a voice signal (bandwidth approximately 5 kHz) from a carrier signal (100kHz).
[y,Fs]=audioread('Signal1.wav');
h=10*sinc(10*(-10:10));
y1=filter(h,1,y);
But ...
2
votes
1answer
88 views
How is a signal with SNR less than unity demodulated?
The title pretty much says it all. What technique can be used to demodulate a signal with SNR less than 1?
0
votes
1answer
358 views
Demodulation on noise
I'm new in DSP, and I'm working on dsp application involving machinery (Diagnostics based on noise), and to do this I need to make DEMON processing.
I want to process the signal like in the picture (...
0
votes
0answers
223 views
Digital section in BPSK demodulator
In BPSK demodulation, The modulated signal is passed by carrier recovery circuit then multiplication then ADC then digital section of demodulator,
What is the digital section ??
Note: The received ...
0
votes
1answer
766 views
Downconverting real signal to IQ baseband
Despite reading various answers on this site and on other sites I am still confused about how to convert a real-valued signal back down to its original IQ baseband values. Note I am still a beginner ...
1
vote
0answers
44 views
Mathematics in selection of RC time constant for an envelope detector for AM
Let the capacitor be charged to voltage $ V(t_0) $ at $ t=t_0 $ and then start discharging. At time $ t \, (>t_0)$, the delayed capacitor voltage is $$ v(t)=V(t_0)\operatorname{exp}(- \frac{t-t_0}{...
-1
votes
1answer
125 views
Distortion in demodulation signal
I'm doing amplitude modulation and demodulation for DSB. the maximum amplitude of my original signal is $1$. After demodulating the signal, I should be getting the original signal which is $1$ but ...
-1
votes
2answers
273 views
How to demodulate DSB-SC
I need help with demodulating DSB-SC signals. I took the appproach of using the FFT as follows: I have a signal. I FFT it. Then i take real and imaginary part of the FFT and translate some values:
<...
1
vote
0answers
62 views
How to find and fix the delay of a modulation
I am creating a model in MATLAB to simulate power line communication, but I found a problem. I'm very new to the DSP area, I get my code below from a MATLAB example.
...
