Questions tagged [demodulation]

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

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How to implement Walsh demodulation in matlab?

1 1 1 1 ==> 0 1 -1 1 -1 ==> 1 1 1 -1 -1 1 -1 -1 1 I have this sequence of walsh spreading ...
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33 views

Does the FFT size matter in OFDM demodulation?

The DFT size in OFDM demodulation is usually matched to the DFT size in the modulation process. This makes modulation/demodulation simple where each FFT bin (i.e., sample) represents one symbol. What ...
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Demodulating a LoRa data symbol

LoRa integrate data into symbols by selecting the starting frequency of an up chirp. The resulting up chirp traverses across BW and arrives at the same place it started. At the demodulator, this chirp ...
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35 views

A communication system

I am solving the following problem as an exercise. I have a signal $$z(t) = x(t)\cos(wt) + y(t)\cos(ut)$$ and we assume $x,y$ to be band-limited continuous time signals. In the frequency domain we ...
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How to demodulate DominoEx-like signal with liquid dsp?

I found a proprietary protocol that is used on ham radio bands. The author have published details,claiming that it's a version of DominoEX with slightly different baud rate and FEC. I want to try to ...
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27 views

Cross-correlation with SDPSK modulation

I'm trying to detect a sync word in a signal using Symmetrical Differential PSK (bit 0 = +90° phase, bit 1 = -90° phase). Given the signal is encoded in the phase difference between two symbols, the ...
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33 views

symbol synchronization

PLL is typically used in carrier synchronization and its diagram is well known, consisting of a multiplier, a low pass filter, and a VCO. In "Phase-locked Loop" at wiki (https://en.wikipedia.org/wiki/...
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34 views

Non coherent detection BFSK demodulation?

I am simulating BER performance of BFSK under AWGN and Rayleigh fading, BFSK has two symbols one entirely on the real plane while other on the complex plane for representing let's say zero and one, ...
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30 views

Recover frequencies from IQ samples

I have a set of IQ data. From those data I'm trying to get the amplitudes and the frequencies of my signal as I then want to plot them vs. time. I am able to obtain the amplitudes by squaring both ...
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What is the BER for multilevel modulated signal

Assume I want to transmit a low or high symbol which can be BPSK modulated. For ordinary BPSK, bit 0 can be mapped to 1+i0 and bit 1 mapped to ...
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23 views

How to demodulate PM modulation

I'm using a sin wave $s_{sc}(t) = d(t)\cos(\omega_{sc}t + \varphi_{sc})$ to modulate a carrier using phase modulation. I'm working on Matlab so I use the pmmod function to do so. It is not too ...
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Demodulating FM Signals. Understanding text from “Communication Systems Engineering” by Proakis

Please help me understand the following text from "Communication Systems Engineering" by Proakis. Text: What I was not able to understand: 1) Why is the transfer function of the FM demodulator ...
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Model of modulator and demodulator in Simulink. Why is MER so lowest?

I created a simple model in Simulink of a quadrature modulator, amplifier and quadrature demodulator. On the oscilloscope(scope in Simulink) and spectrum analyzer the displayed results look normal (at ...
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Demodulation of 4-QAM

Any help to get me started is appreciated. I have an array of values for the 4-QAM where attach is a copy of part of the values of the array. I want to know how do I get the bits 0 and 1s from those ...
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28 views

CDMA scheme that preserves constant envelope (NRZ/ASK shape)

(This is a followup question to Is this a "valid" CDMA modulation?) Is it possible to find a CDMA scheme in which the receiver can only have a simple slicer? In other words, for the ...
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Is this a “valid” CDMA modulation?

I am banging my head against (specific aspects of) CDMA for a few days. At the basic level I am confused about the interrelation between implementations that are modeled as mixing and fully digital ...
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Any DVB-S2 sample streams publicly available on-line?

I'm working on a DVB-S2 receiver and I'd like to be able to test a part of the DSP chain with real-world signals, but getting good sample streams from a digitizer is not terribly easy. Can anyone ...
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26 views

Possibilities to get the amplitude of a signal at specific frequency from IQ

I'm newbie to the dsp topic and my understanding of math symbols is limited. So at the moment I'm little bit lost to find the right resources. I receive an IQ stream from a SDR. Sample rate: 250k/s ...
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53 views

Loop Bandwidth for Carrier Demodulation loop

I am trying to implement a simple MATLAB model for the demodulators for phase modulated signals (PSK) used in communication systems. For the detection of the phase modulated output (PM out in the ...
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59 views

I/Q Signal Power Calculation

I am trying to understand the basics of IQ modulation. The amplitude of a demodulated IQ signal is given as $\sqrt{I^2 + Q^2}$ which is easy to understand from the phasor diagram. Yet, I don't ...
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31 views

Wrong output for phase demodulation

I tried to plot phase demodulated signal and original message signal but there is a significant difference between magnitudes of the message and demodulated signal. I have attached the code and the ...
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Designing a PI filter for a Costas Loop

I am currently trying to implement a Costas Loop in order to demodulate a BPSK signal. Here is the reference block diagram I have been using to design the loop:Costas Loop Block Diagram I originally ...
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183 views

Getting hilbert transform of IQ signal

Im new to communications so this may be a stupid question, but I am somewhat confused. I am trying to train an automatic modulation classification (AMC) algorithm on IQ data from the RadioML dataset. ...
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Using I/Q demodulation/LIA for a fixed-frequency application of several signals - do the phases of the input signals affect the result?

My input is a single signal composed of the sum of four periodic signals, each 4 Hz apart, centered around some resonant f0 typically between 1200 - 1300 Hz; the actual frequencies will change ...
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63 views

GPS CDMA signal acquisition (BPSK modulation)

Sorry, this may be a rookie question: I have a CDMA gps communication in BPSK. Codes have a duration equal to $1\ \text{ms}$ and their length is 1023. At the carrier frequency ($f_c = 1.57524\ \text{...
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123 views

IQ signal FM descrimination using phase derivative

I'm trying to demodulate an FM signal recorded as IQ samples from RTL-SDR at 2.4Msps with RTL-SDR centered on an FM station's frequency. So the input signal is 8 bit IQ baseband at 2.4MSps. The data ...
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142 views

Demodulating wideband FM signal in Octave from recorded baseband IQ samples

Assuming I have a baseband recording of 8 bit IQ samples at 2.4MSps centered on an FM station is it correct to say that after low pass-filtering the complex signal to 240KHz, taking discrete ...
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80 views

Positive slope of BER with a greater frequency deviation?

I am trying to implement a frequency-modulated communication channel on MatLab. However, there is something I don't understand about the sensitivity of the frequency modulator (or the frequency ...
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QAM and APSK error comparision [closed]

Due to the 16QAM and 16APSK characteristic, is there exact comparison between 16QAM and 16APSK BER?
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439 views

DPSK vs PSK Error Probability

BACKGROUND The bit error probability for BPSK under AWGN is easily derived from tail probabilities of Gaussian distributions and results in $$P_e = Q\biggr(\sqrt{\frac{2E_b}{N_o}}\biggl)$$ The ...
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286 views

Demodulation of FSK signal

What kind of FSK signal is this and what demodulation technique can I use to demodulate it. Why is the phase of the 1's changing like that and how does that effect how it needs to be demodulated. I ...
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37 views

RF direct conversion down to DC and signal recovery from IQ

I've previously worked with super-heterodyne receivers where the IF spectral content has been above DC. Reading the below tutorial; direct down conversion receivers are used to mix a signal of ...
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What's wrong with my M-ary ASK modulation demodulation MATLAB code?

My MATLAB code linked below implements ASK modulation of an M-ary signal, impresses it on a carrier, adds AWG noise of various SNRs. Then, for each SNR, demodulates the signal and calculates the ...
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49 views

Mapping soft symbols in DQPSK

I'm trying to soft decode DQPSK. According to this paper the bits are: $b_1 = \mathrm{Re}\{s_n s^*_{n-1}\}, b_2 = \mathrm{Im}\{s_n s^*_{n-1}\}$ If I put 0.707 as a 100% probability of 0: $\begin{...
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How to add multiple sub bands of frequency into on wide band

Context: I am doing a project where I have to sample a video signal from a monitor with an SDR. The data is coming in for each pixel left to right top to bottom. Since my receiver doesn't have a very ...
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44 views

IQ demodulation from specific rate

We have an acquisition hardware in our lab that acquires and digitizes data from a source generating band-limited signal in the MHz range. It samples the signal at a rate of 4 times the center ...
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172 views

Is There Any Filtering Technique with Element Wise Product Only Instead of Convolution?

Generally we apply a filter to reduce noise from signal. For example if the received signal is $S$ we would get a signal $Y$ with reduced noise applying a filter $W$ with the operation Y= convolution(...
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39 views

Diode demodulation for AM

What is the capacitor and resistance at output of LPF meant for in the document it was mentioned that it is DC blocker I don't get it can't message contain DC value.
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Quadrature demodulator. Relationship of sampling rate and error

Task: to estimate the frequency of the power grid signal. I use a quadrature demodulator. I get the I / Q components. I calculate the angle (phi = atan(Q / I)). I differentiate the angle and get the ...
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247 views

What is the minimum sampling rate for QPSK or what is the bandwidth of QPSK signal?

Consider we have created a QPSK signal with a carrier frequency 100kHz. Before applying matched filter or demodulation we need to take samples from the received signal. So what is the minimum ...
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183 views

Amplitude demodulation of sinusidal signal in matlab

AM-demodulation task and I was asked to demodulate the signal in MATLAB and the result should contain three pictures. plotting the $fft$ the (frequency spectrum)of the signal i was able to determine ...
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Derive the LFSR sequence from demodulated bitstream

I'm new here and hope to have good feedback from you. I'm trying to blindly demodulate an RF signal and managed to get a sequence of bits for a preamble. After some research, I'm in fact exactly in ...
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166 views

Getting the bitstream of an unknown RF signal

I am trying to get the bitstream of a signal sent over 433MHz. I have installed SDR# (I'm on Windows), connected my NESDR SMART, and I identified the signal here: I can see there is only one peak ...
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201 views

How can an SDR recover a high-frequency signal?

How can software-defined radios operate at high frequency? The Nyquist rate dictates that you need to sample at twice the frequency to fully recover the signal. If my signal of interest is modulated ...
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61 views

qam demapper why are soft-outputs used?

I'm starting to learn about OFDM QAM demapping, and a lot of documentation points to using "soft-output" algorithms that calculate Log-Likelihood Ratios (LLRs). Why is this method advantageous? My ...
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Effect of down mixing on complex demodulation method

As I know, IQ demodulation (complex demodulation) consists of three steps: Down mixing X(complex demodulation)(t)=X(real signal)(t).{exp⁡[(-i2π(f_demodulation).t)]} low pass filtering decimation ...
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Term for signal waveform correction or demodulation

Let say a periodic signal waveform $v(t)$ can be modeled as: $v(t) = f(\phi) A \sin(2\pi ft + \psi)$ where $A$ is a constant amplitude, $f$ is signal frequency, $t$ is time and $\psi$ is a constant ...
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Help in identifying low speed image transmission protocol over RF

In the seventies I worked for Muirhead on press fax machines that used to transmit pictures over radio and landline as I recall two FM systems were used a carrier 800 Hz modulated +- 150 Hz and 1900Hz ...
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311 views

From IQ to pi/4 DQPSK

I need to decode $\frac\pi4$-DQPSK packets from an SDR, preferably in C#. I have the SDR receiver part done. Now I'm trying to learn how to take the IQ stream and get the packet info from it. I've ...
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113 views

Symbol synchronization with M-QAM. M < 16

I working on M-QAM system using a Cortex-M4 processor. Using a alternating symbol as a preamble, I am able to get carrier lock. Symbol synchronization is then achieved by finding the peak. An early ...

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