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Questions tagged [modulation]

Modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with the amplitude of low-frequence modulating signal which typically contains information to be transmitted.

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Numerically Controlled Oscillator (NCO) for phasor implementation?

If I want to simulate a digital oscillator (or phasor) to modulate an arbitrarily length signal: $$y(t) = \cos(2\pi f_ct)\quad\text{where}\quad t = \frac{n}{f_s}\quad\text{for sample}\quad n$$ What ...
BigBrownBear00's user avatar
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Gardner Timing Recovery for Repeated Symbols

I am implementing the Gardner Timing Error Detection algorithm for a QPSK signal. I understand the concepts behind it but I am curious as to what effect repeated signals can have on the phase lock. ...
Andrew Cragg's user avatar
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Deriving SER & BER for 4QAM, 16QAM and 32QAM

Required to find symbol error rate vs $E_b/N_0$ for 4QAM, 16QAM & 32QAM. Thought that SER & BER are the same but did my research to find that BER is $1/\log_2(M)$ of SER. Could you please ...
John Smith's user avatar
2 votes
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Real-time modulated IIR filter

I've been learning to implement an IIR filter for a synthesizer project. It is now more or less stable when the parameters are constant, but ultimately I want the parameters to be arbitrarily ...
ollpu's user avatar
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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 ...
Dan Sandberg's user avatar
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3 answers
1k views

Processing OBPSK as OQPSK

I'm trying to create and process an OBPSK signal, which, as I understand it, transmits even bits on one axis and the odd bits on the opposite axis, resulting in a constellation with 4 unique points. ...
bruno617's user avatar
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The error probability of 16QAM

The signal constellation for a communication system with 16 equiprobable symbols is shown as below. The channel is AWGN with noise power spectral density of $N_ 0/2.$Using the union bound, find a bound ...
Shine Sun's user avatar
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How can I generate offset QPSK symbols from QPSK symbols

I am trying to generate Offset-QPSK modulated symbols. But I am facing some difficulties. I know how to make QPSK symbols but I am unable to figure out at what stage I have to bring in changes to make ...
wanderer's user avatar
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2 answers
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Envelope behavior dIfference between QPSK, OQPSK and $\pi/4$-QPSK

I am trying to analyze whats the major difference between these three variants of 4PSK. I know that QPSK - signal points are at 0,90,180,270 OQPSK - The bit period of Quadrature component is ...
Aryan Sinha's user avatar
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Range-Doppler Coupling in FMCW

I did some derivation of the IF signal of the FMCW using sawtooth LFM. A chirp with sawtooth LFM is expressed like below $$x_T (t)=\cos\left(2\pi f_c t + \frac{\pi}{T}B (t-mT)^2 \right)$$ Where, $f_c$ ...
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Spectral density of modulated noise process

Suppose we have a noise process $F(t)$. Suppose $F$ is stationary and we know its autocorrelation function $$\rho_F(\tau) \equiv \langle F(0)F(\tau) \rangle$$ where the average is over realizations of ...
DanielSank's user avatar
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baseband and passband modulation

I have a simulink model over 2.4GHz. In the transmitter part, the modulation is O-QPSK modulated baseband instead of passband modulation. In Matlab Help this is the reason of using baseband ...
kate's user avatar
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1 vote
1 answer
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How to generate IQ component for transmitting 2FSK

I am trying to generate IQ components for 2FSK modulation. I have started off from this thread FSK and IQ modulation , but I don't quite understand the IQ TX components plotted in the example there by ...
pexyz's user avatar
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17 votes
6 answers
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Can we break the Shannon capacity?

I have a friend working in wireless communications research. He told me that we can transmit more than one symbol in a given slot using one frequency (of course we can decode them at the receiver). ...
Learning's user avatar
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3 answers
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the relationship between bandwidth and the datarate

One Question of my note is like this. ...
Samuel's user avatar
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7 votes
1 answer
805 views

Simplest All Digital GMSK Modulator

How to simply implement an all digital GMSK modulator with no multipliers? The implementation approach should be applicable to GMSK modulation with $BT=0.5$ or less (where intentional ISI is ...
Dan Boschen's user avatar
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Effect of Passband Slope on QPSK Constellation

What is the effect of a passband slope on a QPSK (or any QAM) constellation? Specifically given a linear slope (in magnitude, not dB), and no phase distortion (linear phase or even zero-phase) how ...
Dan Boschen's user avatar
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4 votes
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Use of pulse shaping in digital modulation

Sorry, I am a little bit confused here cause I thought when we say QPSK, the signal looks like the following. I thought the bits to send/receive depends on the phase shift of the carrier, or is the ...
уве вонг's user avatar
4 votes
1 answer
2k views

Power Spectral Density of Digital Modulations

I want to simulate the power spectral densities of different modulations in MATLAB (without Simulink). Unfortunately I have only very basic understanding of signal processing, hence I struggle with ...
wheeler's user avatar
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3 votes
2 answers
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Relationship between $E_b/N_0$ and $\rm SNR$ with channel coding

I would like to know what would be the relationship between $E_b/N_0$ and $\rm SNR$ when there is a coding rate of $R_c=K/N$. Normally when there is no channel coding according to this link. $$\...
user59419's user avatar
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Conditions for analytical signal reconstruction with the Hilbert Transform (HT)

I'm new to the Hilbert Transform, I was reading the paper: "SISAR Imaging - Radio Holography Signal Reconstruction Based on Receiver-Transmitter Motion", and the next sentence was written in the paper:...
DaDSPGuy's user avatar
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2 votes
2 answers
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Why is the bandwidth doubled with AM?

Let's say I have an arbitrary signal which has the following frequency spectrum and a bandwidth of BNF: Now I use Amplitude Modulation to transport the signal. The frequency spectrum will change ...
paul's user avatar
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1 answer
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Difference between MSK and GMSK?

I try to understand differencies between MSK and GMSK on transmitter side. Is GMSK the same than MSK except that a gaussian filter is applied on bits before modulating them? Is the half symbol delay ...
dsp_curious's user avatar
1 vote
2 answers
454 views

How do audio readers interpolate?

$124$ Hz sampled at $256$ Hz has "beats", but $128$ doesn't - a phenomenon of this question: Whether these are "legitimate" beats is up to interpretation, but suppose the goal is ...
OverLordGoldDragon's user avatar
1 vote
1 answer
671 views

Phase Noise in Constellation Plot

I have the following phase noise plot (-100dBc/Hz @ 1MHz offset and -130dBc/Hz noise floor): The integrated phase jitter for this phase noise is around $4.6^\circ$. According to my understanding the ...
sarthak's user avatar
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1 vote
2 answers
98 views

Why is automatic modulation classification hard?

There is a huge amount of research into automatic modulation classification (AMC) using machine learning.. Why is AMC a hard/difficult problem that we need to use machine learning or even deep ...
Pyfisch's user avatar
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2 answers
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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 ...
Dan Sandberg's user avatar
1 vote
1 answer
757 views

Adding phase noise to a signal results in amplitude variation on a constellation - whats the mistake? *plots inside*

I am attempting to add phase noise to a modulated signal. I am doing this by taking a phase noise mask (single sided 0 Hz to 1 MHz), which shows dBc values away from central value or reference value. ...
Villere_DSP's user avatar
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1 answer
171 views

Are there amplitude and phase characteristics of harmonic signal components?

Nonlinear amplifiers are characterized by their AM/AM and AM/PM. That's what I thought. But now I have a question: The amplitude and phase distortion characteristics, do they only belong to the ...
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Exact formula for 8-PSK BER

Is there an exact formula for the probability of bit error (or bit error rate, BER) for 8-PSK (in the literature, course slides, etc.)? I am not referring to SEP (Symbol Error Probability) but BER. ...
Loran's user avatar
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21 votes
4 answers
92k views

How to mimic/copy/fake someone's voice?

Is there any existing application to sample someone's voice and use it to modulate any other voice or synthesize a text to resemble the original one? For example, this Text-to-Speech Demo by AT&...
clapas's user avatar
  • 313
12 votes
1 answer
7k views

FSK Demodulation, Bit Timing Recovery

I am currently implementing acoustic FSK modulation and demodulation. I am not a signal processing guy so any help about the bit timing recovery would be very appreciated. Currently I implemented the ...
peter's user avatar
  • 125
10 votes
2 answers
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What is a $BT$ (Bandwidth-Time) product with reference to modulation?

I would like to know what does Bandwidth-Time product mean. I understand that Bandwidth ($B$) = 1/Symbol Time ($T$), hence $BT = 1$. But how can it vary? What is its significance? e.g. When we say ...
eecs's user avatar
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6 votes
2 answers
6k views

What is a constant envelope modulation?

The Book "Digital Modulation Techniques" by Fuqin Xiong groups digital modulation schemes into two classes: "constant envelope" and "nonconstant envelope." However, I was surprised by the inclusion ...
nispio's user avatar
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5 votes
1 answer
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Calculating SNR from Frequency Domain

As I am newbie to signals, I have collected an appliance signal in frequency domain as follows: (PSD- Power Spectral Density). So, I need to calculate the SNR (Signal to Noise Ratio) and BER (Bit ...
debugging XD's user avatar
5 votes
3 answers
3k views

What exactly happens with Spread Spectrum Modulation

With regard to DSSS and CDMA(DS), what does it mean to spread a signal over a spectrum of frequencies in terms of individual frequencies? Is it about sending the same signal redundantly on multiple ...
estolua's user avatar
  • 153
5 votes
1 answer
2k views

OFDM training symbol format

For OFDM synchronisation, we are using two training symbols according to the Schmidl and Cox method of frequency synchronization and timing synchronization. The paper says: The first OFDM training ...
Karan Talasila's user avatar
4 votes
1 answer
6k views

How to convert sampled real audio signal to it's IQ components for IQ modulation?

So my question is this: How to convert sampled real audio signal to it's IQ components for IQ modulation? For instance: WHen I have my DSP or FPGA receive a audio signal through a ADC, which is just ...
SpinlockData's user avatar
4 votes
1 answer
2k views

Clock recovery using Mueller and Muller adds noise affecting EVM or SNR (Two cases - GNU Radio & Python code)

The implementation of the Mueller and Muller clock recovery that I am seeing adds a large amount of 'noise' or degradation to the Error Vector Magnitude (EVM) to the symbols on the constellation. This ...
Villere_DSP's user avatar
4 votes
1 answer
5k views

How is the symbol error rate for M-QAM, 4QAM,16QAM and 32QAM derived?

How do you derive the theoretical symbol error rate as a function of $E_\mathrm{b}/N_0$ for 4QAM? I know that the result should be $Q\left(\sqrt{2E_\mathrm{b}/N_0}\right)$ but I am ĺooking for the ...
user1930901's user avatar
4 votes
1 answer
6k views

Baseband vs Passband modulation

I am taking a graduate level course in Networking theory and applications and I am still a bit shaky on the difference between baseband and pass band scheming. The book I am using is Computer Networks ...
Joseph's user avatar
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4 votes
2 answers
9k views

FSK and IQ modulation

I am having trouble understanding the FSK modulation process. There are many ways of demodulating the FSK signal. What is the advantage of performing the FSK using IQ modulation? How to demodulate ...
Fedaa's user avatar
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4 votes
1 answer
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The difference between MSK as CPFSK and OQPSK

I am working on MSK simulation. I have read the Chapter 5 of book entitled Digital Modulation Techniques by Fuqin Xiong. It is said that MSK can be viewed as a Sinusoidal Weighted OQPSK or CPFSK. If ...
Cror2014's user avatar
  • 153
3 votes
1 answer
948 views

obtaining "4 Hz modulation energy"

Could anybody tell me a method to calculate the "4 Hz modulation energy" for a speech signal? Thanks. EDIT I get some details : 4 Hz modulation energy: Speech has a characteristic energy modulation ...
Maystro's user avatar
  • 153
3 votes
1 answer
179 views

About FM signal's proving

My text book (Communication Systems analysis and design P.334, 335) have a FM signal is $s_{FM}(t) = A cos[2\pi[f_c+ks(t)]t+\phi]$ where k is a constant and $\phi$ is the arbitrary phase angles ...
Samuel's user avatar
  • 415
3 votes
1 answer
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Adding AWGN noise with a correct noise power to the signal

I would like to add AWGN noise to my BPSK and QPSK signal. So assume the BPSK signal is x1 and QPSK signal is x2. The ...
justin's user avatar
  • 199
3 votes
2 answers
4k views

Help me understand how Pulse-Amplitude Modulation (PAM) works

Reading on the Internet i learned that PAM is basically a sampling technique which converts an analog signal into a discrete signal. It modulates a train of pulses by varying the amplitudes of the ...
Hadoken's user avatar
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3 votes
3 answers
3k views

How would sigma-delta modulation work in software?

I've recently come across this YouTube video that shows a PCM stream being played back via the 1-bit internal "PC Speaker", and after hours of googling I've come to think this is done via Sigma-Delta ...
Fabio K's user avatar
  • 33
2 votes
1 answer
1k views

How to implement IDFT using the positive frequencies of DFT, modulation and resampling on MATLAB?

This question is a continuation of the discussion at How can a linear operator on DFT vector produce the same vector using only half of the DFT vector?, where the higher level motivation is better ...
igorauad's user avatar
  • 299
2 votes
2 answers
5k 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 ...
tylerjw's user avatar
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