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 ...
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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.
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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 ...
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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 ...
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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 ...
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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. ...
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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 ...
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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 ...
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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 ...
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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).
...
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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 ...
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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 ...
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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.
$$\...
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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 ...
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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:...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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.
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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 ...
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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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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&...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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
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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 ...
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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 ...
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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 ...
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Real and complex low pass equivalent of band-pass signal
A real band-pass signal $s(t)$ with center frequency $f_c$ can always be represented as
$$ s(t) = A(t) \cos(2\pi f_c t) $$
where $A(t)$ is real and can be viewed as amplitude.
Also
$$ s(t) = A(t)...
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How is multiplexing achieved in spread-spectrum modulations like CSS?
I understand why it doesn't interfere with narrowband communication systems but how do different clients communicate in a system like LoRa. Is it time orthogonality like TDM?
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Use of the Dirac delta as a sampling operator
As we are all taught in signal processing classes, the Dirac delta is not a normal function but a generalized function. It is sometimes defined as either the limit of some normal function whose ...
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Finding $E_b/N_0$ when coding rate is $R_c$
I would like to calculate $E_b/N_0$ when the code rate is $R_c$ for BPSK signal. What I got this
$$
E_b/N_0= \frac{1}{2R_mR_c \sigma^2}
$$
and that is the case also according to this page.
$R_m=1$ ...
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