# 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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### Bit error rate curves, theoretical and simulation

The BER is the average number of errors that would occur in a sequence of $n$ bits. When $n = 1$, we can think of the BER as the probability that any given bit will be received in error. Basically, ...
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### Why not use zero-signal in digital transmission?

This is something that bothers me from time to time and has always been hand-waved away with some plausible but non-rigorous explanation. For clarity, consider the QPSK case where we have the ...
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### GNU Radio - PSK Mod block - unexpected constellation diagram

I am simulating a QPSK modulation in GNU radio. Here is the flowgraph: . The source is a binary stream coming from the Random Source block. There are 4 PSK Mod blocks configured identically (4 ...
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### Baseband vs. Passband

I am a bit confused if the following signal is baseband or passband: $f(t) = x(t) \cos(2 \pi f_c t) - j \: y(t) \sin(2 \pi f_c t),$ where $j = \sqrt{-1}$. Since it is clearly not real, I cannot say ...
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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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### Given a real signal, increase modulation frequency

Lets say I receive the signal $$x(t)\cos(\omega_c t)$$ and I want to change the the carrier frequency $x(t)\cos(1.001\omega_c t)$ How can this be done? If I modulated it with a complex exponential, ...
184 views

### Generalized Barker sequences

So we're doing a project where we've decided on QAM-n modulation. I've read up a little bit on synchronization and found Barker sequences, which supposedly has nice autocorrelation properties which ...
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### Determine minimum distance between two symbols in 16-QAM using the average symbol energy

If the probability of bit error for a square M-ary QAM is $P_M = (1-(1-P_\sqrt{M})^2)$ where $P_\sqrt{M} = 2(1-\frac{1}{\sqrt{M}})Q(\sqrt{\frac{3E_s}{(M-1)N_0}})$ and $E_s$ is the average symbol ...
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### Reconstruction of BandPass Signal from Complex Envelope

From what little I've been able to gather, the complex envelope preserves all information required for the reconstruction of the original signal and that it basically sends a low pass version of a ...
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### Example exercise - Shannon's law on PCM-digitized signal

I am studying for a Digital Communications course in my university, and I am presented with the following example exercise. You have a sound signal with spectral components in the 300-3000 Hz range....
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### Passband modulation at 2.4GHz

As a project requirement, I am supposed to modulate a complex baseband signal to a carrier frequency of 2.4 GHz. These are the steps I followed for the baseband modulation and demodulation: Generate ...
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### Why does DPSK constellation shrink when noise is added?

I am generating a DQPSK waveform at complex base band with constellation points on the unit circle and when I add AWG noise the constellation shrinks. The noisy constellation "blob" migrate inside ...
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### What is the spectrum of modulated noise?

I use a white-noise generator in an rf bridge to measure antenna impedance. The receiver is an ordinary AM/CW/SSB communications type, nothing fancy, nothing 'coherent'. As I approach the null of the ...
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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 ...
743 views

### Effect of Pulse shaping on BER

am trying to implement OQPSK modulation with half sine pulse shaping. If I simulate the OQPSK modulation without pulse shaping, the simulated curve is similar to the theoretical value. However, when I ...
957 views

### BER of OQPSK Modulation

I am unable to find out a formula for the BER for the OQPSK Modulation. Currently, I am using the berawgn function from Matlab to calculate the BER for OQPSK but I am looking for an expression for ...
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### What is the difference between upsampling and up conversion (done during signal transmission)? Also is upconversion different from modulation?

Up sampling is when you increase the sample rate of a continuous signal. Modulation is when you, by multiplying with a carrier, shift the base frequency of a signal. But what is up conversion? How is ...
387 views

### WFM SDR and Audio resolution

How does SDR resolution translate to audio resolution when using FM demodulation? For example: using a 8-bit/2.048 Mhz IQ stream, what is the maximum audio sample rate and bit depth that can be ...
463 views

### DTFT of beat signal with shift due to multiplication

I am simulating a FMCW radar (Ramp signal is used for transmission)and I have created the transmit signal from matlab FMCW model ...
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### Question related to Principle of Communication

Why the frequency of carrier wave is always kept at least $10$ times higher than the highest frequency of base band signal? Can you explain me this with a practical example?
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### Frequency modulation of audio signals. Does increasing the pulse width of frequency tone result in larger operating distance?

I have a simple frequency modulation scheme where in I am sending simple textual data by encoding it into specific frequencies(for example 'a' is converted to ASCII value of 97 and I use 10 ...
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### Can OFDM modulate analog signal?

I suppose that OFDM can't modulate analog signal. The basic mathematical description for OFDM is $$v(t)=\sum_{k=0}^{N-1}X_{k}\exp(j2\pi k t /T),\quad 0<t<T$$ In this equation, $X_k$ is a ...
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### Rectangular 8 QAM bit error rate calculation

I am simulating an 8-QAM communication system over an AWGN channel for various signal to noise ratios, in order to plot the average bit error. However I have not been able to derive an equation for ...
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### Must OFDM signal be time-division in a multiple-transmitter and SFN system when the signal is free of spread-spectrum?

The OFDM baseband signal can be demodulated since each subcarrier is orthogonal to another. But In SFN system, i.e., Single Frequency Network, all OFDM signals from several transmitters are in the ...
922 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. ...
181 views

### How does sampling and subsequent resampling affect aliased harmonics?

If I sample a signal with a harmonic higher than half my sample frequency I can predict the aliased frequency easily as $$|F_h-kF_s|$$ But what if after sampling the signal, I re-sample at a lower ...
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### dvb-s to dvb-c direct transmodulation

Is this possible to direct trans modulate DVB-S/S2 -> QI into -> DVB-C/C2 signals without doing it the way DVB-S/S2->Demodulator.ic-Transport Stream -> Modulator.ic-Transport Stream -> DVB-C/C2 ? Qpsk ...
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### Modulating Gaussain Pulse

I'm trying to generate a modulated Gaussian pulse. First I'm generating the pulse in the time domain perform FFT and displaying both in time and frequency, then I'm multiplying it with cosine term (...
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### Minimum Shift Keying (In-phase, Quadrature Components derivation)

In the derivation of the minimum shift keying in-phase and quadrature components in Simon-Haykin Communication Systems 4th ed (p.387-390) we start off with the definition of the signal to be $\ s(t)$...
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### How to simulate two OFDM Users with low complexity FFT/IFFT?

have two User one of them sending over freq (0-B] and the other transmit over (B-2B]. Both of them are using OFDM and each one has Nc subcarriers. I wanted to simulate the received signal using Matlab....
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### Confusion in the spectrum of FSK modulated signal by using matlab fskmod module

I want to do a comparison of power spectral density of BFSK, 4FSK and 8FSK by using matlab baseband module "fskmod".Following is ...
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### Calculate properties of a given Modulated Signal

I'm having a hard time trying to understand signal modulation graphics and how can I calculate/find the properties of the signal. The properties I'm talking are: Max. amplitude Carrier frequency the ...
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### Relationship between Carrier Frequency Offset and the Constellation Diagram

As part of a project I am doing, I have to investigate how having a carrier frequency offset would affect the constellation pattern of the received signal.This question has got me baffled because to ...
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### OFDM violates sampling theorem

The "textbook" OFDM block diagram is as the below figure. But I wonder if it satisfies the sampling theorem. Here, we have N points $X[k]$ before IFFT, and x[n]=\frac{1}{\sqrt{N}}\sum_{k=0}^{N-1} X[...
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### 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 ...
669 views

### MSK signal recoverd though FM Discriminator?

I am attempting to write a FFSK (differentially encoded MSK) modulator. I have found and implemented a demodulator that works with sample data taken from a radio of a FFSK signal. The demodulator ...
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### why LTE doesn't use DC subcarrier in the downlink?

I know LTE doesn't use the DC subcarrier for OFDM/OFDMA modulation for the downlink, but no author gives a detailed explanation to this stuff. Can you tell me the reason behind it? Thank you!
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### phase mod x freq mod equivalence

do any of you know how to convert a FM index to a phase mod index equivalent considering they both have the same carrier and modulator frequency? Is it even possible? This is in respect for sound ...
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### what are and why are sine and cosine modulated integrals used?

I have found the definition of the following formulas in a paper regarding active vibration control, where they are called sine and cosine modulated integrals. $y$ is measurement signal with a strong ...
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### C/C++ library for digital modulation [closed]

Is there a library written in C/C++ that offers functions like QPSK modulation?
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### How to Model the Dispersion Which Is Introduced by an Electro Absorption Modulator (EML)?

I need to model the dispersion which is introduced by an EML in Matlab. The parameters are: Lambda: 1310nm PAM4 power: Pmax = 1.09 mW Pmin = 0.13 mW Bandwidth = 56Gbps
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### Tuning a radio to a certain frequency

I've a fundamental problem with understanding terminology used in DSP. What does it mean to tune a radio (for example, a software defined radio) to a certain carrier frequency $f$? The received signal ...