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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Hilbert Transform from FFT?

For a school project, I'm working on a software-defined radio transmitter intended for the HF amateur radio bands. I'm planning to support SSB transmission with the formula $$f(t) = m(t) \cos(2\pi ...
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18 views

Filter FM and sideband overload

I'm programming a synthesizer for musical purposes. DSP is not my specialty, so I'm hitting a kind of road block here. I'm using a typical 2 pole biquad digital filter. I'm modulating the cutoff at ...
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26 views

FSK demodulator by integration if the samples per symbols is 2

Say I have a binary FSK with +f and -f frequencies and I have two samples per symbol. Let's consider the "1) multiply with ...
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49 views

How Matched filter is transformed due to frequency modulation?

Intro: Consider a signal source S which emits a PAM modulated signal, bits encoded as +g(t) and ...
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72 views

Single frequencies energy from MFCC coefficients

Is it possible to calculate modulation energy of single frequency or narrow band of them (ex. 200Hz to 600Hz)? The problem is, that I need to check for 4Hz energy modulation in waveform signal ...
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53 views

Why does the BER rate change randomly versus the SNR?

I have altered a MATLAB code that simulates the BPSK modulation using a raised cosine filter at the transmitter and a matched filter at the receiver to study how the signal changes in each step. But, ...
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30 views

Bandwidth of M-ary modulation schemes

I am confused with regard to how bandwidth increases with increase in number of bits transmitted for given duration. 1) Usually say in PCM system, when we increase the number of bits (n) for a given ...
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38 views

Frequency spectrum of an amplitude modulated signal

I am talking about a DSB- Suppressed Carrier amplitude modulation. Let message signal be $m(t)=A_m \cos{\omega_c t}$ and carrier signal be $c(t)=A_c \cos{\omega_m t}$ Then the amplitude modulated ...
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26 views

Correlation in DSBSC modulation

Suppose we have a DSBSC signal given by : $$s(t) = 10 \cos (2\pi f t + \phi ) \cdot m(t) $$ where carrier is random signal with phase ($\phi$) uniformly distributed in $[0,2\pi]$. ...
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135 views

Why upsample before modulation?

We're doing a project in which we're sending an OFDM frame, modulated to some appropriate carrier, over a channel. Before modulating, we are instructed to upsample and low-pass it. Is there a good ...
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8 views

Can I feed several modulations with different frequencies to a lock-in amplifier?

And the signals being read back can be decomposed according to those different frequencies? Was planning to implement parallel signal acquisition by averaging these channels, since one channel is ...
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23 views

Determining frequency deviation FM

I am trying to understand the concept of frequency modulation. As written in Wikipedia, if I have a signal containing information $x_m(t)$ and I want to transmit it using frequency modulation, I need ...
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35 views

How do I decode(demodulation) and get original data from audio sample data

Here I'm talking about the less-than-ideal situations, in other words, the audio sample data may have burrs or error bits in it. Encode and decode theory: I am using FSK to encode my original binary ...
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51 views

Resource and reference request: Analytical BER and SER expression for M-QAM systems in fading channels

For modulation techniques such as QAM, berfading() can be used for Rayleigh fading channel. Link1 presents the code for simulating the analytical expression for BER ...
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41 views

Matlab : Doubt in implementing MMSE equalizer - problem in decoding

I am trying to implement a Minimum Mean Square Error Equalizer for training based channel equalization using 64 QAM modulation technique. The code below works for 4 QAM but when I try to generate 64 ...
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57 views

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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369 views

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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43 views

GNU Radio - QT GUI Frequency Sink block - field Bandwidth and signal frequency spectrum

I am simulating QPSK modulation in GNU Radio. The flowgraph is here: File Source is a binary file. Unpacked to packed is packing bits densely so that one incoming byte contains 4 QPSK symbols. ...
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92 views

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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35 views

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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209 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 ...
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56 views

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, ...
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27 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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82 views

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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77 views

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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76 views

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 ...
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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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37 views

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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124 views

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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20 views

Radar Waveforms Simulation

I am looking for a simulation in any software language, preferably Matlab, that shows the steps from generating the radar signal or waveform (chirp, Barker Code) to modulation, and transmission by the ...
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39 views

What types are Radar Chirp and Barker Code Signals

I would like to know if the radar chirp signal and the Barker coded signals are analog or digital before modulating the carrier. In other words, are the radar signals getting to the antenna analog or ...
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43 views

Binary FSK optimal detection rule

Let us consider BFSK modulation with symbols $\in {{1,2}}$. For symbol m the transmitter sends $s_m(t)=\sqrt{P\over T} e^{j2\pi f_mt}$ where $m=1,2$ and $f_m$ is symbol's $m$ carrier frequency. The ...
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46 views

BFSK modulation what signal the transmitter actually sends?

I am trying to understand how modulation with carriers works(transmission part). I will express my question in terms of BFSK for simplicity. Let us condiser BFSK modulation with symbols {1,2}. Then ...
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38 views

Maximum Likelihood carrier phase estimation of $Acos(2\pi f_ct)$

This question refers to the example 5.2-1 of the book "Digital Communications, 5th Edition by John Proakis, Masoud Salehi" (example 6.2-1 in the 4th edition of the book) which asks for the estimate ...
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59 views

Reversible QIM For watermarking

I have read your paper with title "Nested Quantization IndexModulation for Reversible Watermarking and Its Application to Healthcare Information Management Systems". enter link description here ...
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85 views

Very high SNR BPSK modulation

I am using BPSK modulation to modulate a signal in continuous time (making rectangular waveform, multiplying by a carrier). The channel is band-limited and frequency-selective, and has the following ...
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19 views

Basics of Sphere Decoding for MIMO

I am working on a project that involves Spatial Modulation for MIMO channels. This uses a ML (Maximum Likelihood) detector which is computationally intensive. Sphere Decoders are developed to reduce ...
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114 views

BPSK modulation under bandlimited channel

I modulated signal using BPSK modulation and I have series of -1 and 1. Now I have to pass these signal from band limited channel that has frequency response of the form ...
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1answer
70 views

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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73 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 ...
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176 views

Half Sine Pulse Shaping design

The standard of 802.15.4 specfies the following 'The chip sequences representing each data symbol are modulated onto the carrier using O-QPSK with halfsine pulse shaping.' For pulse shaping the ...
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149 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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1answer
84 views

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 ...
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44 views

Fractal Modulation Implementation

I would like to get help/assistance from whom could support me. I am trying to simulate the Fractal Modulation where the modulation and demodulation equations defined as: Modulation Equation ...
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1answer
118 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 ...
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132 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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2answers
115 views

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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52 views

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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62 views

8x4 QAM gray coded in Matlab

I try to modulate and demodulate 8x4-QAM gray code in Matlab (see the picture). However, when I try: ...
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3answers
104 views

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 ...