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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How to use phase codes for modulating a pulse

I am working on phase codes (examples - Frank, P1, P2, Zadoff Chu) to generate minimum side-lobes on matched filtering. I considered a sinosoidal carrier wave at $45\textrm{ mHz}$, and phase modulated ...
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32 views

ssbmod single sideband modulation artifacts

clc; clear all; close all; [c,fs]=audioread('60hz.wav') r=ssbmod(c,160, fs) r=r/max(max(abs(r))) audiowrite('artifacts.wav',r,fs,'BitsPerSample',24) I am trying ...
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Frequency modulation: Implementation and interpolation

Phase modulation is defined as: $$f_c(t+f_{m}(t))$$ That is the carrier $f_c(t)$ is shifted in time by an amount specified by the modulation function $f_m(t)$. To achieve frequency modulation simply ...
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1answer
26 views

Why does QAM use two cycles instead of one per byte?

If you look at this image, you can see that you have 256 possible binary values by modulating the amplitude (the radius of the trigonometric circle) and the phase (the degrees) of the carrier. ...
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12 views

Bandwidth of ofdm symbol in a visible light communication system

What is the difference of the bandwidth of the LED and the optical channel? If ofdm symbols are transmitted over this system, is the bandwidth of ofdm symbol equal to BW of the LED or of the channel.
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48 views

Gardner Timing Recovery for Repeated Sybmols

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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1answer
38 views

Visible light communication and LED modulation

I work on a VLC system in which 16-PAM symbols with complex pilot symbols are as ifft input. I made the ifft output real and positive. Now how should i use these ofdm symbols to modulate LED? Their ...
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1answer
44 views

How to find a know signal in another signal which contains other signals along with the signal i need in python

I am working on BPSK with sound waves a carrier waves. Actually I am modulating my data with some known sync bits along with the information I need to send. So the things I will be having at ...
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1answer
46 views

The little problem with Kalman filter

I am trying to simulate the Kalman Filter. I have the covariance matrix P_{0|0}. Tell me please, how can I get the predicted (a priori) estimate covariance matrix ...
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1answer
24 views

why does the decision boundary change in BPSK? is it true?

I am working on modulation and demodulation of BPSK using python. i made a code for modulation and demodulation,while demodulate i tried to compare my actual data bit stream with demodulated bit ...
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1answer
33 views

How to derive the transmitted signal from a constellation diagram

Let us assume we have $16$ symbols to transmit. We can represent these $16$ symbols by $16$ unique signals and transmit. If at the receiver we can identify these $16$ signals correctly, we have ...
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1answer
171 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 ...
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56 views

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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22 views

Choosing modulation frequencies

A square wave $s(t)$ is modulated by two functions, $y_{1}(t) = \sin (2\pi f_{1}t)$ and $y_{2}(t) = \sin (2\pi f_{2}t)$, which are combined into a single function $x(t) = y_{1}(t)s(t) + y_{2}(t)s(t)$. ...
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26 views

How to calculate transmission capacity of a channel with multiple frequencies? [duplicate]

So I have the following question: If a transmission channel uses an analog carrier wave that is modulated by eight amplitudes and sixteen frequencies per bit time, then what is the ...
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1answer
58 views

How to set a Carrier Wave for DBPSK Modulators in gnuradio?

for a Project I need to build an Audio Modem in GNU Radio. I decided, that it would be the best to use DBPSK Modulation, because that is fast and relatively noise resistant. But as it seems, the ...
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2answers
48 views

M-Array DPSK decoding and encoding

So i'm trying to figure how how to do the encoding and decoding of an M-array Differential Phase Shift Keying (DPSK) signal. I understand how to do it for binary DPSK, but on higher ordered signals I'...
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1answer
29 views

Reasoning Behind Additional Phase Shift in DPSK

In MATLAB's Comm System Toolbox there is an option for 'Phase Rotation', defined as the phase difference between previous and current modulated symbols when the input is zero. This is the first time I'...
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1answer
35 views

how to sample and modulate a gps gold code

I am trying to simulate the data transmission of a GPS satellite. Telecommunications is not my field so I am struggling a bit with some concepts. I managed to generate the Gold code of the GPS ...
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2answers
62 views

Question about decimation/downsampling

I am using an on-chip SAR adc where for some reason I can only get accurate signal reconstruction and filtering when I sample at almost 100 times my desired sampling frequency. Specifically, the ...
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2answers
54 views

Smoothing an LFO Sawtooth Wave

I'm trying to smooth a Sawtooth wave coming out of my LFO. Effectively the transition from 1.0 to -1.0 in a 1 sample step is causing clicks and pops if I modulate my audio signals amplitude with ...
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19 views

Reduction of Sample Size of a Gaussian Pulse

I need to sample a gaussian wave of pulse width of 1 us which is being modulated by a cosine wave of GHz frequency. The different cases that I am interested in are 1) The initial phase of the cosine ...
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42 views

IFFT-based OFDM system

Please explain, mathematically, how can a bank of modulators be replaced with the IFFT in an OFDM system?
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87 views

Audio frequency modulation algorithm

I have a digital audio signal (float samples). I need to apply the Vibrato effect to a signal. "Vibrato" is no common term, but it is the same as the frequency modulation. So, I need to modulate my ...
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19 views

Car engine audible through AM radio — what is this called?

A car's engine rotates in the range of 500 RPM to 6000 RPM. This is in the audible range. The car's engine is activated using spark plugs which are an electrical system at the same frequency (or some ...
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70 views

Question about ASK, correlation, and frequency domain

So I'm currently studying ASK (amplitude shift keying) and how it is modulated and demodulated. The modulation take out data signal, $M(t)$, and multiplies it with our carrier frequency, lets say $\...
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109 views

Is this waterfall characteristic of QAM or OFDM (or something other) modulation?

I recorded this signal at 2.45GHz, it is coming from a camera. Is this QAM or OFDM ? Based on those side-lobes I would guess OFDM but I am not sure. Also there seems to be an interesting preamble ...
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81 views

Root raised cosine pulse shaping peak value

I am using a FIR filter to generate Root Raised Cosine pulse for an IQ modulator. How can I predict the peak value at the output, depending on the roll-off factor of the pulse ? Knowing that : FIR ...
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1answer
101 views

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 f_\...
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21 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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62 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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1answer
56 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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77 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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1answer
96 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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1answer
39 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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1answer
47 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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1answer
37 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 $[0,2\pi]$. If ...
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1answer
207 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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11 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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27 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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67 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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102 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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103 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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131 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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378 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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135 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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1answer
363 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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1answer
44 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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1k 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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59 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, ...