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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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8
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2answers
6k views

PC-to-PC data communication over Sound FSK / PSK / DSSS

For fun and work I've to implement a java based application that can Encode text or data to sound and transmit using PC's speaker and on the receiving side is a microphone with decoder software. I ...
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1answer
2k views

OFDM transmitter data rate

i am simulating OFDM transmitter in matlab....As u all know OFDM consists of different sub systems such as FEC coding, Bit interlever , Modulator , IFFT block and Adding cyclic prefix.... i have ...
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2answers
53k views

the relationship between bandwidth and the datarate

One Question of my note is like this. ...
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0answers
107 views

The transmitted signal of DPSK

I am very confused about how to get the transmit sequence of the DPSK signal. In my lecture notes, teacher give as the following example. ...
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2answers
2k views

Need help understanding 16QAM constellation diagram

Is the identification of each point on the constellation diagram arbitrary as long as the sender and receiver know the mapping? I have seen some diagrams which order in an outward spiral, while ...
2
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1answer
373 views

Envelope following using FFT bin power -> Low pass effect on the modulation transfer function

I am deriving the temporal envelope of a signal (in a particular frequency band) by summing some FFT bin powers and taking the average, I do the FFT frame by frame, windowing and some overlap. ...
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2answers
3k views

Half Subcarrier spacing in LTE Uplink

First post here, trying to make it as good as possible. Do not know how to make the Python code look nice - any tips? :) Anywho - to the main problem: I am currently working on simulating the uplink ...
9
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2answers
1k views

Deep space communications BER and FEC?

What kind of bit error rate do they get from deep space communications (Pioneer, Voyager, et.al.), and what kind of modulation and FEC allows them to recover messages with that microscopic level of ...
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2answers
1k views

Hexagonal Modulator Comparison with Square Modulator

Hexagonal shaped Modulator is designed to get better BER than Square Modulator. The constellation diagram is like the figure: It is supposed to give better BER measurement than Square as it has wider ...
4
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2answers
1k views

Is it possible to transmit and/or receive multiple types of signals at the same time?

Using an inexpensive SDR (such as the USRP or Per Vices Phi), I want to process two or more communication protocols at the same time (e.g. WiFi and GSM). Is it possible to Tx (or Rx) both at the same ...
5
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3answers
2k 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 ...
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1answer
235 views

Why would I want to define a modulation index for each tone (DSB-FC)?

So the exercise is basically a signal $f(t)$ that is going to modulate the carrier $A\cos(\omega_ct)$ using a modulation index of $m=1$. I have to find $A$ and the power of the modulated signal: $$ f(...
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2answers
4k views

Spectrum of FSK signal

I have implemented a simple V.23-like FSK modem in C here. The peculiarity of the chosen modulation is such that 0's and 1's are sent as tones of two different frequencies (2100 Hz and 1300 Hz ...
2
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1answer
769 views

How to Shift Carrier Frequency in QAM Signal?

If I wanted to apply a 100Hz frequency shift to a QAM signal with a 500MHz carrier frequency, I would Demodulate it at the carrier frequency Apply a frequency shift to the original signal Modulate it ...
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6answers
55k views

Why Carrier signal can't have frequency less than Message signal

I know that why we use Carrier of high frequency to send message signal over a long distance, when the frequency is low , energy will be obviously low. To increase the energy of the signal we need to ...
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1answer
521 views

What are the basic categories of operations performed on audio signals to create interesting sounds?

I don't know if this question will make sense as I'm very new to dsp. In my limited foray into audio dsp I've come across: Frequency Modulation Amplitude Modulation Additive Synthesis Subtractive ...
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1answer
1k views

Help with algorithm for modulating oscillator pitch using LFO

I am developing a software emulation of an analog synthesizer. I am trying to modulate the pitch of an oscillator using an LFO. For each sample fed to the computer's sound system, I am calculating ...
9
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3answers
16k views

Why are sidebands generated in AM and FM?

When the signal is modulated onto the carrier in the electromagnetic spectrum, that signal occupies the small portion of the spectrum surrounding the carrier frequency. It also cause sidebands to be ...
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3answers
32k views

Calculate symbol rate for QAM modulation

Not sure if this is the right place to ask, feel free to move it if any other site suits this better. Anyway I am referring to QAM modulation used in US Cable TV. I know it comes under Annex B which ...
9
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1answer
2k views

Frequency Modulation Synthesis Algorithm

Based on what I read, I've made an algorithm for FM sound synthesis. I'm not sure if I did it right. When creating a software synth instrument a function is used to generate an oscillator and a ...
4
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1answer
358 views

Why is privacy scrambling a standalone block in a communications transmitter?

In some telecommunication systems, scrambling of transmitted data is applied to provide some level of security. For example, the communication system might look like: Data -> Scrambling -> ...
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1answer
301 views

Angle modulation spectrum

Is angle modulation spectrum always discrete or this property only holds for periodic modulating signal?
10
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1answer
673 views

What are thoughts on best modulation to use for underwater acoustic communications at low frequencies?

I wanted to ping the DSP hivemind for general thoughts on what would be the best modulation type to use for low frequency underwater communications. I have chosen this project since I can learn a lot ...
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1answer
3k views

What mathematical tools exist for understanding modulated noise?

Suppose we have a signal $n$ that consists of Gaussian white noise. If we modulate this signal by multiplying it by $\sin 2\omega t$, the resulting signal still has a white power spectrum, but ...