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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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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764 views

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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the relationship between bandwidth and the datarate

One Question of my note is like this. ...
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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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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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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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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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338 views

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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117 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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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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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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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 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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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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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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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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1answer
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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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319 views

A query on Power spectral density (PSD)

Say a narrow band signal $n(t)$ has Power Spectral Density (PSD) $S(f)$. If the signal $n(t)$ got multiplied by $\cos(2\pi Ft)$, then what will the PSD of resulting signal in terms of $S(f)$ be? Will ...
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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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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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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 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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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
789 views

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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2answers
91 views

Contradiction between complex baseband and real-valued baseband

Suppose a direct-conversion transmitter+receiver (ideal transmitter) along with its filters. In complex baseband, the filters in the signal chain can be modeled as a complex-valued FIR filter ($y$, $c$...
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QPSK and OQPSK Modulation

In QPSK, after splitting the odd and even bits into the I and Q channels, and then multiplying them with the sine and cosine function, what next am I suppose to do? Do I rearrange them back into ...
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846 views

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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552 views

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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175 views

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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331 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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Recommended literature to learn essential aspects of signals and its propagation [closed]

Where can I learn about signal's features. For instance mean, power, amplitude, frequency, energy, how they propagate in space or any other medium?. What power means its amplitude increases and ...