# Tag Info

## Hot answers tagged modulation

### Are there modulation schemes that use more bandwith than they need to, but don't require a spread-spectrum code to decode? (besides AM)

Yes, analog wideband FM is another example where the occupied bandwidth is wider than the bandwidth of the modulation signal, and provides a similar processing gain to digital spread spectrum ...
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### Does phase shift introduce high frequencies?

The steps in the time domain for unshaped PSK refer to a rectangular baseband modulation waveform. The frequency response of this is a Sinc function which does indeed contain high frequency components,...
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### Understanding homework solution - why are $\{X_t\}$ and $\{Y_t\}$ joint WSS, and finding Wiener filter + error

Now that the OP has responded with his textbook's definition of jointly wide-sense-stationary (WSS) processes as those that are individually WSS and whose cross-correlation function $R_{X,Y}(t_1,t_2)$ ...
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### Help me understand the concept of IQ signals

The important takeaway is: using a radio, you can transmit two signals "at the same time" (technically: over the same bandwidth). One of the signals is known as I (in-phase), the other as Q (...
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### Is BPSK relevant, or does it even exist, in wireless data transmission?

You are mostly correct. The main problem is that the introductory textbook definition of BPSK as a train of square pulses multiplied by a carrier is so simplistic that it hides what is really going on....
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### Raised cosine filter and root raised cosine filter IQ for modulated signal QAM/QPSK

To satisfy the Nyquist criterion to eliminate the inter-symbolic interference (ISI) you need the whole link (TX, Channel and RX) to constitute a raised cosine filter, so you are having the root of the ...
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### Demodulation + LPF gives derivative of modulated signal

Reverse-engineering your 'photodiode-generated' signal from your picture, one can write down: $$ω_1 = 300 \\ ϵ = \pi / 6 \\ ω_2 = 8000 \\ y_{sig}(t) = \sin(ω_1 t + ϵ\cos(ω_2 t))$$ Notice that a &...
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### Demodulation + LPF gives derivative of modulated signal

There is no derivative when using a mixer and low pass filter for phase demodulation. There will be inevitable delay with the filtering and overall set-up which corresponds to a frequency dependent ...
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### How is the normalized power required for unipolar NRZ twice that of polar NRZ?

If the levels of the polar signal were $\pm V$ you would be right, but then it wouldn't be a fair comparison with the unipolar signal with levels $+V$ and zero. A fair comparison would be to have the ...
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### Help me understand the concept of IQ signals

It might be best to compare an IQ signal with complex numbers, or circle on an XY plane, or phasors. As the IQ signal is a sum of sine wave with some amplitude and cosine wave with some amplitude, the ...
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### What is the phase of $Y(\omega)$ in relation to the phase of $X(\omega)$ where $x(t)$ modulated with an exponential carrier that has no phase shift?

Does that rule apply to just the magnitude or the full signal including the phase? The rules applies for the entire signal (magnitude, phase, real part, imaginary part, phase delay, group delay, ...
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### How should I decode Pulse Density Modulation signal?

In addition to the good points made by Marcus, the OP is only simulating one cycle of the reconstructed sine wave, but there will be an initial transient based on the sampling rate and length of ...
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### How should I decode Pulse Density Modulation signal?

Well, probably with a filter of the analog bandwidth of the original signal – there's necessarily an anti-aliasing filter in front of your PDM converter, even if it's just implicit. So, design a low-...
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### General question on where to learn modulation and radio theory

John G. Proakis, Fundamentals of Communication Systems. Second edition, Pearson 2014. Simon Haykin. 2009. Communication Systems (5th. ed.). Wiley Publishing. The 2022 ARRL Handbook for Radio ...
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### What is the most used signal for basic pulse?

The most common pulse used is the “Root Raised Cosine Pulse” (formed with an RRC filter) This is the pulse commonly used in a transmitter and a subsequent RRC filter used in the receiver. The cascade ...
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### Bpsk implementation python

First, the multiplication by 2 and subtraction of 1 transforms the 01-stream to +1 and -1. Then, as you can easily see in the function's documentation, an upsampling by factor L is performed with h ...
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### How to understand haw many matched filters to use?

Only one matched filter is required (if it can filter complex signals), or two (if not). A receiver's front end produces two signals, one called in-phase (I) and the other called quadrature (Q). ...
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### How to derive the error probability for pulse position modulation in digital communication?

2-PPM is an orthogonal modulation scheme just like 2-FSK (i.e. BFSK), and the same BER equation applies to both which is: BER = 0.5 * exp(-(Eb/N0)/2). I hope this still helps -- it's been a while ...
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### delta modulation

First issue; your t is defined incorrectly. It should be: t = np.linspace(0, duration, int(duration * fs)) Secondly, you should ...
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### Why do I find a low frequency oscillation when I add a carrier frequency to my baseband signal ? And Why is my demodulation step not working?

From the OP's plot it appears there is a very small frequency offset (we see 1/2 cycle envelope in 10 seconds consistent with a frequency offset of 1/20th of a Hz). If sampling was at 10 Hz with a 1/...
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### Convolution with an impulse train in time, what happens in frequency domain

since the Fourier transform of the impulse train is itself a impulse train Here is the rub. That's only the case if the impulse train is uniform, i.e. all impulses have the same amplitude. We can ...
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### Help me understand the concept of IQ signals

In SDRs, multiplying a real-valued bandpass signal by a cosine wave, and simultaneously multiplying that real-valued bandpass signal by a sine wave, generates a complex-valued signal that has been ...
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### Pulse amplitude modulation

For getting started with digital communications, I think Sklar ("Digital Communications: Fundamentals and Applications") and Haykin ("An Introduction to Analog and Digital ...
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### How does PAM-4 encoding of a digital signal relate to theoretical *pulse* amplitude modulation?

There are two different concepts at play here sharing the name PAM, and the Wikipedia article is not helpful at all to disentangle them. The first meaning of PAM is related to the problem of ...
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### Why does NB-IoT use standard QPSK in multi-tone transmission, when pi/4 QPSK is implemented for single-tone?

It's hard to know what the actual reasons for these things are; 4G is design by committee (both for the better, and the worse), so that technical, commercial, and compatibility interests all ...
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### I don't understand which signal I should use as a carrier in my excersise

The $\mathrm{sinc}$ function has the following Fourier Transform also shown below: Here in your question the amplitudes do not matter much. Consider the DSB-SC case: We obviously cannot choose the \$\...
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### DS-CDMA Spreading Code Length Selection

So in the first example above, it has a spreading factor of 2 (2 spread symbols per data symbol) and the second example has a spreading factor of 4 (4 spread symbols per data symbol). Therefore, this ...
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### Recognizing different pulse shaping forms (16-QAM modulation)

Yes each of the cases would be easily recognized from the constellations and spectrums shown. We don't provide direct answers to homework questions so as to not bypass the learning opportunity, so I ...
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### How to modulate a signal to a certain frequency in time domain

The OP is not sampling high enough to visibly see a carrier. From inspection of the graph, it appears the time spacing is only 1 ns which corresponds to a sampling rate of 1 GHz. To visibly see the ...
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### What can be done with I/Q data which would otherwise be impossible?

I wanted to add something that might be missing from other answers. Real and Complex Signals A signal that you can see on an oscilloscope is always a real signal, meaning it can be represented by real ...

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