47
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Why can so little digital information be stored on a cassette tape?
I had heard that tape is still the best medium for storing large amounts of data.
well, "best" is always a reduction to a single set of optimization parameters (e.g. cost per bit, ...
- 29.1k
13
votes
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why is the z transform transfer function 1/(z-1) called an integrator?
There are a couple reasons. One is that $(1-z^{-1})$ represents $x[n]-x[n-1]$ which is a finite difference over a very small period of time. and that is an approximation to a differentiator. The ...
- 19.8k
12
votes
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Can humans hear Hilbert transform in audio?
Can humans hear Hilbert transform in audio?
Generally no.
The human auditory system is fairly insensitive to monaural phase shifts. "Monaural" means "same phase shift for both ears&...
- 41.4k
11
votes
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Why do we integrate the modulating function in FM?
You need to integrate the modulating signal because frequency is the time derivative of phase. Therefore, the typical relationship from introductory calculus holds:
$$
\phi_i(t) = \int_{-\infty}^{t} \...
- 24.4k
11
votes
Accepted
Why do digital modulation schemes (in general) involve only two carrier signals?
Ah! They don't generally involve only two degrees of freedom. The ones you've been looking at mostly have, but that's not because they're the only ones used or taught.
Chances are you'll meet one or ...
- 29.1k
10
votes
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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…
Since you say you have matched filters, and you mention non-coherent detection, I think you're ...
- 29.1k
10
votes
Envelope behavior dIfference between QPSK, OQPSK and $\pi/4$-QPSK
Let's look at each in turn:
Standard QPSK:
With standard QPSK, each of the signal points are in quadrature (Note that the signal points in the constellation can be at any arbitrary phase really; ...
- 48.2k
9
votes
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What is a $BT$ (Bandwidth-Time) product with reference to modulation?
The $BT$ product is the bandwidth-symbol time product where $B$ is the $-3\textrm{ dB}$(half-power) bandwidth of the pulse/filter and $T$ is the symbol duration. For different applications you will ...
- 3,356
9
votes
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Numerically Controlled Oscillator (NCO) for phasor implementation?
The NCO is a cyclical counter that can go on indefinitely but is otherwise similar to what you suggest in that you are increment n to set the output rate. It basically is a look up table of all the ...
- 48.2k
8
votes
Why not use zero-signal in digital transmission?
All implementation aspects aside, the constellation you propose performs worse than QPSK in an additve white gaussian noise (AWGN) channel.
I claim this based on simulations that I have run with ...
- 4,215
8
votes
Transmit data through sound between 2 computers (very close distance)
As you have realized, the hard part of doing digital communications is carrier, symbol and frame synchronization, and channel estimation/equalization.
The bad news is that you can't get around these ...
- 14.6k
8
votes
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What is a constant envelope modulation?
You've pointed out a very important distinction between theory and practice. In theory, as suggested by your book and in Fat32's answer, modulation schemes where all information resides in the phase ...
- 87.4k
8
votes
Why can so little digital information be stored on a cassette tape?
High-capacity tape formats use helical scanning. Here I look at why that gives a higher capacity than linear recording with four tracks (one stereo track on each side) like in a compact cassette (C-...
- 13.5k
8
votes
I'm missing something when it comes to understanding FM
In addition to the perspective offered in @Ash's answer, Claude Shannon touches on FM in his paper "Communications in the Presence of Noise" (Proceedings of the IRE, January 1949). He ...
- 11.7k
7
votes
FSK and IQ modulation
What is the advantage of performing the FSK using IQ modulation?
You only need one RF oscillator operating at a single frequency, instead of having 2 (or more in the case of M-ary FSK) oscillators ...
- 121
6
votes
Accepted
Real and complex low pass equivalent of band-pass signal
It's not true that any real-valued band pass signal can be written as shown in your first equation:
$$s(t)=A(t)\cos(\omega_c t)\tag{1}$$
The most general representation of a real-valued band pass ...
- 87.4k
6
votes
Accepted
Why upsample before modulation?
The reason is aliasing. Because the modulation is digital, on the discrete signal, the sampling frequency should be high enough that the channel's frequency band does not extend beyond the Nyquist ...
- 13.5k
6
votes
Audio frequency modulation algorithm
You need to build a time varying delay, where you can modulate the delay amount over time.
The peak delay modulation is a function of your maximum desired frequency shift and the modulation ...
- 41.4k
6
votes
Accepted
Gardner Timing Recovery for Repeated Symbols
Your Gardner Loop would properly "Flywheel" in the absence of symbol transitions. So it would slowly drift off of synchronization, but would not spiral out of control as you describe. This is ideal ...
- 48.2k
6
votes
How is multiplexing achieved in spread-spectrum modulations like CSS?
disclaimer
Because of the lack of document about LoRa CSS in Internet, the analysis below may be wrong with respect to LoRa system, not to the (linear) CSS principle. Any comment or update are ...
- 6,020
6
votes
Why do SDR receivers emit I/Q samples?
The SDR (or any general digital signal processing system) takes the received RF signal, and downconverts it from the carrier frequency to the baseband.
Now, the real bandpass signal from the antenna ...
- 6,178
6
votes
Average bit error and symbol energy
The optimal decision regions are the Voronoi Regions. I dont know, if this is what you are looking after.
...
- 6,178
6
votes
Average bit error and symbol energy
As explained in Maximilian Matthé's answer, the exact computation of the symbol error probability of this constellation (ITU-T V.29 modem standard) is quite complex. However, you can quite easily ...
- 87.4k
6
votes
Accepted
What is the meaning of channel capacity?
1) Is there a connection between the modulation kind and the channel capacity?
The capacity of a channel indicates the upper limit of how many bits can be transmitted per second over the channel with ...
- 12k
6
votes
What is the meaning of channel capacity?
1) Is there a connection between the modulation kind and the channel
capacity?
Channel capacity is usually defined as the number of information (usually measured by the number of bits) can be sent ...
- 6,020
6
votes
Accepted
Difference between Line Code and Keying
I think the Wikipedia definition is limited, and anybody using the terms keying and line coding interchangably is wrong.
A line code is an encoding (or mapping) from bits to pulse amplitudes (...
- 14.6k
6
votes
Accepted
Difference between FFSK and FSK modulation schemes
Fast FSK is just another term for minimum-shift keying (MSK). In the modern literature, the term fast FSK has been almost completely replaced by MSK.
There is a very good tutorial paper on MSK by S. ...
- 87.4k
5
votes
Accepted
Why not use zero-signal in digital transmission?
As a complement to Deve's nice answer:
In regular QPSK, with symbol energy $E_s=1$, the distance between neighboring symbols is $d_{min}=\sqrt2$. For the same (average) symbol energy, the distance ...
- 14.6k
5
votes
IFFT-based OFDM system
Say you want to transmit complex symbols $s_0,s_2,\ldots,s_{N-1}$ using frequency-division multiplexing. In the "bank of modulators" approach, you would assign a carrier frequency $f_k$ to each ...
- 14.6k
5
votes
Accepted
Quadrature modulation for FM and AM
Both amplitude and frequency modulated radio signals nowadays use quadrature modulation and demodulation as a mean to transfer and receive radio signals.
This question is ill-defined – a signal ...
- 29.1k
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