47 votes
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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, ...
Marcus Müller's user avatar
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 ...
robert bristow-johnson's user avatar
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&...
Hilmar's user avatar
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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} \...
Jason R's user avatar
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11 votes
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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 ...
Marcus Müller's user avatar
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 ...
Marcus Müller's user avatar
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; ...
Dan Boschen's user avatar
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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 ...
Gilles's user avatar
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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 ...
Dan Boschen's user avatar
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9 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 ...
Matt L.'s user avatar
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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 ...
MBaz's user avatar
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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-...
Olli Niemitalo's user avatar
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 ...
TimWescott's user avatar
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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 ...
GordonFreeman's user avatar
7 votes

Why do SDR receivers emit I/Q samples?

The SDR (or any general digital signal processing system) receiver takes the received RF signal, and down-converts it from the carrier frequency to the baseband, converting a real bandpass signal to ...
Maximilian Matthé's user avatar
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 ...
Hilmar's user avatar
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6 votes
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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 ...
Dan Boschen's user avatar
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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 ...
AlexTP's user avatar
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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. ...
Maximilian Matthé's user avatar
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 ...
Matt L.'s user avatar
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6 votes
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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 ...
Jim Clay's user avatar
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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 ...
AlexTP's user avatar
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6 votes
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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 (...
MBaz's user avatar
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6 votes
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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. ...
Matt L.'s user avatar
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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 ...
MBaz's user avatar
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5 votes
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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 ...
Marcus Müller's user avatar
5 votes
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Relationship between $E_b/N_0$ and $\rm SNR$ with channel coding

The relationship between SNR and $E_b/N_0$ is independent of the code rate. Note that $E_b$ is the energy per data bit (not the coded bits), and $R_b$ is the (uncoded) data bit rate. As long as you ...
Matt L.'s user avatar
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5 votes
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FSK: non-integer vs integer rmodulation index, peculiar peaks

With integer modulation indices, each symbol is actually an integer number of full oscillations. You DFT that, and get a sharp, discrete spectrum of tones, convolved with the pulse shape. With non-...
Marcus Müller's user avatar
5 votes
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A query on Power spectral density (PSD)

Almost, but let's start at the beginning. If the random process $N(t)$ has a power spectrum then it is at least wide-sense stationary (WSS), i.e., its mean and its autocorrelation function do not ...
Matt L.'s user avatar
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5 votes
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Conversion between Eb/N0 and SNR in spread-spectrum modulation like LoRa CSS?

Let's start by fixing a symbol rate $R_s$ symbols per second. To modulate $R_s$ symbols per second without ISI, Nyquist says that we need a bandwidth at least $BW_0=1/R_s$ Hz. With spread spectrum, ...
AlexTP's user avatar
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