Share Your Experience: Take the 2024 Developer Survey

# Tag Info

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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, ...
• 31.1k
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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 ...
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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&...
• 45.3k

### 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; ...
• 51.9k
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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} \...
• 24.6k
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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 ...
• 31.1k
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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 ...
• 31.1k
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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 ...
• 3,406
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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 ...
• 51.9k

### 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 ...
• 15.3k
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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 ...
• 90.3k

### 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

### 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 ...
• 12.8k

### 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 ...

### 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 ...
• 6,218
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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 ...
• 51.9k

### 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 ...
• 6,595

### 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. ...
• 6,218

### 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 ...
• 90.3k
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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 ...
• 12.1k

### 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 ...
• 6,595
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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 (...
• 15.3k
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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. ...
• 90.3k

### 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 ...
• 15.3k
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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 ...
• 31.1k
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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 ...
• 90.3k
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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-...
• 31.1k
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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 ...
• 90.3k
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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, ...
• 6,595