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.
576
questions
29
votes
6
answers
10k
views
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. So I figured I can store a relatively large amount of data on a cassette tape. I was thinking of a little project to ...
- 393
21
votes
4
answers
92k
views
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&...
- 313
17
votes
6
answers
7k
views
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).
...
- 289
17
votes
1
answer
3k
views
What mathematical tools exist for understanding modulated noise?
Suppose we have a signal $n$ that consists of Gaussian white noise. If we modulate this signal by multiplying it by $\sin 2\omega t$, the resulting signal still has a white power spectrum, but ...
- 3,733
12
votes
3
answers
5k
views
Transmit data through sound between 2 computers (very close distance)
I'm writing an example on transmitting data through sound betwwen 2 computers. Some requirements:
The distance is very close , i.e the 2 computers are basically adjacent to each other
Very little ...
- 269
12
votes
1
answer
6k
views
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 ...
- 125
12
votes
1
answer
720
views
What are the basic categories of operations performed on audio signals to create interesting sounds?
I don't know if this question will make sense as I'm very new to dsp.
In my limited foray into audio dsp I've come across:
Frequency Modulation
Amplitude Modulation
Additive Synthesis
Subtractive ...
- 123
12
votes
2
answers
6k
views
Why do SDR receivers emit I/Q samples?
To my understanding hardware receivers for software-defined radio applications basically take the input signal, mix it with the tuning frequency to remove the carrier frequency and then sample the ...
- 223
11
votes
3
answers
22k
views
Why are sidebands generated in AM and FM?
When the signal is modulated onto the carrier in the electromagnetic spectrum,
that signal occupies the small portion of the spectrum surrounding the carrier frequency. It also cause sidebands to be ...
- 2,145
10
votes
3
answers
75k
views
10
votes
1
answer
751
views
What are thoughts on best modulation to use for underwater acoustic communications at low frequencies?
I wanted to ping the DSP hivemind for general thoughts on what would be the best modulation type to use for low frequency underwater communications. I have chosen this project since I can learn a lot ...
- 9,499
9
votes
3
answers
3k
views
Can humans hear Hilbert transform in audio?
I stumbled upon Hilbert transform when researching single sideband modulation. Apparently when the demodulator frequency is bit off by $\Delta f$, the signal after demodulation and low-pass filtering ...
- 233
9
votes
2
answers
2k
views
Deep space communications BER and FEC?
What kind of bit error rate do they get from deep space communications (Pioneer, Voyager, et.al.), and what kind of modulation and FEC allows them to recover messages with that microscopic level of ...
- 34.7k
9
votes
2
answers
14k
views
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 ...
- 95
9
votes
2
answers
5k
views
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 ...
- 795
9
votes
2
answers
5k
views
Spectrum of FSK signal
I have implemented a simple V.23-like FSK modem in C here.
The peculiarity of the chosen modulation is such that 0's and 1's are sent as tones of two different frequencies (2100 Hz and 1300 Hz ...
- 358
9
votes
1
answer
2k
views
Frequency Modulation Synthesis Algorithm
Based on what I read, I've made an algorithm for FM sound synthesis. I'm not sure if I did it right. When creating a software synth instrument a function is used to generate an oscillator and a ...
- 191
8
votes
2
answers
6k
views
PC-to-PC data communication over Sound FSK / PSK / DSSS
For fun and work I've to implement a java based application that can Encode text or data to sound and transmit using PC's speaker and on the receiving side is a microphone with decoder software.
I ...
- 181
8
votes
1
answer
2k
views
Help with algorithm for modulating oscillator pitch using LFO
I am developing a software emulation of an analog synthesizer. I am trying to modulate the pitch of an oscillator using an LFO. For each sample fed to the computer's sound system, I am calculating ...
- 311
7
votes
6
answers
66k
views
Why Carrier signal can't have frequency less than Message signal
I know that why we use Carrier of high frequency to send message signal over a long distance, when the frequency is low , energy will be obviously low. To increase the energy of the signal we need to ...
- 2,145
7
votes
3
answers
1k
views
Why do we integrate the modulating function in FM?
I've been reading about FM and I keep coming to an expression, where the instantaneous phase
$$\Theta=2\pi f_it+\phi\text, \tag1$$ where
$$f_i=f_c+k_fm(t)\text,\tag2$$
($f_c$ being the base carrier ...
- 195
7
votes
1
answer
302
views
Why would I want to define a modulation index for each tone (DSB-FC)?
So the exercise is basically a signal $f(t)$ that is going to modulate the carrier $A\cos(\omega_ct)$ using a modulation index of $m=1$. I have to find $A$ and the power of the modulated signal:
$$
f(...
- 71
7
votes
1
answer
665
views
Simplest All Digital GMSK Modulator
How to simply implement an all digital GMSK modulator with no multipliers? The implementation approach should be applicable to GMSK modulation with $BT=0.5$ or less (where intentional ISI is ...
- 45.9k
6
votes
3
answers
16k
views
why is the z transform transfer function 1/(z-1) called an integrator?
I am reading up on delta sigma modulators and there this term $\frac{1}{z-1}$ that appears repeatedly and is referred to as an "integrator". Why is this so ?
- 179
6
votes
2
answers
994
views
What is the meaning of channel capacity?
If the transmitted information signal takes values from a modulation constellation, then is there a way to know what the channel capacity is?
Is there a connection between the modulation kind and ...
- 869
6
votes
2
answers
10k
views
Envelope behavior dIfference between QPSK, OQPSK and $\pi/4$-QPSK
I am trying to analyze whats the major difference between these three variants of 4PSK.
I know that
QPSK - signal points are at 0,90,180,270
OQPSK - The bit period of Quadrature component is ...
- 61
5
votes
2
answers
566
views
Why not use zero-signal in digital transmission?
This is something that bothers me from time to time and has always been hand-waved away with some plausible but non-rigorous explanation. For clarity, consider the QPSK case where we have the ...
5
votes
3
answers
3k
views
What exactly happens with Spread Spectrum Modulation
With regard to DSSS and CDMA(DS), what does it mean to spread a signal over a spectrum of frequencies in terms of individual frequencies? Is it about sending the same signal redundantly on multiple ...
- 153
5
votes
2
answers
270
views
Nyquist frequency isn't working
The situation is that I have a signal with linearly increasing frequency,
$$\text{sin}(2\pi\omega(t)t),$$ where $\omega(t)=a+bt$ for some $a$ and $b$, and we constantly sample at one point per second ...
- 53
5
votes
1
answer
66
views
How to Model the Dispersion Which Is Introduced by an Electro Absorption Modulator (EML)?
I need to model the dispersion which is introduced by an EML in Matlab. The parameters are:
Lambda: 1310nm
PAM4 power:
Pmax = 1.09 mW
Pmin = 0.13 mW
Bandwidth = 56Gbps
5
votes
1
answer
320
views
Angle modulation spectrum
Is angle modulation spectrum always discrete or this property only holds for periodic modulating signal?
- 53
5
votes
3
answers
2k
views
Do BPSK vs QPSK have the same performance?
I'm trying to re-learn digital communication theory again and am creating a bit error probability simulation for various modulations. So far I've added BPSK, QPSK, and 8PSK and below is a plot that ...
- 53
5
votes
1
answer
219
views
Is Oversampling a Signal Same as Discretizing the Signal?
I am confused about the new terminology 'oversampling' I have encountered very recently.
To explain it better, I am going to use numerical examples.
Now let's assume I am using a BPSK modulator and my ...
- 162
5
votes
1
answer
2k
views
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 ...
- 1,010
5
votes
1
answer
178
views
how to find frequency response of microphone
hello I want to find the frequency response of a microphone. I give the input signal to my speaker and it produces a specific SPL with specific frequency. on the other side, I read the microphone ...
- 91
5
votes
1
answer
8k
views
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 ...
- 123
5
votes
2
answers
1k
views
Hexagonal Modulator Comparison with Square Modulator
Hexagonal shaped Modulator is designed to get better BER than Square Modulator. The constellation diagram is like the figure:
It is supposed to give better BER measurement than Square as it has wider ...
- 51
5
votes
1
answer
14k
views
QPSK Modulation/Demodulation in C++
I'm trying to implement a QPSK Mod/DeMod system in C++. So far i have a bit generator that generates N bits and stores it into an array:
...
- 51
5
votes
1
answer
248
views
Effect of Passband Slope on QPSK Constellation
What is the effect of a passband slope on a QPSK (or any QAM) constellation? Specifically given a linear slope (in magnitude, not dB), and no phase distortion (linear phase or even zero-phase) how ...
- 45.9k
4
votes
1
answer
24k
views
Deriving SER & BER for 4QAM, 16QAM and 32QAM
Required to find symbol error rate vs $E_b/N_0$ for 4QAM, 16QAM & 32QAM. Thought that SER & BER are the same but did my research to find that BER is $1/\log_2(M)$ of SER. Could you please ...
- 41
4
votes
1
answer
717
views
Why do digital modulation schemes (in general) involve only two carrier signals?
In my digital communication, class we have covered the various modulation schemes, namely QAM and its derivatives (B(A/P)SK, PAM and (Q/M)PSK) as well as BFSK. These two schemes have one or at most ...
- 43
4
votes
2
answers
8k
views
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 ...
- 41
4
votes
2
answers
5k
views
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 ...
- 812
4
votes
3
answers
402
views
What causes this type of distortion in a constellation I/Q plot?
I'm transmitting QPSK through a digital pulse shaping filter (RRC, 35% excess BW, 2 samples per symbol, 64 taps) at a rate of 56Msym/sec.
Receiving it on standard lab equipment (Vector signal ...
- 723
4
votes
1
answer
2k
views
Finding out modulation index and DC offset
I have a question form my teachers, and I cannot understand why I can find out the modulation index form the figure.
The question provide a Figure like this:
And the information signal is a ...
- 405
4
votes
2
answers
589
views
Shannon capacity limit & FEC comparisons
In this figure from Fundamentals of Digital Communications by Madhow , pp 328 there is a comparison of a rate 1/3 turbo code with the shannon limit for rate 1/3 BPSK:
Trying to understand the limit ...
- 723
4
votes
3
answers
597
views
Why is the carrier suppressed by AM-DSB-SC modulation?
Lets say I have a message that is a sine wave at 1KHz. As I understand it, I can perform amplitude modulation by multiplying this signal with a carrier, lets say 10KHz, and this process is essentially ...
- 288
4
votes
2
answers
9k
views
Conversion between Eb/N0 and SNR in spread-spectrum modulation like LoRa CSS?
This question is somewhat related to the one asked here: How is multiplexing achieved in spread-spectrum modulations like CSS?
I am looking at the bit error rate (BER) performance of communication ...
- 43
4
votes
1
answer
5k
views
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 ...
- 197
4
votes
2
answers
2k
views
Is it possible to transmit and/or receive multiple types of signals at the same time?
Using an inexpensive SDR (such as the USRP or Per Vices Phi), I want to process two or more communication protocols at the same time (e.g. WiFi and GSM). Is it possible to Tx (or Rx) both at the same ...
- 239