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.

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Spectrum of a baseband digital signal

I'm building a Continuous-Phase BFSK Transmitter using Python and PlutoSDR. Something that I don't understand is the spectrum of the up-sampled baseband signal - the digital 0's and 1's over-sampled ...
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How do audio readers interpolate?

$124$ Hz sampled at $256$ Hz has "beats", but $128$ doesn't - a phenomenon of this question: Whether these are "legitimate" beats is up to interpretation, but suppose the goal is ...
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Why is 16 APSK arrangement 4 + 12?

Why does constellation arrangement affect the BER ? For example 4 + 12 vs 6 + 10 ? Is it because the correlation coefficient ?
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Power of signal in specific frequency in FM and AM modulation

My professor gave us the following problem: Given a sinusoidal signal with $f_m = 1KHz$ which is put into an AM and FM modulation find the modulation index of FM and AM if you know that (amongst ...
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Real parameters design and computation for a filter, modulator

I design in Gaussian filter for a modulator in MATLAB, which should be later implemented in FPGA. I have an implemented design of the filter and the modulator as well and now I have to determine some ...
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Difference between MSK and CPSK

I'm trying to understand the differences between the MSK and CPSK transmission, but I am not understanding some things about it. I understood that they are two signals without discontinuity, but what ...
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S/P conversion in IQ modulator

"serial to parallel" separats/switchs a signal into the real and imaginary. Even samples are entering the real branch I (imaginary is 0) Odd samples are entering the imaginary branch Q (...
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Seamless Filter Transition for Sawtooth Waveform?

I have an old digital hardware device that tracks a sawtooth waveform's frequency with a high pass filter (to remove aliases) seamlessly - even jumps of multiple octaves retain the converged waveform ...
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Phase of PM signal

Given two signals: s1 is a baseband frequency modulated signal (output of a frequency modulator, FM) and s2 is a baseband phase ...
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Writing an OFDM modem - subcarriers are interferring

I am trying to write an OFDM modem. I've already written a QAM modem, which I'm using as a basis for this project. The way I'm doing this currently is by spinning up several QAM modulators, each with ...
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Message signal and the Envelope of AM wave

Amplitude modulated signal is represented by $$ x(t) = (E_c + E_m \cdot \cos(2\pi f_m t)) \cdot \cos(2\pi f_c t). $$ At t=0, we have max. amplitude i.e, Ec + Em. Since the envelope is periodic, I ...
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Do PSK/QAM modulators (e.g. 4G/5G) fundamentally use more energy per packet than CSS modulators (e.g. LoRa)?

Not sure if this is the right place or even the right question to ask, but googling did not get me much further, so here goes: I'm trying to assess whether the power consumed by an IoT device, based ...
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Understanding FSK and FHSS combination

I am having trouble to understand how to combine Frequency Shift Keying (FSK) with Frequency Hopping Spread Spectrum (FHSS). As far as I understand, A IQ FSK-modulated signal $s(t)$ can be written as $...
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How can an UWB signal (pulse) radiate from an antenna?

This picture compares an uwb- and narrowband-signal: https://cdn.sewio.net/wp-content/uploads/2017/02/UWB-e1486395802254.jpg Like I understand UWB, the signal("pulse") is directly put into ...
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What is the difference between sending pulses and modulating waves?

If you look for amplitude, frequency, phase modulation, you typically get some picture saying you have a wave and you modulate the corresponding parameter (amplitude, frequency, phase). On the other ...
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Phase of AM Signal After Mixer

Let's assume we have a carrier at $f_{c}$, and a message at $f_{m}$ ($f_{c} \gg f_{m}$). Amplitude modulation is used to modulate the message on the carrier. Let's call the modulated carrier $\text{rf}...
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I'm missing something when it comes to understanding FM

I understand why FM is preferred for music: noise is mostly amplitude modulated, FM yields much higher fidelity. I also understand why commercial FM signals have a much larger bandwidth than ...
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Is it possible to obtain a complex lowpass signal directly from its equivalent bandpass signal?

Given the complex lowpass signal $x_l(t)$, its real bandpass equivalent signal with center frequency $f_c$ is \begin{align} x_b(t) &= \text{Re}\{x_l(t) \cdot e^{j2\pi f_c t}\} \\ &= \frac{1}{2}...
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How does analog television chroma signal work with QAM and vestigial sideband?

In NTSC analog television (presumably PAL is similar) the chroma (color) signal is included through a subcarrier which is QAM modulated. This particular QAM modulation is a bit unusual in that besides ...
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Why is Line coding called "Line coding"?

Guys do you now why line coding also called digital base band modulation named "line coding" where does it come? and how is the name related to modulation
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What is the result of taking the real part and imaginary part of a complex signal in the frequency domain?

Suppose that $g(t)$ is a lowpass complex signal with magnitude (solid line) and phase (dashed line) To modulate $g(t)$ into a bandpass equivalent signal $f(t)$ with center frequency $f_c$, we compute ...
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GNURadio GFSK demod missing data

we are trying to develop a flowgraph for cubesat operation. Our flowgraph for includes both downlink and uplink parts in one flowgraph. It uses SoapySDR as a driver of an SDR. Most of the used blocks ...
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Using SSB modulation to frequnecy shift an arbitary signal downwards

I've managed to use SSB digitally to create frequency envelopes such that I can increase frequencies at any arbitrary rate given by my envelop. But I am unable to manage a downward frequency shift. ...
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Is digital (discrete) SSB plausible?

Do any examples of digital SSB modulation exist? If not, is it implausible for some reason? The closest thing I can find is something like 8VSB which comes very close to being single sideband. I read ...
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On-Off keying for wireless communication channel estimation

Let us assume I have $k$ (a fixed number) sensors in a wireless sensor network with unknown channel statistics $\{h_1,h_2 \ldots, h_k\}$. In my system model, each of these $k$ sensors has an ...
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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 ...
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How is IQ-modulation done on the digital side rather than the analog side?

The original way of doing In-phase Quadrature (IQ) modulation is by modulating and mixing on the analog side. I have read that as the digital processing have gotten better, the modulation and mixing ...
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Exact formula for 8-PSK BER

Is there an exact formula for the probability of bit error (or bit error rate, BER) for 8-PSK (in the literature, course slides, etc.)? I am not referring to SEP (Symbol Error Probability) but BER. ...
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Why does the Superheterodyne AM Receiver use an envelope detector?

I'm currently learning about the Superheterodyne AM Receiver and I don't understand why does it use an envelope detector (as suggested here) rather than taking the signal back to its baseband ...
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Why does my output signal look like this?

This is a coherent demodulation of a BPSK signal. I'm using this link as a reference However my demodulated output comes out with too many redundant values compared to the transmitter. This only ...
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Send complex signal and receive the same complex signal, GNU radio

I’m working on a project where I want to send complex symbols like 4-QAM, 8-QAM or 16-QAM for example and demodulate those symbols, the idea is to use the signals as points (like in the constellation ...
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In wireless communications, is it true to say: The more the range, the more the delay spread?

The general idea which can be drawn by reviewing wireless channel models says that the longer the range/distance, the more the delay spread, even in LOS microwave links. But I really wonder why it is ...
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802.11a OFDM Long Preamble Cyclic Prefix

im currently looking at an implementation of the preamble for OFDM in the 802.11a standard, as shown in the pic below What I dont understand is the cyclic prefix (labelled GI2). Based on this picture ...
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What is the difference between a guard band and a cyclic prefix in OFDM?

im trying to understand the difference between a guard band, and the cyclic prefix, or at least the relationship between the two. Prior to now, I was under the interpretation that the cyclic prefix ...
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FM and PM waves

I have to find the FM and PM waves corresponding to this sawtooth signal: I have found out the PM wave as: I am getting the FM wave as this : I have plotted this using Python. Can anyone please ...
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How to implement GMSK model by Thierry Turletti

I'm kind of new to signal processing and trying to implement a GMSK modulator using GMSK in a nutshell by Thierry Turletti to modulate a bunch of binary data and send them over RF antennas. I'm very ...
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Can a cosine modulated complex valued baseband signal be transmitted over physical channels?

I am reading Digital Communication by Lee and Messerschmitt. In Chapter 6 on modulation, the authors say: "Modulating a complex-valued baseband signal with a cosine wave yields complex-valued ...
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What is Homodyne BPSK? [duplicate]

Could someone explain what Homodyne BPSK is? What is a difference between BPSK and Homodyne BPSK? I have read about this type of modulation in researches in optic communication. I surprised how phase ...
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Implementing triangular modulation in Matlab

I am trying to implement a triangular modulation in Matlab, however I am having issues implementing the resulting frequency ramps. I have the following input signal (in reality, this signal is the ...
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Time warping / frequency modulation natural examples?

"Time warping" defined as $$ x(t) \rightarrow x(t - \tau(t)) $$ where $|\tau'(t)| < 1$ ($=1$ is time stopping, $=0$ is time shift, $>1$ is time reversal). Where can this occur? A ...
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Implementing OQPSK in Gnu Radio Companion

I am currently trying to realize this block diagram in Gnu Radio Companion: Before using a file source block with the binary I want to send, I plan on just using a vector with an alternating 1,0 ...
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Meaning of complex envelope in simple terms?

I tried to find a simple explanation of what a complex envelope of a signal is, with no luck. I'm looking for an explanation with simple terms, and possibly that is easy to visualize or imagine, so ...
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MSK receiver for ultra-low SNR

I am designing a low-rate DSSS communication system (~1ms chip period, Spreading Factor 128/256 bits long) for using at ultra low SNR scenarios (~0dB SNR). Due to the problems related to clock ...
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Limiting Bandwidth for QAM and OFDM signal in MATLAB Simulink

currently im creating an application capable of generating QAM and OFDM signal to be transmitted using SDR. The whole application is implemented in MATLAB Simulink using only code generateable ...
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weird Demodulated BPSK waveform

I am using an acoustic wave of 3khz(audio BPSK) as my carrier frequency with a sampling rate of 10k samples per bit. at the receiver end, I play the audio from my phone to my computer, record it ...
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Difference between FFSK and FSK modulation schemes

Can somebody explain to me what is the difference between FFSK (Fast Frequency Shift Keying) and FSK (Frequency Shift Keying) modulation schemes?
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How is it that a dial-up modem can achieve 33.6Kbit/s with only 3100Hz of bandwidth?

My understanding is that plain old telephone service passes frequencies between 300Hz and 3400Hz. How is it that a V.34 modem in the late 90s would be able to achieve data rates of 33,600bits/s with ...
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BPSK(10) and chip rate

I am doing some research have come across signals listed as having the in-phase channels modulated with BPSK(10), etc. I understand the concept of BPSK - Binary Phase Shift Keying, and know the 10 is ...
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Filtering a sum of cosines

The block diagram below represents a linear modulation system operating at the frequency of $1000 Hz$, $f_C = 1000 Hz$, transmitting the message $m(t) = 2\cos(400πt)$ At point B, i got the signal: $$...
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In practice, why is there any overlap in frequency-division multiplexing?

Okay, so I am aware of the math behind perfect reconstruction in filterbank and wavelet theory when there is half-band symmetry. But I don't understand, when we have the computational power to do ...
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