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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Modulate Bipolar(?) signal

I want to modulate this signal if possible with an Arduino, but have no idea what circuit can help me here. Let's ignore the timing and the measurements from the image for a moment, my problem is more ...
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Difference between Line Code and Keying

The following statements are from Wikipedia page of Keying Keying or digital modulation applies to transmitting a digital signal over an analogue passband channel. When a digital signal is ...
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the relationship between bandwidth and the datarate

One Question of my note is like this. ...
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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. So I figured I can store a relatively large amount of data on a cassette tape. I was thinking of a little project to ...
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216 views

Line coding for a modulation order that is not power of 2

In case a symbol encodes a non-integer number of bits, how is done the bit-symbol pairing? For example, we have a 3-levels FSK with bit rate of 1Mbps and a sequence 01011001. What is the symbol ...
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Why is a bandpass filtered analog PM signal still PM and not AM

I know, that in theory a sinusoidally phase modulated (PM) signal with an expression like $\Re(e^{\mathrm{j}k\sin(\omega_s t)} \cdot e^{\mathrm{j}\omega_ct})$ with the signal frequency $\omega_s$, the ...
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what is OQAM (Offset QAM) and why it is required?

Currently I am studying about a modulation technique FBMC (Filter Bank Multicarrier) which is a predecessor of OFDM. The difference with OFDM is that, FBMC does not have a CP (Cyclic Prefix) which is ...
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265 views

Getting hilbert transform of IQ signal

Im new to communications so this may be a stupid question, but I am somewhat confused. I am trying to train an automatic modulation classification (AMC) algorithm on IQ data from the RadioML dataset. ...
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Can the intelligence message of an FM signal be cross-modulated to another center frequency due to non-linearities?

Can the intelligence message of an FM signal be cross-modulated to a a different frequency by non-linearities, but with the FM modulating message remaining (relatively) intact on the new frequency? ...
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Multiply signal $x[k]$ with $\cos(2\pi\nu_0k)$, then given $X(\nu)$ draw resulting function in frequency domain?

Let $$y[k]=x[k]\cdot \cos(2\pi\nu_0k) .\tag{1}$$ Then, given a signal $x[k]$ with the DTFT $X(\nu)$ according to the following figure what will the frequency domain for $Y(\nu)$ look like for a ...
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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 ...
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Use of pulse shaping in digital modulation

Sorry, I am a little bit confused here cause I thought when we say QPSK, the signal looks like the following. I thought the bits to send/receive depends on the phase shift of the carrier, or is the ...
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Cosine modulated impulse response

How do we show $y_0(n) = y_1(n)$ when $h_k[n] = h[n] \cos(\frac{2\pi}{L} k n )$
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QAM Amplitude Levels

I'm working on a project to stream video between 2fpgas by using QAM. While mapping symbols with different amplitude pulses(PAM) a question popped up in my mind. In real life how does communicating ...
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1answer
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How to encode binary sequence if the number of bits are odd to e.g. 4-PAM? (Beginner)

I'm new to signal constellation and trying to understand how M-PAM works. If there is a binary sequence that has on odd number of bits and I want to send a 4-PAM signal, there will be one bit left ...
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Synchronization Accuracy Required For Communications

One of the biggest problems in phase modulated communication is discovering when your signal has arrived. High accuracy in this area is important, as even a quarter wavelength error can cause the ...
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Why does my digital upconversion result in two tones?

I am using Xilinx's RFSoC in I/Q mode. The important point is that in the digital space I have real and complex samples. I take the incoming data and multiply it by a complex sinusoid. In my test ...
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457 views

modulate/demodulate audio file as FSK signal mixed with music signal

What I want to do: I want to encode an audio message inside a regular music file; this shall be decoded by an audio analyzer running on another machine (by listening to the audio playback from the ...
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2k views

Ratio of the power in the sidebands to the total power in conventional AM

Message signal and carrier signal are given as $m=\cos(2 \pi \cdot f_{m} \cdot t) $ $c=A_{c}\cdot \cos(2 \pi \cdot f_{c} \cdot t) $ I was asked to find modulation index $a$ so that ratio of the ...
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279 views

How to find a know signal in another signal which contains other signals along with the signal i need in python

I am working on BPSK with sound waves a carrier waves. Actually I am modulating my data with some known sync bits along with the information I need to send. So the things I will be having at ...
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1answer
783 views

How to generate IQ component for transmitting 2FSK

I am trying to generate IQ components for 2FSK modulation. I have started off from this thread FSK and IQ modulation , but I don't quite understand the IQ TX components plotted in the example there by ...
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435 views

Recover IQ samples from signal

I have a data acquisition device that provides me with an array of integers that represents a modulated signal (let's say QAM16). I would like to recover the I and Q samples from the raw time-domain ...
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47 views

Bandwidth of a modulated signal in analog domain

If i am using QPSK modulation with data rate 4 Mbps with rolloff factor $0.5$, then the bandwidth will be symbol $\rm rate\times (1 + rolloff\ factor)$. So here it will be $\rm 2\ MHz\times 1.5 = 3\ ...
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GNU Radio QPSK 4 Symbols

I'd like to generate a simple QPSK signal in GNU radio, but so far I haven't been able to get it to perform the way I'd like and I'm not sure if this has to do with some misunderstanding I have about ...
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concurrent multiple sound sources seperation for TDoA estimation

consider a room with some sound resources and several mics, these sound resources almost concurrently emit sound signals. As for one mic, it may pick up sound signals from different sound sources ...
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448 views

How to set a Carrier Wave for DBPSK Modulators in gnuradio?

for a Project I need to build an Audio Modem in GNU Radio. I decided, that it would be the best to use DBPSK Modulation, because that is fast and relatively noise resistant. But as it seems, the ...
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181 views

Up-converting a sinusoidal signal

I want to up-convert a baseband sinusoidal signal of frequency $4000 \, \rm{Hz}$ using a carrier frequency of $20\, \rm{KHz}$. I read that one can up-convert a baseband signal to a passband signal ...
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32 views

OFDM Modulation: what's the output of the FFT?

I'm trying to understand how OFDM is used in technologies like Wi-Fi. On the Wikipedia page, an idealized transmitter is presented with this schema: Data is converted from serial to parallel, mapped ...
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392 views

Adding a constant to a bandpass-signal in transmission

I do understand AM-DSB-SC and AM-DSB-TC, but can't see the point in adding a constant DC-offset of 2 in the upper part of this Simulink-model? Source
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484 views

Inter Symbol Interference (ISI) / Equalization in Digital Signal Processing

I am studying the OFDM system and before to start I have decided to study the main concepts of modulation. And I have spent yet a lot of time to understand the concept of an equalization to reduce ISI....
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A communication system

I am solving the following problem as an exercise. I have a signal $$z(t) = x(t)\cos(wt) + y(t)\cos(ut)$$ and we assume $x,y$ to be band-limited continuous time signals. In the frequency domain we ...
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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 ?
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Digitalization of a signal

Suppose I have an analog signal I want to transmit. After sampling and quantization, I can map the samples to bits. So now I have a bit stream that represents the original analog signal. My questions ...
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How to deal with modulator jitter?

I have a question regarding an implementation of a modulator. I guess some people here have an FPGA background. I would like to implement a QPSK modulator of  31 Mbit bitrate using a 125 MHz clock. I ...
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Coding an LFO in C

I want to know how I could implement a Low Frequency Oscilator on a simple synth I've coded in C. First in order to understand how to make this happen I would like just to modulate a sine wave by a ...
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1answer
68 views

Use of I/Q representation for unmodulated Rx Signal

it may be a stupid question but while learning about DSP and Modulation I was wondering, if the I/Q representation of an RF Signal is of any use, when the received signal does not contain any ...
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Max frequency of cosine in SDR

I would like to transmit a 56 MHz real cosine and receive it using SDR with max complex sample rate equals 61.44MSPS and an analog filter with BW = 56MHz (the transceiver is AD9361). Can I do it? How ...
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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 ...
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How are the constellation point coordinates determined in digital modulation

I need to understand where the concept of the distance comes from. What I mean is, how do we know what coordinates are to assign to points in the constellation. For example here for QPSK the points ...
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BFSK modulation coding on MATLAB

Like for BPSK we generate random bits and then data= round(rand(1,num_bit)); %Generate binary data bpskModulated = 2*data-1 % mapping to -1 and +1 Can we do same for BFSK like ...
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modulation depth

When a value for the power dissipated by an AM signal is given, and the depth of modulation is also given. Then you are told to find the modulation depth required to increase the power to a higher ...
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72 views

Sharp EL-5500III (PC-1403) cassette tape encoding

I have an old audio cassette tape of digital data I converted to .wav and am hacking to recover the original data. I demodulated the 4K/2K FSK modulation with minimodem. Then I get stuck with ...
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Is there use of $\pi/8$-DQPSK as shown in MATLAB's documentation?

I was reading MATLAB's documentation on dpskmod. They gave an example of an $\pi/8$-DQPSK. I felt that this is strange as I have seen $\pi/4$-DQSPK and $\pi/8$-...
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Why does the frequency in fft plot of the baseband modulated signal isn't changing at the receiver

I have designed a transceiver system for cellular frequencies(800MHz). On the receiver side, I have converted the band signal to baseband signal through digital mixing. I have added the Inphase and Q ...
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1answer
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Numerically Controlled Oscillator (NCO) for phasor implementation?

If I want to simulate a digital oscillator (or phasor) to modulate an arbitrarily length signal: $$y(t) = \cos(2\pi f_ct)\quad\text{where}\quad t = \frac{n}{f_s}\quad\text{for sample}\quad n$$ What ...
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Pre-envelope of an FM signal $s(t) = A\cos[\omega_ct + B\sin(\omega_xt)]$ [duplicate]

I want to ask a question about pre-envelope of an FM wave: $$s(t) = A\cos[\omega_ct + B\sin(\omega_xt)]$$ Can someone explain briefly how we calculate the pre-envelope of this signal?
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What is difference between Phase shift keying (PSK) and Quadrature Amplitude Modulation (QAM) mathematical equation

I went through a literature and found the following expression for PSK signal. On this basis, what will be the equation for **QAM signal **. Also from where i would be able to read about this equation ...
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Non coherent detection BFSK demodulation?

I am simulating BER performance of BFSK under AWGN and Rayleigh fading, BFSK has two symbols one entirely on the real plane while other on the complex plane for representing let's say zero and one, ...
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Next steps for analyzing this PWM algorithm and choosing a low pass filtering technique?

The Broadcom BCM2711 GPIO controller used by the Raspberry Pi has a hardware PWM implementation option using an algorithm that provides an average value defined by a rational fraction $N/M$ defined as ...
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How to find the noise power in my simulation

I am currently working a tricky communication chain that I want to simulate into Matlab. The chain is like a classic BPSK modulator/demodulator chain, but where the BPSK modulated signal has been ...

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