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.

Filter by
Sorted by
Tagged with
0
votes
1answer
21 views

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 ...
0
votes
3answers
31 views

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 ...
1
vote
1answer
25 views

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 ...
-1
votes
0answers
16 views

How do I prove Energy and Power Signals

How do I prove that if energy of a signal is non-zero and finite and the power of the signal is zero. Also draw conclusions for signals where power is non zero and finite.
0
votes
1answer
29 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 ...
1
vote
1answer
47 views

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 ...
0
votes
1answer
31 views

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 ...
1
vote
1answer
35 views

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 ...
1
vote
1answer
64 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 ...
0
votes
1answer
34 views

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 ...
1
vote
1answer
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\ ...
4
votes
3answers
119 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 ...
0
votes
2answers
31 views

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 ...
0
votes
2answers
64 views

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 ...
0
votes
0answers
23 views

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 ...
0
votes
1answer
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 ...
0
votes
0answers
47 views

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 ...
0
votes
0answers
22 views

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?
0
votes
0answers
38 views

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 ...
-1
votes
1answer
37 views

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 ...
0
votes
0answers
38 views

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, ...
0
votes
1answer
38 views

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 ...
2
votes
0answers
88 views

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 ...
0
votes
1answer
39 views

Channel encoding after digital modulation

Generally, when using channel encoding followed by interleaving, that process should be performed before the modulator and the system structure should be like that : For me, I only use the ...
0
votes
1answer
29 views

How to demodulate PM modulation

I'm using a sin wave $s_{sc}(t) = d(t)\cos(\omega_{sc}t + \varphi_{sc})$ to modulate a carrier using phase modulation. I'm working on Matlab so I use the pmmod function to do so. It is not too ...
0
votes
1answer
44 views

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 $\pi/8$-...
1
vote
3answers
72 views

Nyquist Rate of cosine modulated function

Here's my understanding: $$y(t) = x(t)~ \cos(\Omega_0 t)$$ I take the Fourier transform of y(t) and I get this result: $$Y(\Omega) = \frac{1}{2}X(\Omega - \Omega_0) + \frac{1}{2}X(\Omega + \...
0
votes
0answers
17 views

Representing the signal $ u(t)=A_c \cos (2 \pi f_c t + \beta \cos 2 \pi f_m t) $ in terms of Bessel function

I want to represent the signal $ u(t)=A_c \cos (2 \pi f_c t + \beta \cos 2 \pi f_m t) $ in terms of Bessel function. I have done the exercise. I want someone to check whether what I have done is ...
1
vote
0answers
8 views

Model of modulator and demodulator in Simulink. Why is MER so lowest?

I created a simple model in Simulink of a quadrature modulator, amplifier and quadrature demodulator. On the oscilloscope(scope in Simulink) and spectrum analyzer the displayed results look normal (at ...
1
vote
1answer
39 views

Conditions for analytical signal reconstruction with the Hilbert Transform (HT)

I'm new to the Hilbert Transform, I was reading the paper: "SISAR Imaging - Radio Holography Signal Reconstruction Based on Receiver-Transmitter Motion", and the next sentence was written in the paper:...
0
votes
1answer
29 views

CDMA scheme that preserves constant envelope (NRZ/ASK shape)

(This is a followup question to Is this a "valid" CDMA modulation?) Is it possible to find a CDMA scheme in which the receiver can only have a simple slicer? In other words, for the ...
0
votes
1answer
39 views

Is this a “valid” CDMA modulation?

I am banging my head against (specific aspects of) CDMA for a few days. At the basic level I am confused about the interrelation between implementations that are modeled as mixing and fully digital ...
1
vote
2answers
84 views

MATLAB: Issue with passing data through AWGN Channel [closed]

I am trying to send QAM data through AWGN channel and I have 256 samples/symbol, I have the following code: ...
0
votes
1answer
34 views

Phase Noise in Constellation Plot

I have the following phase noise plot (-100dBc/Hz @ 1MHz offset and -130dBc/Hz noise floor): The integrated phase jitter for this phase noise is around $4.6^\circ$. According to my understanding the ...
-1
votes
2answers
55 views

What is symbol in signal processing?

I am new to signal processing and have been trying to understand the terminology. I came across this statement: "Assuming the signal modulation $\mathfrak{M}$ has an alphabet A of M symbols and the ...
0
votes
1answer
22 views

Please clarify the mandatory condition on Vestigial Sideband Modulation filter?

In VSB filter we have the Transfer function condition as $H(F-F_c)+H(F+F_c)=1$ So can we accept that for the range of $F$ in $(F-df,F_c)$ we have $H(F)$ and for $(F_c,F+dF)$ we have $A-H(-F)$ where $...
0
votes
1answer
51 views

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 ...
0
votes
0answers
21 views

How do you determine the power required for a phase shift keying modulation scheme?

This wiki article has a diagram : which shows how the message "11000110" is conveyed as a waveform. I'm trying to understand how the power to transmit this message can be determined. Do I need ...
0
votes
1answer
40 views

Please, help me interpret my Simulink simulation of AM. Why does carrier not appear in the spectogram?

Carrier is 2 * pi * 25, modulating signal is 2 * pi, all the amplitudes are 1s and zero phase. I realized that I could add a sine wave right at the end. I get a carrier in frequency domain, but my ...
0
votes
1answer
59 views

I/Q Signal Power Calculation

I am trying to understand the basics of IQ modulation. The amplitude of a demodulated IQ signal is given as $\sqrt{I^2 + Q^2}$ which is easy to understand from the phasor diagram. Yet, I don't ...
0
votes
1answer
40 views

Serial to Parallel Converter

in many texts about modulators I have seen there is a component called "Serial to Parallel Converter". For instance, let's consider this scheme and let's focus on the second block (reference): The ...
0
votes
1answer
45 views

Confusion about collection of bits and symbols

I'm taking an intro communications module and I'm quite confused on what the term "symbol" really means? Consider this setup: My understanding is as folllows After the information source, we have ...
0
votes
0answers
35 views

Is this PSK or FSK

I am analysing a captured 433.92MHz signal sampled at 2MHz: If we zoom in: I am thinking this is PSK? Am I wrong? Thanks
0
votes
0answers
19 views

Can you help me to understand Multi-tone FSK, and how I can implement it?

Any paper, book, Matlab file... that you would recommend. Thanks.
1
vote
1answer
32 views

FM: Do rational ratios of carrier to modulator signals really produce harmonic spectra?

I've read that in FM, all rational ratios of the carrier frequency to the modulator frequency produce harmonic spectrum in the FM signal. Link to what I read. I don't understand why this is. If for ...
1
vote
1answer
219 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. ...
1
vote
1answer
27 views

Modulation classification via demodulation confidence?

I'm not sure if this is the right place to post this question, but will try anyway :-) I recently started reading up on the field of automated modulation classification (AMC) where an algorithm ...
0
votes
1answer
64 views

Phase response distortion due to IQ demodulation

I have a bandpass signal, I do IQ demodulation meaning: first step: $IQ(t) = x(t)*exp(-2\pi f_ct)$ second step: low pass using $filtfilt$ function in MATLAB. (in order to avoid phase ...
0
votes
1answer
29 views

inter symbol interference vs digital modulation

I am a little confused after my lecture today. My professor started off with explaining what inter symbol interference (ISI) is and he ended the lecture talking about the different types of digital ...
0
votes
0answers
24 views

What is the range for a demodulated AM signal?

Lets say I perform amplitude modulation (modulation index = 1) of a signal that has a range of [0, 1]. If I demodulate by taking the absolute value of this signal and then low-pass filter it, what ...

1
2 3 4 5
9