# 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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### Demodulation + LPF gives derivative of modulated signal

I'm new in this community and I hope it is the right place to post my question. Unfortunately, signal processing and electronics in general are not my fields, so I'm sorry if the question is trivial. ...
1 vote
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### Does phase shift introduce high frequencies?

In PSK phase modulation scheme, the signal phase is shifted, hence it looks something like this: I cannot understand why this doesn't introduce a set of unwanted high-frequencies, as the steep ...
1 vote
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### Why does NB-IoT use standard QPSK in multi-tone transmission, when pi/4 QPSK is implemented for single-tone?

I've been studying the modulation schemes used in NB-IoT communication, with a particular focus on energy efficiency. I've noticed that QPSK (Quadrature Phase Shift Keying) is used in multi-tone ...
13 views

### Clarification on video about frequency deviation in phase modulation bandwidth

I am watching this video and at 7:12 he calculates the frequency deviation $\Delta f = f_{c}f_{m}A_{m}$ where the $c$ underscript is for "carrier" and the $m$ underscript is for "...
1 vote
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### modulation transfer function and ground resolved distance

I am trying to understand something in remote sensing but lack a background in science and technology so it is difficult. Hopefully this is a reasonable question to ask. In sensing there are different ...
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### Why for bandpass signals complex envelope and pre-envelope signal representations are used in digital communications/analog communications (FM)?

When we need to analyse band pass signals we use complex envelope and preenvelope representations, wherein a signal is given an equivalent low pass representation. My issue is why it is done, though I ...
73 views

### Meaning of roll-off factor 0.5 and bandwidth

We currently have a radio that is transmitting at the following RF params: Modulation: OQPSK Data rate: 500Kbps Uplink coding: BCH I am interested in understanding what is the associated uplink ...
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### I don't understand which signal I should use as a carrier in my excersise

$\DeclareMathOperator{\sinc}{sinc}$ Given 3 signals $x_1(t) = \sinc(t) , x_2(t) = 10\cos(2\pi f_2t)$ and $x_3(t) = 5\cos(2\pi f_1t)$, where $f_2 = 100\text{ kHz}$ and $f_1 = 1\text{ kHz}$. I must ...
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### DS-CDMA Spreading Code Length Selection

I'm trying to wrap my head around the process of selecting DS-CDMA spreading codes, and I'm having trouble understanding the tradeoffs of longer codes. For all scenarios described below, I'm using a ...
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1 vote
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### Omission of 8-PSK and 32-QAM in LTE/5GNR

In 4G LTE/5G NR, the modulation schemes 8-PSK (which is an intermediate scheme between QPSK and 16 QAM) ,32-QAM (which is in between 16 and 64 QAM) are omitted. If the channel is bad , or the distance ...
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### How to get trellis-coded modulation trellis after set partitioning?

Given a 4-PAM modulation and after doing the set partitioning for it, I'm unsure how to arrive at the trellis with the edge labels and the trellis structure as shown below,
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### How to achieve 3 Gbps with 210 MHz bandwidth in 5G?

I read an article from T-Mobile link where they claimed a 3Gbps speedtest with the aggregation of 3 three bands in 5G. How it is possible to make 3 Gbps with a 210 MHz bandwidth and using 256QAM in 5G?...
28 views

### Selecting convolutional code for a M-QAM transmitter

I am tasked in an assignement to select an appropriate rate 1/2 convolution code for a QAM modulated transmitter with the following setup, However, from my understanding of codes and modulation they ...
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### Matlab Filter-Span-In-Symbols property for RRC: source bits lost

I am using the matlab online simulator and taking the course "Wireless communications Onramp" where I need to use a Raised Cosine Transmit Filter to filter the data both in the transmitter ...
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 ...
278 views

### QAM modulation problem with python

I have a IQ signal with a bandwidth of $200\,\text{MHz}$. I do I*cos(2*pi*1000e6*t)-Q*sin(2*pi*1000e6*t), but my signal doesn't shift to carrier frequency ...
1 vote
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### How are discontinuities in quadrature modulated signal QAM physically produced?

In quadrature modulated signals, for instance: I am unclear how the "discontinuities" in the waveform at the junction of each data point can be physically produced? Taking a speaker as an ...
59 views

### Effect of Passband Slope on a BPSK Constellation

What is the effect of a passband slope on a BPSK constellation? (This is a companion question to the related "DSP Puzzle" for QPSK) Specifically given a linear slope (in magnitude, not dB), ...
263 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 ...
68 views

### BER result in MATLAB

I build a pam-2 modulation, then I make a pulse shaping with half sine (matched filter). Then I send it through the AWGN channel. At the end I do down sampling and demodulation. But i have problem ...
1 vote