Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [qam]

22 questions
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Gray code usage in modulation constellations

When mapping symbols of various modulation constellations, Gray code is used such that - each adjacent symbol only differs by one bit. Why do we want small physical changes in the signal to correspond to small changes in the symbol ? Why not use…
shaiko
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How do phase errors appear in the NTSC color subcarrier?

So, NTSC uses a YIQ color space, with the I and Q channels encoded in a color subcarrier using QAM with the carrier suppressed. NTSC had a reputation for poor color reproduction—“Never Twice the Same Color”—and when I look up articles that explain…
Dietrich Epp
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Quadrature modulation Digital to Analog

I want to use an FPGA to generate quadrature modulated signals for use with an RF transceiver (something like MAX2828 ). I am confused specifically about how the digital to analog modulation should be done. Please correct me if this is not…
ronald_s56
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QAM and constellation diagram

Based on this QAM 32 constellation diagram, how it is possible to have the sam values on I and Q axes for different combinations of bits, e.g. 000 and 011 or 000 and 101, as well as other two bits, e.g. 11 and 10. I thought that the they always need…
Quirik
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QAM modulation and link to AM, ASK, PAM

I am a bit confused about QAM modulation. In wikipedia, I found this: It conveys two analog message signals, or two digital bit streams, by changing (modulating) the amplitudes of two carrier waves, using the amplitude-shift keying (ASK) digital…
NickG
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Why does the overshoot exist when transmitter turns on?

I am implementing power amp. with 16-QAM. Because of issue on power consumption, I am using time division duplex (TDD). By TDD, the power amp. turns off if the carrier wave is not needed and vice versa. As represented in the figure, PLL makes 4…
Donghyun Youn
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QPSK/QAM, digital quadrature modulation: square wave as local oscillator possible?

Goal is to build a lab exercise for students to illustrate digital IQ-modulation (QPSK, M-QAM). The bit stream for I and Q are generated by e.g. an Arduino. Is it possible to use a square wave as local oscillator (original and 90-phase shifted) or…
kgmuzu
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How are the neat sinc function shaped carriers produced in OFDM?

I am learning about OFDM and QAM. Every explanation I have read illustrates how the separate carriers are sinc functions that are arranged to overlap in a nice orthogonal way so as to cancel out interference from neighbouring carriers. The part I…
John Spence
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What is the price of increasing the QAM number?

In a QAM modulation scheme, you have a certain number of possible states which have different amplitudes/phases (like 4-QAM, 16-QAM). If you increase the number, for example switch from 16-QAM to 64-QAM, you will get a higher bit rate. But what is…
Alex L
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what relationships exists between the BER vs SNR graphs of QPSK and QAM modulation schemes on data throughput. which scheme does better?

Using QAM and QPSK modulation schemes, RF field measurements like received signal power and pathloss were obtained from where the SNR values were estimated. Their BER values were also calculated and Matlab was used to plot the BER vs SNR graphs for…
ceo
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How is phase recovered from wireless signals?

I've wondered for a long time how phase information is captured for wireless signals. It's used in applications like QAM for decoding symbols and radar beam forming to to locate targets, but I've never been clear on how we can get phase information…
Moppy
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Showing QAM constellation diagramm on signal analyzer

I've been playing with some lab equipment recently in order to learn more about digital modulation techniques. I've connected R&S signal generator SMIQ 03B with the R&S spectrum analyzer FSIQ 3 and observed various modulated signals. I've managed to…
Roker Pivic
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Do we take significance of bit into account while calculating bit error rate?

The question is broadly about bit error rate, but to be concrete, I am asking it in context of 16-QAM. Consider we have a rectangular 16-QAM modulation and also assume that we have grey coding. As I understand, grey coding is helpful because even if…
Learner
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How to make QAM (quadrature amplitude modulation) of a square or sinc wave signal？

I found this discussion of QAM in a communications text book and internet. "...load it into Matlab using imread(), which will give you an array of RxCx3 integers for an RGB colour image. Serialise however you want (e.g. using reshape() to get a…
py py
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How to determine Phase Angle of 16-QAM

I am trying to figure out how the angles for the following input are obtained. For example, why is 0100 -105 degrees and not 45 degrees? Is there a specific method or do we estimate what the angle value is? Some additional info that might help: I…
miu.spiro
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