Questions tagged [qam]

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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, ...
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1answer
185 views

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 ...
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0answers
42 views

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 ...
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1answer
61 views

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 ...
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2answers
133 views

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 ...
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2answers
63 views

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-...
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0answers
39 views

Phase and constellation diagram

I have noticed that when, for example, \$cos(t)\$ is in-phase (I) component of the modulated signal, we can determine the phase from the constellation diagram measured counterclockwise from the ...
2
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1answer
75 views

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 ...
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3answers
633 views

QAM signal equation

I have seen that QAM signal equation is written as sum or substraction between in-phase and quadrature component. Does it really matters if we write QAM signal equation with + or - sign? It depends ...
2
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2answers
422 views

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....
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2answers
514 views

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 ...
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2answers
118 views

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 ...
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2answers
353 views

Why it was not possible to use 256-QAM in the past

What is behind the progress of speed in digital communications? For example going from analog modems to high-speed DSL/DOCSIS on the same old metalic lines... Why wasn't for example 256-QAM possible ...
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0answers
148 views

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 ...
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2answers
48 views

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 ...
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0answers
367 views

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 ...
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423 views

QAM Modulation Frequency vs Carrier Frequency

In QAM (Quadrature Amplitude Modulation) theory what is the relationship between the modulation frequency and the carrier frequency called? It is often stated in QAM tutorials that the carrier ...