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Questions tagged [qam]

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3 answers
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Could QAM using a grid-like distribution be a quantization limitation?

This is a follow up from this previous question discussing why QAM encoding is spaced in a grid like pattern like this one: versus another with more efficient packing: After looking at @Attie and @...
Joshua Walker's user avatar
22 votes
3 answers
2k views

Why does QAM use a grid-like distribution versus a more efficient spacing?

"Stand-Up Maths" recently did a video about QAM/data encoding. He presented a diagram of the encoding spacing for QAM: I'm from a software engineering background and I couldn't help but ...
Joshua Walker's user avatar
0 votes
1 answer
42 views

Bit sharing in IQ channel

In 16 QAM, each channel \$I\$ and \$Q\$ carries bits of the information it wants to encode. For example: if the symbol is (0011) then \$I\$ and \$Q\$ channel carries two bits (00 and 11 respectively). ...
Ananth Tenappan's user avatar
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0 answers
157 views

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 ...
miu.spiro's user avatar
0 votes
1 answer
674 views

Costas Loop QPSK/4QAM

I can use a Costas Loop, modified for QPSK/4QAM and recover the frequency and phase successfully when using a pattern of all 1s or all 0s or a pattern that is repetitive for each I and Q data rail (in ...
user3425949's user avatar
0 votes
1 answer
81 views

Mixer design : IF is +/- DC volts, local oscillator is cosine 9.6 kHz

I am working on a mixer which will be used for 4QAM, QPSK. The local oscillator is 9.6 kHz and the IF would be + or - 1 volt DC in order to have the RF port output either cosine or -cosine. Which ...
user3425949's user avatar
0 votes
1 answer
190 views

What are the M and N values when modulation formats (QPSK,8QAM) are polarization multiplexed?

I always get confused in the terminology of modulation level (M) and number of bits per symbol (N). Please correct me if I am wrong. Because with these values, my question extends to polarization ...
knowledge_seeker's user avatar
2 votes
2 answers
340 views

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 ...
Dietrich Epp's user avatar
1 vote
3 answers
361 views

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, ...
NickG's user avatar
  • 391
3 votes
1 answer
1k 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 ...
shaiko's user avatar
  • 489
1 vote
0 answers
97 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 ...
Donghyun Youn's user avatar
1 vote
1 answer
276 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 ...
kgmuzu's user avatar
  • 13
1 vote
2 answers
829 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 ...
John Spence's user avatar
1 vote
2 answers
135 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-...
Alex L's user avatar
  • 302
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0 answers
58 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 ...
Quirik's user avatar
  • 287
2 votes
1 answer
108 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 ...
ronald_s56's user avatar
0 votes
3 answers
774 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 ...
Quirik's user avatar
  • 287
2 votes
2 answers
991 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....
Quirik's user avatar
  • 287
1 vote
1 answer
858 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 ...
ceo's user avatar
  • 27
1 vote
2 answers
141 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 ...
Moppy's user avatar
  • 111
1 vote
3 answers
468 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 ...
Marki555's user avatar
  • 473
1 vote
0 answers
212 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 ...
Roker Pivic's user avatar
1 vote
2 answers
67 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 ...
Learner's user avatar
  • 83
1 vote
0 answers
567 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 ...
py py's user avatar
  • 11
0 votes
0 answers
622 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 ...
FiddyOhm's user avatar
  • 2,694