Questions tagged [qam]
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25 questions
2 votes
2 answers
343 views
How Many Levels / Trying To Figure out Bit Rate
I'm trying to figure out the following constellation, specifically the amplitude. I am trying to figure out the different levels (M) This particular QAM has 32 states (I get this), but I want to make ...
- 123
0 votes
3 answers
180 views
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 @...
- 325
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 ...
- 325
0 votes
1 answer
68 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). ...
0 votes
0 answers
302 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 ...
- 47
0 votes
1 answer
1k 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 ...
- 186
0 votes
1 answer
116 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 ...
- 186
0 votes
1 answer
254 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 ...
2 votes
2 answers
560 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 ...
- 125
1 vote
3 answers
578 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, ...
- 411
3 votes
1 answer
2k 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 ...
- 635
1 vote
0 answers
118 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 ...
1 vote
1 answer
330 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 ...
- 13
1 vote
2 answers
946 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 ...
- 421
1 vote
2 answers
177 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-...
- 312