# QAM constellation

Discussion in 'Electronic Basics' started by M.Nasiriyan, Nov 24, 2003.

1. ### M.NasiriyanGuest

Hi.
Please consider an uniform and a nonuniform constellation of for
example
16-QAM. As the output we allocate 00, 01, 10 and 11 to the I axe
respectively from the left and the same to the Q axe from the down.
This allocation is the same for both systems. So what is the
difference between two constellation?

Huh ??

3. ### Charles JeanGuest

Would someone please let the Doctor know that it's time for Mr.
Nasiriyan's daily Thorazine injection? Thank you.

4. ### Ross MacGuest

Someone here swallowed the bong water!

5. ### Jean-Christophe MATHAEGuest

IMHO it not a stupid question - but not one for a newsgroup named BASICS ;-)

6. ### MGGuest

For each of the 4 points on the I axis (00,01,10,11) there are 4 points on
the Q axes (00,01,10,11). This constellation is then composed of 16
different points, called symbols.
The receiver and decoder will spit out any one of the 16 symbols you can
make out of 4 bits. Two bits are encoded onto the I axis and the other two
are encoded onto the Q axes.

00_00
00_01
00_10
00_11
01_00
01_01
01_10
01_11
fill in the blanks
11_10
11_11

The underscore character is only for readability, 2 axes, 2 bit per axes,
each symbol received contains 4 bits of information.

Your question is not stupid, and is very basic.

MG

7. ### M.NasiriyanGuest

Thank you for your paying attention. But I think I couldn't explain my
question well. I know every symbol consists of 4 bits ( 2 bits as real
part and 2 for imag.)myself , but this 4 bits is similar for two
different constellations.what I don't know is that how does the
channel differ between two constellations ?