Quadrature Amplitude Modulation

[solomon_13000]

As far as I know when you combine phase modulation with amplitude modulation a total of 16 different signals can be created and this is know an Quadrature Amplitude Modulation.

I need information with references on four different applications of Quadrature Amplitude Modulation (eg modern dialup modems).

Your help is kindly appreciated.

[M/Q]

Interesting stuff to be sure. Awhile ago I was very fascinated by this subject as I wanted to learn how they could put digital data on an analog signal. I also am concerned that this is a school project and we are here to help to be sure, but you need to learn this on your own.

I know of four areas where QAM is used, but I must qualify this with the comment that I am not quite sure if you are totally dealing with digital QAM or analog QAM. But I will mention these and you can research them further. As you mentioned any dialup or fax modem, ADSL, downstream cable data transfer, and digital TV. I also know that stereo AM uses QAM, but I suspect it is analog QAM.

[solomon_13000]

A common application is in PAL and NTSC color television transmission. Color is encoded into two analog signals (called I and Q), which modulate quadrature color carriers.

Modems also use this approach, to increase the data bandwidth they can carry (or, more accurately, to trade bandwidth for error rate or noise immunity).

[solomon_13000]

ADSL uses quadrature amplitude modulation (QAM) to achieve the 15-bitmaximum that any single tone can carry. This technique employs a combination of amplitude modulation and phase shift keying.

[M/Q]

Not sure if you are asking questions or just repeating information?

[solomon_13000]

From my understanding anything that requires modulation and demodulation uses QAM.

[solomon_13000]

I believe I have the answer. :)

[M/Q]

Your statement about mod/demod is not exactly true. There are many methods available to inject analog information into carrier waves. QAM is the prevelant technology for injecting digital information into an analog carrrier.

[solomon_13000]

can I say its a conversion of a digital signal represented by binary (0&1) into an analog signal.

[M/Q]

I would agree with that. You may want to get a bit more specific as there are two general types of QAM, analog and digital.

You may have looked at this but just in case you have not check out this link. I find the Wiki definition to be one of the better ones around.

http://en.wikipedia.org/wiki/Quadrature_amplitude_modulation

[solomon_13000]

PAL and NTSC - Analog QAM
Dial up modem - Analog QAM
ADSL - Digital QAM