Quadrature Modulation!

[chyan]

I am doing a thesis on "The Principle of Quadrature Modulation and
Application".

This topic is based on one of the major topic in modulation in the digital
communication such as QPSK, 8-QPSK, and so on.

I would to know what are the application of the Quadrature Modulation?

Thank you.

[David Belohrad]

Hi,
I think that QAM is used to match two signals to amplitude modulation. Signals are multiplied by cos (wt+phi) and sin(wt+phi). In spectra you get simple AM, where LSB and USB contains each one signal. The second way is for example to generate complex signal.
David



chyan <lch...@tm.net.my> píše v článku <36243...@news1.tm.net.my>...

[Lynch, Frank (BNR:BNRTP:3H71)]

chyan wrote:

> I am doing a thesis on "The Principle of Quadrature Modulation and
> Application".
>
> This topic is based on one of the major topic in modulation in the digital
> communication such as QPSK, 8-QPSK, and so on.
>
> I would to know what are the application of the Quadrature Modulation?
>
> Thank you.

An older example (non digital) if quadrature modulation is putting the color
information on a 3.58 MHz subcarrier for color TV.

Other more recent examples of QPSK, Offset PSK, PI/4 PSK, BPSK, etc
would be the TDMA and CDMA Cellular Telephone Standards.

Frank Lynch
RF Design Engineer
Nortel

[Dan Clingman]

chyan wrote:
>
> I am doing a thesis on "The Principle of Quadrature Modulation and
> Application".
>
> This topic is based on one of the major topic in modulation in the digital
> communication such as QPSK, 8-QPSK, and so on.
>
> I would to know what are the application of the Quadrature Modulation?
>
> Thank you.

Get a copy of "Digital Communications Fundamentals and Aplications" by
Sklar and read it.

[Duncan Barclay]

In article <36243...@news1.tm.net.my>,

"chyan" <lch...@tm.net.my> writes:
> I am doing a thesis on "The Principle of Quadrature Modulation and
> Application".

I take it this isn't at too high a level if you are asking questions
like these...

>
> This topic is based on one of the major topic in modulation in the digital
> communication such as QPSK, 8-QPSK, and so on.
>
> I would to know what are the application of the Quadrature Modulation?

Nearly all modern, high performance, communications systems use
quadrature modulation. The best examples would be GSM (GMSK), digital
video (n-QAM, with n 64, 128, 256 etc, OFDM), xDSL (n-QAM, OFDM).
Some CDMA (direct sequence spread spectrum) systems use QPSK etc.

The cheaper digital standards tend to use FSK in a variety of guises.

Please note that "quadrature" modulation is really a bit of a misnomer.
Quadrature signals are used to represent "complex" (as in imajinary
numbers) modulations. There have been implementations of GSM which use
polar (magnitude and angle) receivers to represent the complex
modulation in GMSK.

Duncan

--
________________________________________________________________________
Duncan Barclay | God smiles upon the little children,
dm...@ragnet.demon.co.uk | the alcoholics, and the permanently stoned.
________________________________________________________________________

[Jan Panteltje]

>chyan wrote:
>>
>> I am doing a thesis on "The Principle of Quadrature Modulation and
>> Application".
>>

>> This topic is based on one of the major topic in modulation in the digital
>> communication such as QPSK, 8-QPSK, and so on.
>>
>> I would to know what are the application of the Quadrature Modulation?
>>

>> Thank you.
>
As far as quadrature modulation goes, I find it often easier to look at it
in the time domain.
If you look at a sine wave of frequency f (amplitude modulated or not), you see that
every 180 degrees ( (1 / 2) period time) the amplitude is guaranteed zero.
Now if you use a second sine wave of frequency f, buy delayed by 1 / 4 period
(90 degrees) (amplitude modulated or not), the maxima of this wave will fall
exactly in the minima of the first one.
Now if we demodulate, not by a simple diode detector, but by sampling the
sum of these waves at t = 0 and t = 0 + (1 / 4) (+90 degrees), then we can
get the original signals back (their amplitude).
So ANY application that needs to send 2 signals on one frequency (carrier)
could use this quadrature modulation system.
If the timing is correct there is no cross talk between the signals at all.
(well not exactly zero, think about the length of the sample period for example).
Jan