Data communication

+2 ♦Avishka RJ ♦™ · February 7, 2015
What does career signal mean??  

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+1 Pere Garau Burguera · February 10, 2015
Carrier signal is a signal (usually sinusoidal) that is used for separating different stuff frequencially. By multiplicating the signal you want to send (in baseband) by a carrier signal with frequency f, you will have the signal centered at that frequency f, and the bandwith of the signal will remain the same.
At the receiver, you then convert the received signal to baseband again (using the f you want), and then filter out the stuff that you don't want at that moment. You then get the original signal you sent. 
In digital communication, you have generally an in-phase and a quadrature component. Part of the bits gets assigned to the in-phase component and the other to the quadrature component. Then, and according to your modulation, you make the pulses in both components, (square, gaussian, etc.) When you have the two analog signals, I(t), and Q(t) (In-phase and quadrature), then you multilpy the in-phase one by cos(2*pi*f0*t), and the quadrature by a 90º offset version of the signal before, -sin(2*pi*f0*t). Then you sum the two signals at the end. f0 will be the carrier signal. This way you have two orthogonal dimensions that you can then separate again at the receiver.

If don't know if you have the knowledge to understand this (and I find it difficult to explain it too). You can ask me for specific things if you want

Check out OFDM for some more complex stuff, like sub-carriers and stuff if you are interested. 
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