I know what complex numbers are, but what actually is a complex signal as opposed to a real signal? I know a little Fourier Transform and in that context it is described as the difference between a cos wave and sin wave signals. But when I read about it in mobile communications it is described as an additional degree of freedom that can be transmitted in parallel. It can't be the Fourier Transform definition since a phase shift does not stop it from interfering with each other. In one text it gives an analogy of transmitting two signals through two wires and combining them at the end. But how can this be done through the air without the two signals interfering? This difference between a wave in the complex plane and the real plane is making me very confused. Please help.