I am not sure, but it sounds like sending different versions of a signal orthogonally in the wide-band and use maximum combining ration techniques to achieve the highest signal to noise ratio available in the channel. Because of orthogonality of the signal components in the frequency domain of the channel, components are independent from each other and thus have cooperating effect on each other. But I am not sure. It sounds like this. If you think I'm wrong please explain more.