Frequency domain reciprocal modulation (FDRM)

Frequency domain reciprocal modulation is a new digital transmission technique that offers an advantage in radio frequency channels afflicted with dynamic multipath. Multipath is a linear distortion that is also known as echoes or ghosts. Bandwidth-efficient digital transmission is very difficult through a channel that has moving ghosts because adaptive equalizers frequently cannot adapt fast enough. This new modulation technique employs two blocks of correlated data to cancel the effects of all linear distortion. The first block of data is immediately followed by a second block which is a reciprocal of the first block in the frequency domain. Assuming approximately the same set of echoes are applied to both blocks, the echoes are cancelled when the two blocks are processed together