Frequency domain reciprocal modulation (FDRM) is a new digital transmission technique that offers an advantage in microwave frequency channels afflicted with dynamic multipath.
The first block of data is immediately followed by a second block which is a reciprocal of the first block in the frequency domain. The first block may be viewed as a special type of orthogonal frequency division multiplexing (OFDM) and the second block may be described as reciprocal OFDM. By sending the blocks sequentially, approximately the same set of echoes are applied to both blocks and the echoes are canceled when the two blocks are processed together. The effects of rapid fades is also canceled by FDRM.