Optimal binary spreading for block OFDM on multipath fading channels

We study the use of block spreading in a multicarrier system to gain diversity advantage over multipath fading channels. The main idea is to split the full set of subcarriers into smaller blocks and spread the data symbols across these blocks via unitary spreading matrices in order to gain multipath diversity across each block at the receiver. We extend the recent work of Bury et. al. (2003), by posing the problem as a finite dimensional optimization problem in which the asymptotic error is minimized over unitary spreading matrices. This formulation allows us to find explicit solutions for the optimal spreading matrices.