  This letter provides a capacity analysis between OFDM and the ideal SC-DFE
when no channel knowledge is available at the transmitter. Through some
algebraic manipulation of the OFDM and SC-DFE capacities and using the
concavity property of the manipulated capacity function and Jensen's
inequality, we are able to prove that the SC-DFE capacity is always superior to
that of an OFDM scheme for 4- and 16-QAM for any given channel. For
higher-order modulations, however, the results indicate that OFDM may only
surpass the ideal SC-DFE capacity by a small amount in some specific scenarios.
