Performance evaluation of code-spread OFDM

When spectral nulls are present in a channel, they can severely degrade or cancel out OFDM tones, resulting in an irreducible error rate. In Code Spread OFDM, each sinewave carries a weighted sum of all the information symbols being transmitted in an OFDM block interval. This creates a more robust modulation scheme which provides substantial performance improvement relative to standard OFDM. In this paper, the MMSE estimator is derived for each symbol for a number of cases, including when the number of carriers is greater than the number of symbols. The performance of both OFDM and CS-OFDM are evaluated with and without error control coding using the FEC techniques typically employed in OFDM standards.