Performance evaluation of Code-Spread OFDM using Vandermonde spreading

Spectral nulls present in a channel can severely degrade or cancel out OFDM tones, resulting in an irreducible error rate. To combat this, standards typically employ forward error correction (FEC) techniques. In code-spread OFDM (CS-OFDM), each sinewave carries a weighted sum of all the information symbols being transmitted in an OFDM block interval. 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 CS-OFDM is evaluated using Hadamard and Vandermonde spreading and compared to standard OFDM1.