Orthogonal Frequency Division Multiplexing (OFDM) is a popular technique used to combat frequency selective fading in multipath channels. When spectral nulls are present in the channel, they can severely degrade or cancel out several OFDM tones, resulting in an irreducible error rate. 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, an 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, Vandermonde, and Discrete Cosine spreading and compared to standard OFDM.
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