Recycling the Cyclic Prefix in an OFDM System

In orthogonal frequency division multiplexing (OFDM) systems, a cyclic prefix (CP) is often used. With traditional reception, the CP is discarded. However, if the length of the CP exceeds the delay spread of the channel, a portion of the CP can be used to improve performance. In the past, Nyquist windowing techniques have been used to recover signal energy from the CP while maintaining orthogonality between symbols. In this paper, a maximum-likelihood (ML) approach is developed, which improves performance further, particularly when the signal-to-noise ratio (SNR) is low. An approximate ML solution is also given which employs a non-Nyquist window.