Recovering Signal Energy From the Cyclic Prefix in OFDM

In orthogonal frequency-division multiplexing (OFDM) systems, a cyclic prefix (CP) is often added at the transmitter and discarded at the receiver. When the length of the CP exceeds the delay spread of the channel, a portion of the CP can be used to recover additional signal energy. In the past, Nyquist windowing techniques have been proposed to recover signal energy, thereby improving performance. In this paper, linear maximum-likelihood (ML) and minimum-mean-square-error (MMSE) approaches are developed, which further improve performance, particularly when the signal-to-noise ratio (SNR) is low. Simpler two-valued windowing (TVW) solutions are also provided, which generally employ one or two non-Nyquist windows.