  An accurate channel estimation is crucial for the novel time domain
synchronous orthogonal frequency-division multiplexing (TDS-OFDM) scheme in
which pseudo noise (PN) sequences serve as both guard intervals (GI) for OFDM
data symbols and training sequences for synchronization/channel estimation.
This paper studies the channel estimation method based on the cross-correlation
of PN sequences. A theoretical analysis of this estimator is conducted and
several improved estimators are then proposed to reduce the estimation error
floor encountered by the PN-correlation-based estimator. It is shown through
mathematical derivations and simulations that the new estimators approach or
even achieve the Cramer-Rao bound.
