The Potential of Unique Words in OFDM

In this paper we propose a novel transmit signal structure and an adjusted and optimized receiver for OFDM (orthogonal frequency division multiplexing). Instead of the conventional cyclic prefix (CP) we use a deterministic sequence, which we call unique word (UW), as guard interval. We show how unique words, which are already well investigated for single carrier frequency domain equalization (SC/FDE) systems, can also be introduced in OFDM symbols. Since unique words represent known sequences, they can advantageously be used for synchronization and channel estimation purposes. Furthermore, the proposed approach introduces correlations along the subcarrier symbols. This allows to apply a highly efficient Wiener LMMSE (linear minimum mean square error) smoother for noise reduction at the receiver. We present simulation results in an indoor multipath environment to highlight the advantageous properties of the proposed scheme.