Coded OFDM by unique word prefix

In this paper, we propose a novel transmit signal structure 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 systems with frequency domain equalization (SC/FDE), 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 a complex number Reed-Solomon (RS-) code structure within the sequence of subcarriers. This either allows for algebraic RS decoding or for applying a highly efficient Wiener smoother succeeding a zero forcing stage at the receiver to further improve the bit error ratio behavior of the system. These beneficial properties are achieved while additionally featuring around the same bandwidth efficiency as conventional CP-OFDM. We present simulation results in an indoor multipath environment to highlight the advantageous properties of the proposed scheme.