On the impact of redundant subcarrier energy optimization in UW-OFDM

Unique word - orthogonal frequency division multiplexing (UW-OFDM) is a novel OFDM concept that uses deterministic sequences, which we call unique words, as guard intervals instead of the conventional cyclic prefixes. Since unique words represent known sequences, they can advantageously be used for synchronization, channel estimation, but also for improving the bit error ratio (BER) behavior of a system. These UWs are created by appropriately loading so-called redundant subcarriers. In this paper, we investigate methods to improve the BER behavior of UW-OFDM by increasing the number of redundant subcarriers (while keeping the length of the UW constant). This gain in the BER performance comes with an increase of the redundancy part and thus with a decrease of the data rate. As such, we present methods to vary the coding rate in UW-OFDM. We present results for the additive white Gaussian noise (AWGN) channel as well as for indoor multipath environments to highlight the advantages of the proposed methods.