Analysis of the Redundant Energy in UW-OFDM

In this paper, we consider unique-word (UW) OFDM, where the guard interval, filled with known samples, is a part of the inverse FFT output. In order to construct the known samples in the UW-OFDM signal, a number of carriers needs to be reserved as redundant carriers. The information modulated on these redundant carriers depends on the transmitted data. However, the energy transmitted on the redundant carriers strongly depends on the positions of these redundant carriers. In this paper, we consider the distribution of the redundant carriers from that is suboptimal but yields an average redundant energy that is close to the minimum, and analytically evaluate the redundant energy as a function of the system parameters, i.e. the FFT length, the number of redundant carriers and the length of the unique word. Based on our results, a simple rule of thumb can be obtained for the selection of the system parameters, which is helpful in the design of UW-OFDM systems.