Joint power-loading and cyclic prefix length optimization for OFDM-based power line communication

The use of a cyclic prefix (CP) in orthogonal frequency-division multiplexing (OFDM) allows to avoid inter-carrier interference (ICI), but also diminishes the efficiency of the modulation scheme. We study the problem of jointly optimizing the CP length and the discrete bit and power-loading under ICI in OFDM, exemplified by its application to power line communication (PLC). We derive a low-complexity linear programming (LP) based performance upper-bound which is applicable to analyze the suboptimality of bit-loading heuristics under varying CP lengths. Furthermore, a branch-and-bound heuristic is proposed for low-complexity CP-length selection. While we do not expect the LP bound to be tight in all possible interference scenarios, our simulation results support the hypothesis that it is sufficiently tight in the range of near-optimal CP lengths in order to provide guidelines for optimal as well as heuristic CP-length selection.