An Optimized OFDM Waveform Design for 6G Industrial Networks

The conventional orthogonal frequency division multiplexing (OFDM) combats inter-symbol interference (ISI) by adding cyclic prefix (CP) at the beginning of OFDM block. Current standardization employs fixed CP duration irrespective of wireless channel characteristics, which is effective for channels with a long root mean-square (RMS) delay spread. However, this is impractical for industrial environments where the channel exhibits a shorter delay spread leading to a more pronounced CP overhead. Therefore, the classical problem of waveform design and optimization has to be revisited for industrial applications in the sixth generation (6G) of wireless communication systems. With the understanding of wave propagation characteristics in industrial environments, in this paper, we first analyze the impact of insufficient CP duration on OFDM and subsequently derive the closed-form expressions for ISI and desired power. Then, we design a multi-objective optimization problem (OP) which determines the minimum required signal-to-noise ratio (SNR) and CP duration conditioned on link reliability. To solve the proposed OP, we adopt the weighted-sum approach that transforms the multi-objective OP into a single-objective OP. We present numerical results for channels with various RMS delay spreads and confirm the spectral efficiency (SE) gains attainable by the proposed method with no need for additional equalization complexities.