CE-OFDM With Phase Rotation and Pulse Shaping for Power-Constrained ISAC

Abstract

Integrated sensing and communication (ISAC) is expected to play a key role in future sixth-generation (6G) networks, where random data-bearing signals are reused to support both communications and sensing, thereby improving time-frequency utilization. In practice, the high peak-to-average power ratio (PAPR) of conventional multicarrier signals incurs severe power-amplifier (PA) back-off and limits both communication throughput and sensing range. Constant-envelope orthogonal frequency division multiplexing (CE-OFDM) is a promising remedy due to its 0-dB PAPR. However, its random nonlinear phase mapping produces high autocorrelation sidelobes, significantly degrading ranging performance. In this paper, we develop an expectation-oriented autocorrelation-function (ACF) design framework for pulse-shaped random CE-OFDM signals. We derive a tractable analytical approximation for the average squared ACF, which decomposes into a pulse-induced pedestal determined by the shaping filter and a phase-dependent leakage term controlled by time-domain phase rotation. Based on this characterization, we formulate an expected integrated sidelobe level (EISL) minimization problem and propose a joint design of phase rotation and Nyquist pulse shaping. We further show that coherent integration across independent transmission slots suppresses residual leakage proportionally to the integration length. Numerical results demonstrate that the proposed design achieves pronounced sidelobe suppression over the prescribed delay interval while preserving the ultra-low PAPR, favorable BER performance, and spectral efficiency of CE-OFDM.