How Does Probabilistic Constellation Shaping Control Ranging Sidelobe Levels in ISAC?
Probabilistic constellation shaping (PCS), originally designed to fill the gap between finite uniform constellations and continuous capacity-achieving input distributions, has recently emerged as a central tool in adjusting the expected integrated sidelobe level (EISL) in integrated sensing and communication (ISAC). In this paper, we show that PCS goes beyond EISL: A large class of PCS methods, termed as type-based PCS, are capable of providing precise control over codeword-wise integrated sidelobe level ratio (ISLR) for systems employing orthogonal frequency division multiplexing (OFDM), thus yielding a stronger sensing performance guarantee than EISL control. We further show that OFDM is almost the only unitary modulation basis whose codeword-wise ISLR can be precisely controlled by type-based PCS. Based upon the analytical results, practical type-based PCS methods compatible with the probabilistic amplitude shaping (PAS) framework are conceived, which achieve higher communication rates than existing ISAC-oriented PCS methods under identical ISLR constraints.