  This paper investigates subspace-based target detection in OFDM integrated
sensing and communications (ISAC) systems, considering the impact of various
constellations. To meet diverse communication demands, different constellation
schemes with varying modulation orders (e.g., PSK, QAM) can be employed, which
in turn leads to variations in peak sidelobe levels (PSLs) within the radar
functionality. These PSL fluctuations pose a significant challenge in the
context of multi-target detection, particularly in scenarios where strong
sidelobe masking effects manifest. To tackle this challenge, we have devised a
subspace-based approach for a step-by-step target detection process,
systematically eliminating interference stemming from detected targets.
Simulation results corroborate the effectiveness of the proposed method in
achieving consistently high target detection performance under a wide range of
constellation options in OFDM ISAC systems.
