{"ID":2874551,"CreatedAt":"2026-06-01T04:54:23.091178241Z","UpdatedAt":"2026-06-01T04:54:23.091178241Z","DeletedAt":null,"paper_url":"https://arxiv.org/abs/2509.04055","arxiv_id":"2509.04055","title":"Constellation Shaping for OFDM-ISAC Systems: From Theoretical Bounds to Practical Implementation","abstract":"Integrated sensing and communications (ISAC) promises new use cases for mobile communication systems by reusing the communication signal for radar-like sensing. However, sensing and communications (S\u0026C) impose conflicting requirements on the modulation format, resulting in a tradeoff between their corresponding performance. This paper investigates constellation shaping as a means to simultaneously improve S\u0026C performance in orthogonal frequency division multiplexing (OFDM)-based ISAC systems. We begin by deriving how the transmit symbols affect detection performance and derive theoretical lower and upper bounds on the maximum achievable information rate under a given sensing constraint. Using an autoencoder-based optimization, we investigate geometric, probabilistic, and joint constellation shaping, where joint shaping combines both approaches, employing both optimal maximum a-posteriori decoding and practical bit-metric decoding. Our results show that constellation shaping enables a flexible trade-off between S\u0026C, can approach the derived upper bound, and significantly outperforms conventional modulation formats. Motivated by its practical implementation feasibility, we review probabilistic amplitude shaping (PAS) and propose a generalization tailored to ISAC. For this generalization, we propose a low-complexity log-likelihood ratio computation with negligible rate loss. We demonstrate that combining conventional and generalized PAS enables a flexible and low-complexity tradeoff between S\u0026C, closely approaching the performance of joint constellation shaping.","short_abstract":"Integrated sensing and communications (ISAC) promises new use cases for mobile communication systems by reusing the communication signal for radar-like sensing. However, sensing and communications (S\u0026C) impose conflicting requirements on the modulation format, resulting in a tradeoff between their corresponding perform...","url_abs":"https://arxiv.org/abs/2509.04055","url_pdf":"https://arxiv.org/pdf/2509.04055v2","authors":"[\"Benedikt Geiger\",\"Fan Liu\",\"Shihang Lu\",\"Andrej Rode\",\"Daniel Gil Gaviria\",\"Charlotte Muth\",\"Laurent Schmalen\"]","published":"2025-09-04T09:36:53Z","proceeding":"eess.SP","tasks":"[\"eess.SP\"]","methods":"[]","has_code":false}