arXiv:2610.21753v1 Announce Type: new Abstract: This paper proposes sensing-assisted OFDM with index modulation (SA-OFDM-IM) for joint communication and localisation over optical wireless systems. In SA-OFDM-IM, a multilayer frequency-domain architecture partitions each layer's admissible subcarriers into disjoint communication and distributed sensing-pilot subsets, applying group-wise index modulation (IM) within the communication subset. A constrained sensing-to-communication energy allocation jointly minimises average bit-error rate (BER) and delay-based localisation root mean square error (RMSE) under a minimum power-domain margin, enabling low-complexity, ordered-energy detection of both sensing and communication subcarriers without exhaustive maximum-likelihood search. Sensing tones are aggregated across the frame to reconstruct the channel frequency response, yielding the line-of-sight (LoS) delay tap and phase-compensated LoS gain for multilateration and, via the proposed delay-aided received signal strength (RSS) refinement. Simulation results indicate that SA-OFDM-IM can achieve up to 5 dB lower SNR requirement in BER and up to three orders of magnitude lower channel-estimation error than DC-biased optical OFDM, while the RSS estimator removes the SNR-independent error floors of delay-only and hybrid-RSS benchmarks to attain sub-delay-bin range and position accuracy, remaining robust under random known and unknown receiver orientations.