Optical Orthogonal Time Frequency Space with Enhanced Joint Delay-Doppler Index Modulation

To address the non-ideal spectral efficiency (SE) and high implementation complexity of the optical orthogonal time-frequency space with joint Delay-Doppler index modulation (OOTFS-JDDIM) system, this paper proposes an enhanced OOTFS-JDDIM (OOTFS-EJDDIM) scheme based on the discrete Zak transform. The main idea of the proposed scheme is to enhance SE by introducing a sparse structure in the delay-Doppler resource blocks. After detailing the signal mapping rules and implementation principles of the proposed scheme, the SE and computational complexity are derived and analyzed. Furthermore, based on the exponential Weibull atmospheric turbulence channel model, the bit error rate (BER) performance of the proposed scheme is simulated and compared with OOTFSJDDIM. The results show that the proposed scheme achieves consistent improvements in spectral efficiency over the OOTFSJDDIM scheme under various parameter configurations, with SNR losses limited to within 1.5 dB and 2 dB under weak and strong turbulence conditions, respectively.