Time-Domain Layered Division Multiplexing for Advanced ISDB-T: Design and Link-Level Evaluation

This paper investigates time-domain layered division multiplexing for coexistence between legacy Integrated Services Digital Broadcasting–Terrestrial and an enhanced terrestrial broadcast service within the same 6 MHz channel. The upper layer follows the legacy waveform, whereas the lower layer employs an advanced waveform with a different fast Fourier transform size and occupied bandwidth. Unlike frequency-domain layered division multiplexing, which requires both layers to share a common orthogonal frequency-division multiplexing parameter set, the proposed approach superposes independently generated waveforms in the time domain after modulation, enabling flexible lower-layer formats up to a 32K-point transform class. We further introduce a unified carrier-to-noise ratio penalty framework referenced to the composite transmit power, which maps service targets to an injection ratio and per-layer modulation-and-coding selections. Link-level simulations validate the analytical trends in additive white Gaussian noise and in a frequency-selective two-path channel with practical channel estimation and equalization, including a multipath estimation-based upper-layer equalizer to mitigate non-orthogonal lower-layer leakage. The results show that multipath effects can be well captured by an additive implementation-loss offset applied to the penalty relationships. Based on the validated framework, we derive practical design guidelines that ensure reliable upper-layer decoding prior to successive interference cancellation while maximizing lower-layer capacity.