Low-Complexity Wideband Channel Estimation for ISAC in Analog Millimeter-Wave Systems
Accurate wideband channel estimation is a key enabler for millimeter-wave (mmWave) integrated sensing and communication (ISAC) systems. In the narrowband scenario, the Transformed Spatial Domain Channel Estimation (TSDCE) method was previously shown to provide fast and accurate angle estimation with substantially lower complexity than conventional compressed-sensing approaches based on orthogonal matching pursuit (OMP). However, wideband ISAC scenarios additionally require delay estimation, making joint angle-delay sparse recovery computationally expensive due to the multidimensional dictionary search. In this paper, we propose a wideband extension of TSDCE, namely TSDCE-TD, which incorporates time-domain support and decouples angle and delay estimation. Two variations are proposed for delay estimation: TSDCE-TD (Dict), which uses a one-dimensional delay dictionary, and TSDCE-TD (FFT), which applies Fast Fourier Transform (FFT) zero-padding interpolation. Path estimates are iteratively refined through successive interference cancellation and alternating angle-delay updates. Simulation results show that the proposed methods outperform OMP-based baselines under practical dictionary sizes, while achieving comparable performance at high-resolution settings with substantially lower computational complexity. Moreover, the angle-delay estimates obtained using the proposed approach enable accurate single-anchor indoor localization in a ray-traced environment, achieving sub-20 cm positioning errors and satisfying practical indoor positioning requirements.