Spatial Spectral Index Modulation for Wideband Near-Field ISAC With Phased-MIMO Array

To simultaneously improve the sensing resolution and spectral efficiency, next-generation integrated sensing and communications (ISAC) intend to employ extremely large-scale (XL) antenna arrays transmitting a wideband signal at a high carrier frequency. This necessitates the consideration of near-field wideband signal model, particularly the prominent beam squint/split effect. In this paper, we investigate the radar-centric ISAC with the phased multiple-input-multiple-output (PhasedMIMO) array radar as the host, and propose a spatial spectral index modulation (SSIM) signaling scheme. In the spatial domain, communication information is embedded into the transmit array configurations via subarray permutation. In the spectral domain, we fully exploit the beam squint effect inherent in a wideband phased array, which is typically sought to be alleviated, to embed information into the indices of subcarriers selected to deliberately steer towards the downlink user. Moreover, we design the beamforming weights of each subarray to preserve the sensing performance over the wide bandwidth. Simulation results are provided for performance evaluation and to demonstrate the effectiveness of the proposed wideband near-field ISAC framework and the SSIM signaling scheme.