Extremely Large Antenna Spacing Method for Enhanced Wideband Near-Field Sensing

TL;DR

This paper introduces an extremely large antenna spacing method for wideband near-field sensing, enabling high-resolution localization with fewer antennas by exploiting near-field effects and super-resolution regions.

Contribution

It proposes an ELAS design for MIMO-OFDM systems that achieves large apertures with few antennas, avoiding grating lobes and enhancing near-field sensing capabilities.

Findings

Significant localization accuracy improvements in near-field conditions.

ELAS design reduces the number of antennas needed for large apertures.

Enhanced resolution surpassing classical bandwidth limits.

Abstract

This paper proposes a monostatic wideband system for integrated sensing and communication (ISAC) at millimeter-wave frequencies, based on multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM). The system operates in a hybrid near-/far-field regime. The transmitter (Tx) operates in the far field (FF) and uses low-complexity beam steering. The receiver (Rx), on the other hand, operates in a pervasive near field (NF), enabled by a very large effective array aperture. To enable a fully digital implementation, we introduce an extremely large antenna spacing (ELAS) design. This design attains the required aperture with only a few widely spaced antenna elements while avoiding grating lobes in the composite Tx-Rx response. We analytically characterize the NF range-angle response of this architecture and study the interplay between NF effects and waveform bandwidth. This leads to the definition of a super-resolution region, where NF propagation at the Rx dominates the achievable range resolution and surpasses the classical, bandwidth-limited resolution. As a case study, we consider an extended target modeled as a collection of scatterers and assess localization performance via maximum-likelihood estimation. Numerical results evaluated in terms of root mean square error (RMSE) and generalized optimal sub-pattern assignment (GOSPA) show that operating in NF conditions with the ELAS-based design yields significant gains compared to a conventional FF baseline at both the Tx and Rx.