Achieving Full-Bandwidth Sensing Performance with Partial Bandwidth Allocation for ISAC

TL;DR

The paper tackles the problem of achieving full-bandwidth delay resolution and unambiguous range for uplink ISAC when sensing is allocated only a fraction of the total bandwidth. It introduces a two-stage delay estimation (TSDE) method that uses a coarse Stage-1 with collocated subcarriers to obtain a wide unambiguous range, followed by a Stage-2 with optimally decimated distributed subcarriers to attain full-bandwidth delay resolution without introducing ambiguity. Theoretical analysis (Theorem 1) shows that full-bandwidth performance can be reached with partial bandwidth B1 = B√ξ/√K as long as the channel delay spread τ_d satisfies τ_d ≤ √(Kξ)/B, with ξ in [1, K/4], and Corollaries describe special cases; simulations demonstrate superior performance of TSDE over conventional collocated-subcarrier methods, approaching full-bandwidth results as the partial bandwidth grows. The approach is particularly beneficial in dense-scatterer environments where bandwidth is limited, delivering improved delay estimation accuracy (NMSE) and detection probability (P_d) for uplink ISAC systems.

Abstract

This letter studies an uplink integrated sensing and communication (ISAC) system using discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-s-OFDM) transmission. We try to answer the following fundamental question: With only a fractional bandwidth allocated to the user with sensing task, can the same delay resolution and unambiguous range be achieved as if all bandwidth were allocated to it? We affirmatively answer the question by proposing a novel two-stage delay estimation (TSDE) method that exploits the following facts: without increasing the allocated bandwidth, higher delay resolution can be achieved via distributed subcarrier allocation compared to its collocated counterpart, while there is a trade-off between delay resolution and unambiguous range by varying the decimation factor of subcarriers. Therefore, the key idea of the proposed TSDE method is to first perform coarse delay estimation with collocated subcarriers to achieve a large unambiguous range, and then use distributed subcarriers with optimized decimation factor to enhance delay resolution while avoiding delay ambiguity. Our analysis shows that the proposed TSDE method can achieve the full-bandwidth delay resolution and unambiguous range, by using only at most half of the full bandwidth, provided that the channel delay spread is less than half of the unambiguous range. Numerical results show the superiority of the proposed method over the conventional method with collocated subcarriers.

Figures (6)

• Figure 1: An illustration of the uplink DFT-s-OFDM based ISAC system.
• Figure 2: The delay resolution and unambiguious range versus $K_1$ and $\eta$.
• Figure 3: Comparison of the proposed TSDE method and the conventional method with collocated subcarriers.
• Figure 4: Illustration of the selection of $\eta^*$ for Stage-2 .
• Figure 5: Compare the proposed TSDE method and conventional method in terms of $P_d$ and NMSE.