OTFS-based Integrated Positioning and Communication Systems with Low-Resolution ADCs

TL;DR

This work addresses joint positioning and communication in OTFS systems under practical hardware constraints by proposing a two-phase OTFS-IPAC framework where uplink positioning estimates channel parameters and user location, enabling downlink zero-forcing beamforming based on those estimates. It introduces a SS-MUSIC-based AoA estimator with iterative interference cancellation for uplink parameter extraction and derives CRLBs for channel parameters and position to establish estimation limits. Simulation results reveal that higher ADC resolutions improve both positioning accuracy and downlink BER, with a 5-bit ADC achieving near-CRLB positioning at moderate SNR and significant BER gains compared to coarser quantization. The findings demonstrate the viability and performance limits of practical OTFS-IPAC systems in high-mobility scenarios and provide quantization-aware benchmarks for design.

Abstract

This paper proposes a two-phase orthogonal time frequency space (OTFS)-based integrated positioning and communication (IPAC) framework under realistic low-resolution analog-to-digital converters (ADCs). In the uplink phase, the positioning signal is used to estimate channel parameters, which are subsequently used to determine the user's position. The spatial smoothing-multiple signal classification algorithm is introduced to estimate the angle-of-arrival, whereas an iterative interference cancellation scheme is conceived for the remaining parameters' estimation. The corresponding Cramer-Rao lower bounds of channel parameters and user position are also derived. During the downlink communication phase, the estimated parameters are exploited to improve beamforming at the base station. Simulation results evaluate the impact of ADC quantizer resolutions. Specifically, it is shown that enhanced downlink bit error rate performance can be achieved with improved uplink positioning, while the use of low-resolution ADCs induces noticeable performance degradation in the OTFS-IPAC system.

Figures (6)

• Figure 1: Illustration of (a) the proposed OTFS-IPAC systems with uplink positioning and downlink communication signals, (b) TDD-based uplink positioning and downlink communication signal frame structure.
• Figure 2: A toy example of SS-MUSIC using the receive array with $N_r=6, L=4$, and $K=6$.
• Figure 3: Uplink MSEs and CRLBs of user position versus SNR, under different quantizer resolutions of ADCs.
• Figure 4: The MSEs and CRLBs of Doppler using different quantizer resolutions of ADCs.
• Figure 5: The MSEs and CRLBs of channel gain, where different quantizer resolutions of ADCs are exploited.