Resolution Limits of Non-Adaptive 20 Questions Estimation for Tracking Multiple Moving Targets

TL;DR

This paper investigates the fundamental limits of non-adaptive 20 questions estimation for tracking multiple moving targets, providing bounds, algorithms, and applications in wireless beam tracking.

Contribution

It derives non-asymptotic and asymptotic bounds for resolution, introduces a computationally efficient thresholding estimator, and extends results to dynamic target models and practical 5G applications.

Findings

Bounds on resolution are achieved by a threshold-based estimator.

The proposed method reduces computational complexity compared to previous schemes.

Results are applicable to practical beam tracking in 5G wireless networks.

Abstract

Motivated by the practical application of beam tracking of multiple devices in Multiple Input Multiple Output (MIMO) communication, we study the problem of non-adaptive twenty questions estimation for locating and tracking multiple moving targets under a query-dependent noisy channel. Specifically, we derive a non-asymptotic bound and a second-order asymptotic bound on resolution for optimal query procedures and provide numerical examples to illustrate our results. In particular, we demonstrate that the bound is achieved by a state estimator that thresholds the mutual information density over possible target locations. This single threshold decoding rule has reduced the computational complexity compared to the multiple threshold scheme proposed for locating multiple stationary targets (Zhou, Bai and Hero, TIT 2022). We discuss two special cases of our setting: the case with unknown initial location and known velocity, and the case with known initial location and unknown velocity. Both cases share the same theoretical benchmark {that applies to} stationary multiple target search in Zhou, Bai and Hero (TIT 2022) while the known initial location case is close to the theoretical benchmark for stationary target search when the maximal speed is inversely proportional to the number of queries. We also generalize our results to account for a piecewise constant velocity model introduced in Zhou and Hero (TIT 2023), where targets change velocity periodically. Finally, we illustrate our proposed algorithm for the application of beam tracking of multiple mobile transmitters in a 5G wireless network.