# 5G Downlink Multi-Beam Signal Design for LOS Positioning

## TL;DR

This paper develops optimal beamforming strategies for 5G downlink positioning in LOS scenarios, minimizing error bounds with different prior knowledge levels, and demonstrates improved performance over existing methods.

## Contribution

It provides a theoretical framework for optimal beam design and power allocation in LOS positioning, including robustness considerations for imperfect channel knowledge.

## Key findings

- Two-beam optimal configuration for perfect prior knowledge
- Robust power allocation strategies for imperfect knowledge
- Outperforms existing methods in simulation results

## Abstract

In this work, we study optimal transmit strategies for minimizing the positioning error bound in a line-of-sight scenario, under different levels of prior knowledge of the channel parameters. For the case of perfect prior knowledge, we prove that two beams are optimal, and determine their beam directions and optimal power allocation. For the imperfect prior knowledge case, we compute the optimal power allocation among the beams of a codebook for two different robustness-related objectives, namely average or maximum squared position error bound minimization. Our numerical results show that our low-complexity approach can outperform existing methods that entail higher signaling and computational overhead.