# Peer-to-Peer Ultra-Wideband Localization for Hands-Free Control of a Human-Guided Smart Stroller
## 1 Introduction
### Human-Guided Robot  
Human-guided robots are controlled directly by the human operator, which allows the operator to interact with the robot explicitly. Various interactive strategies are designed to guide the robot in front of the operator. [PERSON] et al. designed a physical interface to guide the robot by estimating the interaction force [34]. [PERSON] et. al. [35] developed a guiding system in which the user needs to approach the robot in a certain direction to rotate the robot in the opposite direction, analogous to pushing a cart virtually; however, only using this mode causes extra effort when turning a sharp curve happens often. Despite the progress achieved in the mentioned works, human-robot interaction (HRI) in human-guided robots has not been studied thoroughly. Smart walkers could also be categorized as human-guided robots since most of them are controlled by humans explicitly. For example, [PERSON] et al. proposed a method to control a smart walker's rotation based on the face orientation of the user [36]. Smart walker users have direct physical contact with the walker, different from the scenario considered in this work in which the stroller precedes the user by a short distance. Therefore, the considered scenario requires additional supervision from the user over the robot, maintaining it in the field of view of the user. Overall, the explicit interaction methods provide unambiguous commands from the user to the robot, but it increases the user's cognitive load since they have to explicitly control the robot at all times. In the case of a smart stroller, the parents are expected to remain aware of the baby's condition and security as a priority; therefore, we consider that an explicit interaction approach is a suitable choice for the smart stroller regardless of its shortcomings.  
Having investigated the methods of human tracking technologies and human-following and human-guided robots, in this work, we elected to use an ultra-wideband (UWB) localization system in the context of a human-guided stroller. We develop and evaluate a hands-free interface with human direct instruction for the smart baby stroller control utilizing the commercial UWB product. Potentially, the proposed system can leverage existing UWB-enabled smartphones to control the smart stroller, eliminating the need for the additional UWB tag carried by humans and ensuring seamless integration with everyday technology making it more user-friendly and practical.  
The contributions of this paper are as follows:  
1. This study presents information on the preferred positions of the stroller relative to the human based on questionnaires in a smart stroller scenario.
2. This study introduces a model of human-guided hands-free robot control based on the UWB localization system, in particular, the robot spatially precedes the human based on the preferred positions.
3. This study presents quantitative and qualitative evaluations of hands-free control of a smart stroller, compared to joy-stick control, and manual operation of the stroller. The results show the comparable performance between the hands-free interface and the joystick in controlling the stroller. The results of this work also show gender differences in the preference of a control interface, which is presented for the first time in the field of human-guided robot control, to the best of our knowledge.  
In the following sections, we provide a comprehensive analysis of our study. Section 2 introduces the methodology, focusing on the preferred relative position between the human and the stroller, and the control methods employed. Section 3 offers an overview of the prototype developed for the study. In Section 4, we describe the experiments conducted, including Experiment 1: path-following test and Experiment 2: simulated real-life scenario, and the user evaluation. Sections 5 and 6 present and discuss the results separately. Finally, Section 7 concludes the paper with a summary of key insights, implications, and limitations of our work, and potential directions for future research.