# Peer-to-Peer Ultra-Wideband Localization for Hands-Free Control of a Human-Guided Smart Stroller
## 2 Methodology  
### Preferred Relative Positions between the Human and the Stroller  
In a human-following or a human-guided locomotion task, the goal of the control algorithm is to ensure the convergence of the robot to the target pose or position. The criteria for selecting a target pose while following is unspecified but with task-specific reasoning [37]. We investigated the target position in the case of a hands-free smart stroller. We assumed five possible relative positions, Front, Right-front, Side-by-side, Right-behind, and Behind, as noted as a1\(\sim\)a5 separately in Figure 1a. A questionnaire survey was conducted to investigate the preferred relative positions among these five cases. We created five videos to simulate the different relative following positions in motion using a traditional stroller pulled by a rope. Figure 1b illustrates an image from one of the five video simulations of the stroller following the person with the relative position, right front (a2), others are similar to this one, but with different relative positions. We divided the five videos into 10 pairs for comparison. In each pair, the first following type is noted as type 1 and the second as type 2. Participants were asked to watch one group of videos and answer the question, \"Following type 1 is preferred over type 2\" with five answer choices from strongly disagree (\(-1\)) to strongly agree (1). Thirteen participants (aged between 28 to 40 years) joined this survey, all of them are parents who are using a stroller or have used a stroller in recent years. The average preference scores for the five candidate relative positions for all participants are shown in Figure 2. Positive numbers in the score indicate a positive attitude toward the relative pose, and conversely, negative numbers indicate a less favorable attitude toward the relative pose. The results were analyzed using [PERSON]'s Paired Comparison (Nakaya Variation). The results indicated that all participants exhibited a strong preference for the stroller positions: Front, Front-right, and Side-by-side, and showed a marked disfavor for the positions Behind-right and Behind. We hypothesize that these results are related to a preference for the stroller to move in the FOV of the human, giving the parent a better sense of security of the child in the stroller. Notably, positions Front (a1) and Front-right (a2) received the highest preference scores, suggesting general favoritism towards this positioning. Based on these findings, we have selected the Front as the following position for the controller design and development of the proposed system.  
Figure 1: (a) Possible relative positions for the investigation. Five relative positions were considered: a1 (Front), a2 (Right front), a3 (Side-by-side), a4 (Right behind), and a5 (Behind). (b) Sample of the video for preferred position investigation: Right front position as an example, a rope is used to pull a commercialized normal stroller (with a baby doll inside) at a constant speed to imitate the human-following behavior.  
Figure 2: Results of the participants’ preferred position relative to the stroller. The X-axis represents human-stroller relative positions: a1: Front, a2: Right front, a3: Side-by-side, a4: Right behind, a5: Behind (Figure 1a). The Y-axis shows the preference score of all participants for each relative position.