You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Survey on Fall Detection and Fall Prevention Using Wearable and External Sensors 
Chapter Title:  Hirata et al. 
1. Abstract of Cited Paper (BIB001):  As aging progresses, fall accident of the person using the walker is an acute problem. It is necessary to know the situation of the userpsilas fall to prevent it. In this paper, we propose a method for estimating the userpsilas fall by modeling of the user in real time as a solid body link model, and pay attention to the center of gravity of the model. We also propose a method for controlling a passive intelligent walker to prevent the userpsilas fall according to the support polygon and the walking characteristic of the user. We experimented with passive intelligent walker in which we implement the proposed fall prevention control and show the effectiveness of the proposal method.

Literature Review:
Hirata et al. BIB001 proposed a method that calculates the user's center of gravity position based on the user's skeleton model (human model) in the sagittal plane BIB002 . The system uses passive-type walkers for fall prevention. Two conditions were considered for the creation of the human model. First the user must hold the walker with both hands. Second, the user's limbs (legs and arms) must be measured a priori. Two laser range finders were used, one placed at the same height of user's hip joint, and the other one at the lower part of the walker. The first one is used to create the upper section of the skeleton, and the second one for the lower part. The center of gravity of the human model is used to determine whether the user is within a predefined stability region. If the user is outside the stability region the servo brakes will be triggered making the walker stop. As the walker stops, the user has a better support to accommodate himself/herself and return to the stability region.