# A Telepresence Wheelchair with 360-Degree Vision Using WebRTC
## 2 Methods  
### Telepresence Wheelchair with 360-Degree Vision Based on WebRTC  
To enable two-way audio and video communication, we developed and implemented a telepresence wheelchair using a more flexible web real-time communication (WebRTC) framework. WebRTC is a standard that defines a set of communication protocols [12]. Some research about developing real-time applications has been started since the first version of WebRTC was released by Google [13]. Since then, much research has been developed to exploit the WebRTC application. For example, [PERSON], et al. [14] presented a video conferencing system based on WebRTC. While web shopping using WebRTC was explored in [15]. WebRTC applications were also applied for education [16]. However, there has been no previous work which uses WebRTC for a telepresence wheelchair. We have developed a telepresence wheelchair system based on an electric-powered wheelchair platform modified with many add-on external modules. The hardware of the system is illustrated in Figure 1. To achieve the desired features, the powered wheelchair is equipped with a Mac mini-computer, control components, telecommunication interfaces, touchscreen display. To enhance the full field of view, a camera is mounted in front of the wheelchair to capture the dual-fisheye images, and these two parts of the field of view are stitched into a single seamless panorama, and then streamed over the Internet. In particular, the Ricoh Theta S dual-fisheye camera is mounted in front of the wheelchair to provide coverage of the whole surrounding scene at the wheelchair location. As a result, a remote user can see a full view of the surroundings of the wheelchair to control the wheelchair more safely and efficiently. By developing an application programming interface and WebRTC-enabled browser, real-time video communications can be set up. Figure 2 shows 360-degree view telepresence using WebRTC architecture. A remote user can observe the surrounding environment of the wheelchair in real-time over wireless internet connections. From the obtained full field of view, a method for remote control approach to navigate the wheelchair from a remote location to interact with the remote environment must be developed. Figure 1: A telepresence wheelchair equipped with a dual-fisheye camera. For telepresence systems, one of the most important design objectives is to transfer voice, video, control signal, and data in real-time. The performance of data communications is carefully considered and thoroughly explored to understand the behavior of data transmission. The key factors affecting the performance of data transmission are bandwidth, throughput, round-trip-time, and frame rate. As a result, to evaluate the system performance, these important factors are analyzed. The bandwidth (\(W\)) is closely related to the maximum communication channel capacity in bits per second. To determine the maximum rate of transmission of data which can be sent over a link, the bandwidth of a communications link is measured. If the bandwidth is sufficient, the packet delay is very low, and interactive media applications work quite well in terms of user satisfaction. The channel capacity is given by the Shannon-Hartley theorem as follows:  
\[C=W\log_{2}(1+\frac{S}{N}) \tag{1}\]  
where \(S/N\) is a signal-to-noise ratio. For a system transmitting at maximum capacity, the bandwidth efficiency of the system can be written as  
\[\frac{C}{W}=\log_{2}(1+E_{b}\times\frac{C}{N_{o}\times W}) \tag{2}\]  
where \(E_{b}\) is the average received energy per bit, \(N_{o}\) is the noise power density (Watts/Hz). Obviously, the larger the ratio \(\frac{C}{W}\), the greater the bandwidth efficiency is. On the other hand, the throughput is the number of bits transmitted per unit time. A packet contains L bits, and the amount of time devoted to that packet is the actual transmission time (\(L/B\)) plus the propagation delay (\(d/V\)).