## 2 Background and Related Works
### Social Robots and the Telepresence Scenario  
In the last decade, the role of robots in ordinary life has gained momentum and, in the near future, the number of robots acting in contact with people will significantly increase. In addition, notably, service robotics is aiming to develop novel robotic solutions that could positively co-operate with human beings. In particular, a service robotics application as the Telepresence Robot provides a virtual presence to a remote location, using a video conference system. For this peculiarity, often this robot is called \"Skype with wheels\".  
The Telepresence Robot is a particular type of robot that provides a virtual presence in remote locations. To generalize, the Telepresence Robot provides a connection between a user and a distant participant, to perform social interactions or specific tasks.  
In Telepresence applications for interpersonal communication, there are two views: the user's and the participant's view. From the user's view, Telepresence enables the user to project himself/herself to another place by controlling the Telepresence Robot. In the meantime, the user perceives the immersion from the sensory feedback from the remote environment created by Telepresence.  
For interpersonal communication, Telepresence differs from traditional video conferencing by establishing a true sense of shared space among geographically remote people.  
All of the Telepresence Robot systems have common features:  
* Motion system,
* Connection system,
* Video conference system,
* Sensors.  
The motion system provides the ability to move the robot in the environment. In general, it is a wheeled robot remote-controlled by the user. The robot motion is provided by teleoperation or by autonomous navigation. With teleoperation, the user controls the robot using a dedicated application, it is a very simple operation, but it is not easy to move the robot inside a room and along a corridor using only on-board sensors and/or cameras. With autonomous navigation, the user is able to set the goal position on a map; then, the robot reaches the goal position autonomously, avoiding fixed and unexpected [44; 45].  
The connection system provides the network connection. In general, an internet connection is required in order to communicate with remote locations. The internet connection is provided by wireless connection via LAN (Local Area Network) or mobile Internet technologies.  
The video conference system manages the video call between user and participant. Commonly in this system, a simple tablet provides the video conference. On the user's side, the device should have a camera, a microphone and a speaker to provide an optimal communication.  
Sensors perceive the environment in order to interact with it. The motion system requires sensors to detect and avoid obstacles and/or perform autonomous navigation. In addition, the video conference system requires sensors, such as cameras, speakers and microphones.  
In a standard scenario, the user logs into the Telepresence Robot using a general device (computer, tablet or smartphone) via the Internet. In general, the access to the robot is allowed after this authentication. The user interacts with the remote environment by moving the robot and using sensors. Roughly speaking, the user is projected in the remote environment as a virtual presence, in which cameras are the virtual eyes, microphones the virtual ears, and speakers reproduce the user's voice. At the same time, the participant interacts with the robot that enables communication with the user by exchanging audio and video. Often, the Telepresence Robot transmits the video and audio received by the user's device, similarly to standard video conference applications.