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Top1. Introduction
The development of personalized health (p-health) systems requires ensuring reliable communication with high qualities of service, especially in sensitive environments. For example, it is important to ensure the communication links between the patient and the hospital care units in order to have a continuous monitoring so that the hospital staff can detect early pathological markers and overcome patient troubles. For high critical cases, continuous monitoring is done using wired systems between the patient and the base station in order to act as soon as possible if a vital sign reaches an alarm threshold.
However, due to the complexity of these systems when several signs have to be measured, they are not adapted to patients having mobility around a room for example. In the case of a patient victim of stroke and integrated in rehabilitation unit after critical phase, it is still important to ensure a continuous transmission of several vital signs information, as for example blood pressure, respiration rate, electrocardiography (Paksuniemi, Sorvoja, Alasaarela, & Myllyla, 2006). In these cases, wireless monitoring solutions are investigated and are generally based on the use of Radio Frequency (RF) technology. However, in the hospital context, because of the presence of much critical care equipment, it is necessary to ensure a high immunity to interference with other electronic equipments (van Lieshout et al., 2007; Wallin, Marve, & Hakansson, 2005).
In this context, optical wireless technologies appear as a complementary solution to RF ones, having some advantages such as being free of license, compact and low cost, requiring low power consumption with a great level of security in such environments (Carruthers, 2003; Elgala, Mesleh, & Haas, 2011; Khan & Barry, 1997; Gfeller & Bapst, 1979; Ghassemlooy, 2003; Mihaescu, Songue, Besnard, Bouchet, & Liu, 2008; Ramirez-Iniguez & Green, 1999). Moreover, the wavelength range used by optical communication ensures that there is no interference with RF and electronic equipments.
Among the optical communication wave range, infrared (IR) technologies have been studied for several years, in indoor environments generally for WLAN (Wireless Local Area Network) applications (Carruthers, 2003; Elgala et al., 2011; Khan & Barry, 1997; Gfeller & Bapst, 1979; Ghassemlooy, 2003; Mihaescu et al., 2008; Ramirez-Iniguez & Green, 1999). Two main configurations are commonly investigated: Line of Sight (LOS) scheme and diffuse one.
The LOS propagation system is used for point to point communications. This is the most basic technology and so the most commonly investigated. The main drawback is the severe impact of misalignments between optical transmitter and receiver on the path loss. Therefore, when considering patient mobility, it imposes more deployment constraints. On the opposite, for diffuse configuration, the optical transmitter projects a wide-beam on room’s reflecting surface, e.g., ceiling or floor, and the diffuse reflections are used to establish a link to a receiver facing toward the ceiling. In such a scheme, it is not necessary to ensure a perfect aligned path. On the counterpart, there is dispersion due to multipath propagation, which increases path loss and thus the required transmitter power for a given QoS.
In this paper, we investigate the use of wireless IR technology to perform the communication between the IR transmitter placed on the patient body coupled with medical sensors and the base station located on the room ceiling. Based on both LOS and diffuse configurations, our goal is to evaluate the reliability of a vital data transmission system based on IR technology.