# Patient Mobility Support for Indoor Non-Directed Optical Body Area Networks
## 1 Introduction  
Rapid progression of healthcare technologies has been providing numerous benefits for human welfare and has improved the quality of health services provided to patients. These technologies aid doctors and medical professionals in monitoring patient health status in an incessant manner, and thus offer early detection, diagnosis, and monitoring of diseases that facilitate patients with optimal medical assistance [1, 2]. One such promising candidate for healthcare monitoring is wireless body area network (WBAN). Generally, WBAN is based on radio frequency (RF) technologies having wearable sensor devices mounted on the patient's body that are capable of various functions such as sensing, processing, and communicating physiological signals [3, 4]. Despite advantages of RF-based WBAN, such as flexibility and mobility, performance is limited by electromagnetic interference (EMI) and may result in erroneous information transmission. EMI can affect various healthcare devices such as fetal monitors, infusion pumps, syringe pumps, and ventilators [5, 6]. Moreover, the RF transmission of some biomedical signals, such as electroencephalography (EEG), electrocardiography (ECG) and photoplethysmography (PPG), suffers from a lack of precision due to interference, noise, and multi-frequency characteristics of various signals [7]. An alternative method is to employ optical wireless communication (OWC) technology for healthcare applications. The OWC link offers EMI-free data transmission along with minimizing RF health impairment effects around the patient's vicinity and can be employed inside sensitiveenvironments such as an intensive care unit (ICU) where RF-based devices are prohibited. In addition, optical wireless based systems are license free, compact, low cost, and have a high level of security [8; 9]. Recently, an infrared (IR) based patient mobility support scheme was proposed in a diffuse optical configuration [10]. The theoretical analysis of an on-body system with mobility support (both the IR emitter and the receiver placed on the patient body) was conducted using an optical code division multiple access (OCDMA) strategy over diffuse IR optical links [11]. Specifically, the power consumption with three transmitting nodes placed on the body was analyzed. However, there is a trade-off between the performance and the complexity if more medical sensors are employed on the body. Moreover, the analysis was validated only by the statistical approach without any practical or realistic demonstrations. To transmit some biomedical data using visible light communication (VLC), interesting studies were reported in the literature. A biomedical signal, such as an EEG, was transmitted via on-off keying (OOK) modulation using selection combining scheme [12]. It was experimentally demonstrated that this scheme offers a reliable transmission of the biomedical signal using the VLC. Unfortunately, the work did not consider the important issue of mobility support. A multi-patient vital signs data transmission using VLC was also presented. It employed orthogonal codes for separating each patient's data [13]. Like WBAN, patients are likely to move around in a room where an optical body area network (OBAN) (coordinator on the body and receiver at the ceiling) is established. Thus, the patient mobility support is considered one of the most essential and foremost aspects of hospitalized patients. The present study is motivated by the fact that there has been no patient mobility support using VLC links in an OBAN system in the literature. We developed a mobility scheme in an indoor OBAN. To support mobility in an OBAN brings new challenges and issues to the evolution of networks as it encompasses transmitter mobility rather than receiver mobility. The most convenient and performing configuration in OWC is the line-of-sight (LOS) link in which the transmitter and receiver are directed towards each other. The non-LOS (non-directed) mechanism is commonly employed in mobile-receiver based indoor optical wireless communication systems.