## 1 Introduction  
A body area network (BAN), sometimes called a wireless body area network (WBAN), is a network of miniature battery-powered intelligent medical sensors equipped with wireless transmitters, which may be embedded inside the body as implants or mounted on the surface of the body [1, 2]. These sensors usually provide continuous real-time localized or remote health monitoring for medical staff via recording or transmission of physiological data [2]. Typically, the communication link in a BAN may be categorized as intra-body or extra-body [3]. The former type refers to communication between sensors or between sensors and a coordinating device located on the same body, while the latter involves additional communication between sensors located on the body and a remote medical center or personal device via the coordinator [3; 4]. The growth in aged population has increased health spending significantly owing to higher global demand for medical treatment and long-term nursing. Moreover, various infectious pandemics have further elevated health expenditures, pushing professionals to seek technology-oriented and cost-efficient solutions. U.S. healthcare spending was USD 4.3 trillion in 2021, or USD 12,914 per person, and accounted for 18.3% of GDP [5]. While this was less than the unprecedented 19.7% of the GDP in 2020 due to the COVID-19 pandemic, it is higher than 17.6% in 2019 and 2018. It is projected that health expenditures will grow at a rate of 5.1% per year over 2021-2030 [5]. E-health and telemedicine solutions are gaining popularity and being rapidly implemented globally, especially after the outbreak of COVID-19 pandemic, as a means to improve quality of life while reducing health budgets. Therefore, BANs are becoming acknowledged as a major constituent of e-health systems that allows sensing and timely transmission of patients' physiological data from several medical sensors to remotely located medical staff [6]. In this way, the workload and required number of clinical staff can be reduced using e-health solutions, resulting in higher efficiency on the part of medical staff and reduced healthcare expenditures. BANs were first regulated by Task Group IEEE 802.15.6, and a relevant standard based on RF technology was published in 2012 [7]. This standard was stipulated based on a wireless channel model obtained through measurements. Later, it was found that prolonged RF exposure may result in the malfunctioning of medical equipment and even damage the health of patients and medical staff [8]. Therefore, it is envisioned by experts that future BANs should have high throughput while being compatible with the green radio (GR) trend, resistive to EMI, utilize license-free spectrum, and have low installation and maintenance costs, among other requirements [2]. These intended features have recently been realized by integrating BAN and FSO, with the resulting technology being termed OBAN [9]. The intra-body or extra-body communication in OBANs is enabled through light beams in visible or IR range that are modulated with medical sensors data. OBAN is a relatively recent research field; therefore, abundant published work is not yet available. Works related to OBAN published over the past decade include [2; 4; 6; 8; 10; 11; 12; 13; 14; 15; 16; 17]. [PERSON] et al. proposed secure OBAN architectures based on spectral amplitude coding-OCDMA (SAC-OCDMA) [2] and optical chaos [8]. [PERSON] et al. proposed OBANs based on visible light communication (VLC) enabled through a mobile phone camera [4] and via orthogonal spreading codes [10], and discussed patient mobility models [11]. [PERSON] et al. proposed FSO channel characterization and performance analysis with patient mobility [6], an intra-OBAN channel modelling and multiple access scheme [12], and channel modelling between sensors and a coordinator [13]. [PERSON] et al. proposed channel modelling for a diffused optical channel between on-body sensors [14] and a star OBAN topology based on a diffused optical channel and spreading codes [15]. [PERSON] et al.