# Body Area Networks in Healthcare: A Brief State of the Art
## 1 Introduction  
Improvements in several aspects related to quality of life like public access to physicians, medication, good nutrition and safety have produced an increment in the longevity of the population around the world. According to the United Nations, the population aged 60 years and over is estimated at 962 million in 2017 and the growth rate is about 3 percent per year [1]. The population aged 60 and over is expected to be around 2.1 billion in year 2050 and 3.1 billion in 2100. Notice that Japanese aging adults have reached 27% of the population in 2017. Unfortunately, such an increase supposes various inconveniences. For instance, this also means that the percentage of the working population is decreasing each year. For this reason, many governments are experiencing monetary difficulties to cover social security and healthcare costs. In addition, people suffering from chronic diseases is increasing worldwide [2]. In year 2001, 46% of reported deaths in the world were caused by chronic diseases. The World Health Organization predicts that deaths caused by chronic diseases will increase to 57% by year 2020. Diabetes, obesity and cardiovascular diseases, especially in the aging population, cause almost half of the deaths produced by chronic diseases. These diseases affect a great amount of the population, even manifesting earlier in life. Therefore, early detection is imperative to fight against these diseases. Precisely, this can be achieved using noninvasive devices to monitor the health status through detecting and preventing chronic diseases based on a body area network (BAN). A BAN is formed by tiny devices which collect and transmit several kinds of information from multiple sources. BANs are applied in many fields, although some of the most significant application areas are healthcare and medicine. For this reason, BAN applications are usually divided into medical and non-medical applications [3]. In the first case, BANs are used to monitor patients suffering from chronic illnesses such as cardiovascular diseases, asthma or diabetes, among others. In this group of applications, BANs monitor the patients' vital signs permanently and, when a mishap occurs, it alerts the emergency services. The information is available at any time of the day. This helps the medical doctors to provide an accurate diagnosis and treatment. BANs can also help in cases of body rehabilitation and disability support [4]. Not surprisingly, there are many high quality surveys related to BANs that have been published in the last years. In 2011, two early surveys [5,6] focused on BAN/WBAN (wireless BAN) communication types, sensor devices, physical and data link layers, quality of service and security. Afterwards, a new survey [7] showed interest in intrabody communication (IBC) as alternative wireless communication technology, demonstrating mathematical models, IBC transceiver designs and core fundamentals. That same year, the IEEE 802.15.6 standard was used to review on-body, in-body and off-body propagation models in WBANs [8]. Next, an overview of the main applications, technologies, standards, issues and the future of WBANs was reported [9]. The authors also included some real cases and experimental studies. Furthermore, during the last three years, surveys of specific issues within BANs have also been delivered. For instance, security is a fundamental aspect in any network where devices are susceptible to be attacked on sensitive information. This is the reason why many researchers orient their work to the development of techniques to avoid attacks in BANs. An overview of security in BANs, where the authors focused on key agreement schemes and methods used to evaluate security and performance have been introduced [10]. Similarly, there is a review on reliability and fault tolerance in WBAN solutions [11]. There is also a very recent paper that reviews the state-of-the-art of network architecture topologies and applications in Internet of Things (IoT)-based healthcare solutions [12].