## 1 Introduction  
Heart disease is the leading cause of death worldwide. In 2016, 15.2 million people died as a result of ischemic heart disease and stroke globally [1]. In the same year, chronic obstructive pulmonary and lung diseases have killed 3 million and 1.7 million people, respectively, and while diabetes and dementia killed around 3.6 million people. At present, healthcare systems are facing major challenges due to rapid increase in human population, diseases, and health expenditure. According to [2], the healthcare cost in the United States was 17.9% of the total Gross Domestic Product (GDP) in 2017, and it is expected to reach 19.4% by 2027. Based on these statistics, the current healthcare systems require new cost-effective solutions. Wireless Body Area Network (WBAN) [3, 4] has emerged as one of the key technologies to provide long term, remote, and cost-effective health monitoring of patients, thus detecting early signs of diseases and providing feedback in real time [5]. A WBAN is comprised of small and intelligent sensors that are implanted under the human skin or deployed on the human body to monitor vital signs of patients. Such sensors may be used to control several diseases such as heart disease, diabetes, obesity, and other chronic conditions [6]. For example, electrocardiogram patterns may be exploited to improve health status of patients suffering from ischemic heart disease [7]. With the inception of WBAN technology, researchers have focused on evaluating existing standards such as IEEE 802.15.4 [8] for WBAN. However, these standards have not been adapted due to the stringent quality of service requirements of nodes operating in close proximity to human tissues [9].  
The IEEE has developed a new standard called IEEE 802.15.6 that allows wireless communication inside or near the human body, and satisfies the WBAN requirements [10]. This standard employs a Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol that enables access to the channel based on different user priorities and contention window sizes. The current version of the IEEE 802.15.6 CSMA/CA encounters low throughput and high delay when some of the nodes are hidden or exposed. The hidden node problem occurs when a node deployed on the human body may communicate with the hub but may not be able to communicate with other nodes that are communicating with the same hub. The exposed node problem occurs when a node is unable to communicate with the hub due to interference with the neighboring transmission. The hidden and exposed node problems occur in a variety of scenarios including when multiple IEEE 802.15.6 networks sharing the same spectrum coexist with each other or when some of the nodes in a single IEEE 802.15.6 network are hidden or exposed due to body shadowing effects [11]. These problems may also occur when the nodes are deployed on different locations with non-line of sight communication. The RTS/CTS scheme has been proposed to address problems of hidden nodes in IEEE 802.11 and IEEE 802.15.4 networks. The RTS/CTS scheme reduces collisions when nodes are hidden from the hub. In case of problems associated with exposed node, it may increase throughput only when nodes are synchronized and are able to hear the CTS packets. As discussed in [11], the RTS/CTS scheme has to potential to significantly improve performance of the IEEE 802.15.6 CSMA/CA protocol.