# Vertical Handover Algorithm for WBANs in Ubiquitous Healthcare with Quality of Service Guarantees
## 2 Related Work  
WBAN architectures are typically composed of three tiers, such as intra-body (tier-1), extra-body (tier-3) and inter-Body Sensor Network (BSN) communications (tier-2) [7]. These WBAN communication tiers must efficiently deliver the data to the decision makers at the application side with QoS guarantees and must minimize energy consumption. Hence, many solutions have been proposed to support three-tier body sensor network communications; in this paper, we focus on the tier-3 aspect. In extra-body communications, many wireless technologies have recently been investigated in WBAN applications for the purpose of ubiquitous healthcare. Internet/WiFi/Cellular networks are used in CareNet [8], WiMoCA [9], and MIMOSA [10]. In more detail, CareNet effectively addresses reliability as well as privacy-preserving patient data transmission. With its flexibility, WiMoCA can fulfill diverse application requirements in an accurate and timely manner, whereas MIMOSA is a smart architecture for mobile terminals and is optimized for flexibility and low-power short-range radios. Furthermore, the authors in [11] have proposed two novel network models by the integration of Zigbee with WiMAX and an LTE network. A network model with LTE achieved a lower delay transmission in comparison with WiMAX; however, they both can effectively support a high burst of data and are suitable for real-time data transmission. Similarly, an integration of WBAN and LTE has also been investigated to support high user mobility and reduce content delivery delay [12]. In addition, an efficient content distribution scheme was presented to reduce costs and packet loss as well as the increase bandwidth efficiency by leveraging the benefits of Name Data Networking technology [12; 13]. As mentioned previously, a solution that involves integration can help users to transmit/receive content at any time and from anywhere depending on the wireless network coverage in that place. However, these solutions of integration and interoperability will face great challenges in terms of their technological diversity, and one challenge is the handover problem [14; 15]. Therefore, to clarify this problem, we also present some recent studies that pertained to our work. For seamless and secure handoffs in wireless environments, handover decision making can be decided by a single metric or a combination of attributes from a network (bandwidth, Received Signal Strength Indicator (RSSI), security, data rate, latency and reliability) to user preferences and devices (monetary cost, user profile preference velocity and battery power) [16]. A single metric is known as a horizontal handoff decision (HHD), which chooses the best network based on one attribute (e.g., the Received Signal Strength, RSS). The RSS approach proposed in [17] is used in a comparison of the RSS thresholds that are measured by different mobile terminals. When the measured RSS of a wireless network falls below the defined thresholds, the handover procedures to 3G will be activated immediately afterward. Although HHD approaches are simple and easy to implement, they suffer many restrictions, such as unnecessary handovers, high-energy consumption and the ping-pong effect. A combination of attributes is known as vertical handoff (VHD), in which the decision parameters for handover not only consider poor RSS but also the availability of other networks that have better services. Many potential VHD schemes have been conducted in different categories to compare each algorithm to others in terms of complexity, flexibility and reliability, including User-Centric [18], Markov [19], Fuzzy Logic [20], MADM [21] and Game Theory [22]. Among the existing VHD strategies, MADM is one of the schemes that based on strong multi-attributes to select the best from a list of available networks that have medium complexity and high flexibility.