## 2 Literature Review
Its authors propose a three tier architecture for health monitoring systems: (1) an intra-BSN tier, where body sensors collect physiological signals and then send data to a nearby personal server (PS) device; (2) an inter-BSN tier, which represents the communication between PS and one or more access points (APs); and (3) a tier for the use in metropolitan areas with a data base for medical record consulting and medical attention in real time through video conference, calls and text message by cell phones. Section 7 of [13] presents comparative information about some of the different BSN projects that have been conducted and a description of the diverse application areas (military, sports, healthcare) for WBSNs. Although [13] presents relevant information for BAN design, proposals to minimize energy consumption was not addressed. A study of effective routing protocols in WBSNs is given in [14], where issues and challenges in terms of network topology, topological partitioning, body postural movements, short range transmissions, energy efficiency, and the overall network lifetime are addressed. The authors also present a discussion about limited resources, like Radio Frequency (RF) transmission range, poor communication capabilities, storage capacity and low bandwidth. In [15], the authors elaborate different application scenarios for healthcare and human-computer interaction, sensor/actuator devices, radio systems, and interconnection of WBSNs to provide a perspective on the trade-offs between data rate, power consumption, and network coverage. Also, authors presented a review of sensor devices, design characteristics and classifications (chemical, thermal, mechanical, and acoustic). The main contribution relies on an extensive review for the emerging and existing standard Radio Technologies for WBSNs and WPANs like Bluetooth Low Energy, UWB, Bluetooth 3.0, and Zigbee. This review also covers the open technologies like Insteon, Z-Wave, ANT, RuBee, and RFID. To apply these technologies, [15] points out that many issues remain to be addressed, one of those issues being the physical characteristics of sensor/actuator materials and electronic circuits. A second issue is the development and evaluation of improved propagation and channel models. A third issue is the management of resources and networking, and among other issues of importance are security, privacy, and power supply. A detailed investigation of the recent studies in WBSNs, challenges and results in the field from the perspective of the actual standard IEEE 802.15.6 is introduced in [16], with details on challenges and address allocation schemes for routing protocols; security requirements protocols and their energy consumption. A typical architecture of the system for a WBSN is divided into three tiers: Intra-WBSN, Inter-WBSN and Beyond-WBSN. Finally, relevant studies have been conducted with the objective to optimize the BSN lifetime. In MEDISN [17], although some tests are done in hospitals, the coexistence between different technologies and noise signals that can be found inside a building is not evaluated. This evaluation is important to determine how much the network behavior will be affected using a deployment with multiple sensors operating at different transfer rates. With respect to the estimation of energy consumption in a sensor node, authors in [18] show a mathematical model that evaluates the power consumption of the network architecture based on the correct number of cluster heads participating in the network. Our objective is to give readers a relevant overview of important issues in WBSNs in order to set into motion the development of an optimization model. Literature reviewed in this section helps us to understand each part conforming a wireless system for medical care delivery. Unlike the articles reviewed in this section, in our consideration, the meaningful impact is first to recognize the relevance and the influence of the WBSNs application for medical care delivery, especially in emergency situations.