## 2 Literature Review  
Previous surveys have concentrated on the analysis, discussion and global overview of WBSNs with the intention of orienting readers for future research work. It is important to say that there are many topics involved in the study of WBSN platforms, which makes difficult the standardization of ideas for the correct development of WBSNs. The authors in [10] presented a review of wireless sensor technology that divides sensor nodes into wearable sensors and implantable sensors, according to the type of signal acquired (glucose, blood pressure, oxygen saturation, temperature, _etc._). The authors also indicated that power inefficient protocols are the main source of energy waste. Additionally, they presented an efficient routing protocol integrated with the MAC layer and indicated important implementation issues such as: security, authentication, data integrity, confidentiality, availability and privacy. Production of microelectronic chips with new sensing elements and systems for embedded data processing and energy harvesting are important for efficient implementation of WBSN applications [11]. [PERSON], _et al._, in [11] are concerned with the study of energy efficient systems. The authors describe energy requirements, the subsystems of a WBSN node (sensing, data processing, control and communication subsystems), the strategies for data processing, a network topology through Cluster Heads (CH), routing methods, coding and modulation. The limited energy budget for WBSN applications makes necessary the visualization of an efficient use of energy. With respect to access methods, the authors mentioned the need to reduce collisions and transmit data with the minimum power and satisfying QoS parameters. Also, they discuss the challenges to minimize the transmission time, and the use of energy saving modes in network devices. In [12], the authors discussed differences between Wireless Sensor Networks (WSNs) and WBSNs and presented an overview of physical layer properties, including common issues of communicating near or in-body. The paper also presented diverse types of devices with different data rates and energy consumption, as well as the need of quality of service, security and ease-of-use. With respect to energy consumption, it is suggested a combination of energy scavenging and lower energy consumption techniques as an optimal solution to have an autonomous system. The paper also discusses positioning of sensor nodes and its effect over radio wave propagation. Authors mentioned that radio signals may experience great losses due to absorptions of power in tissue, in the case of sensor nodes implanted inside the body. When nodes are located along the body, they divide the propagation of radio waves into: line of sight (LOS) and non-line of sight (NLOS) for testing. Contrary to the WBSN architecture discussed in [10], a two-tier architecture is introduced. The first tier is for the intra-body communications; the sensor nodes are attached to the body and a portable device collects data. The second tier is for communications between the portable device and the internet, and from the internet to a medical server. Furthermore, authors discussed the routing strategies for WPAN's subdivided in two categories: routing based on the temperature of the body and cluster based protocols looking for a minimization of the energy consumption in the network. Finally, the authors pointed out the cross-layer protocols, as a way to improve efficiency. In [13], the main body sensors are reviewed, with a discussion on selected physiological signals, typical network topology and data rates used for each type of sensor. It also introduces issues that affect physical layer protocols such as channel modeling, antenna design for in-body sensors and support for upper layer WBSN protocols for an appropriate balance between data rate, transmission distance and power consumption.