## 4 Energy Efficient Protocols, and Scheduling in WBSNs  
Bluetooth and ZigBee can be used for data transmission between sensor nodes and PS, while Wi-Fi and 4G LTE technology are used for data transmission from PS to a medical center. In this section, we provide a brief descriptive comparison of existing communication protocols for WBSNs including Bluetooth Low Energy, ZigBee, Wi-Fi and 4G LTE, ANT+, NFC and Nike+, see Table 2. We also present medium access control or MAC which provides transmission channel access to multiple sensor nodes. The MAC layer is one of the most convenient options to achieve better energy efficiency in medical application networks. We start by discussing briefly the most common communication protocols in use:  
* ANT+: It is an expanded version of the original ANT protocol to make the devices interoperable in a managed network. It was developed by the sensor company Dynastream in 2004 and it is considered a low power wireless technology. This protocol operates in the 2.4 GHz spectrum. ANT was created with the objective to communicate sports and fitness sensors with a display unit [33], which encourages its application in healthcare and telemedicine areas. Up to 64,000 members could participate in an ANT+ network; in ANT technology, the frequency channel is divided into many communication channels partitioned by time, allowing the sensors to remain in sleep mode for prolonged periods of time achieving important energy savings [34]. * NFC: NFC is for short-range wireless links operating at 13.56 MHz in the high-frequency (HF) band. His range of operation is approximately 4 cm and for this reason and its higher energy consumption compared with other low power wireless technologies (BLE or ANT+), it cannot be considered a direct competitor [34]. NFC involves two devices: an initiator (active) and a target (passive); the initiator actively generates an RF field that can power a passive target. Since passive targets do not require energy source, they can take different forms as tags, stickers, key fobs, or cards. In addition, peer to peer communication is possible, provided that both devices are powered (e.g., data exchange between two smartphones) [35]. * Nike+: It is a wireless technology created by Nike and Apple in 2006, (it will only work with devices of these brands) and operates in the 2.4 GHz spectrum supporting 250 Kbps or 1 Mbps transmission rates [36]. It was developed to monitor user's physical exercise. Nike+ consists on a sensor attached to the body and a receiver, for example, a wrist band, watch or smartphone. * ZigBee: It is a low power wireless protocol based on standard 802.15.4.2003, that was developed for applications that need network flexibility, security, high reliability, low cost, and simplicity. It is an _ad hoc_ self-organizing network, and it was created for short range large-scale networks (over 65,000 for a ZigBee star network [37]) with low duty cycle and secure networking, but with smaller throughput needs and for low data rate applications. There are several covering areas for ZigBee such as: home automation, industrial, medicine, smart energy, telecom services, _etc._ For healthcare, ZigBee provides secure and reliable remote patient monitoring and management, with maintained freedom of mobility [33]. Some medical devices like glucometers, pulse oximeters, electrocardiographs and weight scales support ZigBee protocol. * Wi-Fi: Wi-Fi is based on the IEEE 802.11 standards, letting users surf the Internet at broadband speeds when connected to an access point (AP) or in _ad hoc_ mode. It is ideally suited for large data transfers, but unfortunately, it needs large batteries [33]. Wireless local area networks provide high-speed wireless connectivity and support information access anytime anywhere, allowingvideo-conferencing, voice calls, and video streaming. An important advantage is that all smartphones, tablets and laptops have Wi-Fi integrated, and the main disadvantage for Wi-Fi is high energy consumption even if its throughput is reduced.