# Performance Evaluation of Bluetooth Low Energy: A Systematic Review
## 1 Introduction  
Bluetooth Low Energy (BLE, Bluetooth 4, Bluetooth Smart) is an innovative technology, developed by the Bluetooth Special Interest Group (SIG), which aims to become the best alternative to the huge number of standard wireless technologies already existing and widespread on the market (i.e., IEEE 802.11b (Wi-Fi), ZigBee, ANT+ and Bluetooth Classic (Bluetooth 3.0, Basic Rate/Enhanced Data Rate)). The synergy between good performance and ubiquitous diffusion (today, BLE is available in all PCs, tablets and smartphones) makes BLE an excellent candidate for a great variety of applications: in the medical field for e-health applications [1; 2; 3], e.g., in a body area network [4] (using ECG [5; 6], a heart rate sensor [7; 8], a blood flowmeter [9], EMG for prosthetic hand control [10] and an IMUsensor used for early diagnosis of [PERSON]'s disease [11]; it is also used to monitor respiration, activities and falls [8]), in automotive applications [12; 13], in voice communications [14], for kinematic tracking [15; 16], in domotics for healthcare environments and smart houses [17; 18; 19; 20], for transmission of M-IMU data in game controlling [21], in security systems [22; 23], to understand crowd dynamic [24], and so on. It has been successfully used for position detection and distance measurement using beacon communication. In this modality, different devices or sensors, provided with the BLE interface and placed in a structured environment, are programmed to send broadcast messages (described in Section 2.2.1) so that listener devices (e.g., user's mobile device) can receive them. In this way, it is possible to send some pieces of information about the surrounding area [25], or to detect the user position [26; 27; 28; 29; 30; 31; 32], or to measure the distance between sensor devices in the environment [33; 34], or also to detect the presence of devices, and so people [22; 24; 35; 36; 37; 38]. Moreover, thanks to its versatility and low power consumption, BLE has also been applied in Internet of Things (IoT) technologies [39], for example transmitting Internet Protocol Version 6 (IPv6) packets over Low power Wireless Personal Area Networks [40; 41; 42] (6 LowPAN) in health monitoring application [43]. This has also been possible thanks to the 6 LowPAN work group of the Internet Engineering Task Force (IETF) that has proposed several standards and drafts to specify the header compression scheme for IPv6 packet delivery in low power wireless networks [44]. This fact has also led to the definition of specific function packs, implemented in dedicated MCUs, which allow one to connect 6 LowPan IoT nodes via BLE interfaces [45]. The studied examples strongly benefit from BLE characteristics, in particular its low power consumption, which allows it to be embedded in small devices with low-charge and small batteries, which can also last a few years. For all these reasons, BLE is a good candidate to be a revolutionary technology in the present market of wireless communications. Notwithstanding such promising applications, the BLE still lacks a complete and systematic analysis of its real performance under different experimental conditions, which could help designers to develop optimized devices for specific applications. This review's purpose is to obtain a useful compendium of BLE, describing its main specifications and characteristics and proposing a roadmap to a systematic characterization of its performance, in order to pave the way for further studies. In addition to this, in late 2016, Bluetooth SIG released Bluetooth 5 specifications. This new Bluetooth technology offers improvements in performance, such as range, data rate and advertising channel functionality, and some studies have already tried to find out its characteristics [46; 47]. Our work can also help further studies to systematically analyze this new technology, as already done with BLE.