# A Multiprotocol Wireless Sensor Network for High Performance Sport Applications
## 1 Introduction  
High performance sport, i.e., sport at the highest level of competition, requires advanced technology, as each competitor tries to gain the winning edge through incremental improvement. Data acquisition plays a fundamental role in this competitive environment, as it supplies athletes and coaches with quantitative insights into every aspect of performance [1; 2; 3]. Sensors used in sport data acquisition range from kinematic (GPS units, accelerometers, gyroscopes, velocity meters, etc.) to dynamic (load cells, strain gages, brakes, etc.) and physiological (heart rate monitors, thermometers, etc.) [4; 5; 6; 7; 8; 9; 10]. Several types of sensors are often bundled together: A typical example is the cycling computer that acquires data coming from the global positioning system (GPS), heart rate monitor, power meter, gears, and more [11]. Systems used in sports normally feature a central unit (master node), where the microcontroller (MCU--microcontroller unit) is located, and a series of sensors (slave nodes) [12]. The communication between master and slave nodes can occur via cables (wired sensor network) or be wireless (wireless sensor network, WSN). WSNs are particularly suitable in sport applications, as cables can hinder the motion of the athlete(s) during training and competitions [13]. Nowadays, several wireless protocols are available on the market; Table 1 illustrates the main features of each of them. These vary in topology, application throughput, complexity of the software interface, ease of configuration, addition of extra sensor nodes, transmission range, and power consumption [14; 15; 16; 17; 18; 19; 20; 21; 22]. Concerning the maximum data rate and transmission range, these values must be understood as maximum theoretical values that can be obtained only in an outdoor space free of obstacles and radio interference. For a long time, in the sport device industry, proprietary and incompatible WSN standards only have been used. Indeed, only in early 2000 was a wireless common communication standard suited for sport and health applications defined and agreed among different main vendors (advanced and adaptive network technology--ANT+ [22; 23]). The main features were a very low energy consumption, a high number of connectable nodes, and high robustness to interference. Nowadays, the growing popularity of consumer portable devices, such as tablets and smartphones featuring embedded Bluetooth [23], and more recently, Bluetooth low energy (BLE) [24], has led to a large diffusion of \"apps\" suited for connection with sport systems. For example, when Apple Inc. supplied BLE in its devices, several fitness products were developed with a MAC iOS software to be compatible with these terminals [25]. Thus, today, the development of a new WSN cannot ignore the use of such personal mobile terminals and should leverage the transmission protocols available on them (typically Wi-Fi and Bluetooth). The use of ANT+ on a mobile phone, for example, would require the use of additional hardware. Moreover, today, with 75%, the Android operating system (OS) holds the biggest market share for tablets and smartphones, while Windows and MAC iOS are still dominant in laptop and desktop computers [26]. This requires the development of different software tools depending on the nature of the terminal and the relevant OS. Therefore, from a communication protocol point of view, the constraints in building up an effective WSN suited for sport applications can be identified in the use of personal portable terminals, wide transmission range among the nodes, low power consumption, and easy addition of extra sensor nodes. The transmission range is a particularly severe constraint, as most existing systems for sports are