## 3 The Proposed Solution
### Wireless Network Architecture  
Bluetooth Low Energy [8] operates in the 2.4 GHz ISM band with only 40 channels spaced 2 MHz apart. It is capable of transmitting at a rate of 1 Mbit/s using GFSK modulation. Like Bluetooth Classic, it uses frequency hopping, but it uses an adaptive frequency hopping and has a slower rate. BLE uses three of the 40 channels to advertise, which allows the device discovery. After a device is discovered and connected, the remaining 37 channels are used to transmit data. In a piconet of Bluetooth Classic, each master device establishes the frequency hopping sequence and can have up to seven slave connections. There is no such limitation in BLE, and in fact, \"theoretically\", to a master node can be connected \"hundreds\" of slaves. The relatively short transmission distances between the electrical appliances and the limited amount of data to be transmitted in a certain time interval can be deemed as other important factors in the selection process of the BLE protocol. It is useful to note that the range of BLE radio may be optimized according to the application. The majority of Bluetooth devices on the market today include the basic 30-foot (or 10-meter) range of the Bluetooth Classic radio, but there is no limit imposedby the specification. With BLE, manufacturers may choose to optimize the range to 200 feet (about 67 meters) and beyond, particularly in home sensor applications, where a longer range is a necessity. The proposed network architecture, shown in Figure 2, is composed of several independent wireless cells (WCs), managed by a BLE master device that acts also as the EMU and integrates the smart meter module. The whole WN is composed of all of the WCs within which are the field devices (FDs), which are Bluetooth Low Energy devices dealing with a specific task, or are associated with home appliances through smart plugs. It is easy to deduce that in the proposed network architecture, some of the WCs behave as wireless sensor networks (WSNs), because they can continuously monitor environments with less human effort and are low cost and low power. In fact, through wireless communication, the master node receives and processes data detected by FDs placed inside the WC. It also allows sending user commands or system commands to FD nodes. Furthermore, wireless links allow the communication among mobile devices (such as smart phones or tablets) and the WCs. As a consequence, people can authenticate themselves inside the home automation system and subsequently monitor data detected by sensor nodes and, if needed, send commands. Considering Figure 2, it is useful to evaluate the blocking effects between BLE master and slaves, due to walls or obstacles in rooms. Thanks to a modified modulation, BLE has an approximately 3 dB better link budget compared to Classic Bluetooth. A BLE unit can thereby offer a range of 200-300 m in the line of site without the need for an additional power amplifier. It is important in the aspects of robustness and reliability to have an appropriate placement of several devices in order to bridge temporary obstacles and interference. However, home sensors and actuators often need a range of 20-50 m, whereby it would be not necessary to use power amplifiers. On the contrary, considering that the range of BLE  
Figure 2: The proposed BLE-based wireless network topology. radio may be optimized according to the application, BLE manufacturers may choose to optimize the range, because there is no limit imposed by the BLE specification. The proposed WN enables a variety of use cases; for this reason, a non-exhaustive list of examples is provided below:  
* smart energy: window shades, HVAC, central heating, and so on, may be controlled depending on the information collected by several types of sensors that monitor parameters, such as temperature, humidity, light and presence; as a consequence, unnecessary waste of energy can thus be avoided. * smart meters: they can be used to detect usage peaks and alert the household devices that may be causing them.