# Wireless Sensor Networks for Smart Homes:
## 2 System Model  
Widespread networks of inexpensive wireless sensor devices concede a valuable opportunity to check more precisely the surrounding physical phenomena's when compared to conventional sensing methods. WSNs for smart homes are distinguished by scenarios in which tiny devices, like actuators and sensors, use most of their time in a sleep state and wake up with a given periodicity or when a critical event occurs. The WSN has its design restrictions, correlated with the purpose and the features of the installation context. The latter delimit the extension of the network, the deployment scheme, and the network topology. The network structure considered in this paper is represented in Figure 1 and is composed of several Home Monitoring Cells (HMCs) based on the IEEE 802.15.4 wireless standard [38].  
Two network topologies are maintained by the IEEE 802.15.4, i.e., peer-to-peer and star. Several purposes would typically employ a one-hop star topology. On the contrary, the peer-to-peer topology can be adopted for more elaborate arrangements, like the cluster-tree and mesh networking topologies, and can be the favored option for purposes such as smart homes. An IEEE 802.15.4 network can operate either in beacon-enabled or in non-beacon-enabled mode. In the former method, the transmission is managed by a network coordinator, which delivers regular beacons for synchronization and correlation procedures. In the non-beacon-enabled mode, there are no regular beacons, but the coordinator may unicast beacons to a soliciting device. The transmission among devices in the non-beacon-enabled mode practices the un-slotted CSMA (Carrier Sensing Multiple Access) for decentralized access. Furthermore, in the beacon-enabled method, the standard permits the energy saving by fulfilling the duty cycling, so that all nodes can periodically go to sleep. For this reason, in this paper, the IEEE 802.15.4 network works in the beacon-enabled mode.  
The wireless network for smart home considered in this work is constituted by all the HMCs within which various devices are dealing with a specific task. Considering the IEEE 802.15.4 standard, Reduced Function Device (RFD) nodes evaluate a physical parameter of the monitored environment, such as temperature, humidity, light, smoke density, carbon monoxide, and so on. Suddenly, they send the acquired data to their Full Function Device (FFD) nodes. An FFD node could be a ZigBee router [53]. It forwards data obtained by RFD nodes to the First Pan Coordinator (FPC) that processes information and sends proper command messages to the sensor nodes. It is helpful to note that in the IEEE 802.15.4 the transmission range changes considerably based on the nature of the path that must be in a line of sight (LOS) for the most part. The transmit power level and receiver sensitivity are also characteristics to take into account. Under the favorable conditions, the range can be as high as 1000 m with a clear outdoor path. In this case, proper hardware with range extender is needed to improve the receiver sensitivity and increase the total link budget, enabling up to four times the range of each node in the network. For instance, considering ZigBee PRO [54], sub GHz channels transmission ranges up to 1 km. Most applications cover a shorter range of 10-75 m. Anyhow, it is essential to take into account the energy consumption of battery-powered wireless devices. Accordingly, the Fuzzy Controller presented in this paper, detailed in Section 3, can be a proper solution to ensure adequate power consumption management. This module dynamically handles sampling times to increase the sleeping periods of sensor nodes. In this way, it is feasible to increase energy savings and, at the same time, prolong the batteries and network life-cycle.  
Figure 1: Network architecture.