# Bluetooth Low Power Modes Applied to the Data Transportation Network in Home Automation Systems
## 2 Home Automation Systems
### Bluetooth Applied to Home Automation Systems  
The requirements for a wireless home automation system are fulfilled by Bluetooth standard [14]. This technology has been included in the data transportation network of many home automation solutions [16; 17; 18; 19; 20; 21]. In fact, Bluetooth protocols have significant potential to support deterministic behavior, i.e., real-time, asynchronous communication [22]. Many issues give relevance to the analysis of the wireless networks performance. First, the use of wireless networks for constrained response time applications is increasing. Next, the transmission medium is usually considered as inaccurate. Finally, the latency increases randomly due to both, the retransmissions that the medium inaccuracy leads to, and the unpredictable delay between the delivery of data to the host interface and radio transmission. Therefore, the latency shows a non-trivial variability [10] that should be analyzed. Because of the efforts on Bluetooth, an extensive literature is available on many aspects of Bluetooth networking. Next, the state-of-the-art of Bluetooth networking performance analysis is summarized. The performance is evaluated with QoS metrics. There are two types of metrics: traffic dependent or traffic independent [23]. The first ones involve the specification of a defining source, packets destination and traffic profile. In addition, packet flows are considered. Consequently, the evaluation of traffic dependent metrics is difficult, and traffic independent performance measures are frequently used. The most common of traffic independent performance metrics are the bit error rate (BER), the throughput and the latency. For example, the first two of these metrics, i.e., the BER and throughput, were analyzed under noise and interference conditions [24] in scatternets. Furthermore, a mathematical model to analyze the performance of Bluetooth data links was provided [25], in terms of many metrics, latency included. Some other analytical approaches to the performance of piconets were validated with simulation engines [26; 27; 28]. However, none of the results in these researches was validated in hardware test benches so that the model proposals get close to the real world performance. In addition, some theoretical models to define the communications inside piconets were already proposed. For example, the latency in asynchronous communications in piconets was studied [29],as well as analyzed when particularized for connections using serial port profile [30]. Moreover, the latency in the communications in a piconet follows a step outline with the length of the data packets as a result of the data segmentation [31]. All of them were empirically validated in actual piconets. On the other hand, the file transfer delay (FTD) was introduced in a piconet. It included the time delay of the packet, and the delays due to encapsulation/de-encapsulation, signal propagation and retransmission. Then, an empirical model was proposed to foresee the FTD in a piconet without theoretical support [32]. Generally speaking, the latency in scatternets has barely been analyzed. However, the latency in a three node scatternet was determined [33]. It included a slave-slave gateway. The authors pointed out that the communication between a master and a slave node is not symmetric and involves different latency values. However, a real world scenario should include more than one hop. Real world home automation solutions designers need models of the main metrics of wireless networks, so that they can determine the application range of a specific wireless standard. Actually, low power modes with a defined period of inactivity are almost mandatory in wireless home automation deployments. Theoretical calculations and simulation engines cannot foresee all the real-world issues; thus, empirical models are required to analyze the viability of specific wireless applications [34]. In fact, a few empirical models on latency have been obtained in Bluetooth multi-hop networks [13; 35].