# Low Power Multi-Hop Networking Analysis in Intelligent Environments
## 2 Intelligent Systems at Home
### Bluetooth Applied to Intelligent Systems  
Intelligent systems developers usually make good use of the large amount of technological breakthroughs in the areas of, for instance, wireless sensor systems, wearable electronics, ubiquitous communication, ambient database systems, conversational interfaces, content creation tools, and vision algorithms [21]. As a consequence, an intelligent environment typically is embedded, ubiquitous, anticipatory, responsive, sensitive, adaptive, and transparent [18; 22]. The requirements for an environment to be called intelligent are fulfilled by Bluetooth standard [24]. This technology has been included in the data transportation network of many proposals for intelligent environment systems [26; 27; 28]. Actually, Bluetooth protocols have significant potential to support deterministic behavior, i.e., real-time, asynchronous communication [29]. There are many issues that give relevance to the analysis of the performance of wireless networks. To begin with, there is an increase in the use of wireless networks for constrained response time applications. Secondly, the transmission medium is usually considered as inaccurate. And finally, there is a random increase in latency 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. This increase make the latency show a non-trivial variability [16]. On the other hand, as a result of the efforts in research 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. In fact, the performance is assessed by means of QoS metrics. There are two types of metrics: traffic dependent or traffic independent [30]. The firsts require the specification of a defining source, packets destination and traffic profile. Besides, packet flows are considered. As a consequence, the evaluation of traffic dependent metrics is difficult, and traffic independent performance measures are frequently used. The most common of these last metrics are the bit error rate (BER), the throughput and the latency. For instance, the first two of the traffic independent metrics, i.e., the BER and throughput, were analyzed under noise and interference conditions [31] in scatterers. Moreover, a mathematical model to analyze the performance of Bluetooth data links was provided [32], in terms of many metrics, latency included. But none of the results of these researches were validated in hardware test benches so that the model proposals get close to the real world. In the same way, some other analytical approaches to the performance of piconets were validated with simulation engines [33; 34; 35]. Furthermore, there are several proposals of theoretical models to define the communications inside piconets. For instance, the latency in asynchronous communications in piconets was studied [36], as well as analyzed when particularized for connections using serial port profile [37]. Besides, it was shown that 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 [38]. All of them were empirically validated in actual piconets. On the other hand, the concept of file transfer delay (FTD) was introduced in a piconet, which 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 [39]. On the whole, scatternets have barely been analyzed in terms of latency. The latency in a three node scatternet was determined [40]. It included a slave-slave gateway. Even though they pointed out that the communication between a master and a slave node are not symmetric and involve different latency values, it is a fact that a real world scenario should include more than one hop in the wireless network.