# Bluetooth Low Power Modes Applied to the Data Transportation Network in Home Automation Systems
## 1 Introduction
Bluetooth is a worldwide communication standard without radio emission license cost. It allows for multi-hop networking with low energy consumption. Such features make Bluetooth the chosen wireless technology as the communication standard to implement multi-hop home automation networks. Even though there are differences among the releases of the Bluetooth standard, the chosen release, 2.0, is still on the cutting edge of the technology in terms of multi-hop transmission performance [13]. Then, focusing on obtaining the data that lead to the empirical model for the latency in the wireless communications, a test bench based on commercially available off-the-shelf (COTS) products was developed. Several nodes were developed with some Bluetooth communication modules. Such nodes are integrated into electronic systems for home automation deployments so that they can interconnect via wireless links. Moreover, the middleware to manage the performance of the node at the Host Controller Interface (HCI) level of the radio module was built, and the nodes were configured using high-level commands. Subsequently, the performance of Bluetooth gateways included in multi-hop networks was analyzed in the tests by measuring the end-to-end latency QoS metric. The data were analyzed statistically to limit the errors made in examining a finite set of samples, and the tests were repeated a lot of times. As a result, this paper analyzes the end-to-end latency of the multi-hop communication network to estimate the time performance of the transportation network for home automation systems. Several Bluetooth low power modes for the radio module of the nodes are available. Two typical Bluetooth low power modes have been considered here: sniff and park. The sniff mode keeps the biggest activity when nodes are in low power mode; and the park mode loses the most connectivity while nodes are parked. To the best of the authors' knowledge, there is no empirical latency analysis in Bluetooth low powered multi-hop communications. Therefore, this paper introduces the empirical models for the transmission latency from end-to-end in Bluetooth multi-hop wireless networks when working with Asynchronous Connectionless Links (ACL) in both, park and sniff low power modes. The models will benefit the home automation systems and wireless networks designers providing them with the estimation of the latency that every hop in the communication adds. The rest of the paper is organized as follows. Section 2 introduces a case study of wireless home automation networking. Furthermore, the multi-hop networking capability of Bluetooth standard and the way it is applied to such systems are explained. Next, Section 3 gives the features of the test bench developed in this research. In addition, Section 4 explains the details of the methodology of the tests. In Section 5, the results are discussed. After that, Section 6 proposes some models for the latency in the case study of multi-hop wireless communications networking. Finally, the conclusions are summarized and the future work pointed out in Section 7.