# Low Power Multi-Hop Networking Analysis in Intelligent Environments
## 3 Test Bench  
After implementing some proprietary nodes with Bluetooth connectivity, the test bench was deployed. It was focused on studying the latency on multi-hop communications and included as many gateways as possible in a scatternet. The test bench consisted of a multi-hop wireless network of proprietary nodes based on Bluetooth technology. Figure 2 shows one of the implemented nodes for this research. The nodes included the WT-11 chipset of Bluegiga [43], as well as some general-purpose input and output components and test pins. The chipset included a firmware developed by Cambridge Silicon Radio [44], named BlueCore4 [45], that eases the low power modes defined in the Bluetooth specifications and analyzed in this manuscript, i.e., park and sniff. BlueCore4 includes the HCI Stack (version 19.2) to allow the development of proprietary middleware tailored to the specifications of the application. The proprietary middleware was designed using BlueLab [46], the software tool to develop embedded software given by the manufacturer of the chipset [44]. BlueLab eases the programming of the nodes at the HCI level, the lowest level that any proprietary middleware can access within the Bluetooth protocol stack. Moreover, the middleware included the processing tasks, which were limited to the most basic operations to restrict their influence in the latency. They integrated processes to initialize the communications, present the operation status and route data to other nodes. The data reached the node and they were stored in the input buffer until the processor attended the interruption flag. Similarly, the routines below the HCI level included in the standard define the wait since the data are delivered to the HCI level buffer until they are transmitted by radio. Since the processing tasks in the node were limited, such delay can be assigned to the regular operation of the communication standard.  
On the other hand, there is a wide variety of intelligent environment examples. They are wherever the ambiance can recognize people, personalize to individual preferences or even act upon their behalf [23; 47]. The research in this paper takes into account the deployments of multi-hop networks based on Bluetooth standard inside buildings, as it is the home deployment depicted in Figure 3. Here, the network access nodes are depicted as grey circles. Some sensors, as smoke or temperature ones, would be attached to the nodes, and the network could be accessed by wireless devices, as mobile phones. Besides, even though the mains are usually at hand in such indoor deployments, a battery is included in each node to overcome any failure in the mains that might happen.  
In the test bench, each pair of nodes built a piconet, and the interconnection of piconets formed a multi-hop network with linear topology. It can be said that the linear topology is one of the simplest  
Figure 3: Example of multi-hop network deployment for an intelligent environment inside a home (distances expressed in meters).  
Figure 2: Photography of one of the implemented Bluetooth nodes.  
topologies. However, it is the most suitable topology to study the performance of the desired amount of Bluetooth gateways with the least amount of nodes. In the network deployment, every halfway node performs as gateway and relays the data gathered from other sensor nodes (not depicted) to the DS. The DS keeps all the information available in the system and shares with all the devices through the multi-hop network. On the other hand, there is a network administrator that accesses the data in two ways. They can gain admission to the network through a mobile phone with Bluetooth connectivity or through a computer connected to the node labeled as number one.