Overview
The growing energy consumption of data centers has emerged as a key challenge to the IT industry. In the joint Data center energy management project with IBM's Watson Research Center, we are contributing to the evolution of measurement and management technology (MMT) for acquiring and processing environmental data produced by a data center. The original MMT tool employs a mobile cart with wired sensors for acquiring temperature and humidity data. Air flow readings are taken with a manual sensor. To allow real-time data capturing, we deploy wireless sensors that use IEEE 802.15.4 technology with ZigBee/mesh networking or proprietary protocol stacks, and IBM's MQTT messaging to connect the sensors with monitoring and processing applications. Measurement campaigns are performed in IBM data centers and at customer sites. Temperature maps derived from these measurements are used for identifying hot-spots and cooling inefficiencies. The insights show us what measures need to be taken to improve air flow and cooling efficiency to achieve significant energy savings and better operational reliability of a data center.
Middleware for sensor systems: Publish/subscribe messaging is widely used for efficiently connecting a large number of data sources with multiple applications. Topic lists are maintained by a broker that accepts data published by the sources and passes it to subscribers. This is especially efficient in systems where the data sources are active only infrequently and the applications subscribe only to a subset of the available data. We have developed a version of IBM's MQTT pub/sub messaging protocol to allow operation over wireless links, e.g. ZigBee, Bluetooth, or GPRS. The specification of MQTT-S has been published at mqtt.org, and a lean implementation for low-power sensor nodes is also available. In addition, we are working with IBM business units on customer opportunities where MQTT-S is an important enabler for connecting sensor devices with IBM application environments.
To evaluate the functionality and performance of wireless technologies that are relevant for sensor networking, we have built a sensor system lab that supports IEEE 802.15.4 devices with ZigBee or TinyOS protocol stacks, and multi-hop / mesh networking. ZigBee sensor networks have been deployed in our office building and in the local data center. Each sensor node is equipped with sensors that measure temperature, humidity, and light intensity. To assess the behavior of MQTT-S, we have written several applications that use MQTT-S for capturing sensor data and sending control information to sensor nodes.
We are working on location sensing and routing protocols for tracking objects and persons in indoor environments where GPS is not feasible. Wireless sensor nodes are installed at static reference positions. Mobile nodes estimate their position using radio signal-strength measurements, data derived from inertial navigation sensors, and Kalman filter processing. Positions are broadcast to the static nodes and used by a geographic routing protocol in the wireless mesh network. We have prototyped the concept in a real-time testbed. Measurement results show a position accuracy of 1-2 m. Potential applications include scenarios in the retail industry ("Store of the future"), asset management, and transportation.
Past activities
We participated in the two-year EU project e-SENSE. Together with leading partners from industry and academia, we developed a new architecture for wireless sensor networks and their integration into "beyond 3G" mobile communication systems. We contributed to the e-SENSE system architecture, the design of a lightweight protocol stack ("e-stack"), and novel distributed middleware concepts. A special focus was to develop advanced "cooperative relaying" algorithms and lightweight distributed pub/sub protocols to obtain a scalable, power-efficient multi-hop WSN.
In addition, we participated in the initial phase of follow-on project SENSEI, which focused on the integration of sensors and actuators into the "future Internet" to enable context-aware services. Leading the key technical work package in SENSEI, we contributed to the definition of the initial reference model, system requirements, and functional architecture of the SENSEI system.
Other past activities include projects on ultra-wideband (UWB) radio technology and 802.11x radio LANs.
