Wolfgang Schott

A PRML system for digital magnetic recording

The realization of a digital recording system using partial-response class-IV signaling with maximum-likelihood sequence detection (MLSD) is described. To perform MLSD at the high data rates encountered in recording systems, a simple implementation of the Viterbi detector based on a difference-metric algorithm is developed. Decision-directed schemes for gain control and timing recovery, for tracking variations of the gain and timing phase during data readback, and for fast initial adjustment from a known preamble are presented. The dynamic behavior of the control algorithms was studied by computer simulations. Coding was used to facilitate timing recovery and gain control, to limit the path memory length of the Viterbi detector, and to allow fast and reliable startup of the receiver. The design and properties of rate 8/9 constrained codes are examined. The problem of equalization is addressed, and analog and combined analog/digital filter implementations are developed. A simple adaptive equalizer capable of compensating variations of the recording channel characteristics with track radius and/or head-to-medium distance is described. >

Fast timing recovery for partial-response signaling systems

An algorithm for fast adjustment of the sample-timing phase in receivers for communication or storage systems using partial-response signaling is presented. For initial adjustment of the timing phase, a known preamble is transmitted. At the beginning of adjustment, previous timing-recovery schemes could occasionally hang up for an extended period of time at the unstable equilibrium point halfway between the desired sampling times. The presented algorithm eliminates the hangup problem by introducing a hysteresis effect that greatly diminishes the probability of reversals of the once chosen direction of timing-phase adjustment. Thus, reliable adjustment of the timing phase with a much shorter preamble is possible. The efficiency of the method is demonstrated by computer simulation results.<<ETX>>

Preamble recognition and synchronization detection in partial-response systems

To achieve fast initial gain and timing-phase adjustment in receivers for communication or storage systems using partial-response signaling, a synchronization preamble preceding user data is transmitted. A method for recognizing that synchronization has been achieved and that the preamble is being received, and for detecting the end of preamble is presented. The method is based on a maximum-likelihood test. Its efficiency is demonstrating by computing the probability of not recognizing the preamble when it is actually received and the probability of falsely recognizing the preamble when in fact user data are received.<<ETX>>

Thermal-aware workload scheduling for energy efficient data centers

Increasing heat dissipation density is becoming a limiting factor in air-cooled data centers. The main control objective in data center thermal management is to keep the temperature of all the data processing equipment below a certain threshold and at the same time maximize the energy efficiency of the system. Existing work in this field does not take into account unexpected changes in the workload and neglects the cost of control actions taken by the cooling infrastructure. To address this problem, we derive a thermodynamic model of a data center and propose a novel model-based temperature control strategy that combines air flow control and thermal-aware scheduling. The air flow controller is responsible for the long-term decisions by switching between multiple operating points, whereas the scheduler accounts for short-term fluctuations in the workload that are not predictable. Simulations with synthetic and real workload traces show that we can control the temperatures at the racks in an efficient and stable manner with this approach.

Geographic Routing with Cooperative Relaying and Leapfrogging in Wireless Sensor Networks

A novel geographic routing protocol for multi-hop wireless sensor networks is presented. It exploits the broadcast nature of the wireless channel to enable on-demand cooperative relaying and leapfrogging for circumventing weak radio links. In order to achieve energy efficiency, a metric is introduced for next-hop selection that takes into account information on the residual battery energy, the geographical position of the sensor nodes, and the channel quality of the involved radio links when available. Performance results show that the completely decentralized protocol offers significant benefits by reducing the number of (re)transmissions required to reach the destination. This translates into network-wide energy savings that extend the network lifetime.

The IBM wireless sensor networking testbed

This paper describes the wireless sensor networking testbed built at the IBM Zurich Research Laboratory. The testbed has been used to address a wealth of exciting research challenges. Performance evaluations have been carried out with short-range wireless communication technologies, which are highly relevant for sensor networking such as IEEE 802.15.4/ZigBee networks, Bluetooth WPANs, and IEEE 802.11b WLANs. With the testbed, the merits of wireless mesh networking for range extension and reliability enhancement have been explored. New light-weight messaging protocols for communication between sensors and an application server have been tested which allow to bring messaging-oriented middleware down to very low-end sensors and actuators. In addition, the testbed has been used to develop sensor applications for remote metering and location-sensing

A power-efficient wireless sensor network for continuously monitoring seismic vibrations

We present a novel power-efficient wireless sensor network for continuously monitoring and analyzing seismic vibrations with sensor nodes and forwarding the retrieved information with low-cost relay nodes to backend applications. The applied vibration sensing algorithms are derived from the DIN 4150–3 standard. All nodes in the network are battery-powered and equipped with an IEEE 802.15.4 compatible radio transceiver. The nodes communicate with each other by executing a novel power-efficient protocol stack, which provides all network functions required by the vibration-sensing application and uses a publish/subscribe messaging protocol for communicating between the network nodes and the backend applications. Results obtained in certification and field tests show that the proposed vibration-sensing solution is standard-compliant, and that the wireless vibration sensor network (WVSN) exhibits excellent performance in terms of packet delivery rate, latency, and power efficiency.

An opportunistic energy-efficient medium access scheme for wireless sensor networks

This paper introduces an opportunistic medium-access control (MAC) scheme for controlling the uplink message transfer from sensor nodes to a central controller in wireless sensor networks (WSN). By equipping the controller with multiple antennas to communicate with single-antenna sensors, we propose a scheme that benefits from diversity reception at the controller and leads to a considerable reduction of battery energy consumption in sensor nodes. The performance of the scheme is illustrated using a Rayleigh fading channel model.

A WSN System Architecture to Capture Context Information for beyond 3G Communication Systems

To enable new context-aware applications and services in future communication systems, wireless sensor networks (WSNs) are required to capture the context surrounding the service user and service related objects. This paper introduces a novel configurable architecture for a WSN system that is able to deliver context information from the sensors to the user in different application environments, and allows its efficient integration into third generation (3G) mobile communication systems in particular into the IP multimedia subsystem (IMS). The proposed architecture offers significant advantages compared to the ZigBee architecture.

Location-Based Cooperative Relaying in Wireless Sensor Networks

In this work, we present a novel routing protocol for energy constrained multi-hop wireless sensor networks. The proposed mechanism exploits the broadcast nature of the wireless channel to enable cooperative relaying in an on-demand manner. It also introduces the concept of leapfrogging that aids in circumventing links with weak channels. Further, in order to achieve energy efficiency, we define a novel metric that takes into account both location as well as channel state information for next-hop selection. The protocol is completely decentralized and preliminary analysis shows that the proposed approach offers significant benefits by reducing the number of (re)transmissions required to reach a destination. This translates into network-wide energy savings that can potentially increase the network lifetime.