SeongHwan Cho

Physical layer driven protocol and algorithm design for energy-efficient wireless sensor networks

The potential for collaborative, robust networks of microsensors has attracted a great deal of research attention. For the most part, this is due to the compelling applications that will be enabled once wireless microsensor networks are in place; location-sensing, environmental sensing, medical monitoring and similar applications are all gaining interest. However, wireless microsensor networks pose numerous design challenges. For applications requiring long-term, robust sensing, such as military reconnaissance, one important challenge is to design sensor networks that have long system lifetimes. This challenge is especially difficult due to the energy-constrained nature of the devices. In order to design networks that have extremely long lifetimes, we propose a physical layer driven approach to designing protocols and algorithms. We first present a hardware model for our wireless sensor node and then introduce the design of physical layer aware protocols, algorithms, and applications that minimize energy consumption of the system. Our approach prescribes methods that can be used at all levels of the hierarchy to take advantage of the underlying hardware. We also show how to reduce energy consumption of non-ideal hardware through physical layer aware algorithms and protocols.

Low-power wireless sensor networks

Wireless distributed microsensor systems will enable fault tolerant monitoring and control of a variety of applications. Due to the large number of microsensor nodes that may be deployed and the need for long system lifetimes, replacing the battery is not an option. Sensor systems must utilize the minimal possible energy while operating over a wide range of operating scenarios. This paper presents an overview of the key technologies required for low-energy distributed microsensors. These include power aware computation/communication component technology, low-energy signaling and networking, system partitioning based on computation and communication tradeoffs, and a power aware software infrastructure.

Design considerations for distributed microsensor systems

Wireless distributed microsensor systems will enable the reliable monitoring and control of a variety of applications that range from medical and home security to machine diagnosis, chemical/biological detection and other military applications. The sensors have to be designed in a highly integrated fashion, optimizing across all levels of system abstraction, with the goal of minimizing energy dissipation. This paper addresses some of the key design considerations for future microsensor systems including the network protocols required for collaborative sensing and information distribution, system partitioning considering computation and communication costs, low energy electronics, power system design and energy harvesting techniques.

Energy efficient Modulation and MAC for Asymmetric RF Microsensor Systems

Wireless microsensor systems are used in a variety of civil and military applications. Such microsensors are required to operate for years from a small energy source. To minimize the energy dissipation of the sensor node, RF front-end circuitry must be designed based on system level optimization of the entire network. This paper presents several energy minimization techniques derived from the unique properties of a practical short range asymmetric microsensor system. These include energy efficient modulation schemes, appropriate multiple access protocols, and a fast turn-on transmitter architecture.

Energy-centric enabling tecumologies for wireless sensor networks

Distributed networks of thousands of collaborating microsensors promise a maintenance-free, fault-tolerant platform for gathering rich multidimensional observations of the environment. Because a microsensor node must operate for years on a tiny battery, researchers must apply innovative system-level techniques to eliminate energy inefficiencies that would have been overlooked in the past. In this article we advocate two particular enablers for energy conservation: the ability to trade off performance for energy savings within the node; and collaborative processing among nodes to reduce the overall energy dissipated in the network. New levels of energy efficiency - attained through global system-level perspectives on node and network energy consumption - will enable a future where networks of hundreds, thousands, and eventually many millions of collaborating nodes are as commonplace as todays cellular phone.

An architecture for a power-aware distributed microsensor node

Networks of distributed microsensors are emerging as a compelling solution for a wide range of data gathering applications. Perhaps the most substantial challenge facing designers of small but long-lived microsensor nodes is the need for significant reductions in energy consumption. We propose a power-aware design methodology that emphasizes the graceful scalability of energy consumption with factors such as available resources, event frequency, and desired output quality, at all levels of the system hierarchy. Our architecture for a power-aware microsensor node highlights the collaboration between software that is capable of energy-quality tradeoffs and hardware with scalable energy consumption.

Design Considerations for Energy-Efficient Radios in Wireless Microsensor Networks

In the past few years, wireless microsensor networks have attracted a great deal of attention in the research community. This is due to the applications that will be enabled once wireless microsensor networks are in place. The design of wireless microsensor networks, however, represents a difficult challenge. Since many applications require fault-tolerant, long-term sensing, one important challenge is to design sensor networks that have long system lifetimes. Achieving long system lifetimes is difficult because sensor nodes are severely energy-constrained. In this paper, we demonstrate system-level techniques that adapt and tradeoff software and hardware parameters in response to changes in the requirements of the user, the characteristics of the underlying hardware, and the properties of the environment. By using these power-aware, system-level techniques, we are able to reduce the energy consumption of both general, adaptable systems and dedicated point systems. Moreover, given a specific set of operating conditions for a particular system, we show how energy savings of 50% can be achieved.

Energy efficient protocols for low duty cycle wireless microsensor networks

Emerging distributed wireless microsensor networks will enable the reliable and fault tolerant monitoring of the environment. Such microsensors are required to operate for years from a small energy source, while maintaining a reliable communication link to the base station. The design of energy-aware communication protocols can have a dramatic impact on the network lifetime for such applications. A detailed communication energy model, obtained from measurements, is introduced that incorporates the non-ideal behavior of the physical layer electronics. This includes the start-up energy cost of the RF transceiver, which dominates energy dissipation for short packet sizes. Using this model, various communication layer protocols are explored for asymmetrical sensor networks such as machine monitoring. The paper also proposes the use of a variable bandwidth allocation scheme that exploits spatial distribution of sensors.

Energy-efficient link layer for wireless microsensor networks

Wireless microsensors are being used to form large, dense networks for the purposes of long-term environmental sensing and data collection. Unfortunately these networks are typically deployed in remote environments where energy sources are limited. Thus, designing fault-tolerant wireless microsensor networks with long system lifetimes can be challenging. By applying energy-efficient techniques at all levels of the system hierarchy, system lifetime can be extended. In this paper, energy-efficient techniques that adapt underlying communication parameters will be presented in the context of wireless microsensor networks. In particular, the effect of adapting link and physical layer parameters, such as output transmit power and error control coding, on system energy consumption will be examined.

A 6.5 GHz CMOS FSK modulator for wireless sensor applications

A 6.5 GHz FSK modulator suitable for low power wireless sensor network is presented. The modulator employs closed loop direct VCO modulation to achieve high data rate, variable loop bandwidth technique for fast start-up rates and /spl Sigma/-/spl Delta/ for reduced power consumption in the divider with fine resolution in channel selection. The synthesizer, implemented in 0.25 /spl mu/m CMOS, achieves 20 /spl mu/s start-up time with an effective data rate of 2.5 Mbps while consuming 22 mW.