ITR: MAC Protocols Specific for Sensor Networks (MACSS)

University Of Southern California, Los Angeles CA

Investigators

Abstract

Wireless sensor networking is an emerging technology that has a wide range of potential applications including environment monitoring, smart spaces, medical systems and robotic exploration. While the technology is very promising, it raises serious challenges in network and system design. Sensor networks differ in many ways from than the traditional IP or voice networks, and have their unique features and requirements. Although MAC protocols such as 802.11 and TDMA are ideal for wireless IP or voice, no MAC protocol today meets the needs of sensor networks. This project will execute a systems-driven research program to address these problems through the development of sensor-network specific MAC protocols. Specifically, we are investigating: ADAPTIVITY AND ENERGY EFFICIENCY: Sensor network MACs must be adaptive in several dimensions, including energy consumption, traffic loads, and deployment density. Energy is *the key limitation* for battery-powered sensor nodes. The researchers are investigating and will provide designs for ENERGY CONSERVATION approaches that modify node duty cycle to conserve energy while considering user varying application traffic requirements. One approach to energy conservation is to trigger primary node radios with a paging channel, but this requires a second radio (with corresponding cost, space, and money requirements). Sensor nodes already must operate sensors full time, so the researchers are evaluating the use of sensors (acoustic, seismic, etc.) as a PHYSICAL SENSOR PAGING CHANNEL. MAC INTERACTION WITH THE PHYSICAL LAYER: With low-power, relatively unsophisticated radios, sensor networks applications and MAC protocols are very close to physical layer effects of radio propagation. A serious problem with current sensor applications is dealing with link error conditions such as packet loss and asymmetric communication. Energy-conserving MAC layers already keep track of neighbors, so the researchers will provide a BLACKLISTING SERVICE that allows the MAC to identify and exclude unusable links. The researchers also will study and report on radio POWER CONTROL AND APPLICATION INTERACTIONS to understand how MACs can control neighborhood size. UNIQUE APPLICATION NEEDS OF SENSOR NETWORKS: Sensor networks are fundamentally different from Internet-style networks of peer nodes in several different ways. A first differences is that sensor networks are primarily quiescent, but they occasionally become very active when something is sensed. The researchers will develop a MAC PROTOCOL WITH MULTIPLE OPERATING MODES to allow the MACs to adjust to this ``feast or famine'' traffic load. In addition, energy conservation introduces a *directional bias* in node communication; sleep/wake-up schedules can either add latency to all directions equally, or can allow rapid communication in one direction and slower communication in the other. The researchers will evaluate how controllable MAC-LEVEL DIRECTIONAL BIAS INTERACTS WITH APPLICATION, exploiting it where possible. Finally, the research community has a compelling need for a publicly available, freely modifiable Sensor-MAC protocol for experimentation and simulation. Evaluation of our ideas requires implementation and evolution of a MAC protocol. We will provide this implementation to other researchers for use over existing sensor network radios (with a reference implementation on the UC Berkeley Mote hardware) and in simulation (with a reference implementation in the ns-2 simulator). Thus, in addition to opening up sensor-network-specific MAC protocols as a new subfield of research, this work will serve as a catalyst for wider sensor network research that is sorely in need of an appropriate and modifiable MAC.