TheMulti-Channel Flow-Aware Medium Access Control Protocol

The Multi-Channel Flow-Aware Medium Access Control Protocol for Wireless Sensor Networks Eric B. Decker ∗ Email: cire@soe.ucsc.edu Venkatesh Rajendran ∗ Email: venkat@soe.ucsc.edu Engineering Department 1156 High Street UC Santa Cruz, CA 95064. ∗ Computer Abstract—We introduce the Multi-Channel Flow-Aware Medium Access Control protocol, or (MFLAMA), an energy- efficient, schedule-based, multi-channel medium-access control (MAC) protocol designed for data gathering applications in wire- less sensor networks. MFLAMA improves the channel utiliza- tion by establishing collision-free transmission schedules across multiple channels. Energy efficiency is achieved by preventing packet collisions, idle listening, and transmissions to a node that is not ready to receive packets. We evaluate MFLAMA through extensive simulations and quantify the improvement in channel utilization through the use of multiple channels. Our results indicate that as we increase the number of orthogonal channels used for communication, there is significant improvement in channel utilization and queueing delay. However, we notice a “diminishing returns” effect as we increase the number of channels, i.e., the performance improvements observed decrease with the number of channels beyond a certain threshold. This threshold depends on the topology and traffic flow patterns being used. I. I NTRODUCTION Sensor networks have emerged as an ideal solution to a number of applications with significant scientific and societal relevance. Such applications include environmental monitor- ing, disaster recovery, emergency rescue, tracking mobile objects, etc. Sensor networks typically refer to a collection of low-cost, small nodes that have processing, (wireless) communication, and sensing capabilities. Commercial sensor network radios [1] often support mul- tiple orthogonal communication channels. As shown in Fig- ure 1, channel utilization can be improved by scheduling trans- missions across multiple channels. This particular example illustrates a data gathering application, in which a sink is col- lecting data from all the sensors using a data forwarding tree. For the given traffic flow pattern, only one of the flows can be scheduled for transmission without hidden-terminal collisions using a single channel. However, with multiple channels, three flows (i.e., F d, F e, and F f ) can be scheduled concurrently without hidden-terminal collisions. This work has been partially supported by the U.S. Army Research Office under grant W911NF-05-1-0246, the Baskin Chair in Computer Engineering, NSF grants ANI 0322441 and CNS 0534129, and Wionics Inc. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the U.S. Government. Katia Obraczka ∗ J. J. Garcia-Luna-Aceves ∗† Email: katia@cse.ucsc.edu Alto Research Center 3333 Coyote Hill Road Palo Alto, CA 94304. Email: jj@cse.ucsc.edu † Palo Fig. 1. Multi-channel scheduling in data gathering applications. In our previous work we established the importance of application-aware medium access in sensor networks [2]. In this paper, we introduce the Multi-Channel FLow-Aware Medium Access Control protocol, or MFLAMA, a schedule- based MAC protocol that leverages both the traffic predictabil- ity in some sensor network applications and also the availabil- ity of multiple orthogonal channels. MFLAMA characterizes traffic using directed flows [2] and uses a distributed schedul- ing algorithm to establish transmission schedules across mul- tiple channels. The main features of MFLAMA, as described in detail in Section III, are: (a) distributed, energy-efficient, collision- free transmission scheduling based on two-hop neighborhood information and implicit traffic information across multiple communication channels, (b) low transmission delays with limited processing and storage requirements, and (c) robust operation that accommodates topology changes. We evaluate the performance of MFLAMA through exten- sive simulations. Section IV presents our simulation results which quantify the benefits of multi-channel scheduling. We observe that as we increase the number of orthogonal channels used for communication, there is significant improvement in channel utilization and queueing delay. However, we notice a “diminishing returns” effect as we increase the number of channels, i.e., the performance improvements observed decrease with the number of channels beyond a certain thresh- old. This threshold depends on the topology and traffic flow patterns being used. II. R ELATED W ORK Existing MAC protocols can be categorized as contention- , schedule-, or reservation-based. PAMAS [3] is one of the earliest contention-based proposals to address power efficiency