文档介绍：Sift: A MAC Protocol for Event-Driven Wireless
works
Kyle Jamieson, Hari Balakrishnan Y. C. Tay
MIT Laboratory puter Science Department of Mathematics
Massachusetts Institute of Technology National University of Singapore
Cambridge, MA 02139 tay@
 
jamieson, hari ¡ ***@
May 1, 2003
Abstract
Nodes in works often encounter spatially-correlated contention, where multiple nodes in the same
neighborhood all sense an event they need to transmit information about. Furthermore, in many work
applications, it is sufficient if a subset of the nodes that observe the same event report it. We show that traditional
carrier-sense multiple access (CSMA) protocols like do not handle the first constraint adequately, and do
not take advantage of the second property, leading to degraded latency and throughput as work scales in
size.
We present Sift, a medium access protocol for wireless works designed with the above observa-
tions in mind. Sift is a randomized CSMA protocol, but unlike previous protocols, does not use a time-varying
contention window from which a node randomly picks a transmission slot. Rather, to reduce the latency for the
delivery of event reports, Sift uses a fixed-size contention window and a carefully-chosen, non-uniform probabil-
ity distribution of transmitting in each slot within the window. We show using simulations that Sift can offer up
to a 7-fold latency pared to as the size of the work scales up to 500 nodes. We
then analytically prove bounds on the best latency achievable by a decentralized CSMA-based MAC protocol for
works where one report of each event is enough, and show that es close to meeting this bound.
1 Introduction
Every shared munication channel needs a medium-access control (MAC) protocol by which nodes
contend for the channel and eventually transmit without collisions. Over the past several decades, many MAC pro-
tocols have been designed and several are in operation in work