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| Overview |
Besides complex
techniques like CDMA, most wireless MAC protocols today lose
packets during collisions and cannot differentiate between
packet collisions and channel noise. Therefore, they
unnecessarily avoid simultaneous transmission even though many
radios exhibit the Capture Effect, which is the ability
to correctly receive a strong signal from one transmitter
despite significant interference from other transmitters. We
developed a technique to exploit this effect to
cheaply detect and recover from packet collisions using only
simple, low-power radios that are commonly used in sensor
networks. This technique differentiates between collisions and
channel noise, recovers one of the packets entirely, and can
often identify both transmitters that were involved in the
collision. This allows MAC protocols to be more aggressive by
transmitting while neighbors are also transmitting; if a
collision occurs, one of the packets will actually get through
and feedback can be used to request the lost packets and/or to
prevent such collisions in the future. We demonstrated the
collision detection and recovery technique on a 28 node testbed
and current experiments with new MAC protocols are showing up to
30% gains in bandwidth and latency.
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| Publications |
Kamin Whitehouse, Alec Woo, Fred Jiang, Joseph Polastre, David Culler. "Exploiting the Capture Effect for Collision Detection and Recovery." The Second IEEE Workshop on Embedded Networked Sensors (EmNetS-II). Sydney, Australia. May 30-31, 2005. (ppt) |
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| Data | The data for this project contains two parts. First, the data from the three-node experiment described in the paper. Second, the data from the broadcast storm experiment described in the paper. | |||
| Software | The code for this project contains two parts. First, there is a modification to the old tinyos-1.x radio stack to resynchronize to a packet during a collision, and to store information about the colliding packets. This modification is to a very old radio stack, and is here only as a reference implementation. Second, there is simple code that allows a single GenericBase to coordinate the transmissions of two other nodes using input/output pins. This code was used for the three-node experiment described in our paper. | |||
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Kamin Whitehouse Computer Science Department The University of Virginia 217 Olsson Hall Charlottesville, Virginia 94720 |