22-04-2014, 04:40 PM
MAC Layer Design for Wireless Sensor Networks
Wireless Sensor Networks[.ppt (Size: 728 KB / Downloads: 17)
Introduction
Wireless sensor network
Large number of densely distributed nodes
Battery powered
Multi-hop ad hoc wireless network
Node positions and topology dynamically change
Self-organization
Sensor-net applications
Nodes cooperate for a common task
In-network data processing
Overview of MAC Protocols
Contention-based protocols (contd.)
MACAW — Multiple Access with Collision Avoidance for Wireless - improved over MACA
RTS/CTS/DATA/ACK
Fast error recovery at link layer
IEEE 802.11 Distributed Coordination Function
Largely based on MACAW
Protocols from voice communication area
TDMA — low duty cycle, energy efficient
FDMA — each channel has different frequency
CDMA — frequency hopping or direct sequence
Energy Efficiency in MAC Design
Energy is primary concern in sensor networks
What causes energy waste?
Collisions
Control packet overhead
Overhearing unnecessary traffic
Long idle time
busty traffic in sensor-net apps
Idle listening consumes 50—100% of the power for receiving