11-04-2011, 10:52 AM
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Introduction
Wired telephony network Cellular Network
Need for mobility
Cost of laying new wires
Cellular Network WLAN
IEEE 802.11
Long range (100m), Data throughput of 2-11Mbps
WLAN WPAN
Low-cost, low power, short range, very small size
High rate(802.15.3) – Multi-Media
Medium rate(802.15.1) – Cell phones, PDA, Voice
Low rate (802.15.4) – relaxed QoS, very low power
Zigbee and 802.15.4
ZigBee
Low data rate, low power consumption, wireless networking protocol aimed at automation and remote control applications
802.15.4
Focuses on specification of lower 2 layers of protocol stack
Details specification of PHY and MAC by offering building blocks for “star, mesh, and cluster tree networks”
ZigBee vs. Bluetooth
Simpler, lower data rate, sleeps more often
Leads to longer lifetimes, but less responsive
IEEE 802.15.4 WPAN Standard
WPAN components
Fully Functional Devices (FFD)
Reduced Function Devices (RFD)
Each network has at least one FFD as PAN coordinator
Network Topologies
Star (home automation, PC peripherals, toys, games)
Mesh/Peer-to-Peer (industrial control, WSNs, inventory tracking)
Cluster Tree (special case of Peer-to-Peer with many FFDs)
LR-WPAN Device Architecture
PHY/MAC
802.2 Logical Link Control (LLC)
Service Specific Convergence Sublayer (SSCS)
IEEE 802.15.4 PHY
Features
Activation/Deactivation of radio transceiver
Energy Detection (ED)
Link Quality Indication (LQI)
Channel Selection
Clear Channel Assessment (CCA)
Transmission/Reception of packets over physical medium
Receiver Energy Detection
Estimate of received signal power within bandwidth of channel
Intended for use by network layer for channel selection
Link Quality Indication
Characterization of strength /quality of received packet
Implemented using ED, SNR, or combination
Clear Channel Assessment
Energy above ED threshold
Carrier Sense Only
Carrier Sense with energy above threshold
PHY protocol data unit
SHR – allows receiving device to synchronize with bit stream
PHR – contains frame length information
Variable length payload carriying MAC sublayer frame
IEEE 802.15.4 MAC
Features
Beacon Management
Channel Access
Guaranteed Time Slot (GTS ) management
Frame Validation
Acknowledged Frame Delivery
Association/Dissassociation with PAN coordinator