4. Some needs in the sensor
networks
Thousands of sensors in a small space → Wireless
but sensors are frequently stand alone →Low Power
and sensors are frequently isolated →Moderate Range.
Some of the challenges facing the standards committee
Slide 4 Joe Dvorak, Motorola 9/27/05
5. 802.15.4 General Characteristics
Data rates of 250 kb/s, 40 kb/s and 20 kb/s.
Star or Peer-to-Peer operation.
Support for low latency devices.
Fully handshaked protocol for transfer reliability.
Low power consumption.
Frequency Bands of Operation
16 channels in the 2.4GHz ISM* band
10 channels in the 915MHz ISM band
1 channel in the European 868MHz band.
* ISM: Industrial, Scientific, Medical
Slide 5 Joe Dvorak, Motorola 9/27/05
6. IEEE 802.15.4 MAC
Applications
IEEE 802.15.4
2400 MHz
PHY
IEEE 802.15.4
868/915 MHz
PHY
802.15.4 / ZigBee Architecture
ZigBee
• Packet generation
• Packet reception
• Data transparency
• Power Management
Slide 6 Joe Dvorak, Motorola 9/27/05
10. • Extremely low cost
• Ease of implementation
• Reliable data transfer
• Short range operation
• Very low power consumption
Simple but flexible protocol
IEEE 802.15.4 MAC Overview
Design Drivers
Slide 10 Joe Dvorak, Motorola 9/27/05
11. IEEE 802.15.4 MAC Overview
Typical Network Topologies
Slide 11 Joe Dvorak, Motorola 9/27/05
12. • Full function device (FFD)
– Any topology
– Network coordinator capable
– Talks to any other device
• Reduced function device (RFD)
– Limited to star topology
– Cannot become a network coordinator
– Talks only to a network coordinator
– Very simple implementation
IEEE 802.15.4 MAC Overview
Device Classes
Slide 12 Joe Dvorak, Motorola 9/27/05
13. Full function device
Reduced function device
Communications flow
Master/slave
PAN
Coordinator
IEEE 802.15.4 MAC Overview
Star Topology
Slide 13 Joe Dvorak, Motorola 9/27/05
14. Full function device Communications flow
Point to point Cluster tree
IEEE 802.15.4 MAC Overview
Peer-Peer Topology
Slide 14 Joe Dvorak, Motorola 9/27/05
15. Full function device
Reduced function device
Communications flow
Clustered stars - for example,
cluster nodes exist between rooms
of a hotel and each room has a
star network for control.
IEEE 802.15.4 MAC Overview
Combined Topology
Slide 15 Joe Dvorak, Motorola 9/27/05
16. IEEE 802.15.4 MAC Overview
General Frame Structure
Payload
PHY
Layer
MAC
Layer
MAC Header
(MHR)
MAC Footer
(MFR)
MAC Protocol Data Unit (MPDU)
MAC Service Data Unit
(MSDU)
PHY Header
(PHR)
Synch. Header
(SHR)
PHY Service Data Unit (PSDU)
4 Types of MAC Frames:
• Data Frame
• Beacon Frame
• Acknowledgment Frame
• MAC Command Frame
Slide 16 Joe Dvorak, Motorola 9/27/05
17. • Periodic data
– Application defined rate (e.g. sensors)
• Intermittent data
– Application/external stimulus defined rate (e.g.
light switch)
• Repetitive low latency data
– Allocation of time slots
IEEE 802.15.4 MAC Overview
Traffic Types
Slide 17 Joe Dvorak, Motorola 9/27/05
20. Typical ZigBee-Enabled Device Design
Typical design consist of RF IC and 8-bit
microprocessor with peripherals connected to an
application
Slide 20 Joe Dvorak, Motorola 9/27/05
