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ZigBee Module 구성도. IEEE 802.15.4 LR-WPAN. Low power consumption Frequent battery change is not desired and/or not feasible Low cost Otherwise, wireline alternative may be preferred An application itself may not be attractive High throughput is not required - PowerPoint PPT Presentation
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ZigBee Module 구성도
IEEE 802.15.4 LR-WPAN
Low power consumption Frequent battery change is not desired and/or not feasible
Low cost Otherwise, wireline alternative may be preferred An application itself may not be attractive
High throughput is not required Typically, short-lived sporadic messages Latency or reliability could be more important
IEEE 802.15.4 LR-WPAN
IEEE 802.15.4 LR-WPAN
IEEE 802.15.4 LR-WPAN
IEEE 802.15.4 MAC 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
Network Coordinator Transmits network beacons Sets up a network Manages network nodes Stores network node information Routes messages between paired nodes Receives constantly
Network Node Generally battery powered Searches for available networks Transfers data from its application as necessary Determines whether data is pending Requests data from the network coordinator Can sleep for extended periods
IEEE 802.15.4 MAC Device Classes
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
MAC Features Association, disassociation Acknowledged frame delivery Channel access mechanism Frame validation Guaranteed time slot management Beacon management MAC management has 26 primitives
• cf. 131 primitives of 802.15.1 / Bluetooth
IEEE 802.15.4 MAC Access Mechanisms
Carrier-Sense Multiple Access with Collision Avoidance (CSMA-CA)
Either slotted or unslotted version used• Slotted CSMA-CA in a beacon-enabled network• Unslotted or standard CSMA-CA in networks without beacons
Optionally, contention-free access using Guaranteed Time Slots (GTSs)
GTSGTS Inactive
Beacon BeaconCAP CFP
16 Superframe Slots
IEEE 802.15.4 MAC MAC-Related Parameters
One symbol duration• 16 usec (@2.4GHz), 25 usec (@900MHz), 50 usec (@800MHz)
aUnitBackoffPeriod = 20 symbols• Backoff countdown unit
aBaseSlotDuration = 60 symbols• A superframe slot = aBaseSlotDuration * 2^SO• SO = superframe order
CCA detection time = 8 symbols Random backoff [0,2^BE-1]
• Backoff exponent BE increases by one whenever CCA busy • macMinBE = 0~3 (3 is default)• If macMinBE=0, collision avoidance is disabled for the first tx attempt• aMaxBE = 5 (constant)• aMaxFrameRetries = 3 (constant)
Contention window CW for slotted CSMA-CA• Initially 2, and decreases by one after a CCA idle assessment• To avoid a potential collision with an ACK transmission
IEEE 802.15.4 MAC Power Save Mechanisms
Going to sleep state as often as possible by utilizing:• Inactive mode in superframes• Snooze mode of coordinator
– No beacon transmission in snooze mode• GTS for other devices
Extracting pending messages from coordinator• Using data request command• Message pending indicated in beacon frames
Addressing All devices have unique 64-bit extended addresses 8-bit or 16-bit short addresses can be allocated during
association Addressing modes:
• Network + device identifier• Source/destination identifier
IEEE 802.15.4 MAC General MAC Frame Format
IEEE 802.15.4 MAC MAC Frame Components
Frame control• MAC frame type, Address field format• Controls the ACK – ACK or no ACK
Address Information• Variable number of addresses • 8-bit/16-bit short or 64-bit extended address
Sequence number• Same number use for the subsequent ACK
Frame check sequence (FCS) • CRC-16 for frame integrity check
Four Types of MAC Frames Data Frame Acknowledgment Frame
• After TurnaroundTime (12 symbols) or aUnitBackoffPeriod boundary Beacon Frame
• Specifies devices with pending messages MAC Command Frame
• Association request/response• Data request for pending messages• GTS request/allocation and many others
IEEE 802.15.4 PHY Operating Frequency Bands
IEEE 802.15.4 PHY Channel Frequencies
Modulation Parameters
IEEE 802.15.4 PHY PHY Common Parameters
Transmit Power• Capable of at least 1 mW
Transmit Center Frequency Tolerance - 40 ppm Receiver Sensitivity (Packet Error Rate <1%)
• -85 dBm @ 2.4 GHz band• -92 dBm @ 868/915 MHz band
RSSI Measurement• Packet strength indication• Clear channel assessment (CCA)• Dynamic channel selection
PHY Frame Structure
IEEE 802.15.4 Characteristics
Simpler PHY• One Tx rate per channel• Low Tx power
Simpler MAC• No virtual carrier-sense• No worry about hidden nodes• No RTS/CTS & No fragmentation• No continuous CCA• Relaxed timing requirement
Extensive power saving features Zigbee Stack Requirements
8-bit μC, e.g., 80c51 Full protocol stack <32k Simple node only stack ~4k Coordinators require extra RAM
• Node device database• Transaction table• Pairing table
ZigBee Spec. V1.0
ZigBee Spec. V1.0 ZigBee Coordinator (ZC)
One and only one required for each ZB network. Initiates network formation. Acts as 802.15.4 2003 PAN coordinator (FFD). May act as router once network is formed.
ZigBee Router (ZR) Optional network component. May associate with ZC or with previously associated ZR. Acts as 802.15.4 2003 coordinator (FFD). Participates in multihop routing of messages.
ZigBee End Device (ZED) Optional network component. Shall not allow association. Shall not participate in routing.
ZigBee Spec. V1.0
ZigBee Spec. V1.0
ZigBee Spec. V1.0
ZigBee Spec. V1.0 ZigBee Routing
If you’ve got a routing table entry then use it. If you’ve got a routing table and there’s room for another entry then try route discovery. Otherwise, route along the tree (if you can).
Tree Routing
ZigBee Spec. V1.0 Routing Table
Route Discovery Table
ZigBee Spec. V1.0 Routing Cost
ZigBee Spec. V1.0 Starting a network Permitting a device to join
ZigBee Spec. V1.0 Joining a network Joining by orphaning
ZigBee Spec. V1.0 NWK setting for a residential stack