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