Zigbee intro v5
- 1. etw orks s or N ess Sen Wirel Zig bee c tio n to ntr odu I
- 2. Sensor Network Challenges • Low computational power – Less than 10 MIPS – Low memory budget: 4-10 KB • Limited energy budget – AA batteries provide ~2850 mAh – LiIon and NiMH batteries provide 800-2500 mAh – Solar cells: around 5 mA/cm2 in direct sunlight • Communication?
- 3. Wireless Communication – Wireless communication standards: • IEEE 802.11 a/b/g • Bluetooth • GSM – What makes them unattractive for WSN: • Power hungry (need big batteries) • Complexity (need lots of clock cycles and memory) – New protocol for WSN: • 802.15.4 and Zigbee (ratified in Dec 14, 2004)
- 4. Outline • Why not 802.11 ? • How about Bluetooth? X-10? • What is ZigBee? • ZigBee Protocol: PHY and above • Hardware: CC2420 • Example and discussion
- 5. Technology Space Complexity, Power, Cost 802.11a 802.11b 802.11g 11Mbps 54Mbps Bluetooth 720 kbps 802.15.4 Zigbee 250 kbps “Mica2”/ cc1000 38.4 kbps Data rate
- 6. Wireless Standards ZigBee™ Bluetooth™ Wi-Fi™ GPRS/GSM 802.15.4 802.15.1 802.11b 1XRTT/CDMA Application Monitoring & Cable Web, Video, WAN, Voice/Data Focus Control Replacement Email System Resource 4KB-32KB 250KB+ 1MB+ 16MB+ Battery 100-1000+ 1-7 .1-5 1-7 Life(days) Nodes Per 255/65K+ 7 30 1,000 Network Bandwidth 20-250 720 11,000+ 64-128 (kbps) Range(meters) 1-75+ 1-10+ 1-100 1,000+ Reliable, Cost, Speed, Key Attributes Low Power, Reach, Quality Convenience Flexibility Cost Effective
- 7. Why NOT 802.11 ? The Cost of Throughput • High data rates – up to 11Mbps for b and – up to 54Mbps for g and a) • Distance up to 300 feet, or more with special antennas • High power consumption – Sources about 1800mA when transceiver is operational.
- 8. IEEE 802.11b example • Consider running a mote with 802.11b on two AA batteries. • Consumes 1800mA when transmitting • Assume NiMH battery capacity 2400mA/h • Assume transmitting 1/3 of the time • How long will the batteries last? • Is the given information sufficient for the question asked?
- 9. How About Bluetooth ? ? The Cost of Universalism • Designed for communications between portable and peripheral devices • 720 kbps, 10m range • One master and 7 slave devices in each “Piconet” • Time Division Multiple Access (TDMA) • Frequency hopping to avoid collisions between Piconets – Hop between channels 1600 times a second – 79 channels (1MHz each) to avoid collisions
- 10. Bluetooth (2) • Protocol tailored to many different data types: Audio, Text, Raw data – Makes the protocol rather complex to accommodate for all data types – Needs more memory and clock cycles than we are willing to afford on the Motes • Zigbee needs only about 10-50% of the software in comparison with Bluetooth and WiFi
- 11. How About X-10? ? • Targeted for home automation • Originally used power lines as transmission media. Later RF communication was added. • Mainly used to transmit a few codes to turn on or off other devices, aka. Remote control. • Very simple protocol – 4-bit house code (group address) – 4-bit unit code (device address) – 1-bit on/off command (data)
- 12. X-10 over power line (PHY) • Data (each bit) transmitted on the zero crossing point of the AC (60Hz) – ‘1’ = 1ms burst of 120kHz – ‘0’ = no burst • All messages are sent twice ‘1’ ‘0’ • Frames are separated by 6 clear crossings • What is the data rate?
- 13. X-10 over RF X-10 device controller • Operates at frequency 310MHz in the US Motion • Has to be compatible sensor with the power-line “bridge” modules • Data rate limited to ~20bps X-10 bridge To power-line • Not ideal for WSN
- 14. X-10 video over RF • X10 has a high data rate extension allowing to transmit video over RF at 2.4GHz – Channel A: 2.411 GHz – Channel B: 2.434 GHz – Channel C: 2.453 GHz – Channel D: 2.473 GHz • Proprietary protocol for NTSC video signal transmission • NOT secure!
- 15. What is Zigbee Affordable Simplicity • ZigBee is a published specification set of high level communication protocols for: – Low data rate, low power, low cost wireless systems operating in unlicensed RF domain • Formely known as – PURLnet, RF-Lite, Firefly, and HomeRF Lite • Based on IEEE 802.15.4
- 16. ZigBee Applications • Wireless home security • Remote thermostats for air conditioner • Remote lighting, drape controller • Call button for elderly and disabled • Universal remote controller to TV and radio • Wireless keyboard, mouse and game pads • Wireless smoke, CO detectors • Industrial and building automation and control (lighting, etc.)
- 17. Zigbee General • Low power – battery life multi-month to years • Multiple topologies – star, peer-to-peer, mesh • Addressing space: 64 bits – Question: how many nodes? • Fully hand-shake protocol (reliability) • Range: 50m typical – 5-500m based on environment
- 18. Zigbee Intended Traffic • Periodic data • Intermittent data • Application defined rate (e.g., sensors) • External stimulus defined rate (e.g., light switch) • Low latency data (Q: Any examples?)
- 19. ZigBee and OSI Model OSI 7-Layer Model Technology Examples Layer 7: Application SMTP, FTP, Telnet Layer 6: Presentation ASCII, JPEG, BMP ZigBee… Layer 5: Session RPC Layer 4: Transport TCP, UDP Layer 3: Network IP Layer 2: Data Link • (MAC) Ethernet, ATM 802.15.4 CSMA/CD (Carrier Layer 1: Physical (PHY) Sensing Multiple Access With Collision Detection)
- 20. Zigbee Protocol Stack • ZigBee uses the IEEE 802.15.4 – Low Rate Wireless Personal Area Network (WPAN) standard to describe its lower protocol layers: PHY and MAC *** Layer 2: Data Link (MAC) Layer 1: Physical (PHY) Media
- 21. Zigbee/IEEE 802.15.4 • Dual PHY: 2.4GHz and 868/915 MHz • Data rates: – 250 kbps @ 2.4GHz – 40 kbps @ 915MHz – 20 kbps @ 868MHz • Q: Why would anyone want this? • A: Better penetrates obstacles than @2.4GHz • CSMA-CA channel access – Yields high throughput and low latency for low duty cycle devices
- 22. IEEE 802.15 • IEEE 802.15 is a working group of IEEE that specializes in Wireless PAN standards – 802.15.1: Bluetooth – 802.15.2: Coexistence of PAN and 802.11 – 802.15.3a: UWB (Wireless USB) » High data rate – 802.15.4: WPAN Low Rate » Low data rate but very long battery life (months/ years)
- 23. ZigBee: PHY • The radio uses Digital Spread Spectrum Signaling (DSSS) – Conventional DSSS for 868MHz and 915MHz bands – Orthogonal Signaling (4 bits per symbol) for 2.4GHz band • Number of channels – 16 channels in the 2.4GHz ISM band – 10 channels in the 915MHz – one channel in the 868MHz
- 24. ZigBee: MAC • Employs 64-bit IEEE & 16-bit short addresses • Three device types specified – Network Coordinator – Full Function Device (FFD) – Reduced Function Device (RFD) • Simple frame structure • Reliable delivery of data • Association/disassociation • AES-128 security • CSMA-CA channel access • Optional superframe structure with beacons • Optional GTS mechanism
- 25. ZigBee as Mesh Networking ZigBee Coordinator ZigBee Router/FFD ZigBee RFD
- 26. PHY – MAC Interaction Example PHY MAC Next Layer…
- 27. PHY – MAC Interaction (2) PHY MAC Next Layer…
- 28. ZigBee Upper Layers From www.zigbee.org
- 29. ZigBee Upper Layers • Messaging • Configurations that can be used • Security: – Key setup and maintenance: Commercial, Residential – Defines key types: Master, Link, Network – CCM (unified, simple mode of operation) – More: Key freshness checks, message integrity, authentication (network and device level) • Network layer (NWK) supports three topologies: – Star – Mesh – Cluster-Tree ( = Star + Mesh)
- 30. How A ZigBee Network Forms • Devices are pre-programmed for their network function – Coordinator scans to find an unused channel to start a network – Router scans to find an active channel to join, then permits other devices to join – End Device will always try to join an existing network • Devices discover other devices in the network providing complementary services – Service Discovery can be initiated from any device within the network • Devices can be bound to other devices offering complementary services – Binding provides a command and control feature for specially identified sets of devices
- 31. ZigBee Stack Architecture: Addressing – Every device has a unique 64 bit MAC address – Upon association, every device receives a unique 16 bit network address – Only the 16 bit network address is used to route packets within the network – Devices retain their 16 bit address if they disconnect from the network, however, if they leave the network, the 16 bit address is re- assigned
- 32. ZigBee Stack Architecture: Addressing (2) – NWK broadcast implemented above the MAC: • NWK address 0xFFFF is the broadcast address • Special algorithm in NWK to propagate the message • “Best Effort” or “Guaranteed Delivery” options • Radius Limited Broadcast feature
- 33. ZigBee Routing • Routing table entry: – Destination Address (2 bytes) – Route status (3 bits) – Next Hop (2 bytes) • Route request command frame: – FrameID, Options, RequestID, Destination Address, Path cost • Route reply command frame: – FrameID, Options, Req.ID, Originator Addr, Responder Addr, Path cost • A device wishing to discover or repair a route issues a route request command frame which is broadcast throughout the network • When the intended destination receives the route request command frame it responds with at least one route reply command frame • Potential routes are evaluated with respect to a routing cost metric at both source and destination
- 34. ZigBee NWK Parameters • nwkMaxDepth and nwkMaxChildren • nwkMaxRouters • Size of the routing table • Size of neighbor table • Size of route discovery table • Number of reserved routing table entries • How many packets to buffer pending route discovery • How many packets to buffer on behalf of end devices • Routing cost calculation • nwkSymLink • nwkUseTreeRouting
- 35. Hardware: CC2420 How Stuff Works • Chipcon/Ember CC2420: Single-chip radio transceiver compliant with IEEE 802.15.4 – Low power: • 1.8V supply • Less than 20mA operation current – PHY and encryption in hardware – Open source software available – O-QPSK modulation • Minimizes interference with WiFi and Bluetooth – Low cost (about $5)
- 36. Simplified CC2420 Operation Controller Microcontroller CC2420 Receiver, FIFO ADC Demodulator buffer MAC and Modulator, upper layers DAC Transmitter PHY support
- 37. CC2420 Operation Microcontroller
- 38. Example Choose Wisely • Consider low duty-cycle, large data transfers: • 802.11b – PowerActive = 1300 mW – Assume 40% of 11 Mbps – => 295 nJ/bit • 802.15.4 – Power Active = 60mW – Assume 80% of 250 Kbps – => 300 nJ/bit
- 39. Example: Questions • Power cost summary – 802.11b 295 nJ/bit – 802.15.4 300 nJ/bit • Questions: – Is 802.11b a better choice? – How about wake-up overhead? – How about protocol overhead? – How about small and large data transfers?
- 40. Example: Conclusion • The choice of protocol depends on the application: – An array of wireless video cameras –802.11b or g is probably better – An array of low data rate sensor nodes –802.15.4 is probably better • Must consider several factors, such as – Protocol overhead and payload data size, wake-up overhead, … – …in terms of power, computation, and time.
- 41. More on Zigbee • WEB – Zigbee Alliance http://www.zigbee.org – http://www.palowireless.com/zigbee/ – 802.15.4 - Task Group 4 http://ieee802.org/15/pub/TG4.html – More on the web
- 42. Summary • Most wireless standards are too power hungry and complex for WSN • Zigbee Alliance proposed Zigbee that targets low power WSN systems • Zigbee is NOT equal to 802.15.4, but extends it • When designing a WSN, one must consider various factors before choosing a communication’s protocol.
- 43. Summary (2): • ZigBee is a set of protocols for: – Low data rate (up to 250kbps) – Low Power consumption (months to years on batteries) – Low cost solution • ZigBee addressing: 64 bit and 16 bit. • ZigBee has three types of nodes – Coordinator – Router – End Device