S.rou.2-2 Wireless Sensor Networks Case Study: ZigBee & IEEE802.15.4 S.rou.2 ZigBee & 802.15.4 ZigBee overview IEEE 802.15.4 overview ZigBee & bluetooth End Dr.M.Y.Wu@CSE Shanghai Jiaotong University Shanghai, China Dr.W.Shu@ECE University of New Mexico Albuquerque, NM, USA S.rou.2-3 S.rou.2-4 What is ZigBee? Technology for cost-effective wireless networking solutions based on IEEE 802.15.4 Non-profit industry consortium 6 promoters: Honeywell, Invensys, Mitsubishi, Motorola, Philips, and Samsung > 100 participants Mission statement: To enable reliable, cost-effective, low-power, wirelessly networked, monitoring and control products based on an open global standard. ZigBee Solution Targeted at Home/building automation & controls Consumer electronics & PC peripherals Medical monitoring & Toys Design issues Low-cost & long battery life Simplicity & reliability Networking capability interoperability
S.rou.2-5 S.rou.2-6 Where is ZigBee in wireless market Where is ZigBee in wireless market Bluetooth 2 Data Rate TEXT GRAPHICS INTERNET HI-FI AUDIO STREAMING VIDEO DIGITAL VIDEO MULTI-CHANNEL VIDEO >110 Mb/s UWB/802.15.3a WPAN SHORT < RANGE > LONG ZigBee Bluetooth 2 Bluetooth1 802.11b 802.11a/HL2 & 802.11g LAN PAN 802.11g, 802.11a, HiperLAN 1-54 Mb/s 802.11b (Wi-Fi) 802.11 Bluetooth 1 Mb/s WPAN 20-250kb/s ZigBee Range (meters) WLAN LOW < DATA RATE > HIGH 0 10 100 S.rou.2-7 S.rou.2-8 ZigBee & 802.15.4 History ZigBee applications Proposals Initial MRD RSI/TRD v0.2 ZigBee Proposal to IEEE ZigBee Alliance formed security HVAC AMR lighting control access control BUILDING AUTOMATION CONSUMER ELECTRONICS TV VCR DVD/CD remote IEEE 802.15.4 patient monitoring fitness monitoring PERSONAL HEALTH CARE ZigBee Wireless Control that Simply Works PC & PERIPHERALS mouse keyboard joystick PAR Proposals 1998 1999 2000 2001 2002 Reviews Stand. Complete asset mgt process control environmental energy mgt INDUSTRIAL CONTROL RESIDENTIAL/ LIGHT COMMERCIAL CONTROL security HVAC lighting control access control lawn & garden irrigation
S.rou.2-9 S.rou.2-10 Stack references: ZigBee & IP/UDP Protocol stack End developer applications, designed using application profiles Application interface designed using general profile Topology management, MAC management, routing, discovery protocol, security management Channel access, PAN maintenance, reliable data transport Transmission & reception on the physical radio channel ZA1 ZA2 ZAn IA1 IAn API ZigBee NWK IEEE 802.15.4 MAC (CPS) IEEE 802.15.4 PHY UDP IP 802.2 LLC MAC (SSCS) APPLICATIONS APPLICATION INTERFACE NETWORK LAYER Star/Cluster/Mesh MAC LAYER MAC LAYER PHY LAYER 2.4 GHz 915MHz 868 MHz Application SECURITY ZigBee Stack Customer IEEE 802.15.4 ZigBee Alliance Silicon Full protocol stack <32 k Simple-node stack ~4k Coordinators-node require extra RAM Node device database Transaction table Pairing table 8-bit microcontroller, a simple platform S.rou.2-11 S.rou.2-12 Wireless communication patterns Node numbers and timings One-to-one Simple wire replacement Direct connection between devices One-to-many Centralized control/routing Wi-Fi, GSM, Bluetooth All data have to go through base station Mesh + Multihop Self configuration/healing Full RF redundancy with multiple data paths Fully distributed paradigm 64K network (client) nodes Optimized for timing-critical applications Network join time: ~30 ms Sleeping slave changing to active: ~15 ms Active slave channel access time: ~15 ms Network coordinator Full Function node Reduced Function node Communications flow Virtual links
S.rou.2-13 S.rou.2-14 ZigBee Topology Models ZigBee & 802.15.4 Star Mesh ZigBee overview IEEE 802.15.4 overview ZigBee & bluetooth End Cluster Tree ZigBee coordinator ZigBee Routers ZigBee End Devices S.rou.2-15 S.rou.2-16 IEEE 802.15.4 Basics Frequencies and data rates A simple packet data protocol for lightweight wireless networks Channel Access CSMA/CA: Carrier Sense Multiple Access with Collision Avoidance and optional time slotting Message acknowledgement and an optional beacon structure Released in May 2003, works well for Long battery life, selectable latency for controllers, sensors, remote monitoring and portable electronics Frequency 2.4 GHz 868 MHz 915 MHz Coverage ISM ISM Coverage Worldwide Europe Americas DataRate 250 kbps 20 kbps 40 kbps Channel# 16 1 10
Frequencies and data rates S.rou.2-17 IEEE 802.15.4 & ZigBee stacks S.rou.2-18 Choose to work in one of 27 channels Depending on Availability Congestion state Data rate of each channel 250 kbps for computer peripherals, toys 20-40 kbps for sensors, smart tags, consumer electronics Includes layers up to and including Link Layer Control LLC is standardized in 802.1 Supports multiple network topologies including Star, Cluster Tree and Mesh Low complexity: ZigBee Application Framework 14 PHY primitives 35 MAC primitives 49 primitives total, versus 131 primitives in 802.15.1 (Bluetooth) IEEE 802.15.4 MAC Networking App Layer (NWK) Data Link Controller (DLC) IEEE 802.15.4 LLC IEEE 802.2 LLC, Type I IEEE 802.15.4 868/915 MHz PHY IEEE 802.15.4 2400 MHz PHY IEEE 802.15.4 System Configuration S.rou.2-19 IEEE 802.15.4 MAC S.rou.2-20 Motorola RF Packet Radio Motorola 8-bit MCU Employs 64-bit IEEE & 16-bit short addresses Ultimate network size can reach 2 64 nodes Using local addressing, simple networks of 64K (2 16 ) nodes can be configured, with reduced address overhead Device complexity a simple 8-bit MCU and a pair of AAA batteries! CSMA-CA channel access Simple frame structure, optional superframe structure with beacons GTS mechanism RTS/CTS mechanism is dropped
IEEE 802.15.4 Device Types S.rou.2-21 Device communication S.rou.2-22 Network Coordinator (a special FFD) Maintains overall network knowledge; most memory and computing power Full Function Device (FFD) Full 802.15.4 functionality, all 49 primitives Additional memory, computing power make it ideal for a network router function Could also be used in network edge devices (where the network touches the real world) Reduced Function Device (RFD) Limited (as specified by the standard) functionality to control cost and complexity, 38 primitives @ min configuration General usage will be in network edge devices Difference in their communication patterns An FFD Can talk to RFDS FFDs Operate in three modes PAN coordinator, coordinator, device An RFD Can talk to An FFD Operate in the device mode P2P communication cannot happen between two RFDs Data transmission S.rou.2-23 Power-saving mechanisms S.rou.2-24 Direct data transmission Unslotted CSMA/CA non-beacon-enabled mode Slotted CSMA/CA beacon-enabled mode Indirect data transmission Applicable to data transfer from a coordinator to its devices A device find out if it has a packet by checking the beacon Guaranteed time slot (GTS) data transmission Applicable to data transfer between coordinator & its devices Based on beacon-enabled mode In direct data transmission If the BatteryLifeExtension is TRUE, the receiver is disabled after macbattlifeextperiods backoff periods. So awake about 1/64 of the duration of a superframe. In indirect data transmission A device can enter a low power state (sleeping) after checking the beacon. In GTS data transmission Has a low duty cycle, but relative expensive in power
Self configuration S.rou.2-25 MAC Channel Access S.rou.2-26 Association procedure Select a channel Select an ID for the PAN Determine whether to use beacon or non-beacon If beacon, choose the beacon order & superframe order Assign a 16-bit short address for a device Set BatteryLifeExtension option Orphaning A device is considered orphaned if missed MaxLost-Beacons Non-beacon network Standard ALOHA CSMA/CA communications Positive ACK for successfully received packets Beacon-enabled network Superframe structure For dedicated bandwidth up and low latency Setup by network coordinator to transmit beacons at predetermined intervals 15ms to 252s (15.38ms*2n where 0 n 14) 16 equal-width time slots between beacons Channel access in each time slot is contention free Security & Robust S.rou.2-27 Data Frame format S.rou.2-28 Three security levels specified None Access control lists Symmetric key employing AES-128 802.15.4/ZigBee protocol is very robust Clear channel checking before transmission Backoff and retry if no ACK received Duty cycle of device is usually extremely low One of two most basic and important structures in 15.4 Provides up to 104 byte data payload capacity Data sequence numbering to ensure that all packets are tracked Robust frame structure improves reception in difficult conditions Frame Check Sequence (FCS) ensures that packets received are without error
Acknowledgement Frame Format S.rou.2-29 MAC Command Frame format S.rou.2-30 The other most important structure for 15.4 Provides active feedback from receiver to sender that packet was received without error Short packet that takes advantage of standards-specified quiet time immediately after data packet transmission Mechanism for remote control/configuration of client nodes Allows a centralized network manager to configure individual clients no matter how large the network Beacon Frame (superframe) format S.rou.2-31 Frequencies and Data Rates S.rou.2-32 Beacons add a new level of functionality to a network Client devices can wake up only when a beacon is to be broadcast, listen for their address, and if not heard, return to sleep Beacons are important for mesh and cluster tree networks to keep all of the nodes synchronized without requiring nodes to consume precious battery energy listening for long periods of time The two PHY bands (UHF/Microwave) have different physical, protocol-based and geopolitical characteristics Worldwide coverage available at 2.4GHz at 250kbps 900MHz for Americas and some of the Pacific 868MHz for European-specific markets
PHY Performance S.rou.2-33 Non-Beacon vs Beacon Modes S.rou.2-34 802.15.4 has excellent performance in low SNR environments Non-Beacon Mode A simple, traditional multiple access system used in simple peer and near-peer networks Think of it like a two-way radio network, where each client is autonomous and can initiate a conversation at will, but could interfere with others unintentionally However, the recipient may not hear the call or the channel might already be in use Example of Non-Beacon Network S.rou.2-35 Non-Beacon vs Beacon Modes S.rou.2-36 Commercial or home security Devices Sleep 99.999% of the time Wake up on a regular yet random basis to announce their continued presence in the network ( 12 o clock and all s well ) When an event occurs, the sensor wakes up instantly and transmits the alert ( Somebody s on the front porch ) The Coordinator Mains powered, has its receiver on all the time and so can wait to hear Can allow clients to sleep for unlimited periods of time to allow them to save power Beacon Mode A very powerful mechanism for controlling power consumption in extended networks like cluster tree or mesh Allows all clients in a local piece of the network the ability to know when to communicate with each other Here, the two-way radio network has a central dispatcher who manages the channel and arranges the calls
Example of Beacon Network S.rou.2-37 Growing the Network S.rou.2-38 the ZigBee Coordinator battery-operated also All units in system are now battery-operated Client registration to the network Client unit when first powered up listens for the ZigBee Coordinator s network beacon (interval between 0.015 and 252 seconds) Register with the coordinator and look for any messages directed to it Return to sleep, awaking on a schedule specified by the ZigBee Coordinator Once client communications are completed, ZigBee coordinator also returns to sleep This timing requirement potentially impacts the cost of the timing circuit in each end device Longer intervals of sleep mean that the timer must be more accurate or Turn on earlier to make sure that the beacon is heard, increasing receiver power consumption, or Improve the quality of the timing oscillator circuit (increase cost) or Control the maximum period of time between beacons to not exceed 252 seconds, keeping oscillator circuit costs low In a beacon-environment, growing the network means keeping the overall network synchronized According to pre-existing network rules, the joining network s PAN Coordinator is probably demoted to Router, and passes along information about its network (as required) to the PAN coordinator Beacon information passed from ZigBee Coordinator to now-router, router knows now when to awake to hear network beacon Demoted to router Joining Network Existing network s Coordinator New link established Reliability at different layers S.rou.2-39 Reliability at PHY layer S.rou.2-40 PHY: Direct Sequence with Frequency Agility (DS/FA) MAC: ARQ, Coordinator buffering Network: Mesh Network (redundant routing) Application Support Layer: Security Direct sequence: allows the radio to reject multipath and interference by use of a special chip sequence. The more chips per symbol, the higher its ability to reject multipath and interference. Frequency Agility: ability to change frequencies to avoid interference from a known interferer or other signal source.
Direct Sequence and Frequency Agility S.rou.2-41 Reliability at MAC layer S.rou.2-42 Over the Air Interferer Desired Signal After DS correlation ARQ (acknowledgement request) is where a successful transmission is verified by replying with an acknowledge (ACK). If the ACK is not received the transmission is sent again Coordinator buffering where the network coordinator buffers messages for sleeping nodes until they wake again 2.4 GHz PHY Channels 11-26 5 MHz 2.4 GHz 2.4835 GHz S.rou.2-43 S.rou.2-44 Reliability at network layer Reliability: Mesh Networking Mesh Networking: allows various paths of routing data to the destination device. In this way if a device in the primary route is not able to pass the data, a different valid route is formed, transparent to the user. ZigBee Coordinator (FFD) ZigBee Router (FFD) ZigBee End Device (RFD or FFD) Mesh Link Star Link
S.rou.2-45 S.rou.2-46 ZigBee & 802.15.4 ZigBee overview IEEE 802.15.4 overview ZigBee & bluetooth End Why do we need both technologies? Bluetooth wireless technology Well focused towards voice applications and higher data rate applications (cell phones, headsets, etc.) ZigBee technology Best suited for control and monitoring applications L 3 : Low data rates, Low power, Low costs Ease of use (remote controls, sensor nets, etc.) S.rou.2-47 S.rou.2-48 Optimized for different applications Address different needs ZigBee Smaller packets over large network Mostly Static networks with infrequently used devices Home automation, toys, remote controls, etc. Bluetooth Larger packets over small network Ad-hoc networks File transfer Screen graphics, pictures, hands-free audio, Mobile phones, headsets, PDAs, etc. ZigBee Is better for devices Where the battery is rarely replaced Targets are : Tiny fraction of host power New opportunities where wireless not yet used Bluetooth is a cable replacement for items like Phones, Laptop Computers, Headsets expects regular charging Target is to use <10% of host power
Use different air interface ZigBee DSSS: 11 chips/ symbol 62.5 K symbols/s 4 Bits/ symbol Peak Information Rate ~128 Kbit/second OQPSK with shapping Protocol level: 28Kb Bluetooth FHSS 1 M Symbol / second Peak Information Rate ~720 Kbit / second Protocol level: 250Kb Frequency hop makes it hard to create extended net w/o large syn cost S.rou.2-49 Use different protocols ZigBee Very low duty cycle Start & Mesh networks with up to 2 16 nodes Very long primary battery life applications Ability to remain quiescent for long periods of time without communicating to the network Bluetooth Moderate duty cycle Quasi-static star network with up to 7 client-nodes Used where either power is cycled or main-powered Wire replacement for consumer devices with Moderate data rates Very high QoS Very low, guaranteed latency S.rou.2-50 ZigBee and Bluetooth S.rou.2-51 ZigBee and Bluetooth S.rou.2-52 Silicon Application Application Interface Network Layer Data Link Layer MAC Layer MAC Layer PHY Layer ZigBee Stack Zigbee Application Voice Intercom Headset Cordless Group Call Telephony Control Protocol Silicon Protocol Stack Comparison User Interface vcard vcal vnote OBEX vmessage Dial-up Networking RFCOMM (Serial Port) L2CAP Host Control Interface Link Manager Link Controller Baseband RF Bluetooth Stack Bluetooth Fax Service Discovery Protocol Applications Timing Considerations ZigBee: Network join time = 30ms typically Sleeping slave changing to active = 15ms typically Active slave channel access time = 15ms typically Bluetooth: Network join time = >3s Sleeping slave changing to active = 3s typically Active slave channel access time = 2ms typically ZigBee protocol is optimized for timing critical applications
S.rou.2-53 S.rou.2-54 ZigBee and Bluetooth 802.15.4/ZigBee vs Bluetooth Bluetooth ZigBee AIR INTERFACE FHSS DSSS PROTOCOL STACK 250 kb 28 kb 900 800 700 Li-Coin Cell Battery Life (Beacon Interval vs Heartrate vs Days) At beacon interval ~60s, 15.4/ZigBee battery life approx 750 days BATTERY rechargeable non-rechargeable DEVICES/NETWORK 8 255 LINK RATE 1 Mbps 250 kbps Days 600 500 400 Bluetooth 33 days (park 300 mode @ 1.28s) 200 100 0 802.15.4/ZigBee superior at all beacon intervals greater than 0.246s 60 72 86 104 At beacon interval ~1s, 124 15.4/ZigBee battery life 149 nearly 136 days 179 BT@72bps RANGE ~10 meters (w/o pa) ~30 0.015 0.031 0.062 0.123 0.246 0.492 0.984 1.969 3.937 7.875 15.749 31.498 62.996 125.993 251.986 Comparison Overview Beacon Interval (sec) S.rou.2-55 S.rou.2-56 Comparison of key features WPAN: IEEE 802.15.4 Feature(s) IEEE 802.11b Bluetooth ZigBee Power Profile Hours Days Years Complexity Very Complex Complex Simple Nodes/Master 32 7 64000 Latency up to 3 secs up tp 10 secs 30ms Range 100 m 10m 70m-300m Extendability Roaming possible No YES Data Rate 11Mbps 1Mbps 250Kbps Security Authentication Service Set ID (SSID) 64 bit, 128 bit 128 bit AES and Application Layer user defined 802.15.4a: Alternative PHY with lower data rate as extension to 802.15.4 Properties: precise localization (< 1m precision), extremely low power consumption, longer range Two PHY alternatives UWB (Ultra Wideband): ultra short pulses, communication and localization CSS (Chirp Spread Spectrum): communication only 802.15.4b: Extensions, corrections, and clarifications regarding 802.15.4 Usage of new bands, more flexible security mechanisms 802.15.5: Mesh Networking Partial meshes, full meshes Range extension, more robustness, longer battery live