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Wireless Sensor NetworksCase Study: ZigBee & IEEE802.15.4
S.rou.2
Dr.M.Y.Wu@CSEShanghai Jiaotong University
Shanghai, China
Dr.W.Shu@ECEUniversity of New Mexico
Albuquerque, NM, USA
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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ZigBee & 802.15.4
ZigBee overviewIEEE 802.15.4 overviewZigBee & bluetoothEnd
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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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.
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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ZigBee Solution
Targeted atHome/building automation & controlsConsumer electronics & PC peripheralsMedical monitoring & Toys
Design issuesLow-cost & long battery lifeSimplicity & reliabilityNetworking capabilityinteroperability
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Where is ZigBee in wireless marketSH
OR
T
<
RA
NG
E>
LO
NG
LOW < DATA RATE > HIGH
PAN
LAN
TEXT GRAPHICS INTERNET HI-FI AUDIO
STREAMINGVIDEO
DIGITALVIDEO
MULTI-CHANNELVIDEO
Bluetooth1
Bluetooth 2ZigBee
802.11b
802.11a/HL2 & 802.11g
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Where is ZigBee in wireless market
Range (meters)
WLAN
20-250kb/s
Bluetooth
Bluetooth 2
ZigBee
802.11
Data Rate
WPAN
WPAN
1 - 54 Mb/s 802.11b (Wi-Fi)
802.11g, 802.11a, HiperLAN
UWB/802.15.3a
1 Mb/s
>110 Mb/s
0 10010
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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ZigBee & 802.15.4 History
ZigBee
IEEE 802.15.4
1998 1999 2000 2001 2002
RSI/TRDProposals
Initial MRD v0.2
PAR
Proposalto IEEE
ProposalsStand.
CompleteReviews
ZigBee Allianceformed
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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ZigBee applications
ZigBeeWireless Control that
Simply Works
RESIDENTIAL/LIGHT
COMMERCIAL CONTROL
CONSUMER ELECTRONICS
TVVCRDVD/CDremote
securityHVAClighting controlaccess controllawn & garden irrigation
PC & PERIPHERALS
INDUSTRIALCONTROL
asset mgtprocess controlenvironmental
energy mgt
PERSONAL HEALTH CARE
BUILDING AUTOMATION
securityHVAC
AMRlighting control
access control
mousekeyboardjoystick
patient monitoring
fitness monitoring
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Stack references: ZigBee & IP/UDP
IEEE 802.15.4 PHY
IEEE 802.15.4 MAC (CPS)
ZigBee NWK
MAC (SSCS)802.2 LLC
IP
API UDP
ZA1 ZA2 … ZAn IA1 IAn
Transmission & reception on the physical radio channel
Channel access, PAN maintenance, reliable data transport
Topology management, MAC management, routing, discovery
protocol, security management
Application interface designed usinggeneral profile
End developer applications, designed using application profiles
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Protocol stack
Full protocol stack <32 k
Simple-node stack ~4k
Coordinators-noderequire extra RAMNode device databaseTransaction tablePairing tablePHY LAYER
2.4 GHz 915MHz 868 MHz
MAC LAYERMAC LAYER
NETWORK LAYERStar/Cluster/Mesh
APPLICATION INTERFACE
APPLICATIONS
SiliconApplication ZigBee Stack
Customer
IEEE802.15.4
ZigBee Alliance
SECURITY
8-bit microcontroller, a simple platform
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Wireless communication patterns
One-to-one Simple wire replacementDirect connection between devices
One-to-manyCentralized control/routing
Wi-Fi, GSM, Bluetooth All data have to go through “base station”
Mesh + MultihopSelf configuration/healingFull RF redundancy with multiple data pathsFully distributed paradigm
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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• 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 coordinatorFull Function nodeReduced Function node
Communications flowVirtual links
Node numbers and timings
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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ZigBee Topology Models
ZigBee coordinator
ZigBee Routers
ZigBee End Devices
Star
Cluster Tree
Mesh
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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ZigBee & 802.15.4
ZigBee overviewIEEE 802.15.4 overviewZigBee & bluetoothEnd
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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IEEE 802.15.4 Basics
A simple packet data protocol for lightweight wireless networksChannel Access
CSMA/CA: Carrier Sense Multiple Access with Collision Avoidance and optional time slotting
Message acknowledgement and an optional beacon structureReleased in May 2003, works well for
Long battery life, selectable latency for controllers, sensors, remote monitoring and portable electronics
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Frequencies and data rates
1040 kbpsAmericasISM915 MHz
120 kbpsEurope868 MHz
16250 kbpsWorldwideISM2.4 GHz
Channel#DataRateCoverageCoverageFrequency
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Frequencies and data rates
Choose to work in one of 27 channelsDepending on
AvailabilityCongestion stateData rate of each channel
250 kbps for computer peripherals, toys20-40 kbps for sensors, smart tags, consumer electronics
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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IEEE 802.15.4 & ZigBee stacks
Includes layers up to and including Link Layer ControlLLC is standardized in 802.1
Supports multiple network topologies including Star, Cluster Tree and MeshLow complexity:
14 PHY primitives 35 MAC primitives49 primitives total, versus 131 primitives in802.15.1 (Bluetooth) IEEE 802.15.4 MAC
IEEE 802.15.4 LLC IEEE 802.2LLC, Type I
IEEE 802.15.42400 MHz PHY
IEEE 802.15.4868/915 MHz PHY
Data Link Controller (DLC)
Networking App Layer (NWK)
ZigBee Application Framework
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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IEEE 802.15.4 System Configuration
Motorola RF Packet Radio Motorola 8-bit MCU
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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IEEE 802.15.4 MAC
Employs 64-bit IEEE & 16-bit short addressesUltimate network size can reach 264 nodes Using local addressing, simple networks of 64K (216) nodes can be configured, with reduced address overhead
Device complexitya simple 8-bit MCU and a pair of AAA batteries!
CSMA-CA channel accessSimple frame structure, optional superframe structure with beaconsGTS mechanismRTS/CTS mechanism is dropped
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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IEEE 802.15.4 Device Types
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 primitivesAdditional memory, computing power make it ideal for a network router functionCould 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 configurationGeneral usage will be in network edge devices
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Device communication
Difference in their communication patternsAn FFD
Can talk toRFDSFFDs
Operate in three modesPAN coordinator, coordinator, device
An RFD Can talk to
An FFDOperate in the device mode
P2P communication cannot happen between two RFDs
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Data transmission
Direct data transmissionUnslotted CSMA/CA
non-beacon-enabled modeSlotted CSMA/CA
beacon-enabled mode
Indirect data transmissionApplicable to data transfer from a coordinator to its devicesA device find out if it has a packet by checking the beacon
Guaranteed time slot (GTS) data transmissionApplicable to data transfer between coordinator & its devices
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Power-saving mechanisms
Based on beacon-enabled modeIn 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 transmissionA device can enter a low power state (sleeping) after checking the beacon.
In GTS data transmissionHas a low duty cycle, but relative expensive in power
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Self configuration
Association procedureSelect a channelSelect an ID for the PANDetermine whether to use beacon or non-beacon
If beacon, choose the beacon order & superframe orderAssign a 16-bit short address for a deviceSet BatteryLifeExtension option
OrphaningA device is considered orphaned if missed MaxLost-Beacons
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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MAC Channel Access
Non-beacon networkStandard ALOHA CSMA/CA communicationsPositive ACK for successfully received packets
Beacon-enabled networkSuperframe structure
For dedicated bandwidth up and low latencySetup 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 beaconsChannel access in each time slot is contention free
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Security & Robust
Three security levels specifiedNoneAccess control listsSymmetric key employing AES-128
802.15.4/ZigBee protocol is very robustClear channel checking before transmissionBackoff and retry if no ACK receivedDuty cycle of device is usually extremely low
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Data Frame format
One of two most basic and important structures in 15.4Provides up to 104 byte data payload capacityData sequence numbering to ensure that all packets are trackedRobust frame structure improves reception in difficult conditionsFrame Check Sequence (FCS) ensures that packets received are without error
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Acknowledgement Frame Format
The other most important structure for 15.4Provides active feedback from receiver to sender that packet was received without errorShort packet that takes advantage of standards-specified “quiet time”immediately after data packet transmission
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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MAC Command Frame format
Mechanism for remote control/configuration of client nodesAllows a centralized network manager to configure individual clients no matter how large the network
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Beacon Frame (superframe) format
Beacons add a new level of functionality to a networkClient devices can wake up only when a beacon is to be broadcast, listen for their address, and if not heard, return to sleepBeacons 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
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Frequencies and Data Rates
The two PHY bands (UHF/Microwave) have different physical, protocol-based and geopolitical characteristics
Worldwide coverage available at 2.4GHz at 250kbps900MHz for Americas and some of the Pacific868MHz for European-specific markets
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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PHY Performance
802.15.4 has excellent performance in low SNR environments
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Non-Beacon vs Beacon Modes
Non-Beacon ModeA simple, traditional multiple access system used in simple peer and near-peer networksThink 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 unintentionallyHowever, the recipient may not hear the call or the channel might already be in use
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Example of Non-Beacon Network
Commercial or home securityDevices
Sleep 99.999% of the timeWake 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 CoordinatorMains 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
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Non-Beacon vs Beacon Modes
Beacon ModeA very powerful mechanism for controlling power consumption in extended networks like cluster tree or meshAllows all clients in a local piece of the network the ability to know when to communicate with each otherHere, the two-way radio network has a central dispatcher who manages the channel and arranges the calls
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Example of Beacon Networkthe ZigBee Coordinator battery-operated also
All units in system are now battery-operatedClient 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 itReturn to sleep, awaking on a schedule specified by the ZigBee CoordinatorOnce 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 orTurn on earlier to make sure that the beacon is heard, increasing receiver power consumption, orImprove the quality of the timing oscillator circuit (increase cost) orControl the maximum period of time between beacons to not exceed 252 seconds, keeping oscillator circuit costs low
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Growing the Network
In a beacon-environment, growing the network means keeping the overall network synchronizedAccording 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 coordinatorBeacon information passed from ZigBee Coordinator to now-Router, router knows now when to awake to hear network beacon
Demoted to router
New link established
Existing network’s
Coordinator
Joining Network
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Reliability at different layers
PHY: Direct Sequence with Frequency Agility (DS/FA)
MAC: ARQ, Coordinator buffering
Network: Mesh Network (redundant routing)
Application Support Layer: Security
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Reliability at PHY layer
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.
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Direct Sequence and Frequency Agility
2.4 GHz
Channels 11-26
2.4835 GHz
5 MHz
2.4 GHz PHY
Over the Air After DS correlation
Interferer Desired Signal
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Reliability at MAC layer
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
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Reliability at network layer
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 passthe data, a different valid route is formed, transparent to the user.
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Reliability: Mesh Networking
ZigBee End Device (RFD or FFD)
ZigBee Router (FFD)
ZigBee Coordinator (FFD)
Mesh Link
Star Link
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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ZigBee & 802.15.4
ZigBee overviewIEEE 802.15.4 overviewZigBee & bluetoothEnd
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Why do we need both technologies?
Bluetooth wireless technologyWell focused towards voice applications and higher data rate applications (cell phones, headsets, etc.)
ZigBee technologyBest suited for control and monitoring applicationsL3: Low data rates, Low power, Low costsEase of use (remote controls, sensor nets, etc.)
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Optimized for different applications
ZigBeeSmaller packets over large networkMostly Static networks with infrequently used devicesHome automation, toys, remote controls, etc.
BluetoothLarger packets over small networkAd-hoc networksFile transfer Screen graphics, pictures, hands-free audio, Mobile phones, headsets, PDAs, etc.
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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ZigBeeIs better for devices Where the battery is ‘rarely’replacedTargets are :
Tiny fraction of host powerNew opportunities where wireless not yet used
Address different needs
Bluetoothis a cable replacement for items like Phones, Laptop Computers, Headsetsexpects regular chargingTarget is to use <10% of host power
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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ZigBeeDSSS: 11 chips/ symbol62.5 K symbols/s 4 Bits/ symbolPeak Information Rate~128 Kbit/secondOQPSK with shappingProtocol level: 28Kb
BluetoothFHSS1 M Symbol / secondPeak Information Rate ~720 Kbit / secondProtocol level: 250KbFrequency hop makes it hard to create extended net w/o large syn cost
Use different air interface
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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ZigBeeVery low duty cycleStart & Mesh networks with up to 216 nodes Very long primary battery life applicationsAbility to remain quiescent for long periods of time without communicating to the network
Use different protocols
BluetoothModerate duty cycleQuasi-static star network with up to 7 client-nodes Used where either power is cycled or main-poweredWire replacement for consumer devices with
Moderate data ratesVery high QoSVery low, guaranteed latency
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Silicon
PHY Layer
MAC LayerMAC Layer
Data Link Layer
Network Layer
ZigBeeStack Application
Application Interface
Application
Protocol Stack Comparison
Silicon
RFBaseband
Link Controller
Voic
e
Link ManagerHost Control Interface
L2CAP
TelephonyControlProtocol
Inte
rcom
Hea
dset
Cor
dles
sG
roup
Cal
l
RFCOMM(Serial Port)
OBEX
BluetoothStack Applications
vCar
dvC
alvN
ote
vMes
sage
Dia
l-up
Net
wor
king
Fax ServiceDiscoveryProtocol
User Interface
Zigbee Bluetooth
ZigBee and Bluetooth
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Bluetooth:• Network join time = >3s• Sleeping slave changing to active = 3s typically• Active slave channel access time = 2ms typically
ZigBee:• Network join time = 30ms typically • Sleeping slave changing to active = 15ms typically• Active slave channel access time = 15ms typically
Timing Considerations
ZigBee protocol is optimized for timing critical applications
ZigBee and Bluetooth
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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ZigBee and Bluetooth
Bluetooth ZigBee
AIR INTERFACE FHSS DSSS
PROTOCOL STACK 250 kb 28 kb
BATTERY rechargeable non-rechargeable
DEVICES/NETWORK 8 255
LINK RATE 1 Mbps 250 kbps
RANGE ~10 meters (w/o pa) ~30
Comparison Overview@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Li-Coin Cell Battery Life(Beacon Interval vs Heartrate vs Days)
0
100
200
300
400
500
600
700
800
900
0.01
5
0.03
1
0.06
2
0.12
3
0.24
6
0.49
2
0.98
4
1.96
9
3.93
7
7.87
5
15.7
49
31.4
98
62.9
96
125.
993
251.
986
Beacon Interval (sec)
Day
s
607286104124149179BT@72bps
Bluetooth 33 days (park mode @ 1.28s)
802.15.4/ZigBee superior at all beacon intervals greater than 0.246s
At beacon interval ~1s, 15.4/ZigBee battery life
nearly 136 days
At beacon interval ~60s, 15.4/ZigBee battery life
approx 750 days
802.15.4/ZigBee vs Bluetooth
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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Feature(s) IEEE 802.11b Bluetooth ZigBeePower Profile Hours Days YearsComplexity Very Complex Complex Simple
Nodes/Master 32 7 64000
Latency up to 3 secs up tp 10 secs 30ms
Range 100 m 10m 70m-300mExtendability Roaming possible No YESData Rate 11Mbps 1Mbps 250Kbps
SecurityAuthentication Service Set
ID (SSID)64 bit, 128 bit
128 bit AES and Application Layer user defined
Comparison of key features
@ by Dr.Shu@UNM & Dr.Wu@SJTU
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WPAN: IEEE 802.15.4
802.15.4a:Alternative PHY with lower data rate as extension to 802.15.4Properties: precise localization (< 1m precision), extremely low power consumption, longer rangeTwo PHY alternatives
UWB (Ultra Wideband): ultra short pulses, communication and localizationCSS (Chirp Spread Spectrum): communication only
802.15.4b:Extensions, corrections, and clarifications regarding 802.15.4Usage of new bands, more flexible security mechanisms
802.15.5: Mesh NetworkingPartial meshes, full meshesRange extension, more robustness, longer battery live