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Requirements of IoT Wireless Networks
Huge number of devices Heterogeneous devices Low power consumption Robust Information Security
物聯網無線傳輸技術與應用- 4
Sensor Network Requirements Networks form by themselves Scale to large sizes Operate for years without manual intervention Extremely long battery life (years on AA cell),
low infrastructure cost (low device & setup costs) low complexity and small size
Low device data rate and QoS Standardized protocols allow multiple vendors to interoperate
物聯網無線傳輸技術與應用- 7
What is ZigBee Alliance? An organization with a mission to define reliable, cost effective, low-
power, wirelessly networked, monitoring and control products based on an open global standard
Alliance provides interoperability, certification testing, and branding
物聯網無線傳輸技術與應用- 8
IEEE 802.15 working group IEEE 802 LAN/MAN Standards Committee
802.1 Higher Layer
LAN Protocols Working Group
... 802.11 Wireless Local Area Networks Working Group
... 802.15 Wireless Personal
Area Networks Working Group
802.16 Broadband Wireless
MAN Working Group
802.17 Resilient
Packet Ring Working Group
TG1 WPAN/Bluetooth
Task Group
TG2 Coexistence Task Group
TG3 WPAN High Rate
Task Group
TG4 WPAN Low Rate
Task Group 物聯網無線傳輸技術與應用- 9
Why Zigbee?
Low power consumption Low cost Low offered message throughput Supports large network orders (<= 65k nodes) Low to no QoS guarantees Flexible protocol design suitable for many
applications 物聯網無線傳輸技術與應用- 10
ZigBee network applications
BUILDING AUTOMATION
SecurityHVACAMR
Lighting ControlAccess Control
PERSONAL HEALTH CARE
Patient monitoringFitness monitoring
INDUSTRIALCONTROL
Asset MgtProcess Control
EnvironmentalEnergy Mgt
PC & PERIPHERALS
MouseKeyboardJoystick
ENERGY MGT. & EFFICIENCY
Demand ResponseNet MeteringAMI, SCADA
TELECOM SERVICES
M-commerceInfo ServicesObject Interaction (Internet of Things)
HOME CONTROL
SecurityHVACLighting ControlAccess ControlIrrigation
CONSUMER ELECTRONICS
TVVCRDVD/CDUniversal Remotes
物聯網無線傳輸技術與應用- 11
ZigBee/IEEE 802.15.4
PHY 868MHz / 915MHz / 2.4GHz
MAC
Application
Network (NWK) Star / Mesh / Cluster-Tree
Security 32- / 64- / 128-bit encryption
API
ZigBee Alliance
IEEE 802.15.4
Customer ZigBee Alliance - (software) -Network, Security & Application layers -Brand management IEEE 802.15.4
- (hardware) -Physical & Media Access Control
ZigBee continues to work closely with the IEEE to ensure an integrated and complete solution for the market
物聯網無線傳輸技術與應用- 12 Silicon Stack App
General Characteristics Data rates of 250 kbps , 20 kbps and 40kpbs. Star or Peer-to-Peer operation. Support for low latency devices. CSMA-CA channel access. Dynamic device addressing. Fully handshaked protocol for transfer reliability. Low power consumption. Channels:
16 channels in the 2.4GHz ISM band, 10 channels in the 915MHz ISM band 1 channel in the European 868MHz band.
Extremely low duty-cycle (<0.1%) 物聯網無線傳輸技術與應用- 13
IEEE 802.15.4 Device Types There are two different device types :
A full function device (FFD) A reduced function device (RFD)
The FFD can operate in three modes by serving as Device Coordinator PAN coordinator
The RFD can only serve as: Device
物聯網無線傳輸技術與應用- 14
FFD vs RFD 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
物聯網無線傳輸技術與應用- 15
Star topology
Full Function Device (FFD) Reduced Function Device (RFD) Communications Flow
Network coordinator
Master/slave
Network coordinator
物聯網無線傳輸技術與應用- 16
Peer to peer topology
Communications Flow Full Function Device (FFD)
Point to point Tree
物聯網無線傳輸技術與應用- 17
Network Topologies (cont’d) Cluster Tree Topology
PAN Coordinator Cluster Head
PAN Coordinator
Cluster ID 0
CID 1
CID 2
CID 3
CID 4
CID 5
物聯網無線傳輸技術與應用- 18
ZigBee Network Model (Mesh)
ZigBee coordinator (FFD) ZigBee Router (FFD) ZigBee End Device (RFD or FFD) Star Link Mesh Link
物聯網無線傳輸技術與應用- 19
ZigBee Network Model Two or more devices communicating on the same
physical channel constitute a WPAN. A WPAN includes at least one FFD (PAN coordinator) Each independent PAN will select a unique PAN
identifier
物聯網無線傳輸技術與應用- 20
Device addressing
Each device has a unique IEEE 64-bit extended address Used for direct communication in the PAN
A device also has a 16-bit short address Allocated by the PAN coordinator when the device
associates with its coordinator.
物聯網無線傳輸技術與應用- 21
IEEE 802.15.4 PHY overview
PHY functionalities: Activation and deactivation of the radio transceiver Energy detection within the current channel Link quality indication for received packets Clear Channel Assessment (CCA) for CSMA-CA Channel frequency selection Data transmission and reception
物聯網無線傳輸技術與應用- 22
868MHz/ 915MHz PHY
2.4 GHz
868.3 MHz
Channel 0 Channels 1-10
Channels 11-26
2.4835 GHz
928 MHz 902 MHz
5 MHz
2 MHz
2.4 GHz PHY
IEEE 802.15.4 PHY Overview
Operating frequency bands
物聯網無線傳輸技術與應用- 23
Frequency Bands and Data Rates
The standard specifies two PHYs : 868 MHz/915 MHz DSSS +BPSK PHY (11 channels)
1 channel (20Kb/s) in European 868MHz band 10 channels (40Kb/s) in 915 (902-928)MHz ISM band
2450 MHz DSSS + O-QPSK PHY (16 channels) 16 channels (250Kb/s) in 2.4GHz band
物聯網無線傳輸技術與應用- 24
PHY Frame Structure PHY packet fields
Preamble (32 bits) – synchronization Start of packet delimiter (8 bits) – shall be formatted as “11100101” PHY header (8 bits) –PSDU length PSDU (0 to 127 bytes) – data field
Preamble Start of Packet
Delimiter
PHY Header
PHY Service Data Unit (PSDU)
4 Octets 0-127 Bytes
Sync Header PHY Payload
1 Octets 1 Octets
Frame Length (7 bit)
Reserve (1 bit)
物聯網無線傳輸技術與應用- 25
802.15.4 MAC Functionalities
Beacon Management Beacon generation (for coordinators) Beacon synchronization
Channel access (slotted or unslotted CSMA-CA) Guaranteed time slot management (QoS) Acknowledgement frame delivery Security mechanisms (AES)
物聯網無線傳輸技術與應用- 26
Superframe
A superframe is divided into two parts Inactive: all station sleep Active:
Active period will be divided into 16 slots 16 slots can further divided into two parts
Contention access period (CAP) Contention free period (GTS, Guaranteed Time Slot)
InactiveGTSGTS
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
BeaconBeacon
CAP CFP
SD=aBaseSuperframeDuration*2SOsymbols(Active)
BI=aBaseSuperframeDuration*2BOsymbols
物聯網無線傳輸技術與應用- 27
Superframe Beacons are used for
starting superframes synchronizing with other devices announcing the existence of a PAN informing pending data in coordinators
In a “beacon-enabled” network, Devices use the slotted CAMA/CA mechanism to contend for the
usage of channels FFDs which require fixed rates of transmissions can ask for
guarantee time slots (GTS) from the coordinator 物聯網無線傳輸技術與應用- 28
Superframe The structure of superframes is controlled by two parameters:
beacon order (BO) : decides the length of a superframe superframe order (SO) : decides the length of the active potion in a
superframe
For a beacon-enabled network, the setting of BO and SO should satisfy the relationship 0≦SO≦BO≦14
For channels 11 to 26, the length of a superframe can range from 15.36 msec to 215.7 sec (= 3.5 min).
物聯網無線傳輸技術與應用- 29
Superframe
BO-SO 0 1 2 3 4 5 6 7 8 9 ≧10 Duty cycle (%) 100 50 25 12 6.25 3.125 1.56 0.78 0.39 0.195 < 0.1
Each device will be active for 2-(BO-SO) portion of the time, and sleep for 1-2-(BO-SO) portion of the time
Duty Cycle:
物聯網無線傳輸技術與應用- 30
Data Transfer Model (I) Data transferred from device to coordinator
In a beacon-enable network, a device finds the beacon to synchronize to the superframe structure. Then it uses slotted CSMA/CA to transmit its data.
In a non-beacon-enable network, device simply transmits its data using unslotted CSMA/CA
Communication to a coordinator In a beacon-enabled network
Communication to a coordinator In a non beacon-enabled network
物聯網無線傳輸技術與應用- 31
Data Transfer Model (II-1)
Data transferred from coordinator to device in a beacon-enabled network: The coordinator indicates in
the beacon that some data is pending.
A device periodically listens to the beacon and transmits a Data Requst command using slotted CSMA/CA.
Then ACK, Data, and ACK follow …
Communication from a coordinator In a beacon-enabled network
物聯網無線傳輸技術與應用- 32
Data transfer model (II-2)
Communication from a coordinator in a non beacon-enabled network
Data transferred from coordinator to device in a non-beacon-enable network: The device transmits a Data
Request using unslotted CSMA/CA.
If the coordinator has its pending data, an ACK is replied.
Then the coordinator transmits Data using unslotted CSMA/CA.
If there is no pending data, a data frame with zero length payload is transmitted.
物聯網無線傳輸技術與應用- 33
Channel Access Mechanism
Two type channel access mechanism: beacon-enabled networks slotted CSMA/CA
channel access mechanism non-beacon-enabled networks unslotted CSMA/CA
channel access mechanism
物聯網無線傳輸技術與應用- 34
Slotted CSMA/CA algorithm In slotted CSMA/CA
The backoff period boundaries shall be aligned with the slot boundaries i.e. the start of first backoff period is aligned with the start of the
beacon transmission The MAC sublayer shall ensure that the PHY layer commences all
of its transmissions on the boundary of a backoff period
物聯網無線傳輸技術與應用- 35
Slotted CSMA/CA algorithm (cont.) Each device maintains 3 variables for each transmission
attempt NB: number of times that backoff has been taken in this attempt (if
exceeding macMaxCSMABackoff, the attempt fails) BE: the backoff exponent which is determined by NB CW: contention window length, the number of clear slots that
must be seen after each backoff always set to 2 and count down to 0 if the channel is sensed to be clear The design is for some PHY parameters, which require 2 CCA for efficient
channel usage. Battery Life Extension:
designed for very low-power operation, where a node only contends in the first 6 slots
物聯網無線傳輸技術與應用- 36
GTS Concepts (I) A guaranteed time slot (GTS) allows a device to operate
on the channel within a portion of the superframe A GTS shall only be allocated by the PAN coordinator The PAN coordinator can allocated up to 7 GTSs at the
same time The PAN coordinator decides whether to allocate GTS
based on: Requirements of the GTS request The current available capacity in the superframe
物聯網無線傳輸技術與應用- 39
GTS Concepts (II)
A GTS can be deallocated At any time at the discretion of the PAN coordinator or By the device that originally requested the GTS
A device that has been allocated a GTS may also operate in the CAP
A data frame transmitted in an allocated GTS shall use only short addressing
物聯網無線傳輸技術與應用- 40
GTS Concepts (III) Before GTS starts, the GTS direction shall be specified as
either transmit or receive Each device may request one transmit GTS and/or one receive
GTS
A device shall only attempt to allocate and use a GTS if it is currently tracking the beacon
If a device loses synchronization with the PAN coordinator, all its GTS allocations shall be lost
The use of GTSs be an RFD is optional
物聯網無線傳輸技術與應用- 41
Association Procedures (1/2) A device becomes a member of a PAN by associating
with its coordinator Procedures
Beacon (pending address)
ACK
Association req.
Coordinator Device
Data req.
ACK
Association resp.
ACK
Scan channel
Wait for response
Make decision
物聯網無線傳輸技術與應用- 42
Association Procedures (2/2) In IEEE 802.15.4, association results are announced in
an indirect fashion. A coordinator responds to association requests by
appending devices’ long addresses in beacon frames
Devices need to send a data request to the coordinator to acquire the association result
After associating to a coordinator, a device will be assigned a 16-bit short address.
物聯網無線傳輸技術與應用- 43
Individual Frame Format
• Beacon frame format
• Data frame format
Octets:2 1 4/10 0/5/6/10/14 2 variable variable variable 2
Frame Control
Sequence Number
Addressing fields
Auxiliary Security Header
Superframe Specification
GTS fields
Pending address fields
Beacon Payload
FCS
MHR MAC Payload MFR
Octets:2 1 (see7.2.2.2.1) 0/5/6/10/14 variable 2
Frame Control Sequence Number
Addressing fields Auxiliary Security Header
Data Payload FCS
MHR MAC Payload MFR
物聯網無線傳輸技術與應用- 45
Individual Frame Format (cont’d)
• Acknowledgement frame format
• MAC command frame format
Octets:2 1 2
Frame Control Sequence Number FCS
MHR MFR
Octets:2 1 (see7.2.2.4.1) 0/5/6/10/14 1 variable
2
Frame Control
Sequence Number
Addressing fields
Auxiliary Security Header
Command Frame
Identifier
Command Payload
FCS
MHR MAC Payload MFR
物聯網無線傳輸技術與應用- 46
ZigBee Network Layer Overview
ZigBee coordinator ZigBee router ZigBee end device
(a) (b) (c)
Three kinds of networks are supported: star, tree, and mesh networks
物聯網無線傳輸技術與應用- 47
ZigBee Network Layer Overview Three kinds of devices in the network layer
ZigBee coordinator: responsible for initializing, maintaining, and controlling the network
ZigBee router: form the network backbone ZigBee end device: must be connected to router/coordinator
In a tree network, the coordinator and routers can announce
beacons. In a mesh network, there is no regular beacon.
Devices in a mesh network can only communicate with each other in a peer-to-peer manner
物聯網無線傳輸技術與應用- 48
In ZigBee, network addresses are assigned to devices by a distributed address assignment scheme
ZigBee coordinator determines three network parameters the maximum number of children (Cm) of a ZigBee router the maximum number of child routers (Rm) of a parent node the depth of the network (Lm)
A parent device utilizes Cm, Rm, and Lm to compute a parameter called Cskip which is used to compute the size of its children’s address pools
Address Assignment
−⋅−−+
=−−⋅+= −−
(b) Otherwise ,1
1(a) 1 if ),1(1
)( 1
RmRmCmRmCm
RmdLmCmdCskip dLm
物聯網無線傳輸技術與應用- 49
If a parent node at depth d has an address Aparent, the nth child router is
assigned to address Aparent+(n-1)×Cskip(d)+1
nth child end device is assigned to address Aparent+Rm×Cskip(d)+n
C
A
B
Cm=6Rm=4Lm=3
Addr = 0, Cskip = 31
Addr = 1, Cskip = 7
Addr = 32, Cskip = 7
Addr = 63, Cskip = 7
Addr = 125
Addr = 126
Addr = 30
Addr = 31
Addr = 33, Cskip = 1
Addr = 38
Addr = 40, Cskip = 1
Addr = 39
Addr = 45
Addr = 64, Cskip = 1
Addr = 92
C
0 1 32 63
Cskip=31 Total:127 94 For node C
125 ,126 32 node A
物聯網無線傳輸技術與應用- 50
ZigBee Routing Protocols In a tree network
Utilize the address assignment to obtain the routing paths
In a mesh network:
Routing Capability: ZigBee coordinators and routers are said to have routing capacity if they have routing table capacities and route discovery table capacities
There are 2 options: Reactive routing: if having “routing capacity” Tree routing: if having no routing capacity
物聯網無線傳輸技術與應用- 51
ZigBee Tree Routing
C
A
B
Cm=6Rm=4Lm=3
Addr = 0, Cskip = 31
Addr = 1, Cskip = 7
Addr = 32, Cskip = 7
Addr = 63, Cskip = 7
Addr = 125
Addr = 126
Addr = 30
Addr = 31
Addr = 33, Cskip = 1
Addr = 38
Addr = 40, Cskip = 1
Addr = 39
Addr = 45
Addr = 64, Cskip = 1
Addr = 92 When a device receives a packet, it first
checks if it is the destination or one of its child end devices is the destination If so, accept the packet or forward it to a
child Otherwise, relay it along the tree
Example:
38 45 38 92
物聯網無線傳輸技術與應用- 52
ZigBee Mesh Routing
Route discovery by AODV-like routing protocol The cost of a link is defined based on the packet delivery probability on
that link
Route discovery procedure The source broadcasts a route request packet Intermediate nodes will rebroadcast route request if
They have routing discovery table capacities The cost is lower
Otherwise, nodes will relay the request along the tree The destination will choose the routing path with the lowest cost and then send a route reply
物聯網無線傳輸技術與應用- 53
Routing in a Mesh network: Example
S
aC
T
D
Discard route request B
UnicastBroadcastWithout routing capacity
route replyroute req.
route req.
route req.route req.
route req.
物聯網無線傳輸技術與應用- 54
Summary of ZigBee network layer Pros Cons
Star 1. Easy to synchronize 2. Support low power operation 3. Low latency
1. Small scale
Tree 1. Low routing cost 2. Can form superframes to support sleep
mode 3. Allow multihop communication
1. Route reconstruction is costly 2. Latency may be quite long
Mesh 1. Robust multihop communication 2. Network is more flexible 3. Lower latency
1. Cannot form superframes (and thus cannot support sleep mode)
2. Route discovery is costly 3. Needs storage for routing table
物聯網無線傳輸技術與應用- 55
Zigbee Application Layer Application Support Sublayer (APS) Zigbee Device Object (ZDO) Application Framework
containing manufacturer defined application objects
物聯網無線傳輸技術與應用- 57
Application Support Sub-Layer Provide an interface between the network layer (NWK) and the application
layer (APL) through a general set of services APSDE
provide the data transmission service support fragmentation and
reassembly of packets provide reliable data transport
APSME provide security services binding of devices establishment and removal of
group addresses maintains a database of managed objects
物聯網無線傳輸技術與應用- 58
Application Framework Environment for hosting manufacture defined application objects on Zigbee devices Uses APSDE-SAP interface
executing standard network functions managing protocol layers in the Zigbee device
Data service, provided by APSDE-SAP, includes request, confirm, response and indication primitives for data transfer
Up to 240 distinct application objects can be defined on an endpoint indexed from 1 to 240.
Application object represents different application types (or profiles) defined on a single Zigbee device
Endpoints (8-bit field) address specific application objects on a single Zigbee Device
物聯網無線傳輸技術與應用- 59
Application Profiles and Application Objects
Application profiles are agreements for messages, message formats and processing actions enable applications to create an interoperable, distributed application
between applications that reside on separate devices In the context of a profile, a group of related attributes is termed a
"cluster" and identified with a clusterId. Application Objects (APOs)
encapsulate a set of attributes (data entities representing internal state, etc.)
provides functionalities (services) for setting/retrieving values of these attributes
物聯網無線傳輸技術與應用- 60
Device Profile Must be implemented by all nodes in the Zigbee network Zigbee Device Objects (ZDO) implement this profile
provide a base class of functionality that provides an interface between the application objects, the device profile and the APS
Utilizes APS Data Services to transport messages Four key inter-device communication functions
Device and Service Discovery End Device Bind and Unbind Binding Table Management Network Management
物聯網無線傳輸技術與應用- 61
What is IEEE 802.11ah
IEEE 802.11 – Wi-Fi Wireless LAN IEEE 802.11 a/b/g/n/ac/ad
IEEE 802.11ah – Wireless transmission for IoT An energy efficient protocol allowing
thousands of indoor and outdoor devices
物聯網無線傳輸技術與應用- 63
Brief in 802.11ah
Band: Sub 1 Ghz (license-exempt) OFDM + MIMO (similar to .11n and .11ac) Long transmission range: > 1 km
Modified MAC and PLCP Saving power Support ~6000 devices Heterogeneous devices
物聯網無線傳輸技術與應用- 64
Use Case: Smart sensors and meters
Wide Area
GasMeter
WaterMeter
PowerMeter
Distributed Automation
Device
Neighbor Area Home Area
Wireless communication linkWired communication link
Proposed infrastructure
Data Collector & Control
IEEE 802.11ahAP
Distributed Automation
Device
source: IEEE 802.11-11/0457r0
物聯網無線傳輸技術與應用- 65
Use Case: Backhaul Aggregation
Wireless Sensor/Actor Network using IEEE802.15.4g PHY *Low data rate; <200kbps. *Low power; battery operation for >5years.
15.4g-11ah Router
11ah AP 2nd use case Backhaul Network
1st use case: Wireless Remote I/O *Aggregate many I/O points
15.4g-11ah Router
11ah AP
Backbone network Control Stations *Execute Feedback Control
Analog I/O, Digital I/O Analog I/O, Digital I/O
source: IEEE 802.11-11/0457r0 物聯網無線傳輸技術與應用- 66
Not adopted use cases
Media streaming for home entertainment Electronic menu and coupon distribution Indoor and outdoor location AP power saving
物聯網無線傳輸技術與應用- 68 ■
Physical Components in 802.11 Networks Access points (APs)
perform the wireless-to-wired bridging function Wireless Medium
A fixed frequency band (channel) will shared among all APs and stations
Stations Distribution system (DS)
a logical component of 802.11 used to forward frames to their destinations
Station
Wireless medium
Access Point
Distributionsystem
物聯網無線傳輸技術與應用- 69
WLAN – IEEE 802.11 (WiFi) Network Structure (I)
Independent BSS
Access Point
Infrastructure BSS
Independent Basic Service Set (IBSS)
Infrastructure Basic Service Set (BSS)
物聯網無線傳輸技術與應用- 70
WLAN – IEEE 802.11 (WiFi) Network Structure (II)
AP1
AP2
AP3 AP4
BSS1
BSS2
BSS3
BSS4
Router
Internet
Extended Service Set (ESS)
Distribution System
物聯網無線傳輸技術與應用- 71
IEEE 802.11 MAC (1) Basic mechanisms
CSMA/CA Carrier Sense Multiple Access w/ Collision Avoidance
RTS/CTS mechanism To prevent Hidden Node Problem
Positive acknowledgement Distributed Coordination Function (DCF)
Non-persistent CSMA/CA medium access method
物聯網無線傳輸技術與應用- 73
IEEE 802.11 MAC (2) Hybrid coordination function (HCF)
(optional) Point Coordination Function (PCF) Providing Contention-Free Service via Point Coordinator (PC)
(For QoS Enhancement) EDCA - Contention-Based channel access HCCA - Controlled channel access
物聯網無線傳輸技術與應用- 74
Positive Acknowledgement Acknowledge is required for each data frame.
If there is no ack sent back before timeout, the frame is regarded to be lost
物聯網無線傳輸技術與應用- 75
Hidden Node Problem Caused by the stations sharing same channel can
not ‘see’ each other. Collision will occur frequently
node A node B node C
Area reachable by node A Area reachable by node C
A B C
t1
Collision Cos’ wireless transceivers are half-duplex.
ok ok
物聯網無線傳輸技術與應用- 76
RTS/CTS Mechanism (I) To solve hidden node problem
node A node B node C
Area reachable by node A Area reachable by node C
A B C
RTS
CTS
Frame
ACK
RTS: I want to send to B 500 bytes
CTS: OK A, go ahead, so everybody quiet
Data: the 500 bytes of data from A to B
ACK: B received the data OK, so an ACK
RTS: Ready-To-Send CTS: Clear-To-Send
物聯網無線傳輸技術與應用- 77
DCF
Non-persistent Approach Contention still occur with very small probability
(Source: IEEE 802.11-2007) 物聯網無線傳輸技術與應用- 78
Example of DCF Operations
Station 1
Station 2
Station 3
Station 4
DIFS DIFS Packet arrival at MAC
busy
Backoff=9
Backoff=5
Backoff=7
busy
DIFS 9-5=4
7-5=2
busy
DIFS 4-2=2
busy
物聯網無線傳輸技術與應用- 79