Transcript IEEE 802.15.4 Low-Rate Wireless PAN (LR

IEEE 802.15.4
Low-Rate Wireless PAN
(LR-WPAN)
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Wireless Sensor Network Standards
IEEE 802.15.4 Low-Rate Wireless PAN
ZigBee
6LoWPAN
IEEE 1451
standards for connecting smart transducers to
networks
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Wireless Sensor Network Standards
End developer applications,
designed using application ZA1
profiles
Application interface designed using
general profile
Topology management, MAC
management, routing, discovery
protocol, security management
ZA2
…
API
IA1
IA2
IAn
Transport
6LowPAN
ZigBee NWK
Channel access, PAN maintenance,
reliable data transport
Transmission & reception on the
physical radio channel
802.2 LLC
MAC (SSCS)
IEEE 802.15.4 MAC (CPS)
IEEE 802.15.4 PHY
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802.15.4 with Five Key Words
Very low cost
Very low power consumption
Low complexity
Low rate
Short range
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Basic Radio Characteristics
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802.15.4 Applications Space
Home Networking
Automotive Networks
Industrial Networks
Interactive Toys
Remote Metering
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High-Level Characteristics
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802.15.4 Architecture
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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
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Network Topology
PAN
Coordinator
Full function device
Reduced function device
Star
Cluster tree
Point to point
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LR-WPAN: Data Rate
DSSS
Tx range: 10 ~ 75 m at 0 dBm (1 mW)
Band
Symbol rate
Modulation
Bit rate
channels
868 MHz
20 Ksps
BPSK
20 Kbps
1
915 MHz
40 Ksps
BPSK
40 Kbps
10
2.4 GHz
62.5 Ksps
O-QPSK
250 Kbps
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MAC Features
 Generating network beacons if the device is a coordi
nator
 Synchronizing to beacons
 PAN association, disassociation
 Optional acknowledged frame delivery
 Employing the CSMA/CA for channel access
mechanism
 Guaranteed time slot management
 MAC management has 35 primitives
RFD has 24 primitives
cf. 131 primitives of 802.15.1 / Bluetooth
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Superframe Structure
 For some applications requiring dedicated bandwidth to achieve low latencies
 A superframe is divided in 16 time slots
 CAP:
•
•
Slotted CSMA-CA channel access (beacon-enabled network)
Unslotted or standard CSMA-CA in networks (non beacon-enabled network)
 CFP: Optionally, contention-free access using Guaranteed Time Slots (GTSs) in beaconenabled netrwork
 aBaseSuperframeDuration = 60 symbols/slot * 16 slots = 960 symbols
 15.36 ms at 250 kbps, 24 ms at 40 kbs, 48 ms at 20 kbps
 BO (Beacon Order)
 How often the PNC transmits a beacon, 0 ≤ BO ≤ 14 (15.36 ms ~ 251.65824 sec)
 15 if non beacon
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Unslotted CSMA-CA
 Backoff periods of a device not related to that of any
other device
Therefore, synchronization is not required
 CCA – Clear Channel Assessment to check if channel is
busy or idle
aTurnaroundTime
Another Device’s Transmission
Frame
Transmission
Backoff
Number
2
1
Frame
arrival
BE=3
 2 selected
0 8
7
6
5
4
Perform CCA, and
finds channel busy
BE=4  8 selected
14
3
2
1
0
Perform CCA, and
finds channel idle
Slotted CSMA-CA
 Backoff period boundaries aligned by the periodic
beacon transmission
 It also implies that they are aligned with superframe
slot boundaries (for GTS) as Slot = n *
aUnitBackoffPeriod
BCN
aTurnaroundTime
Another Device’s Transmission
CW=
2
1
0
Frame
Transmission
Backoff
Number
2
1
Frame
arrival
BE=3
 2 selected
0
8
7
6
5
4
Perform CCA, and
finds channel busy
BE=4  8 selected
15
3
2
1
0
Perform CCA, and
finds channel idle
Inter-frame Spacing
Acknowledged transmission
Long frame
ACK
tack
ACK
Short frame
LIFS
tack
SIFS
Unacknowledged transmission
Long frame
Short frame
LIFS
SIFS
aTurnaroundTime  tack  (aTurnaroundTime (12 symbols) + aUnitBackoffPeriod (20 symbols))
LIFS > aMaxLIFSPeriod (40 symbols)
SIFS > aMacSIFSPeriod (12 symbols)
Short frame: frame size <= aMaxSIFSFrameSize
Long frame: otherwise
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MAC addressing
All devices have IEEE addresses (64 bits)
Short addresses (16 bits) can be allocated
Addressing modes
PAN identifier (16 bits)+ device identifier (16/64 bits)
Beacon frame: no destination address
General Frame Format
PHY Layer
MAC
Layer
Payload
Synch.
Header
(SHR)
PHY Header
(PHR)
MAC Header
(MHR)
MAC Service Data Unit
(MSDU)
MAC Protocol Data Unit (MPDU)
PHY Service Data Unit (PSDU)
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MAC Footer
(MFR)
General MAC Frame Format
Octets:2
Frame
control
1
0/2
0/2/8
0/2
Destination
Source
Destination
Sequence
PAN
PAN
address
number
identifier
identifier
Addressing fields
0/2/8
Source
address
MAC header
variable
2
Frame
payload
Frame
check
sequence
MAC
payload
MAC footer
Frame control field
Bits: 0-2
3
4
5
6
7-9
Frame type
Sequrity
enabled
Frame
pending
Ack. Req.
Intra PAN
Reserved
Beacon frame
Data frame
Acknowledgement frame
MAC command frame
10-11
Dest.
addressing
mode
12-13
Reserved
14-15
Source
addressing
mode
Destination in
Beacon frame
source PAN id is
skipped
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Data Frame format




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
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Acknowledgement Frame Format
 Provides active feedback from receiver to sender
that packet was received without error
 Short packet that takes advantage of standardsspecified “quiet time” immediately after data
packet transmission
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MAC Command Frame Format
 Mechanism for remote
control/configuration of client
nodes
 Allows a centralized network
manager to configure
individual clients no matter
how large the network
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Beacon Frame format
Bits: 0-3
Beacon
order
4-7
8-11
Superframe Final CAP
order
slot
12
Battery life
extension
13
Reserved
14
15
PAN
Association
coordinator
permit
 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
 Minimum beacon PPDU length = 136 bits / 250 Kbps = 544 μsec
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MAC Data Primitives
Primitive
Request
Confirm
Indication
MCPS-DATA
Required
Required
Required
MCPS-PURGE
Optional for Optional for
RFD
RFD
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Response
Data Transfer: no-beacon mode
Device  Coordinator
Originator
higher layer
Originator
MAC
MCPS-DATA.request
Recipient
MAC
Recipient
higher layer
Data frame
Acknowledgment (if requested)
MCPS-DATA.indication
MCPS-DATA.confirm
Coordinator  Device
Indirect
transmission
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Data Transfer: Beacon Mode
Device  Coordinator
Coordinator  Device
Coordinator
higher layer
Coordinator
MAC
Device
MAC
Device
higher layer
MCPS-DATA.request
(indirect)
Beacon frame
Data request
Acknowledgement
Data frame
Acknowledgment
MCPS-DATA.indication
MCPS-DATA.confirm
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Management Service
Access to the PIB
Association / disassociation
GTS allocation
Message pending
Node notification
Network scanning/start
Network synchronization/search
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MAC Management Primitives
Primitive
Request
Confirm
MLME-GET
Required
Required
MLME-SET
Required
Required
MLME-ASSOCIATE
Required
Required
MLME-DISASSOCIATE
Required
Required
MLME-GTS
Required
Required
Optional for RFD Optional for RFD
Required
Required
Optional for RFD Optional for RFD
MLME-RX-ENABLE
Required
MLME-SYNC
Required
Required
MLME-SYNC-LOSS
MLME-RESET




Required
Required
MLME-ORPHAN
MLME-START
Optional for RFD Optional for RFD
Required
MLME-COMM-STATUS
MLME-SCAN
Response
Optional for RFD Optional for RFD Optional for RFD
MLME-BEACON-NOTIFY
MLME-POLL
Indication
Required
Required
Required
Access to the PIB
Association / disassociation
GTS allocation
Message pending
 Node notification
 Network scanning/start
 Network synchronization/search
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Association
Device
higher layer
Device
MAC
MLME-ASSOCIATE.request
Coordinator
MAC
Coordinator
higher layer
Association request
Acknowledgment
MLME-ASSOCIATE.indication
aResponseWaitTime
MLME-ASSOCIATE.response
Data request
Acknowledgment
Association response
Acknowledgement
MLME-ASSOCIATE.confirm
MLME-COMM-STATUS.indication
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Disassociation
=
Originator
higher layer
Originator
MAC
Recipient
MAC
Recipient
higher layer
MLME-DISASSOCIATE.request
Disassociation notification
Acknowledgment
MLME-DISASSOCIATE.confirm
MLME-DISASSOCIATE.indication
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Data Polling
Device
higher layer
Device
MAC
Coordinator
MAC
MLME-POLL.request
No data pending
at the coordinator
Data request
Acknowledgment (FP = 0)
MLME-POLL.confirm
Data pending
at the coordinator
Device
higher layer
Device
MAC
Coordinator
MAC
MLME-POLL.request
Data request
Acknowledgment (FP = 1)
Data
Acknowledgement
MLME-POLL.confirm
MCPS-DATA.indication
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ED SCAN
When a prospective PAN coordinator to select a
channel
Measure peak energy in each requested
channel
Discard every frame received while scanning
Return energy levels
Active Scan
Device
higher layer
Device
MAC
 When FFD wants to
locate any coordinator
within POS
Coordinator
MAC
MLME-SCAN.request
st
Set 1 Channel
Beacon request
CSMA
ScanDuration
 A prospective coordinator
selects PAN ID
 Prior to device association
 Receive beacon frames
only
Beacon
 macPANId = 0xffff
Set 2
nd
 Send beacon request
command
Channel
Beacon request
 Destination PAN ID = 0xffff
MLME-SCAN.confirm
 Return PAN descriptors
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Passive Scan
Device
higher layer
Device
MAC
Coordinator
MAC
MLME-SCAN.request
st
Set 1 Channel
ScanDuration
Beacon
Set 2
nd
Channel
No beacon request
command
Device to prior to
association
Receive beacon
frames only
macPANId = 0xffff
MLME-SCAN.confirm
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=
Orphan Scan
Coordinator
higher layer
Coordinator
MAC
 Device attempts to
relocate its coordinator
 For each channel, send
orphan notification
command
Device
MAC
Orphan notification
MLME-ORPHAN.indication
 Dest PAN id, dest short
addr = 0xffff
MLME-ORPHAN.response
Coordinator realignment
MLME-COMM-STATUS.indication
 Only the original
coordinator will reply
 Receive coordinator
realignment command
frame only
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Differences from 802.11 WLAN
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
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Power Save Mechanisms
Going to sleep state as often as possible by
utilizing:
Inactive mode in superframes
Backoff periods when macRxOnWhenIdle is reset.
GTS for other devices
Extracting pending messages from coordinator
Using data request command
Message pending indicated in beacon frames
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LR-WPAN: Low Duty Cycle
 Beacon interval
(max) 960 symbols * 214 = 15,728,640 symbols
At 250 Kbps, (min) 15.36 msec ~ (max) 251.65824 sec
(over 4 min)
 Beacon duty cycle
544 μsec / 251.65824 sec = 0.000216% (lowest possible)
Non-beacon mode is also possible
 Example: 0.1% duty cycle
10 mW active, 10 μW standby → 19.99 μW average power
AAA battery with capacity of 750mAh, regulated to 1V
Battery life: 37,519 hours ≈ 4.28 years
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LR-WPAN: Imperfect Time Bases
εTbeacon
εTbeacon
TC
εRX Tbeacon
εRX Tbeacon
Uncertainty due
to imperfect
receiver time
base
“Ideal” beacon
receiver
reception time
εTX Tbeacon
εTX Tbeacon
“Ideal” beacon
transmitter
[Guti03]
transmission time
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Uncertainty due
to imperfect
transmitter time
base
LR-WPAN: Duty Cycle vs. Cost
Lowest possible duty cycle of a receiver is
(2ε·Tbeacon + TC) / Tbeacon
Duty cycle is
limited by the time base tolerance ε
No matter how long Tbeacon is made
IEEE 802.15.4 is designed to support
Time base tolerance as great as ±40 ppm
(note) lowest duty cycle = 2.16 ppm
Use of inexpensive reference crystals
Lower duty cycle requires more stable time base
Increases the cost of time base
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IEEE 802.15.4a
 Scope and Description:
 Develop an alternate physical layer (PHY) for data
communication with
•
•
•
•
•
•
high precision ranging / location capability (1 meter accuracy and better)
high aggregate throughput
and ultra low power
scalability to data rates
longer range
lower power consumption and cost.
 The alternate PHY is an (optional) amendment to the current
IEEE 802.15.4-2003 LR-WPAN standard.
 802.15.4a became an official Task Group in March 2004; with its
committee work tracing back to November 2002.
 Current Status
 The baseline is two optional PHYs
• UWB Impulse Radio (operating in unlicensed UWB spectrum)
• Chirp Spread Spectrum (operating in unlicensed 2.4GHz spectrum)
 The UWB Impulse Radio will be able to deliver communications
and high precision ranging.
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IEEE 802.15.4b
 Scope and Description
 Resolve ambiguities, provide corrections, removing unnecessary
complexity, and define enhancements to the current IEEE
802.15.4-2003 standard. The revised standard will be backward
compatible.
 Enhancements
 support for distributing a shared time-base
 Support for group addressing
 Extensions of the 2.4GHz derivative modulation
• Yields higher data rates at the lower frequency bands
 Support of Beacon-Enabled Cluster Tree network.
• IEEE802.15.4 does not support while 15.4b does
 Protection of broadcast and multicast frames possible
 Easier setup of protection parameters possible
 Possibility to vary protection per frame, using a single key
 Optimization of storage for keying material
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