1. IEEE 802.15.4 Low-Rate Wireless PAN (LR-WPAN)

2. Wireless Sensor Network Standards
IEEE Low-Rate Wireless PAN
ZigBee
6LoWPAN
IEEE 1451
standards for connecting smart transducers to networks

3. Wireless Sensor Network Standards
1: Web Services Architecture
Wireless Sensor Network Standards
End developer applications, designed using application profiles
ZA1
ZA2 …
IA1
IA2
IAn
Application interface designed using
general profile
API
Transport
ZigBee NWK
6LowPAN
Topology management, MAC management, routing, discovery protocol, security management
802.2 LLC
MAC (SSCS)
Channel access, PAN maintenance, reliable data transport
IEEE MAC (CPS)
Transmission & reception on the physical radio channel
IEEE PHY

4. 802.15.4 with Five Key Words Very low cost Very low power consumption
Low complexity
Low rate
Short range 4

5. Basic Radio Characteristics

6. 802.15.4 Applications Space Home Networking Automotive Networks
Industrial Networks
Interactive Toys
Remote Metering 6

7. High-Level Characteristics7

8. Architecture 8

9. 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 9 9

10. Network Topology Star Point to point Cluster tree PAN Coordinator
Full function device
Reduced function device
Cluster tree
Point to point

11. 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
40 Kbps 10
2.4 GHz
62.5 Ksps
O-QPSK
250 Kbps 16

12. MAC Features Generating network beacons if the device is a coordinator
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 / Bluetooth 12

13. 1: Web Services Architecture
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 beacon-enabled 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 ~ sec)
15 if non beacon

14. 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 14

15. 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 15

16. Inter-frame Spacing Short frame: frame size <= aMaxSIFSFrameSize
Long frame: otherwise

17. 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

18. General Frame Format

19. General MAC Frame Format
Frame control field
Destination in Beacon frame
Beacon frame
Data frame
Acknowledgement frame
MAC command frame
source PAN id is skipped

20. 1: Web Services Architecture
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

21. Acknowledgement Frame Format
1: Web Services Architecture
Acknowledgement Frame Format
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

22. MAC Command Frame Format
1: Web Services Architecture
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

23. 1: Web Services Architecture
Beacon Frame format
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

24. MAC Data Primitives

25. Data Transfer: no-beacon mode
Device  Coordinator
Coordinator  Device
Indirect
transmission

26. Data Transfer: Beacon Mode
Device  Coordinator
Coordinator  Device

27. Management Service Access to the PIB Association / disassociation
GTS allocation
Message pending
Node notification
Network scanning/start
Network synchronization/search

28. MAC Management Primitives
1: Web Services Architecture
MAC Management Primitives
Access to the PIB
Association / disassociation
GTS allocation
Message pending
Node notification
Network scanning/start
Network synchronization/search

29. Association

30. Disassociation

31. Data Polling No data pending at the coordinator

32. 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

33. Active Scan When FFD wants to locate any coordinator within POS
A prospective coordinator selects PAN ID
Prior to device association
Receive beacon frames only
macPANId = 0xffff
Send beacon request command
Destination PAN ID = 0xffff
Return PAN descriptors

34. Passive Scan No beacon request command Device to prior to association
Receive beacon frames only
macPANId = 0xffff

35. Orphan Scan Device attempts to relocate its coordinator
For each channel, send orphan notification command
Dest PAN id, dest short addr = 0xffff
Only the original coordinator will reply
Receive coordinator realignment command frame only

36. Differences from 802.11 WLAN Simpler PHY Simpler MAC
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

37. 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 37

38. LR-WPAN: Low Duty Cycle
Beacon interval
(max) 960 symbols * 214 = 15,728,640 symbols
At 250 Kbps, (min) msec ~ (max) sec (over 4 min)
Beacon duty cycle
544 μsec / sec = % (lowest possible)
Non-beacon mode is also possible
Example: 0.1% duty cycle
10 mW active, 10 μW standby → μW average power
AAA battery with capacity of 750mAh, regulated to 1V
Battery life: 37,519 hours ≈ 4.28 years

39. LR-WPAN: Imperfect Time Bases
εTbeacon TC
εTbeacon
[Guti03]
εRX Tbeacon
εRX Tbeacon
Uncertainty due to imperfect receiver time base
“Ideal” beacon
reception time
receiver
εTX Tbeacon
εTX Tbeacon
“Ideal” beacon
transmission time
Uncertainty due to imperfect transmitter time base
transmitter

40. 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 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

41. 1: Web Services Architecture
IEEE a
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 LR-WPAN standard.
a 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.

42. 1: Web Services Architecture
IEEE b
Scope and Description
Resolve ambiguities, provide corrections, removing unnecessary complexity, and define enhancements to the current IEEE 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.
IEEE 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