Impact of mobility on the
IoT MAC infrastructure :
IEEE 802.15.4e TSCH and
LLDN platform
Speaker: Po-Hung Chen
Advisor: Dr. Ho-Ting Wu
2016/04/01
Outline
• Introduction
• IEEE 802.15.4e
• TSCH
• LLDN
• Challenges and approaches
• Simulation Setting
• Simulation Result
• Conclusion
• Reference
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Introduction
• In mobility node scenario, this paper evaluates the connectivity and
radio duty cycle between IEEE 802.15.4e TSCH and LLDN mode.
• And shows some challenges and approach for TSCH and LLDN mode.
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IEEE 802.15.4e
• IEEE 802.15.4 is a standard which specifies the physical layer and mac
layer for low-rate wireless personal area networks (LR-WPANs) and it
has defined it in 2003.
• It’s used CSMA/CA.
• IEEE 802.15.4e is the first MAC amendment which has defined in
2012.
• There are two important mode of operation:
• Time slotted channel hopping(TSCH)
• Low latency deterministic network(LLDN)
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IEEE 802.15.4e(Cont.)
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IEEE 802.15.4e(Cont.)
• Tree Topology
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IEEE 802.15.4e(Cont.)
IEEE 802.15.4
Frequency is
2405+5(k-11)MHz,
k=11~26
(0 ~15)
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TSCH
Time slotted channel hopping(TSCH) combines
• Time slotted access
• Predictable and bounded latency
• Guaranteed bandwidth
• Multi-channel communication
• increased network capacity
(More node can communication at the same time using different channels)
• Channel hopping
• mitigates the effects of interference and multipath fading
• improves reliability
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TSCH(Cont.)
• Time slotted access
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TSCH(Cont.)
The timeslots in the slotframe structure is categorized into three types:
• Tx
• Rx
• SHARED Tx
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TSCH(Cont.)
Channel hopping
PHchannel = ASN + channelOffset % Nch
• PHchannel : physical channel
• ASN: absolute slot number
• Nch : number of channels
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TSCH(Cont.)
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TSCH(Cont.)
• A time slot is 10ms.
• This is not defined by the standard.
• In IEEE 802.15.4 operating in the 2.4 GHz frequency band,
a maximum-length frame of 127bytes takes about 4ms to transmit,
a shorter ACK takes about 1ms.
• It leaves 5ms to radio turnaround, packet processing, and security
operations.
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TSCH(Cont.)
The special Enhanced Beacons(EBs) for TSCH
• Synchronization information
• Channel hopping information
• Timeslot information
• Initial link and slotframe information
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TSCH(Cont.)
• FAST Association Mechanism (FastA)
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LLDN
• Low Latency Deterministic Mode (LLDN)
• In order to meet the stringent low latency requirements of industrial
applications.
• IEEE 802.15.4e has presented the LLDN mode and according to the
standard, within less than 10ms the coordinator must be able to
collect data from 20 devices.
• LLDN works only on star topology and PAN coordinator can support
more than 100 devices ,and use TDMA.
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LLDN(Cont.)
The reasons why LLDN can collect data from 20 devices within less than
10ms.
1. Reduced MAC frame header.
2. Coordinator scheduled the time slot to avoid collision.
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LLDN(Cont.)
• LLDN superframe structure
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LLDN(Cont.)
• LLDN superframe with separate GACK
GACK (group acknowledgement)
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LLDN(Cont.)
The LLDN mode has classified the network lifecycle into three different
transmission modes:
• Discovery state
• Configuration state
• Online state
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LLDN(Cont.)
• LLDN network
association procedure
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Challenges and approaches
TSCH
Issue
Impact
Multiple frequency channels
Increase the scanning time
Undefined beaconing mechanism
Mobile nodes can’t detect the existence
of coordinator
Undefined timeslots management
scheme
Mobile nodes added/deleted will change
the number of timeslot; means changing
ASN value and desynchronization
Undefined mechanism that defines the
existence of SHARED TX slots
Mobile nodes association; lack of these
slots will prevent mobile nodes from
associating to the network
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Challenges and approaches(Cont.)
LLDN
Issue
Impact
The mobile nodes are limited to associate
only during the discovery state
The mobile nodes will be disconnected
during the whole online state period
The LLDN has no defined approach to
change between the states
The nodes will stay in a single defined
state
During the discovery and configuration
The nodes are obligated to transmit only
states, the node can’t send readings which
during the online state
will increase the latency of data
Star topology network and single hop
communication
Needs for high number of coordinators to
cover the entire deployment area
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Simulation Setting
• Simulation parameters
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Simulation Setting(Cont.)
• Simulation mode:
• TSCH
• LLDN
• LLDN no interference
• Simulation slotframe/superframe size : 0.5s, 2s
• Simulation transmission range, number of coordinators :
(50m, 9), (100m, 4)
• LLDN online superframe to discovery and configuration superframes
ratio is 5 to 1.
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Simulation Result
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Simulation Result(Cont.)
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Simulation Result(Cont.)
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Simulation Result(Cont.)
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Simulation Result(Cont.)
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Simulation Result(Cont.)
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Conclusion
• Node mobility is an upcoming challenge in the IoT.
• In this paper, a study of TSCH and LLDN in mobility node scenario.
• Simulations show that TSCH has better connectivity but higher RDC
than the default implementation of the LLDN.
• After ignoring the impact of interference, the LLDN shows better RDC
and highest connectivity ratio than TSCH.
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Conclusion(Cont.)
• Hence, the best approach for the LLDN mode is to combine the
concept of channel hopping to the uplink.
• In TSCH mode, the appropriate practice is defining a beaconing
strategy that sets the beacon structure which facilitates the
association process.
And the beaconing has to be fixed to a single frequency channel so as
to has a low scanning time.
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Reference
• Yaarob Al-Nidawi; Harith Yahya; Andrew H. Kemp, “Impact of mobility on the IoT MAC infrastructure: IEEE
802.15.4e TSCH and LLDN platform” in 2015 IEEE 2nd World Forum on Internet of Things (WF-IoT), Dec. 2015,
pp.478-483
• Domenico De Guglielmo; Alessio Seghetti; Giuseppe Anastasi; Marco Conti, “A performance analysis of the
network formation process in IEEE 802.15.4e TSCH wireless sensor/actuator networks” in 2014 IEEE Symposium
on Computers and Communication (ISCC), June 2014, pp1-6
• Mashood Anwar; Xia Yuanqing, “IEEE 802.15.4e LLDN: Superframe configuration for networked control systems”
in 2014 33rd Chinese Control Conference (CCC), July 2014, pp.5568-5573
• T. Watteyne; A. Mehta and K. S. J. Pister, “Reliability Through Frequency Diversity: Why Channel Hopping Makes
Sense”, Performance Evaluation of Wireless Ad Hoc, Sensor, and Ubiquitous Networks(PE-WASUN), Oct. 2009,
pp116-123
• IEEE Standard 802.15.4 -2003
• IETF RFC 7554 -2015
• Michael Bahr (Siemens AG), “Low Latency Deterministic Networks (LLDN) base text for IEEE 802.15.4 REVc SB01
Waikoloa”, in IEEE 802.15 Documents, Aug. 2015
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Thank you for listening.
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