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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [ Time Slotted, Channel Hopping MAC ] Date Submitted: [ 1 Sep, 2008 ]

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slide1

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Submission Title: [Time Slotted, Channel Hopping MAC]

Date Submitted: [1 Sep, 2008]

Source: [Kris Pister, Chol Su Kang, Kuor Hsin Chang, Rick Enns, Clint Powell, José A. Gutierrez, Ludwig Winkel] Companies [Dust Networks, Freescale, Emerson, Siemens AG]

Address: [30695 Huntwood Avenue, Hayward, CA 94544 USA;890 N. McCarthy Blvd, Suite 120, Milpitas, CA 95035 USA; 8000 West Florissant Avenue St. Louis, Missouri 63136 USA; Siemensallee 74, Karlsruhe, Germany]

Voice: [+1 (510) 400-2900, +1 (408) 904-2705, +1 (650) 327-9708, +1 (480) 413-5413, +1 (314) 553-2667,+49 (721) 595-6098]

E-Mail: [ [email protected], [email protected], [email protected], [email protected], [email protected], [email protected],[email protected] ]

Re: [n/a]

Abstract: [This document proposes extensions for IEEE802.15.4 MAC]

Purpose: [This document is a response to the Call For Proposal, IEEE P802.15-08-373-01-0043]

Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.

Kris Pister et al.

slide2

Time Slotted, Channel Hopping MAC

(TSCH)

Kris Pister – UC Berkeley/Dust Networks

Chol Su Kang - Dust Networks

Kuor Hsin Chang - Freescale

Rick Enns - Consultant

Clinton Powell - Freescale

José A. Gutierrez – Emerson

Ludwig Winkel – Siemens

September, 2008

Kris Pister et al.

target applications
Target Applications

Industrial and commercial applications with a particular focus on:

  • Equipment and process monitoring
  • Non-critical control
  • Diagnostics/predictive maintenance
  • Asset management

Kris Pister et al.

requirements
Requirements
  • Industrial-Grade Reliability and robustness in the presence of multipath, path obstructions and interference
    • Industrial and commercial environments
    • Sustained operation in the presence of non-standards based communications systems
  • Long operational life for battery powered devices (> 5 years)
  • Co-existence
  • Flexible and scale-able
  • Easy wireless network deployment and maintenance

Kris Pister et al.

tsch accepted proven practical
TSCH- Accepted, Proven & Practical
  • Time Slotted, Channel Hopping (TSCH) technology is the basis for the wireless network of two industrial standards
    • HART Foundation (www.hartcomm2.org - over 200 companies worldwide): WirelessHART- published 9/07
    • ISA (www.isa.org – over 30,000 members worldwide): ISA100 Committee, ISA100.11a working group- in working group draft
  • TSCH has been implemented by multiple companies on multiple 2.4 GHz IEEE std. 802.15.4 platforms

Kris Pister et al.

timeslot access
Timeslot Access

CCA: RX startup, listen, RX->TX

Slot Frame Cycle

Unallocated Slot

Allocated Slot

Tx

Transmit Packet: Preamble, SFD, Headers, Payload, CRC

RX startup or TX->RX

RX ACK

Rx

RX startup

RX packet

Verify MIC

Calculate ACK MIC

Transmit

ACK

RX/TX turnaround

timeslot

TX/RX packet

TX/RX ACK

Devices are configured with a slotframe and timeslots to communicate with each other.

Kris Pister et al.

timeslot basics
Timeslot Basics

All devices in the same network synchronize slotframes

All timeslots are contained within a slotframe cycle

Timeslots repeat in time: the slotframe period

Device-to-device communication within a timeslot includes packet Tx/Rx & ACK Tx/Rx

Configurable option for CCA before transmit in timeslots

Kris Pister et al.

timeslot operation in devices
Timeslot Operation In Devices

Devices use timeslots to:

  • Schedule when they wakeup to transmit or listen
  • Keep time synchronized
    • Specification on time difference tolerances
    • Time synchronization mechanisms
  • Time the sequence of operations
    • Allow the source and destination to set their frequency channel
    • Listening for a packet
    • Sending a packet
    • Listening for an ACK
    • Generating an ACK
  • Synchronizes channel hops
  • Provide time to higher layers

Kris Pister et al.

sample timeslot processing
Sample Timeslot Processing

Kris Pister et al.

link types
Link Types
  • Dedicated Link – assigned to one device for transmission and to one or more devices for reception
    • A dedicated broadcast link is assigned to all devices for reception
  • Shared Link – assigned to more than one device for transmission
    • ACK failures detect collisions
    • A slot based back-off algorithm resolves collisions

Kris Pister et al.

channel hopping
Channel Hopping

Slot n+2

Slot n

Slot n-2

Slot n-1

Slot n+1

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

802.15.4 Channels

  • Combined with timeslot access to enhance reliability

Kris Pister et al.

channel hopping1
Channel Hopping
  • Mitigate Channel Impairments
    • Channel hopping adds frequency diversity to mitigate the effects of interference and multipath fading
  • Increase Network Capacity
    • One timeslot can be used by multiple links at the same time

Kris Pister et al.

link timeslot channel offset
Link = (Timeslot , Channel Offset)

D

B

One Slot

Time

Chan.

offset

A

BA

CA

DA

C

BA

BC

E

F

BE

BF

  • The two links from B to A are dedicated
  • D and C share a link for transmitting to A
  • The shared link does not collide with the dedicated links

Kris Pister et al.

channel hopping2
Channel Hopping

Time

BA

(ch 15)

BA

(ch25)

BA

(ch18)

CA

DA

CA

DA

CA

DA

Channel Offset

BA

BA

BA

BC

BC

BC

BE

BF

BE

BF

BE

BF

ASN=

N*4

N*4+1

N*4+2

N*4+3

(N+1)*4

CycleN+2

Cycle N+1

Cycle N

  • Each link rotates through k available channels over k cycles.
    • Ch # = Chan Hopping Seq. Table ( ( ASN + Channel Offset) % Number_of_Channels )
  • Blacklisting can be defined globally and locally.

Kris Pister et al.

timeslot timing offsets
Timeslot Timing Offsets

T1

T2

T4

T3

RX ACK

Transmitter

prepare to receive

CCA

TX Packet

TsRxAckDelay

TsCCAOffset

AWT

TsTxOffset

process packet,

prepare to ack

RX Packet

TX ACK

Receiver

prepare to receive

TsRxOffset

PWT

TsTxAckDelay

R1

R2

R3

End

of

timeslot

Start

of

timeslot

= transmitting packet

Timeslot with Acknowledged Transmission

= receiver on

= receiving packet

PWT = TsPacketWaitTime

AWT = TsAckWaitTime

Kris Pister et al.

timeslot timing offsets cont d
Timeslot Timing Offsets (Cont’d)

T1

T2

T4

T3

Idle receive

Transmitter

prepare to receive

CCA

TX Packet

TsRxAckDelay

TsCCAOffset

AWT

TsTxOffset

RX Packet

Receiver

prepare to receive

process packet, decide not to ack

TsRxOffset

PWT

R1

R2

End

of

timeslot

Start

of

timeslot

= transmitting packet

= receiver on

Timeslot with Unacknowledged Transmission

= receiving packet

PWT = TsPacketWaitTime

AWT = TsAckWaitTime

Kris Pister et al.

timeslot timing offsets cont d1
Timeslot Timing Offsets (Cont’d)

T1

T2

Transmitter

no ack expected

CCA

TX Packet

TsCCAOffset

TsTxOffset

RX Packet

Receiver

process packet, decide not to ack

prepare to receive

TsRxOffset

PWT

R1

R2

End

of

timeslot

Start

of

timeslot

= transmitting packet

= receiver on

Timeslot with Unacknowledged Broadcast

= receiving packet

PWT = TsPacketWaitTime

AWT = TsAckWaitTime

Kris Pister et al.

timeslot timing offsets cont d2
Timeslot Timing Offsets (Cont’d)

Transmitter

idle

Receiver

prepare to receive

idle

Idle rx

TsRxOffset

PWT

R1

R2

End

of

timeslot

Start

of

timeslot

Timeslot with Idle Receive

= receiver on

PWT = TsPacketWaitTime

Kris Pister et al.

time synchronization
Time Synchronization

TCCA

TCCA

TCCA

TCCA

Transmit Packet: Preamble, SFD, Headers, Payload, FCS

TProcessing

TACK

Transmit Packet: Preamble, SFD, Headers, Payload, FCS

TProcessing

TACK

Transmit Packet: Preamble, SFD, Headers, Payload, FCS

TProcessing

TACK

Tg

Tg

Tg

Tg

Transmit Packet:

Preamble, SFD,

Headers, Payload, FCS

Early

Perfect

Late

Tcomm = TTXPacket+TProcessing+TACK

Timeslot Period

TProcessing includes the processing of FCS and MIC validation as well as FCS and MIC generation for ACK. It’s the time from the last bit of the packet to the first bit of the preamble of the ACK.

Kris Pister et al.

time synchronization1
Time Synchronization

Acknowledgement-based Synchronization

Transmitter node sends a packet, timing at the start symbol.

Receiver timestamps the actual timing of the reception of start symbol

Receiver calculates TimeAdj = Expected Timing – Actual measured Timing

Receiver informs the sender TimeAdj

Transmitter adjusts its clock by TimeAdj

Kris Pister et al.

time synchronization cont d1
Time Synchronization (Cont’d)

Received Packet-based Synchronization

Receiver timestamps the actual timing of the reception of start symbol

Receiver calculates TimeAdj = TimeExpected (expected arrival time) – Actual timing

Receiver adjusts its own clock by TimeAdj

A node can be synchronized to more than one parent (i.e. timing reference nodes)

Kris Pister et al.

non conflicting timeslot assignment
Non-conflicting Timeslot assignment
  • Devices with multiple radios can be given one or more offsets.
  • Devices can be given one or more slots in a particular slotframe.
  • Devices with management ability can be given a block of (slot,offset)s

slot

Chan. offset

Kris Pister et al.

non conflicting timeslot assignment1
Non-conflicting timeslot assignment

Multiple slotframes with different lengths can operate at the same time.

4 cycles of the 250ms slotframe are shown, along with a 1000ms slot frame

There are never collisions if the 1000ms slot frame uses only the empty slots of the 250 ms slot frame

250ms

250ms

250ms

250ms

1,000ms

Kris Pister et al.

set slotframe
SET-SLOTFRAME
  • Request (Device Management  TSCH MAC)
    • Add, delete, or change a slotframe
    • Parameters: slotframe Id, operation, slotframe size, channel page, channel map, active flag
  • Confirm (TSCH MAC  Device Management)
    • Reports the results of SET-SLOTFRAME request command
    • Parameters: slotframe Id, status

Kris Pister et al.

set link
SET-LINK
  • Request (Device Management  TSCH MAC)
    • Add, change, or delete a link
    • Parameters1: operation type=ADD or CHANGE, link handle, frame Id, timeslot, channel offset, link options, link type, node addresses
    • Parameters2: operation type=DELETE, link handle
  • Confirm (TSCH MAC  Device Management)
    • Indicates the result of add, change or delete link command
    • Parameters: status, link handle

Kris Pister et al.

tsch mode
TSCH-MODE
  • Request (Device Management  TSCH MAC)
    • Puts the MAC to TSCH mode of operation
    • Parameters: none
  • Confirm (TSCH MAC  Device Management)
    • Reports the result of the TSCH-MODE request
    • Parameters: status

Kris Pister et al.

listen
LISTEN
  • Request (Device Management  TSCH MAC)
    • Request the MAC to search for a network
    • Parameters: channel page, 802.15.4 channel, duration
  • Confirm (TSCH MAC  Device Management)
    • Reports when the MAC completes the listen operation
    • Parameters: status
  • Indication (TSCH MAC  Device Management)
    • Indicates that the MAC received an ADVERTISEMENT packet while listening
    • Parameters: link quality, PAN ID, channel map, join priority, slotframes, links in each slotframe (these parameters, except link quality, are received in ADVERTISEMENT packet)

Kris Pister et al.

new tx option in existing primitive
New TX Option in Existing Primitive

MCPS.DATA.request Primitive

  • In TSCH Mode, the Next Higher Layer (NHL) may provide TSCH MAC a list of links. The NHL may choose the links the MSPDU may be transmitted on. The TSCH MAC selects the next available link from the list.

Kris Pister et al.

examples of tsch capability
Examples of TSCH Capability

Data collection

100 pkt/s per access point channel using 10 ms slots*

1600 pkt/s (16*100) network capacity with no spatial reuse of frequency

Radio duty cycle (power consumption)

Near theoretical limit for networks with moderate to high traffic

~0.02% for very low traffic networks

Latency

10ms / PDR (Packet Delivery Rate) per hop: best case

Statistical, but well modeled

* 10 ms slots are an example – the standard can define a range of slot sizes that can be selected for use

Kris Pister et al.

built in flexibility
Built-In Flexibility

Trade performance and power

Sample & reporting rate

Latency

Reliability

Throughput

High bandwidth connections

Tradeoffs can vary with

Time

Location

Events

Use power intelligently if you’ve got it

Highest performance with powered infrastructure

Kris Pister et al.

tsch summary
TSCH Summary
  • Proven technology- aligns with several industrial wireless standards
  • Meets the requirement for commercial and industrial monitor and process control applications
  • Extends the capabilities of the existing IEEE 802.15.4-2006 MAC

Kris Pister et al.

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