IEEE 802.15 <subject>

1
Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
An Analysis of 802.15.4-Based Mesh Network
Architecture Date Submitted 18 May,
2006 Source Ho-In Jeon (1), Yong-Bae Kim (2),
Beom-Joo Kim (2), Jun-Seon Beck (2), Yeonsoo Kim
(3) Company Dept. Electronic Engineering,
Kyung-Won University (KWU) (1), LeiiTech Inc.
(2) Advanced Technology Lab., KT (3)
Address San 65, Bok-Jung-Dong, Sung-Nam-Shi,
Kyung-Gi-Do, Republic of Korea Voice 1
82-31-753-2533, Voice 2 82-19-9101-1394
FAX [phone], E-Mailjeon1394_at_korn
et.net Re This work has been supported by
HNRC of IITA. Abstract This document
proposes an Analysis of 802.15.4-Based Mesh
Network Architecture. Purpose Final Proposal
for the IEEE 802.15.5 Standard 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.
2
An Analysis of 802.15.4-Based Mesh Network
Architecture

• Ho-In Jeon (1) and Yeonsoo Kim (2)
• (1) Kyung-Won University, HNRC of IITA,
• Republic of Korea, and
• (2) Advanced Technology Lab., KT

3
Contents

• Introduction
• Issues of Mesh Networks
• Goals of WPAN Mesh Network
• Operating Principles of Mesh Network
• Superframe Structrue for Mesh Network
• Beacon Scheduling Fundamentals with BOP Concept
• Analysis of BOP and CAP Durations
• Conclusion

4
Issues of Mesh Networks

• Beacon Scheduling for Collision Avoidance
• Reduction of Power Consumption with Beacon
  Network
• Non-beacon-Enabled Network cannot provide a
  power-efficient operational mode
• Beacon Aggregation for throughput enhancement in
  the case of two or more PANs merging.
• Efficient Real-Time Short Address Allocation
  Algorithms
• Savings of Address Spaces
• Routing Algorithm Proactive or Reactive
• Power-Efficient Operation Mode
• Support of Time-Critical or Delay-Sensitive
  Applications
• Adoption of RTS/CTS or resource Reservation for
  Data Transmission

5
Goals of WPAN Mesh Network

• High speed as well as Low Speed WPAN
• High throughput
• Low latency
• Sensor Network
• Easy Network Configuration
• Fast and Efficient Short Address Allocations
• Possible Usage of Control Channel with
  single/multiple transceiver/radio solutions
• Centralized/Decentralized Beacon Scheduling
  and/or Aggregation for Spatial Frequency Reuse
• Data services
• Isochronous
• Asynchronous

6
Operating Principles of Mesh Networks

• Devices are associated sequentially, one by one.
• The relation between parent and children are
  characterized by association request and
  response.
• My parent and children are my neighbors.
• All devices I can hear are my neighbors.
• When an association request is granted by
  multiple nodes, the new node decides to associate
  with the node which has lower depth.
• When depth information is the same, he decides to
  associate with the node which transmits his
  beacon earlier than others.

7
Beacon Scheduling - Fundamentals

• Every node sends his beacon with beacon payload
  containing its depth information, its Beacon
  Transmission Time Slot (BTTS), and BTTSs
  occupied by his neighbors and neighbors
  neighbors.
• The first beacon slot can be used only by the PNC
  for the protection of PANs basic information.
• Solid blue line represents the Parent-Child
  relations based on associations, while red line
  represents directly reachable.
• Every mesh device shall transmit his beacon
  during the BOP (Beacon-Only Period) at the BTTS
  scheduled in a distributed manner.

2
1
PNC
CAP
BOP
3
1
1
2
3
8
Beacon Payload Info. for Beacon Scheduling

• When a node sends his beacon with beacon payload
  shown below, the receiver nodes can obtain the
  information of the BTTS occupied by its neighbors
  and its neighbors neighbors.
• The beacon scheduling is performed by choosing
  the smallest time slot of the BOP slots which
  avoids the time slots occupied by neighbors and
  its neighbors neighbors.

ltInformation contained in the beacon payloadgt
9
Beacon Scheduling
14
16
17
12
18
13
11
15
19
2
5
9
20
1
6
PNC
8
10
4
3
7
10
Beacon Scheduling
2
1
PNC
3
BOP
CAP
1
3
2
11
Beacon Scheduling
2
5
9
1
6
8
10
PNC
4
3
7
BOP
CAP
1
2
3
4
5
6
7
9
8
10
12
Beacon Scheduling
14
16
17
12
13
11
15
2
5
9
1
6
8
10
PNC
4
3
7
BOP
CAP
1
2
3
4
5
6
7
9
13
8
12
14
15
10
11
16
17
13
Beacon Scheduling Performed
4
14
2
16
6
3
17
12
18
11
13
7
10
11
3
15
6
19
2
5
2
9
10
5
9
20
1
1
6
2
6
4
8
10
4
PNC
3
7
8
3
7
BOP
CAP
1
3
4
5
6
2
7
8
9
13
18
10
11
12
14
15
20
16
17
19
14
An Analysis of BOP and CAP Durations

• The beacon scheduling allows 20 nodes to be
  located in one PAN with the topology shown by
  using only 11 BTTSs.
• It may be important to analyze the efficiency of
  the Mesh Network architecture with BOP concepts.
• The analysis is based upon the ratio of the CAP
  duration to Superframe Duration compared with
  legacy 15.4 devices.
• The efficiency can be improved by adopting
  adaptive BOP duration, or increasing the
  transmission rate.

15
Beacon Payload Format
16
Time Interval for Sending One Beacon

• The length of Beacon payload for beacon
  scheduling requires 11 Bytes (88 Bits)
• The length of beacon frame without beacon payload
  is 11 Bytes
• The length of PPDU header is 6 Bytes.
• The total transmission time of the beacon for
  beacon scheduling is 28 Bytes which require 28 x
  8 x 4 usec 896 usec.
• RX-to-Tx turnaround time requires at least 12
  symbols ( 192 usec)
• Therefore, the time length for the PAN to allow
  one beacon to be transmitted in the BOP becomes
  1,088 usec (896 192 usec).
• In order to cover 1,088 usec, we need 4
  aUnitBackoffPeriods (1,280 usec), which is the
  minimum time interval for sending 1 beacon in the
  case that 64 beacons are allowed in the BOP.

17
802.15.4 Superframe Structure and Timing
Efficiency 99.6
Beacon
Beacon
CAP
CFP
GTS 1
GTS 2
Inactive
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
2
1
0
SlotD (Slot Duration)
SlotD aBaseSlotDuration 2SO symbols
60 2SO symbols 0.96 2SO msec
SD (Superframe Duration) SD aBaseSuperframeDurat
ion 2SO symbols 960 2SO symbols
15.36 2SO msec
BI (Beacon Interval) aBaseSuperframeDuration
2BO symbols
960 2BO symbols 15.36 2BO msec
18
Superframe Timing with SO 3 and BO 4
BOP
Efficiency 33.3 when BTTS 64
aUnitBackoffPeriod 320 usec
.
Inactive
B1
B1
B2
B3
B64
CAP
0.192msec Rx-Tx Turnaround Time
0.896msec
1.280msec
Duration of BOP with 64 Beacons 1.280 x
64 81.920 msec
Duration of CAP with 64 Beacons 12.288 -
81.920 40.960 msec
SD (Superframe Duration) aBaseSuperframeDuratio
n 2SO symbols 15.36 2SO msec
122.88 msec
BI (Beacon Interval) aBaseSuperframeDuration
2BO symbols 960 2BO symbols 15.36
2BO msec 245.76 msec
19
Superframe Timing with SO 4 and BO 5
BOP
Efficiency 66.7 when BTTS 64
aUnitBackoffPeriod 320 usec
.
Inactive
B1
B1
B2
B3
B64
CAP
0.192msec Rx-Tx Turnaround Time
0.896msec
1.280msec
Duration of BOP with 64 Beacons 1.280 x
64 81.920 msec
Duration of CAP with 64 Beacons 245.76 -
81.920 163.840 msec
SD (Superframe Duration) aBaseSuperframeDuratio
n 2SO symbols 15.36 2SO msec
245.76 msec
BI (Beacon Interval) aBaseSuperframeDuration
2BO symbols 960 2BO symbols 15.36
2BO msec 491.52 msec
20
Superframe Timing with SO 4 and BO 5
BOP
Efficiency 87.5 when BTTS 32
aUnitBackoffPeriod 320 usec
.
Inactive
B1
B1
B2
B3
B32
CAP
0.192msec Rx-Tx Turnaround Time
0.768msec
0.960msec
Duration of BOP with 64 Beacons 0.960 x
32 30.720 msec
Duration of CAP with 64 Beacons 245.76
30.720 215.040 msec
SD (Superframe Duration) aBaseSuperframeDuratio
n 2SO symbols 15.36 2SO msec
245.76 msec
BI (Beacon Interval) aBaseSuperframeDuration
2BO symbols 960 2BO symbols 15.36
2BO msec 491.52 msec
21
Superframe Timing with SO 4 and BO 5
BOP
Efficiency 93.75 when BTTS 16
aUnitBackoffPeriod 320 usec
.
Inactive
B1
B1
B2
B3
B16
CAP
0.192msec Rx-Tx Turnaround Time
0.704msec
0.960msec
Duration of CAP with 64 Beacons 245.76
15.36 230.40 msec
Duration of BOP with 64 Beacons 0.960 x
16 15.36 msec
SD (Superframe Duration) aBaseSuperframeDuratio
n 2SO symbols 15.36 2SO msec
245.76 msec
BI (Beacon Interval) aBaseSuperframeDuration
2BO symbols 960 2BO symbols 15.36
2BO msec 491.52 msec
22
Observations on Beacon Scheduling Concept

• The BOP duration with 64 beacons was 81.920 msec,
  which can be considered to inefficient.
• Legacy 15.4 device spends at least 3
  aUnitBackoffPeriod which is 0.960 msec.
• The efficiency of the legacy device for the data
  transmission with SO 4 and BO 5 is 99.6.
• The efficiency of the mesh device with beacon
  scheduling for the data transmission with SO 4
  and BO 5 is 66.7.
• One solution for improving the efficiency is to
  reduce the number of BTTS.
• Other solution is to increase the transmission
  rate.

23
Conclusions and Discussions

• Mesh network requires a lot of problems to be
  solved
• Beacon conflicts and Data Conflicts
• Short Address allocations
• Hidden and Exposed Node Problems
• Delay-Sensitive Applications
• Power-Saving Mechanism
• Proposed a solution of avoiding beacon conflict
  by
• Beacon scheduling
• Proposed a solution of efficient address
  assignment
• Address allocated in real-time by using LAA
  field.
• Solved Running out of address space problem.
• Proposed an architecture for WPAN Mesh which
  reflects the real service scenarios.

24
Acknowledgment

• This work has been supported by Advanced
  Technology Lab. of KT.