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

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 , 200 6] Source: [Ho-In Jeon (1), Yong-Bae Kim (2), Beom-Joo Kim (2), Jun-Seon Beck (2), Yeonsoo Kim (3)]

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

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  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: [+82-31-753-2532], E-Mail:[jeon1394@kornet.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. Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  2. An Analysis of 802.15.4-Based Mesh Network Architecture Ho-In Jeon (1) and YeonsooKim (2) (1) Kyung-Won University, HNRC of IITA, Republic of Korea, and (2) Advanced Technology Lab., KT Ho-In Jeon (KWU) and Yeonsoo Kim (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 Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  4. 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 Issues of Mesh Networks Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  5. 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 Goals of WPAN Mesh Network Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  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. Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  7. Beacon Scheduling - Fundamentals • Every node sends his beacon with beacon payload containing its depth information, its Beacon Transmission Time Slot (BTTS), and BTTS’s occupied by his neighbors and neighbor’s neighbors. • The first beacon slot can be used only by the PNC for the protection of PAN’s 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 3 2 Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  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 neighbor’s 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 neighbor’s neighbors. <Information contained in the beacon payload> Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  9. Beacon Scheduling 14 16 17 12 18 13 11 15 19 2 5 9 20 1 6 PNC 8 10 4 3 7 Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  10. Beacon Scheduling 2 1 PNC 3 CAP BOP 1 3 2 Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  11. Beacon Scheduling 2 5 9 1 6 8 10 PNC 4 3 7 BOP CAP 1 3 4 5 6 2 7 8 9 10 Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  12. Beacon Scheduling 14 16 17 12 13 11 15 2 5 9 1 6 8 10 PNC 4 3 7 CAP BOP 1 3 4 5 6 2 9 13 7 8 12 14 15 10 11 16 17 Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  13. Beacon Scheduling Performed 4 14 2 6 16 3 17 12 18 11 13 7 10 11 3 6 15 19 2 5 2 9 10 5 9 1 20 1 2 6 6 4 8 10 PNC 4 3 7 8 3 7 BOP CAP 1 3 4 5 6 2 9 13 18 7 8 12 14 15 20 10 11 16 19 17 Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  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 BTTS’s. • 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. Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  15. Beacon Payload Format Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  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 withoutbeacon payload is 11 Bytes • The length of PPDUheader 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 least12 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. Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  17. 802.15.4 Superframe Structure and Timing Efficiency = 99.6% Beacon Beacon CFP CAP GTS #1 GTS #2 Inactive 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 1 2 SlotD (Slot Duration) SlotD = aBaseSlotDuration × 2SO [symbols] = 60 × 2SO [symbols] = 0.96 × 2SO [msec] SD (Superframe Duration) SD = aBaseSuperframeDuration * 2SO [symbols] = 960 * 2SO [symbols] = 15.36 * 2SO [msec] BI (Beacon Interval) = aBaseSuperframeDuration * 2BO [symbols] = 960 * 2BO [symbols] = 15.36 * 2BO [msec] Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  18. Superframe Timing with SO = 3 and BO = 4 BOP Efficiency = 33.3% when BTTS = 64 aUnitBackoffPeriod = 320 usec ………. B3 Inactive B1 B2 B64 B1 CAP 0.192[msec]: Rx-Tx Turnaround Time 0.896[msec] 1.280[msec] 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) = aBaseSuperframeDuration * 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] Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  19. Superframe Timing with SO = 4 and BO = 5 BOP Efficiency = 66.7% when BTTS = 64 aUnitBackoffPeriod = 320 usec ………. B3 Inactive B1 B2 B64 B1 CAP 0.192[msec]: Rx-Tx Turnaround Time 0.896[msec] 1.280[msec] 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) = aBaseSuperframeDuration * 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] Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  20. Superframe Timing with SO = 4 and BO = 5 BOP Efficiency = 87.5% when BTTS = 32 aUnitBackoffPeriod = 320 usec ………. B3 Inactive B1 B2 B32 B1 CAP 0.192[msec]: Rx-Tx Turnaround Time 0.768[msec] 0.960[msec] 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) = aBaseSuperframeDuration * 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] Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  21. Superframe Timing with SO = 4 and BO = 5 BOP Efficiency = 93.75% when BTTS = 16 aUnitBackoffPeriod = 320 usec ………. B3 Inactive B1 B2 B16 B1 CAP 0.192[msec]: Rx-Tx Turnaround Time 0.704[msec] 0.960[msec] 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) = aBaseSuperframeDuration * 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] Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  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. Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  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. Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

  24. Acknowledgment • This work has been supported by Advanced Technology Lab. of KT. Ho-In Jeon (KWU) and Yeonsoo Kim (Advanced Technology Lab., KT)

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