Jan, 2009

1. Jan, 2009 Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Beacon Scheduling for Tree Topology Networks ] Date Submitted: [Jan, 2009] Source: [Ning Gu, Liang Zhang, Liang Li, Xiao Tao, Haito Liu, Betty Zhou] Company [Vinno, SIMIT, Huawei] Address [] Voice:[], FAX: [], E-Mail:[liang_1@yahoo.com] Re: [IEEE 802.15.4e group] Abstract: [Beacon Scheduling for Tree Topology Networks] Purpose: [] 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. Slide 1 Ning Gu , Liang Zhang, Haito Lui

2. Mesh and Tree Topology in WSN • Mesh networking is distributed, adaptive and self-organized, which meets ideal WSN’ features, but • If synchronized beacon is applied, mesh topology is very difficult to design. • An highly efficient network layer is required for data routing. • CSMA/CA is mainly used in Mesh and its long channel listening period does not meet WSN’s intention of power saving. • A reliable and stable mesh networks requires a complex and long network start procedure. • The ROM and RAM of mote might not be sufficient for mesh protocol code size. • Tree networking is suitable for building a practical WSN due to following reasons: • Most application can be implemented in tree topology. • Network resources are allocated by PAN coordinator, which helps developing a balanced topology structure. • No routing protocol is needed, any data is sent to parent node and destined to the PAN coordinator. • Each node is synchronized with its parent node, therefore, TDMA in slot allocation can be achieved in centralized way, which guarantees reliable data transmission and power saving. • No need to involve CSMA/CA algorithm. system can work in sleep mode besides Tx slot and Rx slot. • Occupy less hardware resources and easy for code developing and test.

3. Slot Allocation in TDMA • Time Slots are resources for allocating when applying TDMA algorithm, so slot allocation mechanism must be efficient, fair and adaptive. • Inappropriate slot allocation may result in: • Resources waste (slot number or length might be over allocated) • Data conflict (slots are assigned to same nodes) • Restrict network scale (improper beacon scheduling) • Long transmission latency (not adaptive allocation) • Unbalanced topology structure distribute • TDMA establishment shall be application oriented. Slot length and node working cycle must meet application feature.

4. The Slot Concept Based on Bitmap in Superframe • The B-slot, P-slot, C-slot, M-slot is similar to the Bitmap concept. This structure is compliant with EGTS Alliance’s MSF. • The defined P-slot part is a uplink GTS for sending data to parent node while the C-slot is the downlink GTS for receiving data from child nodes. • The defined M-slot is a part to work the same as CAP. Vinno suggests that nodes send data frame in GTS while CAP is only responsible for command frame transmission. • There is no particular inactive period in EGTS Alliance’s superframe structure, but unused slots could be treated as inactive period. • More slots shall be added into the superframe and the maximum slot number is related to the maximum nodes that a node could linked. • The bitmap slots allocation. • Bitmap contains two parts: the downlink bitmap and uplink bitmap. • The length of each bitmap in each MSF equals to 1 byte. • Bit with value 1 means this slot is vacant while bit with value 0 means this slot is not available. • P-slot can be merged into uplink bitmap with one bit being cleared for each MSF (use this cleared slot for communication with parent node). • C-slots be merged into downlink bitmap indicates the child nodes’ EGTS usage situation. Note: bitmap of slots allocation is centralized within each MSF.

5. The Detail of Joint Superframe Structure

6. Beacon Scheduling definition • The Beacon Scheduling definition is as: • Beacon interval consists of consecutive superframe. The number of superframe is defined by MO. • There is one CAP slot and one beacon for each superframe, The beacon slot from the first superframe is used by superframe owner for beacon reception (sync) while the other beacon slots are used for beacon transmission. • The number of GTS of each superframe shall be no more than the maximum child number of superframe owner. • Superframe features of beaconed coordinator is configured by MO (not only BO) and SO. • With the Scheduling Beacon, the adaptive TDMA operation may be available for WPAN.

7. Beacon Scheduling Set up for Tree Topology • Beacon scheduling method • Each node maintains a SD bitmap to represent usage of its multiple SD. For instance, SD bitmap 01010000 means SD bank 2 and SD bank 4 are vacant and other SD bank are occupied. • Childdevicealready knows parent node’s vacant SD bitmap (the vacant SD bitmap is contained in beacon frame and updated once SD is occupied, and the length of this SD bitmap is decided by SO and MO). • Device obtains neighbor node’s vacant SD information by scanning during those vacant SD. • Do AND operation between those vacant SD bitmap and obtains a “mutual vacant SD bitmap”. • Pick the first available SD from mutual vacant SDbitmapand transmits own beacon and notifies this scheduling information to its parent nodes during M-slot or EGTS. • Construct own vacant SD bitmap based on mutual vacant SD bitmap and insert this bitmap information into own beacon frame.

8. Beacon Scheduling based on SD Bitmap