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Quick Convergecast in ZigBee/IEEE 802.15.4 Tree-Based Wireless Sensor Networks

Quick Convergecast in ZigBee/IEEE 802.15.4 Tree-Based Wireless Sensor Networks. 交通大學 High-Speed Communication & Computing Laboratory 指導教授 : 曾煜棋教授. Convergecast in Zigbee/IEEE802.15.4. Zigbee/IEEE802.15.4 tree-based Wireless Sensor Network contains: One sink (Zigbee Coordinator)

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Quick Convergecast in ZigBee/IEEE 802.15.4 Tree-Based Wireless Sensor Networks

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  1. Quick Convergecast in ZigBee/IEEE 802.15.4 Tree-Based Wireless Sensor Networks 交通大學 High-Speed Communication & Computing Laboratory 指導教授:曾煜棋教授

  2. Convergecast in Zigbee/IEEE802.15.4 • Zigbee/IEEE802.15.4 tree-based Wireless Sensor Network contains: • One sink (Zigbee Coordinator) • Some Full function devices (Zigbee Routers) • Some reduced function devices (Zigbee end device) • Each Zigbee router is responsible for collecting sensed data from end devices associated with it and relaying incoming data to the sink.

  3. Overview of IEEE802.15.4 and Zigbee Standard • A Zigbee router can announce a beacon to start a superframe • Each superframe consists of an active portion followed by an inactive portion. • Each active portion consists of 16 equal-length slots and can further partitioned into a contention access period (CAP) and a contention free period (CFP) • CAP: Slotted CSMA/CA is used in CAP • CFP: FFDs which require fixed transmission rates can ask for guarantee time slots (GTSs)

  4. An example of Convergecast in a ZigBee/IEEE 802.15.4 Tree-Based network • On receiving parent router’s beacon, and end device has to wake up for an active portion to sense the environment and communication with its coordinator. • To avoid collision with its neighbor, a router should shift its active portion by a certain amount.

  5. Motivation • Assuming that routers relay packets in contention-free guarantee time slots (GTSs). • The collected sensory data of A in the k-th superframe can be sent to C via the GTS of C in the k-th superframe • The superframe of B in the k-th superframe appears after that of C, the collected data of B in the k-th superframe can only be relayed to C along the GTS of C in the (k+1)-th superframe. • The delay can be eliminated if the active portion of B in the k-th superframe appears before that of C

  6. Motivation and problem • The delay in not negligible because of the low duty cycle design of IEEE802.15.4. • Our goal is to solve a minimum delay beacon scheduling problemfor quick convergecast in ZigBee/IEEE 802.15.4 tree-based wireless sensor networks.

  7. Problem definition • Minimum delay Beacon scheduling problem: • Given G=(V,E) and k available slots • Find the interference-free slot assignment s(i), such that the convergecast latency L(G) is minimized. where L(G) is the maximum of all nodes’s report latencies.

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