Time Shift Grouping Access in IEEE 802.15.4 MAC Beacon Mode for Layered-Tree Networks

The IEEE 802.15.4/ZigBee attracts much attention as an energy-efficient and flexible low-rate wireless protocol for ubiquitous networks. This paper proposes a new active period assignment method called Time Shift Grouping Access (TSGA) in IEEE 802.15.4/ZigBee beacon mode for cluster-tree networks. By dividing top-level routers into two groups and using different time slots for accessing PAN coordinator, throughput bottleneck in Contention Access Period (CAP) is reduced. Beacon frame collision between subnets is also avoided by introducing different long spreading codes. Thus, low power intermittent operation with beacon is possible in each subnetwork. Simulation results show that the proposed method presents a better network throughput and reduces energy consumption by 1/2 to 1/3.