Authors: Joaquim Azevedo, Filipe Santos, Maurício Rodrigues, and Luís Aguiar Form : IET Wireless Sensor Systems Speaker: Hao-Wei Lu sleeping zigbee networks at the application layer

Outline 2 Abstract Introduction Synchronisation Synchronised sleeping technique Evaluation Conclusions

Abstract 3 ZigBee/IEEE is one of the most used standards for low-power applications. However, full function devices (FFD) must be always active to route data in a mesh network. The objective of this work is to implement a sleeping technique at the application layer that enables sleep mode for all nodes of a ZigBee network

Abstract (Cont.) 4 A large network is organised into smaller groups to reduce latency and packet collisions. The active interval of each node is dynamically adapted to the network operation to optimise the energy consumption. The results demonstrated energy savings of about 95% for networks containing up to 20 nodes per group and wake up periods longer than 2 min.

Introduction 5 Wireless sensor networks (WSNs) are being used in several different areas, such as environmental monitoring, industrial systems, buildings and infrastructure monitoring, precision agriculture and so on. Enabling sensor nodes to enter sleep mode has been considered one of the most effective solutions to reduce energy consumption and extend the lifetime of a WSN.

Introduction (Cont.) 6 Several sleep/wakeup schemes have been proposed to enhance the performance of the sensor nodes. Sensor-medium access control (S-MAC) is a well- known protocol used to improve energy efficiency by ordering all network devices to sleep in a periodic manner. timeout-MAC (T-MAC) is similar to S-MAC but saves more energy by introducing an adaptive duty cycle.

Introduction (Cont.) 7 The proposed technique not only provides data collection but also allows data transfer between different nodes. Furthermore, it is provided the sleep mode to all nodes of a ZigBee mesh network and protection against message losses.

Synchronisation 8 The ZigBee protocol does not provide synchronisation in mesh topologies. Therefore the development of an appropriate sleeping technique at the application layer also requires a synchronisation routine implemented in this layer.

Synchronisation (Cont.) 9 The collision avoidance method used in the ZigBee is the carrier sense multiple access with collision avoidance (CSMA/CA). These networks suffer from packet losses even with the existence of this mechanism.

Synchronisation (Cont.) 10

Synchronisation (Cont.) 11

Synchronisation (Cont.) 12 The synchronisation mechanism implemented at the application layer produces a rough approximation of the notion of time at each node. However, this approximation may alleviate the competition between nodes to obtain access to the channel.

Synchronised sleeping technique 13 SST scheme  The basic idea of the proposed synchronised sleeping technique (SST) is to provide the sleep mode to all nodes of a ZigBee network, which includes FFDs.  SST allows FFDs to sleep during network idle periods, which provides energy savings.

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Synchronised sleeping technique(Cont.) 15 Message recovery  In a ZigBee network message losses are common even with the existence of the MAC CSMA/CA algorithm. However, robustness against message losses may be required for some nodes.  The technique also considers this issue by recovering lost messages

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Evaluation 19 Synchronisation and clock drift results SST evaluation Message recovery

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Conclusion 26 A technique is proposed to enable all nodes in a ZigBee network to enter sleep mode. Compared with other techniques, the latency is lower and data transfer between nodes inside a group is allowed. Comparing the energy consumption for a network with and without the SST technique, energy savings for networks with at least 10% of routers were achieved.

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