SOTP: A Self-Organized TDMA Protocol for Wireless Sensor Networks

There is considerable interest in studying protocols for sensor networks. However due to the wide variation of sensor network applications and the constraints on hardware/software, existing protocols may only serve a specific sensor network application well or may be difficult to implement on real sensor nodes. In this paper, self-organized TDMA protocol (SOTP) for wireless sensor networks is presented. SOTP applies a cross layer protocol design approach to serve the application-specific and data-centric nature of wireless sensor networks. A TDMA based MAC scheme is used together with combining routing information during time slot allocation. This cross layer combination also helps to simplify node design and achieve energy efficiency. Several techniques are used in order to achieve collision-free slot allocation in a multi-hop network environment. Firstly, in the network set-up phase, a "carrier sensing" slot is introduced for channel contention, which prevents collision in data transmission slots. Secondly, although in SOTP sensor nodes are organized in an ad-hoc manner, the time slot allocation is determined centrally so that the collision-free state is adaptive to network topology changes. During the self-organization period, reverse scheduling is applied in slot allocation to reduce transmission delay. Simulation results show that SOTP can outperform the LEACH protocol with energy savings of up to 70%