This paper presents the design and performance evaluation of a delay attack-resilient clock synchronization scheme (abbreviated to DARCS) for wireless sensor networks. In order to provide both synchronization accuracy and robustness, we propose a novel three-way handshake-based protocol, which completely excludes non-deterministic factors such as random backoff durations and unexpected hardware interrupts in a software manner and, in this way, the node can accurately estimate the relative clock offset and the end-to-end delay between a pair of nodes. Consequently, DARCS makes it possible to correct time synchronization errors as well as to detect delay attacks precisely. The simulation results show that DARCS achieves a higher synchronization accuracy and is more resilient to delay attacks than the other popular time synchronization schemes.

Many applications in wireless sensor networks (WSNs) require the energy efficiency and scalability. Although IEEE 802.15.4/Zigbee which is being considered as general technology for WSNs enables the low duty-cycling with time synchronization of all the nodes in network, it still suffer from its low scalability due to the beacon frame collision. Recently, various algorithms to resolve this problem are proposed. However, their manners to implement are somewhat ambiguous and the degradation of energy/communication efficiency is serious by the additional overhead. This paper describes an Energy-efficient BOP-based Beacon transmission Scheduling (EBBS) algorithm. EBBS is the centralized approach, in which a resource-sufficient node called as Topology Management Center (TMC) allocates the time slots to transmit a beacon frame to the nodes and manages the active/sleep schedules of them. We also propose EBBS with Adaptive BOPL (EBBS-AB), to adjust the duration to transmit beacon frames in every beacon interval, adaptively. Simulation results show that by using the proposed algorithm, the energy efficiency and the throughput of whole network can be significantly improved. EBBS-AB is also more effective for the network performance when the nodes are uniformly deployed on the sensor field rather than the case of random topologies.

In this letter, we propose an energy efficient hybrid architecture, the Hybrid MAC-based Robust Architecture (HMR), for wireless sensor networks focusing on MAC layer's scheduling and adaptive security suite as a security sub layer. A hybrid MAC layer with TDMA and CSMA scheduling is designed to prolong network life time, and the multi-channel TDMA based active/sleep scheduling is presented. We also present the security related functionalities needed to employ a flexible security suite to packets dynamically. Implementation and testbed of the proposed framework based on IEEE 802.15.4 are shown as well.

This paper presents the design and performance evaluation of a power-controlled topology optimization and channel assignment scheme for Hybrid MAC (abbreviated PTOCA) in wireless sensor networks that require comparatively high data rate communications. In order to maximize the network performance, PTOCA is designed with a cross-layer concept of MAC and network layers, which provides multi-channel TDMA scheduling based on the information of the network topology optimized by transmission power control. The simulation results show that by using the proposed scheme, the network throughput and energy efficiency can be significantly improved. PTOCA is also more effective in improving the network performance when the nodes are uniformly deployed on the sensor field rather than when they are randomly distributed.