This paper investigates active period selection for cluster-based WSNs employing traffic adaptive IEEE 802.15.4 beacon enabled medium access control (MAC) under spatial non-uniform traffic and cluster mobility environments, and proposes a simple autonomous distributed superframe duration (SD) selection scheme to enhance network performance under such environments. The proposed scheme autonomously selects an active SD at each cluster head (CH) by using beacon reception power monitoring (conducted in distributed control manner) and also introduces a beacon status notice from sensor nodes (SNs) to their parent CHs in order to prevent unnecessary SD selection at CHs. Moreover, SD reuse mechanism and joint operation with previously proposed distributed backoff mechanism are proposed for the proposed SD selection scheme to further enhance the network performance. The results of computer simulation show that the proposed scheme can improve both the transmission and power efficiency performance of cluster-based WSNs under spatial non-uniform traffic and cluster mobility environments.

It is known that demand and supply power balancing is an essential method to operate power delivery system and prevent blackouts caused by power shortage. In this paper, we focus on the implementation of demand response strategy to save power during peak hours by using Smart Grid. It is obviously impractical with centralized power control network to realize the real-time control performance, where a single central controller measures the huge metering data and sends control command back to all customers. For that purpose, we propose a new architecture of hierarchical distributed power control network which is scalable regardless of the network size. The sub-controllers are introduced to partition the large system into smaller distributed clusters where low-latency local feedback power control loops are conducted to guarantee control stability. Furthermore, sub-controllers are stacked up in an hierarchical manner such that data are fed back layer-by-layer in the inbound while in the outbound control responses are decentralized in each local sub-controller for realizing the global objectives. Numerical simulations in a realistic scenario of up to 5000 consumers show the effectiveness of the proposed scheme to achieve a desired 10% peak power saving by using off-the-shelf wireless devices with IEEE802.15.4g standard. In addition, a small-scale power control system for green building test-bed is implemented to demonstrate the potential use of the proposed scheme for power saving in real life.

The traffic adaptive 2-level active period control has been proposed as a traffic adaptation mechanism to handle temporal and spatial (geographical) traffic fluctuations in cluster-based wireless sensor networks (WSNs) employing IEEE802.15.4 medium access control (MAC). This paper proposes a traffic adaptive distributed backoff control mechanism for cluster-based WSNs with the traffic adaptive 2-level active period control to enhance the system performance, especially transmission performance. The proposed mechanism autonomously adjusts the starting time of the backoff procedure for channel accesses in the contention access period (CAP) specified by the IEEE802.15.4 MAC, and then distributes the channel access timing over a wide range within the CAP, which can mitigate channel access congestion. The results of computer simulations show that the proposed mechanism can improve the transmission delay performance while keeping the enhancement in throughput and energy consumption at the cluster-based WSNs under non-uniform traffic environments.

Temporal and spatial (geographical) fluctuations, which are present in the traffic of wireless sensor networks (WSNs), have a significant affect on the transmission performance and power consumption of WSNs. Several medium access control (MAC) mechanisms have been proposed for IEEE802.15.4 cluster-based WSNs to counter the temporal and spatial traffic fluctuations. However, these mechanisms cannot always achieve simultaneous improvement in both transmission performance and power consumption. In this paper, we propose two enhanced 2-level active period control mechanisms, BI&CAP control and BI&SD&CAP control, to achieve higher system performance than conventional control mechanisms. Various computer simulation results demonstrate the effectiveness of the proposed mechanisms for WSNs with various traffic fluctuations.

Traffic adaptive 2-level active period control has been proposed to enhance system performance in cluster-based wireless sensor networks (WSNs) employing IEEE 802.15.4 medium access control (MAC) under temporal and spatial (geographical) non-uniform traffic environments. This paper proposes an adaptive method of controlling the backoff window for traffic adaptive 2-level active period control. The proposed method adjusts the size of the backoff window according to the length of the current active period, which is determined by 2-level active period control, and the time position for channel access in the active period. The results evaluated through computer simulations reveal that the proposed method can improve throughput as well as achieve high energy efficiency in cluster-based WSNs with non-uniform traffic distributions.

With the increasing number of crimes and accidents in which children are becoming involved, there is a growing demand for devices to safeguard children's security by detecting their locations on their way to and from school. This paper proposes a system that uses an IEEE802.15.4-standard network to detect children's locations. To overcome the susceptibility of radio interference from nearby wireless LANs, frequency division multiplexing is applied to this IEEE802.15.4-based network, toward improving data acquisition from terminal units. The effectiveness of the system was field-tested with elementary school students who used about 400 IEEE 802.15.4-compliant terminal units. An experiment verified that the use of frequency division multiplexing in an environment where radio interference by wireless LANs is strong allowed the network to double the success rate of information communication from terminal units relative to that without frequency division multiplexing. In the experiment for detecting elementary schoolers' arrival at and departure from school, the terminal detection rate was 99% and the terminal detection rate on the designated school routes was 90%. These results prove the effectiveness of the system in detecting locations.

In March, 2007, IEEE802.15.4a was standardized as a low-rate and low-power UWB system for sensor networks. In general, detection of the IEEE802.15.4a signal is considered to be difficult because of its low transmitting power density and low duty cycle. However, if detecting of the IEEE802.15.4a signal is available, it is possible to avoid interference issues both among the IEEE802.15.4a systems and between the 15.4a and other UWB systems. This letter proposes a simple detection method using non-coherent detectors. The possibility of detecting of the IEEE802.15.4a signal by proposal detection method was examined. By conducting experiments with an emulated 15.4a RF signal, the signal detection probability was examined, and 15.4a signal from the range of about 11 meters in the radius could be detected. From this observation, the CSMA/CA method with detecting the signal in 15.4a system may be applied for alternative access method for 15.4a systems.