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Industrial applications of wireless sensor networks require timeliness in exchanging messages among nodes. Although IEEE 802.15.4 provides a superframe structure for real-time communication, a real-time message-scheduling algorithm is still required to schedule a large number of real-time messages to meet their timing constraints. We propose a distance-constrained real-time offline message-scheduling algorithm which generates the standard specific parameters such as beacon order, superframe order, and guaranteed-time-slot information and allocates each periodic real-time message to superframe slots for a given message set. The proposed scheduling algorithm is evaluated and analyzed extensively through simulations. In addition, a guaranteed time service is implemented in a typical industrial sensor node platform with a well-known IEEE 802.15.4-compliant transceiver CC2420 and ATmega128L to verify the feasibility of the guaranteed time service with the schedule generated by the proposed scheduling algorithm. Through experiments, we prove that the real system runs accurately according to the schedule calculated by the proposed algorithm.

With low-power consumption, small code and data size, evolvability as design criteria, we develop an evolvable operating system (EOS) for wireless sensor network applications. The EOS provides memory space efficient thread management, collaborative thread communication model and network stack. It also supports power management of microcontroller and radio transceiver, and network wide time synchronization function. Above all, the most important feature is the concept of evolvability with which the operating system itself can be easily configurable and upgradeable.

Radionuclide impact of the Fukushima Dai-ichi nuclear power plant accident on the distribution of radionuclides in seawater of the NW Pacific Ocean is compared with global fallout from atmospheric tests of nuclear weapons. Surface and water column samples collected during the Ka'imikai-o-Kanaloa (KOK) international expedition carried out in June 2011 were analyzed for 134Cs, 137Cs, 129I and 3H. The 137Cs, 129I and 3H levels in surface seawater offshore Fukushima varied between 0.002–3.5 Bq L−1, 0.01–0.8 μBq L−1, and 0.05–0.15 Bq L−1, respectively. At the sampling site about 40 km from the coast, where all three radionuclides were analyzed, the Fukushima impact on the levels of these three radionuclides represents an increase above the global fallout background by factors of about 1000, 50 and 3, respectively. The water column data indicate that the transport of Fukushima-derived radionuclides downward to the depth of 300 m has already occurred. The observed 137Cs levels in surface waters and in the water column are compared with predictions obtained from the ocean general circulation model, which indicates that the Kuroshio Current acts as a southern boundary for the transport of the radionuclides, which have been transported from the Fukushima coast eastward in the NW Pacific Ocean. The 137Cs inventory in the water column is estimated to be about 2.2 PBq, what can be regarded as a lower limit of the direct liquid discharges into the sea as the seawater sampling was carried out only in the area from 34 to 37° N, and from 142 to 147° E. About 4.6 GBq of 129I was deposited in the NW Pacific Ocean, and 2.4–7 GBq of 129I was directly discharged as liquid wastes into the sea offshore Fukushima. The total amount of 3H released and deposited over the NW Pacific Ocean was estimated to be 0.1–0.5 PBq. These estimations depend, however, on the evaluation of the total 137Cs activities released as liquid wastes directly into the sea, which should improve when more data are available. Due to a suitable residence time in the ocean, Fukushima-derived radionuclides will provide useful tracers for isotope oceanography studies on the transport of water masses during the next decades in the NW Pacific Ocean.

To prolong the lifetime of nodes in wireless sensor networks, both transmission cost and processing power should be minimized. For this purpose, we propose a new direct source channel mapping method which utilizes large bandwidth. The system combines a closed-loop Differential Pulse Code Modulation (DPCM) source coder followed by pulse position modulation (PPM) transmission. To accommodate closed-loop prediction over a noisy channel an additional feedback channel is used. Two or more sequential samples are predicted at a time and combined before transmission, thus reducing transmission cost further. Simulations performed on both an auto regressive AR(1) source and a test image over additive white Gaussian noise (AWGN) channel show that our proposed system can achieve significant energy saving for both noiseless and noisy feedback channels without delay. We therefore propose a new framework for direct joint source channel mapping utilizing large bandwidth. Our system combines a closed-loop DPCM encoder followed by pulse position modulation (PPM) transmission. The source data redundancy is removed by DPCM. The closed loop prediction in DPCM is achieved by using a feedback channel from the receiver back to the transmitter. The major advantage of the system is its simple implementation on sensor nodes, while still achieves significant energy efficiency, robustness to error and performs without delay. The system provides an effective way for bandwidth expansion with high expansion factors which is complicated to achieve with the previous approaches (2-3). We investigate our system in both noiseless and noisy feedback channels. PPM transmission can be used in noisy feedback link which can achieve nearly same performance for both noiseless and noisy feedback channel.

We propose a real-time message scheduling algorithm which is applied to schedule periodic real-time messages in IEEE 802.15.4 for LR-WPAN (low rate wireless personal area network). The standard allows GTSs (guaranteed time slots) in the optional use of a superframe structure in a beacon-enabled network to be used to exchange real-time messages. To utilize these features of the standard efficiently, a proper message scheduling algorithm is needed. The proposed offline message scheduling algorithm which is based on a distance constrained scheduler generates the standard specific parameters including BO, SO, and GTS information to schedule the given message set. The algorithm is evaluated by simulation and the guaranteed time service using the schedule is implemented and evaluated on CC2420DB which is a prototyping platform including an IEEE 802.15.4 compliant transceiver of Chipcon AS.