Today, localization of nodes in Wireless Sensor Networks (WSNs) is a challenging problem. Especially, it is almost impossible to guarantee that one algorithm giving optimal results for one topology will give optimal results for any other random topology. In this study, we propose a centralized, range- and anchor-based, hybrid algorithm called RH+ that aims to combine the powerful features of two orthogonal techniques: Classical Multi-Dimensional Scaling (CMDS) and Particle Spring Optimization (PSO). As a result, we find that our hybrid approach gives a fast-converging solution which is resilient to range-errors and very robust to topology changes. Across all topologies we studied, the average estimation error is less than 0.5 m. when the average node density is 10 and only 2.5% of the nodes are beacons.

We examined how spatial disparity between the auditory and visual stimuli modulated the audio-visual (A-V) prior entry effect. Spatial and temporal proximity of multisensory stimuli are crucial factors for multisensory perception in most cases (e.g. [1],[2]). However our previous research[3],[4] suggested that this well-accepted hypothesis was not applicable to the A-V prior entry effect. In order to examine the effect of the spatial disparity on the A-V prior entry effect, six loudspeakers and two light emitting diodes (LEDs) were used as stimuli. The loudspeakers were located at 10, 25, and 90 degrees from the midline of the participants to both right and left sides. A preceding sound was presented from one of these six loudspeakers. After the preceding sound, two visual targets were presented successively at a short interval and participants judged which visual target was presented first. Two colour changeable ('red' or 'green') LEDs were used for the visual targets and participants judged the order of visual targets by their colour not by their side in order to avoid the response bias as much as possible. The visual targets were situated at 10 degrees or 25 degrees from the participants' midline to both right and left in the Experiment 1. Results showed a biased judgment that the visual target at the sound presented side was presented first. The amplitude of the A-V prior entry effect was greater when the preceding sound source was more apart from the midline of participants. This effect of spatial separation indicated that the clarity of either right or left side of the preceding sound enhanced the amplitude of the A-V prior entry effect (Experiment 2). These results challenge the belief that the spatial proximity of multisensory stimuli is a crucial factor for multisensory perception.

Recent advancements in the ubiquitous sensor network field have brought considerable feasibility to the realization of a ubiquitous society. A ubiquitous sensor network will enable the cooperative gathering of environmental information or the detection of special events through a large number of spatially distributed sensor nodes. Thus far, radio frequency identification (RFID) as an application for realizing the ubiquitous environment has mainly been developed for public and industrial systems. To this end, the most existing applications have demanded low-end antennas. In recent years, interests of ubiquitous sensor network have been broadened to medical body area networks (BAN), wireless personal area networks (WPAN), along with ubiquitous smart worlds. This increasing attention toward in ubiquitous sensor network has great implications for antennas. The design of functional antennas has received much attention because they can provide various kinds of properties and operation modes. These high-end antennas have some functions besides radiation. Furthermore, smart sensor nodes equipped with cooperated high-end antennas would allow them to respond adaptively to environmental events. Therefore, some design approaches of functional antennas with sensing and reconfigurability as high-end solution for smart sensor node, as well as low-end antennas for mobile RFID (mRFID) and SAW transponder are presented in this paper.

This paper presents an efficient time slot assignment algorithm for a wireless sensor and actor network (WSAN), which consists of stationary sensors for detecting events and mobile actors for performing tasks. TDMA protocols are suitable for WSAN due to time-critical tasks, which are assigned to actors. In order to improve the performance of TDMA protocol, a time slot assignment algorithm should generate not only efficient TDMA scheduling but also reduce periodic run-time overhead. The proposed algorithm offers O(δ2) run-time in the worst case, where δ is the maximum number of one-hop and two-hop neighbors in the network. The average run-time in simulation results is far less than O(δ2), however, while the maximum number of assigned slots is bounded by O(δ). In order to reduce the run-time further, we introduce two fundamental processes in the distributed slot assignment and design the algorithm to optimize these processes. We also present an analysis and verify it using ns-2 simulations. Although the algorithm requires time synchronization and prior knowledge of two-hop neighbors, simulation results show that it reduces the run-time significantly and has good scalability in dense networks.

PIN diodes for digital X-ray detection as a single photon counting sensor were fabricated on a floating-zone (FZ) n-type (111), high resistivity (5-10 kΩcm) silicon substrates (500 µm thickness). Its electrical properties such as the leakage current and the breakdown voltage were characterized. The size of pixels was 100 µm100 µm. The p+ guard-ring was formed around the active area to reduce the leakage current. After the p+ active area and guard-ring were fabricated by the ion-implantation, the extrinsic-gettering on the wafer backside was performed to reduce the leakage current by n+ ion-implantation. PECVD oxide was deposited as an IMD layer on front side and then, metal lines were formed on both sides of wafers. The leakage current of detectors was significantly reduced with a guard-ring when compared with that without a guard ring. The leakage current showed the strong dependency on the gap distance between the active area and the guard ring. It was possible to achieve the leakage current lower than 0.2 nA/cm2.

This study is to investigate new schemes for distributing cryptographic keys in sensor networks. Sharing a key is the very first step to realize secure communication over an untrusted network infrastructure, but commonly used cryptographic techniques cannot be employed for sensor networks due to the restriction of computational resources of sensor nodes. A practical solution to this issue is to predistribute cryptographic keys in sensor nodes before they are deployed. A focal point in this solution is the choice of keys that are assigned to a sensor node. Eschenauer et al. considered to choose keys randomly, and Chan et al. also followed the random choice approach. We consider in this paper a new approach in which keys are assigned according to a basic algebraic geometry. The performance of the proposed scheme is investigated analytically.

In this paper, a routing protocol referred to as Directed Diffusion with Stepwise Interest Retransmission (DD/SIR) for wireless sensor networks is proposed to mitigate power consumption considering node mobility. In DD/SIR, a sink retransmits interest. The propagation areas of the interest are narrowed stepwisely. In addition, according to the number of hops between the sink and sensor nodes, the data transmission timing is controlled sequentially. By both theoretical analysis and computer simulation, we evaluate the performance of DD/SIR. We show that DD/SIR can mitigate control overhead and realize low power operation without degrading data reachability to the sink. Especially, at a small number of data sending nodes, DD/SIR is more effective than the conventional routing.

In this paper, we revisit a generally accepted opinion: implementing Elliptic Curve Cryptosystem (ECC) over GF(2m) on sensor motes using small word size is not appropriate because XOR multiplication over GF(2m) is not efficiently supported by current low-powered microprocessors. Although there are some implementations over GF(2m) on sensor motes, their performances are not satisfactory enough to be used for wireless sensor networks (WSNs). We have found that a field multiplication over GF(2m) are involved in a number of redundant memory accesses and its inefficiency is originated from this problem. Moreover, the field reduction process also requires many redundant memory accesses. Therefore, we propose some techniques for reducing unnecessary memory accesses. With the proposed strategies, the running time of field multiplication and reduction over GF(2163) can be decreased by 21.1% and 24.7%, respectively. These savings noticeably decrease execution times spent in Elliptic Curve Digital Signature Algorithm (ECDSA) operations (signing and verification) by around 15-19%. We present TinyECCK (Tiny Elliptic Curve Cryptosystem with Koblitz curve - a kind of TinyOS package supporting elliptic curve operations) which is the first implementation of Koblitz curve on sensor motes as far as we know. Through comparisons with existing software implementations of ECC built in C or hybrid of C and inline assembly on sensor motes, we show that TinyECCK outperforms them in terms of running time, code size and supporting services. Furthermore, we show that a field multiplication over GF(2m) can be faster than that over GF(p) on 8-bit Atmega128 processor by comparing TinyECCK with TinyECC, a well-known ECC implementation over GF(p). TinyECCK with sect163k1 can generate a signature and verify it in 1.37 and 2.32 secs on a Micaz mote with 13,748-byte of ROM and 1,004-byte of RAM.

Impulse ultra-wideband (UWB) is an attractive technology for large ad hoc sensor networks due to its precise ranging capacity, multi-path fading robustness and low radiation power. The transient and carrier-less nature of low radiation pulse and harsh multipath channel condition makes it cumbersome to implement carrier sensing. We proposed clear channel assessment (CCA) based on preamble-assisted modulation (PAM) for UWB sensor networks. Preamble symbols are periodically inserted into the frame payload in the time domain to serve as regular feature for reliable CCA. We simulated the CCA performance in the multipath UWB channel model developed by IEEE 802.15.4a. PAM and CCA configurations were optimized for the distributed carrier sense multiple access protocol. PAM was accepted by 802.15.4a group as an optional feature. Furthermore, the multiplexed preamble symbols can be exploited for channel estimation to improve communication and ranging.

This letter presents the first experimental results that confirm the restorability of Rayleigh backscatter traces from a single-mode fiber measured by using a coherent optical time domain reflectometer (OTDR) with a precisely frequency-controlled light source. Based on this restorability, we can measure the distributed strain and temperature along the fiber with a very high measurand resolution that is one to two orders of magnitude better than that provided by Brillouin-based techniques for a long length of fiber.

This work presents an ultra-low-voltage ultra-low-power weak inversion composite MOS transistor. The steady state power consumption and the linear swing signal of the composite transistor are comparable to a single transistor, whereas presenting very high output impedance. This work also presents two interesting applications for the composite transistor; a 1:1 current mirror and an extremely low power temperature sensor, a thermistor. Both implementations are verified in a standard 0.35-µm TSMC CMOS process. The current mirror presents high output impedance, comparable to the cascode configuration, which is highly desirable to improve gain and PSRR of amplifiers circuits, and mirroring relation in current mirrors.

In this paper, proactive data filtering (PDF) algorithm is proposed for data aggregation (or data fusion) in wireless sensor networks. The objective of the algorithm is to further reduce the energy consumption when sensor nodes perform data aggregation. In many applications, the sensor field will be overwhelmed by unnecessary and redundant sensory information when the sink node disseminates a query throughout the sensor field. In order to reduce the energy consumption, our scheme employs intelligent decision logic in the sensor node which delays or deactivates the transmission of its response. A performance evaluation shows that data aggregation with the PDF significantly improves energy-efficiency.

Automated capture and retrieval of experiences at home is interesting due to the wide variety and personal significance of such experiences. We present a system for retrieval and summarization of continuously captured multimedia data from Ubiquitous Home, a two-room house consisting of a large number of cameras and microphones. Data from pressure based sensors on the floor are analyzed to segment footsteps of different persons. Video and audio handover are implemented to retrieve continuous video streams corresponding to moving persons. An adaptive algorithm based on the rate of footsteps summarizes these video streams. A novel method for audio segmentation using multiple microphones is used for video retrieval based on sounds with high accuracy. An experiment, in which a family lived in this house for twelve days, was conducted. The system was evaluated by the residents who used the system for retrieving their own experiences; we report and discuss the results.

A direct-sequence ultra-wideband impulse radio (DS-UWB-IR) system is developed for low-power wireless applications such as wireless sensor networks. This system adopts impulse radio characterized by a low duty cycle, and a direct-sequence 0.7-GHz bandwidth, which enables low-power operation and extremely precise positioning. Simulation results reveal that the system achieves a 250-kbps data rate for 30-m-distance wireless communications using realistic specifications. We also conduct an experiment that confirms the feasibility of our system.

In this paper, we propose a novel MAC protocol with the patterned preamble technique to improve performance in terms of low power, channel utilization, and delay in wireless sensor networks. B-MAC is one of typical MAC protocols for wireless sensor networks using the duty cycle in order to achieve low-power operation. Since it works in an asynchronous fashion, B-MAC employs extended preamble and preamble sampling techniques. Even if it has outstanding performance in idle state, the overhead of these techniques is very large when packets are sent and received, because there is a lot of waste in the traditional preamble method. Instead of the simple preamble, our proposed MAC solution is to introduce more intelligent preamble with some patterns consisting of 2 phases (Tx phase & Ack phase). With this concept we implement real source code working on the mica2 platform with Tinyos-1.x version. Also, the test set-up is presented, and the test results demonstrate that the proposed protocol provides better performance in terms of delay compared to B-MAC.

In this paper, an analytical model is proposed to compute the optimal number of clusters that minimizes the energy consumption of multi-hop wireless sensor networks. In the proposed analytical model, the average hop count between a general node (GN) and its nearest clusterhead (CH) is obtained assuming a uniform distribution. How the position of the sink impacts the optimal number of clusters is also discussed. A numerical simulation is carried out to validate the proposed model in various network environments.

This paper describes a smart thermal sensing chip with an integrated vertical bipolar transistor sensor, a Sigma Delta Modulator (SDM), a Micro-Control Unit (MCU), and a bandgap reference voltage generator for biomedical application by using 0.18 µm CMOS process. The npn bipolar transistors with the Deep N-Well (DNW) instead of the pnp bipolar transistor is first adopted as the sensor for good isolation from substrate coupling noise. In addition to data compression, Micro-Control Unit (MCU) plays an important role for executing auto-calibration by digitally trimming the bipolar sensor in parallel to save power consumption and to reduce feedback complexity. It is different from the present analog feedback calibration technologies. Using one sensor, instead of two sensors, to create two differential signals in 180phase difference input to SDM is also a novel design of this work. As a result, in the range of 0 to 80 or body temperature (375), the inaccuracy is less than 0.1 or 0.05 respectively with one-point calibration after packaging. The average power consumption is 268.4 µW with 1.8 V supply voltage.

A single-chip ubiquitous sensor network (USN) system-on-a-chip (SoC) for small program memory size and low power has been proposed and integrated in a 0.18-µm CMOS technology. Proposed single-chip USN SoC is mainly consists of radio for 868/915 MHz, analog building block, complete digital baseband physical layer (PHY) and media access control (MAC) functions. The transceiver's analog building block includes a low-noise amplifier, mixer, channel filter, receiver signal-strength indication, frequency synthesizer, voltage-controlled oscillator, and power amplifier. In addition, digital building block consists of differential binary phase-shift keying (DPSK) modulation, demodulation, carrier frequency offset compensation, auto-gain control, embedded 8-bit microcontroller, and digital MAC function. Digital MAC function supports 128 bit advanced encryption standard (AES), cyclic redundancy check (CRC), inter-symbol timing check, MAC frame control, and automatic retransmission. These digital MAC functions reduce the processing power requirements of embedded microcontroller and program memory size by up to 56%. The cascaded noise figure and sensitivity of the overall receiver are 9.5 dB and -99 dBm, respectively. The overall transmitter achieves less than 6.3% error vector magnitude (EVM). The current consumption is 14 mA for reception mode and 16 mA for transmission mode.

One challenging issue of sensor networks is extension of overall network system lifetimes. In periodic data gathering applications, the typical sensor node spends more time in the idle state than active state. Consequently, it is important to decrease power consumption during idle time. In this study, we propose a scheduling scheme based on the history of RTS/CTS exchange during the setup phase. Scheduling the transmission during transfer phase enables each node to turn off its RF circuit during idle time. By tracing ongoing RTS/CTS exchange during the steady phase, each node knows the progress of the data transfer process. Thereby, it can wait to receive packets for data aggregation. Simulation results show a 160-260% longer system lifetime with the proposed scheduling scheme compared to the existing approaches.

Sensor networks are often deployed in unattended environments, thus leaving these networks vulnerable to false data injection attacks in which an adversary injects forged reports into the network through compromised nodes, with the goal of deceiving the base station or depleting the resources of forwarding nodes. Several research solutions have been recently proposed to detect and drop such forged reports during the forwarding process. Each design can provide the equivalent resilience in terms of node compromising. However, their energy consumption characteristics differ from each other. Thus, employing only a single filtering scheme for a network is not a recommendable strategy in terms of energy saving. In this paper, we propose a fuzzy-based adaptive filtering scheme selection method for energy saving. A fuzzy rule-based system is exploited to choose one of three filtering schemes by considering the false traffic ratio, the security threshold value, distance, and the detection power of the filtering scheme. The adaptive selection of the filtering schemes can conserve energy, and guarantee sufficient resilience.