We propose a simple asynchronous UWB (Ultra Wide Band) position location algorithm with low complexity, power consumption and processing delay. In the proposed algorithm, only a single RTTX (Round-Trip Transmission) of UWB pulses is utilized based on the ToA (Time of Arrival) principle. Hence, the proposed algorithm decreases power consumption and processing delay as compared to the basic ToA based on triple RTTXs. Moreover, unlike the TDoA (Time Difference of Arrival) algorithm, the proposed algorithm can perform the position location with low complexity since it does not require strict synchronization between multiple beacons. Simulation results using IEEE 802.15.4a UWB channel models reveal that the proposed algorithm achieves closely comparable position location performance of the basic ToA and TDoA algorithms.

Advances in smart card technology encourages smart card use in more sensitive applications, such as storing important information and securing application. Smart cards are however vulnerable to side channel attacks. Power consumption and electromagnetic radiation of the smart card can leak information about the secret data protected by the smart card. Our paper describes two possible hardware countermeasures that protect against side channel information leakage. We show that power analysis can be prevented by adopting photo-coupling techniques. This method involves the use of LED with photovoltaic cells and photo-couplers on the power, reset, I/O and clock lines of the smart card. This method reduces the risk of internal data bus leakage on the external data lines. Moreover, we also discuss the effectiveness of reducing electromagnetic radiation by using embedded metal plates.

In ubiquitous networks, Mobile Nodes (MNs) often suffer from performance degradation due to the following two reasons: (1) reduction of signal strength by the movement of an MN and intervening objects, and (2) radio interference with other WLANs. Therefore, handover initiation based on quick and reliable detection of the deterioration in a wireless link condition arising from the above two reasons is essential for achieving seamless handover. In previous studies, we focused on a handover decision criterion and described the problems related to the two existing decision criteria. Furthermore, we showed the effectiveness of the number of frame retransmissions through simulation experiments. However, a comparison of the signal strength and the number of frame retransmissions could not be examined due to the unreliability of the signal strength in simulations. Therefore, in the present paper, by employing FTP and VoIP applications, we compare the signal strength and the number of frame retransmissions as a handover decision criterion with experiments in terms of (1) and (2) in a real environment. Finally, we clarify the problem of the signal strength in contrast to the effectiveness of the number of frame retransmissions as a handover decision criterion.

Congestion in WSN increases the energy dissipation rates of sensor nodes as well as the loss of packets and thereby hinders fair and reliable event detection. We find that one of the key reasons of congestion in WSN is allowing sensing nodes to transfer as many packets as possible. This is due to the use of CSMA/CA that gives opportunistic medium access control. In this paper, we propose an energy efficient congestion avoidance protocol that includes source count based hierarchical and load adaptive medium access control and weighted round robin packet forwarding. We also propose in-node fair packet scheduling to achieve fair event detection. The results of simulation show our scheme exhibits more than 90% delivery ratio even under bursty traffic condition which is good enough for reliable event perception.

We experimentally demonstrated polarization-mode dispersion (PMD) compensation by distributing polarizers with only 1 degree of freedom (DOF) along the transmission line. The average power penalty was measured to be 0.4 dB by inserting four compensators, where average differential group delay was 47% of bit period.

In this paper, we investigate a detection ordering scheme of OSIC (Ordered Successive Interference Cancellation) systems suitable for power controlled MIMO transmission. Most studies about power controlled systems have mainly focused on strategies for transmitter, while the ordering scheme optimized at open-loop system has not been modified. In a conventional ordering scheme, the ordering process is done according to the largeness and smallness relation of each sub-stream's SNR. Unlike the conventional scheme, we derive an optimized detection ordering scheme that uses proximity to the optimal SNR. Because of error propagation, our proximity based algorithm is not valid for open-loop MIMO system in many cases. An optimization problem analysis and simulation results show that the system using the proposed ordering scheme outperforms the system using the conventional ordering scheme. Furthermore, due to the nature of QR decomposition, the proposed scheme shows not only lower implementation complexity but also better BER performance compared with the conventional scheme based on pseudo-inverse.

This paper presents some structures of artificial coplanar waveguide with very slow phase velocity and their applications to a design of compact 3-dB branch-line couplers. The slow-wave structure is constructed by periodically loading both of series inductance and shunt capacitance. First, a basic miniature branch-line coupler is designed and consequently considerable size-reduction of about 1/4 is obtained. Next, a broadband design technique is described using open-circuited quarter-wavelength series-stubs added at each port as a matching network. By size-reducing the series-stubs and branchline sections, a very compact broadband coupler with a good hybrid performance over a wide bandwidth of 31 percent or more is realized. The design concepts and procedures are verified both numerically and experimentally.

Recently, many studies reported various advanced e-Health service systems in patient care monitoring utilizing sensor networks and questionnaire systems. We propose an informant driven e-Health service system for the identification of heart rate related mental stress factors with a simple operation of informant-client model. Through performance analysis, we show that the proposed system is a cost-effective stress identification system applicable to mobile wireless networks.

In this paper, we consider consecutive burst transmission with burst loss recovery based on Forward Error Correction (FEC) in which redundant data is transmitted with multiple bursts. We propose two burst generation methods: Out-of Burst Generation (OBG) and In-Burst Generation (IBG). The OBG generates a redundant burst from redundant data, while the IBG reconstructs a burst from an original data block and a part of the redundant data. For both methods, the resulting bursts are transmitted consecutively. If some bursts among the bursts are lost at an intermediate node, the lost bursts can be recovered with the redundant data using FEC processing at the destination node. We evaluate by simulation the proposed methods in a uni-directional ring network and NSFNET, and compare the performances of the proposed methods with the extra-offset time method. Numerical examples show that the proposed methods can provide a more reliable transmission than the extra-offset time method for the OBS network where the maximum number of hops is large. Moreover, it is shown that the end-to-end transmission delay for our proposed methods can be decreased by enhancing the FEC processor or by increasing the number of FEC processors.

In this letter, we propose an efficient scheme for combining scheduling and channel allocation functions in multi-channel systems such as an orthogonal frequency division multiple access (OFDMA). In our approach, the scheduling function is embedded in the channel allocation function in an implicit manner, and the implicit scheduler only translates quality-of-service (QoS) requirements into a set of constraints on channel allocation. The channel allocation problem is then formulated as a linear programming (LP) problem, and the optimal solution can be easily obtained through various LP algorithms. Through extensive numerical experiments, it is demonstrated that the proposed scheme can maximize the cell throughput under the given QoS requirements.

Spatial power/ground level variation causes power/ground level mismatch between driver and receiver, and the mismatch affects gate propagation delay. This paper proposes a timing analysis method based on a concept called "PG level equalization" which is compatible with conventional STA frameworks. We equalize the power/ground levels of driver and receiver. The charging/discharging current variation due to equalization is compensated by replacing output load. We present an implementation method of the proposed concept, and demonstrate that the proposed method works well for multiple-input gates and RC load model.

Assuming there are short time periods in which only one source is active, a new approach for source separation is proposed. An affine projection adaptation algorithm with a non-orthogonal constraint shows excellent noise immunity, a high convergence rate, and good tracking capability to efficiently obtain a solution to the separation filters.

This paper presents a self-reconfigurable adaptive FIR filter system design using dynamic partial reconfiguration, which has flexibility, power efficiency, advantages of configuration time allowing dynamically inserting or removing adaptive FIR filter modules. This self-reconfigurable adaptive FIR filter is responsible for providing the best solution for realization and autonomous adaptation of FIR filters, and processes the optimal digital signal processing algorithms, which are the low-pass, band-pass and high-pass filter algorithms with various frequencies, for noise removal operations. The proposed stand-alone self-reconfigurable system using Xilinx Virtex4 FPGA and Compact-Flash memory shows the improvement of configuration time and flexibility by using the dynamic partial reconfiguration techniques.

For formal verification of large-scale digital circuits, a method using satisfiability checking of logic with equality and uninterpreted functions has been proposed. This logic, however, does not consider specific properties of functions or predicates at all, e.g. associative property of addition. In order to ease this problem, we introduce "equivalence constraint" that is a set of formulas representing the properties of functions and predicates, and check the satisfiability of formulas under the constraint. In this report, we show an algorithm for checking satisfiability with equivalence constraint and also experimental results.

In this paper, we describe a method of applying Collaborative Filtering with a Machine Learning technique to predict users' preferences for clothes on online shopping malls when user history is insufficient. In particular, we experiment with methods of predicting missing values, such as mean value, SVD, and support vector regression, to find the best method and to develop and utilize a unique feature vector model.

A compact OTA suitable for low-voltage active-RC and MOSFET-C filters is presented. The input stage of the OTA utilises the NMOS pseudo-differential amplifier with PMOS active load. The output stage relies upon the dual-mode feed-forward class-AB technique (based on an inverter-type transconductor) with common-mode rejection capability that incurs no penalty on transconductance/bias-current efficiency. Simulation results of a 0.5-V 100-kHz 5th-order Chebyshev filter based on the proposed OTA in a 0.18 µm CMOS process indicate SNR and SFDR of 68 dB and 63 dB (at 50 kHz+55 kHz) respectively. The filter consumes total power consumption of 60 µW.

In this paper, we propose a new code set which has very low spectral peak to average ratio (SPAR) and good correlation properties for DS-UWB. The codes which have low SPAR are suitable for DS-UWB system which operates in UWB (3.110.4 GHz) because they can utilize more power than high SPAR codes can do. And, in order to reduce inter symbol interference (ISI) and inter piconet interferences, the codes which have good auto- and cross-correlation properties must be used. In this paper, we propose three items; (1) a new code generation method which can generate good SPAR and auto-correlation codes, (2) code selection criteria, and (3) a code set, which has been selected according to the proposed selection criteria. The proposed code set has SPAR reduced about 0.22 dB and GMF improved by 30% compared to the previous code set while it is maintaining almost same cross-correlation properties. Each code of the proposed code set, therefore, has gained 1.43 dB SIR on an average compared to that of the previous code set.

The time division duplex cellular system can support various downlink and uplink traffic ratios by setting the downlink and uplink transmission periods appropriately. However, it causes severe co-channel interference problem when some cells are active in the downlink while the others are in the uplink [2]. To mitigate this problem, a resource allocation scheme combined with sectorization is proposed for orthogonal frequency division multiple access. Simulations demonstrate that the proposed scheme improves both spectral efficiency and outage performance compared to the conventional allocation schemes.

This paper proposes an algorithm for calculating routes that considers the include route constraint while minimizing cost. A route with include route constraint has to traverse a group of assigned nodes. The trouble when calculating a route that satisfies an include route constraint is that routes set in different sections may traverse the same link. In order to prevent this violation (overlap), we introduce an alternate route selection policy. Numerical results show that the probability of finding appropriate routes (no overlap) is more than 95% with the proposed algorithm while only 35% with the conventional algorithm.

In this research, we focused on fair bandwidth allocation on the Internet. The Internet provides communication services based on exchanged packets. The bandwidth available for each customer is often fluctuated. Fair bandwidth allocation is an important issue for ISPs to gain customer satisfaction. Static bandwidth allocation allows an exclusive bandwidth for specific traffic. Although it gives communications a QoS guarantee, it requires muany bandwidth resources as known as over-provisioning. In contrast with static control, dynamic control allocates bandwidth resources dynamically. It therefore utilizes bandwidth use more effectively. However, it needs control overhead in monitoring traffic and estimating the optimum allocation. The Transmission Control Protocol, or TCP is the dominant protocol on the Internet. It is also equipped with a traffic-rate-control mechanism. An adaptive bandwidth-allocation mechanism must control traffic that is under TCP control. Rapid feedback makes it possible to gain an advantage over TCP control. In this paper, we propose an Adaptive Bandwidth Allocation (ABA) mechanism as a feedback system for MPLS. Our proposal allows traffic to be regulated adaptively as its own weight value which can be assigned by administrators. The feedback bandwidth allocation in the previous work needs round-trip control delay in collecting network status along the communication path. We call this "round-trip feedback control." Our proposal, called "one-way feedback control," collects network status in half the time of roundtrip delay. We compare the performance of our one-way feedback-based mechanism and traditional round-trip feedback control under a simulation environment. We demonstrate the advantages of our rapid feedback control has using experimental results.