This paper describes the measurement techniques of emissions from UWB devices discussed in ITU-R task group (TG) 1/8 to study the compatibility between ultra-wideband (UWB) devices and radiocommunication services. This paper also provides the background idea behind the measurement methods, as the final output of the discussion, i.e. ITU-R Recommendation, will not contain any citations to the references, nor any "educational" description of the theoretical background.

This paper introduces the concept of measuring double directional channels in ultra wideband (UWB) systems. Antenna-independent channel data were derived by doing the measurements in a wooden Japanese house. The data were useful for investigating the impact of UWB antennas and analyzing waveform distortion. Up to 100 ray paths were extracted using the SAGE algorithm and they were regarded as being dominant. The paths were then identified in a real environment, in which clusterization analyses were done using the directional information on both sides of the radio link. Propagating power was found to be concentrated around the specular directions of reflection and diffraction. This led to the observation that the spatio-temporal characteristics of extracted paths greatly reflected the structure and size of the environment. The power in the clusters indicated that the estimated 100 paths contained 73% of the total received power, while the rest existed as diffuse scattering, i.e., the accumulation of weaker paths. The practical limits of path extraction with SAGE were also discussed. Finally, we derived the scattering loss and intra-cluster properties for each reflection order, which were crucial for channel reconstrucion based on the deterministic approach.

Short-range propagation measurements were carried out using ultra wideband (UWB) and continuous wave (CW) signals on a rectangular aluminum conductive plate, simulating typical office desks, with and without a low vertical metal partition panels. The frequency of the UWB signal spanned from 3.1 to 10.6 GHz and that of the CW signal was 6.85 GHz. A vector network analyzer and two omnidirectional UWB antennas were used to obtain the frequency-domain response of the propagation paths. With the partition panel, the CW reception level showed approximately a 20-dB spatial variation, induced by the interference between the direct and the reflected waves, but the UWB reception level had no particular plunges. The additional losses were also measured when the 500-mm propagation path was blocked with a human arm, a coffee cup, and a copy paper pile and when the receiving antenna was covered with a human palm on the plate without the partition panel. The maximum additional propagation losses were found as follows: 10-12 dB by a human arm, 10 dB with a coffee cup, and 2 dB with a paper pile. Further additional loss caused by a palm covering the antenna was found to be 10 to 12 dB, mainly due to palm absorption.

This paper shows activities of the ultra wideband (UWB) research and development consortium organized by the National Institute of Information and Communications Technology (NICT). Fully CMOS monolithic microwave integrate circuits (MMICs) are designed and fabricated both for the multiband OFDM and the impulse radio. UWB transceivers are constructed with the MMICs as their front-end devices and evaluated by some measurements such as time domain waveform, spectrum, error vector magnitude, and so on. To show the application capabilities of the UWB transceivers, two kinds of video transmission system are constructed and demonstrated.

The present paper discusses a new construction of UWB pulses within the framework of soft-spectrum adaptation. The employed basis functions are B-splines having the following properties: (i) The B-splines are time-limited piecewise polynomials. (ii) The first-order B-splines are rectangular pulses and they converge band-limited functions at the limit that their order tends to infinity. (iii) There are an analog circuit and a fast digital filter for the generation of B-splines. Simple application of Gram-Schmidt orthonormalization process to the shifted B-splines results in a few basic pulses, which are well time-limited and have a broad band width, but do not comply with the FCC spectral mask. A constrained approximation technique is proposed for adaptively designing pulses so that they approximate target frequency characteristics. At the cost of using eleven shifted B-splines, an example set of four pulses comforting the FCC spectral mask is obtained.

Ultra Wideband (UWB) communication system utilizing impulse signals is attractive technique which can achieve high data rate with low complexity and low power consumption. In this impulse based UWB system, lots of different shaped pulses have been considered to represent more information bits per symbol. In order to detect these different shaped UWB signals at the receiver, the synthesized template generation method using several elementary waveforms is effective. In this paper we design and analyze this synthesized template waveform instead of the conventional matched filter technique. The synthesis of UWB template waveform can be achieved as combinations of orthogonalized elementary waveforms with Fourier coefficients. By adjusting the number of elementary waveforms and their coefficients, it is possible to detect several types of UWB signals. The orders of approximation corresponding to different number of elementary waveforms are analyzed and the bit error rate properties are then investigated in AWGN and multipath fading channels. In addition, the proposed system can capture more energy by adjusting its coefficients adaptively under the multipath environment and reduce the effect of Intra-Pulse Interference (IPI) which is occurred when the propagation channel is not separable, that is, multipath components spaced closer than the typical pulse width. We show the design of the adaptive template synthesis method and its performance compared with conventional Rake receiver.

This paper proposes wavelet packets for use in ultra wideband communications. The pulse shapes that are generated are quasi orthogonal and have almost identical time duration. After normalization, an M-ary signaling set can be constructed allowing higher data rate. Finally, the performance of such a system when multipath propagation occurs is investigated by computer simulations. In order to combat multipath fading, a Rake receiver using coherent channel estimation is designed. This channel estimation is carried out using adaptive algorithms such as least-mean square (LMS), normalized least-mean square (NLMS), or recursive least square (RLS) algorithms which adapt the received signal given a reference signal.

In this paper, we evaluate the computational complexity and the performance of the RAKE receivers for the Direct Sequence--Ultra Wideband (DS-UWB) with considering the accuracy of channel estimation in a multipath channel. As RAKE receivers for DS-UWB, we consider the maximal-ratio combining (MRC)-RAKE, the minimum mean square error (MMSE)-RAKE, and the MRC-RAKE-Equalizer that is the MRC-RAKE followed by a liner equalizer. Generally, if the channel estimation is perfect, as the number of fingers or taps increases, the performance of each receiver is improved, however the computational complexity of each receiver increases. In practice, the channel estimation is not perfect. The channel estimation error makes their performances degraded. Therefore, the performances of the RAKE receivers depend on the accuracy of channel estimation. Consequently, we evaluate the computational complexities and the Bit Error Rates (BERs) of MRC-RAKE, MMSE-RAKE, and MRC-RAKE-Equalizer with considering the accuracy of channel estimation for DS-UWB. We show that the accuracy of channel estimation affects the BER of each receiver significantly. We also show that when the accuracy of channel estimation is high, MRC-RAKE-Equalizer can achieve the better BER than MMSE-RAKE with less computational complexity, while MMSE-RAKE can achieve the better BER than MRC-RAKE-Equalizer when the accuracy of channel estimation is low.

In this paper we present a novel method for improving RAKE receiver reception in UWB systems. Due to the fact that practical pulses that can be produced for UWB-IR (Ultra Wideband-Impulse Radio) may occupy a longer time than the typical multipath resolution of the actual UWB channel, multiple channel components may arrive within this typical pulse width. Performance degradation may occur due to the resulting intrapulse (overlapping received pulses) interference. We here propose an adaptive, pilot aided RAKE receiver for UWB communications in the multipath environment. The proposed system estimates the actual received signal with intrapulse interference in each RAKE finger using projections onto a Hadamard-Hermite subspace. By exploiting the orthogonality of this subspace it is possible to decompose the received signal so as to better match the template waveform and reduce the effects of intrapulse interference. By using the projections onto this subspace, the dimension of the received signal is effectively increased allowing for adaptive correlator template outputs. RAKE receivers based on this proposal are designed which show significant performance improvement and require less fingers to achieve required performance than their conventional counterparts.

Performance of Rake reception of Ultra Wideband (UWB) signals is evaluated from energy capture perspective. In addition to ordinary all Rake (ARake) and selective Rake (SRake) receivers which are considered in conventional spread spectrum communications, we introduce optimum ARake and SRake receivers which include the estimation of delay of the combining multipaths. Impact of pulse-width is discussed on their performances considering the relationship between pulse-width and fading. Time hopping M-ary pulse position modulation (TH-MPPM) and binary phase shift keying (TH-BPSK) are considered as modulation schemes. Extensive simulation results are presented showing the performances of the Rakes introduced using IEEE 802.15.3a UWB channel models (CM1 to CM3). Performance of MPPM is shown for various values of M and modulation parameters. The impact of pulse-width is illustrated mainly using BPSK. It is shown that the total energy capture (i.e. by ARake) strongly depends on the pulse-width, and the shorter the pulse-width the more is the amount. The energy capture also varies a lot for employing either optimum or ordinary Raking method. Energy capture by SRake additionally strongly depends on the number of combined paths until the number is 20 for optimum SRake and 10 for ordinary SRake; however, afterwards saturating effects are seen. Several aspects regarding the performance versus complexity issue of Rake receivers are also discussed.

This paper presents a low-complexity equalization for M-ary biorthogonal keying based direct sequence ultra wideband (MBOK DS-UWB) systems. We focus on a Viterbi equalizer, which is based on maximum likelihood sequence estimation (MLSE). To reduce the computational complexity of MLSE-based equalizer, we use two strategies. One is the use of delayed-decision feedback sequence estimation (DDFSE), which is a hybrid estimation between MLSE and decision feedback estimation (DFE). And the other is the truncation of state transition in MLSE by considering MBOK pulse mapping. The reduced complexity sequence estimation is named as reduced state (RS)-DDFSE. By the use of RS-DDFSE, the complexity of Viterbi equalizer for MBOK DS-UWB is significantly reduced, by comparison with that of MLSE. The performance of RS-DDFSE based equalizer is evaluated on multipath fading channel models provided by IEEE802.15.3a. An analysis on trellis diagram of RS-DDFSE and simulation results show that the impact on error rate performance generated by the complexity lower is slight.

Ad hoc networks are becoming an interesting research area, as they inherently support unique network applications for the wireless communications in a rugged environment, which requires rapid deployment and is difficult to be provided by an infrastructure network. Many issues need to be addressed for the ad hoc networks. In this paper, we propose an efficient distributed coordination function on the media access control protocol to enhance the power conservation of mobile hosts by using a power control algorithm and the network throughput of an ad hoc network by using an algorithm for simultaneous frame transmissions. Extensive simulation is studied to evaluate the improvement of the proposed method. The results of the simulation exhibit significant improvement to the standard access control protocol. With slight improvement of network throughput, up to 85% of the consumed energy was able to be saved in compared to the standard protocol and up to 7 times of the energy efficiency was enhanced with the proposed method.

Dly-ACK scheme in IEEE 802.15.3 MAC is designed to reduce the overhead of the ACK frame in MAC layer and improve the channel utilization. However, how to using the Dly-ACK is open for implementation. In this paper, we propose an adaptive Dly-ACK scheme for both TCP and UDP traffic. We first point out the problems of applying fixed Dly-ACK scheme to these two traffic scenarios and show that the system performance is rather poor and the causes of these problems are presented. Based on our observations, two enhancement mechanisms for fixed Dly-ACK are then proposed. The first one is to request the Dly-ACK frame adaptively or change the burst size of Dly-ACK according to the transmitter queue status. The second is a retransmission counter to enable the destination DEV to deliver the MAC data frames to upper layer timely and orderly. Simulation results show that, with our enhancements, the system performance can be improved significantly compared with the conventional Imm-ACK and fixed Dly-ACK. We also investigate the impacts of some important parameters such as the buffer size on the system performance. Some important guidelines for the Dly-ACK design are given. Finally, it is worth to point out that our Dly-ACK enhancements are compatible with the standard and it is transparent to the upper layer protocols, i.e., either UDP or TCP.

This paper studies power spectrum density (PSD) of multi-user aggregate time hopping (TH) ultra wideband (UWB) signal with asynchronous transmission and synchronous transmission. TH codes under consideration are deterministic periodic code and random integer code. Based on the PSD, the in-band interference power for TD SCDMA is investigated as function of UWB system parameters. Two UWB modulations, TH pulse position modulation (PPM) and TH BPSK, are considered for calculating the in-band interference power. The numerical results indicate that asynchronous transmission is an effective way to decrease the peak in-band interference caused by multi-user aggregate TH-PPM UWB signal. Although increasing the maximum of time hopping code elements can smooth the PSD of TH UWB signal, it is not a good idea for reducing the peak in-band interference for TD SCDMA. For the random integer TH code, while only TH UWB continuous spectral exists in TD SCDMA band or multi-user signals of TH UWB are transmitted asynchronously, the in-band interference for TD SCDMA is in proportion to the number of the UWB users. For TD SCDMA in which band discrete spectral line exists the in-band interference caused by TH UWB with synchronous transmission is in proportion to the square of the number of the UWB users.

An impulse generation circuit using an SRD was made as an experiment. The circuit, which is used for UWB pulse radars, etc., was designed using PSpice, a SPICE simulator. Since there is no SRD model in SPICE, the pn junction model was substituted. The experimental and simulated waveforms were compared, and could be made almost to match by adjusting the parameters of the SPICE diode model.

In this letter a planar tapered-slot-fed annular slot antenna with band-notched characteristics is presented for ultra-wideband radios. By etching a narrowband resonance slit on the non-radiating part of the antenna, the proposed antenna is capable of not only reducing the interference at the WLAN bands but also of avoiding the spatial-dependent bandstop characteristics that have commonly occurred in previous works.

We propose a new two-stage blind separation and deconvolution strategy for multiple-input multiple-output (MIMO)-FIR systems driven by colored sound sources, in which single-input multiple-output (SIMO)-model-based ICA (SIMO-ICA) and blind multichannel inverse filtering are combined. SIMO-ICA can separate the mixed signals, not into monaural source signals but into SIMO-model-based signals from independent sources as they are at the microphones. After the separation by the SIMO-ICA, a blind deconvolution technique for the SIMO model can be applied even when each source signal is temporally correlated and the mixing system has a nonminimum phase property. The simulation results reveal that the proposed algorithm can successfully achieve separation and deconvolution of a convolutive mixture of speech, and outperforms a number of conventional ICA-based BSD methods.

This investigation proposed two array beamformers SPFDBB (Soft Penalty Frequency Domain Block Beamformer) and FDABB (Frequency Domain Adjustable Block Beamformer). Compared with the conventional beamformers, these frequency-domain methods can significantly reduce the computation power requirement in ASR (Automatic Speech Recognition) based applications. Like other reference signal based techniques, SPFDBB and FDABB minimize microphone's mismatch, desired signal cancellation caused by reflection effects and resolution due to the array's position. Additionally, these proposed methods are suitable for both near-field and far-field environments. Generally, the convolution relation between channel and speech source in time domain cannot be modeled accurately as a multiplication in the frequency domain with a finite window size, especially in ASR applications. SPFDBB and FDABB can approximate this multiplication by treating several frames as a block to achieve a better beamforming result. Moreover, FDABB adjusts the number of frames on-line to cope with the variation of characteristics in both speech and interference signals. A better performance was found to be achievable by combining these methods with an ASR mechanism.

The linear complexity and its stability of periodic sequences are of fundamental importance as measure indexes on the security of stream ciphers and the k-error linear complexity reveals the stability of the linear complexity properly. The k-error linear complexity of periodic sequences is defined to be the smallest linear complexity that can be obtained by changing k or fewer bits of the sequence per period. For 2pⁿ-periodic binary sequences, where p is an odd prime and 2 is a primitive root modulo p², we present and prove the unique expression of the linear complexity. Moreover we show a relationship between the linear complexity and the minimum value k for which the k-error linear complexity is strictly less than the linear complexity.

Traffic sign recognition usually consists of two stages: detection and classification. In this paper, we describe the classification stage using the ring-partitioned method. The proposed method uses a specified grayscale image in the pre-processing step and ring-partitioned matching in the matching step. The method does not need carefully prepared many samples of traffic sign images for the training process, alternatively only the standard traffic signs are used as the reference images. The experimental results show the effectiveness of the method in the matching of occluded, rotated, and illumination problems of the traffic sign images with the fast computation time.

In this paper, we present a novel iterative MPEG super-resolution method based on an embedded constraint version of Adaptive projected subgradient method [Yamada & Ogura 2003]. We propose an efficient operator that approximates convex projection onto a set characterizing framewise quantization, whereas a conventional method can only handle a convex projection defined for each DCT coefficient of a frame. By using the operator, the proposed method generates a sequence that efficiently approaches to a solution of super-resolution problem defined in terms of quantization error of MPEG compression.

Iris recognition is to identify a user based on the iris texture information which exists between the white sclera and the black pupil. Iris recognition system has been in the limelight for high-security biometric applications due to the advantages of non-contact characteristics and the highest recognition performance among biometric systems. Conventional iris recognition systems consist of the iris camera and the processing unit, like a PC or an embedded control box. The iris camera captures the user's iris images and transfers them to the processing unit. In the processing unit, the captured images are processed and recognition is performed. For fast recognition, it is very important to capture the user's focused eye image at fast speed. If not, the total recognition time is increased and it makes the user feel much inconvenience. In previous researches and systems, they use the focusing method which has been used for general landscape scenes without considering the characteristics of iris image. So, they take much focusing time sometimes, especially in the case of the user with glasses. To overcome such a problem, we propose a new iris image acquisition method to capture the user's focused eye image at very fast speed. It can be applicable to the users both with and without glasses.

Howling is very annoying problem to the hearing-aid users and it limits the maximum usable gain of hearing aids. We propose a new feedback cancellation system by inserting a time-varying decorrelation filter in the forward path. We use a second-order all-pass filter with control parameters whose time variation is implemented using a low-frequency modulator. A noticeable reduction of weight-vector misalignment is achievable using our proposed method.

In this paper, we present a minimum-maximum exclusive weighted-mean filtering algorithm with adaptive window. Image pixels within the varying size of the window are ranked and classified as minimum-maximum and median levels, and then passed through the weighted-mean of median level and identity filters, respectively. The filtering window size is adaptively increasing according to noise ratio without noise measurement. Extensive simulations show that the proposed filter performs better than other median/rank-type filters in removing impulse noise of highly corrupted images.

The frequency estimate for a real sinusoid provided by the periodogram has a bias which is particularly severe for a short observation interval. In this paper, two improvements to the periodogram are proposed to reduce this bias. The first method transforms the real tone to a complex sinusoid while the second algorithm subtracts the negative spectral line from the received signal, prior to applying the periodogram. The performance of the two methods is illustrated by comparing with the periodogram and Quinn's interpolation as well as Cramér-Rao lower bound.

Robust path following is an issue with practical importance to the ship industry. This paper studies the robust tracking problem for an underactuated navigator. The global robust controller is proposed to force the navigator to follow any smooth time-varying trajectory, despite the existence of the environmental disturbances. It is verified that the tracking errors are ultimately confined to an arbitrarily small ball of the origin.

This letter studies a simple nonautonomous chaotic circuit constructed by adding an impulsive switch to the RCL circuit. The switch operation depends on time and on state variable through a refractory threshold. The circuit exhibits various chaotic attractors, periodic attractors and related bifurcation phenomena. The dynamics can be analyzed using 1-D return map focusing on the time-dependent switching moments. Using a simple test circuit model typical phenomena are verified in PSPICE simulations.

Non-supersingular elliptic curves are important for the security of pairing-based cryptosystems. But there are few suitable non-supersingular elliptic curves for pairing-based cryptosystems. This letter introduces a method which allows the existing method to generate more non-supersingular elliptic curves suitable for pairing-based cryptosystems when the embedding degree is 6.

Visual secret sharing (VSS) scheme is a perfect secure method that protects a secret image by breaking it into shadows. Unlike other secret sharing schemes, the VSS scheme can be easily decoded by the human visual sight when staking the shadows. We replace a pixel in the secret image by m sub pixels in the shadow image and the value m is called as pixel expansion. In general, most papers are dedicated to find the minimum m for a VSS scheme, i.e. a smaller shadow size. However, it seems that no one studies how to trade the shadow size for the contrast. In this paper, we take the lead in studying size-adjustable VSS schemes such that one can choose appropriate shadow size and the recovered image contrast for practical use.

The explicit construction of a universal source code for correlated sources is presented. The construction is based on a technique of simulated random coding algorithms [5]. The proposed algorithm simulates the random generation of linear codes. For every pair of correlated sources whose achievable rate region includes a given pair of encoding rates, the decoding error rate of the proposed algorithm goes to zero almost surely as the block length goes to infinity.