This paper describes a new method for estimating the direction of arrival (DOA) using a nonlinear microphone array system based on complementary beamforming. Complementary beamforming is based on two types of beamformers designed to obtain complementary directivity patterns with respect to each other. In this system, since the resultant directivity pattern is proportional to the product of these directivity patterns, the proposed method can be used to estimate DOAs of 2(K-1) sound sources with K-element microphone array. First, DOA-estimation experiments are performed using both computer simulation and actual devices in real acoustic environments. The results clarify that DOA estimation for two sound sources can be accomplished by the proposed method with two microphones. Also, by comparing the resolutions of DOA estimation by the proposed method and by the conventional minimum variance method, we can show that the performance of the proposed method is superior to that of the minimum variance method under all reverberant conditions.

To improve the reliability and efficiency of multicast transmissions in wireless systems, a novel retransmission procedure is desired. In this paper, the representative acknowledgment scheme for reliable wireless multicast communications is proposed that offers quite a low packet loss rate. The proposed protocol carries out retransmissions in the datalink layer within the wireless region, and retransmissions do not affect the traffic in the wired region. The representative acknowledgment scheme employs both positive acknowledgment (ACK) and negative acknowledgment (NACK) to achieve reliable multicast transmissions and reduces the number of responses to be returned by forming groups of stations in the cell. One of the members in a group, called a representative station, returns a response for a received data frame while the others return a NACK if necessary. With this scheme, reliable multicast transmissions are enabled in wireless communications without spending much time as in conventional reliable multicast protocols. The performance of the proposed protocol is evaluated by numerical analyses and by computer simulation. The results show that 30% or more decrease in transmission time is achieved in a typical wireless environment.

High-speed digital data transmission services with mobile equipment are becoming available. Though the visual signal is one of the expected media to be used with such transmission capabilities, the bandwidth of visual signal is much broader than the provided transmission bandwidth in general. Therefore efficient video encoding algorithms have to be introduced. The ITU-T Recommendation H.263 and ISO/IEC MPEG-4 are very powerful encoding algorithms for a wide range of video sequences. But a large amount of bits are generated in highly active scenes to encode them using such conventional methods. This results in frame skipping and degradation of decoded picture quality. In order to keep these degradations as low as possible, we proposed a Dynamic Resolution Conversion (DRC) method of the prediction error. In the method, a reduced resolution encoding is carried out when the input scene is highly active. Simulation results show that the proposed scheme can improve both coding frame rate and picture quality in a highly active scene. We also present in this paper that some analysis for the performance of the DRC method under the error prone environment that is inevitable with mobile communications.

We examine delay performance of packets from constant bit rate (CBR) traffic whose delay is affected by non-real-time traffic. The delay performance is analyzed by solving the Σ Di/G/1 queue with vacations. Our analysis allows heterogeneous service time and heterogeneous interarrival time. Thus, we can get the impact of packet length of a stream on the delay time of other streams. We then give various numerical results for enterprise multimedia networks, which include voice, video and data communication services. From our quantitative evaluation, we conclude that packet length of video traffic has large influence on the delay time of voice traffic while voice traffic gives a little impact on the delay time of video traffic.

A low sidelobe two-beam waveguide slot array is designed and measured. The antenna structure should be symmetrical for realizing two symmetrical beams which imposes restriction in slot design for the sidelobe and the gain. The slot coupling distribution is optimized numerically for side-lobe suppression under the condition of the structural symmetry. The first side-lobe level is minimized for the specific antenna efficiency in the continuous source model. This synthesis is reinforced by the full wave slot analysis using the method of moments. The design is confirmed by experiments using a one-dimensional array at 12 GHz and the good agreements between the predictions and the measurements are observed.

An appropriate call admission control in the next generation wireless networks is expected to make efficient use of scarce wireless resource and improve quality-of-service, while supporting multimedia services. On one hand, blocking handoff calls is normally more annoying than blocking new calls. On the other hand, blocking new calls reduces resource utilization. More importantly, handoff call arrival rate depends strongly on call holding time. A novel Call-Holding-Time-Based Random Early Blocking (CHTREB) scheme is proposed to achieve the aforesaid goals in a two-tier cellular voice/data network. With CHTREB, new calls are accepted according to some acceptance probability taking into account the call hloding time difference between voice and data calls. An iterative algorithm is developed to calculate performance measures of interest, i.e., new call blocking probability and forced termination probability. First, simulation results are shown to verify analytical results. Then, numerical results are presented to show the robustness of CHTREB. It is found that CHTREB outperforms TR and CHTREB-FAP under both stationary and nonstationary traffic scenarios. Last but not least, the studied 2-tier system is compared with 1-tier counterpart. It is shown that 2-tier system performs better in terms of average number of handoffs per data call.

Orthogonal Frequency Division Multiplexing-Direct Sequence/Code Division Multiple Access (OFDM-DS/CDMA) systems provide frequency diversity gain avoiding inter symbol interference (ISI) in a frequency selective fading channel. However, path diversity gain can not be obtained by using conventional OFDM-DS/CDMA schemes. This paper proposes a new multiple antenna transmission system with combined path diversity and frequency diversity. Signal of each antenna is delayed by several chips to create artificial path diversity as well as frequency diversity of multi-carrier transmission in which can then be combined by using a RAKE receiver. Therefore multiple antenna transmission scheme creates a path diversity effect on uncorrelated signals in multi-carriers from each antenna. The received uncorrelated signals can be processed by Maximum Ratio Combining (MRC) diversity without ISI at a RAKE receiver even when we use FFT modulation. As a result, we can obtain combined path diversity and frequency diversity gain effectively by the RAKE system with the combination of multiple antennas.

We propose a dynamic assignment method of radio channels using their qualities and data packet sizes. In this method, a high quality channel is assigned for long packets and a low quality channel is assigned for short packets. Assuming a packet transfer method based on PHS (Personal Handy System) procedure, the transfer speed and delay characteristics are investigated by computer simulation and compared with conventional method (i.e. random assignment). Both the transfer speed characteristics and delay performance are improved under light traffic load.

One of the disadvantages of compressed data is their vulnerability, that is, even a single corrupted bit in compressed data may destroy the decompressed data completely. Therefore, Variable-to-Fixed length Arithmetic Coding, or VFAC, with error detecting capability is discussed. However, implementable error recovery method for compressed data has never been proposed. This paper proposes Burst Error Recovery Variable-to-Fixed length Arithmetic Coding, or BERVFAC, as well as Error Detecting Variable-to-Fixed length Arithmetic Coding, or EDVFAC. Both VFAC schemes achieve VF coding by inserting the internal states of the decompressor into compressed data. The internal states consist of width and offset of the sub-interval corresponding to the decompressed symbol and are also used for error detection. Convolutional operations are applied to encoding and decoding in order to propagate errors and improve error control capability. The proposed EDVFAC and BERVFAC are evaluated by theoretical analysis and computer simulations. The simulation results show that more than 99.99% of errors can be detected by EDVFAC. For BERVFAC, over 99.95% of l-burst errors can be corrected for l 32 and greater than 99.99% of other errors can be detected. The simulation results also show that the time-overhead necessary to decode the BERVFAC is about 12% when 10% of the received words are erroneous.

A K-band MMIC subharmonically pumped mixer integrating local oscillator (LO) amplifier has been developed. For up-converter application, it is necessary to reduce the leakage of second harmonic component of LO frequency to RF port, which is generated by nonlinear operation of LO amplifier. A quasi-lumped short-circuited stub using microstrip structure has been successfully applied to the MMIC mixer to enhance 2fLO-suppression. We propose a new configuration of a quasi-lumped short-circuited stub, which reduces the influence of parasitic elements of via-holes. The developed MMIC has a one-stage LO amplifier and it has shown about 10 dB-improvement of 2fLO-suppression compared to conventional configuration using a quarter-wavelength short-circuited stub.

This paper describes a method for classification of hematoxylin and eosin (HE)-stained breast tumor images into benign or malignant using the adaptive searching ability of artificial organisms. Each artificial organism has some attributes, such as, age, internal energy and coordinates. In addition, the artificial organism has a differentiation function for evaluating "malignant" or "benign" tumors and the adaptive behaviors of each artificial organism are evaluated using five kinds of texture features. The texture feature of nuclei regions in normal mammary glands and that of carcinoma regions in malignant tumors are treated as "self" and "non-self," respectively. This model consists of two stages of operations for detecting tumor regions, the learning and searching stages. At the learning stage, the nuclei regions are roughly detected and classified into benign or malignant tumors. At the searching stage, the similarity of each organism's environment is investigated before and after the movement for detecting breast tumor regions precisely. The method developed was applied to 21 cases of test images and the distinction between malignant and benign tumors by the artificial organisms was successful in all cases. The proposed method has the following advantages: the texture feature values for the evaluation of tumor regions at the searching stage are decided automatically during the learning stage in every input image. Evaluation of the environment, whether the target pixel is a malignant tumor or not, is performed based on the angular difference in each texture feature. Therefore, this model can successfully detect tumor regions and classify the type of tumors correctly without affecting a wide variety of breast tumor images, which depends on the tissue condition and the degree of malignancy in each breast tumor case.

Processes in image recognition include target detection and shape extraction. Active Net has been proposed as one of the methods for such processing. It treats the target detection in an image as an energy optimization problem. In this paper, a problem of the conventional Active Net is presented and the new Active Net is proposed. The new net is improved the ability for detecting a target. Finally, the validity of the proposed net is confirmed by experimental results.

The hardware-software codesign of distributed embedded systems is a more challenging task, because each phase of codesign, such as copartitioning, cosynthesis, cosimulation, and coverification must consider the physical restrictions imposed by the distributed characteristics of such systems. Distributed systems often contain several similar parts for which design reuse techniques can be applied. Object-oriented (OO) codesign approach, which allows physical restriction and object design reuse, is adopted in our newly proposed Distributed Embedded System Codesign (DESC) methodology. DESC methodology uses three types of models: Object Modeling Technique (OMT) models for system description and input, Linear Hybrid Automata (LHA) models for internal modeling and verification, and SES/workbench simulation models for performance evaluation. A two-level partitioning algorithm is proposed specifically for distributed systems. Software is synthesized by task scheduling and hardware is synthesized by system-level and object-oriented techniques. Design alternatives for synthesized hardware-software systems are then checked for design feasibility through rapid prototyping using hardware-software emulators. Through a case study on a Vehicle Parking Management System (VPMS), we depict each design phase of the DESC methodology to show benefits of OO codesign and the necessity of a two-level partitioning algorithm.

We propose a low-cost, high-uniformity, and low excess loss star coupler. The proposed star coupler comprises a planar lightguide, a diffuser, and polymer optical fibers (POFs). High-uniformity of optical power distribution was enabled by utilizing the diffused light transmission. Input light is diffused by the diffuser that is attached between the input POFs and the planar lightguide and transmitted through the planar lightguide. The optimum width-to-length ratio of the lightguide is clarified through simulations and experiments. We fabricated the star couplers based on the optimum width-to-length ratio for evaluation. The fabricated 1616 star coupler showed the excellent uniformity at the distribution ratio of 0.8 dB and the excess loss of 3.3 dB. The fabricated star coupler also provides a wide tolerance for misalignment. The maximum number of nodes to assure high transmission quality and the bandwidth of the proposed star coupler are discussed. The proposed star coupler is remarkably cost effective since it can be produced by injection-molding technology. The proposed star coupler enables easy multi-channel interconnection.

By combining the technology of all-optical saturable absorbers and the diffractive optics, a scheme of all-optical time division demultiplexing module is investigated. Following authors' proposal, design, test fabrication of the optical platform in the previous paper, this paper focuses on the characterization of switching performance. Using a multiple quantum well saturable absorber of InGaAs/InAlAs composition, and gain switched semiconductor laser pulses of 25 ps pulse width, the switching function was demonstrated experimentally at wavelength of 1.55 µm. The switching on-off ratio was compared among 4 lens configuration, 2 lens configuration (2L) and free space, collinear geometry. No degradation was observed in the case of 2 lens configuration in comparison to collinear illumination. Thus the feasibility of all-optical switch module with power efficiency and high speed is predicted, under the assumption of the progress in sub-micron lithography.

As mobile communication systems have been widespread and the needs for new service grows, IMT-2000 systems have largely been researched and developed for standardization. Among them, Wideband CDMA (WCDMA) solution is standardized in the 3rd Generation Partnership Project. In WCDMA system, voice and high data rate services are supported through dedicated traffic channels, however other packet based services with short duration are provided by using common channels. Data users are allowed to transmit a short message based on a contention manner via the reverse common channels. The basic Common Packet Channel (CPCH) mechanism has been proposed and adopted for accessing common channels. It consists of three phases: Random Access Phase, Collision Resolution Phase, and Data Transmission Phase. To enhance the resource usage efficiency, the CPCH mechanisms with channel assignment or status monitoring have been proposed. They can improve the performance, however increase the system complexity. Up to now, performances of the CPCH mechanisms have been discussed and studied based on computer simulations. Numerical results have been obtained by using S-G analysis, but they are different from simulation results. In this paper, we analyze the CPCH mechanisms by using the Equilibrium Point Analysis (EPA). And we compare computer simulation results with analytical results.

12-channel DC to 622-Mbit/s/ch optical transmitter and receiver have been developed for high-capacity and rather long (about 100 m) bit-parallel raw data transmission in intra- and inter-cabinet interconnection of large-scale switching, routing and computing system. Bit-parallel raw data transmission is done by using a bit-by-bit operational automatic decision threshold control receiver circuit with a DC-coupled configuration, the pin-PDs with their anodes and cathodes separated in a channel-by-channel manner, and a receiver preamplifier with a low-pass filter. The transmitter consists of a 12-channel LD sub-assembly unit and a LD driver LSI. The LD sub-assembly unit consists of a 12-channel array of high temperature characteristic 1.3-µm planar buried hetero-structure (PBH) LDs and 62.5/125 graded-index multi-mode fibers (GI62.5 MMFs). The 1.3-µm PBH LDs and the GI62.5 MMFs are optically coupled by passively visual alignment technology on the Si V-groove. The receiver consists of a 12-channel pin-PD sub-assembly unit and a receiver LSI. The pin-PD sub-assembly unit consist of a 12-channel array of pin-PDs and GI62.5 MMFs. They are optically coupled by using a flip-chip bonding on the Si V-groove. The transmitter and receiver each have eleven data channels and one clock channel. The size is as small as 3.6 cc for each modules, and the power consumptions are 1.7 W (transmitter) and 1.35 W (receiver). They transmitted a bit-parallel raw data through a 100-meter ribbon of GI62.5 MMFs in an ambient temperature range of 0-70C. They provide a synchronous PECL interface parallel link for with a 3.3-V single power supply.

This paper presents an efficient method for estimating maximum simultaneous switching noise (SSN) of ground interconnection networks in CMOS systems. For the derivation of maximum SSN expression we use α-power law MOS model and an iterative method to reduce error that may occur due to the assumptions used in the derivation process. The accuracy of the proposed method is verified by comparing the results with those of previous researches and HSPICE simulations under the present process parameters and environmental conditions.

We have proposed parallel optical interconnection technology, or ParaBIT, for high-throughput, low-cost optical interconnections and already developed a prototype parallel optical interconnect module called "ParaBIT-0," which has a total throughput of 28 Gb/s (700 Mb/s 40 channels). We are now developing a compact, high-throughput module called "ParaBIT-1," which has a total throughput of 60 Gb/s (1.25 Gb/s 48 channels) and is designed to achieve the highest-ever throughput density of 3.3 Gb/s/cc. In this paper, we describe the packaging structure, optical coupling structure and transmission characteristics of ParaBIT-1. We also discuss the technical prospect of realizing a parallel optical interconnect module with the bit rate of 2.5 Gb/s/ch.

Recently, Vatan, Roychowdhury and Anantram have presented two types of revised versions of the Calderbank-Shor-Steane code construction, and have also provided an exhaustive procedure for determining bases of quantum error-correcting codes. In this paper, we investigate the revised versions given by Vatan et al., and point out that there is no essential difference between them. In addition, we propose an efficient algorithm for searching for bases of quantum error-correcting codes. The proposed algorithm is based on some fundamental properties of classical linear codes, and has much lower complexity than Vatan et al.'s procedure.