In this paper, we propose a novel spatial filtering technique for orthogonal frequency division multiplexing (OFDM) signals called "VIrtual Subcarrier Assignment (VISA)." Here, virtual subcarrier is a subcarrier which is not used for data transmission. When a wireless terminal is equipped with multiple antennas, VISA can easily achieve a space division multiple access (SDMA) by assigning a different spectral position of virtual subcarrier to a different user. To realize VISA in an already-existing OFDM-based wireless local area network (WLAN), we discuss an antenna weight control method in the preamble of a signal burst format designed for the IEEE802.11a standard and evaluate the bit error rate (BER) performance in typical indoor wireless environments.

This paper outlines the method of constructing single-electron logic circuits based on the binary decision diagram (BDD), a graphical representation of digital functions. The circuit consists of many unit devices, BDD devices, cascaded to build the tree of a BDD graph. Each BDD device corresponds to a node of the BDD graph and operates as a two-way switch for the transport of a single electron. Any combinatorial logic can be implemented using BDD circuits. Several subsystems for a single-electron processor have been constructed using semiconductor nano-process technology.

This paper presents a methodology based on congruent transformation for distributed interconnects described by state-space time-delays system. The proposed approach is to obtain the passive reduced order of linear time-delays system. The unified formulations are used to satisfy the passive preservation. The details of the mathematical proof and a couple of validation examples are given in this paper.

In this letter, a blind frequency offset estimation algorithm is proposed for OFDM systems. The proposed method exploits the intrinsic phase shift between neighboring samples in a single OFDM symbol, incurred by a frequency offset. The proposed algorithm minimizes a novel cost function, which is the squared error of the candidate frequency offset compensated signals from two different observation windows. Also, the solution of the proposed algorithm is given by an explicit equation, which does not require any iterative calculation. It is shown that the performance of the proposed method is better than those of the conventional methods, especially in the presence of multipath channels. This is due to the fact that the proposed method is insensitive to inter-symbol interference (ISI).

Currently, multiband orthogonal frequency division multiplexing (MB-OFDM) is considered to be one of the modulation schemes of UWB and is being actively investigated. It is necessary to provide low-cost receivers for consumers to receive wide support for the MB-OFDM system. Such receivers can be achieved by utilizing direct-conversion architecture. Direct-conversion architecture suffers from IQ imbalance. IQ imbalance causes intercarrier interference (ICI) in the demodulated signals. In this paper, a new scheme of IQ imbalance compensation using transmit diversity is proposed. This scheme enables the system to achieve frequency diversity and simultaneously compensates for the influence of IQ imbalance. It is shown that the performance of the proposed scheme is better than that of the conventional IQ imbalance compensation scheme.

In this paper, a multiuser receiver based on a Gaussian Mixture Sigma Point Particle Filter (GMSPPF), which can be used for joint channel coefficient estimation and time delay tracking in CDMA communication systems, is introduced. The proposed algorithm has better improved estimation performance than either Extended Kalman Filter (EKF) or Particle Filter (PF). The Cramer-Rao Lower Bound (CRLB) is derived for the estimator, and the simulation result demonstrates that it is almost completely near-far resistant. For this reason, it is believed that the proposed estimator can replace well-known filters such as the EKF or PF.

We propose a scheme by which Broadcast Satellite/Communication Satellite- radio frequency (BS/CS-RF) converted TV signals are transmitted over optical fiber, and also propose a simultaneous Frequency Modulation (FM) converted CATV and BS/CS-RF converted TV optical transmission system as one of its applications. To confirm the proposals, we demonstrate the simultaneous transport of FM converted CATV signals and BS/CS-RF converted TV signals over a single optical fiber. In the experiments, 40 carriers of AM-VSB CATV channels, 30 carriers of 64-QAM digital TV channels, 8 carriers of FM/TC8PSK BS-TV channels, and 12 carriers of QPSK CS-TV channels are simultaneously transmitted. For optical access network application, the practical transmission length of 15 km over 1.3 µm-zero-dispersion optical fiber can be achieved by using dispersion compensation fiber (DCF).

Rapid eye motion, or so called saccade, is a very quick eye motion which always occurs regardless of our intention. Although the line of sight (LOS) with saccade tracking is expected to be used for a new type of computer-human interface, it is impossible to track it using the conventional video camera, because of its speed which is often up to 600 degrees per second. Vision Chip is an intelligent image sensor which has the photo receptor and the image processing circuitry on a single chip, which can process the acquired image information by keeping its spatial parallelism. It has also the ability of implementing the very compact integrated vision system. In this paper, we describe the vision chip architecture which has the capability of detecting the line of sight from infrared eye image, with the processing speed supporting the saccade tracking. The vision chip described here has the pixel parallel processing architecture, with the node automata for each pixel as image processing. The acquired image is digitized to two flags indicating the Purkinje's image and the pupil by comparators at first. The digitized images are then shrunk, followed by several steps of expanding by node automata located at each pixel. The shrinking process is kept executed until all the pixels disappear, and the pixel disappearing at last indicates the center of the Purkinje's image and the pupil. This disappearing step is detected by the projection circuitry in pixel circuit for fast operation, and the coordinates of the center of the Purkinje's image and the pupil are generated by the simple encoders. We describe the whole architecture of this vision chip, as well as the pixel architecture. We also describe the evaluation of proposed algorithm with numerical simulation, as well as processing speed using FPGA, and improvement in resolution using column parallel architecture.

We introduce an extension of Golay complementary sequences in which, for each sequence, there exists another sequence such that the sum of aperiodic autocorrelation functions of these two sequences for a given multiple L-shift (L≥1) is zero except for the zero shift. We call these sequences multiple L-shift complementary sequences. It is well-known that the peak-to-average power ratio (PAPR) value of any Golay complementary sequence is less than or equal to 2. In this paper, we show that the PAPR of each multiple L-shift complementary sequence is less than or equal to 2L. We also discuss other properties of the sequences and consider their construction.

For point-to-point mobile visual communications, layered video has been utilized to adapt to time-varying channel capacity over noisy environments. From the perspective of the HVS (Human Visual System), it is necessary to minimize the loss of visual quality by specifically maintaining the throughput of visually important regions, objects and so on. Utilizing the prioritized bitstreams generated according to each layer, the throughput can be improved for given channel statistics. In this paper, we define the transmission gain and measure the improved performance when the throughput of ROI (Regions Of Interest) is increased relative to visually unimportant regions over a capacity limited mobile channel.

LSI testing is critical to guarantee chips are fault-free before they are integrated in a system, so as to increase the reliability of the system. Although full-scan is a widely adopted design-for-testability technique for LSI design and testing, there is a strong need to reduce the test data Volume, scan-in Power dissipation, and test application Time (VPT) of full-scan testing. Based on the analysis of the characteristics of the variable-to-fixed run-length coding technique and the random access scan architecture, this paper presents a novel design scheme to tackle all VPT issues simultaneously. Experimental results on ISCAS'89 benchmarks have shown on average 51.2%, 99.5%, 99.3%, and 85.5% reduction effects in test data volume, average scan-in power dissipation, peak scan-in power dissipation, and test application time, respectively.

A hardware algorithm for integer division is proposed. It is based on the radix-2 non-restoring division algorithm. Fast computation is achieved by the use of the radix-2 signed-digit (SD2) representation. The algorithm does not require normalization of the divisor, and hence, does not require an area-consuming leading-one (or zero) detection nor shifts of variable-amount. Combinational (unfolded) implementation of the algorithm yields a regularly structured array divider, and sequential implementation yields compact dividers.

A 3 dimensional (3D) error diffusion method based on edge detection for flat panel display (FPD) is presented. The new method diffuses errors to the neighbor pixels in current frame and the neighbor pixel in the next frame. And the weights of error filters are dynamically adjusted based on the results of edge detection in each pixel's processing, which makes the weights coincide with the local edge feathers of input image. The proposed method can reduce worm artifacts and improve reproduction precision of image details.

A novel method to simplify decision functions of support vector machines (SVMs) is proposed in this paper. In our method, a decision function is determined first in a usual way by using all training samples. Next those support vectors which contribute less to the decision function are excluded from the training samples. Finally a new decision function is obtained by using the remaining samples. Experimental results show that the proposed method can effectively simplify decision functions of SVMs without reducing the generalization capability.

Designable task allocation systems which consist of identical agents using stochastic automata are suggested. From the viewpoint of the group response and the individual behavior, the performances of a simple model and an improved one are compared numerically. Robots experiments are performed to compare between the two models.

In current IP-based networks, the application of window-based end-to-end flow control, including TCP, to ensure reliable flows is an essential factor. However, since such a flow control is provided by the end hosts, end-to-end control cannot be applied to decision-making in a time-scale shorter than the round-trip delay. We have previously proposed a diffusion-type flow control mechanism to realize the extremely time sensitive flow control that is required for high-speed networks. In this mechanism, each network node manages its own traffic only on the basis of the local information directly available to it, by using predetermined rules. The implementation of decision-making at each node can lead to optimal performance for the whole network. Our previous studies showed that the mechanism works well, by itself, in high-speed networks. However, to apply this mechanism to actual networks, it needs to be able to coexist with other existing protocols. In this paper, we investigate the performance of diffusion-type flow control coexisting with TCP. We show that diffusion-type flow control can coexist with TCP and the two can be complementary. Then, we show that a combination of both controls achieves higher network performance than TCP alone in high-speed networks.

In this paper, a multistage parallel interference canceller (MPIC) with multiple-beam reception for a DS-CDMA system is proposed to suppress multiple access interference (MAI) effectively. Its aim is to reduce the computational complexity of the conventional MPIC cascaded with an adaptive array antenna. It employs multiple fixed beams based on phased array and selects suitable beams to demodulate the transmitted signal of each user. Then it suppresses residual interference signals by the MPIC cascaded with multiple-beam receiver. Its bit error rate (BER) performance is evaluated by computer simulations assuming an uplink single-chip-rate multiple-spreading-factor DS-CDMA system over both exponentially decaying 5-path and equal average power 2-path Rayleigh distributed channels. When there are 16 users in an 120-sectored single cell, the proposed receiver with 6-element array antenna and 2-stage MPIC shows better or comparable BER performance compared with that of the conventional receiver. Moreover, the proposed receiver with 8 beams can reduce the number of complex multiplications to about 40% of that of the complexity-reduced conventional receiver over 5-path channels.

We have researched high dimensional parity-check (HDPC) codes that give good performance over a channel that has a very high error rate. HDPC code has a little coding overhead because of its simple structure. It has hard-in, maximum detected bit flipping (MDBF) decoding that has reasonable decoding performance and computational cost. In this paper, we propose a modified algorithm for MDBF decoding and compare the proposed MDBF decoding with conventional hard-in decoding.

In this article, the security of double-block-length hash functions with the rate 1 is analyzed, whose compression functions are composed of block ciphers with their key length twice larger than their block length. First, the analysis by Satoh, Haga and Kurosawa is investigated, and it is shown that there exists a case uncovered by their analysis. Second, a large class of compression functions are defined, and it is shown that they are at most as secure as those of single-block-length hash functions. Finally, some candidate hash functions are given which are possibly optimally collision-resistant.

Providing multimedia services with a quality-of-service guarantee in mobile wireless networks presents more challenges due to user's mobility and limited bandwidth resource. In order to provide seamless multimedia services in the next-generation wireless networks, efficient call admission control algorithm must be developed. A novel borrowing-based call admission control policy is proposed in this paper as a solution to support quality-of-service guarantees in the mobile multimedia wireless networks. Based on the existing network conditions, the proposed scheme makes an adaptive decision for bandwidth allocation and call admission by employing attribute-measurement mechanism, dynamic time interval reservation strategy, and service-based borrowing strategy in each base station. We use the dynamically adaptive approaches to reduce the connection-blocking probability and connection-dropping probability, and to increase the bandwidth utilization, while the quality-of-service guarantees can be maintained at a comfortable level for mobile multimedia wireless networks. Extensive simulation results show that our proposed scheme outperforms the previously proposed scheme in terms of connection-blocking probability, connection-dropping probability, and bandwidth utilization, while providing highly satisfying degree of quality-of-service in mobile communication systems.