The effect of feedback delay and channel estimation error on closed-loop transmit diversity (CTD) systems is investigated in time-selective Rayleigh fading channels. Based on a minimum mean square error (MMSE) channel estimator, the variance of the estimation error is formulated in terms of fading index and the number of transmit antennas. A bit error rate (BER) expression for the CTD system is analytically derived as a function of channel estimation error, feedback delay, and fading index. It is shown that the BER performance of the CTD system improves as the length of training symbols increases and/or the frame length decreases. In the CTD system, more accurate channel estimation scheme is required to achieve its full gain as the number of employed transmit antennas increases. It is also found that the CTD system is applicable to the slowly moving channel environments, such as pedestrians, but not for fast moving vehicles.

An efficient data transmission interface for VLSI systems, Multi-Bit Parallel Code Division Multiple Access (MB/P-CDMA) interface, has been designed with 0.35 µm CMOS technology. The proposed interface achieves 1.12 Gb/s data rate (80 MHz, 8 bit bus) using multi-bit transmission at each clock per transmitter. The proposed CDMA interface ensures higher speed operation than conventional interface even in noisy environments. Each of the transmitters and receivers occupies the die area of 290 360 µm2 and 240 280 µm2, respectively.

Many simulated annealing algorithms use the Cauchy neighbors for fast convergence, and the conventional method uses the product of n one-dimensional Cauchy distributions as an approximation. However, this method slows down the search severely as the dimension gets high because of the dimension-wise neighbor generation. In this paper, we analyze the orthogonal neighbor characteristics of the conventional method and propose a method of generating symmetric neighbors from the n-dimensional Cauchy distribution. The simulation results show that the proposed method is very effective for the search in the simulated annealing and can be applied to many other stochastic optimization algorithms.

This paper investigates a random-interleaver-based approach to space-time coding. The basic principle is to employ a good forward error correction (FEC) code and transmit randomly interleaved codewords over an antenna array. A low-cost estimation technique is considered. The complexity involved grows only linearly with the number of transmit antennas. Near-capacity performance can be achieved with moderate complexity.

Direct manipulation by hand is an intuitive and simple way of positioning objects in an immersive virtual environment. However, this technique is not suitable for making precise adjustments to virtual objects in an immersive environment because it is difficult to hold a hand unsupported in midair and to then release an object at a fixed point. We therefore propose an alternative technique using a virtual 3D gearbox widget that we have designed, which enables users to adjust values precisely. We tested the technique in a usability study along with the use of hand manipulation and a slider. The results showed that the gearbox was the best of the three techniques for precise adjustment of small targets, in terms of both performance data and subject preference.

In this paper, a novel carrier-sense multiple-access (CSMA) scheme for UWB ad-hoc network is proposed and evaluated. UWB is a kind of spread spectrum communication and it is possible to detect the distance between the nodes. With this positioning capability of the UWB systems, DS-CDMA (DS-UWB) scheme with variable spreading factor is used. In this paper, a novel CSMA scheme that employs the correlation of the spreading code is proposed.

We propose use of QR factorization with sort and Dijkstra's algorithm for decreasing the computational complexity of the sphere decoder that is used for ML detection of signals on the multi-antenna fading channel. QR factorization with sort decreases the complexity of searching part of the decoder with small increase in the complexity required for preprocessing part of the decoder. Dijkstra's algorithm decreases the complexity of searching part of the decoder with increase in the storage complexity. The computer simulation demonstrates that the complexity of the decoder is reduced by the proposed methods significantly.

Much of the work on faces in computer vision has been focused on face recognition or facial expression analysis, but has not been directly related with face direction detection. In this paper, we propose a vision-based approach to detect a face direction from a single monocular view of a face by using a facial feature called facial triangle, which is formed by two eyebrows and the lower lip. Specifically, the proposed method introduces simple formulas to detect face rotation, horizontally and vertically, using the facial triangle. It makes no assumption about the structure of the face and produces an accurate estimate of face direction.

Wavelet packet modulation (WPM) using the discrete wavelet transform is a multiplexing transmission method in which data is assigned to wavelet subbands having different time and frequency resolutions. The WPM keeps data transmission throughput even in tone and impulse interference environments that cannot be achieved with conventional multiplexing methods such as TDM (Time division multiplexing) or OFDM (Orthogonal frequency division multiplexing). In this paper, we propose an effective multicarrier transmission method of WPM for wireless mobile communications. First, the transmission characteristics of WPM in fading environments are minutely investigated. Then, taking the advantage of the WPM and the OFDM that has an equalizing technique in multipath fading environments, we propose a multimode transmission method using them. The adaptive transmission in those fading and interference environments is achieved by using the multimode transmission. Their transmission performances are evaluated by computer simulations.

In this paper, the previous definition of the Reverse Jacket matrix (RJM) is revised and generalized. In particular, it is shown that the inverse of the RJM can be obtained easily by a constructive approach similar to that used for the RJM itself. As new results, some useful properties of RJMs, such as commutativity and the Hamiltonian symmetry appearing in half the blocks of a RJM, are shown, and also 1-D fast Reverse Jacket transform (FRJT) is presented. The algorithm of the FRJT is remarkably efficient than that of the center-weighted Hadamard transform (CWHT). The FRJT is extended in terms of the Kronecker products of the Hadamard matrix. The 1-D FRJT is applied to the discrete Fourier transform (DFT) with order 4, and the N-point DFT can be expressed in terms of matrix decomposition by using 4 4 FRJT.

This paper presents a novel decoding strategy called combined iterative demapping/decoding (CIDD), for coded M-ary biorthogonal keying-based direct sequence ultra-wideband (MBOK DS-UWB) systems. A coded MBOK DS-UWB system consists of a convolutional encoder, an interleaver, and an MBOK DS-UWB pulse mapper. CIDD improves the error rate performance of MBOK DS-UWB systems by applying the turbo principle to the demapping and decoding processes at the receiver side. To develop the CIDD, a soft-in/soft-out MBOK demapping algorithm, based on the max-log-MAP algorithm, was derived. Simulation results showed that using CIDD siginificantly improved the error rate performance of both static and multipath fading channels. It was also shown that the computational complexity of CIDD is comparable to that of the Viterbi decoding used in [133,171]8 conventional convolutional coding.

This paper proposes a bandwidth allocation algorithm and a demand accommodation algorithm guaranteeing utility max-min fairness under bandwidth constraints. We prove that the proposed algorithms can fairly split network resources among connections and achieve call admission control considering the fairness among different types of applications. We then formulate three different network design problems to maximize the total utility of all customers, the number of users accommodated in the network, and the average utility of the customers accommodated in the network. To solve the problems, we extend the conventional network design algorithms considering utility max-min fair share, and numerically evaluate and compare their performance. Finally, we summarize the best algorithms to design the utility max-min fair share networks considering the operation policy of network providers.

The window flow control based end-to-end TCP congestion control may cause unfair resource allocation among multiple TCP connections with different RTTs (round trip times) at a bottleneck link. In this paper, in order to improve this unfairness, we propose the active ECN which is an ECN based active queue mechanism (AQM). A bottleneck router with the proposed mechanism marks TCP segments with a probability which depends on the RTT of each connection. By enabling the TCP senders to reduce their transmission rate when their packets are marked, the proposed mechanism can realize the same transmission rate among TCP connections with different RTTs. Furthermore, the active ECN can directly mark ACKs from TCP receivers, while the conventional ECN marks TCP segments coming from the TCP senders. As a result, the queue length distribution at the bottleneck link gets stabilized, because the sender can quickly react to the marking according to variation of the queue length.

The operation of a polarization mode dispersion (PMD) compensator using a polarizer and a Faraday rotator-based polarization controller (FRPC) is analyzed in detail, and the compensation performance is experimentally evaluated in 40 Gbit/s operation. The evaluation results show that a wide range of differential group delay over a bit period can almost be completely compensated using the PMD compensator. The characteristics of electrical spectrum-based signal monitoring methods are investigated in detail, and the results shows advantages of a low frequency band monitoring method that produces about double the wider dynamic range than a fundamental repetition frequency monitoring method. The automated PMD compensator using a polarizer and a FRPC driven by the low frequency band monitoring method is experimentally investigated using a terrestrial 40 Gbit/s wavelength division multiplexing system involving 350-km installed single-mode fibers. The PMD compensator produces highly stable signal performance in the field environment for a long term and reduces the standard deviation of the Q-factor distribution.

We present a built-in self-reconfiguring system for a mesh-connected processor array where faulty processor elements are compensated for by spare processing elements located in one row and one column. It has advantages in that the number of spare processing elements is small and additional control circuits and networks for changing interconnections of processing elements is so simple that hardware overhead for reconfiguration is also small. First, to indicate the motivation to the proposed reconfiguration scheme, we briefly describe other schemes with the same number of spares as that of the proposed scheme where faulty processing elements are replaced using straight shifts toward spares, and compare their reconfiguration probabilities to each other. Then, we show that a variant of the proposed scheme has the highest probability. Next, we present a built-in self-reconfiguring system for the scheme and formally prove that it works correctly. It can automatically replace faulty processors by spare processors on detecting faults of processors.

We describe elements of a fast integral equation solver for large periodic and partly periodic finite array systems. A key element of the algorithm is utilization (in a rigorous way) of a block-Toeplitz structure of the impedance matrix in conjunction with either conventional Method of Moments (MoM), Fast Multipole Method (FMM), or Fast Fourier Transform (FFT)-based Adaptive Integral Method (AIM) compression techniques. We refer to the resulting algorithms as the (block-)Toeplitz-MoM, (block-)Toeplitz-AIM, or (block-)Toeplitz-FMM algorithms. While the computational complexity of the Toeplitz-AIM and Toeplitz-FMM algorithms is comparable to that of their non-Toeplitz counterparts, they offer a very significant (about two orders of magnitude for problems of the order of five million unknowns) storage reduction. In particular, our comparisons demonstrate, that the Toeplitz-AIM algorithm offers significant advantages in problems of practical interest involving arrays with complex antenna elements. This result follows from the more favorable scaling of the Toeplitz-AIM algorithm for arrays characterized by large number of unknowns in a single array element and applicability of the AIM algorithm to problems requiring strongly sub-wavelength resolution.

Unlike most of the previous work for smart antennas that covered each area individually (antenna-array design, signal processing and communications algorithms and network throughput), this paper may be considered as a review of comprehensive effort on smart antennas that examines and integrates antenna array design, the development of signal processing algorithms (for angle of arrival estimation and adaptive beamforming), strategies for combating fading, and the impact on the network throughput. In particular, this study considers problems dealing with the impact of the antenna design on the network throughput. In addition, fading channels and tradeoffs between diversity combining and adaptive beamforming are examined as well as channel coding to improve the system performance.

The unfairness problem among TCP connections has been proved to be very severe in the IEEE 802.11-based wireless ad hoc networks because the hidden station problem still exists and the binary exponential backoff algorithm always favors the latest successful station. In this paper, a novel protocol, neighbor-medium-aware MAC (NEMA-MAC), is proposed to improve the TCP fairness. By adding a medium (channel) state field in the head of the traditional IEEE 802.11 MAC frame, the NEMA-MAC protocol provides a communication mechanism to resolve the hidden station problem. In addition, when a collision occurs, the new backoff algorithm makes the senders cooperatively adjust the contention window according to their local and neighbors' channel usage indexes. The simulation results show that TCP sessions can acquire satisfying fairness and increase the throughput in the NEMA-MAC-based multihop ad hoc networks.

From the bifurcation viewpoint, this study examines a boost PFC converter with average-current-mode control. The boost PFC converter is considered to be a nonlinear circuit because of its use of a multiplier and its large duty cycle variation for input current control. However, most previous studies have implemented linear analysis, which ignores the effects of nonlinearity. Therefore, those studies were unable to detect instability phenomena. Nonlinearity produces bifurcations and chaos when circuit parameters change. The classical PFC design is based on a stable periodic orbit that has desired characteristics. This paper describes the main bifurcations that this orbit may undergo when the parameters of the circuit change. In addition, the instability regions in the PFC converter are delimited. That fact is of practical interest for the design process. Moreover, a prototype PFC circuit is introduced to examine these instability phenomena experimentally. Then, a special numerical program is developed. Bifurcation maps are provided based on this numerical study. They give a comprehensive outstanding for stability conditions and identify stable regions in the parameter space. Moreover, these maps indicate PFC converter dynamics, power factors, and regulation. Finally, numerical analyses and experimentation show good agreement.

Intensity-noise characteristics of stable multi-mode Fabry-Perot semiconductor lasers are analyzed experimentally and theoretically. Mode-partition noise caused by optical filtering and propagation through optical fibers is investigated by evaluating the relative intensity noise and signal-to-noise ratio. The experimental results indicate that the simplified two-mode analysis provides a good approximation. Suppression of the mode-partition noise by nonlinear gain is experimentally confirmed.