The paper discusses the possibility of building semiconductor lasers whose wavelength stays nearly constant with ambient temperature variation. Several factors affecting the lasing wavelength change with temperature variation in both distributed feedback lasers and Fabry-Perot lasers are addressed and the optimum design of bandgap temperature dependence for the active layer material is discussed. It is pointed out that the most important challenge we face in building temperature-insensitive wavelength lasers is the development of a temperature-insensitive bandgap material for the active layer. Based on published data, it is speculated that such a laser could be developed using a Hg1-xCdxTe/CdTe double heterostructure. Although no data is available yet, we expect a Ga1-xInxAs1-yBiy III-V alloy semiconductor can be used for this purpose. Recently reported T1xIn1-x-yGayP III-V alloy semiconductor might be another promising candidate. Such lasers will greatly advance applications of WDM (Wavelength-Division-Multiplexing) technology to optical fiber communication systems and contribute to network innovations.

The Time-Slicing paradigm is a newly developed method for the training of neural networks for speech recognition. The neural net is trained to spot the syllables in a continuous stream of speech. It generates a transcription of the utterance, be it a word, a phrase, etc. Combined with a simple error recovery method the desired units (words or phrases) can be retrieved. This paradigm uses a recurrent neural network trained in a modular fashion with natural connectionist glue. It processes the input signal sequentially regardless of the input's length and immediately extracts the syllables spotted in the speech stream. As an example, this character string is then compared to a set of possible words, picking out the five closest candidates. In this paper we describe the time-slicing paradigm and the training of the recurrent neural network together with details about the training samples. It also introduces the concept of natural connectionist glue and the recurrent neural network's architecture used for this purpose. Additionally we explain the errors found in the output and the process to reduce them and recover the correct words. The recognition rates of the network and the recovery rates for the words are also shown. The presented examples and recognition rates demonstrate the potential of the time-slicing method for continuous speech recognition.

This paper describes how to effectively use discriminative training based on Minimum Classification Error (MCE) criterion for a small amount of data in order to attain the highest level of recognition performance. This method is a combination of MCE training and Vector-Field-Smoothed Bayesian learning called MAP/VFS, which combines maximum a posteriori (MAP) estimation with Vector Field Smoothing (VFS). In the proposed method, MAP/VFS can significantly enhance MCE training in the robustness of acoustic modeling. In model training, MCE training is performed using the MAP/VFS-trained model as an initial model. The same data are used in both trainings. For speaker adaptation using several dozen training words, the proposed method has been experimentally proven to be very effective. For 50-word training data, recognition errors are drastically reduced by 47% compared with 16.5% when using only MCE. This high rate, in which 39% is due to MAP, an additional 4% is due to VFS, and a further improvement of 4% is due to MCE, can be attained by enhancing MCE training capability by MAP/VFS.

In the envisaged Universal Mobile Telecommunications System (UMTS), the satellite component will have to provide services to mobile or, in some cases, hand held terminals with a required grade of user co-operation and link availability in various communication environments. This may require the capability of the satellite link to cope with more severe multipath environments than those for which mobile satellite links are most frequently designed (maritime or open rural applications); unfortunately, when the mobile radio channel is affected by multipath and a coherent demodulation is chosen, the phase synchronisation can be a critical issue. To satisfactorily deal with the arising difficulties, a dual channel demodulation is a viable and efficient strategy for the forward link, since only one common pilot channel is needed in this case. If the same dual channel demodulation is considered for the return link, an unacceptable capacity reduction may result. In this paper, some synchronisation strategies are analysed and an efficient dual channel demodulation scheme is proposed for the return link of a satellite DS-CDMA mobile communication system; furthermore, the impact on the overall system performance or capacity is analysed.

Asynchronous Transfer Mode (ATM) is considered to bo the key technology for realizing B-ISDN. This paper discusses current research on ATM switching nodes for high-speed communication networks. Although some ATM switching nodes have been deployed, much work continues for resolving problems as regards operations and maintainability, such as ATM layer performance evaluation including layered management scheme upon detection of line failure, function test methods regarding channel connectivity for multicasting, and real-time ATM traffic-monitoring mechanism with QoS control. To achieve sufficient ATM node maintainability, the ATM cell transfer quality on the VP and VC levels should be ensured both within the ATM nodes and between adjacent ATM nodes. Since ATM switching nods handle many kinds of virtual paths and virtual channels, each channel's connectivity must be confirmed. This paper proposes ATM layer performance evaluation concept, layered management scheme upon detection of line failure, function test methods for a multicast switch using test cells that periodically pass through pre-determined switching path routes. It also proposes the concept of test cell generation for simulating multiplexed ATM test cells taking ATM truffic characteristics into account. Furthermore, this paper describes a fault diagnosis scheme using test cells that can continually observe the entire ATM connection length in the system. A real-time traffic monitoring hardware configuration and an interface with software control are also discussed and it is clarified that the required functions can be realized by using commercially available DSPs.

For quasi millimeter-wave and millimeter-wave high-speed wireless communications over wireless LANs and wireless ATMs, narrow beam antennas have been shown to provide high transmission quality by suppressing the troublesome multipath effect. However, the diameter of sector antennas needed to create the narrow beams rapidly increases with the sector number. In addition, the cylindrical shape of typical sector antennas does not suit portable terminals. This paper shows a methodology for designing planar sector antennas that overcomes these problems. The proposed antenna uses two kinds of beams and the antenna gains are equalized in all sectors. The antenna is developed as a 4-beam subarray fed by a planar Butler matrix circuit. The design method of the subarray and an evaluation of its characteristics in the 20 GHz band are discussed.

Recently, various efficient algorithms for solving combinatorial optimization problems using BDD-based set manipulation techniques have been developed. Minato proposed O-suppressed BDDs (ZBDDs) which is suitable for set manipulation, and it is utilized for various search problems. In terms of practical limits of space, however, there are still many search problems which are solved much better by using conventional branch-and-bound techniques than by using BDDs or ZBDDs, while the ability of conventional branch-and-bound approaches is limited by computation time. In this paper, an extension of APPLY operation, named APPRUNE (APply + PRUNE) operation, is proposed, which performs APPLY operation (ZBDD construction) and pruning simultaneously in order to reduce the required space for intermediate ZBDDs. As a prototype, a specific algorithm of APPRUNE operation is shown by assuming that the given condition for pruning is a threshold function, although it is expected that APPRUNE operation will be more effective if more sophisticated condition are considered. To reduce size of ZBDDs in intermediate steps, this paper also pay attention to the number of cared variables. As an application, an exact-minimization algorithm for generalized Reed-Muller expressions (GRMs) is implemented. From experimental results, it is shown that time and memory usage improved 8.8 and 3.4 times, respectively, in the best case using APPRUNE operation. Results on generating GRMs of exact-minimum number of not only product terms but also literals is also shown.

In this paper stochastic aradient adaptive filters using the Sign or Sign-Sign Algorithm are analyzed based upon general assumptions on the reference signal, additive noise and particularly jointly distributed tap errors. A set of difference equations for calculating the convergence process of the mean and covariance of the tap errors is derived with integrals involving characteristic function and its derivative of the tap error distribution. Examples of echo canceller convergence with jointly Gaussian distributed tap errors show an excellent agreement between the empirical results and the theory.

This paper deals with performance evaluation of CDMA based on DS/SS/GMSK signaling with the differential detection over multipath Rayleigh fading channels. To demodulate DS/SS/GMSK signals, we consider differential detection, which does not need a carrier recovery. The bit-error-rate performance is evaluated in the presence of thermal noise and multipleaccess interferences under the multipath Rayleigh fading environment. To improve the performance, we also consider adoption of a RAKE receiver.

This paper presents a new method for the selftuning control of nonminimum phase discrete-time stochastic systems using approximate inverse systems obtained from the leastsquares approximation. Using this approximate inverse system the gain response of the system can be made approximately unit and phase response exactly zero. We show how unstable polezero cancellations can be avoided. This approximate inverse system can be used in the same manner for both minimum and nonminimum phase systems. Moreover, the degrees of the controller polynomials do not depend on the approximate inverse system. We just need an extra FIR filter in the feedforward path.

In this paper, we propose a clustering based linear ordering algorithm which consists of global ordering and local ordering. In the global ordering, the algorithm forms clusters from n given vertices and orders the clusters. In the local ordering, the elements in each cluster are linearly ordered. The linear order, thus produced, is used to obtain optimal κ-way partitioning based on scaled cost objective function. When the number of cluster is one, the proposed algorithm is exactly the same as MELO [2]. But the proposed algorithm has more global partitioning information than MELO by clustering. Experiment with 11 benchmark circuits for κ-way (2 κ 10) partitioning shows that the proposed algorithm yields an average of 10.6% improvement over MELO [2] for the κ-way scaled cost partitioning.

We propose a novel feeding circuit for a 30 GHz planar multibeam antenna applied to high-speed wireless communication systems. The feeding circuit is a bi-layer 8-port Butler matrix constructed with phase adjusted slot-coupled hybrids and branch-line hybrids. The new circuit configuration eliminates troublesome vias and line crossings, so it can be manufactured by traditional photolithograph. The feeding circuit is designed by using the spectral domain moment method considering bonding film effects. A prototype of a multibeam antenna which has seven pencil-beams with 10 beamwidths is manufactured and tested; the beam scan angle error is less than 3 at 30 GHz.

An important aspect of traffic safety is the development of aids that extend the driver's time and motion perception. One promising candidate is the compact, lightweight millimeter-wave FM-CW radar now being widely studied. Although the homodyne FM-CW radar is well known form its simplicity, it has a relatively low S/N ratio. This paper describes the principles behind our newly-developed heterodyne FM-CW radar and it's evaluation results. The heterodyne FM-CE radar generates sidebands by switching a front-end amplifier and also uses the heterodyne detection technique for gaining sensor sensitivity. The heterodyne FM-CW radar's signal to noise ratio was 19.5 dB better than previously designed homodyne FM-CW radar.

In outdoor fields such as construction, mining and agriculture, there is an increasing demand for autonomous vehicles to reduce labor costs. Also, a positioning system is one key technology required for autonomous vehicle systems. For the purpose of expanding the potential of millimeter-wave applications, we have developed a positioning system in the 77-79 GHz frequency band, using the hyperbolic radio navigation method. This system operates in a restricted area with a radius of about a few hundred meters. A spread spectrum with a PN code is used as the ranging signals. We realized about 0.1 m in positioning accuracy.

New interference cancellation technique using time division reference signal is proposed for optical synchronous code-division multiple-access (CDMA) systems with modified prime sequence codes. In the proposed system one user in each group is not allowed to access the network at each time, and this unallowable user's channel is used as a reference signal for other users in the same group at the time. The performance of the proposed system using an avalanche photodiode (APD) is analyzed where the Gaussian approximation of the APD output is employed and the effects of APD noise, thermal noise, and interference for the receiver are included. The proposed cancellation techniqus is shown to be effective to improve the bit error probability performance and to alleviate the error floor when the number of users and the received optical power are not appreciably small.

The one of the problems in the satellite packet communication system is the existence of a long time delay, which may cause an improper packet access control resulting in a great deal of degradation of the system performance. In this paper, we clarify the effect of long time delay on the performance of CDMA ALOHA systems and then propose a new access control protocol, called Modified Channel Load Sensing Protocol (MCLSP), for the CDMA ALOHA systems. As a result, we show that a significant improvement in the throughput performance was obtained with MCLSP even in the presence of a long time delay.

A V-band compact monolithic up-converter and down-converter were designed and tested. Each frequency converter was highly integrated with RF and LO amplifiers into a single compact chip. To avoid undesirable resonance, the chip width was limited to 0.9 mm. The up-converter has a balanced configuration to suppress undesired LO leakage. Using the uniplanar concept, the chip size of each frequency converter was greatly reduced to only 2.6 mm2. Measured performance of the up-converter includes conversion gain of-10.6 dB3.3 dB for a bandwidth of 10 GHz, and LO leakage is more than 10 dB below LO input. The down-converter shows a conversion gain of -0.4 dB2.0 dB.

In this paper we propose a direct sequence spread spectrum (DS/SS) modulation method which employs Gaussian-filtered minimum shift keying (GMSK) and permits simple code acquisition. A transmitter which includes a conventional GMSK modulator and pseudo-noise (PN) code generator can achieve the proposed modulation method. The received signal can be demodulated by four-phase correlator which can obtain the correlation value of received signal even if phase difference exists between the transmitter and the receiver. The modulation method employs phase-shift-keying (PSK) by modulating the phase of transmitted PN code for data transmission. We carried out hardware experiments and the measured bit error performance ensures the validity of this modulation method. Then we designed and developed a demodulator LSI which is applicable to a modulation method such as the DS/GMSK/PSK. The LSI is suitable for demodulation of spreadspectrum signal which can be demodulated by four-phase correlator.

Memory Sharing Processor Array (MSPA) architecture has been developed as an effective array processing architecture for both reduced data storages and increased processor cell utilization efficiency [1]. In this paper, the MSPA design methodology is extended to the VLSI synthesis of a serial input processor array (Pa). Then, a new bit-serial input multiplier and a new data serial input matrix multiplier are derived from the new PA. These multipliers are superior to the conventional multipliers by their smaller number of logic-gate count.

In this paper, we describe effects of oddcorrelation functions and band-limitation filters for direct-wave reception systems using broadband spread-spectrum (B-SS) techniques. The receiver of this system is synchronized to the direct-wave. First, the effects of odd-correlation functions are investigated by using M-sequences and random sequences. The effects of even-correlation functions for those sequences can be easily obtained by using results of effects of odd-correlation functions for random sequences. Here we derive a novel function of odd-correlation variance for M-sequence, which is obtained theoretically. Consequently, we show the advantage of M-sequence which is used as spreading sequence. As a reason, in the odd-correlation function of M-sequence, small values are taken near the synchronous phase where harmful scattered-waves exist, strongly. Next, the effects of both odd-correlation function and band-limitation filter are studied by using several kinds of filters. Here we discuss the difference of characteristics in case that despreading sequence of bandlimited pulse or that of rectangular pulse is used in the correlator of the receiver. The technique despreading by rectangular pulse can be achieved a high speed signal processing and equipment miniaturizing because of utilization of switching circuit. We show the advantage of despreading sequence of rectangular pulse, when the limitation bandwidth of transmitting signal takes a small value. Because the characteristics of the correlation function between transmitting sequence of bandlimited pulse and despreading sequence of rectangular pulse can be kept better than that between the transmitting sequence and despreading sequence of bandlimited pulse. As these results, in severe bandlimited direct-wave reception systems using B-SS techniques, M-sequence of rectangular pulse as despreading sequence is most suitable.