This paper outlines technical trend of multimedia mobile and broadband wireless access systems utilizing comprehensive concept and new categorization of wireless access. It is pointed out that mobile communications have much potential market in future high-speed data or IP (Internet Protocol)-based traffic. Categorization of three kinds of wireless access is presented based on the definition adopted by the Radiocommunication Sector in ITU. IMT (International Mobile Telecommunications)-2000 and broadband wireless LANs (Local Area Networks) each representing mobile and nomadic wireless access will bring about a turning point to a new era that wireless communications become dominant media in access networks. With this perspective technical subjects, spectrum consideration and deployment scenario for these systems are discussed.

The explicit formula for the coefficients of maximally linear digital differentiators is derived by the use of Taylor series. A modification in the formula is proposed to extend the effective passband of the differentiator with the same number of coefficients.

This paper proposes a coherent detection scheme that can reduce the estimation errors of the carrier phase due to Gaussian noise in communication systems where pilot symbol assisted modulation is employed to compensate for Rician fading distortion. This paper introduces two functions in addition to conventional fading estimation methods using Wiener interpolation, etc. The first is the weighted average function for reducing the estimation errors of the fading distortion detected by pilot symbols. The second is the moving average function for estimating the phase errors that are residual after being compensated for by the estimated fading distortion. This paper evaluates the bit error rate (BER) performance for the proposed method in both Rician fading channel and additive white Gaussian noise (AWGN) channel by computer simulation. Simulation results verify that the BER performance of the proposed method is superior to that of a conventional method in both Rician fading channel and AWGN channel. Simulation results also confirm that the degradation of the BER performance of the proposed method is only 0.1 dB in AWGN channel and only 0.3 dB in Rician fading channel compared with the theoretical curves even if we reduce the number of computations by simplifying the calculation of interpolation coefficients optimized for Wiener interpolation.

This paper proposes a short delay, error-resilient video transmission scheme for mobile radio channels. Compressed video data are sensitive to channel error. Video coding schemes such as H. 263 use variable length coding so channel error can cause synchronization failure in the decoder and fatally degrade the reconstructed video sequence by triggering intra- and inter-frame error propagation. ARQ prevents all forms of error propagation but significantly increases the transmission delay of the video frame. We propose a new error control scheme to reduces the delay incurred by ARQ; the receiving buffer can transmits the video frame data to the video decoder even if not all ARQ frames containing the video frame are received. The encoder transmits additional information, the Macro Block (MB) size, in the video frame header. Upon receiving this information, the receiving buffer can determine MB length which allows MB de-synchronization to be prevented. For example, if an ARQ frame is lost, the decoder determines the position of the missing MB and replace this MB with the equivalent block in the previous video frame; this prevents intra-frame error propagation. When all ARQ frames are received and decoded correctly, the video frame in the reference video memory is replaced with the correctly decoded one. Simulation results show that the proposed scheme can minimize the delay and the reduction in frame rate caused by retransmission control without intra- and inter-error propagation.

Traffic management schemes such as Connection Admission Control (CAC), policing, and traffic shaping are important to provide multimedia communications with better Quality of Service (QoS). In the conventional model, admission control and policing are done at intermediate nodes, and traffic shaping is done at the edge of a network. However, QoS of communications should be defined between tasks or threads rather than between hosts. Therefore traffic management inside a host is as important as that in networks. We propose software-based traffic management architecture over a real-time microkernel. The architecture focuses on the interface between a network driver and user threads calling the driver. We categorized services of communication threads into three classes: Real-Time at Guaranteed Rate (RT-GR), Real-Time at Available Rate (RT-AR), and Best-Effort (BE). Our architecture is designed for an environment containing a mixture of these services. In the architecture, a sender periodic thread of RT-GR or RT-AR is executed such that the sending rate matches a user-specified rate. The network driver monitors the per-flow rate of injected data and discards the data if the injected rate exceeds the user-specified rate. To avoid the continuous discarding of data, the sending thread can adjust its sending rate by periodically looking at logged data concerning the rate. RT-AR service can achieve more than the specified rate when bandwidth is available. The scheme of software traffic management is effective in attaining higher throughput not only for full-duplex Ethernet but also for ATM because the difference of rate between hardware and software is reduced. In this paper, we describe the design and implementation of the software-based traffic management architecture on Real-Time Mach. The results of performance evaluations demonstrate that our traffic management scheme performs well for full-duplex Ethernet.

Non-stationary glint noise is often observed in a radar tracking system. The distribution of glint noise is non-Gaussian and heavy-tailed. Conventional recursive identification algorithms use the stochastic approximation (SA) method. However, the SA method converges slowly and is invalid for non-stationary noise. This paper proposes an adaptive algorithm, which uses the stochastic gradient descent (SGD) method, to overcome these problems. The SGD method retains the simple structure of the SA method and is suitable for real-world implementation. Convergence behavior of the SGD method is analyzed and closed-form expressions for sufficient step size bounds are derived. Since noise data are usually not available in practice, we then propose a noise extraction scheme. Combining the SGD method, we can perform on-line adaptive noise identification directly from radar measurements. Simulation results show that the performance of the SGD method is comparable to that of the maximum-likelihood (ML) method. Also, the noise extraction scheme is effective that the identification results from the radar measurements are close to those from pure glint noise data.

Linear signal analysis (LSA) is the conventional method of estimating the playback voltage and pulse width in linearly operating shielded GMR heads. To improve the accuracy of LSA, a new, highly precise LSA which includes the effect of the magnetization distribution in the medium and inhomogeneous biasing by domain control magnets, was developed. Utilizing this new LSA to calculate the playback waveforms, the calculated peak voltage and pulse width were compared with the experimental values and agreement within 10% was obtained. As the result of estimation using the new LSA, it is considered that the use of a vertical-type spin-valve head will make it possible to achieve a recording areal density of 40 Gb/in2.

In this paper, we will present a study of the time-dependence effect in alumite perpendicular media at different thicknesses. Important parameters of the time-dependence effect such as magnetic viscosity and activation volume are investigated. Viscosity as a function of applied field (viscosity curve) exhibits a short plateau at a low field and then decreases monotonously with increasing field. After correcting for the demagnetizing field, the shape of the intrinsic viscosity curves changes to the well-known shape of the viscosity curve of in-plane media, i. e. , they have a peak near Hc. The intrinsic viscosity curves obtained from the experiments were fitted to an analytical model by Chantrell et al., from which, we found that the effective switching volumes obtained by fitting are much smaller than the column volumes, indicating that the reversal mechanism is incoherent.

Ring head recording on single-layer perpendicular recording media was studied by a simple simulation analysis based on a loop tracing method considering only the perpendicular component. Although the assumed model was primitive, the simulation results qualitatively well explained the experimental results such as a decrease in output at high recording currents and its relaxation upon using a smaller gap-length head. The simulation results revealed that achievable recorded magnetization is, in general, much smaller than the saturation value due to a broad distribution of the ring head field, but a medium with a steeper slope in the perpendicular M-H loop could improve the recording performance. This was confirmed experimentally for the medium with a steeper loop slope, though the medium exhibited a larger medium noise at high densities. It was suggested that the development of perpendicular recording for higher output and lower noise could be performed for both media with a small and steep loop slope. The former should be improved by means of the recording head while the latter by the media. A large improvement is expected for both cases.

This paper proposes a design method of STC for discrete unstructured systems based on D-L networks. The proposed scheme determines the control input composed of arbitrary system matrices of constructed D-L networks, and thus it makes it possible to design the STC for unstructured systems whose priori knowledges are not available. The simulation results show that the proposed scheme provides satisfactory performances both in MPS and NMPS for the STC design of unstructured systems.

This paper proposes a novel DS/CDMA system with code-diversity techniques constituted by a simple system to suppress multiple access interference (MAI) without estimating the PN sequence of interference at the receiver. In the transmitter, the data signal is modulated with a sum of several PN sequences, and, two types of code- diversity reception are proposed, (1) maximal-ratio combining (MRC) code-diversity by autocorrelation, and (2) MRC code-diversity by anti-crosscorrelation. By computer simulations, it is shown that MRC code-diversity by anti-crosscorrelation is superior to the other one. It is also shown that MRC code-diversity by anti-crosscorrelation can improve BER more effectively for the interference which takes the phase to degrade BER at the worst. Next, to design the optimum number of branches for code-diversity, average BERs are calculated for several combinations of codes in code-diversity. As a result, the optimum number of branches varies for each combination of codes, however, it is decided from 3 to 7 branches. Finally, the effectivity of the proposed system in a near-far problem is presented.

To improve frequency efficiency or user capacity in multi-path fading environments, we introduce and investigate an orthogonal multi-carrier frequency hopping-code division multiple access (FH-CDMA). These improvements are achieved by combining the orthogonal frequency division multiplexing (OFDM) and FH-CDMA schemes. The basic idea has been previously proposed by the authors. The aim of study in this paper is to evaluate the performance of this scheme in various environments. The theoretical analysis of bit error rate (BER) performance in this paper includes the effects of frequency selective fading in land mobile communications and of nonlinear amplification in satellite communications. A modified scheme of controlling transmission power to be controlled according to the number of simultaneously accessing users is also discussed. This modified scheme improves BER performance for frequency selective fading when the number of simultaneously accessing users in a cellular zone is small. Furthermore, an error-correcting code and its erasure decoding are applied in order to reduce errors due to hits in asynchronous FH/CDMA for reverse link as well as errors due to fading and noise.

This paper proposes an associative memory neural network whose limiting state is the nearest point in a polyhedron from a given input. Two implementations of the proposed associative memory network are presented based on Dykstra's algorithm and a fixed point theorem for nonexpansive mappings. By these implementations, the set of all correctable errors by the network is characterized as a dual cone of the polyhedron at each pattern to be memorized, which leads to a simple amplifying technique to improve the error correction capability. It is shown by numerical examples that the proposed associative memory realizes much better error correction performance than the conventional one based on POCS at the expense of the increase of necessary number of iterations in the recalling stage.

This paper proposes a novel spread spectrum (SS) modem for random access satellite communication systems that employs digital matched filters. The proposed modem employs a parallel structure to ensure detection of packet arrival. Code timing detection with a combination of a coarse detector and a fractional error detector reduces the sampling rate while maintaining the BER performance. An in-symbol pilot multiplexing scheme is also proposed for fast and stable carrier synchronization with a simple hardware. A performance evaluation shows that the proposed modem achieves the UW miss-detection probability of 10-4 at the Eb/No of 0 dB. The overall BER performance achieved in experiments well agrees simulation.

In this paper, a type of multi-carrier direct sequence code division multiple access (MC-DS-CDMA) system which uses frequency spread coding is proposed and investigated for the down-link. An MC-DS-CDMA system is a combined system of CDMA and multi-carrier modulation. This system is often categorized as a "serial to parallel (S/P) type" system because serial to parallel converted data symbols are transmitted. They use different sub-carriers which are narrow-band DS waveforms. In this system, benefits of path or frequency diversity can not be obtained because of the narrow-band transmission of each data symbol. In order to benefit from the diversity, we propose to adopt frequency spread coding in an MC-DS-CDMA system. The proposed system exploits frequency diversity without additional redundancy, i. e. , no frequency or time redundancy is required to improve the performance. Computer simulation is carried out in a frequency selective fading channel and the results show its effectiveness in terms of average bit error rate (BER). Furthermore, the proposed system is compared with a multi-carrier (MC-) CDMA system which is often categorized as a "copy type" system and a single-carrier (SC-) DS-CDMA system using a RAKE receiver.

We have developed a diagnostic Case-Based Reasoning (CBR) system, Doctor, which infers possible defects in a home electrical appliance and lists up necessary service parts. The CBR is suitable to build a diagnostic system for the field service because the CBR imitates how experienced service technicians infer and is able to learn defect trends and novel repair cases from a service report database. In order to apply a CBR system to this real-world problem, Our system has the following new features: (1) Its CBR mechanism utilizes not only repair cases, but also diagnostic rules that are elicited from human experts so that accurate diagnosis can be achieved. (2) Its casebase maintenance mechanism updates the casebase and adapts it to the changing real world.

We propose a model for fault tolerant 3D processor arrays using one-and-half track switches. Spare processors are laid on the two opposite surfaces of the 3D array. The fault compensation process is performed by shifting processors on a continuous straight line (called compensation path) from a faulty processor to a spare on the surfaces. It is not allowed that compensantion paths are in the near-miss relation each other. Then, switches with only 4 states are needed to preserve the 3D mesh topology after compensating for faults. We give an algorithm in a convenient form for reconfiguring by hardware the 3D mesh arrays with faults. The algorithm can reconfigure the 3D mesh arrays in polynomial time. By computer simulation, we show the survival rates and the reliabilities of arrays which express the efficiencies of reconfiguration according to the algorithm. The reliabilities are compared with those of the model using double tracks for which the near-miss relation among compensation paths is allowed, but whose hardware overhead is almost double of that of the proposed model using one-and-half track. Finally, we design a logical circuit for hardware realization of the algorithm. Using the circuit, we can construct such a built-in self-reconfigurable 3D mesh array that the reconfiguration is done very quickly without an aid of a host computer.

One of the problems in multi-carrier modulation is nonlinear distortion due to nonlinearity of channels, such as in HPA (High Power Amplifier). This problem is also true of multi-carrier SS (Spread Spectrum) systems. In this paper, an inter-modulation compensation scheme for multi-carrier M-ary/SS system is proposed. We propose two methods to control the sequences transmitted in parallel to avoid the occurrence of severe inter-modulation distortion. One is the "package sequence selection" method, which requires slight redundancy. The other method is based on error correction code, which requires no additional frequency or power except the redundancy for error correction. We confirm the validity of our proposed scheme by computer simulation, and the BER (Bit Error Rate) performance in an AWGN (Additive White Gaussian Noise) channel is presented.

This paper proposes a method to construct smaller binary decision diagrams for characteristic functions (BDDs for CFs). A BDD for CF represents an n-input m-output function, and evaluates all the outputs in O(n+m) time. We derive an upper bound on the number of nodes of the BDD for CF of n-bit adders (adrn). We also compare complexities of BDDs for CFs with those of shared binary decision diagrams (SBDDs) and multi-terminal binary decision diagrams (MTBDDs). Our experimental results show: 1) BDDs for CFs are usually much smaller than MTBDDs; 2) for adrn and for some benchmark circuits, BDDs for CFs are the smallest among the three types of BDDs; and 3) the proposed method often produces smaller BDDs for CFs than an existing method.

The constant modulus algorithm (CMA) of the adaptive array has been developed for suppressing the co-channel interference and the intersymbol interference in mobile communications. In this paper a novel CMA for the hybrid of the adaptive array and equalizer (HAE) is proposed to combat the problems of insufficient degrees of freedom and mainbeam multipath interferers. The HAE with CMA utilizes the constant modulus property for the output signal of the HAE to adjust the weight vectors of the array and equalizer simultaneously. The co-channel interferers can be canceled by the array and the multipath interferers can be removed by the array or the equalizer following the array in the HAE. Therefore, the array in the HAE with CMA may need less number of elements than that required by the CMA array which cancels both the co-channel interferers and multipath interferers. Besides, the presence of the mainbeam multipath interferers, which may seriously degrade the performance of the CMA array, has much less effect on the HAE with CMA since it can be suppressed by the equalizer instead of the array. Simulation results are presented to demonstrate the merits of the CMA for the HAE.