An integrated slider-suspension system was designed and prototyped. The structure of this system has a full flying air-bearing surface in the leading part with a contamination-resistant feature, and it accommodates a slider with a 5-15 nm head-disk spacing at the trailing part. Performance analysis and simulation were conducted to validate the high performances of the design. Two key issues, the rigid motions (vibrations) and the elastic motions of the slider, were investigated systematically. For the rigid motions, it was found that the natural frequencies of the slider system are dependent on the disk contact stiffness and that the slider vibrations under excitation exhibit various nonlinear resonance. For the elastic motions, the average elastic response of the slider body under the random interaction of the interface was derived and characterized.

The effect of surface roughness is crucial for contact recording and proximity recording. In this paper a probability model is developed for investigation of the influence of surface roughness on flying performance and the contact force of the slider. Simulations are conducted for both the contact recording slider and the proximity recording slider, and the results are well coordinated with the reported experimental results and the self-conducted experimental results. Studies are further extended to the characterization of the roughness of the air bearing surface and the disk surface that may support head/disk spacing between 5 nm and 15 nm.

A head-disk spacing tester that includes the effect of lubricant will be necessary if the slider-disk interaction is to be considered. The interaction and interaction induced spacing variation can be quantitatively characterized by optical method and by replacing the functional disk media with a glass disk covered with a carbon layer and a lubricant layer of the same materials and the same layer thickness as the functional disk media. This paper reports a tester configuration based on that concept. Experimental investigations into the nanometer spaced head-disk interface with such a setup are presented also. Results indicate that the lubricant plays an important role in slider-disk interaction and the vibration of the slider-disk interface. Two types of interface vibration were noticed: contact vibration and bouncing vibration. For the bouncing case, the natural frequency of air-bearing and its fold frequencies will be excited and air-bearing plays more important role in the determination of the slider vibration, comparing with the contact-vibration case.

Thermal stability of anisotropic and isotropic Co alloy thin-film media is investigated. The orientation ratio of CoCrTa(Pt)/Cr media was controlled by the mechanical texture of the NiP/Al substrates. Bulk magnetic properties, delta M curves and time decay of magnetization in the circumferential and radial directions were measured. The maximum magnetic viscosity coefficient calculated from the time decay of magnetization in the circumferential direction was higher than that in the radial direction for a mechanically textured sample, while it was similar in both directions for a non-textured sample. The magnetic viscosity coefficient in the circumferential direction is smaller than that in the radial direction when the reverse field is in the range of the demagnetization field for thin-film recording media. This implies that an anisotropic sample (namely, a sample with a high orientation ratio) will be more thermally stable when it is not exposed to a large external magnetic field.

Three basic ideas for enhancing the performance of extended EPRML (EEPRML) are described in detail. The first is the modification of the EEPRML impulse response in order to minimize the bit error rate of read signals from magnetic recording channels. This modification can improve the signal to noise ratio (S/N) of conventional extended partial response maximum likelihood (EPRML) by approximately 1 dB. The second is the introduction of 16/17 (3;11) maximum transition run code (MTR). This code can completely eliminate error events of more than four consecutive bits from modified EEPRML error events, and reduce the probability of minimum distance error events occurring by one eighth. Finally, dominant error events such as {0e0}, {0ee0}, {0eee0}, and {0e00e0} before 16/17 (3,11) MTR decoding can be corrected by employing cyclic redundancy check code (CRCC) with soft decision decoding. The symbol "e" represents one bit error, namely, "1" to "0" or vice versa and "0" represents a correct bit. Total performance has been evaluated by computer simulations using an isolated waveform similar to actual read signals and additive white Gaussian noise. Consequently, it has been confirmed that modified EEPRML with 16/17 (3;11) MTR code and CRCC can improve the S/N of conventional EPRML by approximately 4 dB at a bit error rate of 10-6.

Guided Scrambling (GS) is used for control of the runlength within code blocks, such as d or k, as well as for DC component suppression. A code designed by the GS technique, called a weakly constrained code, does not strictly guarantee the imposed k-constraint, but rather generates code blocks that violate the prescribed constraint with very low probability. In this case, the code rate and efficiency become very high, compared with typical RLL codes using a small constrained length. In this paper, weakly constrained codes based on the convolutional GS and GF-addition GS generate the weakly k-constraint sequences. The probability that a code block violates the k-constraint is measured. To show the superior performance of the GS, the occurrence probability of each runlength is also investigated and compared with the 24/25(0, 8) block code which has a high code rate and adheres to channel constraints. We also compare it with the runlength distribution of a maxentropic RLL sequence and show that the statistical property of the GS-encoded sequences is similar to that of the maxentropic RLL sequence on runlength distribution.

This paper describes the design and implementation of a multi-threaded Distributed Shared Memory (DSM) system, called Cohesion, which provides high programming flexibility and latency masking, and supports load balancing. Cohesion offers a parallel programming environment which is very similar to that on a multiprocessors system. Threads could be created recursively in this environment, and users are not required to handle the locations of the threads. Instead of supporting a shared variable model, Cohesion provides a global shared address space among all nodes in the system. The space is further divided into three regions, i. e. , release, conventional, and object-based memory, each is applied with different consistency protocol. In this paper, the design issues in an ordinary thread system, such as thread management, load balancing, and synchronization, have been reconsidered with the memory management provided by the DSM system. Several real applications have been used to evaluate the performance of the system. The results show that multi-threading usually has better performance than single-threading because the network latency can be masked by overlapping communication and computation. However, the gain depends on program behavior and the number of threads executed on each node in the system.

This paper proposes a new maximal ratio combining (MRC) frequency diversity automatic-repeat-request (ARQ) scheme suitable for high-speed orthogonal frequency division multiplexing (OFDM) systems that is based on the conventional packet combining ARQ scheme. The proposed scheme regularly changes the previously prepared subcarrier assignment pattern at each retransmission according to the number of retransmissions. This scheme sharply reduces the number of ARQ retransmissions and much improves the throughput performance in slow fading environments by virtue of the frequency diversity effect while it requires no complex adaptive operations. Computer simulation results show that the proposed scheme reduces the required number of retransmissions to about 3 at the accumulative correct packet reception rate (ACPRR) of 0.9.

Recent attractive high-speed networks require network file servers with high-speed read performance to deliver huge multimedia files, like voice or movie files. This paper proposes new design and implementation techniques that yield high-speed file servers based on UNIX. The techniques are request reduction, in which contiguous blocks on UNIX file system (UFS) are gathered for reducing the number of command requests from the file system to the device driver, and a direct access method for cutting through the buffer cache mechanism. A file server prototype based on a general-purpose personal computer (PC) is constructed and its performance is evaluated. The preliminary results show that the prototype achieves high-speed file read performance in excess of 100 Mbytes/s even on an OpenBSD PC-UNIX system with 3 RAID controllers and 9 hard drives in RAID level 0 configuration.

This paper proposes an adaptive list-output Viterbi equalizer (LVE) with fast compare-select operation, in order to achieve a good trade-off between bit error rate (BER) performance and processing speed. An LVE, which keeps several survivors for each state, has good BER performance in the presence of wide-spread intersymbol interference. However, the LVE suffers from large processing delay due to its sorting-based compare-select operation. The proposed adaptive LVE greatly reduces its processing delay, because it simplifies compare-select operation. In addition, computer simulation shows that the proposed LVE causes only slight BER performance degradation due to its simplification of compare-select operation. Thus, the proposed LVE achieves better BER performance than decision-feedback sequence estimation (DFSE) without an increase in processing delay.

This paper describes a digital delay-lock Loop (DLL) to which delta-sigma (Δ Σ) modulation technique is applied in order to reduce circuit elements. The DLL is evaluated in both transient and steady-state behavior by theoretical analysis, computer simulations and circuit experiments. Not deteriorated by the internally generated Δ Σ-modulation noise, the DLL shows good tracking performance in transient response and steady-state RMS jitter of phase error against additive white Gaussian noise. Using the proposed DLL most parts of receiving circuits are realized by digital integrated circuits. After realizing the circuit, power-line communication system with spread spectrum is possibly expected in a small size with low cost.

In this paper, we describe an implementation of analog neural network system with on-line learning capability. A learning rule using the simultaneous perturbation is adopted. Compared with usage of the ordinary back-propagation method, we can easily implement the simultaneous perturbation learning rule. The neural system can monitor weight values and an error value. The exclusive OR problem and a simple function problem are shown.

This paper addresses an important issue on the spreading bandwidth of direct sequence code division multiple access (DS-CDMA) cellular mobile radio systems: does wider spreading bandwidth provide larger capacity? And if so, to what extent? The capacity of the perfect power controlled reverse link is evaluated by computer simulation for 1.25 MHz and 5 MHz spreading bandwidths under various sets of propagation channel parameters (path loss decay factor, shadowing standard deviation, shadowing correlation, number of resolved propagation paths) and antenna diversity reception.

This paper proposes a new polling-based dynamic slot assignment (DSA) scheme. With the rapid progress of wireless access systems, wireless data communication will become more and more attractive. In wireless data communication, an efficient DSA scheme is required to enhance system throughput, since the capacity of radio links is often smaller than that of wired links. A polling-based DSA scheme is typically used in centralized slot assignment control systems. It, however, is difficult to assign the slots to the targeted mobile terminals in a fair-share manner if only a polling-based scheme is used, especially in unbalanced-traffic circumstances, as revealed later. To solve this problem, we propose the exponential decreasing and proportional increasing rate control as is employed in available bit rate (ABR) service in ATM so that fair slot assignment is achieved even in heavily-unbalanced-traffic circumstances. Moreover, so that an AP operating with a large number of MTs can avoid long transmission delays, a polling-based resource request scheme with random access is featured in a new algorithm. Simulations verify that the proposed scheme offers fair slot assignment for each user while maintaining high throughput and short delay performance.

This paper use a site-specific model to characterize the performance of millimeter wave BPSK system with single cochannel interference. Shooting and bouncing ray/image techniques are applied to compute the impulse responses for concrete-wall-partition rooms and plasterboard-wall-partition rooms. By using the impulse responses of these multipath channels, the BERs (Bit Error Rates) for high-speed BPSK (binary phase shift keying) systems with phase and timing recovery circuits are calculated. In addition, the carrier-to-interference ratio is also computed. Numerical results show that the interference for the plasterboard-wall-partition rooms is more severe than that for the concrete-wall-partition rooms.

In this paper, a token-controlled network with exhaustive service strategy is analyzed. The mean and variance of service time of a station, and the mean token rotation time on the network are derived under the condition that the buffer capacity of each station is individually finite. For analysis, an extended stochastic Petri-net model of a station is presented. Then, by analyzing the model, the mean service time of a station and the mean token rotation time are derived, as functions of the given network parameters such as the total number of stations on the network, the arrival rate of frames, the transmission rate of frames, and the buffer capacity. The variance of service time of a station is also derived. By examining derived results, it is shown that they exactly describe the actual operations of the network. In addition, computer simulations with sufficient confidence intervals help to validate the results.

This paper focuses on flow control in high-speed and large-scale networks. Each node in the network handles its local traffic flow only on the basis of the information it knows. It is preferable, however, that the decision making of each node leads to high performance of the whole network. To this end, the relationship between local decision making and global performance of flow control is the essential object. We propose phenomenological models of flow control of high-speed and large-scale networks, and investigate the stability of these models.

Hallen's integral equation for cylindrical antennas is modified to deal with finite gap excitation. Because it is based on more realistic modeling, the solution is more accurate, and the convergence is guaranteed. The new equation is written with a new excitation function dependent on the gap width. The moment method analysis is presented where the piecewise sinusoidal surface current functions are used in Galerkin's procedure. Total, external and internal current distributions can be determined. Numerical results for cylindrical antennas with wide variety of gap width and radius are shown, and are compared with the numerical results by the Pocklington type integral equation and those by measurement.

A shared buffer ATM switch loaded with bursty input traffic is modeled by a discrete-time queueing system. Also, the unbalanced and correlated routing traffic patterns are considered. An approximation method to analyze the queueing system under consideration is developed. To overcome the problem regarding the size of state space to be dealt with, the entire switching system is decomposed into several subsystems, and then each subsystem is analyzed in isolation. We first propose an efficient algorithm for superposing all the individual bursty cell arrival processes to the switch. And then, the maximum entropy method is applied to obtain the steady-state probability distribution of the queueing system. From the obtained steady-state probabilities, we can derive some performance measures such as cell loss probability and average delay. Numerical examples of the proposed approximation method are given, which are compared with simulation results.

In future multimedia mobile communication systems, heterogeneous users will require very different and time-varying transmission rates. Thus, they should be supported with a novel approach that can accommodate the fluctuating data rates in wireless channels. In this paper, a simple method that is used to admit the rates successfully is proposed. The method is also distributed in a sense that it can be implemented at each mobile without any interaction with other mobiles. The method consists of power control with a higher SIR (signal to interference ratio) target and periodic adjustment of the data rate. We prove a good rate admission property of the proposed method and verify its performance with numerical investigation.