Multiple-input multiple-output (MIMO) systems can improve the spectral efficiency of a wireless link, by transmitting several data streams simultaneously from different transmit antennas. However, at the receiver, multi-stream detection is needed for extracting the transmitted data streams from the received signals. This letter considers ordered successive detection (OSD) for multi-stream detection. OSD consists of several stages, and at each stage only one data stream is chosen to be detected among the remaining streams according to a specified ordering metric. OSD has been formulated using both the zero forcing (ZF) and minimum mean square error (MMSE) criteria. This letter clarifies the reason behind the superiority of OSD using the MMSE criterion to OSD using the ZF criterion through the investigation of the relation between their ordering metrics. For uncorrelated MIMO channels, we show that both ordering metrics yield the same performance for OSD using either ZF or MMSE criterion. Accordingly, the superiority of OSD using the MMSE criterion to OSD using the ZF criterion is clarified to be a direct result of the inherent superiority of MMSE nulling to ZF nulling, and to be independent of the ordering operation. Performance comparisons of OSD and maximum likelihood detection are also given for modulation schemes of different sizes.

An adaptive filtering algorithm based on the sliding window criterion is known to be very attractive for violent changing environments. In this paper, a new sliding window linearly constrained recursive least squares (SW-LC-RLS) algorithm based on the modified minimum mean squared error (MMSE) structure is devised for the RAKE receiver in direct sequence spread spectrum code-division multiple access (DS-SS CDMA) system over multipath fading channels, where the channel estimation scheme is accomplished at the output of adaptive filter. The proposed SW-LC-RLS algorithm has the advantage of having faster convergence property and tracking ability, and can be applied to the environments, where the narrowband interference is joined suddenly to the system, to achieve desired performance. Via computer simulation, we show that the performance, in terms of mean square errors (MSE), signal to interference plus noise ratio (SINR) and bit error rate (BER), is superior to the conventional LC-RLS and orthogonal decomposition-based LMS algorithms based on the MMSE structure.

Optimistic log-based rollback recovery protocols have been regarded as an attractive fault-tolerant solution in distributed systems based on message-passing paradigm due to low overhead in failure-free time. These protocols are based on a Piecewise Deterministic (PWD) Assumption model. They, however, assumed that all logged non-deterministic events in a consistent global recovery line must be determinately replayed in recovery time. In this paper, we give the impossibility of deterministic replaying of logged non-deterministic event in a consistent global recovery line as a Ω Line Problem, because of asynchronous properties of distributed systems: no bound on the relative speeds of processes, no bound on message transmission delays and no global time source. In addition, we propose a new optimistic log-based rollback recovery protocol, which guarantees the deterministic replaying of all logged non-deterministic events belonged in a consistent global recovery line and solves a Ω Line Problem in recovery time.

In provisioning packet data service on wireless cellular networks, a scheme of altering connection status between mobile and base stations appeared intending to efficiently utilize resource during idle periods. In such a scheme, connection components are sequentially released as an idle period persists, while the transmitting station converts to an transmission activity mode as the station is loaded with packets. However, actual resume of transmission activity is postponed by connection retrieval time to restore lost connection components. In general, an idle period affects the following connection retrieval time, which in turn produces an impact on the forthcoming idle period. Such chain reaction also makes a significant influence on overall packet delay performance. In this paper, as a way of improving packet delay performance, we propose two schemes identified as conservative extension and load threshold schemes. In the conservative extension scheme, we intentionally extend connection retrieval times so that each connection retrieval time is guaranteed not to be lower than a certain value. On the other hand, according to the load threshold scheme, a retrieval of lost connection components is postponed until packets are accumulated at the transmitting station up to a prescribed threshold. An increase in the value and threshold incurs an additional stand-by before resuming transmission activity in both proposed schemes. In turn, such intentional stand-by may contribute to regulating the length of idle period and connection retrieval time, and subsequently improving packet delay performance. To inspect the impact of conservative extension and load threshold schemes on packet delay performance, we first investigate the properties of idle periods. Secondly, for Poisson packet arrivals, we present an analytical method to exactly calculate the moments of packet delay time (at steady state) in each scheme. From numerical examples, we confirm the existence of non-trivial optimal value and threshold minimizing average packet delay or packet delay variation and conclude that conservative extension and load threshold schemes are able to enhance packet delay performance in various environments.

There has recently been considerable interest in research on wearable non-grounded force display. However, there have been no developments for the communication of nonverbal information (ex. tennis and golf swing). We propose a small and lightweight wearable force display to present motion timing and direction. The display outputs a torque using rotational moment and mechanical brakes. We explain the principle of this device, and describe an actual measurement of the torque and torque sensitivity experiments.

The accuracy of channel estimation significantly affects the performance of coherent rake receiver in DS-CDMA systems. It is desirable for improved channel estimation to employ a channel estimation filter (CEF) whose bandwidth is adjustable to the channel condition. In this paper, we consider the use of moving average (MA) FIR filters as the CEF since it is simple to implement and can provide relatively good receiver performance. First, we optimize the tap size of the MA FIR CEF so as to minimize the mean squared error of the estimated channel impulse response. For practical applications, we propose a low-complexity adaptive channel estimator (ACE), where the tap size of the MA FIR CEF is adjusted based on the estimated channel condition by exploiting the correlation characteristics of the received pilot signal. Numerical results show that the use of the proposed ACE can provide the receiver performance comparable to that of Wiener CEF without exact a priori information on the operating condition.

This paper presents the improvement of the transient response and stability for a two-stage DC-DC converter by removing the output inductor. The conventional two-stage converter consists of a buck converter used as the first stage and a half-bridge converter used as the second stage. The proposed circuit topology removing the output inductor and the conventional topology are compared. Removing the output inductor results in the system-order reduction of the transfer function. As a result, the stability is improved, and the crossover frequency of the open-loop transfer function becomes higher. The effectiveness of the proposed circuit topology was experimentally confirmed.

In this paper, we propose an advanced structure of the interface circuit, called a wrapper, for Globally Asynchronous Locally Synchronous (GALS) systems. The proposed wrapper is composed of a sender module and a receiver module. The sender module carries out data transfers in an efficient way by decoupling dependency between an external handshake protocol and an internal clock. The decoupling effect allows the external handshake protocol and the internal clock to be executed in a concurrent way and hence allows the wrapper to show better performance. We have designed our wrapper at the transistor level with 0.35-µm technology. When we compare our decoupled wrapper with two conventional wrappers based on pausible clocking scheme, our simulation results show that performance improvement is about 8-13% and 13-56%, respectively.

Recent growth in computer communications has led to an increased requirement for high-speed backbone networks. In such high-speed networks, the principle adopted for a time-sensitive flow control mechanism should be that of autonomous decentralized control. In this mechanism, each node in a network manages its local traffic flow only on the basis of the local information directly available to it, although it is desirable that the individual decisions made at each node lead to high performance of the network as a whole. In our previous studies, we have investigated the behavior of local packet flows and the global performance achieved when a node is congested, and proposed the diffusion-type flow control model. However, since we used a simple and homogeneous network model in the evaluation, the results cannot be generalized. In this paper, we propose an extension of the diffusion-type flow control model in order to apply it to networks with inhomogeneous configurations. We show simulation results for two cases: different propagation delays and multiple bottlenecks. Both results show that the proposed diffusion-type flow control achieves high and stable performance even if the network is congested.

An upgrade scheme using identical sending lights and local lights for optical amplifier systems based on homodyne detection is described. Optimum receiving loss for maximizing the SNR is analytically derived for the proposed configuration where the local taped lights are low level to avoid a sending power decrease. Derived formulas describing the optimum loss condition and the maximum SNR show that 10 Gbit/s systems can be cost effectively upgraded to 40 Gbit/s systems with the same repeater spacing.

We numerically and experimentally investigated the upgradability of the longest and the typical segments of the JIH system. Through these studies, we confirmed that a 100 GHz-spaced 25 42.7 Gbit/s transmission with the total capacity of 1 Tbit/s can be attainable even by using NRZ signal and standard FEC for the typical segments. We also found that RZ signal format was desirable for the longest segment and a further wide system margin could be expected by using adjacent channel polarization control and advanced FEC technologies.

We analyze the Lagarias-Odlyzko low-density attack precisely, and show that this low-density attack can be applied to the Chor-Rivest and the Okamoto-Tanaka-Uchiyama cryptosystemes, which are considered to be secure against the low-density attack. According to our analysis, these schemes turn out to be no longer secure against the low-density attack.

Application area of mixed signal technology is currently expanded to digital communication, networking, and digital storage systems from conventional digital audio and video systems. Digital consumer electronics are emerged and their markets are extremely increased. Rapid progress of integrated circuit technology has enabled a system level integration on a SoC. Thus mixed signal SoC becomes a majority in LSI industry. Almost all the analog functions should be realized by CMOS technology on SoC, yet some difficulties such as a low transconductance, a large mismatch voltage, and a large 1/f noise should be solved. CMOS device has been considered as a poor device for the analog use, however in reality, it has attained a remarkable progress for analog applications. CMOS device has a variety of circuit techniques to address its own issues and also has an analog performance that increases rapidly with technology scaling. The mixed signal SoC needs a new development strategy and design methodology that covers from system level to device level for addressing tough needs for a shorter development time, a lower cost, and a higher design quality. The optimizations over analog and digital and over system to device must be established for the development success. Difficulty of low voltage operation of further scaled CMOS in analog circuits will be the most serious issue. This results in the saturation of performance and increase of cost. The system level optimization over analog and digital, digital calibration and compensation, and the use of sigma-delta modulation method will give us the solution.

In this paper we give the necessary and sufficient conditions for 2-dimensional discrete-time systems described by the signum function to be stable.

This letter discusses the performance of online SNR estimation including fading parameter estimation for parallel combinatorial SS (PC/SS) systems. The PC/SS systems are partial-code-parallel multicode SS systems, which have high-rate data transmission capability. Nakagami-m distribution is assumed as fading channel model to cover a wide range of fading conditions. The SNR and fading parameter estimation considered in this letter is based on only a statistical ratio of correlator outputs at the receiver. Numerical results show that SNR estimation performance with fading parameter estimation is close to the one in the case of perfect fading parameter information, if the number of transmitting PN codes is less than a half of assigned PN codes.

The unpredictable behavior of cache memory makes it difficult to statically analyze the worst-case performance of real-time systems. This problem is further exacerbated in the case of preemptive multitask systems because of inter-task cache interference, called Cache-Related Preemption Delay (CRPD). This paper proposes an approach to analyzing the tight upper bound on CRPD which a task might impose on lower-priority tasks. Our method finds the program execution path which requires the maximum number of cache blocks using an integer linear programming technique. Experimental results show that our approach provides up to 69% tighter bounds on CRPD than a conservative approach.

In this letter, adaptive modulation and coding (AMC) is combined with multiple input multiple output (MIMO) multiplexing to improve the throughput performance of AMC. In addition, a system that adopts selection transmit diversity (STD) in the AMC-MIMO multiplexing system, AMC-STD-MIMO multiplexing system, is proposed. STD in our simulation selects 2 transmission antennas from 4 antennas and AMC-MIMO multiplexing process operates with the selected antennas. The computer simulation is performed in a flat Rayleigh fading channel. The results show that the proposed AMC-STD-MIMO multiplexing system achieves the SNR gain of 4.0 dB, compared to the AMC-MIMO multiplexing system at 3 Mbps throughput.

Classical models of speech recognition assume that a detailed, short-term analysis of the acoustic signal is essential for accurately decoding the speech signal and that this decoding process is rooted in the phonetic segment. This paper presents an alternative view, one in which the time scales required to accurately describe and model spoken language are both shorter and longer than the phonetic segment, and are inherently wedded to the syllable. The syllable reflects a singular property of the acoustic signal -- the modulation spectrum -- which provides a principled, quantitative framework to describe the process by which the listener proceeds from sound to meaning. The ability to understand spoken language (i.e., intelligibility) vitally depends on the integrity of the modulation spectrum within the core range of the syllable (3-10 Hz) and reflects the variation in syllable emphasis associated with the concept of prosodic prominence ("accent"). A model of spoken language is described in which the prosodic properties of the speech signal are embedded in the temporal dynamics associated with the syllable, a unit serving as the organizational interface among the various tiers of linguistic representation.

This paper provides methods for construction of pairing-based cryptosystems based on non-supersingular elliptic curves.

Nagauta (長唄) is one of the classical styles of Japanese singing. It has very original and unique prosodic patterns, where abrupt and sharp changes of F0 are often observed at mora (Japanese speech unit) transitions. This F0 change is sometimes found even within a single mora. In this paper, we propose a model to synthesize this unique F0 pattern by considering the abrupt and sharp changes as grace notes. Nagauta's original scores contain no strict descriptions of tones and durations. Therefore, the baseline melody realized in a performance depends on the singer and it is difficult to predict the baseline melody by looking only at the scores. In this paper, the baseline melody is explicitly given to a singer in the form of the standard notation and the singer is asked to sing the song in Nagauta style. By taking the standard score as input, the proposed model simulates the F0 pattern generated by the singer under this condition. Further, this paper shows an interesting phenomenon about power movements at the sharp F0 changes. Acoustic analysis of Nagauta singing samples reveals that the sharp increases of F0 and the sharp decreases of power are synchronized. Although no discussion on physiological mechanisms of this phenomenon is done in this paper, another model is proposed to generate the unique power patterns. Evaluation experiments are done with young Japanese listeners and their results indicate high validity of the two proposed models.