The Energy-aware Multi-mode Accelerator eXtension [24],[25] (EMAX) is equipped with distributed single-port local memories and ring-formed interconnections. The accelerator is designed to achieve extremely high throughput for scientific computations, big data, and image processing as well as low-power consumption. However, before mapping algorithms on the accelerator, application developers require sufficient knowledge of the hardware organization and specially designed instructions. They also need significant effort to tune the code for improving execution efficiency when no well-designed compiler or library is available. To address this problem, we focus on library support for stencil (nearest-neighbor) computations that represent a class of algorithms commonly used in many partial differential equation (PDE) solvers. In this research, we address the following topics: (1) system configuration, features, and mnemonics of EMAX; (2) instruction mapping techniques that reduce the amount of data to be read from the main memory; (3) performance evaluation of the library for PDE solvers. With the features of a library that can reuse the local data across the outer loop iterations and map many instructions by unrolling the outer loops, the amount of data to be read from the main memory is significantly reduced to a minimum of 1/7 compared with a hand-tuned code. In addition, the stencil library reduced the execution time 23% more than a general-purpose processor.

We propose the concept of an integrated coherent photonic wireless transmitter based on the simultaneous injection locking of two monolithically integrated distributed feedback (DFB) laser diodes (LDs) using an optical frequency comb (OFC). We characterize the basic operation of the transmitter and demonstrate that two injection-locked integrated DFB LDs are sufficiently stable to generate the carrier signal using a uni-traveling-carrier photodiode (UTC-PD) for a real-time error-free (bit error rate: BER < 10-11) coherent transmission with a data rate of 10 Gbit/s at a carrier frequency of 97 GHz. In the coherent wireless transmission, we compare the BER characteristics of the injection-locked transmitter with that of an actively phase-stabilized transmitter and show that the power penalty of 8-dB for the injection-locked transmitter is due to the RF spurious components, which can be reduced by integrating the OFC generator (OFCG) and LDs on the same chip. Our results suggest that the integration of the OFCG, DFB LDs, modulators, semiconductor optical amplifiers, and UTC-PD on the same chip is a promising strategy to develop a practical real-time ultrafast coherent millimeter/terahertz wave wireless transmitter.

This paper proposes a novel direction-of-arrival (DOA) estimation method that can reduce performance degradation due to angular spread. Some algorithms previously proposed for such estimation make assumptions about the distributions of amplitude and phase for incident waves because most DOA estimation algorithms are sensitive to angular spread. However, when the assumptions are inaccurate, these algorithms perform poorly as compared with algorithms without countermeasures against angular spread. In this paper, we propose a method for selecting an appropriate DOA estimation algorithm according to the channel vector of each source signal as estimated by independent component analysis. Computer simulations show that the proposed method can robustly estimate DOA in environments with angular spread.

This paper reviews a recent progress in terahertz wireless communications enabled by photonics technologies. After briefly summarizing transceiver configurations with electronics and photonics technologies, photonics-based approaches to achieving over 100-Gbit/s data rates are discussed. Then, some of our updated results on real-time wireless transmission experiments using discrete components are shown at data rates up to 50 Gbit/s. Finally, integration technologies are described by demonstrating latest advances in integrated optical sources and transmitters.

To design high quality three-dimensional integrated circuits (3-D ICs), the effect of process and design parameters on delay must be adequately understood. This paper presents an electrical circuit model of an entire structure in through silicon via (TSV) based 3-D ICs with a new equation for on-chip interconnect capacitance and then proposes an effective model for evaluating signal propagation delay in vertically stacked chips. All electrical parameter values can be calculated by the closed-form equations without a field solver. The delay model is constructed with the first- or second-order function of each parameter to the delay obtained from a typical structure. The results obtained by on-chip interconnect capacitance equations and delay model are in excellent agreement with those by a field solver and circuit simulator, respectively. We also show that the model is very useful for evaluating effects of the process and design parameters on vertical signal propagation delay such as the sensitivity and variability analysis.

In 1973, Arimoto proved the strong converse theorem for the discrete memoryless channels stating that when transmission rate R is above channel capacity C, the error probability of decoding goes to one as the block length n of code word tends to infinity. He proved the theorem by deriving the exponent function of error probability of correct decoding that is positive if and only if R>C. Subsequently, in 1979, Dueck and Körner determined the optimal exponent of correct decoding. Arimoto's bound has been said to be equal to the bound of Dueck and Körner. However its rigorous proof has not been presented so far. In this paper we give a rigorous proof of the equivalence of Arimoto's bound to that of Dueck and Körner.

This report describes an all-digital phase-locked loop (ADPLL) using a temperature compensated settling time reduction technique. The novelty of this work is autonomous oscillation control word estimation without a look-up table or memory circuits. The proposed ADPLL employs a multi-phase digitally controlled oscillator (DCO). In the proposed estimation method, the optimum oscillator tuning word (OTW) is estimated from the DCO frequency characteristic in the setup phase of ADPLL. The proposed ADPLL, which occupies 0.27×0.36mm2, is fabricated by a 65 nm CMOS process. The temperature compensation PLL controller (TCPC) is implemented using an FPGA. Although the proposed method has 20% area overhead, measurement results show that the 47% settling time is reduced. The average settling time at 25°C is 3µs. The average reduction energy is at least 42% from 0°C to 100°C.

Up to now, broadband THz time-domain system has been developed and widely used for THz inspection system; however for many THz devices for THz band wireless communication, narrow-band system would be preferred rather than typical broadband system. In this work we established a narrowband and time-domain THz radiation and detection system and characterized uncooled microbolometer-based THz imagers using that system. The central frequency of generated narrowband THz wave was 850 GHz. This system enables simultaneous measurement of pulse energy and waveform of THz pulse using a superconducting transition edge sensor for measuring energy and electro-optic sampling for measuring THz waveform. We used this system to evaluate the performance of uncooled THz imagers; IRV-T0831 and T0832 from NEC. Noise equivalent power (NEP) of approximately 0.22 pW/Hz1/2 was achieved in case of T0832 at less than 1 THz which is lower than NEP value of previous reports.

An earthquake is a destructive natural disaster, which cannot be predicted accurately and causes devastating damage and losses. In fact, many of the damages can be prevented if people know what to do during and after earthquakes. Earthquake education is the most important method to raise public awareness and mitigate the damage caused by earthquakes. Generally, earthquake education consists of conducting traditional earthquake drills in schools or communities and experiencing an earthquake through the use of an earthquake simulator. However, these approaches are unrealistic or expensive to apply, especially in underdeveloped areas where earthquakes occur frequently. In this paper, an earthquake drill simulation system based on virtual reality (VR) technology is proposed. A User is immersed in a 3D virtual earthquake environment through a head mounted display and is able to control the avatar in a virtual scene via Kinect to respond to the simulated earthquake environment generated by SIGVerse, a simulation platform. It is a cost effective solution and is easy to deploy. The design and implementation of this VR system is proposed and a dormitory earthquake simulation is conducted. Results show that powerful earthquakes can be simulated successfully and the VR technology can be applied in the earthquake drills.

An incremental relaying protocol is a promising scheme for preventing the inefficient use of resources in half-duplex cooperative relay networks. In particular, the incremental selection amplify-and-forward (ISAF) relaying scheme is a well-designed protocol under the condition that the source-to-destination (SD) link is static during the two transmission phases. However, from a practical viewpoint, the SD link is not static but varies with time, and thus the ISAF relaying scheme may not work well in the field. In this work, we first show that the outage performance of the ISAF relaying scheme may decrease when the SD link is not static during the two transmission phases. We then propose a modified version of the ISAF relaying scheme which overcomes such a limitation of the ISAF relaying scheme under time-varying environments. Finally, numerical and simulation results are provided to support our findings.

The primitive called public key encryption with non-interactive opening (PKENO) is a class of public key encryption (PKE) with additional functionality. By using this, a receiver of a ciphertext can prove that the ciphertext is an encryption of a specified message in a publicly verifiable manner. In some situation that a receiver needs to claim that a ciphertext is NOT decrypted to a specified message, if he/she proves the fact by using PKENO straightforwardly, the real message of the ciphertext is revealed and a verifier checks that it is different from the specified message about which the receiver wants to prove. However, this naive solution is problematic in terms of privacy. Inspired by this problem, we propose the notion of disavowable public key encryption with non-interactive opening (disavowable PKENO) where, with respect to a ciphertext and a message, the receiver of the ciphertext can issue a proof that the plaintext of the ciphertext is NOT the message. Also, we give a concrete construction. Specifically, a disavowal proof in our scheme consists of 61 group elements. The proposed disavowable PKENO scheme is provably secure in the standard model under the decisional linear assumption and strong unforgeability of the underlying one-time signature scheme.

This paper considers universal lossless variable-length source coding problem and investigates the Bayes code from viewpoints of the distribution of its codeword lengths. First, we show that the codeword lengths of the Bayes code satisfy the asymptotic normality. This study can be seen as the investigation on the asymptotic shape of the distribution of codeword lengths. Second, we show that the codeword lengths of the Bayes code satisfy the law of the iterated logarithm. This study can be seen as the investigation on the asymptotic end points of the distribution of codeword lengths. Moreover, the overflow probability, which represents the bottom of the distribution of codeword lengths, is studied for the Bayes code. We derive upper and lower bounds of the infimum of a threshold on the overflow probability under the condition that the overflow probability does not exceed ε∈(0,1). We also analyze the necessary and sufficient condition on a threshold for the overflow probability of the Bayes code to approach zero asymptotically.

A terahertz-wave communication system directly connected to an optical fiber network is promising for application to future mobile backhaul and fronthaul links. The possible broad bandwidth in the terahertz band is useful for high-speed signal transmission as well as radio-space encapsulation to the high-frequency carrier. In both cases, the low-latency feature becomes important to enhance the throughput in mobile communication and is realized by waveform transport technology without any digital-signal-processing-based media conversion. A highly precise optical frequency comb signal generated by optical modulation and the vector signal demodulation technology adopted from advanced optical fiber communication technologies help perform modulation and demodulation with impairment compensation at just the edges of the link. Terahertz wave, radio over fiber, waveform transport, coherent detection, multilevel modulation, radio on radio.

The multiterminal hypothesis testing problem with zero-rate constraint is considered. For this problem, an upper bound on the optimal error exponent is given by Shalaby and Papamarcou, provided that the positivity condition holds. Our contribution is to prove that Shalaby and Papamarcou's upper bound is valid under a weaker condition: (i) two remote observations have a common random variable in the sense of Gácks and Körner, and (ii) when the value of the common random variable is fixed, the conditional distribution of remaining random variables satisfies the positivity condition. Moreover, a generalization of the main result is also given.

In the study of the capacity problem for multiple access channels (MACs), a lower bound on the error probability obtained by Han plays a crucial role in the converse parts of several kinds of channel coding theorems in the information-spectrum framework. Recently, Yagi and Oohama showed a tighter bound than the Han bound by means of Polyanskiy's converse. In this paper, we give a new bound which generalizes and strengthens the Yagi-Oohama bound, and demonstrate that the bound plays a fundamental role in deriving extensions of several known bounds. In particular, the Yagi-Oohama bound is generalized to two different directions; i.e, to general input distributions and to general encoders. In addition we extend these bounds to the quantum MACs and apply them to the converse problems for several information-spectrum settings.

Determining an effective way to reduce computation complexity is an essential task for adaptive echo cancellation applications. Recently, a family of partial update (PU) adaptive algorithms has been proposed to effectively reduce computational complexity. However, because a PU algorithm updates only a portion of the weights of the adaptive filters, the rate of convergence is reduced. To address this issue, this paper proposes an enhanced switching-based variable step-size (ES-VSS) approach to the M-max PU least mean square (LMS) algorithm. The step-size is determined by the correlation between the error signals and their noise-free versions. Noise-free error signals are approximated according to the level of convergence achieved during the adaptation process. The approximation of the noise-free error signals switches among four modes, such that the resulting step-size is as close to its optimal value as possible. Simulation results show that when only a half of all taps are updated in a single iteration, the proposed method significantly enhances the convergence rate of the M-max PU LMS algorithm.

DTNs (Delay/Disruption-Tolerant Networks) composed of mobile nodes in low node-density environments have attracted considerable attention in recent years. In this paper, we propose a CD-BCAST (Contact Duration BroadCAST) mechanism that can reduce the number of message forwardings while maintaining short message delivery delays in DTNs composed of mobile nodes. The key idea behind CD-BCAST is to increase the probability of simultaneous forwarding by intentionally delaying message forwarding based on the contact duration distribution measured by each node. Through simulations, we show that CD-BCAST needs substantially less message forwardings than conventional mechanisms and it does not require parameter tuning under varieties of communication ranges and node densities.