A multi-path structure is proposed for reduction in effect of digital substrate noise which degrades analog circuit performance. As an example low-pass filters are implemented in a 0.18-µm CMOS process. 11-dBm reduction in digital substrate noise is achieved as compared with a conventional structure.

Sampling clock jitter degrades the dynamic range of an analog-to-digital converter (ADC). In this letter, a low-power low-noise clock signal generator for ADCs is described. As a clock signal generator, a ring-VCO-based charge pump PLL is used to reduce power dissipation within a given jitter specification. The clock signal generator is fabricated on a CMOS chip with 200-MSPS 10-bit ADC. The measured results show that the ADC keeps a 60-MHz input bandwidth and 53-dB dynamic range and a next-generation mobile wireless terminal can be realized with the ADCs and the on-chip low-power clock generator.

In this review paper we showcase recent activities on silicon photonics science and technology research in Hong Kong regarding two important topical areas--microresonator devices and optical nonlinearities. Our work on silicon microresonator filters, switches and modulators have shown promise for the nascent development of on-chip optoelectronic signal processing systems, while our studies on optical nonlinearities have contributed to basic understanding of silicon-based optically-pumped light sources and helium-implanted detectors. Here, we review our various passive and electro-optic active microresonator devices including (i) cascaded microring resonator cross-connect filters, (ii) NRZ-to-PRZ data format converters using a microring resonator notch filter, (iii) GHz-speed carrier-injection-based microring resonator modulators and 0.5-GHz-speed carrier-injection-based microdisk resonator modulators, and (iv) electrically reconfigurable microring resonator add-drop filters and electro-optic logic switches using interferometric resonance control. On the nonlinear waveguide front, we review the main nonlinear optical effects in silicon, and show that even at fairly modest average powers two-photon absorption and the accompanied free-carrier linear absorption could lead to optical limiting and a dramatic reduction in the effective lengths of nonlinear devices.

In this letter, a computational approach for solving cross-coupled algebraic Riccati equations (CAREs) is investigated. The main purpose of this letter is to propose a new algorithm that combines Newton's method with a gradient-based iterative (GI) algorithm for solving CAREs. In particular, it is noteworthy that both a quadratic convergence under an appropriate initial condition and reduction in dimensions for matrix computation are both achieved. A numerical example is provided to demonstrate the efficiency of this proposed algorithm.

This paper addresses the problem of maximizing the protocol capacity of 802.11e networks, under the assumption that each access category (AC) has the same packet length. We prove that the maximal protocol capacity can be achieved at an optimal operating point with the medium idle probability of , where Tc* is the duration of collision time in terms of slot unit. Our results indicate that the optimal operating point is independent of the number of stations and throughput ratio among ACs, which means the proposed analytical results still hold even when throughput ratio and station number are time-varying. Further, we show that the maximal protocol capacity can be achieved in saturated cases by properly choosing the protocol parameters. We present a parameter configuration algorithm to achieve both efficient channel utilization and proportional fairness in IEEE 802.11e EDCA networks. Extensive simulation and analytical results are presented to verify the proposed ideas.

LSI on-chip optical interconnections are discussed from the viewpoint of a comparison between optical and electrical interconnections. Based on a practical prediction of our optical device development, optical interconnects will have an advantage over electrical interconnects within a chip that has an interconnect length less than about 10 mm at the hp32-22 nm technology node. Fundamental optical devices and components used in interconnections have also been introduced that are small enough to be placed on top of a Si LSI and that can be fabricated using methods compatible with CMOS processes. A SiON waveguide showed a low propagation loss around 0.3 dB/cm at a wavelength of 850 nm, and excellent branching characteristics were achieved for MMI (multimode interference) branch structures. A Si nano-photodiode showed highly enhanced speed and efficiency with a surface plasmon antenna. By combining our Si nano-photonic devices with the advanced TIA-less optical clock distribution circuits, clock distribution above 10 GHz can be achieved with a small footprint on an LSI chip.

Burn-in is a widely used method to improve the quality of products or systems after they have been produced. In this paper, optimal burn-in procedures for a system with two types of failures (i.e., minor and catastrophic failures) are investigated. A new system surviving burn-in time b is put into field operation and the system is used under a warranty policy under which the manufacturer agrees to provide a replacement system for any system that fails to achieve a lifetime of at least w. Upper bounds for optimal burn-in time minimizing the total expected warranty cost are obtained under a more general assumption on the shape of the failure rate function which includes the bathtub shaped failure rate function as a special case.

The Earth will require sustainable electricity sources equivalent to 3 to 5 times the commercial power presently produced by 2050. Solar Power Satellite (SPS) is one option for meeting the huge future energy demand. SPS can send enormous amounts of power to the Earth as the form of microwave (MW). A highly efficient microwave power transmission (MPT) system is needed for SPS. A critical goal of SPS is to maintain highest Beam Efficiency (BE) because the microwaves from SPS will be converted to utility power unlike the MW from communication satellites. Another critical goal of SPS is to maintain Side Lobe Levels (SLL) as small as possible to reduce interference to other communication systems. One way to decrease SLL and increase BE is the edge tapering of a phased array antenna. However, tapering the excitation requires a technically complicated system. Another way of achieving minimum SLL is with randomly spaced element position but it does not guarantee higher BE and the determination of random element position is also a difficult task. Isosceles Trapezoidal Distribution (ITD) edge tapered antenna was studied for SPS as an optimization between full edge tapering and uniform amplitude distribution. The highest Beam Collection Efficiency (BCE) and lowest SLL (except maximum SLL) are possible to achieve in ITD edge tapering and ITD edge tapered antenna is technically better. The performance of ITD is further improved from the perspective of both Maximum Side Lobe Level (MSLL) and BE by using unequal spacing of the antenna elements. A remarkable reduction in MSLL is achieved with ITD edge tapering with Unequal element spacing (ITDU). BE was also highest in ITDU. Determination of unequal element position for ITDU is very easy. ITDU is a newer concept that is experimented for the first time. The merits of ITDU over ITD and Gaussian edge tapering are discussed.

This paper proposes several cepstral statistics compensation and normalization algorithms which alleviate the effect of additive noise on cepstral features for speech recognition. The algorithms are simple yet efficient noise reduction techniques that use online-constructed pseudo-stereo codebooks to evaluate the statistics in both clean and noisy environments. The process yields transformations for both clean speech cepstra and noise-corrupted speech cepstra, or for noise-corrupted speech cepstra only, so that the statistics of the transformed speech cepstra are similar for both environments. Experimental results show that these codebook-based algorithms can provide significant performance gains compared to results obtained by using conventional utterance-based normalization approaches. The proposed codebook-based cesptral mean and variance normalization (C-CMVN), linear least squares (LLS) and quadratic least squares (QLS) outperform utterance-based CMVN (U-CMVN) by 26.03%, 22.72% and 27.48%, respectively, in relative word error rate reduction for experiments conducted on Test Set A of the Aurora-2 digit database.

Mesh networking technologies for both high-rate and low-rate wireless personal area networks (WPANs) are under development by several standardization bodies. They are considering to adopt distributed TDMA MAC protocols to provide seamless user mobility as well as a good peer-to-peer QoS in WPAN mesh. It has been, however, pointed out that the absence of a central controller in the wireless TDMA MAC may cause a severe performance degradation: e.g., fair allocation, service differentiation, and admission control may be hard to achieve or can not be provided. In this paper, we suggest a new framework of resource allocation for the distributed MAC protocols in WPANs. Simulation results show that our algorithm achieves both a fair resource allocation and flexible service differentiations in a fully distributed way for mesh WPANs where the devices have high mobility and various requirements. We also provide an analytical modeling to discuss about its unique equilibrium and to compute the lengths of reserved time slots at the stable point.

In mass disasters such as earthquakes, fire disasters, tsunami, and terrorism, dental records have been used for identifying victims due to their processing time and accuracy. The greater the number of victims, the more time the identification tasks require, since a manual comparison between the dental radiograph records is done by forensic experts. Addressing this problem, this paper presents an efficient dental radiograph recognition system using Phase-Only Correlation (POC) for human identification. The use of phase components in 2D (two-dimensional) discrete Fourier transforms of dental radiograph images makes possible to achieve highly robust image registration and recognition. Experimental evaluation using a set of dental radiographs indicates that the proposed system exhibits efficient recognition performance for low-quality images.

This paper deals with the scattering of a TM plane wave from a periodic grating with single defect, of which position is known. The surface is perfectly conductive and made up with a periodic array of rectangular grooves and a defect where a groove is not formed. The scattered wave above grooves is written as a variation from the diffracted wave for the perfectly periodic case. Then, an integral equation for the scattering amplitude is obtained, which is solved numerically by use of truncation and the iteration method. The differential scattering cross section and the optical theorem are calculated in terms of the scattering amplitude and are illustrated in figures. It is found that incoherent Wood's anomaly appears at critical angles of scattering. The physical mechanisms of Wood's anomaly and incoherent Wood's anomaly are discussed in relation to the guided surface wave excited by the incident plane wave. It is concluded that incoherent Wood's anomaly is caused by the diffraction of the guided surface wave.

HMAC is one of the most famous keyed hash functions, and widely utilized. In order to design secure hash functions, we often use PGV construction consisting of 64 schemes, each of which utilizes a block cipher. If the underlying block cipher is ideal, 12 schemes are proven to be secure. In this paper, we evaluate the security of these schemes in view of side channel attacks. As it turns out, HMACs based on 11 out of 12 secure PGV schemes are vulnerable to side channel attacks, even if the underlying block cipher is secure against side channel attacks. These schemes are classified into two groups based on their vulnerabilities. For the first group which contains 8 schemes, we show that the attacker can reveal the whole key of HMAC, and selectively forge in consequence. For the other group which contains 3 schemes, we specify the importance of the execution sequence for the inner operations of the scheme, and refine it. If wrong orders of operations are used, the attacker can reveal a portion of the key of HMAC. Hence, the use of HMACs based on such PGV schemes as they are is not recommended when the resistance against side channel attacks is necessary.

In this letter, we propose an efficient resource allocation scheme that improves the system performance by reducing the signaling overhead for voice over Internet protocol (VoIP) services in the IEEE 802.16e OFDMA system. We theoretically analyze the performance of the proposed allocation scheme and carry out a computer simulation to evaluate the FA scheme.

We focus on the relationship between the linearization method and linear complexity and show that the linearization method is another effective technique for calculating linear complexity. We analyze its effectiveness by comparing with the logic circuit method. We compare the relevant conditions and necessary computational cost with those of the Berlekamp-Massey algorithm and the Games-Chan algorithm. The significant property of a linearization method is that it needs no output sequence from a pseudo-random number generator (PRNG) because it calculates linear complexity using the algebraic expression of its algorithm. When a PRNG has n [bit] stages (registers or internal states), the necessary computational cost is smaller than O(2n). On the other hand, the Berlekamp-Massey algorithm needs O(N2) where N ( 2n) denotes period. Since existing methods calculate using the output sequence, an initial value of PRNG influences a resultant value of linear complexity. Therefore, a linear complexity is generally given as an estimate value. On the other hand, a linearization method calculates from an algorithm of PRNG, it can determine the lower bound of linear complexity.

In a key scheduling algorithm (KSA) of stream ciphers, a secret key is expanded into a large initial state. An internal state reconstruction method is known as a general attack against stream ciphers; it recovers the initial state from a given pair of plaintext and ciphertext more efficiently than exhaustive key search. If the method succeeds, then it is desirable that the inverse of KSA is infeasible in order to avoid the leakage of the secret key information. This paper shows that it is easy to compute a secret key from an initial state of RC4. We propose a method to recover an -bit secret key from only the first bits of the initial state of RC4 using linear equations with the time complexity less than that of one execution of KSA. It can recover the secret keys of which number is 2103.6 when the size of the secret key is 128 bits. That is, the 128-bit secret key can be recovered with a high probability when the first 128 bits of the initial state are determined using the internal state reconstruction method.

Recently Tate pairing and its variations are attracted in cryptography. Their operations consist of a main iteration loop and a final exponentiation. The final exponentiation is necessary for generating a unique value of the bilinear pairing in the extension fields. The speed of the main loop has become fast by the recent improvements, e.g., the Duursma-Lee algorithm and ηT pairing. In this paper we discuss how to enhance the speed of the final exponentiation of the ηT pairing in the extension field F36n. Indeed, we propose some efficient algorithms using the torus T2(F33n) that can efficiently compute an inversion and a powering by 3n + 1. Consequently, the total processing cost of computing the ηT pairing can be reduced by 16% for n=97.

In this paper, we propose a leakage-resilient and proactive authenticated key exchange (called LRP-AKE) protocol for credential services which provides not only a higher level of security against leakage of stored secrets but also secrecy of private key with respect to the involving server. And we show that the LRP-AKE protocol is provably secure in the random oracle model with the reduction to the computational Diffie-Hellman problem. In addition, we discuss about some possible applications of the LRP-AKE protocol.

We have derived the novel extended UTD (Uniform Geometrical Theory of Diffraction) solution and the novel modified UTD solution for the back scattering of an incident whispering gallery (WG) mode on the edge of a cylindrically curved conducting sheet. By comparing with the reference solution obtained from the integral representation of the scattered field by integrating numerically along the integration path, we have confirmed the validity and the utility of the novel asymptotic solutions proposed in the present study. It is shown that the extended UTD solution can be connected smoothly to the modified UTD solution on the geometrical boundary separating the edge-diffracted ray and the surface-diffracted ray.

A digital signature does not allow any alteration of the document to which it is attached. Appropriate alteration of some signed documents, however, should be allowed because there are security requirements other than the integrity of the document. In the disclosure of official information, for example, sensitive information such as personal information or national secrets is masked when an official document is sanitized so that its nonsensitive information can be disclosed when it is requested by a citizen. If this disclosure is done digitally by using the current digital signature schemes, the citizen cannot verify the disclosed information because it has been altered to prevent the leakage of sensitive information. The confidentiality of official information is thus incompatible with the integrity of that information, and this is called the digital document sanitizing problem. Conventional solutions such as content extraction signatures and digitally signed document sanitizing schemes with disclosure condition control can either let the sanitizer assign disclosure conditions or hide the number of sanitized portions. The digitally signed document sanitizing scheme we propose here is based on the aggregate signature derived from bilinear maps and can do both. Moreover, the proposed scheme can sanitize a signed document invisibly, that is, no one can distinguish whether the signed document has been sanitized or not.