Two design parameters, SNR and correlation, are key factors for enhancing channel capacity in MIMO systems. Achieving high SNR and low correlation is desirable in antenna design. This paper discusses the relation between channel capacity and these two parameters, and presents simple formulas of this relation for propagation channels and antenna coupling of mobile terminals. According to these guidelines, indoor base station antennas are designed and examined using propagation measurements. We also present a suitable antenna design for mobile terminal antennas and based on a realistic propagation model, predicted the channel capacity of the antenna.

The main benefit of HECC is that it has much smaller parameter sizes and offers equivalent security as ECC and RSA. However, there are still more researches on ECC than on HECC. One of the reasons is that the computation of scalar multiplication cannot catch up. The Kummer surface can speed up the scalar multiplication in genus two curves. In this paper, we find that the scalar multiplication formulas of Duquesne in characteristic p > 3 on the Kummer surface are not correct. We verify and revise the formulas with mathematical software. The operation counts become 29M + 2S for new pseudo-addition formulas and 30M + 10S for doubling ones. And then we speed up the scalar multiplication on the Kummer surface with Euclidean addition chains.

Cognitive radio technology, which allows secondary user (SU) to utilize the spectrum holes left by primary user (PU), was proposed to solve spectrum under-utilization problem. However, due to sensing error, SU's transmission will bring negative effects to PU's communication. Recently, cooperative relay technology was introduced to solve this problem. In this paper, a cooperative framework, which allows SU to act as a relay for primary link when needed, is considered and then a cognitive relay scheme is proposed. In order to maximize SU's throughput while keeping the system stable, we study and obtain SU's optimal strategy (i.e., relaying strategy and power allocation) by a constrained optimization problem. Since energy consumption is also an important problem for cognitive radio networks, we also investigate SU's optimal strategy to maximize SU's energy efficiency while keeping the system stable. The numerical results show that the cognitive relay scheme can achieve higher throughput and energy efficiency than reference schemes.

One of the most challenging issues in wireless sensor networks is extension of the overall network lifetime. Data aggregation is one promising solution because it reduces the amount of network traffic by eliminating redundant data. In order to aggregate data, each sensor node must temporarily store received data, which requires a specific amount of memory. Most sensor nodes use static random access memory (SRAM) or flash memory for storage. SRAM can be implemented in a one-chip sensor node at low cost; however, SRAM requires standby energy, which consumes a lot of power, especially because the sensor node spends most of its time sleeping, i.e. its radio circuits are quiescent. This study proposes two types of divided SRAM: equal-size divided SRAM and equal-ratio divided SRAM. Simulations show that both proposed SRAM types offer reduced power consumption in various situations.

Establishment of a practical software protection method is a major issue in software distribution. There are several approaches to the issue; however, no practical, secure method for mobile phone applications has been proposed. In this paper, we propose a new software protection scheme combined with a tamper-proof device (TPD) in order to achieve computational security against illegal analysis and copying of the target program. Our scheme achieves a reasonable level of security for encoding the data and variables in a program. The program on a mobile phone deals only with encoded data that is difficult to compromise, and the TPD plays a role of decoding execution results. We implemented the proposed scheme on a 3G mobile phone and a user identification module (UIM). An analysis and copying of the protected program impose exponential computation complexities under our attack model.

Equivalent Transmission Path (ETP) model-based BER map method was proved to be used in fast estimating Bit Error Rate (BER) of Single-Input Single-Output Orthogonal Frequency Division Multiplexing (SISO-OFDM) system, where the delay spreading exceeds the guard interval. In this paper, we propose a method for evaluating transmission characteristics of Single-Input Multiple-Output Orthogonal Frequency Division Multiplexing (SIMO-OFDM) system with application to maximum ratio combining diversity at the reception. The simulation results show that the proposed approximation method is able to be used in estimating trasmission characteristics with high accuracy not only for SISO-OFDM system but also for SIMO-OFDM system.

Radar networks show an interesting potential for safety and comfortable applications such as short-range automotive monitoring system or indoor monitoring. This paper presents our novel estimation algorithm of a target position. Especially we evaluate the performance about estimation accuracy and resistance to ghost targets under multipath environment. In above applications, the robust estimation is needed because the receivers tend to output corrupted measurement data. The corrupted data are mostly generated by multipath, sensitivity of receivers. As a result of computer simulations, our algorithm has fine accuracy and robust detections compared with a popular trilateration algorithm.

The probe used in the conventional SAR measurement is usually calibrated in a well filled with tissue-equivalent liquid surrounded by a rectangular waveguide and a matching dielectric window in the frequency range from 800 MHz to 3 GHz. However, below 800 MHz, the waveguides are too large to be used for the calibration. Therefore, we have developed another technique of calibrating the SAR-probe, that is, relating the output voltage of the probe to the field intensity produced by a reference antenna in the tissue-equivalent liquid by using two-antenna method. In this paper, the calibration system using the reference dipole antennas in the liquid at 450 MHz, 900 MHz and 2450 MHz is presented and far-field gain of the reference antenna and calibration factor of the SAR-probe are measured and compared with those obtained by using the conventional waveguide system.

In the scattering problem of periodic gratings, at a low grazing limit of incidence, the incident plane wave is completely cancelled by the reflected wave, and the total wave field vanishes and physically becomes a dark shadow. This problem has received much interest recently. Nakayama et al. have proposed “the shadow theory”. The theory was first applied to the diffraction by perfectly conductive gratings as an example, where a new description and a physical mean at a low grazing limit of incidence for the gratings have been discussed. In this paper, the shadow theory is applied to the analyses of multilayered dielectric periodic gratings, and is shown to be valid on the basis of the behavior of electromagnetic waves through the matrix eigenvalue problem. Then, the representation of field distributions is demonstrated for the cases that the eigenvalues degenerate in the middle regions of multilayered gratings in addition to at a low grazing limit of incidence and some numerical examples are given.

A formalization of authentication trust is proposed for federated identity management systems. Identity federation facilitates user interaction with Web services that control access, but it is more difficult for a service provider to evaluate the assurance of a user's identity if the creation and propagation of user authentication assertions involve different authentication authorities and mediators. On the basis of this formal representation, an aggregated trust value is calculated for evaluating the trustworthiness of a user's identity from the user's authentication assertions propagated through multiple entities while preventing misbehavior or threats to manipulate the trust value.

Network structure has a great impact both on hazard spread and network immunization. The vulnerability of the network node is associated with each other, assortative or disassortative. Firstly, an algorithm for vulnerability relevance clustering is proposed to show that the vulnerability community phenomenon is obviously existent in complex networks. On this basis, next, a new indicator called network “hyper-betweenness” is given for evaluating the vulnerability of network node. Network hyper-betweenness can reflect the importance of network node in hazard spread better. Finally, the dynamic stochastic process of hazard spread is simulated based on Monte-Carlo sampling method and a two-player, non-cooperative, constant-sum game model is designed to obtain an equilibrated network immunization strategy.

An iterative inter-track interference (ITI) cancelling scheme is described for multi-track signal detection in nonbinary (NB)-LDPC-coded two-dimensional magnetic recording. The multi-track iterative ITI canceller that we propose consists of multi-track soft interference cancellers (SICs), two-dimensional partial response (TDPR) filters, noise-predictive max-log-MAP detectors, and an NB-LDPC decoder. TDPR filters using an ITI-suppressing tap-weight vector mitigate ITI in the first iteration. Multi-track SICs and TDPR filters adjusted to the residual two-dimensional ISI signals efficiently detect multi-track signals in the latter iterations. The simulation results demonstrated that our proposed iterative multi-track ITI canceller achieves frame error rates close to those obtained in a non-ITI case in media-noise-dominant environments when the both-side off-track ratio is up to 50%.

This paper presents the iterative progressive numerical methods (IPNMs) based on the induced dimension reduction (IDR) theorem. The IDR theorem is mainly utilized for the development of new nonstationary linear iterative solvers. On the other hand, the use of the IDR theorem enables to revise the classical linear iterative solvers like the Jacobi, the Gauss-Seidel (GS), the relaxed Jacobi, the successive overrelaxation (SOR), and the symmetric SOR (SSOR) methods. The new IPNMs are based on the revised solvers because the original one is similar to the Jacobi method. In the new IPNMs, namely the IDR-based IPNMs, we repeatedly solve linear systems of equations by using a nonstationary linear iterative solver. An initial guess and a stopping criterion are discussed in order to realize a fast computation. We treat electromagnetic wave scattering from 27 perfectly electric conducting spheres and reports comparatively the performance of the IDR-based IPNMs. However, the IDR-based SOR- and the IDR-based SSOR-type IPNMs are not subject to the above numerical test in this paper because of the problem with an optimal relaxation parameter. The performance evaluation reveals that the IDR-based IPNMs are better than the conventional ones in terms of the net computation time and the application range for the distance between objects. The IDR-based GS-type IPNM is the best among the conventional and the IDR-based IPNMs and converges 5 times faster than a standard computation by way of the boundary element method.

As the fundamental component of dynamic spectrum access, implementing spectrum sensing is one of the most important goals in cognitive radio networks due to its key functions of protecting licensed primary users from harmful interference and identifying spectrum holes for the improvement of spectrum utilization. However, its performance is generally compromised by the interference from adjacent primary channels. To cope with such interference and improve detection performance, this paper proposes a non-coherent power decomposition-based energy detection method for cooperative spectrum sensing. Due to its use of power decomposition, interference cancellation can be applied in energy detection. The proposed power decomposition does not require any prior knowledge of the primary signals. The power detection with its interference cancellation can be implemented indirectly by solving a non-homogeneous linear equation set with a coefficient matrix that involves only the distances between primary transmitters and cognitive secondary users (SUs). The optimal number of SUs for sensing a single channel and the number of channels that can be sensed simultaneously are also derived. The simulation results show that the proposed method is able to cope with the expected interference variation and achieve higher probability of detection and lower probability of false alarm than the conventional method in both hard combining and soft combining scenarios.

In this paper, we present a maximum a posteriori probability (MAP) approach to the problem of blind estimation of single-input, multiple-output (SIMO), finite impulse response (FIR) channels. A number of methods have been developed to date for this blind estimation problem. Some of those utilize prior knowledge on input signal statistics. However, there are very few that utilize channel statistics too. In this paper, the unknown channel to be estimated is assumed as the frequency-selective Rayleigh fading channel, and we incorporate the channel prior distributions (and hyperprior distributions) into our model in two different ways. Then for each case an iterative MAP estimator is derived approximately. Performance comparisons over existing methods are conducted via numerical simulation on randomly generated channel coefficients according to the Rayleigh fading channel model. It is shown that improved estimation performance can be achieved through the MAP approaches, especially for such channel realizations that have resulted in large estimation error with existing methods.

We consider the position estimation system for targets which exist in near wide area. The system has multiple sensors and estimates the position with multiple receivers. In the past, if receivers were arranged on a straight line, the large position error in the same direction of the line is generated. In order to reduce the error, we propose a novel estimation algorithm using transmitter's directivity information. Our system use directional emission made by an array of antennas in a transmitter. In this paper, the error characteristic which should be solved is introduced firstly. After that, our algorithm is presented. Finally the performance of the error reduction is shown by computer simulations. And we also confirm the reduction by experimental trials. The results indicate good reduction of the error.

Various network services, such as virtual private network, cloud computing and Internet protocol television, are often provided across multiple network operators. The difficulty in managing the quality of service across multiple operator domains is the barrier to adoption especially to service level agreement-sensitive and mission critical cases. Federating network resources among operators is necessary to manage the quality of service across operators. To manage network resources of other operator domains, the network operator's federation mechanisms aiming at a future open access network model are essential. In this paper, the mechanisms of the signaling process as well as the capability of the bandwidth broker are proposed for open access networking, where multiple operators are connected via a common access network operator. Considering that both the next generation network and the non-next generation network architectures must coexist, we have analyzed federation mechanisms for establishing practical functional extensions to existing bandwidth broker implementations for the federation signaling. Based on the analysis, the designs of the federation signaling and the required bandwidth broker functional models are proposed. The proposed design is prototyped and the demonstration of the federation signaling shows that the federation mechanism can assure the bandwidth of a targeted live data stream on demand across the trunk and the access network operators even under a congested situation.

In dense passive radio frequency identification (RFID) systems, code division multiple access (CDMA) techniques can be used to alleviate severe collisions and thus enhance the system performance. However, conventional CDMA techniques are challenging to implement, especially for passive tags due to cost and power constraints. In this paper, we design a CDMA-based multi-reader passive ultra high frequency (UHF) RFID system in which a reader detects only the strongest tag signal and a tag uses Gold codes only on the preamble and the data bits of RN16 without increasing its clock frequency. We present a new communication procedure based on dynamic framed slotted ALOHA (DFSA). In order to optimize the system, we theoretically analyze the system performance in terms of slot capacity and identification rate, and formally show how the code length and the number of readers affect the identification rate. Furthermore, we propose an effective method for tag estimation and frame size adjustment, and validate it via simulations. Through an example, we demonstrate how the analysis-based technique can be used to optimize the system configurations with respect to the number of readers and the number and length of Gold codes.

We propose a novel channel model of satellite-to-ground optical transmission to achieve a global-scale high-capacity communication network. In addition, we compose an effective channel coding scheme based on low-density generator matrix (LDGM) code suitable for that channel. Because the first successful optical satellite communication demonstrations are quite recent, no practical channel model has been introduced. We analyze the results of optical transmission experiments between ground station and the Optical Inter-orbit Communications Engineering Test Satellite (OICETS) performed by NICT and JAXA in 2008 and propose a new Markov-based practical channel model. Furthermore, using this model we design an effective long erasure code (LEC) based on LDGM to achieve high-quality wireless optical transmissions.

Recently, a novel approach to color image compression based on colorization has been presented. The conventional method for colorization-based image coding tends to lose the local oscillation of chrominance components that the original images had. A large number of color assignments is required to restore these oscillations. On the other hand, previous studies suggest that an oscillation of a chrominance component correlates with the oscillation of a corresponding luminance component. In this paper, we propose a new colorization-based image coding method that utilizes the local correlation between texture components of luminance and chrominance. These texture components are obtained by a total variation regularized energy minimization method. The local correlation relationships are approximated by linear functions, and their coefficients are extracted by an optimization method. This key idea enables us to represent the oscillations of chrominance components by using only a few pieces of information. Experimental results showed that our method can restore the local oscillation and code images more efficiently than the conventional method, JPEG, or JPEG2000 at a high compression rate.