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.

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.

Error analysis of the multilevel fast multipole algorithm is studied for electromagnetic scattering problems. We propose novel error prediction and control methods and verify that the computational error for scattering problems with over one million unknowns can be precisely controlled under desired digits of accuracy. Optimum selection of truncation numbers to minimize computational error also will be discussed.

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%.

In this paper, we present known-key attacks on block cipher Rijndael for 192-bit block and 256-bit block. Our attacks work up to 8 rounds for 192-bit block and 9 rounds for 256-bit block, which are one round longer than the previous best known-key attacks. We then search for the parameters for the ShiftRow operation which is stronger against our attacks than the one in the Rijndael specification. Finally, we show a parameter for 192-bit block which forces attackers to activate more bytes to generate a truncated differential path, and thus enhances the security against our attacks.

This paper proposes a differential fault analysis on the stream cipher MUGI, which uses two kinds of update functions of an intermediate state. MUGI was proposed by Hitachi, Ltd. in 2002 and is specified as ISO/IEC 18033-4 for keystream generation. Differential fault analysis (DFA) is a type of fault analysis, which is considered to be a serious threat against secure devices such as smart cards. DFA on MUGI was first proposed at ICISC 2010 [25]; however, the attack condition for the successful attack such as the position into which the fault is injected was restricted. In this paper, we extend the attack methods which are more practical, based on a one-byte and a multi-byte fault models using the relationship between two kinds of update functions that are mutually dependent. In the proposed attack, the attacker can know the position affected by the fault injection even if he has no control of the timing of the fault injection. As a result, a 128-bit secret key can be recovered using 13 pairs of correct and faulty outputs on average.

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.

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.

Handoff plays an important role in vehicular networks due to high movement of vehicles. To provide seamless connectivity under Access Points (AP), this paper proposes an adaptive handoff triggering method to minimize communication time for a vehicle with an AP switch (i.e., whether and when to trigger a handoff process). In the proposed method, combined with an improved data transmission rate based trigger, handoff triggering decision is executed based on three different communication methods (called C-Dire, C-Relay and C-ALLRelay) to minimize the transmission delay when a vehicle moves from an AP to another. Transmission delay is derived through considering vehicle mobility and transmission rate diversity. The simulation results show that the proposed method is proven to be adaptive to vehicular networks.

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.

This letter presents a criterion for selecting a transmit antenna subset when ZF detectors followed by Rake combiners are employed for spatial multiplexing (SM) ultra-wideband (UWB) multiple input multiple output (MIMO) systems. The presented criterion is based on the largest minimum post-processing signal to interference plus noise ratio of the multiplexed streams, which is obtained on the basis of QR decomposition. Simulation results show that the proposed antenna selection algorithm considerably improves the BER performance of the SM UWB MIMO systems when the number of multipath diversity branches is not so large and thus offers diversity advantages on a log-normal multipath fading channel.

This paper presents the efficiency of a sensing database and caching (SDB) for cognitive radio systems. The proposed SDB stores regulatory information from regulatory databases, and contains sensing information by distributed sensing schemes. Preliminary information processing for instance indexing, sorting, or applying some models or algorithms, etc. can be performed for the stored data. Available information and the results of the information processing are provided to cognitive radios in order to determine available spectrum and to facilitate dynamic spectrum access at lower sensing cost but higher sensing quality. The SDB is implemented in local networks, therefore information exchange between SDB and the cognitive radios can be realized at low latency and the amount of signaling traffic to global network can be reduced. This paper analyzes the effect of SDB and the performance evaluation was done in a certain condition. As a result, by deploying SDB a system can achieve up to 20% of reduction of sensing activities and maximum 1.3 times higher sensing quality.

Using a single-site lightning location technique, a new portable lightning location system is developed. We incorporate an attitude detection technique using inertial sensors to detect an accurate electromagnetic field vector of sferics by palm-sized electromagnetic sensors which can have arbitrary attitude. The present paper describes the concept and the performance of the developed prototype of the portable system.

This paper presents a new non-interactive multi-trapdoor commitment scheme from the standard RSA assumption. Multi-trapdoor commitment is a stronger variant of trapdoor commitment. Its notion was introduced by Gennaro at CRYPTO 2004. Multi-trapdoor commitment schemes are very useful because we can convert a non-interactive multi-trapdoor commitment scheme into a non-interactive and reusable non-malleable commitment scheme by using one-time signature and transform any proof of knowledge into a concurrently non-malleable one (this can be used as concurrently secure identification). Gennaro gave concrete constructions of multi-trapdoor commitment, but its security relies on stronger assumptions, such as the strong RSA assumption and the q-strong Diffie-Hellman assumption as opposed to our construction based on the standard RSA assumption. As a corollary of our results, we constructed a non-interactive and reusable non-malleable commitment scheme from the standard RSA assumption. Our scheme is based on the Hohenberger-Waters (weak) signature scheme presented at CRYPTO 2009. Several non-interactive and reusable non-malleable commitment schemes (in the common reference string model) have been proposed, but they all rely on stronger assumptions (such as the strong RSA assumption). Thus, we give the first construction of a non-interactive and reusable non-malleable commitment scheme from the standard RSA assumption.

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.

In Wireless Sensor Networks (WSNs), authentication is a crucial security requirement to avoid attacks against secure communication, and to mitigate against DoS attacks exploiting the limited resources of sensor nodes. Resource constraints of sensor nodes are hurdles in applying strong public key cryptographic based mechanisms in WSNs. To address the problem of authentication in WSNs, we propose an efficient and secure framework for authenticated broadcast/multicast by sensor nodes as well as for outside user authentication, which utilizes identity based cryptography and online/offline signature (OOS) schemes. The primary goals of this framework are to enable all sensor nodes in the network, firstly, to broadcast and/or multicast an authenticated message quickly; secondly, to verify the broadcast/multicast message sender and the message contents; and finally, to verify the legitimacy of an outside user. This paper reports the implementation and experimental evaluation of the previously proposed authenticated broadcast/multicast by sensor nodes scheme using online/offline signature on TinyOS and MICA2 sensor nodes.

Since the number of server providing the facilities for users is usually more than one, remote user authentication schemes used for multi-server architectures, rather than single server circumstance, is considered. As far as security is concerned, privacy is the most important requirements, though some other properties are also desirable in practice. Recently, a number of dynamic ID-based user authentication schemes have been proposed. However, most of those schemes have more or less weaknesses and/or security flaws. In the worst case, user privacy cannot be achieved since malicious servers or users can mount some attacks, i.e., server spoofing attack and impersonation attack, to identify the unique identifier of users and masquerade of one entity as some other. In this paper, we analyze two latest research works and demonstrate that they cannot achieve true anonymity and have some other weaknesses. We further propose the improvements to avoid those security problems. Besides user privacy, the key features of our scheme are including no verification table, freely chosen password, mutual authentication, low computation and communication cost, single registration, session key agreement, and being secure against the related attacks.

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.

In this letter, signal to interference plus noise ratio (SINR) performance is analyzed for orthogonal frequency division multiplexing (OFDM) based amplify-and-forward (AF) relay systems in the presence of carrier frequency offset (CFO) for fading channels. The SINR expression is derived under the one-relay-node scenario, and is further extended to the multiple-relay-node scenario. Analytical results show that the SINR is quite sensitive to CFO and the sensitivity of the SINR to CFO is mainly determined by the gain factor and the different power of the direct link channel and relay link channel.

Epidemic Routing is a data delivery scheme based on the store-carry-forward routing paradigm for sparsely populated mobile ad hoc networks. In Epidemic Routing, each node copies packets in its buffer into any other node that comes within its communication range. Although Epidemic Routing has short delay performance, it causes excessive buffer space utilization at nodes because many packet copies are disseminated over the network. In this paper, aiming at efficient buffer usage, we propose an XOR-based delivery scheme for Epidemic Routing, where nodes encode packets by XORing them when their buffers are full. Note that existing delivery schemes with coding are active coding, where source nodes always encode packets before transmitting them. On the other hand, the proposed scheme is passive coding, where source nodes encode packets only when buffer overflow would occur. Therefore, the behavior of the proposed scheme depends on the buffer utilization. More specifically, if sufficient buffer space is available, the proposed scheme delivers packets by the same operation as Epidemic Routing. Otherwise, it avoids buffer overflow by encoding packets. Simulation experiments show that the proposed scheme improves the packet delivery ratio.