Hot spot service based on wireless LANs is expected to play an important role in the beyond 3G wireless networks. Although spatial coverage is very limited, a comfortable and higher speed compared with a cellular system is available there. However, there might exist nodes that cannot communicate directly with an Access Point (AP) because of the distant location or the shadowing due to obstacles. Accordingly, the introduction of two-hop relaying to the hot spot is useful to extend the coverage and avoid the dead spot. However, the throughput per node is getting decreased as the hot spot coverage area increases. Therefore, in this paper, we propose a scheme to reuse the same channel spatially wherever possible and apply it to the HiperLAN/2 based wireless LAN hot spot with two-hop relaying to compensate for the decrease of the throughput per node. Namely, we modify the HiperLAN/2 protocol in such a way that a time slot is reused at the nodes spatially separated far enough not to cause packet collision. Thus, the throughput is expected to be improved and confirmed by a theoretical analysis and computer simulations.

Recently, low-density parity-check (LDPC) codes have attracted much attention. LDPC codes can achieve the near Shannon limit performance like turbo codes. For the LDPC codes, the reduced complexity decoding algorithms referred to as uniformly most powerful (UMP) BP- and normalized BP-based algorithms were proposed for BPSK on an additive white Gaussian noise (AWGN) channel. The conventional BP and BP-based algorithms can be applied to BPSK modulation. For high bit-rate transmission, multilevel modulation is preferred. Thus, the BP algorithm for multilevel modulations is proposed in . In this paper, we propose the BP algorithm with reduced complexity for multilevel modulations, where the first likelihood of the proposed BP algorithm is modified to adjust multilevel modulations. We compare the error rate performance of the proposed algorithm with that of the conventional algorithm on AWGN and flat Rayleigh fading channels. We also propose the UMP BP- and normalized BP-based algorithms for multilevel modulations on AWGN and flat Rayleigh fading channels. We show that the error rate performance of the proposed BP algorithm is almost identical to that of the algorithm in, where the decoding complexity of the proposed BP algorithm is less than that of the algorithm in. We also show that the proposed BP-based algorithms can achieve the good trade-off between the complexity and the error rate performance.

In this paper, the design of signature waveforms for asynchronous CDMA systems equipped with a correlation receiver is first considered. Optimal signature waveforms that minimize the average multiple access interference (MAI) at the output of a correlation receiver are found, while satisfying the constraint on available transmission bandwidth. Comparison to signature waveforms previously obtained for synchronous systems is also made to justify the superior performance of the designed signature waveforms in asynchronous systems. Furthermore, for direct-sequence CDMA (DS-CDMA) systems with random signature sequences, the use of multiple chip waveforms is also proposed as a means of suppressing MAI. Bandwidth constrained multiple chip waveforms that maximize the signal-to-interference ratio (SIR) at the output of each correlation receiver are found. Numerical results show that by using double chip waveforms instead of a single chip waveform, it is possible to reduce the MAI by 10% for a fixed transmission bandwidth (or equivalently, to save about 10% of transmission bandwidth for a given SIR requirement). The advantage of using double chip waveforms is also demonstrated in terms of the bit error rate (BER), whose calculation is based on our extension to Holtzman's approximation in.

High-frequency characteristics of SiGe heterojunction bipolar transistors with different emitter sizes are studied based on pulsed measurements. Because the self-heating effect in transistors will enhance the Kirk effect, as the devices operate in high current region, the measured cutoff frequency and maximum oscillation frequency decrease with measurement time in the pulsed duration. By analyzing the equivalent small-signal device parameters, we know the reduction of cutoff frequency and maximum oscillation frequency is attributed to the reduction of transconductance and the increase of junction capacitances for fixed base-emitter voltage, while it is only attributed to the degradation of transconductance for fixed collector current. Besides, the degradation of high-frequency performance due to self-heating effect would be improved with the layout design combining narrow emitter finger and parallel-interconnected subcells structure.

We proposed a one-way trapdoor permutation f based multi-signature scheme which can keep tighter reduction rate. Assuming the underlying hash functions are ideal, our proposed scheme is not only provably secure, but are so in a tight. An ability to forge multi-signatures with a certain amount of computational resources implies the ability to invert a one-way trapdoor permutation f (on the same size modulus) with about the same computational effort. The proposed scheme provides the exact security against Adaptive-Chosen-Message-Attack and Adaptive-Insider-Attack by . can also attack in key generation phase, and act in collusion with corrupted signers.

Image rectification is a method of aligning epipolar lines of image pairs taken from widely variant viewpoints. Using the rectified images, we can easily obtain corresponding points. This paper presents a rectification method for object segmentation. Using the rectified image pairs obtained with the proposed method, we are able to find the reliable disparity and estimate the 3D depth of the pixel that is effective in the object segmentation.

An efficient architecture for a FPGA symmetry FIR filter is proposed that employs 2-bit parallel-distributed arithmetic (2-bit PDA). The partial product is pre-calculated and saved into the distributed ROM. This eliminates the large amount of logic needed to compute multiplication results. The proposed architecture consumes less area and offers higher speed operation because the multiplier is omitted.

In this work, a novel Multiple Valued Exclusive-Or Sum Of Products (MVESOP) minimization formulation is analyzed and an algorithm is presented that detects minimum MVESOP expressions when the weight of the function is less than eight. A heuristic MVESOP algorithm based on a novel cube transformation operation is then presented. Experimental results on MCNC benchmarks and randomly generated functions indicate that the algorithm matches or outperforms the quality of the state of the art in ESOP minimizers.

IP multicast is seen as an efficient way of encouraging multimedia services such as Internet TV and Videoconferencing because it can deliver packets to multiple users while efficiently using network resources. Source Specific Multicast (SSM) is suggested as the IP multicast routing protocol and it can construct multicast trees efficiently. However it increases multicast forwarding table entries and fails to handle source mobility. This paper proposes the Unicast Extension Multicast Protocol (UMP) to solve these problems. In the protocol, only the routers that act as branching points keep multicast forwarding table entries, and packets are delivered between these routers using IP unicast. This prevents the multicast forwarding table entries from burdening other non-branch routers. Additionally, UMP supports source mobility by using the recursive join messages to prevent the creation of redundant paths while supporting source mobility.

A differential electromagnetic transducer (DET) was implemented using micro electro mechanical system (MEMS) technology for use in an implantable middle ear (IME) system. The DET is designed to have good vibration efficiency and structure that can't be interfered by the external environmental magnetic field. In order to preserve the uniform vibration performance, the MEMS technology was introduced to manufacture the elastic membrane using polyimide that is softer than silicon. Using the finite element analysis (FEA), vibration characteristics are simulated and designed so that the resonance frequency of the membrane is closed to that of the middle ear. The results of the vibration experiments of the developed DET showed excellent results. We implemented the IME system using a DET and implanted it into a dog. This showed the IME system performed well in a living body.

Cryptography and Coding Theory are closely related in many respects. Recently, the problem of "decoding Reed Solomon codes" (also known as "polynomial reconstruction") was suggested as an intractability assumption to base the security of protocols on. This has initiated a line of cryptographic research exploiting the rich algebraic structure of the problem and its variants. In this paper we give a short overview of the recent works in this area as well as list directions and open problems in Polynomial Reconstruction Based Cryptography.

The high-end telecom terminal and PDAs, sometimes called Personal Trusted Devices (PTDs) are programmable, have tens of megabytes memory, and rather fast processors. In this paper we analyze, when it is energy-efficient to transfer application data compressed over the downlink and then decompress it at the terminal, or compress it first at the terminal and then send it compressed over up-link. These questions are meaningful in the context of usual application code or data and streams that are stored before presentation and require lossless compression methods to be used. We deduce an analytical model and assess the model parameters based on experiments in 2G (GSM) and 3G (FOMA) network. The results indicate that if the reduction through compression in size of the file to be downloaded is higher than ten per cent, energy is saved as compared to receiving the file uncompressed. For the upload case even two percent reduction in size is enough for energy savings at the terminal with the current transmission speeds and observed energy parameters. If time is saved using compressed files during transmission, then energy is certainly saved. From energy savings at the terminal we cannot deduce time savings, however. Energy and time consumed at the server for compression/decompression is considered negligible in this context and ignored. The same holds for the base stations and other fixed telecom infrastructure components.

Currently, the IP infrastructure is widely available, which reduces the deployment and implementation cost of IP-based wireless networks. But, the corresponding researches on Quality of Service (QoS) in wireless mobile networks have not been done sufficiently. Although All-IP network has gotten the spotlight for both wired and wireless integrated networks, it has some unavoidable defects as it is based on best-effort IP transmission technologies. By focusing our attention on this point, we propose an Advanced QoS Provisioning Scheme (AQPS) that can provide satisfied QoS for multimedia applications based on accurate traffic measurements. With the AQPS, we consider 1xEV-DV system as a target system, extract QoS requirements for this system, and develop a corresponding QoS provisioning method using CDMA traffic measurement. The AQPS is designed to estimate delay parameters between a mobile station and a BTS (or repeater), verify whether the mobile station can support RSVP or not, operate a corresponding scheduler, and assign appropriate time slots based on traffic classes. One of the interesting results of this research is that the capability of distinguishing BTS' traffic from repeater's traffic helps save implementation cost of CDMA systems. The AQPS has been verified to outperform the existing system used in the current CDMA network and to efficiently manage network resources by computer simulations.

This paper proposes "Handover with Proactive Anchor Router Relocation and Data Buffering" to suppress packet loss and packet miss-ordering during handover. To prevent packet miss-ordering, anchor router is proactively relocated to the optimal position before the mobile terminal performs handover. And, to eliminate packet loss during handover, anchor router buffers the packet only during handover. Moreover, anchor router assigns sequential numbers to the buffered packets to eliminate duplicate packet reception. Simulation results show that our proposal eliminates packet miss-ordering and duplicate reception while preventing packet loss.

Service differentiation has been a subject of research for the past few years in the IETF; and in the current Internet, IP flows are mostly treated in a best-effort approach. However, for next generation networks it is expected that users would like to obtain service differentiation based on their preferences or profiles as well as the different types of multimedia they opt to receive or send. In addition, current Quality of Service (QoS) provisioning architectures have been designed mostly for the fixed networks without taking into consideration the wireless or radio links special requirements, such as low bandwidth availability, error prone communications, etc. In this paper we propose a QoS provisioning architecture for next generation networks that uses a hybrid approach to deal with both the wireless and wired (fixed) part of the network. For administering the scarce resource of the radio environment, we have developed a resource allocation algorithm based on micro-economic principles that uses associated piecewise linear utility functions which describe the benefit a user receives from the allocation of various amounts of resource. For the wired part of the network we have also developed a Core-Stateless Utility based Rate allocation Framework (SURF) for performing traffic policing where the flow's requirements are expressed using utility functions. The core routers maintain no per-flow state and implement a simple packet level admission control algorithm that is based on a threshold utility value that is computed dynamically. To tie in these two mechanisms, we developed a signaling mechanism that collect network statistics when a user starts a call and a QoS administrator entity (or Broker) perform the computations for allocating resources based on the information of available resources in the fixed and the wireless sections of the network. A comparison between the hybrid approach and the SURF approach to show the performance of the proposed architecture is presented later in the paper.

The objective of this research is to compare the performance of the Matrix Pencil Method (MPM) and well known root-MUSIC algorithm for high resolution DOA estimation. Performance of each technique in terms of the probability of resolution and SNR in the presence of noise is investigated. Simulation results show that the MPM has a superior resolution to the root-MUSIC algorithm.

The rapid spread of cellular phones in recent years has facilitated not only voice communication but also Internet access via the cellular phone system, and in addition, subscriber demand has led to a diversification in the services provided. One service in high demand is the seamless use of cellular phones in both public and private wireless network areas. In the data world, there is already such an application in the form of public and private use of wireless LAN. However, an increase in the number of users would require the realization of low-cost, easy-to-install very small base stations (VSBS) that use the frequency band efficiently in order to allow private use of ordinary cellular phones. To bring such VSBS into effect, a technology that autonomously selects frequencies which do not interfere with the public communication system from out of the publicly used frequency band is essential for turning such VSBS into reality. This paper proposes a frequency selection algorithm that actively uses cellular phone features such as frequency selection and received signal level measurement, and discusses the results of verification experiments.

The present state of IEC and JIS standards is reviewed on measurement methods of low-loss dielectric and high-tempera-ture superconductor (HTS) materials in the microwave and millimeter wave range. Four resonance methods are discussed actually, that is, a two-dielectric resonator method for dielectric rod measurements, a two-sapphire resonator method for HTS film measurements, a cavity resonator method for microwave measurements of dielectric plates and a cutoff circular waveguide method for millimeter wave measurements of dielectric plates. These methods realize the high accuracy sufficient for measurements of temperature dependence of material properties.

Authentication codes (A-codes, for short) are considered as important building blocks for constructing unconditionally secure authentication schemes. Since in the conventional A-codes, two communicating parties, transmitter and receiver, utilized a common secret key, and such A-codes do not provide non-repudiation. With the aim of enhancing with non-repudiation property, Simmons introduced A2-codes. Later, Johansson formally defined an improved version of A2-codes called, the A3-codes. Unlike A2-codes, A3-codes do not require an arbiter to be fully trusted. In this paper, we clarify the security definition of A3-codes which may be misdefined. We show a concrete attack against an A3-code and conclude that concrete constructions of A3-codes implicitly assumes a trusted arbiter. We also show that there is no significant difference between A2-codes and A3-codes in a practical sense and further argue that it is impossible to construct an "ideal" A3-codes, that is, without any trusted arbiter. Finally, we introduce a novel model of asymmetric A-codes with an arbiter but do not have to be fully trusted, and also show a concrete construction of the asymmetric A-codes for the model. Since our proposed A-code does not require fully trusted arbiters, it is more secure than A2-codes or A3-codes.

A random number generator composed of single electron devices is presented. Due to stochastic behavior of electron tunneling process, single electron devices have intrinsic randomness. Using its randomness, a true random number generator can be implemented. Although fluctuation of device parameters degrades the performance of the proposed circuit, we show that the adjustment of the bias voltages can compensate the fluctuation.