Multiple access interference (MAI) due to many simultaneous users is the main factor that limits the performance of DS-CDMA system. Multiuser detection is a method to avoid performance degradation due to MAI. We propose a blind multiuser detection method based on the algorithm consisting of two-stage decoding process, i.e., linearly constrained constant modulus (LCCM) and iterative least squares (ILS). The computer simulations confirmed that the algorithm is near-far resistant and that the proposed method is effective in the application to the slow fading channels.

Hierarchical Mobile IPv6 (HMIPv6) has been proposed to accommodate frequent mobility of terminals within the Internet. It utilizes a router, named Mobility Anchor Point (MAP), so that networks can manage mobile terminals without floods of signaling message. Note here that, particularly in a wide area network, such as a mobile communication network, it is efficient to distribute several MAPs within the same network and make the MAP domains cover overlapped areas. This enables the network to manage the terminals in a flexible manner according to their different mobility scenarios. The method described in the Internet-Draft at the IETF, however, lets mobile terminals select its MAP. This may cause load concentration at some particular MAPs and/or floods of signaling messages, because the terminals may not select a feasible MAP in a desirable manner. In this paper, a MAP selection method in distributed-MAPs environment is proposed. It reduces signaling messages to/from outside networks without load concentration at any particular MAPs. Finally, we show that the proposed method works effectively by simulation experiments.

A performance comparison is developed between a chaotic communication system and a spread spectrum system with similar features in terms of bandwidth and transceiver structure but based on more conventional Gold sequences. Comparison is made in the presence of noise and multipath contributions which degrade the channel quality. It is shown that, because of its more favourable correlation properties, the chaotic scheme exhibits lower error rates, at a parity of the bandwidth expansion factor. The same favourable correlation properties are also used to explain and show, through a numerical example, the benefits of chaotic segments in a multi-user environment.

Network-oriented car navigation systems (off-board navigation systems) have become a hot topic cause of the expanding car navigation and active wireless communication markets. This paper examines the map downloading architecture, which realizes practical off-board navigation systems. We focus on practical technologies for present low speed wireless communication networks, such as with a 9.6 kbps transfer speed. We propose a new off-board navigation architecture, which combines a cost-effective map downloading system and a guide information downloading system. The proposed architecture can reduce the download data size to within about 50-100 kbytes for destination setting and route guidance. It has about a 1-2 minutes response time and about a 30-60 yen communication cost for a PDC (Personal Digital Cellular) wireless communication network in Japan. We consider this communication cost has a potential for a commercial off-board navigation system.

We present an efficiency improvement on an existing unlinkable divisible e-cash system. In the based e-cash system, an e-coin can be divided to spent, and thus the exact payments are available. Furthermore, to protect customer's privacy, the system also satisfies the unlinkability in all the payments, which is not satisfied in other existing divisible e-cash systems. The unlinkability means the infeasibility of determining whether two payments are made by the same customer. However, in the unlinkable divisible e-cash system, the payment protocol needs O(N) computations, and thus inefficient, where N indicates the divisibility precision. For example, in case of N=100,000, about 200,000 exponentiations are needed for the worst. We improve the payment protocol using the tree approach. In case of N=100,000, the protocol with our improvement needs only about 600 exponentiations for the worst. This good result can be obtained for other N which is more than about 100.

In this letter, we investigate the blind channel estimation in MIMO-OFDM systems based on the second-order statistics of the channel outputs only. We exploit the cyclostationarity induced by OFDM with cyclic prefix, establish the sufficient identifiability conditions, and develop a subspace algorithm. Finally, we demonstrate the validity of the algorithm by computer simulations.

This paper assesses the performance of the handoff algorithm based on distance and RSSI measurements in a multi-cellular environment by computer simulation. The algorithm performs a handoff if handoff initiation conditions, handoff possible conditions, and handoff selective conditions are met. The performance criteria are based on the average number of handoffs, the crossover points and the average number of outages. Numerical results are presented to demonstrate the feasibility of the algorithm. The performance of the distance-assisted handoff algorithm is compared with that of a conventional algorithm that utilizes signal strength alone. Overall, the distance-assisted algorithm exhibits higher performance in average number of handoffs and the crossover points, yet exhibits a higher number of outages on average than the conventional algorithm.

As we move toward the transition to the IPv6 next generation network environment, it is necessary to realize heterogeneous communications between IPv6 and IPv4 terminals without sacrificing any convenience or frameworks of current communication methods. Mechanisms that satisfy such requirements are called translators. This paper categorizes various translator mechanisms and clarifies their characteristics. As a result of analyses, this paper proposes a SOCKS-based IPv6/IPv4 Translator, and describes its design and implementation. Compared with other translator mechanisms, the SOCKS-based translator have small constraints and good characteristics. For example, it can integrate DNS name resolving procedures, which is an important mechanism for the transition. The translator has already been implemented and it has been proved that it can support typical communication services such as telnet, ftp, http, mail without any problems.

A number of schemes have been proposed for communication using chaos over the past years. Regardless of the exact modulation method used, the transmitted signal must go through a physical channel which undesirably introduces distortion to the signal and adds noise to it. The problem is particularly serious when coherent-based demodulation is used because the necessary process of chaos synchronization is difficult to implement in practice. This paper addresses the channel distortion problem and proposes a technique for channel equalization in chaos-based communication systems. The proposed equalization is realized by a modified recurrent neural network (RNN) incorporating a specific training (equalizing) algorithm. Computer simulations are used to demonstrate the performance of the proposed equalizer in chaos-based communication systems. The Henon map and Chua's circuit are used to generate chaotic signals. It is shown that the proposed RNN-based equalizer outperforms conventional equalizers.

Subband adaptive array (SBAA) has been realised as a promising method to perform space-time signal processing in mobile communications. Recently, several schemes of SBAA have been introduced. However, theoretical analysis of SBAA performance has been only limited to case of SBAA without using decimation. In this paper, we introduce a novel method to analyse the performance of SBAA using critical sampling with localised feedback scheme. We first provide a detailed analysis of the SBAA performance in the case of single path and multipath fading environment. The simulation results are then presented to verify the proposed method.

This paper proposes a multi-hop wireless link system for radio access networks (RANs) of new generation mobile communication systems. The performance of the multi-hop wireless link system is evaluated from the viewpoints of total output power, co-frequency interference characteristics, and the system frequency bandwidth based on a comparison with that of the single-hop wireless link system, which is currently used as a RAN. The proposed system is effective in realizing an enormous approach link capacity from both the total output power and the co-frequency interference viewpoints. From the system frequency bandwidth viewpoint, the optimum number of relays in the multi-hop connection is determined to be three hops in a line-of-sight propagation environment in order to minimize the frequency bandwidth for transferring traffic. We conclude that the multi-hop wireless link system is suitable for new generation mobile communication systems.

Since the penetration of VSAT services is rapidly increasing, more earth stations will operate around airports than is currently true. This makes it essential to evaluate accurately and efficiently the impairment of received signals due to blockage by aircraft. This paper proposes developing an aircraft model using a thin, planar polygon to represent the aircraft projection and to apply GTD with corner diffraction terms. The effectiveness and applicability of the method is then examined numerically. It is demonstrated that the results measured in the Ku-band around two airports are a good match with the numerical simulations even when the distance between the aircraft and the stations is small.

Adaptive optimization of the notch bandwidth of a lattice-based adaptive infinite impulse response (IIR) notch filter is presented in this paper. The filter is used to improve the performance of a direct sequence spread spectrum (DSSS) binary phase shift keying (BPSK) communication system by suppressing a narrow-band interference at the receiver. A least mean square (LMS) algorithm used to adapt the notch bandwidth coefficient to its optimum value which corresponds to the maximum signal to noise ratio (SNR) improvement factor is derived. Bit error rate (BER) improvement gained by the DSSS communication system using the filter with the optimized notch bandwidth is also shown. Computer simulation results are compared with those obtained analytically to demonstrate the validity of theoretical predictions for various received signal parameters.

Future wireless communication systems will provide mobile terminals with high bit-rate transmissions for accessing broadband wired networks. In this paper, we envisage a Time Division Multiple Access - Time Division Duplexing (TDMA-TDD) air interface and we propose a Medium Access Control (MAC) protocol, named Dynamic Scheduling - TDD (DS-TDD), that allows guaranteeing the QoS of different traffic classes and efficiently supports uplink/downlink traffic asymmetries. The DS-TDD performance is theoretically analyzed. Moreover, the DS-TDD protocol is compared with another scheme proposed in the literature. Finally, the impact of packet errors on the DS-TDD performance is evaluated.

An LCD Driver IC includes more than 300 buffer amplifiers on a single chip. The phase compensation capacitors (on-chip Miller capacitors) for the amplifiers are more than 1000 pF and occupy a large chip area. This paper describes a two-gain-stage amplifier in which an on-chip Miller capacitor is not used for phase compensation in an LCD Driver IC. In the proposed amplifier, phase compensation is achieved only by a newly introduced zero, which is formed by the load capacitance and a phase compensation resistor connected between the output of the amplifier and the capacitive load. Designs of the phase compensation resistor and the amplifier before compensation are discussed, considering a typical load capacitance range. The test chip was fabricated. The newly introduced zero successfully stabilized the amplifier. The chip area for the amplifier was reduced by 30-40%, compared with our previously reported one. The current consumption of the amplifier was only 5 µA. The experimental results of the fabricated test chip support that the proposed amplifier is suitable to an LCD driver IC with a smaller chip area.

A hybrid data transmission technique for multimedia satellite broadcasting is proposed. The main-channel data and sub-channel data are simultaneously transmitted using QPSK modulation and 2ASK modulation, respectively, but the latter modulation timing is offset by half the main-channel QPSK symbol length in time. The BER performance in a Gaussian channel, the transmission bandwidth, and the transmit power peak factor are theoretically analyzed for various impulse responses of the sub-channel transmit filter. It is found that the use of the sub-channel transmit filter having a sine impulse response minimizes the sub-channel BER while keeping the transmission bandwidth and the transmit power peak factor lower than those of CAPSK transmission.

To diffuse multimedia information services, communication networks must guarantee the quality of services (QoSs) requested by users. In addition, users should be allowed to observe the network in order to customize their own services. A new network management architecture is therefore essential. It must perceive not only node connectivity, but also network failure points and the traffic situation dynamically. This paper introduces the network map as such an architecture on personalized multimedia communication networks and proposes multiple QoS routing using the network map. Moreover, a prototype system is built in order to verify the availability of the network map.

Wireless network systems introducing both of the cellular concept and the ad-hoc concept have been proposed. Communication between two nodes in a cell is guaranteed by relaying capability of the base station in these systems. Additionally, two nodes can directly communicate with each other while they are close to each other. We call this type of network a two-hop wireless network. The teletraffic performance of this network depends on various parameters such as the size of a cell, location of nodes, the communication range of nodes, channel assignment schemes, teletraffic behavior and so on. The purpose of this paper is to theoretically analyze the teletraffic performance of the network, which has been evaluated by computer simulation, by introducing a simple model. This paper shows a technique to analyze the performance in this model. Also, this paper considers the range in which the two-hop wireless network works well for the efficient use of channels.

In evaluating the teletraffic of mobile communication networks, it is important to model the motion of terminals. In the previous migration model, mobility characteristics of terminals, such as cell dwell time, have been expressed by a single probability distribution. In this paper, we discuss the modeling of the cell dwell time of terminals in each cell. Using measured data we show that cell dwell time differs from cell to cell and follows log-normal distributions rather than conventional exponential distributions.

In this paper, we propose an efficient algorithm of quick routing for private Wireless ATM (Asynchronous Transfer Mode) networks. This algorithm uses hierarchical source routing, which first establishes a connection between the sending node and the home node (which has the terminal location information), and then, partially releases the connection and reroutes it between the sending node and the receiving node. This results in less delay than found in other conventional routing methods, and avoids passing through congested nodes, because this algorithm uses traffic estimation based on queuing theory. We also show the effectiveness of this algorithm with the use of computer simulations.