In wireless mobile environments, data requests based on the location of mobile clients (MCs) have increased. The requested data, called location-dependent data (LDD), may be uncertain if MCs use terms of general distance like "near". Fuzzy theory allows us to represent uncertainty without sharp boundaries. In this paper we quantify the fuzziness and propose a method for constructing the data region of LDD by the degree of the distance between LDDs' and MCs' locations. In simulation studies, we evaluate the LDD regions (LDRs) in various situations: MCs' extensive and intensive queried pattern in data regions of two "near" senses and civilized regions with regional features. Our performance evaluation shows that the number of database accesses in proposed LDRs can be reduced in each case.

An adaptive backstepping and high order sliding modes control algorithm is proposed for output tracking of mobile robots. The controller can greatly reduce the chattering due to conventional sliding modes technique. The proposed algorithm has certain robustness with respect to the external random disturbances and good adaptability with respect to the parametric uncertainty. The effectiveness of the proposed control strategy is demonstrated by simulations studies.

This paper first presents an active integrated antenna configuration designed for broadband mobile wireless access systems using the 25-GHz band. This active integrated antenna comprises a microstrip antenna array and RF front-end circuits adopting spatial power combining schemes for reduced power consumption of the power amplifiers. Furthermore, the antenna and RF circuits are integrated into each side of a thick copper backing plate and both are connected through microstrip line /slot transitions. The developed active integrated antenna achieves the output power of 14.6 dBm and a noise figure of less than 5 dB. The wireless system using the developed active integrated antenna achieves a 6-dB improvement in the packet error rate compared to that using a passive antenna with the same array design as the active integrated antenna. Furthermore, we obtained the first license of the active integrated antenna for commercial use in high-speed wireless communication systems in Japan.

A clustering scheme for ad hoc networks is aimed at managing a number of mobile devices by utilizing hierarchical structure of the networks. In order to construct and maintain an effective hierarchical structure in ad hoc networks where mobile devices may move at high mobility, the following requirements must be satisfied. (1) The role of each mobile device for the hierarchical structure is adaptive to dynamic change of the topology of the ad hoc networks. The role of each mobile device should thus change autonomously based on local information in each mobile device. (2) The overhead for management of the hierarchical structure is small. The number of mobile devices in each cluster should thus be almost equivalent. This paper proposes an adaptive multihop clustering scheme for highly mobile ad hoc networks. The results obtained by extensive simulation experiments show that the proposed scheme does not depend on mobility and node degree of mobile devices in the network, which satisfy the above requirements.

This paper focuses on a global ultrasonic system for self-localization of a mobile robot. The global ultrasonic system consists of some ultrasonic generators fixed at some arbitrary position in the global coordinates and two receivers in the moving coordinates of the mobile robot. This system is used to obtain the state vector of the mobile robot in the global coordinates from the distance measurement between the ultrasonic generator and the receiver. In order to avoid the cross-talk and to synchronize the ultrasonic sensors, the sequential cuing technique using small-sized radio frequency module is adopted. An extended Kalman filter algorithm is used to process the noisy ultrasonic signal and to estimate the state vector. Computer simulations and experiments are conducted to verify the effectiveness of the proposed global ultrasonic system.

In our previous research, we proposed a nonlinear digital filter to Estimate the Smoothed and Differential values of the sensor inputs by using Sliding mode system (ESDS). This estimator is able to eliminate impulsive noise efficiently from time series data. We applied this filter to processing outputs of robot sensors, and it became possible to perform robust environment recognition. ESDS is designed using a theory of variable structure system (VSS) with sliding mode. In short, ESDS is a nonlinear filter. Therefore, it is very difficult to clarify the behavior of the system analytically. Consequentially, we deal with the step function with impulsive noise as an example, and we attempt to eliminate this impulsive noise by keeping the sudden shift of signals. In this case, there is a trade-off between the noise elimination ability and the tracking performance for an input signal. Although ESDS is a nonlinear filter, it has the same trade-off as linear filters such as a low-pass filter. In order to satisfy these two conditions simultaneously, we use two filters whose parameters are independent of each other. Furthermore, in order to repress the adverse affect of impulsive noise in the steady-state, we introduced the boundary layer. Generally, a boundary layer is used so as to inhibit the harmful effect of chattering. Chattering is caused in the sliding mode system when the state of the system vibrates on the switching line of a sliding mode system. By introducing the boundary layer to ESDS, we can repress the adverse effect of impulsive noise in the steady-state. According to these considerations, we clarify the relationship between these characteristics of ESDS and the arbitrary parameters.

A novel scheme of subband adaptive array for multicode Direct Sequence Code Division Multiple Access (DS-CDMA) is proposed in this paper. The proposed scheme has a flexible configuration which allows basestation to be able to dynamically adapt to multirate transmission requests from subscribers. It is shown that the novel scheme can effectively suppress multiple access interferences (MAI) by appropriately forming main beam toward the desired user while pointing beampattern nulls toward MAI sources. Moreover, the combination of the subband adaptive array with the so-called cyclic prefix spreading code CDMA is also proposed to mitigate multipath fading and maximize diversity gain in multipath fading environment.

European research Framework Programs and in particular their impact on international standardization for the development of third generation mobile communication systems are reviewed, which are currently being deployed. In 2002 the European Commission launched the 6th Framework Program. In parallel, research on systems beyond third generation started already. Therefore, international organizations such as the Wireless World Research Forum (WWRF) were established. WWRF and other international activities are presented. The vision of the Wireless World is developed from the user perspective, where already a high degree of international harmonization was achieved. The building blocks of the Wireless World and the resulting necessary major research areas are summarized. Future research projects on systems beyond third generation will focus on these topics. Global cooperation will be an important prerequisite to achieve harmonized future standards. Therefore, the 6th Framework Program of the European Commission will provide an important platform for international cooperation. The 6th Framework Program is described in detail.

This paper presents a two-tier coordinated checkpointing algorithm which can reduce the number of messages by being composed of two levels in mobile computing. Thus mobile devices have a high mobility and are lack of resources (e.g., storage, bandwidth, and battery power), traditional distributed algorithms like coordinated checkpointing algorithms could not be applied properly in mobile environment. In our proposed two-tier coordinated checkpointing algorithm, the messages to be transferred are requested by the mobile hosts and are handled by the appropriate MSS's (Mobile Support Stations). And the broadcast messages are handled by MSS instead of relaying the messages to all the mobile hosts directly as with the previous algorithms. This can reduce the communication cost and maintain the overall system consistency. In wireless cellular network, mobile computing based on a two-tier coordinated checkpointing algorithm reduces the number of synchronization messages. We perform performance comparisons by parametric analysis to show that a two-tier coordinated checkpointing algorithm can reduce communication cost compared to the previous algorithms in which the messages are directly sent to the mobile hosts.

A novel interference reduction method, transmit power and window control (TPWC), is proposed to enhance the system capacity in the downlink of code division multiple access (CDMA) cellular packet systems. TPWC measures the propagation conditions and calculates the required instantaneous transmit power between a base station (BS) and a mobile station (MS). Then, TPWC sends packets only during a transmit time-window, in which the packets can be sent with less power than a predetermined threshold. TPWC reduces the average transmit power at the cost of an extra transmission delay at the BS. Computer simulations show that TPWC enhances the system capacity by two-fold in a CDMA cellular packet system when each MS has a loading ratio of 0.5 and an average delay allowance of 5 ms for the unit packet length of 1 ms. Furthermore, this paper proposes a multi-link packet transmission (MLPT) scheme in order to reduce the delay caused by TPWC. When an MS is at the cell edge, packets are distributed by MLPT to multiple BSs, from which packets are sent to the MS; thus, the transmission delay can be reduced by utilizing the transmit windows of each BS.

Radio access networks (RANs) for new generation mobile communication systems are required to construct economical high capacity networks. An optical wireless link is expected as a solution to the linking method in the construction of these networks. The optical wireless link provides high bit-rate transmission and allows for easy installation. However, optical-waves are severely attenuated in free-space transmission due to weather conditions and cannot provide a high level of link availability in long-distance communications. This paper describes the applicability of an optical wireless link to the RAN based on obtained atmosphere propagation properties from experiments on an 800-nm band optical wireless link from the viewpoint of link availability. The experimental results show that the BER performance of the optical wireless link exhibits a sufficiently low power penalty of less than 1 dB compared to that of the optical fiber link. Moreover, the results confirm that atmosphere attenuation of an 800-nm band optical wave due to fog and rainfall can be estimated by using a simple estimation equation. The optical wireless link could be used for RAN approach links with the range of less than 350 m to achieve the link outage rate of 0.004% from the viewpoint of the link budget design.

A computed torque controller for a dynamic model of nonholonomic mobile robots with bounded external disturbance is proposed to treat the adaptive tracking control problem using the separated design method. A velocity controller is first designed for the kinematic steering system to make the tracking error approaching to zero asympotically. Then, a computed torque controller is designed such that the true mobile robot velocity converges to the desired velocity controller. In each step, the controllers are designed independently, and this will simplify the design of controllers. A novel stability analysis involving the estimation of some differential inequalities is also given to guarantee the stability of the closed-loop system. Moreover, the regulation problem and the tracking problem will be treated using the proposed controller. In particular, the mobile robots can globally follow any path such as a straight-line, a circle and the path approaching to the origin. Furthermore, the problems of back-into-garage parking and the parallel parking problem can also be solved using the proposed controller. Some interesting simulation results are given to illustrate the effectiveness of the proposed tracking control law.

This paper proposes "Mobility-Aware TCP" to solve the problem that arises with New-Reno TCP if Post Registration Handover is used. In Mobility-Aware TCP, when the MT holds an unreturned ACK after handover, lost segments are retransmitted by Flow Control instead of Congestion Control. Therefore, the sender can retransmit segments without throttling the transmission rate. Moreover, if there is no ACK, the MT chooses retransmission schemes that can get higher throughput. Computer simulations compare Mobility-Aware TCP to New-Reno TCP with Post Registration Handover, and New-Reno TCP without Post Registration Handover. The simulations show that the proposal can maintain high throughput even in the face of high segment loss or long handover latency.

This paper proposes a new signal peak power reduction technique, Peak Reduction based on Control Signal Insertion (PRCSI), for broadband mobile communications based on multi-channel signaling schemes. PRCSI reduces the peak power with a peak control signal that is generated symbol-by-symbol; no signal band expansion is incurred because the peak control signal is inserted into the transmission signal band. PRCSI can achieve 4 dB peak power reduction for 8-carrier signaling, while the Eb/N0 value required to achieve 10-3 average BER is 1 dB larger with PRCSI than without it. This BER performance degradation can effectively be compensated by the proper use of Trellis coding. The proposed technique is applied to OFDM transmission systems with large carrier number. The proposed technique can achieve 3-dB peak power ratio for 128-carrier OFDM signals with less than 1-dB performance degradation at the BER of 10-3.

The IMT-2000 service launched in 2001 in Japan is expected to popularize multimedia services such as videophone, visual mail, video, and music distribution. With the rapidly increasing demand for high-speed mobile multimedia and the need to support diversified requirements of users, wireless Quality of Service (QoS) resource management has become an important and challenging issue. In order to improve the system capacity and rate of satisfied users, in this paper, a novel wireless QoS resource management scheme is proposed to carry out radio resource cooperative control among base stations. Computer simulations indicate that the proposed QoS resource cooperative control exhibits superior performance over conventional ones, and that a higher rate of satisfied users is achieved.

A field trial, within a suburban macro-cell environment, of a space-time (ST) equalizer for TDMA mobile communication systems is described. The ST equalizer was a cascade connection of two array processors for a four-antenna array and a two-branch-metric-combining maximum-likelihood sequence estimation (MLSE) that was designed to obtain full space- and path-diversity gains from first-arrival and one-symbol-delayed signals while suppressing excessively long-delayed inter-symbol interference (ISI). The radio frequency was 3.35 GHz, the transmission rate was 4.096 Mb/s, and the modulation was QPSK. The long-delayed ISI reduction and the space-path diversity effect of the ST equalizer was validated by Eb/N0 vs. bit-error-rate (BER) curves with respect to delay spread and antenna spacing as compared with the case of an array processor alone being used.

In this paper, we present a CDN (Content Delivery Network) architecture for mobile streaming service in which content segmentation, request routing, pre-fetch scheduling, and session handoff are controlled by SMIL (Synchronized Multimedia Integration Language) modification. In this architecture, mobile clients simply follow modified SMIL files downloaded from a portal server; these modifications enable multimedia content to be delivered to the mobile clients from the best surrogates in the CDN. The key components of this architecture are 1) content segmentation with SMIL modification, 2) on-demand rewriting of URLs in SMIL, 3) pre-fetch scheduling based on timing information derived from SMIL, and 4) SMIL updates by SOAP (Simple Object Access Protocol) messaging for session handoffs due to client mobility. This architecture enhances streaming media quality for mobile clients while utilizing network resources efficiently and supporting client mobility in an integrated and practical way. The current status of our prototype on a mobile QoS testbed "MOBIQ" is also reported in this paper.

We propose a new closed-loop power control scheme for wireless mobile communication systems using an adaptive step size. The proposed scheme selects the basic power control step size by considering the speed of the mobile station and a variable step size by using instantaneous companding logic based on power control command bit patterns. We show its improved performance in view of the standard deviation of received power at the base station in consideration of channel BER.

Intelligent paging uses the sequential paging technique with additional user information in order to reduce the paging delay cost and the paging load cost. Our proposed paging scheme uses distribution density information of users as required additional user information. This letter addresses an optimal paging sequence and introduces formulas to calculate the paging costs. These formulas are necessary to evaluate the performance of location management. The paging delay cost and the paging load cost for the proposed paging scheme and two other paging schemes are calculated and numerical analyses for these paging schemes are performed. Results show how the paging delay cost and the paging load cost vary as either the paging request arrival rates or the number of cells in an LA increases. The proposed paging scheme is more efficient in view of both the paging delay cost and the paging load cost.

A reconfigurable coprocessor for ETSI-GSM voice coding application domain is presented, synthesized and tested. An average overall reduction of more than 55% cycles with respect to standard RISC processors with DSP features is obtained. Such improvement together with locality and temporal correlation allows a reduction of power consumption, while standard interfacing technique ensures maximum flexibility.