In this paper, we present an alternative design, RBMoM (Range-Based Mobile Multicast), for efficiently supporting multicast for mobile hosts on the Internet. The current version of Mobile IP proposes two approaches to support mobile multicast, which are remote subscription and bi-directional tunneling. The former provides the shortest routes for delivery of multicast datagrams to mobile hosts; the latter hides host mobility from all other members of the group (therefore, no any overhead in the multicast tree maintenance). RBMoM intends to trade off between the shortest delivery path and the frequency of the multicast tree reconfiguration by controlling the service range of the multicast home agent (MHA). Actually, we will find that remote subscription and bi-directional tunneling are the extremes of RBMoM. From the point of view of the MHA and the service range concepts, RBMoM is a generalization of both approaches and a unifying mobile multicast approach. The simulation results show that RBMoM can adapt to the fluctuation of both host movement and the number of mobile group members, and has much better performance than the current two IP mobile multicast solutions.

The paper proposes a transmitter diversity scheme with a desired signal selection for the mobile communication systems in which the severe cochannel interference (CCI) is assumed to occur at the base station. The feature of the proposed scheme is that the criterion of the downlink branch selection is based on the desired signal power estimated by the correlation between the received signal and the unique word at the matched filter. Moreover, the unique word length control method according to the instantaneous SIR is applied to the proposed scheme, taking account of the uplink transmission efficiency. Computer simulation results show that the proposed scheme provides the better performance than the conventional transmitter diversity in the severe CCI environments, and that the unique word length control method applied to the proposed scheme decreases the unique word length without the degradation of the transmission quality, comparing with the fixed unique word length method.

One major breakthrough on the communication society recently is the extension of networking from wired to wireless networks. This has made possible creating a mobile distributed computing environment and has brought us several new challenges in distributed protocol design. Obviously, wireless networks do have some fundamental differences from wired networks that need to be paid special attention of, such as lower communication bandwidth compared to wired networks, limited electrical power due to battery capacity, and mobility of processes. These new issues make traditional recovery algorithm unsuitable. In this paper, we propose an efficient algorithm with O(nr) message complexity where O(nr) is the total number of mobile hosts (MHs) related to the failed MH. In addition, these MHs only need to rollback once and can immediately resume its operation without waiting for any coordination message from other MHs. During normal operation, the application message needs O(1) additional information when it transmitted between MHs and mobile support stations (MSSs). Each MSS must keep an ntotal_h*n cell_h dependency matrix, where O(ntotal_h) is the total number of MHs in the system and ncell_h is the total number of MHs in its cell. Finally, one related issue of resending lost messages is also considered.

There are more and more information services provided on the wireless networks. Due to long network delay of wireless links, transactions will be long-lived transactions. In such a situation, the occurrence of handoff is inevitable, and thus a wireless link held by a mobile unit crossing cell boundaries might be forced to terminate. It is undesirable that an active transaction is forced to terminate. A queueing scheme has been proposed to solve the problem of forced termination of transactions in our previous research. However, when 2PL protocol is employed, suspending an active transaction will elongate the lock holding time and thus degrade the system performance. In this paper, we propose two guard channel schemes (GCS), static and dynamic, to reduce the probability of forced termination of transactions. In dynamic GCS, the number of channels reserved in a base station is dynamically assigned according to the number of transaction calls which may handoff to this cell while the number of guard channels is fixed in static GCS. An analytic model based on Markov chain is derived to evaluate the system performance. The correctness of this model is verified by simulation. The experimental results show that a significant improvement is achieved by using the dynamic GCS.

Nowadays, when people colloquially use the word "wireless," they almost always mean a portable telephone. Over the last 10 years, there has been tremendous growth in the mobile communications markets not only in Japan but also worldwide. For these 10 years, the most popular service has been dominated by voice communication. However, modern mobile communications systems are shifting their focus from solely voice communication to electronic mailing and Internet access. From now, we will evolve into a wireless multimedia society, where a combination of mobile communications and the Internet will play an important role. Wireless technology is the core of mobile communications systems. This article, which focuses on wireless technology, looks at how mobile communications systems have evolved over the last 10 years and looks to the future of advanced wireless technologies that will be necessary to realize a true wireless multimedia society in the coming decade.

In this paper we propose a mobile positioning method based on a recursive least squares (RLS) algorithm for suppressing the non-line of sight (NLOS) effects in cellular systems. The proposed method finds the position of a mobile station from TOAs measured by three BSs. Simulation results show that the proposed method has a fast convergence time and greatly reduces the positioning error especially in NLOS situations. Thus it is expected that the proposed method can be effectively used in a dense urban environment.

The concept of wireless ad hoc networking has unique features in which neither base stations nor wired backbone networks are required and a mobile node can communicate with a partner beyond the transmission range by multihopping. In this paper, innovations and issues in ad hoc network technologies are reviewed. The concept of a general-purpose ad hoc network is identified as a step toward next-generation ad hoc network development. The concept of an open community network is then presented as a vision for general-purpose ad hoc networks. An open community network is a novel information infrastructure for local communities based on wireless multihopping technologies, which may support an advanced information-oriented society in the twenty-first century. As a case study, an experimental system using PHS (Personal Handy Phone System) is described and some research issues for developing an open community network are identified.

Frequency-selective fading due to multipath propagation is serious hindrance in high-speed TDMA mobile communications. An adaptive antenna has been proposed to reduce the frequency-selective fading and realize path-diversity. This paper presents a criterion which selects multipath signals and weighting factors for combining them. First, we describe a selection criterion which chooses the multipath signals for the path-diversity. We propose a ratio of signal power to error power for the criterion. Furthermore, we propose weighting factors which realize approximately the maximal ratio combining. Computer simulation results show that the proposed selection criterion and weighting factors reveal excellent performance.

Causal message ordering in the context of group communication ensures that all the message receivers observe consistent ordering of events affecting a group as a whole. This paper presents a scalable causal multicast protocol for mobile distributed computing systems. In our protocol, only a part of the mobility agents in the system is involved in group computations and the resulting size of control information in messages can be kept small. Our protocol can outperform qualitatively the counterparts in terms of communication overhead and handoff complexity. An analytical model is also developed to evaluate our proposal. The performance results show that the proposed protocol is promising.

Bluetooth wireless technology is short-range and low cost wireless interface, which is optimized for mobile devices providing very low power consumption. However, a scope of Bluetooth application areas is not limited to mobile devices but expands to fixed equipment as well. Not only Bluetooth functions as cable replacement but also it can establish ad-hoc wireless network for voice and data simultaneously. Due to nature of 2.4 GHz ISM frequency band, Bluetooth is equipped with various data packets selection to minimize throughput degradation. Also, to secure connecting to the right target devices, Bluetooth includes authentication and encryption for communication links.

A hybrid system in which mobile terminals (MTs) themselves select whether to communicate directly or via base stations (BSs) from communication conditions, "cellularad-hoc united communication system," has been proposed by the authors. It has been confirmed to have effective channel usage and battery consumption, especially for MTs which tend to communicate with partners which are close together, such as operational mobile robots. In this paper, the hybrid system is examined with respect to handoff rate. This hybrid system uses two modes, a cellular mode and an ad-hoc mode. The former mode is for communication using BSs and the latter is for direct communication. Thus, there will be two kinds of handoffs. One is the ordinary one between BSs and the other is between the two modes. Such a system may suffer from frequent handoffs. Thus the handoff rate of the system was examined. However, by the addition of a simple hysteresis characteristic, the handoff rate was held down closer to that of a pure cellular system in a multipath environment.

This paper investigates the influence of the number of antennas, the angle difference between the direction of arrival (DOA) of the desired signal and those of interfering signals, and the antenna arrangement on the BER performance of the coherent adaptive antenna array diversity (CAAAD) receiver in the wideband DS-CDMA (W-CDMA) reverse link. Experiments assuming high-rate interfering users were conducted in a radio anechoic room using a three-sectored antenna with a 120-degree beam (maximum number of antennas was six). The experimental results showed that the degree to which the interference was suppressed from high-rate users of the CAAAD receiver was significantly increased by increasing the number of antennas, especially when the number of interfering users was larger than degree of freedom of the CAAAD. It was also verified that although the BER performance of the CAAAD receiver significantly improved compared to a single sectored antenna, the improvement remarkably decreased when the DOA difference between the desired signal and interfering signals was within approximately 10-15 degrees irrespective of the number of antennas. Finally, we show that the BER performance difference between the linear and conformal arrangements was small when using the three-sectored antenna.

In DS-CDMA (including W-CDMA), a received signal can be resolved into multiple paths to be Rake combined. An important design problem of the Rake receiver is how to accurately search the paths with a sufficiently large signal-to-interference plus background noise power ratio (SIR). This paper investigates the performance of a coherent Rake receiver using pilot symbol-assisted channel estimation with fast transmit power control, and thereby optimizes three key parameters: the total averaging period, Tavg, consisting of a combination of coherent summation and power summation; each period of the summations for measuring the average power delay profile; and path-selection threshold M from the generated power delay profile. We used a path search algorithm, which searches the paths that have M times greater average signal power than the interference plus background noise power measured in the average power delay profile generated using time-multiplexed pilot symbols. It was clarified by both simulation and laboratory experiments that when M = 4, Tavg = 50-100 msec, and the number of slots for coherent accumulation R = 2, the required average transmit Eb/N0 for obtaining the average BER of 10-3 is almost minimized with and without antenna diversity for both ITU-R Vehicular-B and average equal power L-path delay profile model, in which each path suffered independent Rayleigh fading. The paper also shows that based on the field experiments, the path search algorithm with optimized path-selection parameters is robust against actual dynamic changes in the power delay profile shape.

It is well-known that TCP often experiences severe performance degradation in mobile networks since packet losses not related to network congestion occur frequently due to host mobility. In this paper, we propose a new packet buffering method to address such a problem without the scalability problem in Mobile IP based networks. For this purpose, we first investigate the performance of TCP Tahoe without considering packet buffering through the simulation. Our simulation result shows that in most cases, the smooth handoff by the route optimization extension of Mobile IP standard cannot prevent the degradation of TCP performance due to handoffs, although it is designed to reduce the number of packets dropped during the handoff. It also shows that in utilizing the route optimization extension, the TCP performance sometimes becomes worse even than the case of the base Mobile IP unless its smooth handoff makes less than four packets be dropped during the handoff. Such results mean that at least for TCP, the smooth handoff is not useful unless the route optimization extension supports the buffering method, which makes handoffs be transparent to transport layer protocols by recovering the packets dropped during the handoff. We then investigate the effects of packet buffering on the performance of TCP. We modify the route optimization extension in order to support packet buffering at the base station, but it is a very minor change. Finally, we discuss some problems that should be addressed to recover the packets dropped during the handoff by the buffering method without giving a worse impact on the performance of TCP, and propose our solution to solve those problems.

The execution model of mobile code inherits from traditional remote execution model such as telnet that needs two conditions. First, the proper program must exist in advance in the remote system. Second, there should be a process in the remote system waiting for requests. Therefore mobile code also bears the same conditions in order to be executed in a remote system. But these conditions constrain an important aspect of mobile code, which is the dynamic extension of system functionality. In this paper we propose a new approach, named Function Message that enables remote execution without these two conditions. Therefore, Function Message makes it easy and natural for mobile codes to extend system functionality dynamically. This paper describes the design of Function Message and implementation on Linux. We measure the overhead of Function Message and verify its usefulness with experimental results. On the ATM network, Function Message can be about five times faster than the traditional remote execution model based on exec().

This paper presents the fast cell search time performance based on laboratory and field experiments of a 2-step cell search algorithm that uses scrambling code masking for inter-cell asynchronous wideband DS-CDMA (W-CDMA) mobile radio. The scrambling code is masked at different time positions during each scrambling period on the forward-link common control channel (CCH) to detect the scrambling code timing at the mobile receiver. Experiments were conducted using the CCH-to-dedicated traffic channel (DTCH) power ratio, R of 3 dB, 10 DTCHs, and 16 scrambling codes in a single-cell and two-cell models. The field experimental results show that the cell search time of about 600 msec was achieved in vehicular environments at the detection probability of 90% and the average received Eb/N0 (N0 is the background noise without interference) of 13-15 dB for DTCH, even in the worst case scenario when the received signal power ratios of the CCH from two cell sites were 0 dB. The cell search time that was achieved with the 3-step cell search algorithm previously proposed by the authors is estimated from the experimental results; the cell search can be accomplished within about 720 msec at a probability of 96% for 512 scrambling codes and 16 scrambling code groups.

The Internet is a heterogeneous and rapidly evolving environment. New information services have been added, modified, and diversified, while legacy services have been abandoned. Users' requirements for services are also changing very quickly. It is becoming very difficult to find required information services from extremely huge amount of information in the Internet. It is necessary to design information service system, which can meet user's heterogeneous requirements for services, adaptability of services to cope with ever-changing situation and to provide assurance. Faded information field architecture and Push/Pull Mobile Agent (MA) technologies are proposed as basic components of autonomous information service system to achieve these goals. The system is proposed from users' and providers' point of view, therefore we present a technique for balancing users' and providers' communication cost based on `through rate' for faded information field realization. On the basis of this technique, autonomous information allocation algorithm is proposed, in which each node may determine information amount based on push/pull cost. The effectiveness of the proposed algorithm is shown through simulation.

GSRI Pragmatic TCM, which is a Pragmatic Trellis Coded Modulation allowing bandwidth expansion, has been proposed. In [1], it is shown that this scheme can achieve higher performance than conventional Pragmatic TCM scheme. On the other hand, a real-time video multimedia communication is one of the possible applications for the third generation mobile communication systems. This video multimedia communication system needs a multiplexer which mixes various types of media such as video, voice and data into a single bitstream. ITU-T has standardized H.223 Annex A, B, C and D multimedia multiplexing protocols for low bit-rate mobile communications. This paper evaluates the performance of the GSRI Pragmatic TCM with an application of a mobile multimedia system using H.223 Annex D multiplexing scheme and MPEG-4 video coding.

The a-Si TFT characteristics were studied for process temperatures of as low as 100C. The a-Si TFT kept normal characteristics for process temperature of as low as 150C. The a-Si TFT bias temperature stability was evaluated and degradation of stability initiated at around 150C. The characteristics of a-Si TFT fabricated on plastic substrates were the same as those of a-Si TFT fabricated on glass substrates at low process temperature. TFT-LCD fabricated at a process temperature lower than the glass transition temperature of plastic substrates indicated good display image. These results indicate the possibility of fabricating TFT-LCD on plastic substrates, which would promote the application of a-Si TFT-LCD for mobile devices.

Blind channel estimation algorithm which is applicable to the time-variant channel under frequency-selective fading is proposed. The condition on the blind channel identifiability using temporally and spatially oversampled data is shown. The proposed algorithm consists of two stages. At the first stage, the channel equalization matrix is estimated by taking account of the time-variant characteristics of the channel. At the second stage, the signals and the channel matrix are alternately estimated by using the finite alphabet property of the transmitted symbols. Periodical return from the second stage to the first makes the blind estimation algorithm feasible for the time-variant channel with fast fading. The simulation results confirm the fast convergence property and the effectiveness of the proposed algorithm in coping with the frequency-selective fading.