Technical advances in the development of portable computers and wireless communications enable users to take part in distributed computing even while moving. The resulting environment is subject to be constrained by the mobility of users and the nature of the cordless medium. In this paper we propose a commit protocol for providing low-powered mobile hosts with two phase commit service which is a powerful technique to implement atomic actions in distributed systems, with some important aspects such as low power consumption, efficient mobility management, subject oriented service binding and effective disconnection handling to well adapt to a mobile computing environment.

As a means of CDMA network evolution toward future wireless services, a spectral overlay of narrowband CDMA (N-CDMA) and wideband CDMA (W-CDMA) systems is proposed in [8]. In order to justify the overlaying strategy, the reverse link capacity is examined in the same work. Although the capacity of conventional CDMA cellular systems is usually limited by the reverse link, the limit could occur at the forward link depending on the transmission technologies adopted by specific CDMA proposals. Especially, the number of users that can be simultaneously accommodated in the system would be limited by the forward link in future mobile service environments where unequal traffic is offered between two links. In this paper, we first examine the forward link capacity of the spectrally overlaid narrowband and wideband CDMA (N/W CDMA) system. And we compare it with the reverse link capacity to obtain the overall performance. The effects of various parameters on the capacity of N/W CDMA system are numerically evaluated for different mobile environments.

On the reverse (mobile-to-base) link of direct sequence code division multiple access (DS-CDMA) mobile radio, closed-loop fast transmit power control (TPC) must be sufficiently fast to track fast multipath fading. However, in urban areas, the line-of-sight (LOS) path may appear abruptly when a mobile station appears from behind a building and later suddenly the LOS may disappear, resulting in an abrupt path-loss change in the order of 30 to 40 dB. This "on-off" path loss change can be considered as a special case of shadowing. This "on-off" shadowing causes two problems at the base station: generation of severe multiple access interference (MAI) to other users when the LOS path appears and degradation of the quality of its own signal when the LOS path disappears. This paper proposes a new closed-loop fast TPC based on Markov-state transitions (called Markov fast TPC). State transition is determined by the past history of the received binary TPC commands sent from the base station. The TPC step size is associated with each state. By changing the step size between as small as 0.8 dB and as large as 4 dB, the Markov fast TPC can better track "on-off" shadowing as well as multipath fading compared to conventional one-state closed-loop fast TPC. A new SIR estimation method used in TPC command generation is also proposed. The TPC error is evaluated by computer simulation to demonstrate the adaptability of the proposed Markov fast TPC in a Rayleigh fading channel superimposed by "on-off" shadowing.

The world of mobile communications has undergone dramatic changes in recent years. Since the Personal Digital Cellular (PDC) system of digital mobile communications became commercially available in Japan in 1993, the number of subscribers has increased to the extent that almost 30% of the Japanese population are subscribed. Furthermore, the increasing sophistication of communications, such as the growing popularity of the Internet and expansion of our spheres of existence, have led to demand for new applications, such as use on a global scale. Many new technologies are also being introduced, such as the IMT-2000 system and the IN system which are slated to be introduced at the end of 2000. Based on the above and in view of the increasing scale and sophistication of mobile communications networks, the time has come to reexamine the configuration within networks of SCPs, which perform subscriber data management and service control. This paper focuses on the functions of subscriber data management and service control, classifies data necessary for mobile networks and using the signal number of common networks as a guide considers the optimum arrangement of data and control nodes. The paper also examines reliability measures for SCPs to ensure the reliability of increasingly large-scale networks.

A model that combines free-space loss (proportional to the square of distance d) and excess loss has been known to assess the microwave line-of-sight (LOS) path loss in street microcell environments. The excess loss represents the effects of shadowing obstacles. We measure the path loss at the 3.35, 8.45, and 15.75 GHz frequencies in an urban environment, and analyze the distance characteristics of the pass loss for mobile antenna heights of 2.7, 1.6, and 0.5 m. Results show that using a new model that bases on a dα formula instead of d2 in the conventional model produced a better fit to the measured data. They also show that lowering the mobile antenna to a height of 0. 5 m made it possible to virtually ignore the excess loss factor and, instead, use the dα formula to assess the path loss characteristics.

An ad hoc wireless network is a collection of mobile hosts that self-forming a temporary network without any required intervention of centralized system. In such environment, mobile hosts, which are not within transmission range from each other, require some other intermediate hosts to forward their packets to form a multi-hop communication. In this paper, an ad hoc network is modeled as a graph. Two nodes within the transmission range of each other are connected by an edge. Given a finite set of mobile nodes, a finite set of edges and a new multicast request, the wireless multicast tree problem (WMTP) is to find a multicast tree for the request so that the multicast loss probability is minimized. We prove the WMTP is NP-complete and a heuristic algorithm, called Degree-Based Multicast Routing Algorithm (DBMRA), is proposed. Based on the DBMRA, one algorithm was proposed to establish backup nodes for the multicast tree to improve the reliability. A node is needed to be backup only when it has a high probability to disconnect the multicast tree seriously. The qualification of a node to be backup is subject to a computed threshold, which is determined by a statistic analysis. The theoretical and experimental analyses are presented to characterize the performance of our algorithms.

There is currently a need for development of a new frequency band to enable creation of next-generation mobile communication systems. Of the potential bands, the 3 GHz and over microwave band holds the greatest promise. Experimental studies on the delay characteristics of multipath propagation must be conducted in order to achieve high-speed transmission in the microwave band. We have developed a system for measuring the microwave broadband propagation delay profile over 100 MHz spread bandwidths in the 3, 8 and 15 GHz bands. Our experiments confirmed system performances of 20-ns resolution, 40-µs maximum measurable delay, relative amplitude error of within 3 dB and dynamic range of over 60 dB. We used our system to measure delay profiles on an urban area with line of sight, particularly, in terms of the effects of mobile antenna height. Typical examples are presented. Analysis showed that delay spreads increased with transmit/receive distance and decreased with the higher antenna height.

This paper discusses microwave path-loss characteristics as a function of mobile antenna height in an urban line-of-sight environment. Measurements were made in metropolitan Tokyo with high-density buildings, using base station antenna heights of 4 and 8 m. We describe the path-loss characteristics of vehicle-mounted mode (mobile antenna height is 2.7 m) and portable mode (mobile antenna heights are 1.6 and 0.5 m). Dependence of path loss on the distance between base and mobile stations was analyzed. This reveals that the break points shift to the near side in the vehicle-mounted mode. This phenomenon can be interpreted by the existence of an effective height h of the road. The typical value of h was found approximately 1.4 m. In the portable mode, on the other hand, break points were not observed. The mobile antenna heights (1.6 and 0.5 m) in this mode are close to or less than the average height (1-2 m) of pedestrians on the sidewalk; and the received waves at the mobile station are often disturbed by pedestrians. This explains the nonexistence of break points in portable mode. The average attenuation coefficients is observed 3.2 in this mode. The attenuation coefficients tend to be larger at lower base station antenna heights and narrower road widths.

This letter proposes a diffusion model that considers both mobility and multimedia based on the user population process to examine the effects of multimedia in mobile communications. As an application example of this model, the shared bandwidth that can be used by one user in packet communications is evaluated. In this model, the user speed and variation in the number of users in a cell are interrelated with respect to mobility. By examining the shared bandwidth behavior based on multimedia teletraffic characteristics, assuming that the number of simultaneously-communicating users within a cell have self-similarity, we found that shared bandwidth and its variance are not dependent on self-similarity but that variance in the shared bandwidth is dependent on user speed.

In this paper, efficient data transmission methods in wire and wireless interworking environments are studied in the case of handover occurring. To provide efficient mobile data service based on TCP, the wire and wireless interworking module with analysis function of TCP frame header protects the duplicated transmission of TCP frames. Also, by using the forwarding mechanism of status information and buffered data in the interworking module, it is possible to recover frame loss occurring in handover quickly. According to simulation results, proposed method has better performance than conventional method in view of throughput and delay. The reason is due to the fact that duplicated transmission is prevented and data recover is performed very quickly because buffered data is forwarded without loss in the case of handover.

Multimedia mobile communication systems with high-speed radio transmission supported by asynchronous transfer mode (ATM) technologies have been intensively studied over the last few years. Smaller radio zones termed microcells and picocells will be used in this kind of mobile communication systems for the purpose of high-speed radio transmission. When the coverage of a radio zone is smaller, the amount of traffic per radio zone is relatively low. It is not possible to use the cable circuits connecting the switch and base stations in an efficient manner because of the lack of the scale effect of traffic. With smaller radio zones, moreover, handoff occurs frequently as a mobile station moves. The switch is required a large capacity to handle the processing of frequent handoffs. This paper proposes a mobile network architecture controlled by the concentrated grouping of base stations. A special feature of this configuration is the ability of the network's switches to efficiently accommodate numerous base stations that control small radio zones. It can also lighten the handoff control load of switches; the effect of handoff frequency reduction is evaluated with computer simulation.

This paper presents the radiation characteristics of a circularly polarized conical beam spherical slot array antenna for applying to the mobile satellite communication subscriber. The structure of the antenna is easy to fabricate i. e. , a ring of perpendicular slot pairs cut on an outer surface of a concentric conducting spherical cavity enclosed by the conducting conical surface with the simple feeding structure, and a linear electric probe excited at the center of the inner surface of the cavity. Radiation fields of a spherical slot array antenna are calculated by superposing the patterns of all the slots. From the numerical results of the radiation pattern, in both elevational and azimuthal planes, it is obvious that the conical beam is realized. The elevational beam direction is low, which is suitable for installing in the land mobile subscriber unit located far from the equator. The tracking system is not necessary because the azimuthal pattern is omnidirectional. Directivity of the antenna for various spherical radii and angles of slot positions are illustrated as the guidelines for the design. Experimental results are in good agreement with the predictions.

Cell loss is one of the most important metrics of quality of service in ATM mobile communication systems. This loss can be suppressed by introducing buffer memories in the network, but that sacrifices delay. This paper proposes a lossless handover scheme for ATM mobile communication networks that can suppress delay fluctuations, and presents a subjective evaluation of MPEG2 images with various buffer memory sizes.

Even though BiCMOS process has an ability to make both BJT and MOSFET on single-chip, only BJT has been used for BiCMOS Si-MMIC LNA because of its low noise and high gain performance under low d. c. supply power. But the distortion performance of BJT should be improved for the receiver applications in some wireless systems. In this paper, intermodulation distortion characteristics comparison is carried out between BJT and MOSFET fabricated in the same BiCMOS process by the analysis based on the simplified transistor models with extracted device parameters. The analytical result shows that MOSFET has lower intermodulation distortion characteristics compared with BJT, and the result is evaluated by the measurements. In order to obtain both low distortion and low noise characteristics, a two-stage Si-MMIC LNA is developed by using BJT as the 1st stage and MOSFET as the 2nd stage of LNA. The fabricated LNA performs NF of 2.45 dB, gain of 19.3 dB, IIP3 of14.6 dBm and OIP3 of 4.7 dBm under 3 V/7.2 mA d. c. supply power.

Technologies used to characterize and compensate nonlinearities in microwave power amplifiers are discussed. First, a complex power series representation that allows both amplitude and phase nonlinearities to be dealt with simultaneously is proposed, and in order to estimate the 3rd-order complex coefficient phase of practical amplifiers, two kinds of experimental measurement methods are proposed. Next, the fundamental circuit configuration of IF cuber predistortion linearizer that compensates 3rd-order intermodulation distortion is derived from a nonlinear analysis using complex power series representation. Two practical cuber predistorters for the 6-GHz TWTA and the 800-MHz FET-PA are demonstrated. Moreover, the unique nonlinear compensation technology of side-band inversion is introduced for microwave relay system using TWTAs. Finally, the self-adjusting feed-forward (SAFF)-PA developed for digital cellular base stations is reviewed.

In this paper, we describe a new way of mobility support for the Internet and Intranet called "Unified Access." Different from other similar proposed technologies like Mobile IP, our scheme is more easy to use, secure, and have the full backward compatibility with existing equipments which are already used.

This paper proposes a phase-rotating phase-shift keying (PSK) modulation and shows that its narrow-band version is suitable for Viterbi equalization. The proposed PSK has the following features: 1) a spectrum shaping of the transmit/receive filters does not need to be restricted to the Nyquist criterion; 2) the transmitted data sequence is rotated for every symbol in order to reduce noise-correlation at the receiver. First, this paper discusses a performance degradation of bit error rate of Viterbi equalizers in the presence of the sampling timing offset or under time-dispersive frequency selective fading. Next, computer simulation confirms that π/2-shifted binary PSK with narrow-band spectrum shaping filter, which includes offset QPSK for its special case, solves the above mentioned performance degradation, keeping good spectrum efficiency equal to M-ary PSK.

This paper proposes a newly developed dual-frequency antenna for 800 MHz and 1500 MHz band use. A uniformly spaced array configuration, originally designed for a 800 MHz analog system, is extended to yield dual frequencies operations. An important characteristic of a base station antenna is low sidelobe level in order to suppress inter-cell interference. In the case of a uniformly spaced array configuration, sidelobe levels are increased by the emergence of grating lobes at higher frequencies. Electrical beam tilt also degrades the sidelobe level. As does the change in the excitation coefficients of the array elements at higher frequencies. These three factors are studied theoretically to yield practical sidelobe levels. One more important beam characteristic is the sector beam in the horizontal plane. The same beam width in two frequency bands is achieved by designing the novel reflector shape and determining the proper array element positions in front of the reflector. Practical antenna characteristics are confirmed by designing, manufacturing, and testing a base station antenna.

TCP Redirection (TCP-R) is an extension of TCP, which maintains active TCP connections when the disconnection occurs due to IP address changes. In mobile computing environments, IP addresses may be changed frequently as the host moves across subnets or changes network devices. However, it is difficult for most stateful network applications to work continuously in that situation. There is much research to support such dynamics in the network layer, but these attempts in the IP layer tend to incur some complexity. This paper intends to investigate the end-to-end mobility support in the transport layer. We developed a simple redirection mechanism for TCP, which enables us to keep our working activities continuous without any intermediate agents for IP packet forwarding. We also show that TCP-R enables the intentional replacement of IP addresses, which is useful for certain network services. We implemented and evaluated a prototype of TCP-R. The measured performance indicates that TCP-R can realize continuous operation with minimal overhead and complexity.

In a mobile computing environment, in which communication channels are limited and have low-bandwidths, mobile transactions are long-lived and frequently disconnected with their wireless network in processing. Such peculiarities of mobile transactions make existing transaction scheduling schemes inadequate and raise new challenging research problems. In this paper, we propose a new scheduling scheme called OTS/MT (Optimistic Timestamp Scheme for Mobile Transactions) for mobile transaction scheduling. OTS/MT is based on an optimistic approach that is suitable for low data contention, and prevents indefinite postponement and cascading delay which are major drawbacks of the existing optimistic concurrency control scheme and the timestamp ordering scheme. In addition, the OTS/MT algorithm is inherently a deadlock-free scheduling scheme. In order to schedule mobile transactions, OTS/MT postpones the detection of conflict between mobile transactions until transaction commit time to improve the performance deterioration of TO. In this paper, we attempt to show that this application of optimism to TO is justified by way of simulation.