In this paper, we propose the distributed stable marriage problem and apply it to planning for cooperative works of autonomous mobile robots and battery charger stations. We develop and analyze a distributed algorithm to determine the partner by message communication.

This paper proposes a novel Doppler frequency shift compensation technique to achieve terrestrial and low earth orbit (LEO) satellite dual mode DS/CDMA terminals robust to high Doppler shift and multipath fading. In order to satisfy the requirements of wide dynamic range and high accuracy simultaneously, the proposed scheme employs two stage compensation scheme, i.e., coarse compensation to keep dynamic range of about 100 kHz and fine compensation to satisfy its resolution of about 30 Hz, using block demodulation technique. Computer simulation results show that the proposed scheme can sufficiently compensate for the offset frequency up to the range of about 100 kHz at the terrestrial and LEO satellite combined mobile communication systems.

A circularly polarized omnidirectional antenna consisting of a vertical sleeve dipole and three pairs of titled parasitic elements set around it is proposed. The antenna is useful to mobile communication because the use of circular polarization allows us to suppress the effect of multi-path reflection waves (inverse rotation) caused by building walls and surface of the ground. The antenna with an omnidirectional pattern has a simple structure without a feeding network for radiating circular polarization. To understand the radiation characteristics of the proposed antenna, an approximation theory using the induced electromotive force method is introduced. As an example, using a fixed spacing of a quarter wave-length between the vertical dipole and the parasitic elements, the possibility of generation of circular polarization is examined. Then the computational results of the axial ratio and the input impedance are compared with the results of the numerical analysis using the moment method and the experimental result. The radiation characteristics of the antenna can be understood by using the approximation theory introduced here. As a summary of the study, the contour map of the axial ratio of circular polarization is depicted using the moment method. For practical design of this antenna, a small correction factor should be multiplied to the calculated results. From the experimental results, the proposed antenna has a gain of 2 dBi and 3 dB band-width with an axial ratio of about 8%.

We analyzed the operation speed of the resonant tunneling logic gate, MOBILE, using a simple equivalent circuit model and varying parameters of I-V characteristics and capacitance of RTTs(resonant tunneling transistors). The switching time for large peak-to-valley(P/V)current ratios is smaller at small Vbmax(maximum bias voltage), but larger at large Vbmax than that for small P/V ratios in the case of present I-V characteristics with flat valley current. It is also demonstrated that the MOBILE operation fails if the bias voltage rises too fast, when the capacitance of the load and the driver is different due to the displacement current through the capacitance. These behaviors can be explained by considering the potential diagrams of the circuit.

For Nakagami-Rice fading environment which seems to become a principle propagation environment in the next generation wideband and high-capacity mobile systems such as personal communications, we have previously proposed an approximated evaluation scheme for wideband digital transmission characteristics such as errors due to intersymbol interference of multipath waves. We called the scheme 'Equivalent Transmission-Path (ETP) Model.' In this paper, through a discussion about more general equivalent propagation channel expressions, we clarify a theoretical foundation of the ETP model and extend the model to have an ability of expression of instantaneous fading condition varying with time. Also the appropriateness of the instantaneous expression is examined by a computer simulation analysis. Based on this model, statistics of link quality and service availability in Nakagami-Rice fading environments are discussed.

Microcellular systems are suitable as personal mobile communication systems because of their high channel re-use efficiency and low transmission power. To implement a microcellular system, the antennas of base stations should be low enough, compared to the buildings around them, to reduce the interference to or from other base stations. In high-speed digital mobile radio communications, the time delay spread caused by multipath propagation is a significant factor in determining the maximum data transmission rate. In the case of a low-antenna-height microcellular system, the propagation characteristics rapidly change when the mobile terminal moves from a line-of-sight (LOS) location to a non-line-of-sight (NLOS) location. In this paper, the time dealy spread characteristics under LOS and NLOS conditions are examined using a geometrical street model which has a reflecting wall at one end of the street on which the base station is located. The RMS delay spreads are calculated using optical ray theory, taking into consideration the wedge diffraction on the street corner. If a reflecting wall exists, the RMS delay spread increases as the mobile terminal moves away from the base station under LOS conditions, or away from the street corner under NLOS conditions. The calculated results agree with the experimental results if measuring equipment noise is taken into consideration.

For mobile/personal satellite systems, an ARQ protocol with low transmitter/receiver complexity as well as high throughput performance in a long Round-Trip-Delay (RTD) and even in a bad channel condition is required. In this paper, a new Selective-Repeat (SR) ARQ with multicopy retransmission is proposed and a performance on an AWGN channel is analyzed. The proposed scheme can be viewed as a modified version for SR + Stutter (ST) Scheme 2 [6]. The basic idea of the strategy is to repeat only erroneous blocks stored in the vN block transmitter buffer multiple times, when v consecutive retransmissions in SR mode are received in error, where N denotes RTD in blocks. Numerical analysis and simuration results in the case of N block transmitter/receiver buffer show that the proposed scheme presents better performance than SR + ST scheme 2 of 2N block buffer, especially that the robustness in the high BER region is remarkable.

This paper compares the performance of an indoor cellular system in terms of capacity and channel assignment delay for different Dynamic Channel Assignment (DCA) and Fixed Channel Assignment (FCA) schemes. We refer to specific group of DCAs, namely Channel Segregation and Reuse Partitioning (RP). Our main concern is to show that these DCA schemes offer better performance than FCA. Since the structure and floor layout of a building will have a major influence on the propagation and hence on the cell shape, a path loss simulator is developed for predicting the path loss which is used in evolving base station layouts. Computer simulation, based on Monte Carlo method, is carried out using the path loss values and the base station layouts. The results indicate that increased traffic capacity can be achieved with all DCAs in comparison with FCA. The highest capacity and a shorter channel assignment delay are delivered by Self-Organized Reuse Partitioning DCA scheme.

This paper considers the evaluation of the acquisition performance for an access channel preamble based on the random access procedure of direct sequence code division multiple access (DS/CDMA) reverse link. The parallel acquisition technique that employs the single-dwell and multiple-dwell (double-dwell) detection schemes is investigated. The acquisition performance for two detection schemes is compared in terms of the acquisition probablity and the mean acquisition time. The parallel acquisition is done by a bank of N parallel I/Q noncoherent correlators. Expressions on the detection, false alarm, and miss probabilities of the single-dwell and multiple-dwell (double-dwell) detection schemes are derived for the multiple H1 cells and multipath Rayleigh fading channel. Comparing the single-dwell detection scheme with the multiple-dwell (double-dwell) detection scheme in the case of employing the parallel acquisition technique in the reverse link, the numerical results show that the single-dwell detection scheme provides a better performance.

A pilot symbol-assisted coherent multistage interference canceller (PSA-COMSIC) using recursive channel estimation is proposed for DS-CDMA mobile radio cellular systems. In the proposed scheme, since the channel variation due to fading is recursively estimated at each interference canceling stage, the accuracy of channel estimation is successively improved. The bit error rate (BER) performances against average Eb/N0 (signal energy per bit-to-noise power spectral density ratio) and capacity in the isolated cell are investigated by computer simulations. The simulations demonstrate that the capacity using the PSA-COMSIC with recursive channel estimation is about 1.6 times higher than that of the conventional matched filter receiver with channel coding and bit-interleaving in the interference-limited environments.

The reverse link performance of coherent multicode DS-CDMA [4], [5] under multipath Rayleigh fading environments is evaluated by computer simulation. It is demonstrated that the combined use of pilot symbol assisted (PSA)-coherent RAKE, channel coding, antenna diversity, and transmit power control is powerful in lowering the required signal energy per information bit-to-interference plus additive white Gaussian nose (AWGN) power spectrum density ratio (Eb/Io) which is an important parameter in determining the link capacity. It is also demonstrated that with slight performance degradation, high rate data transmission is realized by using multiple orthogonal spreading codes in parallel (orthogonal multicode transmission). Based on the simulated link performance, the reverse link cell capacity and link budget are also evaluated. It is found that parameter η=Io/No plays an important role in controlling the cell capacity and the maximum allowable path loss, where No is the AWGN power spectrum density.

This paper is concerned with the study of fast-frequency-hopped spread-spectrum multiple-access (FFH-SSMA) digital systems employing antenna diversity and noncoherent binary frequency-shift-keying (FSK) modulation operating through an indoor radio multipath Rayleigh channel. The diversity technique of equal gain combing (EGC) is considered in our study. It is assumed that the frequency-hopping rate is equal to the bit rate.

In this paper, we propose a timing constrained database system which accesses a database at a host computer via a mobile support server with a wireless portable computer running in mobile computing environments, so that we can provide seamless database access between a communication cell and the host computer even if the user of the portable computer moves from one communication cell to another. Then, we also provide some new kind of database cache algorihm, such as all-cell-cache, neighbour-cell-cache, 1-cell-skip-cache, 2-cell-skip-cache and 3-cell-skip-cache methods, each of which manages the data downloading and uploading among the host database and some cell databases at the mobile support servers so as to minimize the database access fault probability when the user moves from one communication cell to another. And, we show the averaged database access time and the averaged database cache hit ratio which are computed by simulating each of the above database cache algorithms with random variables generation method. Finally, we conclude that each above cache alogorithm is advantageous to the database in mobile computineg einvironments.

In future mobile radio, high-speed transmission and efficient spectrum utilization will be important. However, multipath propagation with large delay difference and cochannel interference are obstacles to the advanced mobile communication system. An adaptive antenna can suppress multipath signals and cochannel interference signals. This paper reviews basic performance of multipath fading reduction and cochannel interference suppression using the adaptive antenna. After a brief explanation of adaptive antenna concepts, we show simulation and experimental results of the fading reduction. It is pointed out that the adaptive antenna cancels multipath signals with large delay difference strongly. This feature is very important for high-speed TDMA systems. Moreover, it is shown from simulation results that the adaptive antenna improves the spectrum efficiency by suppressing the cochannel interference signals.

In this paper, we present an exact analysis and an efficient matrix-analytic procedure to numerically evaluate the performance of cellular mobile networks with hand-off. In high-capacity micro-cell cellular radio communication networks, a cell boundary crossed by moving users can generate many hand-off attempts. This paper considers such a priority scheme that some channels and buffers are reserved for hand-off calls to reduce the forced termination of calls in progress. Performance characteristics we obtained include blocking probability, channel utilization, average queue length and average waiting time for hand-off calls. Using the matrix-analytic solution for the stationary state probability distribution, we also derive the probability distribution of the waiting time of a hand-off call. Numerical results show how priority can be provided to hand-off calls according to the number of reserved channels and buffer size. They also clarify the effect of the hand-off priority scheme on the standard deviation of waiting time of a hand-off call.

This paper is a brief survey of mobile applications of meteor burst communications (MBC). Though the capacity of MBC systems is generally not large, this unique long distance communication method has at least two selling points when applied to mobiles. First of all, it is cheap. Secondly, it can easily offer nationwide seamless service. Thus, since the late 1980s, mobile MBC systems have been attracting interests of the industry. Although MBC is today a well established communication technique, there are some difficulties to be overcome before it is widely applied to mobile systems. Two most serious problems are the rather large antenna size and high transmitter power inherent to this beyond line of sight communication which relies on weak reflections of low VHF (typically 35 to 50 MHz) radio waves from ionized meteor trails. Some reduced sized antennas which can be mounted on the roofs of trucks have been tested. The problem of large peak power (a few hundred watts for mobile remotes) is much alleviated by the very low duty cycle (usually less than 1%) of remote transmitters due to their bursty transmissions responding to the probe signals from the master station via infrequent meteor reflections. In this paper, some land and maritime mobile MBC systems are brieflyintroduced.

The paper deals with the evaluation of performance of current cellular systems which are required to accommodate in an already operating system a wide range of new services, with different quality requirements (on delays, retransmission rates, etc.), and often characterised by a high burstiness (i. e. with relatively short traffic bursts, interleaved by comparatively long silence periods). To this end, an extension of packet communications is appealing for its inherent flexibility; standardisation of packet protocols for data transmission over idle GSM channels is in progress, and a similar service exploiting AMPS radio and network resources is already specified as Cellular Digital Packet Data. In both cases voice traffic retains a higher priority. The paper focuses on the evaluation of the effect of this additional traffic on existing voice traffic in a GSM Phase 2+ system. Although voice calls experience the same channel availability, their performance are worsened by the higher co-channel interference due to the higher average channel occupancy. This impairment cannot be tackled, as a matter of course, by increasing the re-use distance as this would affect the overall system capacity. The paper suggests the use of smart planning strategies capable to ease control of interference levels with a negligible impact on system complexity and signalling load.

This paper investigates the performance of an integrated voice and data transmission protocol that can be used in mobile communication networks, e.g. mobile cellular and LEOGEO satellite networks. Voice and data are concentrated at place such as base station in a cellular network. Time sensitive voices are supported by the concentrator in the manner of TDMA. Loss sensitive data are collected, stored, and transmitted using idle TDMA slots. Data users transmit data to the concentration point using ALOHA protocol. Characterization of data arrivals to the concentrator is done by the method of moment matching. The emphasis of this study is on the data performance in terms of packet loss rate, average buffer occupancy, and mean packet waiting time. It is demonstrated through numerical examples that a buffer of reasonable size is good enough to offer satisfactory performance. The analysis is also validated by computer simulations.

Fundamental microwave key devices used in achieving compact mobile/portable telephones (raidio units) are discussed. The historical development flow of the systems and radio units are introduced, with respect to the 800-/900-MHz and 1.5-GHz Japanese cellular radio systems. The design concept of the developed radio units is briefly described. Tehnical requirements for RF circuits are reviewed and the developed key devices are practically applied to the circuits. Key factors in the requirements are also shown. Finally. future trends fro the key devices are surveyed from the stand point of achieving a smaller and more light weight pocket radio unit.

A multi-terminal serial optical link(MSOL) achieves very simple and cost effective radio cell configurations because only one pair of fibers is needed. In addition, low cost Fabry-Perot laser diodes(FP-LDs) can be employed. MSOL has a substantial problem in that the beat noise degrades the C/N in the up-link. To reduce this noise, we propose using an automatic wavelength-offset control(AWOC) circuit. The AWOC circuit offsets the LD wavelength by controlling the laser bias current to minimise the RF band beat noise which is inherent in MSOL systems, and enables high C/N optical-microwave transmission. An experimental MSOL consisting of 5 radio access stations, each equipped with AWOC, is constructed to estimate the noise free dynamic range for 800-MHz 20-carrier signal transmission. The up-link comprises a single mode fiber connecting five 1.3-µm FP-LDs operating at 0.2 mW. The down-link consists of a single mode fiber and one 1.3-µm Distributed Feedback type Laser Diode(DFB-LD) emitting at 4.0 mW. The experimental device achieves over 15 dB noise reduction compared to MSOL without AWOC in the temperature range of 0 to 40. By using the proposed AWOC, MSOL can achive low cost optical fiber RF microcell systems that are easy to install. Additionally, when we install MSOL in the radio base station, the links become more cost effective than coaxial cable links; they offer a wide dynamic range and higher transmission quality.