In this paper, authors propose a linear array antenna using two bifilar helical antenna elements placed along the helix axis to reduce beam direction movement according to frequency change. The beam direction movement of this proposed array antenna is smaller than that of a conventional bifilar helical antenna. Also, the gain of this proposed array antenna is higher than that of the conventional helical antenna for a cross point angle of radiation patterns at the different transmit and receive(Tx and Rx) frequencies. The conventional helical antenna is suitable for vehicle antennas in mobile satellite communication systems such as the MSAT system because it owns circularly polarized omni-directional radiation pattern and its thin pole form. However, this antenna has a disadvantage that the beam direction in an elevation plane moves according to frequency change. In the proposed array antenna, the beam direction movement is about 9 smaller than that of the conventional bifilar helical antenna on condition that antenna total length is 4.83 λ0, antenna diameter is 0.12 λ0, and frequency change is from 0.957f0 to 1.043f0(f0 is center frequency and λ0 is free space wavelength at f0). Also, the Tx and Rx gains of this proposed array antenna at the cross point angle between Tx and Rx beams are about 2 dB higher than that of the conventional bifilar helical antenna on the same condition.

This paper proposes a directive antenna diversity reception scheme for an adaptive modulation/time division multiple access (TDMA)/time division duplex (TDD) system to achieve high quality, high bit rate and high spectral efficient data transmission in high mobility land mobile communication environments. In mobile stations, a directive antenna is applied to equivalently reduce the observed variation speed of the fading channel. At each branch, the offset frequency (foff) and foff-canceled fading variation are estimated to improve accuracy of the propagation path characteristics estimation even in high maximum Doppler frequency (fd) environments. Computer simulation confirms that the proposed scheme can achieve successful variable rate transmission in fast fading environments.

A new transmit permission control scheme applicable in multi-cell communication systems is proposed. In this scheme, by prohibiting the transmissions from the users with relatively high propagation loss to their connecting hub stations, level of multiple access interference is decreased, and hence throughput characteristics are improved. Moreover, we continue our discussion to propose two adaptive forms of the transmit permission control scheme, in which the prohibition condition becomes more intelligent by considering the level of the offered traffic loads to hub stations. These methods are utilized in a slotted Aloha random transmission of the spread spectrum packets, and on the uplinks of a low earth orbit satellite communication system as an example of the multi-cell systems. It is shown that the adaptive schemes exhibits significantly improved characteristics at all offered traffic loads in these systems.

This paper proposes an adaptive modulation system with a punctured convolutional code for land mobile communications to achieve high quality, high bit rate, and high spectral efficient data transmission in multipath fading environments. The proposed system adaptively controls the coding rate of the punctured convolutional code, symbol rate, and modulation level according to the instantaneous fading channel conditions. During good channel conditions, the modulation parameters are selected to increase the transmission rate as much as possible with satisfying a certain transmission quality. As channel conditions become worse, lower rate modulation parameters are applied or transmission is stopped. The performances in fading environments are evaluated theoretically and by computer simulations. The results show that the proposed system can realize higher quality transmission without the degradation in average bit rate compared to conventional adaptive modulation systems.

Exploitation of air interfaces for mobile communications is rapidly increasing because of diversified service demands, technology trends and radio propagation conditions. This paper summarizes the radio and optic interaction devices and systems that can solve the future problems resulting from spreading demands in mobile multimedia communications. The concept of the Virtual Free Space Network (Radio Highway Network) is proposed for universal mobile access networks that can support any mobile service or radio air-interface. As one example of the proposed network, the optical TDMA network for radio is analyzed and results of some theoretical calculations are shown.

This paper addresses approaches to enhancement of performance of the CMA (Constant Modulus Algorithm) adaptive array antenna in multipath environments that characterize the mobile radio communications. The cost function of the CMA reveals that it has an AGC (Automatic Gain Control) procedure of holding the array output voltage at a constant value. Therefore, if the output voltage by the initial weights is different from the object value, then the CMA may suffer from slow convergence because suppression of the multipath waves is delayed by the AGC behavior. Our objective is to improve the convergence characteristics by adopting the differential CMA for the adaptive array algorithm. First, the basic performance of the differential CMA is clarified via computer simulation. Next, the differential CMA is incorporated into the eigen-beamspace system in which the eigenvectors of the correlation matrix of array inputs are used in the BFN (Beam Forming Network). This BFN creates the optimum orthogonal multibeams for radio environments and works helpfully as a preprocessor of the differential CMA. The computer simulation results have demonstrated that the differential CMA with the eigen-beamspace system has much better convergence characteristics than the conventional CMA with the element space system. Furthermore, a modified algorithm is introduced which gives the stable array output voltages after convergence, and it is confirmed that the algorithm can carry out more successful adaptation even if the radio environments are changed abruptly.

Empirical studies confirm that the received radio signals in certain cellular systems are well modelled by Nakagami statistics. Therefore, performing relevant systems studies can be potentially useful to a system designer. A very useful statistical measure for characterizing the performance of a mobile radio system is the probability of outage, which describes the fraction of time that the signal-to-interference ratio (SIR) drops below some threshold. A more refined criterion for the outage is the failure to simultaneously obtain a sufficient SIR and a minimum power level for the desired signal. Thus, we derive new expressions for the probability of outage where a mobile unit receives a Nakagami desired signal and multiple, independent, cochannel Nakagami interferers. A salient feature of our results is that, unlike some previous studies, the outage expressions do not restrict the Nakagami fading parameter, m, to strictly integer values. Furthermore, since the received signals in mobile radio also experience log-normal shadowing, we analyze the case where the received signals are modelled by a composite of Nakagami and log-normal distributions. Outage probabilities are computed and graphically presented for several cases. The effect of specifying a minimum signal requirement for adequate reception is found to introduce a floor on the outage probability. It is also found that shadowing in macrocellular systems severely degrades the desired quality of service by increasing the reuse distance necessary for a given outage level.

Information capture is a very desirable and important function in portable computers. The "Multimedia Notebook" is a portable tool for capturing information in multimedia format, which includes photos, voice, and handwritten memos. Recent portable units, sometimes called PDA (Personal Digital Assistants) or Communicators, have PIM (Personal Information Manager) software and some communication facility. Their purpose is to enlarge the desktop environment to follow the user outside the office. This is one application of portable equipment, however we felt that hand-held equipment can also be used for more general information capture. In the past, information capture was limited, because people had to carry bulky equipment to the information source. Recent portable computers that have the capability to handle still and motion pictures, voice, and handwritten drawings allow the implementation of more information capture capabilities. Capture of handwritten notes has already been implemented on portable equipment like PDAs. However, this application doesn't make the most of its potential. We feel that the Multimedia Notebook should integrate handwritten memos with pictures and voice. The advantage is that users can capture what they watch and hear easily in a variety of media for later review. The information in each medium complements the others. When arranging the recorded information, it is easy to use each medium efficiently. We have examined the human interface and designed it for user-friendliness and to be comparable to pen and paper. The prototypes also have a capture buffer which can operate continuously to capture voice and pictures that would otherwise be lost because of the user's delay in starting to record.

The influence of cochannel, adjacent channel and intermodulation constraints on the capacity of the frequency band in the dynamic channel allocation problem is estimated. Algorithms including a backtracking phase with partial reassignment of currently assigned requirements are proposed. Numerical examples show a strong possibility of a 20% capacity improvement compared to the conventional strategies.

CDMA cellular land network (CCLN) consists of base stations connected to selector bank subsystem. In the case of considering only the voice traffics, CCLN can be designed based on E1/T1 physical line and HDLC protocol with fixed or variable length. However, it is necessary to support not only voice but also data traffics in CDMA cellular system. Thus, it is needed to use physical lines efficiently to increase bandwidth efficiency and transmission speed. However, the conventional CCLN has some problems that the bandwidth is wasted because each BTS has its own private line. In this paper, the method using Distributed Queue Dual Bus (DQDB) Metropolitan Area Network (MAN) as a CDMA interconnect subsystem (CIS) is considered, and the performances of conventional and proposed methods constructing CIS are analyzed by computer simulation. According to the simulation results, if the traffics from all mobile stations are uniformly distributed among all BTSs, the performances of both conventional and proposed methodology have turned out to be almost equal. However, the performance of methodology using the DQDB MAN is much better than that of conventional method, in the case that the traffics from all mobile stations are nonuniformly distributed.

This paper presents an improved neural network for channel assignment problems in cellular mobile communication systems in the new co-channel interference model. Sengoku et al. first proposed the neural network for the same problem, which can find solutions only in small size cellular systems with up to 40 cells in our simulations. For the practical use in the next generation's cellular systems, the performance of our improved neural network is verified by large size cellular systems with up to 500 cells. The newly defined energy function and the motion equation with two heuristics in our neural network achieve the goal of finding optimum or near-optimum solutions in a nearly constant time.

In the millimeter-wave propagation inside of figure U guideway of maglev, a multipath model using the ray-tracing method is presented. Prediction shows that delay spread is exceedingly small and high speed data transmission more than 100Mbps is possible without an equalizer.

This paper discusses advanced wireless communication technologies for achieving future high-speed mobile radios. Mainly, five technical fields are considered, that is, multi-level modulation for transmitting high-capacity information signal, advanced adaptive wireless system flexibly changing modulation level, symbol rate and traffic according to fading conditions, adaptive multicarrier system transmitting multimedia signals by changing the number of carrier according to the capacity of the signals, new CDMA techniques for mapping different bit rate services onto the same allocated bandwidth at the same time, and optical-linked microcellular communication system with millimeter wave air interface.

A new concept for a navigation and communication satellite system has been proposed. The navigation satellite system that forms the basis of the proposed system has been studied by one of the authors and extended to add a mobile communication function to the system. The satellite system consists of 15 satellites in quasi-geostationary orbit (QGEO) that have a geostationary altitude and high inclination and provide global coverage and positioning capability to the observer through only reception of the range measurement signals generated at the satellites, which are in the same configuration as the satellites in Global Positioning System (GPS), Three satellites out of the 15 satellite are designated to install a subsystem for mobile satellite communication in order to satisfy mobile communication convenience as required in a Future Air Navigation System's (FANS) concept of International Civil Aviation Organization (ICAO). The case studies of 15-satellites constellations demonstrate not only an acceptable positioning accuracy over the whole globe, but also an accuracy distribution weighted on the north pole region as an example of a weighted accuracy distribution. The addition of a mobile communication function suggests a unified system of satellite navigation and communication, which might provide convenience for the civil aviation industry, because the two functions currently depend on different systems.

In this paper, the spread spectrum code hopping (CH) system, which has some analogy to frequency hopping systems, is described. The CH system has robustness to code interference that restriction of kinds of PN matched filters (MFs) will cause. The mean acquisition time is shown by theoretical analysis and computer simulation. The acquisition rate results under a single code interference, which seriously affects direct sequence systems, and an asynchronous two-user channels are obtained. Moreover, using theoretical analysis and computer simulation, the bit error rate (BER) performance under single code interference is evaluated. It is shown that CH systems perform better than conventional ones under single code interference.

Mobile communications have been developing rapidly in recent years. In Japan, a new digital cellular system and digital trunked radio system were introduced. Soon a new personal communication system and road information system will be introduced. Other than those systems, many new mobile communication systems are being developed. These are new pager systems, future public land mobile communication systems, wireless card system and anti-collision radar system etc.

With a view toward the improvement of life-saving rate, the advancement of emergency radio system was attempted. The telemetry technique was introduced to the mobile communication from a running ambulance. A system was newly developed which enables us to transmit the information of an emergency patient from an ambulance to an emergency room of a hospital. This system can transmit an audio signal, physiological signals such as an ECG and a blood oxygen level, as well as a color image. In the experiment, the feasibility of this technique was verified. In the test of its practical usefulness, the following points were evaluated using a mobile telephone line and an emergency radio link. With the regular condition of the communication link, the stability of signal transmission was reasonably well. The fidelity of the transmitted signal was satisfactory for the use of an emergency medicine.

Wide bandwidth of 30MHz was achieved by 3-IDT SAW resonator filters using 36Y-X LiTaO3 substrates at 800MHz. The filter, which has fractional bandwidth of 3.6%, can be applied for several mobile communication systems. Low insertion loss of 1.7 dB was obtained by taking parallel arranged configuration, which proved to be 0.4 dB better than simple cascade-connected configuration.

Low-power technology for front-end GaAs ICs and hybrid IC (HIC) for a mobile communication equipment will be presented. For low-power operation of GaAs front-end ICs, new techniques of the intermediate tuned circuits, the single-ended mixer, dualgate MESFETs, and the asymmetric self-aligned LDD process were investigated. The designed down-converter IC showed conversion gain of 21 dB, noise figure of 3.5 dB, 3rd-order intercept point in output level (IP3out) of 4.0 dBm, image-rejection ratio of 20 dB at 880 MHz, operating at 3.0 V of supply voltage and 5.0 mA of dissipation current. The down-converter IC was also designed for 1.9 GHz to obtain conversion gain of 20 dB, noise figure of 4.0 dB, IP3out of 4.0 dBm, image-rejection ratio of 20 dB at 3.0 V, 5.0 mA. The up-converter IC was designed for 1.9 GHz using the same topology of circuit and showed conversion gain of 15 dB, IP3out of 7.5 dBm, and 1 dB compression level of -8 dBm with -20 dBm of LO input power, operating at 3.0 V, 8.0 mA. Another approach to the low-power operation was carried out by HIC using the GaAs down-converter IC chip. The HIC was designed for 880 MHz to show conversion gain of 27 dB, noise figure of 3.3 dB, IP3out of 3.0 dBm, image-rejection ratio of 12 dB, at 2.7 V, 4.5 mA. The HIC measures only 8.0 mm6.0 mm1.2 mm.

Mobile communication networks need public key cryptosystems that offer both low computation cost and user authentication. Tatebayashi et al. showed a key distribution protocol for such networks at Crypto'89 based on low exponent RSA. This paper shows that their protocol is not secure. We also present two types of secure and efficient key distribution protocols.