In the future asynchronous transfer mode (ATM) networks, an efficient virtual path (VP) control strategy must be applied to guarantee the network has high throughput with tolerable node processing load. The multistage VP control may be the best candidate since the tasks in this method are shared by the central node and local nodes, and it allows us to track the traffic changes while maintain a good state of the VP topology by reconfiguring it at regular or need based intervals. In this paper, we focus on the VP topology optimization problem in the multistage VP control. We first present the problem formulation in which the tradeoff between the network throughput and processing costs is considered, and then employ an algorithm based on a route-neuron Hopfield neural network (HNN) model to solve this problem. The numerical results demonstrate the HNN can converge to optimal solutions with high probability and stability while in other cases to near optimal solutions if the values of the system parameters in the route-neuron model are chosen according to some empirical formulas provided in this paper.

This paper proposes a novel representation scheme for self-healing networks, and estimates the performance of restoration algorithms in terms of survivability. This representation is based on that of ring networks. For an arbitrary topology, the network is partitioned into ring sub-networks which are independent of each other, and we consider an extended network constructed by the concatenation of the ring sub-networks. After the statement of the general case, examples of a self-healing ring and a Digital Cross-connect System(DCS)based network are described.

A mobility management scheme that reduces signaling traffic load and connection setup time is a pivotal issue in designing future personal communication service (PCS) networks to satisfy Quality of Services requirements and use network resources efficiently. Particularly, required is scalable mobility management, to meet the explosive growth in number of users for the current second-generation wireless communication systems, and to materialize PCS concepts such as terminal, personal, and service mobility. Many mobility management schemes have been proposed for the reduction of signaling traffic. However, these schemes have not been sufficiently compared using a unified performance measure that is free of assumptions as to mobility model or database architecture. In this paper, we categorize the various mobility management schemes for advanced PCSs in distributed environments into four types and clarify the appropriate domain for each type. To do this, we settled on the number of signals at connection setup and location registration as a unified performance measure, since this value closely relates to connection setup time and network efficiency. We found two kinds of schemes with replicating and caching functions of user information that are extremely effective for reducing signaling load and hence connection setup time. These schemes are appropriate when the probability that a user is in his/her home area is relatively small or the connection setup rate is relatively high compared to the location registration rate. These are the most likely situations in the advanced PCS for global environments.

In this paper, the design issues of ATM LAN emulation (LANE) in a mobile environment are addressed and investigated. One of the most important issues is to support the transparent services for mobile stations. We show that the wireline LANE model, defined by the ATM Forum, for the legacy LANs (Ethernet/FDDI/token ring) is not efficient enough to handle a handoff. On occurring a handoff, the ATM network has to maintain network connections and reroute data to the new location of mobile stations. Combined with the conventional cellular handoff schemes, the wireline LANE-based data rerouting is performed at the base station. As a result, a communication path between two mobile stations may become inefficient when the station moves, e. g. , the path elongates and incurs extra processing overheads. To overcome this problem, we suggest maintaining a separate connection for each pair of mobile stations instead of each pair of LANs (as defined in the ATM Forum). Following on this suggestion, an extensive cellular handoff scheme is proposed for an ATM-based wireless network. In the proposal, the rerouting decision is furnished at the ATM switch. It shows that this scheme not only meets the basic handoff requirements (data continuity and transparency), but also offers smaller handoff latency and a shorter path. A path migration scheme is also suggested to migrate an inefficient path to a better one, if any. The effectiveness of the proposed handoff scheme for the wireless LAN emulation service is evaluated by analysis. Some implementation issues and the cost/performance tradeoffs between additional connections (one for each pair of mobile stations) required and bandwidth waste caused by path elongation are studied.

For Cable-To-The-Air network providing a seamless access network in both indoor and outdoor, direct optical switching CDMA scheme is newly proposed to multiplex any types of radio signals. In two types of connection methods, optical switch connection and optical coupler connection systems, the received carrier-to-interference-plus-noise power ratios are theoretically analyzed. It is clarified that in the optical switch connection connection system, by introducing the additional optical gain at each radio base station, the carrier-to-interference-plus-noise power ratios for all radio base stations and the connected number of radio base stations can be improved compared with the OC connection system.

The chirp noise effect in a directly modulated semiconductor laser diode (LD) is experimentally studied. A previous theoretical study reported that, when an LD is directly modulated, turn-on jitter caused by spontaneous emission, combined with chromatic dispersion, becomes a source of noise in fiber transmission and restricts system performance. This paper points out that, on the contrary, imperfection in LD driving circuits causes chirp noise and limits transmission performance in actual systems. Experiments regarding dependence of chirp noise on LD modulation conditions are also presented, which show that a high relaxation oscillation frequency and a short turn-on delay time are preferable from the viewpoint of chirp noise.

This paper describes the recently developed 816 delivery and coupling switch (DC-switch) boards for constructing a 320-Gb/s throughput (2. 5 Gb/s 8 multiplexed wavelengths 16 incoming/outgoing link pairs) optical path cross-connect (OPXC) system based on wavelength path (WP) and virtual wavelength path (VWP) schemes. The DC-switch-based OPXC system, compared with conventional space division switch (SD-switch)-based OPXC system architecture, is shown to be superior in terms of; i) high link modularity, ii) upgradability from WP network to VWP network, iii) better transmission characteristics, and iv) lower total switching power consumption. Therefore, the DC-switch-based OPXC system can realize cost-effective optical path networks. The developed DC-switches exploit the silica-based planar lightwave circuit (PLC) technologies, and DC-switch board size is 300330 mm² (one switch). The worst values of the insertion loss of the board, ON/OFF ratio, and polarization dependent loss are 14. 5 dB, 34 dB and 0. 5 dB, respectively. Moreover, even though switching is realized by thermo-optic effects, the optical output level varies by only 0. 7 dB and 0. 8 dB for ON- and OFF-state signals, respectively, when the environmental temperature is varied from 5 to 65 .

Error performance as well as ATM cell transfer characteristics in a new category of wireless access systems is discussed. Relocatable wireless access with neutral feature between the fixed and mobile systems can convey Mbit/s-order capacity with fairly high quality under line-of-sight propagation. It is an important question for such wireless access systems whether they are able to form a part of wired networks satisfying performance objectives specified in ITU-T Recommendations. This paper analyzes the characteristics of relocatable systems under Gamma-distribution fading environments, and clarifies quantitative relations between Bit Error Rate (BER), Severely Errored Second (SES), Errored Second (ES) and Cell Loss Ratio (CLR) in a calculation model employing QPSK and typical HEC (Header Error Control). Thus it is demonstrated for the first time that in most cases the dominant parameter is the SES objective. Also it will be possible for a relocatable system with appropriate fade margin to meet the ITU-T performance specifications.

This paper aims at developing forward link power control methods for CDMA cellular systems. The purpose is to allocate available power to as many mobiles as possible. When a power allocation in the network is fixed, the power assigned to the cell where rare mobiles communicate is wasting, and moreover, is prohibitive if other cells fall short of transmitting power. In this case, re-allocation is necessary. Power control in this paper takes the form of allocating pilot and traffic power according to the different needs from each cell. Especially, the pilot power control method tends to balance nonuniformly imposed load through the network, and hence helps the network resources be utilized equally. With the proposed pilot control method, the number of simultaneously communicating mobiles increases by 10-25% over the reference methods.

In this paper, a modified multi-step SIR-based down-link power control method is proposed. The main idea is to predict the variation of Rayleigh fading from the received signal-to-interference ratio and then to track it in time. A computer program is developed to simulate the performances of this new method as well as the original multi-step SIR-based method. Simulation results show that, of the two, the former performs better than the latter, even if the bit error rate of power control command is around 0. 001.

Field experiments using the 2 GHz carrier frequency band were conducted nearby Tokyo to evaluate the effect of joint use of Rake combining and antenna diversity and also the effect of spreading chip rate (or bandwidth) on the achievable bit error rate (BER) performance and the mobile station transmit power distribution of power controlled coherent DS-CDMA reverse-link (mobile-to-base). Four chip rates, 0. 96, 1. 92, 3. 84, and 7. 68 Mcps, were used. The command interval and power step size of the fast transmission power control (TPC) used in the experiments, 1. 25 ms and 1 dB, respectively, were based on measurements of signal-to-interference plus background noise power ratio (SIR) after Rake combining. The field experiments demonstrate that the joint use of antenna diversity and Rake combining significantly improves the BER performance and, furthermore, that increasing the chip rate improves the BER performance and decreases the transmit power because of enhanced Rake combining through an increase in the number of resolved paths.

The authors propose a novel waveguide two-way power divider, named as τ-junction, in a feed waveguide of a single-layer slotted waveguide array antenna. This junction occupies only a small space and is placed in the middle of a cascade of several power dividers. It suppresses the long line effect and widens the bandwidth of the feed waveguide. The junction has two inductive walls; one is for suppressing the reflection and the other is for controlling the ratio of divided power to the two output ports. Analysis using Galerkin's method of moments is verified by experiments of a 4 GHz-band model. We install the junctions in a 12 GHz-band single-layer slotted waveguide array. The gain reduction at the band-edge is suppressed.

This paper proposes a novel bidirectional rod antenna (BIRA) comprising a collinear antenna and parasitic wires as a base station antenna for a street microcell. The spacing between the collinear antenna and the parasitic wire, and the length of the parasitic wires, which are the design parameters obtaining a bidirectional pattern, are investigated using the moment method. The results show that wide spacing enlarges the bandwidth obtaining the bidirectional pattern, however it decreases the gain. Furthermore, to enlarge the bandwidth, a BIRA with arc parasitic plates whose radius is the same as that of the radome is also proposed. The configuration can be constructed using the same exterior as the BIRA with parasitic wires. It is also shown that the arc parasitic plates enlarge the bandwidth in proportion to the area projected onto the tangential plane at the center of the arc. Finally, a prototype of the proposed antenna is shown.

Huynen has already provided a method to decompose a Mueller matrix in order to retrieve detailed target information in a polarimetric radar system. However, this decomposition sometimes fails in the presence of small error or noise in the elements of a Mueller matrix. This paper attempts to improve Huynen's decomposition method. First, we give the definition of stable decomposition and present an example, showing a problem of Huynen's approach. Then two methods are proposed to carry out stable decompositions, based on the nonlinear least square method and the Newton's method. Stability means the decomposition is not sensitive to noise. The proposed methods overcomes the problems on the unstable decomposition of Mueller matrix, and provides correct information of a target.

A new approach for the flow control of available bit rate service in ATM network is proposed using supervisory control theory upon discrete event models. According to the approach, each rate controller adjusts the input source traffic within a specific zone decided by the supervisor. In this way, the proposed control scheme ensures congestion avoidance and the maximal successful transmission rate of the input source traffic in a fair manner upon a simplistic way of explicit rate setting for resource management cells.

We demonstrate that the frequency modulated video signals in the subcarrier multiple access optical network can be satisfactorily transmitted using our proposed method, that broadens an optical spectrum by multiplying the subcarrier signals by an additional signal and that reduces optical beat interference, even if the wavelengths of four Fabry-Perot laser diodes are very close each other.

Channel holding time distributions in typical cross- and cigar-shaped urban microcells is determined. Practical low-tier-user behaviors in urban areas, such as turning at intersections, entering a buildings, as well as variable user speed and direction are considered. The results are useful in analyzing system traffic and in choosing the best cell shape in urban microcellular systems.

We propose an approach to obtain the relation between the number of voice call users and the number of data call users in the reverse link of a DS-CDMA cellular system with mixed rate traffic. The analyzed results show that as the number of data call users with high bit rate increases, the number of allowable voice call users decreases rapidly and linearly.

The Rician factor is an important parameter in evaluating the outage probability and reuse distance of cellular systems. From the measurement of 1. 8 GHz radio propagation in outdoor urban microcells, it is found that the measured pdf of the Rician factor for low tier systems follows a lognormal distribution and the factor is independent on the propagation distance.

A technique for generating the standard EM fields with arbitrary wave impedance at the center of a TEM cell is proposed in this letter. We can realize the experimental system and obtain the measured results to agree well with the calculated results. This technique is useful for the EMS test and the calibration of EM probe because the wave impedance can be easily adjusted only with step attenuator.