This paper proposes a design method of impedance stabilization network (ISN) which can measure disturbance at balanced multiple-pair telecommunication ports for both analog and digital signal transmission. The proposed design method of ISN is studied on the basis of the equivalent circuit of ISN and the requirements for ISN. The parameters for designing of ISNs up to 100-wires are studied and determined. An ISN for 4-wire signal ports is constructed on the basis of the proposed design method, and the characteristics of the ISN are experimentally examined. The results show the ISN satisfies the requirements for ISN. Furthermore, the measurement deviation is within 1dB compared with other ISN, and the disturbance measured by the ISN shows a good correlation with that measured by a current probe.

This work presents a scalable and high performance prediction protocol for optical networks. In the proposed protocol, we develop a mathematical model to maintain the stability of a network system by prediction based on the traffic temporal locality property. All the critical factors, including transceiver tuning time, propagation delay, and processing time for dealing with control packets, are considered in the proposed prediction protocol. Furthermore, our protocol can resolve the bottlenecks attributed to control signaling and electronics processing. The performance evaluation reveals that the proposed scheme can yield the higher bandwidth efficiency and incur a lower packet delay than those of the TDM and conventional reservation schemes. Also, the proposed protocol can flexibly support any scaled network system such as MANs or LANs.

In an optical submarine cable transmission system, small size, low consumption power, and high reliability are required for inline repeaters. The structure of the inline repeater should be a simple single stage. The design of erbium doped fiber (EDF) itself is very important for the inline repeater to achieve broad bandwidth, high output power, and low noise figure. We designed and developed high alumina co-doped erbium doped fiber amplifiers (EDFAs) for long-haul, high-capacity WDM transmission systems. We investigated the trade-off relationship between the gain flatness and the output power to optimize the EDF length. We obtained high performance, including a slightly sloped gain flatness of +0.04 dB/nm at 1550 nm, a superior noise figure of 4.7 dB, and a relatively large output power of +11.5 dBm for an EDF length of 5 m using a 1480-nm pumping laser diode. We applied gain-equalizers (GEQs) using Mach-Zehnder type filters with different FSRs to accurately compensate for the EDFAs ' gain-wavelength characteristics. The main GEQs have free-spectral-ranges (FSRs) of 48-nm, which are about 2 times as long as the wavelength difference between a 1558-nm EDFA gain peak and a 1536-nm EDFA gain valley. Using a circulating loop with the above EDFAs and GEQs, we performed the broad wavelength bandwidth. The achieved signal wavelength bandwidth after 5,958-km transmission was 20 nm. We successfully transmitted 700-Gbit/s (66 10.66-Gbit/s) WDM signals over 2,212 km. The combination of high alumina co-doped silica EDFA and large FSR GEQ is attractive for long-haul, high-capacity WDM transmission systems.

In this paper, we analytically study the effects of overlap and overlay structure on the quality of service (QoS) of Low Earth-Orbital Satellite (LEOS) communication systems. We consider two-layered overlay of cells and intentional overlap of neighboring small cells. In order to measure the QoS, the probabilities of rejection of a newly arrived call (blocking) and forced termination due to failure of a handover (call dropping) are derived. In addition to these measures, the largest traffic intensity which guarantees the required blocking and dropping probabilities is also used.

A per-connection end-to-end call admission control (CAC) problem is solved in this paper to allocate network resources to an input session to guarantee its quality of service (Qos) requirements. In conjunction with the solution of the CAC problem, a traffic descriptor is proposed to describe the loss rate and the delay bound Qos requirements of the connection to be set up as well as the statistical characteristics of the associated input traffic which is modeled as a linear mean function plus a (zero-mean) fractional Brownian motion. The information in the traffic descriptor is sufficient to determine the allocation of channel bandwidth and buffer space to the input traffic in a network which employs leaky bucket shapers and scheduling algorithms to guarantee the Qos requirements. The CAC problem is solved by an iterative algorithm of which there are two stages in each iteration: one is responsible for the search of a candidate end-to-end routing path and the other for the verification of the legitimacy of this candidate path to meet the Qos requirements and for the allocation of resources in such a legitimate path.

An efficient scheme for establishing the multicast-path on ATM network is to configure the tree-shaped path via several intermediate copy nodes. This scheme needs the multicast routing control. Thus, restricting the number of copy nodes was proposed since it make this control fast and simple. However, if restricted number of copy nodes is fixed in the network design, multicast traffic will concentrate around copy nodes, and as a result, the possibility of occurring congestion will be higher. In our research, we permit restricted number of nodes as intermediate nodes which branch the tree-shaped path at routing, and name this permission "copy-token. " Namely, the node which has "copy-token" is defined as the copy node. Our research purpose is to distribute the multicast traffic by adaptively allocating "copy-token" to nodes which satisfy the conditions of both the priority for multicasting such as lower offered load and the geographical distribution at the same time. Finally, we evaluate the performance of our proposed routing scheme on the blocking probability through computer simulations.

We have already proposed a regional PC communication network system that provides a LAN environment and group communication services to the customers. A Low-end Card (LECard) is set up in the subscriber's household and provides the popular Ethernet interface (10Base-T). A multiplex-port brouter (MBR) was developed to accommodate a lot of customers in a cost-effective manner. Ethernet packets are transferred through each subscriber channel between the LECard and the MBR using the HDLC protocol. The LECard and the MBR are controlled by the group management server (GMS) to realize the group communication system. The performance of an experimental system in ordinary use must be evaluated before bringing the system into practical use. However, it is difficult to prepare a number of PCs and to use them at the same time to evaluate the performance degradation seen in multiple-access. This paper presents a newly developed multiple-access simulator for evaluating MBR performance. The simulator connects to the MBR under test through a multiplexed signal interface. It simulates the conditions in which many LECards and PCs are connected to an MBR and they access the network at the same time. The basic function of the LECard, passing the MAC addresses of subordinate PCs to GMS, and the packet generating function of the PCs are implemented in the simulator. Ethernet packets are transmitted to all ports of the multiplexed interface. MBR throughput in the experimental system was evaluated by transmitting Ethernet packets from/to the simulator. The results show that the MBR package has a processing speed of about 4000 PPS. They also show that the degradation in user port performance is slight up to approximately 20% of the active ratio, i. e. 20% of the users access at the same time.

In this paper, we present a new approach for the design of partially adaptive broadband beamformers with the generalized sidelobe canceller (GSC) as an underlying structure. The approach designs the blocking matrix involved by utilizing a set of P-regular, M-band wavelet filters, whose vanishing moment property is shown to meet the requirement of a blocking matrix in the GSC structure. Furthermore, basing on the subband decomposition property of these wavelet filters, we introduce a new dynamic subband selection scheme succeeding the blocking matrix. The scheme only retains the principal subband components of the blocking matrix outputs based on a prescribed statistical hypothesis test and thus further reduces the dimension of weights in adaptive processing. As such, the overall computational complexity, which is mainly dictated by the dimension of adaptive weights, is substantially reduced. The furnished simulations show that this new approach offers comparable performance as the existing fully adaptive beamformers but with reduced computations.

This paper focuses on introducing a highly efficient data structure that effectively captures the multipath phenomenon needed for accurate propagation modeling and fast propagation prediction. We propose a new object representation procedure called circular representation (CR) of microwave masking objects such as buildings, to improve over the conventional vector representation (VR) form in fast ray tracing. The proposed CR encapsulates a building with a circle represented by a center point and radius. In this configuration, the CR essentially functions as the basic building block for higher geometric structures, enhancing the efficiency more than when VR is used alone. Only one CR is needed to represent one building while several wall vectors are required in VR. As a result, a significant computational reduction can be achieved in ray tracing by the proposed method. Our aim is to show CR as a solution to achieving efficiency in data structuring for effective propagation prediction modeling. We show that the computational load is reduced by the proposed method. Further reduction is shown attainable using the hierarchical structure of CR in a deterministic propagation model, undergoing ray tracing. The simulation results indicate that the proposed CR scheme reduces the computational load proportionally to the number of potential scattering objects while its hierarchical structure achieves about 50% of computational load reduction in the hierarchical octree structure.

The long spikes have been often recorded at the multiples of the electron cyclotron frequency in the ionograms of the topside sounders observed in low latitudes. There has not been sufficient explanation for the physical cause for occourrence of the long spike so far. Here, by interpreting this phenomenon as receiving the trapped cyclotron harmonic wave, some analyses for the length of spike are done not only from the viewpoint of the sweeping property of the frequency spectrum of the transmitted pulse but also from that of the mutual positional relation between the propagation path and the orbit of the sounder. The cause of forming a single spike and a graphical calculation method for the long spike are proposed, respectively. Thus, the cause and the fine structure of long spike consisting of superposed spikes are clarified.

We present an architecture of a VOD system employing proxy servers. The proposed VOD system provides efficient and reliable VOD services and solves the problems caused by traditional VOD systems of centralized, hierarchical or distributed architecture. The proxy servers are placed between video servers and user systems. The proxy server is a small size video server that has not only caching function but also intelligence such as VCR-like video stream control or navigation of other proxy/video servers to search for a selected video program. Using a VOD system of the proposed architecture, the VOD services can be provided to more users because it reduces the workload of video servers and network traffic. We provide the performance model of the system. Service availability is also analyzed. The proposed architecture shows better performance and availability than the traditional VOD architectures.

Reverse link performance analysis in single-code and multi-code CDMA systems is presented. Results show that the single-code system yields better performance than does the multi-code system in terms of link capacity and signal power. This improvement increases as spreading bandwidth is reduced and the number of spreading codes assigned to a user is increased.

In modems for burst transmission of digital data, rapid carrier and clock synchronization are essential. Typically, frequency correction occurs prior to phase recovery since estimators are sensitive to frequency offsets. In this paper, we derive the bit error rate (BER) performance of a M-ary phase shift keying (MPSK) receiver in a closed form when there is no frequency offset estimator. Then we derive a relationship of the required burst length for certain BER with frequency offset estimator. To obtain the BER=10^-4, approximately we need the burst length of 101 at E_b/N₀=10 dB and 69 at E_b/N₀=15 dB.

In order to maintain the communications quality at a target level, signal-to-interference ratio (SIR)-based transmission power control methods have been developed in CDMA cellular systems. These power control methods, however, do not necessarily improve system efficiency when there is a large geographic deviation in traffic because they only control power levels. A shift in the cell boundary can control traffic balance between cells. In this paper, we evaluate the optimum location of the cell boundary and the power levels when a mobile station adaptively selects a base station (BS) for each of uplink and downlink under non-uniform traffic. Because of the asymmetry in system structure between uplink and downlink, the optimum cell boundaries are not always coincident for both the two links; the location of the cell boundary is found to migrate according to the loss in orthogonality in the downlink.