IP multicast is very useful mechanism to deliver data to a large number of receivers such as interactive multimedia sessions. It can not accommodate the heterogeneity of the receivers including network heterogeneity. We propose a multicast traffic controller(s) in a router to solve such situation. A traffic controller has a filter to moderate the output data rate to a link. It makes use of Time-to-Live (TTL) threshold to specify the minimum requirement of a packet. Multimedia data are encoded into multiple layers; basic layer and enhanced layers. By associating TTLs of data layers and the threshold of the filter, we can moderate the traffic by dropping the data of less significant layer. The threshold is dynamically modified according to the local network traffic and link traffic. Our scheme also helps a network and a link(s) avoid from congestion and accommodate other types of traffic at the same time.

In universal personal telecommunication (UPT) environments, UPT networks retain information related to incall/outcall registration in UPT user service profiles in order to provide incoming UPT calls for UPT users in any location who have registered at a terminal. As UPT networks support incall registration, terminal users can be different from terminal owners, and several UPT users can register for incoming calls on a single terminal. Therefore, appropriate third-party protection procedures are needed to protect the rights of terminal owners. A terminal profile database can be used to store information regarding terminal states and incall UPT users registered on a terminal in order to enable third-party protection procedures. In order to manage information within both the terminal profile and the service profile, we propose a request-based scheme for incall registration/deregistration of UPT users and incall registration resets of terminal owners. We evaluate the performance of the scheme in terms of; 1) total cost and, 2) the number of terminal profile accesses per unit time for a terminal.

In this paper, a new multicast routing method for layered streams is proposed. This method is an extension of the weighted greedy algorithm (WGA) and uses two kinds of weight values to refine the link distance. It can cope with dynamic change in the group members without multicast tree re-construction. The method is compatible with the RSVP and can be utilized in existing shared tree type routing protocols such as CBT and PIM sparse mode. The network resources can be utilized efficiently; furthermore, the loss rate of member's requests to receive more layers can be reduced by this routing method when a sufficient number of nodes have the packet filtering function and a sufficient number of hops is permitted.

A scheme is proposed to exploit statistical multiplexing to support connections with diverse characteristics and requirements. Previous designs on measurement-based admission control mainly focused on strategies that consider the worst case traffic source model to guarantee QoS bounds for all connections. In this paper, we develop a simple mechanism in which statistical multiplexing gain as well as QoS is considered to achieve higher bandwidth utilization. An accurate formula for the cell loss probability which combines measurments with the Gaussian approximation is presented for a new traffic model. Furthermore we enhance the performance of this mechanism through real-time measurements of traffic and monitoring of QoS.

In reliable multicast communications, lost information due to packet loss should be re-multicasted. NAK-based retransmission scheme is said to be effective for scalable reliable multicast communications because it can avoid implosion of control packets. When the source sends packets faster than receiver's ability, packet loss due to buffer overflow occurs constantly at corresponding receivers. With this constant packet loss, implosion of control packets degrades total throughput seriously even in the case of NAK-based retransmission scheme. In order to prevent this kind of constant packet loss at receivers, flow control scheme should be implemented for reliable multicast communications. In the paper, we propose a new flow control scheme suitable for NAK-based retransmission scheme. From the viewpoint of flow control, receiving a NAK indicates that transmission rate is too high. However, in multicast communications, multiple NAKs may be generated for a corresponding packet. If the transmission rate is decreased simly by receiving a NAK, the rate may be decreased excessively. In the paper, logging information of transmission rate stored at the sender is proposed to be effective to prevent the transmission rate. Performance evaluation by computer simulation shows that the proposed scheme notably improves throughput performance compared with the case of no flow control.

A new type of a linear decorrelating receiver, named Pseudo-Decorrelator, for asynchronous code division multiple access systems over a Rayleigh fading multipath channel is presented in this paper. Starting with the analyis of the multiple access components of the decision statistics, the outputs of a bank of matched filters, the (K 3K) cross-correlation matrix for each bit is obtained. The non-square cross-correlation matrix is then inverted using the concept of Penrose's generalized inverse of a matrix. In this receiver, the detection process can be started before the whole sequence is received at the receiver, and computing the inverse of a (KN KN) cross-correlation matrix, generally required for linear decorrelating receivers, can be avoided because it is enough to compute only the generalized inverse of a (K 3K) cross-correlation matrix for each data bit. Here, K is the number of users and N is the length of input data sequence. Simulation results are also presented for K-user systems over a Rayleigh fading multipath channel.

An efficient ARQ scheme based on the packet combining technique is investigated for multi-carrier modulation systems. In multi-carrier modulation systems, several sub-carriers are used for high data rate transmission and their individual received signal quality becomes different from one sub-carrier to others in a frequency selective fading channel. Therefore by changing the assignment of data to the sub-carriers in the retransmission packets, the distortion between the previous transmitted packet and the newly retransmitted one will be different. This is the principle of the proposed adaptive data order rearrangement for a packet combining ARQ scheme, which can achieve more diversity gain in packet combining and improve the ARQ performance. From the results of the theoretical analysis and the computer simulation, it is confirmed that the proposed packet combining ARQ with the proposed operation can achieve the better performance in terms of the average packet transmission success probability. In addition, this proposed scheme is also compared with the conventional multi-carrier modulation ARQ scheme based on the partial retransmission of a packet. The computer simulation results demonstrate that the proposed scheme has also advantage against the latter one, and it is considered to be as a more efficient ARQ scheme for multi-carrier modulation systems.

The cable TV (CATV) network is an ideal backbone for PCS due to its prevalent and broadcast nature. This significantly reduces the implementation costs and the handoff overheads. This paper proposes two architectures for the CATV-based PCS system. In the first architecture, each base station is equipped with multiple fixed receivers to provide fast and seamless handoffs for mobile users. Nevertheless, the hardware cost for this implementation is relative expensive. To overcome this, in the second architecture, each base station is equipped with only one tunable receiver. This simple and economic architecture suffers from the possibility of offset conflict when mobile terminals handoff between cells. Three offset assignment algorithms based on the concepts of random assignment, neighbor usage, and clustering, respectively are proposed to solve the offset conflict problem. Simulation results indicate the one with the concept of clustering performs much better than the other two schemes in terms of offset conflict probability.

A variable partition duplex scheme on packet reservation multiple access protocol (VPD-PRMA) is analyzed in this paper. We assume a four-state speech model for a conversational pair and successfully obtain performance measures by approximate Markovian analysis. Analytical results show that they quite fit simulation results; and VPD-PRMA can get higher statistical multiplexing gain than fixed partition duplex (FPD)-PRMA, due to the trunking effect. We further investigate the effect of design parameters of permission probability and enlarged reservation duration on system performance by computer simulation. Simulation results shows that it exists appropriate values for these two design parameters so that the packet dropping probability can be minimized. The adjustment of permission probability can greatly improve the performance of uplink traffic with slight deterioration of the performance of downlink traffic; the provision of enlarged reservation duration scheme can enhance the system performance.

The formulation of the wall admittance of a circular microstrip antenna by the spectral domain method is presented. The circular microstrip antenna is calculated using the cavity model. The electromagnetic fields within the antenna cavity are determined from the impedance boundary condition at the side aperture. The contribution from the region outside the antenna is taken into account by the wall admittance. The wall admittance is defined by the magnetic field produced by the equivalent magnetic current at the aperture. The magnetic field is calculated by the spectral domain method. The wall admittances obtained by this method are compared with the results calculated by Shen. The calculated input impedances of the microstrip antenna agree fairly well with the experimental data for the substrate thickness of up to 0.048λ_g. The formulation of wall admittance presented here is easily applicable to arbitrarily shaped microstrip antennas.

In this paper there suggested is a bifurcated (or multiple) input-queued ATM switch in which a buffer for each input port is divided into multiple (m) buffer blocks, i. e. , bifurcated buffers, for enhancement of the limited throughput of the ordinary input-queued switch using a single FIFO. As the contention/arbitration rule for the bifurcated input-queued switching scheme, free and restricted contention rules are come up with and discussed. The free rule allows an input port to switch up to m cells at the cost of internal speedup. With the restricted rule, on the other hand, an input port can switch no more than one cell in a time slot so that the switch operates at the same speed as the external link speed. The throughput bound for the bifurcated input-queued switch is analyzed for both rules through the generalization of the analysis by Karol et al. The throughput bound approaches to 1.0 as m becomes large enough, irrespective of the contention/arbitration rule.

Frequency chirping induced in an electorabsorption (EA) modulator can degrade transmission performance because of the chromatic dispersion of fiber. This letter studies the frequency chirping in an EA modulator from the viewpoint of the influence of the modulation bandwidth. Both simulations and experiments, in which fiber transmission was carried out applying modulation signals of different bandwidths to an EA modulator, show that a large bandwidth causes small degradation in the transmission performance. This result is attributed to the short chirping time that occurs when a large bandwidth signal is applied.

We are concerned with a CDMA cellular system with unbalanced traffic environment such that a cell with high traffic should be assigned a frequency additional to the common one shared with its neighboring cells. To remove quality-dropping inter-cell hard handoffs, the cell with high traffic was first partitioned into three regions. Then, the common frequency is assigned in the outermost region, and the additional frequency is operated in the innermost region, whereas both the common frequency and the additional frequency are operated in the middle region. This frequency assignment strategy is shown not only to remove inter-cell hard handoffs without requiring extra hardware, but also to reduce intra-cell hard handoffs.

Radio waves propagating through tunnels are strongly attenuated in the presence of discontinuities such as bends and branches. The useful structural modifications are requested to get better circumstances for radio waves in tunnels. In this paper, we propose several modifications arranged in a conventional T-junction of two-dimensional tunnels and analyze the transmission characteristics of radio waves by using the finite volume time domain (FVTD) method.