E. Van Lil

Fast link adaptation for TFRC after a handover

TCP-friendly rate control(TFRC) is an equation-based congestion control mechanism that competes fairly with TCP but has a much lower throughput variation, which makes it a better choice for streaming over the Internet. It is known that in a mobile network environment, after a handover TFRC can overshoot or under utilize the new link if the conditions there differ from those of the old link. There are different factors that affect the TFRC performance during a handover. In this paper we focus on the impact of the change in the round trip time, an aspect that is largely overlooked in the literature compared with bandwidth disparity. We find that even if the same bandwidth is assured on the new link, changes in the link latency will still cause TFRC performance degradation after the handover. A fast link adaptation mechanism is thus proposed to address the problem. Simulations show that this mechanism helps TFRC to adjust quickly to the new link without consecutive packet loss or long-time bandwidth under utilization.

Project Driven Graduate Network Education

In this paper projects for engineering students are described. Three different practical subjects on networking are suggested: a point-to-point link, a VoIP implementation on a LAN and an Office network. These projects are set up to offer Master students in Electrical Engineering (Telecommunications option) of the University of Leuven (K.U.Leuven) a realistic practical background. The authors consider such projects as a necessity, supplementary to the theory. With those projects, the leap to industry after graduation becomes easier to take.

Uniform spherical distributions for adaptive array applications

This study investigates optimal three dimensional antennas for adaptive applications. The choice of the antenna element distribution on the spherical surface is governed by the desire to maintain a nearby constant pattern. Spherical arrays provide wide scan coverage with low grating lobe levels. We calculate the uniform distribution of a set of antennas on a sphere. Based on formulas of the spherical trigonometry, we show all the possible exact uniform distributions. It is astonishing, that only five possible solutions can be found. In this paper, the co-ordinates and the figures of these regular polyhedrons are shown. Because the number of possible uniform spherical distributions is limited, the number of elements that can be placed uniformly without approximation on a spherical surface is also limited to 20.

Transfer Characteristics Modeling of Four-Conductor Cables in Power-Line Communications

This paper presents an approach to model the transfer function of a four-conductor power-line cable for power-line communications. The model is derived from multiconductor transmission-line theory by taking into account all couplings between the conductors. The model allows one not only to determine the transfer function, but also the interference characteristics of that transmission medium. The transfer function for a straight line without branches is obtained first, and then crosstalk is derived. Finally, an N-branch network is simplified based on a generalization of the transmission matrix method. The transfer characteristics of the equivalent network are derived in a similar way as for a straight line.

A fast adaptation mechanism for TCP vertical handover

In this paper we propose a vertical handover mechanism for TCP to deal with the delay and bandwidth change during the handover. The proposed mechanism relies on the interaction between the sender and the receiver during the handover and requires no a prior information of the new path. The adaptation is triggered by a handover notification at the receiver and finishes in about two round-trip time. Furthermore, it solves the problem of packet reordering and spurious retransmission timeout as well which are also common during vertical handovers. Simulation results show that our mechanism improves TCP performance in various vertical handover scenarios.

Mobility control beyond 3G systems

This paper deals with the issues of mobility control in mobile networks and the consequences for future generation networks. Mobility involves the update of the location information of the mobile user, as well as the redirection of the dataflow. Especially the latter is very challenging for network developers. Answers to this problem have been proposed for connection oriented networks, but, for connectionless networks, there is still no satisfying proposal. Hence this has consequences on architectural options for future networks in general, taking the impact of mobility into consideration.

A tunable discrete traffic generator based on a hierarchical scheme of Bernoulli sources

In this paper we present an efficient method for the generation of a discrete series of traffic. The method is based on a superposition of hierarchical Bernoulli sources and generates non-Gaussian distributions. This way self-similar traffic can be generated with an arbitrary combination of Hurst parameter, variance and mean. The method is fully parameterized before generating the trace, which avoids the need for post-processing. Contrary to other methods, the method also allows calculating the trace point by point. The described hierarchical scheme offers a generic framework for fitting the variance-time behavior and can be combined with other stochastic sources.

Current antenna research at K. U. Leuven

Four antenna research projects at the Katholieke Universiteit Leuven are described. In the first project, four different methods for the transformation of plane-polar near-field data to far-field antenna characteristics have been compared, and the method with the best performance (accuracy versus computer time) has been implemented on an HP 1000 and on a VAX under VMS. In the second project, a test method has been developed to detect faulty columns in three-dimensional array antennas. The method is based on a reconstruction technique, and has been implemented in an air-surveillance secondary radar system. In the third project, the transmission-line model developed for rectangular microstrip antennas has been implemented and verified for linear and planar arrays. The software package runs on a PC, as well as on VAX workstations. In the fourth project, a software package, running on a VAX under VMS, has been developed based on a moment-method approach for the analysis of multiprobe, multipatch configurations in stratified-dielectric media. The procedure developed contains features to improve the convergence, accuracy and efficiency of the moment method.<<ETX>>

Leaf initiated join handover evaluation

In order to achieve full integration between wired and wireless ATM, a transparent mobile wireless interface to the wired ATM network is required. This paper describes a signalling framework for the handover: the handover is obtained only using standardised UNI 4.0 signalling, without the introduction of mobile specific signalling entities in the fixed network. It is a soft‐forward handover scheme, enabling the handover to comply with the QoS guarantees of the connection. This is achieved using the Leaf Initiated Join (LIJ) capability standardised by UNI 4.0. The handover signalling is proposed taking the propagation characteristics at 60 GHz into account. The evaluation of the performance is performed analytically taking both Poisson and self‐similar traffic into account. The research underlying this paper is performed in collaboration with the ACTS MEDIAN project AC006.

Comparison of design methods for binomial matching transformers

The binomial transformer is a well known concept in impedance matching. By the use of multiple quarter wavelength sections broadband matching is achieved. Many textbooks handle the problem starting from the approximated theory of small reflections. In this paper, a new and exact derivation for the impedances of the different sections is given. It is shown that not the section coefficients must satisfy a binomial distribution (as commonly used), but a transformation of these coefficients. Furthermore, an alternative formulation starting form the theory of small reflections is given. The results of the different methods are compared. It is shown that the alternative formulation gives the best agreement with the exact method.The binomial transformer is a well known concept in impedance matching. By the use of multiple quarter wavelength sections broadband matching is achieved. Many textbooks handle the problem starting from the approximated theory of small reflections. In this paper, a new and exact derivation for the impedances of the different sections is given. It is shown that not the section coefficients must satisfy a binomial distribution (as commonly used), but a transformation of these coefficients. Furthermore, an alternative formulation starting form the theory of small reflections is given. The results of the different methods are compared. It is shown that the alternative formulation gives the best agreement with the exact method.