Alen Bazant

Signal propagation modeling in power-line communication networks

In this paper, we present a propagation model for the power-line communication (PLC) networks, based on the frequency-domain analysis. First, we set a simple two-port model of the network. Then, we calculate a complex attenuation factor from z-parameters, expressed in terms of impedances, easily calculable/measurable from the network ports. We explain simultaneously calculation and measurement methods based on the same principle, and then compare the results with direct measurements performed in the network designed for this purpose. We provide all of the elements for a simple end efficient propagation model. They include propagation by crosstalk between different circuits in, for example, three-phase networks, as well as the influence of the loads connected to the ports of different circuits in such networks. We have concluded that the model is suitable for PLC channels simulations that give very accurate results and enable modeling of wide-band channel characteristics.

Absolute Delay Variation Guarantees in Passive Optical Networks

This paper addresses the problem of providing absolute delay variation guarantees in passive optical networks and their optical coding enhanced counterparts. We analyze the components of frame delay variation in these settings and propose a dynamic bandwidth allocation algorithm that provides the optical line terminal with mechanisms to ensure that frame delay variation never breaches a predefined value. Furthermore, we provide simulation results and analyses to show that the proposed algorithm does not breach delay variation bounds. We also provide a lower bound analysis for providing absolute delay variation guarantees for both scenarios and show the duality between absolute delay and delay variation guarantees.

Bandwidth and delay guaranteed polling with adaptive cycle time (BDGPACT): a scheme for providing bandwidth and delay guarantees in passive optical networks

This paper addresses the problem of providing bandwidth and delay guarantees in passive optical networks. To resolve this problem we propose an algorithm that provides absolute bandwidth and delay bound guarantees. Simulation results show that the proposed algorithm does not breach bandwidth and delay bounds for guaranteed service traffic even under the highest loads. Additionally, we analyze the lower bound for providing delay guarantees.

Fixed-Data-Rate Power Minimization Algorithm for OFDM-Based Power-Line Communication Networks

In this paper, we present a suboptimal integer bit allocation algorithm that minimizes power output for given user demands in multiuser orthogonal frequency-division multiplexing (OFDM) systems implemented in downlink transmission of power-line communication (PLC) networks. Assuming complete knowledge of a channel and the predetermined data rates for every user, the presented algorithm solves the power minimization problem analytically. The simulation results have shown significant advantages of this approach, especially in comparison with algorithms that deal with the problem of user data rate demands in an iterative manner. Compared to iterative algorithms, the proposed algorithm proves to be a much more effective solution regarding processing time and computational complexity. In addition, the losses in its power allocation efficiency due to its suboptimal approach remain very small in cases where the number of users does not exceed half the number of available subchannels.

Web content management system based on XML native database

We identify problems in complex Web application implementations. In more detail, we address the problem of content management and specific components of such a system. We also present our implementation of a Web content management system (WCMS), which is based on relational database and XML technologies. It also uses some rather new concepts and technologies like XForms and a native XML database.

Predictive playout delay adaptation for Voice over Internet

Packet switching is an effective technology for integrating voice and data in a single network. An example for such a kind of a network is Internet. New service is emerging, and it is a Voice over Internet Protocol (VoIP). An important aspect of packet-switched voice is the reconstruction of a continuous stream of speech from the set of packets that arrive at the destination DTE (data terminal equipment). Because of the statistical nature of packet switching, each packet can encounter a different amount of delay in traversing a packet network. The problem described in this paper is how to design an appropriate voice reconstruction strategy that reproduces acceptable-quality speech from packets that arrive with varying delay. The basic idea proposed is to measure a delay jitter between several points on the Internet. Our voice traffic generator, implemented on a workstation, sends packets that are 20 ms long. The receiver measures the inter-arrival time and keeps track of mixed sequences and lost packets. The measurement results are given in a form of average delay jitter. The receiver also keeps a record of all relevant packet information in a text file that is used as an input to a delay jitter predictor. A traffic prediction element predicts talk-spurt characteristics and directly influeuces playout delay. For the prediction element, we propose an adaptive neuro-fuzzy inference system (ANFIS).

A Practical Method for Extraction of High-Frequency Parameters of Distribution Cables

Cable parameter extraction is needed for many practical purposes. The main motivation for this research came from a need to extract high-frequency properties of cables used for indoor electricity distribution because they can be utilized for transmission of communication signals, too, by means of the power-line carrier (PLC) technology. These cables have relatively high specific losses, so that indoor broadband PLC applications can use frequencies up to some 30 MHz. In this paper, cable features in the frequency range from 5 to 30 MHz, belonging to the high-frequency band, were studied. The purpose of this paper is to describe a practical method by which the cable parameters in the mentioned indicated frequency range can be extracted rather accurately from measured complex reflection coefficients at a cable end when the other end is terminated by precise open and short terminations, using very simple equipment. The parameters extracted in this way can be used for very precise modeling of real-life multiterminal distribution networks.

Adaptive Grant Extension in OC-Enhanced PONs

We present a distributed mechanism termed Adaptive Grant Extension (AGE) for grant-size adjustment in Optical Coding (OC)-enhanced Passive Optical Networks (OC-PONs). AGE exploits the real-time queue updates of OC-PONs to allow the Optical Network Unit (ONU) to extend its transmission beyond the grant provided by the Optical Line Terminal (OLT), thus reducing average frame delay. We discuss the parameters and requirements of AGE in OC-enhanced Ethernet PONs (EPONs). Our simulations show delay gains reaching 9% over OC-PONs.

Downstream bit rate calculation for ADSL2+ loops limited with far-end crosstalk

In this paper an efficient method for downstream bit rate calculation on ADSL2+ local loops limited by crosstalk is presented. Crosstalk is one of the most limiting factors in broadband cable communications. In order to calculate bit rate of ADSL2+ loops we have done an in-depth analysis of a local telecom operators cable infrastructure in terms of crosstalk. On the basis of measurements carried out on twisted quad cables in a frequency range up to 2.2 MHz, we have derived theoretical models of far-end crosstalk (FEXT) and insertion gain. The measurements were performed on cables that are part of an operating infrastructure, not on cables on a reel, thus providing a true insight into the situation telecoms worldwide are facing today. The results indicate that number and assignment of ADSL2+ to loops in a cable binder have a great impact on a bit rate. Strategy of allocating ADSL2+ to loops inside the cable binder reduces level of interference between users, allowing, in this case, traffic prediction and dynamic access to spectrum available in a cable. Presented bit rate calculation method and crosstalk models are crucial foundation for spectrum management used in a process of local loop unbundling, which is lawful obligation of numerous incumbent telecom operators.

Voice traffic performance measurement in packet networks

Quality of voice transportation over packet networks depends on three critical parameters: packet loss, absolute packet delay and packet delay variation (jitter). Common practical problem is how to estimate voice quality for a different number of voice sources with different source characteristics in target networks. Important characteristics of a voice source are: rate (packets per second), packet length (depending on a type of compression), type of source (VBR or CBR) and statistical description. In this paper we propose methodology and practical approach for systematic measurement of voice traffic parameters in respect to varying voice source characteristics. Measurement results that are conducted with presented methodology on an experimental DiffServ network are given, too.