Uniqueness of solutions of piecewise linear resistive networks withtwo terminal resistors

Consider a network comprising two terminal linear, piecewise linear resistors and independent sources. Contrary to widely held belief, it is shown that the determinant sign condition (i.e. the Jacobian determinant is nonzero and has the same sign in all the regions) is both necessary as well as sufficient to guarantee uniqueness of solutions of these networks. For this purpose the existence of a specific hybrid matrix is not required     

Linear filtering and piecewise linear correlation functions

For a class of piecewise linear correlation functions, it is shown that optimal linear mean-square filtering is achieved with a finite number of samples of the process for any finite observation interval. The class of correlation functions is defined by a particular property of the points at which they change slope. Conditions are discussed under which an arbitrary piecewise linear function is a correlation function. An example demonstrating various aspects of the theory is given, and applications of the theory are considered.     

Designing reliable networks with short paths

We present a technique for constructing highly reliable networks in which locations consist of pairs of redundant vertices and in which every pair of locations has a pair of short disjoint paths connecting them. One of the paths between locations has one hop and, in most cases, the other path between locations has two hops. We further show that the networks have as few edges as possible and the vertices in the networks have nearly as small a degree as possible.     

Behavioral and macro modeling using piecewise linear techniques

In this paper we will demonstrate that most digital, analog as well as behavioral components can be described using piecewise linear approximations of their real behavior. This leads to several advantages from the viewpoint of simulation. We will also give a method to store the resulting linear segments in a compact way, in order to avoid storage problems.     

Global corporate communications with integrated services digital networks

This paper presents proposals and justification for standards governing the implementation of integrated service digital networks (ISDN). Using several programming protocols in a layered architecture provides continuing service during system evolution. The authors use a corporate communications environment for examples as the most probable initial implementation of the networks described. Some ISDN sites are operating, although not yet on a global scale, and present the building blocks for more advanced services in the near future. The authors present arguments supporting a concerted effort be started now to establish global standards for ISDN, so that design and development can comply in the most time-effective manner.     

Wireless ultrawideband communications and sensor networks

An actively advancing branch of wireless ultrawideband communications is considered. Direct chaotic transceivers of two types are described. The transceivers were developed at the Institute of Radio Engineering and Electronics, Russian Academy of Sciences. Application of these transceivers in wireless sensor networks is demonstrated.     

Color image enhancement with high saturation using piecewise linear gamut mapping

Most of the color image enhancement algorithms are implemented in two stages: gray scale image enhancement, which finds the target intensity, and then gamut mapping of the original color coordinates to the target. Therefore, hue preserving gamut mapping is an essential and crucial step, which influences colorfulness. In conventional color mapping methods, color saturation is reduced after intensity modification, which deteriorates subjective image quality. In this paper, a new color enhancement algorithm resulting in high color saturation is proposed. The proposed method employs multiplicative and additive color mapping to improve color saturation without clipping of a color component for increased target intensity as well as decreased cases. This new scheme is fast and effective, therefore, it can be employed to real time applications such as video signal processing.     

Microwave communications systems and networks in Hungary

The approaches of microwave communications in Hungary are surveyed. Microwave communication systems developed over the last several decades are presented and an overview of the Hungarian microwave communications networks is given emphasizing the methods meeting the user's needs. The special features of the Hungarian equipment development and network structure is also discussed     

Modelling and planning fixed wireless networks

Abstract  

This paper describes a mathematical model for the automated design of fixed wireless access networks (FWA) through the automatic selection and configuration of base station sites. An optimisation algorithm is presented which generates the fixed wireless access network infrastructure design, and results are presented to illustrate the use of the model and its implementation. Economic measures based on the net present value (NPV) are defined to assess the financial viability of potential network designs. The NPV is used within the mathematical optimization framework to produce cost-effective deployments that maximize economic performance while maintaining technical constraints on the network. The model takes into account time-varying input parameters on CapEx, OpEx, revenues and subscriber requirements to model the dynamic nature of the market. Technical radio constraints taken into account include downlink area coverage, interference, capacity and availability. The model and optimisation framework are illustrated by considering the deployment and configuration of infrastructure for three scenarios representing urban, suburban and rural regions. Experiments illustrating the staged deployment of infrastructure over a number of time periods are also presented.     

Dynamic TDD and fixed cellular networks

There are many benefits in using time division duplex (TDD) instead of frequency division duplex (FDD) schemes in fixed wireless cellular systems. To name a few; channel reciprocity for the single carrier frequency used on both up and downlinks will allow easy access to channel state information, reduced complexity of RF design, much higher flexibility in handling dynamic traffic, simpler frequency plan, etc. However, there exists a serious limiting factor in using dynamic-TDD (D-TDD) in cellular systems. This is due to a steady interference on uplinks in a cell, caused by downlink transmissions of other cells. Simulation results show in D-TDD cellular systems, performance is unacceptable, when omni-directional antennas are used at base stations. Simulation results have also demonstrated a great potential for smart antennas in fixed D-TDD bandwidth-on-demand wireless systems     

Analysis of hierarchical cellular networks with mobile base stations

In this paper, we develop and evaluate a hierarchical cellular architecture for totally mobile wireless networks (TMWNs). Extensive performance tests were conducted to evaluate the performance of a two‐tier system and compare its throughput, handoff blocking rate and new call success rate with those obtained by a one‐tier model. Our tests have shown that when the total number of channels is kept the same, the two‐tier system outperformed the one‐tier counterpart under all load conditions. Under the constraint of equal power consumption, the two‐tier system still achieved improvement over the one‐tier system, especially at light and medium load levels. The improvement of the two‐tier system over the one‐tier system was observed to diminish as the degree of randomness in the mobility model is reduced; scenarios where the one‐tier system outperforms the two‐tier system are given. Load balancing schemes based on the concept of reversible handoffs are introduced and their performance improvements are analyzed. Comparison results on the percentage of terminal coverage are presented. An analytical model to compute the new call and handoff blocking probabilities in TMWN is given and evaluated. The model extends the Markov chain approach previously used in hierarchical architectures with stationary base stations and uses a corrected derivation for the handoff blocking probability. Copyright © 2002 John Wiley & Sons, Ltd.     

Personal communications services through the evolution of fixed andmobile communications and the intelligent network concept

New telecommunications services tend to consider fixed network subscribers' requirements as well as mobile network subscribers' requirements. On one hand, subscribers of fixed networks would like to benefit from the mobility offered in mobile networks. On the other hand, mobile subscribers would like to access to services inherent in fixed networks. Personal communications services (PCS) meet this trend while allowing fixed and mobile convergence. In this environment, the application of intelligent networks (INs) to fixed and mobile networks is very convenient to realize PCS. Thus, the natural advancement of telecommunications systems (fixed and mobile) consists in the definition of new telecommunications architectures which take into account technologies from both fixed and mobile environments. This article studies how the IN is used to support mobility and interworking for PCS. Although mobility management already exists in cellular networks like GSM, it is desirable to use the IN concept to introduce flexibility. In addition, the IN allows the introduction of new supplementary services in PCS. Furthermore, the IN concept can be utilized to provide necessary networking functions for the integration of fixed and mobile networks. This article also highlights the involvement of IN in the definition of the global communications systems such as Telecommunication Information Networking Architecture (TINA), Universal Mobile Telecommunications System (UMTS), and International Mobile Telecommunications in the year 2000 (IMT2000)     

Designing multihop wireless backhaul networks with delay guarantees

As wireless access technologies improve in data rates, the problem focus is shifting towards providing adequate backhaul from the wireless access points to the Internet. Existing wired backhaul technologies such as copper wires running at DSL, T1, or T3 speeds can be expensive to install or lease, and are becoming a performance bottleneck as wireless access speeds increase. Longhaul, non-line-of-sight wireless technologies such as WiMAX (802.16) hold the promise of enabling a high speed wireless backhaul as a cost-effective alternative. However, the biggest challenge in building a wireless backhaul is achieving guaranteed performance (throughput and delay) that is typically provided by a wired backhaul. This paper explores the problem of efficiently designing a multihop wireless backhaul to connect multiple wireless access points to a wired gateway. In particular, we provide a generalized link activation framework for scheduling packets over this wireless backhaul, such that any existing wireline scheduling policy can be implemented locally at each node of the wireless backhaul. We also present techniques for determining good interference-free routes within our scheduling framework, given the link rates and cross-link interference information. When a multihop wireline scheduler with worst case delay bounds (such as WFQ or Coordinated EDF) is implemented over the wireless backhaul, we show that our scheduling and routing framework guarantees approximately twice the delay of the corresponding wireline topology. Finally, we present simulation results to demonstrate the low delays achieved using our framework.     

Performance analysis of hierarchical cellular networks with queueing and user retrials

How to efficiently utilize the scarce radio channel resource while maintaining the desired user‐perceived quality level and improved network performance is a major challenge to a wireless network designer. As one solution to meet this challenge in cellular mobile networks, a network architecture with hierarchical layers of cells has been widely considered. In this paper, we study the performance of a hierarchical cellular network that allows the queueing of both overflow slow‐mobility calls (from the lower layer microcells) and macrocell handover fast‐mobility calls that are blocked due to lack of free resources at the macrocell. Further, to accurately represent the wireless user behaviour, the impact of call repeat phenomenon is considered in the analysis of new call blocking probability. Performance analysis of the hierarchical cellular structure with queueing and call repeat phenomenon is performed using both analytical and simulation techniques. Numerical results show that queueing of calls reduces forced call termination probability and increases resource utilization with minimal call queueing delay. It is also shown that ignoring repeat calls leads to optimistic estimates of new call blocking probability especially at high offered traffic. Copyright © 2005 John Wiley & Sons, Ltd.     

Analysis and enhancements to piecewise linear comparametric image registration.

This correspondence details enhancements to previous work on piecewise linear comparametric image registration. The enhancements come in the form of slope constraints and knots' location selection in the comparametric modeling. An analysis of the properties of comparametric functions leads to two general slope constraints that, along with a knot location selection based on the reference image's pixel value distribution, serves to reduce error and sensitivity to the number of segments considered as well as allow for the solution to cases in which there are gaps in the comparagram. Results on real images are presented.     

Mobility management in current and future communications networks

This article describes current and proposed protocols for mobility management for public land mobile networks (PLMNs), Mobile IP, wireless ATM, and satellite networks. The integration of these networks is discussed in the context of the next evolutionary step of wireless communications networks. First, a review is provided of location management algorithms for PCS implemented over a PLMN. The latest protocol changes for location registration and handoff are investigated for Mobile IP, followed by a discussion of proposed protocols for wireless ATM and satellite networks. Finally, an outline of open problems to be addressed by the next generation of wireless network service is discussed     

Radio communications: components, systems and networks

This is an introduction to the special section of papers from DySPAN 2007 - the IEEE Symposium on New Frontiers in Dynamic Spectrum Access Networks that was held on April 17-20, 2007 in Dublin, Ireland.