Andreas Eisenblätter

Integrated Access Point Placement and Channel Assignment for Wireless LANs in an Indoor Office Environment

Wireless Local Area Network (WLAN) is currently among the most important technologies for wireless broadband access. The IEEE 802.11 technology is attractive for its maturity and low equipment costs. The overall performance of a specific WLAN installation is largely determined by the network layout and the radio channels used. Optimizing these design parameters can greatly improve performance. In this paper, access point (AP) placement and channel assignment are optimized using mathematical programming. Traditionally, these decisions are taken sequentially; AP placement is often modeled as a facility location problem, channel assignment as an (extended) graph coloring problem. Treating these key decisions separately may lead to suboptimal designs. We propose an integrated model that addresses both aspects simultaneously and thereby balances the two optimization objectives. Computational results show that indeed the integrated approach is superior to the sequential one.

Frequency Planning and Ramifications of Coloring

This paper surveys frequency assignment problems coming up in planning wireless communication services. It particularly focuses on cellular mobile phone systems such as GSM, a technology that revolutionizes communication. Traditional vertex coloring provides a conceptual framework for the mathematical modeling of many frequency planning problems. This basic form, however, needs various extensions to cover technical and organizational side constraints. Among these ramifications are

Modelling Feasible Network Configurations for UMTS

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UMTS radio network evaluation and optimization beyond snapshots

-coloring and list coloring. To model all the subtleties, the techniques of integer programming have proven to be very useful. The ability to produce good frequency plans in practice is essential for the quality of mobile phone networks. The present algorithmic solution methods employ variants of some of the traditional coloring heuristics as well as more sophisticated machinery from mathematical programming. This paper will also address this issue. Finally, this paper discusses several practical frequency assignment problems in detail, states the associated mathematical models, and also points to public electronic libraries of frequency assignment problems from practice. The associated graphs have up to several thousand nodes and range from rather sparse to almost complete.

Wireless network design: solution-oriented modeling and mathematical optimization

Telecommunications operators worldwide are facing the challenge of deploying UMTS. These networks have to meet consumers’ expectations, tight budget constraints and governmental regulations. The careful dimensioning of the radio access infrastructure plays an essential role in achieving these goals.

Public UMTS radio network evaluation and planning scenarios

A new evaluation scheme for universal mobile telecommunications system (UMTS) radio networks is introduced. The approach takes the complex coupling of coverage and capacity through interference into account. Cell load estimates, otherwise obtained through Monte-Carlo simulation, can now be approximated without time-consuming iterative simulations on user snapshots. The two cornerstones are the generalization of interference coupling matrices from user snapshots to average load and the emulation of load control by an analytical scaling scheme. Building on the new evaluation scheme, two novel radio network optimization algorithms are presented: an efficient local search procedure and a mixed integer program that aims at designing the coupling matrix. Computational experiments for optimizing antenna tilts show that our new approaches outperform traditional snapshot models

Optimization methods for UMTS radio network planning

As the telecommunication industry matures, there is vital interest in good network designs. Many planning tasks in wireless networks are particularly complex and challenging. A solution-oriented modeling approach can help to devise efficient automatic planning and optimization schemes. This article discusses how good mathematical models can be obtained for real-world problems, which model structures facilitate good computational behavior, and which advanced tools are available for solving such models. The trade-off between capturing the fine characteristics of technologies and the simplicity of the model is illustrated for several technologies and example problems

Capacity optimization for UMTS: Bounds and benchmarks for interference reduction

A library of three public and realistic scenarios for UMTS radio networks was compiled within the EU-funded project MOMENTUM. We illustrate the contents of these scenarios and demonstrate the importance for detailed data by some cross-checks with common simpler models from the literature. The scenarios are valuable to research for several reasons. Being public, the datasets can be used freely in the scientific community. In similar situations, the availability of public benchmark data has stimulated research over years and has significantly contributed to the reproducibility and comparability of computational results. Being realistic, the scenarios are far more detailed than those typically used for publications; they help scientists to better establish or to improve on the practical relevance of their results.

Multistage stochastic programming in strategic telecommunication network planning

The UMTS radio network planning problem poses the challenge of designing a cost-effective network that provides users with sufficient coverage and capacity. We describe an optimisation model for this problem that is based on comprehensive planning data of the EU project Momentum. We present heuristic mathematical methods for this realistic model, including computational results.

Mathematical Optimization Models for WLAN Planning

UMTS has been designed as the next platform for mobile mass market communication. After a slow start, the usage of UMTS in terms of subscribers and volume is picking up momentum. Following the initial coverage-driven phase, network capacity is moving into focus. During network planning and optimization, cell capacity can be improved by explicitly designing for minimal interference. This article introduces planning methodologies that allow to minimize interference overhead while maintaining the established network coverage. Our main contribution is the first practicable approach for comparing interference to lower bounds and benchmarks. This comparison on realistic datasets suggests that our optimization methods produce first-class results.