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.

The performance evaluation of W-CDMA networks is intricate as cells are strongly coupled through interference. Pole equations have been developed as a simple tool to analyze cell capacity. Ample scientific contributions have been made on their basis. In the traditional forms, the pole equations rely on strong assumptions such as homogeneous traffic, uniform users, invariant downlink orthogonality. These assumptions are not met in reality. Hence, the pole equations are typically used during initial network dimensioning only. Actual network (fine-) planning requires a more faithful analysis of individual cell's capacity. Complex analytical analysis or Monte-Carlo simulations are used for this purpose.

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.

Abstract — The recent surge of new viruses and host attacks in the Internet and the tremendous propagation speed of selfdistributing attacks has made network security a pressing issue. To protect an end-system, it must continuously be patched and additional security tools like an Intrusion Prevention System (IPS) are needed. The main problems are the effort for the users and network performance: The last years have shown that many users neither maintain their computers nor run an IPS. Accordingly, their systems remain vulnerable. On the other hand, the operation of an IPS inevitably decreases network performance as all packets are analyzed for malicious content before being forwarded. We recently proposed the operation of a flexible overlay network of intrusion prevention systems running on top of programmable routers to mitigate these issues. With this architecture, security services can be dynamically distributed in the network. In this paper, we leverage this flexibility for minimizing the impact of intrusion prevention on network performance. Based on measurement from experiments with a prototype implementation of a programmable router, we derive an analytical description of the impact of a single active router on the network. This is then used to formulate two mixed integer optimization models for finding placement strategies for security services. Using detailed simulations on two example networks we show that the optimized strategies perform significantly better than reference placement strategies, including centralized intrusion prevention. I.

Within the last decade, the orthogonal frequency- division multiplexing (OFDM) transmission scheme has become part of several standards for wireless systems. Today, OFDM is even a candidate for fourth-generation wireless systems. It is well known that dynamic OFDMA systems potentially increase the spectral efficiency. They exploit diversity effects in time, space, and frequency by assigning system resources periodically to terminals. Informing the terminals about new assignments creates a signaling overhead. Up to now, this overhead has not been taken into account in studies on dynamic orthogonal frequency-division multiplexing access (OFDMA) systems. Yet this is crucial for a realistic notion of the performance achieved by dynamic approaches. In this paper, we close this gap. We introduce two forms of representing the signaling information and discuss how these affect system performance. The study of the signaling impact on the performance is conducted for an exemplary dynamic approach. We find that the throughput behavior of dynamic OFDMA systems is significantly influenced by the signaling overhead. In many situations, neglecting the overhead leads to wrong performance conclusions. Also, the performance difference between dynamic and static schemes is now much more sensible to the specific parameter set of the transmission scenario (e.g., frame length, subcarrier number, etc.). This leads to the proposal of access points which should adapt certain system parameters in order to provide optimal performance.