Christian M. Mueller

A Cell Outage Detection Algorithm Using Neighbor Cell List Reports

Base stations experiencing hardware or software failures have negative impact on network performance and customer satisfaction. The timely detection of such so-called outage or sleeping cells can be a difficult and costly task, depending on the type of the error. As a first step towards self-healing capabilities of mobile communication networks, operators have formulated a need for an automated cell outage detection. This paper presents and evaluates a novel cell outage detection algorithm, which is based on the neighbor cell list reporting of mobile terminals. Using statistical classification techniques as well as a manually designed heuristic, the algorithm is able to detect most of the outage situations in our simulations.

Adaptive fairness control for a proportional fair LTE scheduler

In cellular OFDMA networks, there exists a fundamental trade-off between the achievable cell capacity and the degree of fairness among the users in the cell. Several scheduling algorithms have been proposed which try to balance this tradeoff. The parameterization of these scheduling algorithms to achieve a certain desired fairness level is non-trivial. We show that the optimal fairness parameter settings depend on the system state, such as the current cell load. Our main contribution is a design of a self-optimizing scheduler architecture which includes a controller element that dynamically adjusts the fairness parameters of the scheduler. We demonstrate that with this design, an operator-defined reference fairness level is maintained in scenarios with fluctuating load and thus cell throughput can be improved. It is applicable for a class of proportional fair scheduling algorithms and can be adapted to other algorithms allowing to influence the fairness level.

Network-based Mobility with Proxy Mobile IPv6

This paper presents a handover delay analysis of network- based handovers with Proxy Mobile IPv6 and compares its performance to Mobile IPv6. Recommendations are given to avoid excessive handover delays due to timer and configuration mechanisms in the IPv6 specification. Furthermore, extensions are proposed to make Proxy Mobile IPv6 applicable to make- before-break handovers in multi-interface scenarios. Finally, by leveraging functions of a Multi-Radio Resource Management, handover execution can be adapted to the actual radio conditions on the terminal.

Evaluation of the Automatic Neighbor Relation Function in a Dense Urban Scenario

Self-organizing network (SON) capabilities are an important feature of coming LTE networks. An automated configuration of neighbor cell lists, the so-called Automatic Neighbor Relation (ANR) function, is one of the first SON features being deployed in commercial networks. In this paper, we present simulation results of the convergence time of the ANR function in a dense urban scenario. We model the corresponding cell identifier measurements and the X2 setup in a detailed way. Our results show that even for sparse user densities, the network achieves good handover performance within the first two hours. We further propose a blacklist method which can significantly reduce measurement overhead in the mobile terminals during the network auto-configuration period.

Analysis of interactions between Internet data traffic characteristics and Coordinated Multipoint transmission schemes

Several studies have shown the potential of Coordinated Multipoint (CoMP) transmission schemes to increase spectral efficiency. However, most CoMP algorithms are susceptible to outdated channel state information, which is a consequence of inter-eNodeB signaling over the backhaul network. User traffic variation constitutes another time-varying process which interacts with CoMP algorithms. These interactions usually are undesired and can reduce achievable CoMP gains in practical settings. We analyze these interactions using an abstract CoMP model and realistic traffic patterns. We propose two different ways to initiate coordinated transmission and present an analysis of the resulting coordination gains and transmission delays at the application layer. Our analysis reveals that traffic characteristics have significant impact on coordination gains as seen by a user.

Transmit mode selection schemes for distributed coordinated transmission of data traffic

Coordinated Multi-Point transmission schemes have a large potential to increase spectral efficiency in cellular networks. While the physical layer aspects of coordinated transmission received a lot of attention, its integration into higher layers yet remains to be investigated. In this work, we analyze the transmit mode selection for coordinated and uncoordinated transmission of data traffic. We propose two transmit mode selection schemes to decide whether to use coordinated transmission for an object or not. One scheme is based on object size, the other one is based on queue state. We derive the optimal parameter settings for our selective coordination schemes and show how they improve system performance.

A Novel Sampling Method for the Spatial Frequencies of Sinusoid-Based Shadowing Models

Careful modeling of the radio channel characteristics is an important issue for system level simulations. While a number of detailed path loss, shadowing and fast fading models can be found in literature, many of them entail large computational efforts and hence lead to long simulation times, or require huge amounts of memory. In this paper, we focus on shadowing models with two-dimensional correlation properties. We present handover performance evaluations as a use case from which requirements to the modeling of the shadow fading are derived. For different implementations of the shadow fading in system level simulations, we discuss their pros and cons and then focus on the sum of sinusoid model proposed by Cai and Giannakis [1]. Our main contribution lies in a new frequency sampling method to determine the coefficients of the sinusoidal waveforms. We show that this new method, denoted as Power Sampling Method (PSM), allows for a significant reduction of the number of sinusoids while the correlation properties of the shadow fading channel are preserved.

Interference mitigation by distributed beam forming optimization

Inter-cell interference is a major issue in OFDMA networks. One approach to reduce the amount of interference is to use beam forming antennas. Further interference mitigation is achieved if neighbor base stations coordinate the directions of their beams. This paper presents a novel distributed interference coordination algorithm using main-lobe steering beam formers. Our algorithm does not require any explicit signaling between base stations. Also, it does not require any additional channel measurements to be signaled to the base stations besides those already performed for basic operation. Our evaluations show that significant performance gains can be achieved even with non-greedy traffic. Index Terms – Interference coordination, beam forming antennas, COMP

Algorithms for Hotspot Coverage Estimation Based on Field Strength Measurements

Cellular networks are more and more complemented by wireless LAN hotspots. However, when users are mobile, the small coverage area of hotspots is a challenge for the access network discovery and selection. Network selection mechanisms can be improved if, in addition to terminal-based measurements, hotspot information can be retrieved from an information service. In this context, the coverage area is one of the most important characteristics of hotspots. This paper studies algorithms for the precise estimation of hotspot coverage areas based on field strength measurements performed by individual terminals. Different approaches for interpolation, vectorization and complexity reduction of measurement data are presented and evaluated in different scenarios by means of simulation. As a result, guidelines for the optimal parametrization of these algorithms are presented.

A realistic reference simulation environment for typical urban areas

The increasing complexity in nowadays networks enforces the need for automation and a better understanding of radio network modeling. To ensure comparability of simulation results we propose a common simulation environment for the IC 1004. The aim of this paper is to actuate discussions on the desirable content of a common simulation environment.