Simon Plass

Positioning Algorithms for Cellular Networks Using TDOA

In this paper, we investigate the performance of positioning algorithms in wireless cellular networks based on time difference of arrival (TDoA) measurements provided by the base stations. The localization process of the mobile station results in a non-linear least squares estimation problem which cannot be solved analytically. Therefore, we use iterative algorithms to determine an estimate of the mobile station position. The well-known Gauss-Newton method fails to converge for certain geometric constellations, and thus, it is not suitable for a general solution in cellular networks. Another algorithm is the steepest descent method which has a slow convergence in the final iteration steps. Hence, we apply the Levenberg-Marquardt algorithm as a new approach in the cellular network localization framework. We show that this method meets the best trade-off between accuracy and computational complexity

Fast decoding of rank-codes with rank errors and column erasures

This paper describes the decoding of Rank-Codes with different decoding algorithms. A new modified Berlekamp-Massey algorithm for correcting rank errors and column erasures is described. These algorithms consist of two decoding steps. The first step is the puncturing of the code and the decoding in the punctured code. The second step is the column erasure decoding in the original code. Thus decoding step is about half as complex as the known algorithms

Investigations on Link-Level Inter-Cell Interference in OFDMA Systems

This paper addresses investigations and modeling of inter-cell interference of a next generation cellular orthogonal frequency division multiplexing access (OFDMA) transmission system on the link-level. Different strategies, i.e., Gaussian approximation (GA) and binomial method, for modeling the intercell interference are given and investigated. Furthermore, the influence of the closest interfering cells and time synchronization offsets are in the focus. Concluding from the investigations, the GA for the inter-cell interference is an appropriate modeling in the case of single antenna systems and linear receivers

Modeling and analysis of a cellular MC-CDMA downlink system

The concept of a multi-cell environment for an MC-CDMA downlink scenario is presented; it is based on a propagation model taking into account path loss and shadowing. The interference of adjacent cells is studied and the Gaussian approximation (GA) is investigated for simplifying the interference simulation. The major influence of the interfering cells is restricted to the peripheral area of the desired cell. In particular, it is shown, by simulations, that the GA for the impinged interference signals is an appropriate assumption. This drastically decreases the simulation complexity for a high number of interfering cells, e.g., one or two tiers around the desired cell.

Synchronization Algorithms for Positioning with OFDM Communications Signals

This paper covers positioning techniques for cellular networks using orthogonal frequency division multiplexing (OFDM) communications signals. These methods are based on symbol-timing synchronization algorithms to find the starting point for the underlying OFDM symbols of the incident signals. Commonly used approaches are, e.g., the Schmidl-Cox algorithm and the Minn algorithm. These algorithms are investigated w.r.t. their positioning capabilities. Furthermore, they are extended to improve the performance in multipath environments and to achieve a sufficient accuracy with weak signals from neighboring out-of-cell base stations.

Soft Cyclic Delay Diversity and its Performance for DVB-T in Ricean Channels

Cyclic delay diversity (CDD) provides additional diversity in Rayleigh fading channels, and therefore, improves the system performance. For line-of-sight (LOS) propagation, e.g., the additive white Gaussian noise channel, the implementation of CDD yields to a performance loss. The power distribution among the transmit (TX) antenna branches is a further parameter which can freely be chosen for optimizing the system performance and allows to switch on/off CDD softly. The idea is to feed different power levels into the multiple TX antenna branches rather than distributing the TX power uniformly among the TX antennas. We exemplarily implement the soft CDD principle to the terrestrial digital video broadcasting system (DVB-T). We consider a Ricean multipath fading channel, which allows to control the ratio of LOS and non-LOS propagation power via the Ricean factor for simulations. Simulation results for 2-TX and 4-TX antenna CDD show that antenna power weighting significantly reduces the SNR loss in LOS propagation by the cost of a slight degradation of the SNR gain in non-LOS scenarios.

Combining Wireless Communications and Navigation -The WHERE Project

Wireless communications and navigation have different constraints to cope with. On the one hand, communication systems traditionally aim at high spectral efficiency with specific requirements such as low latency and low power consumption. On the other hand, navigation is usually based on the transmission of known data signals at low data rates with fine synchronization capabilities for efficient signal acquisition and tracking. The ICT project WHERE (Wireless Hybrid Enhanced Mobile Radio Estimators) will focus on exploiting the positioning information to enhance communications -and vice versa- within heterogeneous and/or cooperative wireless systems. The paper gives an overview and outlines the upcoming goals of the FP7-ICT project WHERE. The WHERE project is an ICT STREP project involving 14 partners. It started in January 2008 and is running until June 2010.

Cellular Cyclic Delay Diversity for Next Generation Mobile Systems

In this paper, we address a new method called cellular cyclic delay diversity (C-CDD) to a cellular mobile radio communications system. A promising candidate for a next generation mobile downlink is multi-carrier code division multiple access (MC-CDMA). The C-CDD technique is exemplarily applied to MC-CDMA. The cyclic delay diversity technique increases the diversity in a system by cyclically shifted replicas of the transmitted signal over several transmit antennas. For improving the performance at the cell border in a cellular system, we introduce the cyclic delay diversity principle by sending replicas of the desired signal including a cyclic shift from adjacent base stations. The resulting C-CDD scheme is standard conformable. Therefore, no additional change in the mobile terminal is needed to exploit the C-CDD. The influence of the cyclic delay to a cellular MC-CDMA system is investigated. Furthermore, simulation results show the significant improvement of the performance at the cell border by using C-CDD in an MC-CDMA cellular system for different transmission scenarios.

An Overview of Cyclic Delay Diversity and its Applications

We recall the principles of cyclic delay diversity (CDD) and discuss the properties and impact of this transmit antenna diversity technology. Different applications motivate variations of the CDD principle. This variants are briefly introduced and discussed. We show the application to several types of wireless systems, in particular terrestrial digital video broadcasting, cellular mobile radio communications systems and a wireless communications system using adaptive bit loading. Simulation results show the benefits of CDD for these kind of systems.

Positioning Based on Factor Graphs

This paper covers location determination in wireless cellular networks based on time difference of arrival (TDoA) measurements in a factor graphs framework. The resulting nonlinear estimation problem of the localization process for the mobile station cannot be solved analytically. The well-known iterative Gauss-Newton method as standard solution fails to converge for certain geometric constellations and bad initial values, and thus, it is not suitable for a general solution in cellular networks. Therefore, we propose a TDoA positioning algorithm based on factor graphs. Simulation results in terms of root-mean-square errors and cumulative density functions show that this approach achieves very accurate positioning estimates by moderate computational complexity.