Gerd Wölfle

Database correlation for positioning of mobile terminals in cellular networks using wave propagation models

Many new services for mobile radio networks rely on a precise location of the mobile terminal. Especially in urban environments, multipath propagation leads to very complex scenarios without line-of-sight between the mobile and the different base stations. In these situations, a location technique based on simple delay evaluations and/or GPS is not accurate enough or not applicable. In this paper, a database correlation method for the positioning of mobile terminals is presented which yields precise results in urban environments. The approach is based on propagation models utilized for the planning of mobile radio networks. The results of the propagation models during the planning process define a look-up-table. By evaluating the measured path losses and available propagation times between the mobile terminal and several base stations, the positions of mobile terminals in urban environments can reliably be predicted.

Measurement of building penetration loss and propagation models for radio transmission into buildings

The investigation of radio transmission into buildings is getting more and more important. Models for the propagation into buildings enable the calculation of the indoor field strength coverage based on the given outdoor coverage. In order to develop and to calibrate such propagation models several measurements of the building penetration loss with different transmitter locations were undertaken and evaluated. Additionally, the empirical, semi-empirical and deterministic models we developed are presented in this paper.

Verifying path loss and delay spread predictions of a 3D ray tracing propagation model in urban environment

In this paper path loss and delay spread predictions of a 3D ray tracing software are compared to wideband radio channel measurements made in Helsinki city center. Measurements were carried out in the 2 GHz band by using a wideband radio channel sounder, which gives out complex channel impulse responses. Reference delay spreads were obtained from power delay profiles, and path losses were available after appropriate cable calibration measurements. Comparisons between measurement and propagation predictions were made in cases where a realistic directional BS antenna was placed (a) slightly below the rooftop level and (b) slightly above the rooftop level. For propagation modeling a fully 3D ray optical model was used.

Automatic optimization algorithms for the planning of wireless local area networks

The planning of WLAN infrastructures that supply large buildings or areas requires the consideration of many aspects and therefore is a difficult task if done manually. In this paper, a method is presented that allows one to optimize such networks automatically. The approach is based on predictions of the received power to account for the propagation conditions that have a major impact on the performance of WLANs. The optimization is applied to a set of possible locations where access points can be installed. Out of this set, a minimum selection of locations is made to meet the given requirements. These consist of the determination of areas with different priorities and the definition of further parameters. It not only takes into account the required coverage and capacity but also the interference situation. The arising co-channel interference is minimized by an appropriate assignment of the available carrier frequencies. The discussed approach may not find the global optimum in all cases, but it yields a suggestive result based on the locations defined by the network planner. Due to the very short computation time, different configurations can be analyzed very quickly.

Dominant paths for the field strength prediction

An algorithm for the determination of the dominant paths for indoor wave propagation is presented. The algorithm computes a tree of the relations between the rooms inside the building and the branches of the tree are used for the determination of the dominant paths. Based on these dominant paths, three different prediction models are presented and compared with one another and with measurements. Two of the three models are based on neural networks, trained with measurements and the third model is an empirical model. With the neural prediction models a good generalization is achieved and they are very accurate in buildings not used for the training of the neural network.

Field strength prediction in indoor environments with neural networks

A new model for the field strength prediction for mobile communication networks inside buildings is presented. The model is based on artificial neural networks, trained with measurements. In contrast to other neural prediction models a good generalization is achieved, so the prediction results are also very accurate in buildings not used for the training of the neural network. Two algorithms for the selection of the training patterns for the neural networks are presented and compared to each other.

Advanced ray‐optical wave propagation modelling for urban and indoor scenarios including wideband properties

Ray-optical propagation models are often utilized for the prediction of the field strength (and delay spread) in mobile radio networks. However, the practical usage of these deterministic models is limited by their high computational demands. A new method for the acceleration of ray-optical models is presented in this paper. It is based on a single preprocessing of the database in which the mutual visibility relations between the walls and the edges of the buildings are determined. The propagation model is implemented for urban and indoor scenarios, and comparisons with measurements show the gain in computation efficiency as well as in achieved prediction accuracy.

Measurements and 3D Ray Tracing Propagation Predictions of Channel Characteristics in Indoor Environments

In this paper path loss, delay and angular spread predictions of a 3D ray tracing propagation tool are compared to spatially resolved wideband radio channel measurements performed in a modern office building. Measurements were carried out in the 5 GHz band by using a wideband radio channel sounder, which gives out complex channel impulse responses. Reference rms delay spread and angular spreads at transmitter and receiver were obtained from SAGE processed super-resolution data, and path losses were available from sounder matched filter outputs after appropriate calibrations. Comparisons between propagation predictions and measurements were made in different indoor scenarios including office, lobby and cafeteria environments. For propagation modelling a full 3D ray optical model was used.

Combined urban and indoor network planning using the dominant path propagation model

With the growing interest for broadband mobile services in mobile communication networks, the investigation of radio transmission in and into buildings is getting more important. Popular empirical and deterministic models for the propagation inside buildings compute the field strength based on the inner structure of the buildings (walls, furniture). But for current and future wireless networks (3G, B3G, WLAN, WiMax,..), the neighboring buildings must also be considered to avoid interference problems in these buildings. Additionally the indoor coverage of outdoor transmitters must be analyzed to guarantee a high QoS even inside buildings. A new concept for the prediction of the field strength in such hybrid scenarios (urban and indoor) is presented in this paper. This new concept does not rely only on the direct ray (like empirical models) and it does not consider hundreds of rays for a single radio link (like ray tracing). The new model focuses on the most dominant path between transmitter and receiver. It allows the computation of the transition from an urban to an indoor scenario and vice versa, thus allowing an accurate computation of the received power inside and around buildings. The new model is validated with various measurements and shows a good accuracy.

Simulator for performance analysis in UMTS FDD networks with HSDPA

High speed downlink packet access (HSDPA) is a technology to extend the peak data rates and capacity of 3G mobile data transmission systems. It targets especially favorable radio channel environments with the possibility to use higher order modulation and higher code rates. Furthermore fast retransmissions and enhanced scheduling algorithms can be used to boost data rates and to provide the required quality of service (QoS). A dynamic W-CDMA system level simulator has been extended to enable the simulation of packet switched services with special focus on HSDPA. The complete simulation system contains traffic sources that create sequences of packets for each active user equipment (UE), models the protocol stack and provides the possibility to collect performance indicators, e.g. sector packet data throughput, page throughput, and packet delays, in different scenarios for offline analysis. The simulation tool will be described and some example results concerning packet data performance of HSDPA will be shown.