Philipp Wertz

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.

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.

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.

Wideband propagation modelling for indoor environments and for radio transmission into buildings

With the introduction of wireless broadband services in indoor environments there is a growing interest in propagation models for the mobile radio channel inside buildings. Because of the increasing transmission rates propagation models should be able to calculate the field strength coverage as well as the wideband properties for these indoor scenarios. This paper presents a new ray optical approach, which enables the prediction of field strength, delay spread and impulse response within a very short computation time. Additionally, simulation results gained with the new model are compared to measurements of the different wideband channel parameters.

Location dependent CDMA orthogonality in system level simulations

In system simulations of WCDMA radio networks, a constant value for the orthogonality factor is often assumed in the whole considered area of interest to determine the network performance. This factor is used to scale the intra-cell interference, which has an important impact on the network performance. However, the orthogonality factor is not constant, but depends on the individual channel profile between transmitter and receiver, as well as on the receiver implementation. Therefore, this factor is different for every particular user. In a new approach, the orthogonality factor is calculated dependent on the above parameters for each receiver point individually. Comparisons of this new approach with the simple constant value approach are presented. The results show that the assumption of a constant orthogonality factor within a cell may lead to unrealistic results in system level simulations, especially if interference sensitive high bit rate services are considered, e.g., the packet transmission technology HSDPA (high speed downlink packet access). Especially in the field of performance analysis for network planning and design, it is important to obtain an accurate performance estimate with a correlation to the predicted area, instead of average values for the whole simulation area.

Deterministic Propagation Model for the Planning of Hybrid Urban and Indoor Scenarios

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, W-LAN, 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(s) between transmitter and receiver. The parameters of these paths are determined (e.g. path length, number and type of interactions, material properties of objects, ...) and are used for the prediction of the path loss. This model allows also 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. For the validation of the new model, measurements were made

Wave propagation modeling inside vehicles by using a ray tracing approach

With the growing demand for sensors and actors in the automotive technology, a wireless concept for the data exchange between different system components inside a vehicle becomes interesting. In order to describe and thus assess the mobile radio channel in the vehicle, simulations are required. For low frequencies, full wave simulations using the method of moments are well suited. For higher frequencies, these models become inadequate as regards the computational effort. This paper discusses the demand for models that can describe the radio channel inside vehicles at high frequencies and presents an appropriate ray tracing approach. The results of a measurement campaign are used to validate the proposed ray optical model.

Deterministic propagation models for radio transmission into buildings and enclosed spaces

With the growing interest for broadband mobile services in 3rd generation mobile communication networks, the investigation of radio transmission into vehicles and buildings is getting more important. Models for the propagation into vehicles and buildings enable the calculation of the field strength or received power inside these objects. The inner structure of the vehicles (e.g. metal parts) and buildings (inner walls, furniture) as well as the surroundings (other vehicles, buildings) must be considered, and also different construction materials must be taken into account. A deterministic ray tracing approach has been developed, enabling the computation of the transition from an urban scenario to an indoor scenario and vice versa, thus allowing a very accurate computation of the field strength or received power inside vehicles or buildings. Due to the ray tracing technique, the approach can also be utilized to evaluate wideband properties of the mobile radio channel by computing its impulse response. In order to validate such propagation models, measurements inside and outside a building were made.

Impact of Building Database Accuracy on Predictions with Wave Propagation Models in Urban Scenarios

The accuracy of predictions with wave propagation models depends significantly on the quality of the building databases, as they show discrepancies when compared to reality. This is due to the inaccuracies of the photometric methods used to create these databases, but also to the fact that new buildings are raised or old buildings are pulled down. However, propagation models should feature a certain robustness against these inaccuracies. In this paper, the sensitivity of different propagation models for urban scenarios with respect to building database inaccuracies is analyzed. The main focus is the comparison of the dominant path model with a Ray Tracing model, but the results are also put in relation to the empirical COST 231 Walfisch-Ikegami model. Furthermore, the possibilities of an automatic database simplification to reduce calculation times are investigated, and it is shown that ray tracing computation times can be reduced up to 50% with only slight decreases in the accuracy by applying suitable simplification algorithms. For the evaluation of the influence on the accuracy also path loss measurements in different scenarios were used

Fast and Enhanced Ray Optical Propagation Modeling for Radio Network Planning in Urban and Indoor Scenarios

With the increasing number of subscribers in mobile communications there is a growing interest in propagation models for the mobile radio channel in urban scenarios and inside buildings. Because of the increasing transmission rates propagation models should be able to predict the field strength coverage as well as the wideband properties for these scenarios.