Malgorzata Porebska

Verification of a Hybrid Ray-Tracing/FDTD Model for Indoor Ultra-Wideband Channels

For development and optimization of ultra-wideband (UWB) based localization and imaging algorithms deterministic channel models are needed, which provide realistic channel impulse responses for given indoor scenarios. As the considered frequency band is 3.1 to 10.6 GHz the dimensions of objects in most indoor scenarios are small compared to the wavelength at lower frequencies. To simulate wave propagation properties in such scenarios an existing ray-tracing model has been combined with the finite difference time domain method (FDTD). The scattering properties of small objects are computed using FDTD and incorporated in a ray-tracing simulation as single scattering points. The simulation results are compared to measurements in a complex laboratory scenario. This comparison shows that the combined ray-tracing/FDTD model provides in complex indoor scenarios higher precision for propagation paths with small delay time. However the overall improvement of the simulation quality is limited and in comparison to the potential improvement by considering the diffuse scattering in the ray-tracing simulation almost negligible.

Investigating the influence of the antennas on UWB system impulse response in indoor environments

UWB applications will primarily be used in indoor environments due to the power constraints given by the FCC in 2002. Therefore, investigating and modeling the indoor propagation of ultra wideband signals is of great interest. It has been shown, how a narrowband ray tracing tool developed at the Institut fur Hochstfrequenztechnik und Elektronik describing indoor wave propagation can be extended to ultra wideband channels, and first simulation results describing the channel impulse response without antenna influence have already been reported. In this paper, antennas are taken into consideration by combining data of measured complex antenna patterns with the extended Ray Tracing method whereas the antennas are typical UWB antennas. The impulse response of the UWB system including antennas is called system impulse response. Since frequency dependent complex pattern information is used, the system impulse response includes the transient response of the antennas in the time domain. After determining the UWB system impulse response, the differences between channel impulse response and system impulse response are investigated. Furthermore, in both cases, a distance estimation between transmitter and receiver is performed to investigate the impact of antennas in UWB localization applications.

Investigations on the Applicability of Diversity Techniques in Ultra Wideband Radio

This paper presents an investigation on the achievable gain in ultra wideband (UWB) indoor propagation channels through the application of diversity and multiple input multiple output (MIMO) techniques. Both, signal to noise ratio and channel capacity are investigated based on simulation results from a ray-optical simulator. In particular the different behavior of classic diversity approaches and spatial multiplexing MIMO is regarded.

Influence of Antenna Performance and Propagation Channel on Pulsed UWB Signals

The main objective of UWB antennas is capability of radiation over very wide bandwidth. But this is not a sufficient condition for proper operation with a pulse based system because different antennas radiate the pulses in different forms. That is why a temporal behavior of an antenna has to be also taken into account during the design. Also during propagation in a real environment the radiated signal will undergo additional distortion due to multi path propagation effects. In this paper firstly the quality measures of an UWB antenna are described followed by the description of main radiation principles supported by examples and measurement results. The focus will be put on relationship between antenna types and applicability to UWB systems. Next possibilities to model an UWB channel are described followed by a discussion of its influence on UWB system performance.

Comparing UWB Freespace Propagation and Indoor Propagation Including Non-ideal Antennas

Electromagnetic wave propagation of UWB signals can be interpreted as a superposition of narrowband electromagnetic wave propagation for a large set of frequencies. Since channel and antenna radiation patterns depend on frequency, describing and modeling the system transfer function of a UWB system including channel and antennas is more challenging compared to a narrowband system. This paper compares mathematical modeling of UWB freespace propagation to the more realistic case of UWB multipath propagation in indoor scenarios. Simulation results based on 3D Ray Tracing visualize the effect of both indoor channel and antennas on the UWB transmit signal in an indoor scenario, and finally, it is demonstrated, how signal distortions can be compensated by inverse filtering using an estimated system transfer function.

Simulation and Measurement Based Correlation Estimation for Ultra Wideband Antenna Arrays

In order to optimize the performance of diversity antenna systems for communications applications it is desirable to have little correlation between the signals at the different receiving antennas. This paper deals with the estimation of the correlation coefficients of a linear ultra wideband antenna array in an indoor propagation scenario. A suitable approach for the estimation procedure is described and applied to propagation simulation results as well as to measurement results. Correlation coefficients obtained from the proposed estimation procedure are compared to analytically calculated correlation coefficients in order to verify the estimation procedure.

Performance of Downlink Spatial-Multiplexing in Realistic Urban Multi-User MIMO Channels

In this paper the performance of user specific beamforming, waterfilling, block diagonalization, and successive optimization is compared to the performance of a conventional SISO reference system in a single cell with a sectorized BS and several MTs. Whereas in the SISO reference system as well as in the beamforming and waterfilling algorithm the MTs are multiplexed by a conventional multiplexing method (TDMA, FDMA, CDMA) the two multi-user MIMO algorithms allow users to share the same spectrum by multiplexing them in space. Several multi-user scenarios are generated by means of a realistic urban channel model. The channel model incorporates a model of the city of Karlsruhe, a mobility model as well as a ray-tracing based wave propagation model. Simulation results show clearly the potential of downlink spatial-multiplexing to improve the system capacity, to reduce the exposure (power density) and to reduce the transmit power and therefore the operating costs in future cellular mobile radio systems.

Influence of multipath propagation on UWB imagery

In this paper the influence of multipath propagation on the quality of UWB imagery is analyzed. Typical UWB imaging methods like time domain migration consider only propagation paths with one reflection at the object of interest. In most scenarios the paths of higher order are attenuated sufficiently to neglect them. However, in scenarios containing metallic objects (e.g indoor factory scenarios) multiple reflections can occur without strong attenuation of the signal. In this paper the influence of these multiple reflections on the generated image is investigated.

Performance of Downlink Spatial-Multiplexing in Urban Macrocellular Multi-User MIMO Scenarios

The aim of this paper is to compare the performance of different smart antenna algorithms to the performance of a conventional SISO reference system in an urban multi-user MIMO scenario. A single cell with three 120 deg sectors and several moving users is used for evaluation. The scenario as well as the channel information is generated by means of a realistic urban channel model that consists of a model of the city of Karlsruhe, a mobility model and an accurate ray-tracing based wave propagation model. The smart antenna algorithms under test are two single-user MIMO algorithms (user specific beamforming, waterfilling) and two multi-user MIMO algorithms (block diagonalization, successive optimization). Simulation results show clearly the potential of downlink spatial-multiplexing to improve the system capacity, to reduce the exposure, the transmit power and therefore also the operating costs in future cellular mobile radio systems

Base station antenna synthesis for high sites CDMA networks

An optimal high site base station antenna, consisting of a 16-element array has been synthesized with the Orchard-Elliott algorithm. The synthesis results from the definition of an ideal elevation pattern based on a set of evaluation criteria, which link CDMA system performance with a simplified propagation model. The use of these simplified criteria and propagation model to adequately represent a CDMA cellular system is validated with help of a full Ray-tracing simulator.