PhD Thesis:

Publications in Journals:

Abstracts:

Correlation Properties of Extended m-Sequences: In this article the correlation properties of extended m-sequences are treated and compared to those of m-sequences. Extended m-sequences are obtained from m-sequences inserting an additional element per period yielding periods 2^n where n is an integer. It turns out that extended m-sequences provide good autocorrelation but poor crosscorrelation properties. This behaviour is similar to that of m-sequences.

Design Study for a CDMA-Based Third Generation Mobile Radio System: This paper focuses on a CDMA design study for future third-generation mobile and personal communication systems such as FPLMTS and UMTS. In the design study, a rigorous top down approach is adopted starting from the most essential objectives and requirements of universal third-generation mobile systems. Emphasis is laid on high flexibility with respect to the implementation of a wide range of services and service bit rates including variable rate and packet services. Flexibility in frequency and radio resource management, system and service deployment, and easy operation in mixed-cell and multioperator scenarios are further important design goals. The system concept under investigation is centered around an open and flexible radio interface architecture based on asynchronous direct-sequence CDMA with three different chip rates of approximately 1, 5, and 20 Mchip/s.

The presented CDMA system concept forms the basis for an experimental test system (testbed) which is currently under development. This experimental system concept has been jointly established by the parnters in the European RACE project R2020 (CODIT). The paper describes the radio transmission scheme and appropriate receiver principles and presents first performance results based on simulations.

Iterative Interference Cancellation for FFH/MFSK Systems: In this contribution iterative interference cancellation is introduced to improve system spectral efficiency in fast frequency hopping multiple access systems. The proposed algorithm iteratively cancels interference from users whose symbols have already been estimated. Both an interference-only channel and a frequency selective fading channel are considered. Noncoherently detected M-ary frequency shift keying is employed and all users are time-aligned at the receiver.

An Algorithm for Joint Detection in Fast Frequency Hopping Systems: In this contribution an algorithm for joint detection in fast frequency hopping / multiple frequency shift keying (FFH/MFSK) multiple access (MA) systems is presented. The new algorithm -- referred to as REC algorithm -- evaluates ambiguities which occur during the decision process and iteratively reduces the number of candidate symbols. The REC algorithm is of low complexity, suitable for every addressing scheme, and effective for both an interference-only channel and a fading channel. For the interference-only channel the REC algorithm enables maximum likelihood (ML) joint detection with low computational effort.

Fade Slope Statistics of 40 GHz Beacon Signals: Fade slope statistics for negative and positive slopes are presented which are obtained by propagation measurements of the 40 GHz beacon signal of the italian satellite ITALSAT. Especially, the fade slope and the 3 dB time duration introduced here are evaluated. Measured fade slopes of up to 3.2 dB/s were recorded. However, in 99.99% of the fading event time the fade slopes are < 1.9 dB/s.

Frequency Hopping CDMA Over Mobile Radio Channels: The purpose of this contribution is to determine the performance of fast frequency hopping / code division multiple access (FFH/CDMA) systems over mobile radio channels as specified by global system for mobile communications (GSM) and to compare the results to those obtained under the commonly made assumption that signals on different carriers fade independently to each other. Uplink and downlink scenarios are considered and the various delay power profiles are taken into account. It is shown that GSM channel models may provide significantly larger bit error rates than above mentioned assumption. Furthermore, uplink and downlink turn out to perform very similar.

Impact of Seasonal and Diurnal Variations on Satellite System Design in V-Band: In the framework of the ITALSAT campaign various European institutions carried out propagation measurements at V-band. In this frequency band signal reception in a satellite-to-Earth or Earth-to-satellite path may suffer severely from signal attenuation due to meteorological effects such as rain, snow, hail, fog, clouds etc., where rain provides the most significant contribution.
In this paper a joint analysis of the ITALSAT propagation measurement campaigns at 39.6 GHz (precisely 39.592 GHz) carried out at both Oberpfaffenhofen, close to Munich, Germany, and Spino d‘Adda, close to Milan, Italy, is presented. For both stations long-term attenuation statistics are available and reveal that signal attenuation due to meteorological effects depends very much on the season and on the time of the day.
Signal attenuation can be compensated by an appropriate fade margin. In this paper we show that the required fade margin to guarantee a target link availability has to be chosen very carefully, since it depends very much on the time interval upon which availability is defined. We consider complete years, ITU-R recommendations, all single months of the year, worst months, and spring, summer, fall and winter. Furthermore, we evaluate diurnal variations for 4 day time intervals: 00:00-06:00, 06:00-12:00, 12:00-18:00, and 18:00 24:00.

Generator of Time Series of Rain Attenuation: Results of Parameter Extraction: Rain attenuation has a significant impact on the availability of millimeter wave communication systems. In order to dynamically simulate such radio systems, several generators of artificial time series of rain attenuation have been developed. This paper briefly describes the DLR channel model and presents the results of model parameter extraction from time series measured on terrestrial microwave paths in the Czech Republic.

Two approaches for effective modelling of rain-rate time-series for radiocommunication system simulations: This paper describes two methods for generating synthetic rain rate time-series that could be used in simulations of the performance of radiocommunication systems operating above 10 GHz. Rain rates are modelled given their widespread availability and also because it can be linked to signal attenuation in an approximate manner given that they show significant correlation. The proposed models are based on hierarchic Markov chains. Rain and no rain events are simulated by the outer chain which simulates the rain event duration according to the experimental statistics. The inner chain of both models deals with the rain intensity generation. Thus, the models produce simulated rain samples whose statistics fit very accurately those of the experimental data without using any stored rain time series.

Joint Statistics of Slant-Path Attenuation in Distant Sites Measured with ITALSAT at 40 GHz: In this paper we present the results of a joint statistical analysis of attenuation in satellite communication links at 39.6 GHz, based on four years of data collected in distant sites (d > 300 km) during the ITALSAT campaign. The degree of statistical dependence is expressed by the statistical dependence index, defined as the joint probability to exceed a common attenuation threshold, normalized to the value of that joint probability determined for the ideal case of statistical independence between the two sites.

Author: Uwe.Fiebig@dlr.de   Last Change: October 2006.