Uwe-Carsten Fiebig

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 partners 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. >

Development and validation of time-series synthesizers of rain attenuation for Ka-band and Q/V-band satellite communication systems

The aim of this paper is to present recent developments in terms of propagation time-series synthesizers, carried out in the framework of the ESA study 16865/03/NL/EC Development of propagation models for telecommunication satellite systems (ONERA Final Report RF 4/07757/DEMR, 2004). The paper is composed of three parts: a review of the initial requirements related to propagation time series for system performance simulation, a description of a collection of rain attenuation time-series synthesizers and of their related input parameters, and a comparative analysis of the output characteristics of these time-series synthesizers as compared with experimental data collected during the OLYMPUS and ITALSAT propagation experiments.

Soft-decision and erasure decoding in fast frequency-hopping systems with convolutional, turbo, and Reed-Solomon codes

In this contribution we present an exhaustive treatment of various coding and decoding techniques for use in fast frequency-hopping/multiple frequency shift keying multiple-access systems. One of the main goals is to show how reliability information on each received bit can be derived to enable soft-decision decoding. Convolutional codes as well as turbo codes are considered applying soft-decision, erasure, and hard-decision decoding. Their performance is compared to that of previously proposed Reed-Solomon with either errors-only or errors-and-erasures decoding. A mobile radio environment yielding a frequency-selective fading channel is assumed. It is shown that the application of turbo codes and convolutional codes with soft decision decoding can allow for a comparable number of simultaneously transmitting users to Reed-Solomon codes with errors-and-erasures decoding. Furthermore, the advantage of soft decisions is shown, which can be applied to a widely and growing range of channel codes. The pertinent technique of calculating soft decisions is described in the paper.

Delay-Dependent Doppler Probability Density Functions for Vehicle-to-Vehicle Scatter Channels

Novel joint delay Doppler probability density functions for vehicle-to-vehicle communications channels are introduced. Prior measurements of vehicle-to-vehicle channels have unveiled their nonstationarity; thus, the wide-sense stationary and also the uncorrelated scattering assumption for such channels is often violated, which makes their modeling challenging. In this work it is proposed to exploit geometry-based stochastic modeling to cope with the nonstationarity of vehicle-to-vehicle channels. To this end, delay-dependent Doppler pdfs are derived for arbitrary times. It is assumed that scatterers are randomly distributed on an ellipse with two moving vehicles being in its foci. The proposed approach allows reducing the dimensionality of the resulting problem. This in turn leads to a significantly simplified derivation of the delay-dependent Doppler pdfs for general vehicle-to-vehicle propagation environments; moreover, the resulting computations can be performed almost fully analytically. By combining the calculated Doppler pdf with a delay pdf, the joint pdf of delay and Doppler is obtained. The joint pdf then can be put into relation with the generalized local scattering function. The presented modeling approach is simple yet very scalable and accurate, which allows its application in different vehicular scenarios. The obtained modeling results correspond very well with measurement data reported in prior works.

Validation of the Synthetic Storm Technique as Part of a Time-Series Generator for Satellite Links

This letter presents results on the suitability of the so-called synthetic storm technique (SST) for simulating signal attenuation time-series in a V-band satellite link. The focus is on both single rain events and the overall statistical behavior. Signal attenuation time-series can be used in computer simulations which shall help optimize fade mitigation techniques in wireless millimeter- wave communication systems where rain is the dominant source of signal attenuation. In this letter, the investigations reported are based on measured 40-GHz satellite beacon attenuation time-series.

Comparison of L- and C-Band Satellite-to-Indoor Broadband Wave Propagation for Navigation Applications

In order to compare satellite-to-indoor wave propagation characteristics between L-band and C-band for satellite navigation applications, the German Aerospace Center (DLR) conducted a measurement campaign in June 2008. The measurements were performed at 1.51 GHz for L-band and at 5.2 GHz for C-band with a broadband signal of 100 MHz bandwidth. A mobile crane was used as transmitter platform. The receiving antenna was mounted on a model train which ran through various rooms in order to capture channel characteristics with a high spatial resolution. Standard statistical results are given in terms of power delay profile, received energy, mean delay, delay spread and number of paths for various transmitter heights and receiver locations. To show the impact of the satellite-to-indoor propagation channel on navigation receivers, the error of the delay-locked-loop (DLL) receiver and an experimental upper bound for multipath mitigation receivers is given. The analysis shows, that C-band is more sensitive to the building layout compared to L-band. Due to building material, C-band wave propagation is subjected to higher entry loss. In terms of positioning performance, L- and C-band show similar performances in the bias seen by the DLL estimator. For multipath mitigation receivers, L-band outperforms C-band especially for higher elevations.

Multipath Assisted Positioning with Simultaneous Localization and Mapping

This paper describes an algorithm that exploits multipath propagation for position estimation of mobile receivers. We apply a novel algorithm based on recursive Bayesian filtering, named Channel-SLAM. This approach treats multipath components as signals emitted from virtual transmitters, which are time synchronized to the physical transmitter and static in their positions. Contrary to other approaches, Channel-SLAM considers also paths occurring due to multiple numbers of reflections or scattering as well as the combination. Hence, each received multipath component increases the number of transmitters resulting in a more accurate position estimate or enabling positioning when the number of physical transmitters is insufficient. Channel-SLAM estimates the receiver position and the positions of the virtual transmitters simultaneously; hence, the approach does not require any prior information, such as a room-layout or a database for fingerprinting. The only prior knowledge needed is the physical transmitter position as well as the initial receiver position and moving direction. Based on simulations, the position precision of Channel-SLAM is evaluated by a comparison to simplified algorithms and to the posterior Cramér-Rao lower bound. Furthermore, this paper shows the performance of Channel-SLAM based on measurements in an indoor scenario with only a single physical transmitter.

Measurement of the l-band air-to-ground channel for positioning applications

In the paper, we present results from flight trials conducted to investigate the characteristics of the L-band air-to-ground radio channel for positioning applications. We discuss the employed hardware setup, synchronization concept, calibration procedures, and investigated flight patterns. It is shown that the setup is suitable for investigating both multipath structure and absolute propagation time of the radio signals. The power delay and Doppler power profiles, as well as the time-of-arrival estimation accuracy, are presented. Manuscript

A Wideband Satellite-to-Indoor Channel Model for Navigation Applications

In indoor environments the accuracy of positioning by global navigation satellite systems suffers significantly from signal blockage, reflection and diffraction. To develop advanced receiver position algorithms working in harsh propagation environments, accurate channel simulators are necessary. In this contribution, we propose a novel and accurate wideband satellite-to-indoor channel model for testing and validating range estimation algorithms for positioning. Compared to the state of the art, the proposed channel model is able to reproduce the spatial characteristics of the wideband propagation channel for a moving receiver. The model is based on a hybrid approach combining physical-deterministic and stochastic methods. In this perspective, waves diffracted and transmitted by walls, windows and doors are considered by using physical-deterministic near field methods. For indoor originated paths occurring due to reflections on walls, a hybrid approach is used. The random behavior of scattered waves is stochastically modeled. Finally, the outcome of the proposed channel model is compared to measured channel sounder data. This comparison reveals that the proposed channel model accurately models satellite-to-indoor propagation effects.

Time-variant channel modeling with application to mobile radio based positioning

Time based positioning by terrestrial mobile radio as a complement to global navigation satellite systems has gained remarkable attention. As an essential tool to develop suitable algorithms for positioning with mobile radio signals, models of the wireless channel for this application are significant. However, there is still a lack of channel models suitable for positioning applications. In this paper we propose a geometry-based statistical time variant model to validate the accuracy of positioning algorithms. A statistically generated equivalent reflector is used to characterize each single path in the impulse response. Moreover, a model is proposed which accurately models the movement of each equivalent reflector. It is shown that the proposed channel model accurately fits with measurement data.