Multipath-enhanced device-free localization (MDFL) systems determine presence and location of objects and users not necessarily equipped with localization devices. For localization, MDFL systems exploit user-induced changes in the power of all received signal components, including both line-of-sight and multipath components (MPCs). In this work, we therefore provide a statistical fading model that describes user-induced changes in received power specifically for MPCs. The model is derived and validated empirically using an extensive set of wideband and ultra-wideband measurement data. Since the localization performance of MDFL systems strongly depends on the information about the propagation paths within the wireless network, we further propose a Bayesian calibration approach that estimates the location of the reflection points of MPCs caused by single-bounce reflections. For MPCs caused by single-bounce reflections, the solution space of possible locations of reflection points is constrained to the delay ellipse, which allows the formulation of a computationally efficient one-dimensional estimation problem. Eventually, the problem is solved by sequential Bayesian estimation. The applicability of the proposed approach is demonstrated and evaluated using measurement data. Independent of the underlying measurement system, the Bayesian calibration approach is shown to robustly estimate the locations of the reflection points in different environments. Finally, the localization results of MDFL for an indoor scenario confirm the applicability of the Bayesian calibration approach.

This paper presents a statistical analysis of the main components of the aircraft-to-aircraft channel based on the wideband channel measurements conducted between two aircraft in the VHF/UHF band at 250 MHz. We consider multiple flight segments where the aircraft flew at diverse altitudes and used different antennas for transmission and for reception, alternating between a top and a bottom antenna. In each scenario of interest, we analyse the power and the small-scale fading of the envelope of the direct line-of-sight component and of the specular reflection component off a lake. For both components, we compare the measured average power with the theoretical free-space path loss, and the measured small-scale fading with multiple well-known statistical distributions. The results show that the envelope of both components is strongly affected by the geometry, the location of the antennas, and by the aircraft fuselage itself. The different scenarios yield significant variations in the average power and in the distribution of the small-scale fading. A Rician distribution shows the best fit for the line-of-sight component envelope. The component reflected off the lake can be modeled by a Rician distribution when it is not obstructed or strongly affected by the aircraft fuselage, and by a Nakagami distribution otherwise. The parameters of the best-fitting distributions, including the Rician K-factor, are provided for the different scenarios.

In this contribution we take a look into the future and investigate so-called massive UAV (unmanned aerial vehicle) scenarios in the VLL (very low level) airspace with UAV densities ranging from 50 to 500 UAVs per km2. We predict that UAVs will fly autonomously and use a beaconing system similar to that used today in road and maritime traffic to warn of collisions. For this purpose, UAVs regularly broadcast short beacon messages which include their current positions and trajectories. However, beacon messages may not be received correctly due to congestion on the radio channel. As in vehicular environments, the loss of several successive beacon messages sent by a certain UAV can have dramatic consequences, since conflicting trajectories cannot be identified. In our work, we derive the relation between failures on the communications channel and the probability of collisions between UAVs. Eventually, we show that an ALOHA type beaconing system with a bandwidth of 1 MHz can handle massive UAV scenarios.

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.

This paper compares our non-stationary geometric- stochastic channel model for vehicle-to-vehicle scatter channels with measurement data collected in a vehicle-to-vehicle measurement campaign. The measurements were conducted on a forest road near Munich at 5.2 GHz using a car mounted transmitter and receiver platform. The data is evaluated in terms of delay and Doppler frequency and then compared to a scaled version of the joint delay Doppler probability density function. The close agreement between the analytical and empirical data confirms the utility of our non-stationary geometric stochastic model.

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.

This study aims to characterize and model the rain fields in the North-West of Spain from weather radar images. The study includes the modeling of these images according to two well known rain cell models: EXCELL and HYCELL. For this analysis, a procedure to detect rain fields and an algorithm for identifying rain cells within the images is presented. This work is part of an on-going activity trying to develop dynamic space-time models for rain fields for simulating rain induced effects on millimeter wave communication systems.

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.

The estimation of the decoded bit error rate is treated for low rate services in a mobile radio environment. The considered system is based on code division multiple access (CDMA) techniques. Taking into account that the mobile radio channel is subject to great variations due to different environments, fading effects, and various vehicle speeds it is difficult to estimate accurately the decoded bit error rate. The presented scheme does not make use of the channel estimation. The estimation of the decoded bit error rate is based only on the estimation of the channel bit error rate and on statistics of the burst lengths of erroneous channel bits. It is shown that the performance of the applied scheme is well suited for the estimation of the decoded bit error rate.

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.>