Gerhard Steinböck - Academia.edu (original) (raw)

Papers by Gerhard Steinböck

For decades the terrestrial radio channel has been characterized andmodeled for communication pur... more For decades the terrestrial radio channel has been characterized andmodeled for communication purpose only, e.g. to design wireless systems and/or to assess their performance by means of Monte Carlo simulations. e recent emergence of localization capabilities in terrestrial wireless systems demand for novel channel models that, in addition, accurately emulate the locationdependent features of real channels. In this thesis we address and provide answers to the central questions of the cause, the ešect and the modeling of the dišuse component observed in delay power spectra measured in indoor environments. We show that this component carries a signicant portion of the total received power. us, the accurate modeling of it is of prime importance for both communication and positioning. To clarify the cause of the dišuse component we rst experimentally investigate the spread in delay and direction of multipath components in an indoor environment. e results indicate small per-path-compon...

12th European Conference on Antennas and Propagation (EuCAP 2018), 2018

The utilization of massive multiple-input multipleoutput (MIMO) antenna arrays at the base statio... more The utilization of massive multiple-input multipleoutput (MIMO) antenna arrays at the base station (BS) side has been identified as an enabling technique for 5G communication systems. To evaluate the true end-to-end performance of BS's, an over-the-air (OTA) radiated method is required. In this paper, we present a sectorized multi-probe anechoic chamber (MPAC) configuration equipped with a switch box for massive MIMO BS OTA testing. Simulations were performed for a BS equipped with an 8 × 8 planar array of half-wavelength element spacing at 3.5 GHz, where 1 m measurement range and 8 active OTA probes are considered. Due to the important role of beamforming techniques in 5G antenna arrays, the Bartlett beamforming power patterns under the channel models reproduced in the MPAC setups are utilized to quantify the channel emulation accuracy. Index Terms-antenna arrays, MIMO systems, performance testing, multi-probe anechoic chamber (MPAC). • an anechoic chamber, which is used to shield external unwanted interference and unintended reflections inside

IEEE Access, 2020

This paper analyzes the performance of well-known precoding schemes for massive multiple-input mu... more This paper analyzes the performance of well-known precoding schemes for massive multiple-input multiple-output (MMIMO) systems. The investigations are based on extensive measurements made with a sounding system capable of capturing the dynamic channels towards users moving in many different outdoor scenarios. Assuming ideal channel state information (CSI), results show that the mean sum-rate of the maximum ratio transmission (MRT) precoder varies considerably with the scenario, e.g., from 6.5 to 14.5 bit/s/Hz (10%-and 90%-percentiles) for a 64 element uniform linear array (ULA) at the base station (BS), while the zero-forcing (ZF) and signal to leakage and noise ratio (SLNR) precoders are more robust and higher performing with variation from 13.4 to 16.3 bit/s/Hz in the same conditions. However, when the CSI is non-ideal the performance drops. With the CSI delayed corresponding to movement of about 1/5 of a wavelength, the ZF and SLNR mean sum-rate is 60-92% of that achieved with ideal CSI (10%-and 90%-percentiles). More statistics for different massive array sizes with both delay and frequency offset CSI are given in the paper. INDEX TERMS Cellular communications, channel sounding, massive MIMO, multiuser , precoding, radio propagation measurements, sum-rate, time-varying channel.

2016 IEEE 27th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), 2016

We consider a ray-tracing tool, in particular the METIS map based model for deterministic simulat... more We consider a ray-tracing tool, in particular the METIS map based model for deterministic simulation of the channel impulse response. The ray-tracing tool is extended by adding a geometric stochastic propagation graph to model additional stochastic paths and the dense multipath components observed in measurements. The computational complexity of ray-tracing typically prohibits the inclusion of the dense multipath component or limits it to the early part of the impulse response. Due to computational reasons and for lack of detailed information is the description of the environment for ray-tracing often very simplistic, e.g. plain walls and thus neglecting the structures on the building facades, window frames, window sills, etc. Thus in measurements there are often additional components observed that are not captured by these simplistic ray-tracing implementations. In this contribution we introduce a flexible concept of a hybrid model that allows to simulate computationally efficient ...

IEEE Transactions on Antennas and Propagation, 2021

This article reports the comparison of multipath channels of outdoor small cells at 28 GHz simula... more This article reports the comparison of multipath channels of outdoor small cells at 28 GHz simulated by point-cloud-based ray tracer and those from measurements. The comparison shows that the ray tracer is capable of reproducing measured channels with reasonable accuracy, given proper permittivity values set for major building walls. The accuracy, however, depends on the types of point clouds we input to the ray tracer: 1) raw point cloud from laser scanning measurements of the cellular site; 2) flattened point cloud where structural details of the environments are all lost like what we find in publicly available digital maps; and 3) processed point cloud where missing sections are complemented, flat and rough sections of surfaces are identified and wedges are detected. For condensed parameters of channels such as path loss, delay, and angular spreads, ray tracing with the processed and raw point clouds shows equally good accuracy. In contrast, the ray tracing with the processed point cloud shows clear advantage of accuracy over that with the raw point cloud when simulating physical propagation paths. The raw point cloud produces many spurious paths that do not exist in measurements, whereas the processed point cloud reproduces multipath richness in form of many weak diffracted paths that are found in measurements and cannot be reproduced by diffuse scattering. Ray tracing with the flattened point cloud is in least agreement with measurements. Still, first-order specular reflections from large smooth walls are reproduced well by ray tracer with any of the tested point clouds. We thereby demonstrate the superiority of using the processed point cloud as inputs to ray tracer to obtain multipath channels with the highest fidelity to measurements.

2018 IEEE 29th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), 2018

This paper studies suitability of two polarimetric diffuse scattering models of electromagnetic f... more This paper studies suitability of two polarimetric diffuse scattering models of electromagnetic fields at 28 GHz from a facade of a modern shopping center. The models are integrated into our in-house ray-based wave propagation simulation tool. Parameter values of the scattering models are estimated in reference to polarimetric channel sounding at the same site. We found that Lambertian model represents the measured scattering better than SLD model as the facade elements are made of heterogeneous materials and non-uniformly oriented, leading to backscattering equally strong as forward scattering. The parameter values giving the best fit of the scattering models to measurements are in line with the previously reported values in the literature for below-6GHz RF.

IEEE Transactions on Antennas and Propagation, 2021

This paper presents a massive multiple-input multiple-output outdoor measurement campaign with bi... more This paper presents a massive multiple-input multiple-output outdoor measurement campaign with bidirectional angular discrimination. Two dynamic user arrays of eight elements each, are measured simultaneously. Multiuser consistency and spatial consistency is important for proper modelling and simulation of dynamic users in massive-MIMO channels. This paper will investigate the common scatterers between two moving users by considering the power contribution from physical objects to each user. Inter-user distance and user alignment in the direction of dominant scatterers are also considered. Paths are estimated from wideband dual directional beam-scanning. A method is developed to group the paths based on delay and angular development along the measured tracks. The estimated delay and angle of each path, along with ray tracing simulations, are used to map the interactions of each path to surrounding walls or objects. The power contributions from objects are compared to determine common scatterers between users, which can cause larger correlation and a reduced MIMO capacity.

IEEE Antennas and Wireless Propagation Letters, 2020

This paper analyses the impact of inter-user distance and angular separation on the channel corre... more This paper analyses the impact of inter-user distance and angular separation on the channel correlation and achievable sum-rate for a massive multiple-input multiple-output system in non line of sight conditions. The investigation is based on outdoor measurements on a channel sounding system capturing the dynamic channel of two user arrays. The paper analyses correlation and sum-rate with varying inter-user distance and angular separation of dominant beams towards the users. A large span of correlation and sum-rate values are found across the range of distances and angular separation. The investigation shows a moderate link between inter-user distance and correlation, but a strong impact on correlation is found only for low angular separation of the users. The results of this non line of sight (NLOS) scenario suggest that a distance based criteria alone is not sufficient to accurately model shared clusters and correlation.

IEEE Transactions on Vehicular Technology, 2018

Wave propagation in tunnels for vehicle-to-vehicle (V2V) communications scenarios is characterize... more Wave propagation in tunnels for vehicle-to-vehicle (V2V) communications scenarios is characterized by multiple diffuse reflections on tunnel surfaces as well as specular reflections on other objects inside the tunnel, leading to a non-stationary fading process. Such a fading process is difficult to model by ray tracing (RT), requiring a prohibitively high computational complexity due to the large number of diffuse reflections. In this work we propose two new ideas for modeling diffuse reflections in a non-stationary scenarios: (i) We partition the non-stationary fading process into multiple stationarity regions with a given extent in time and frequency for which approximate wide-sense stationarity can be assumed; (ii) we propose a hybrid model, tightly interlinking RT with a propagation graph, such that vertices for the propagation graph are obtained from interaction points calculated by RT for each stationarity region. We compare our hybrid model with measurement data in terms of the timevariant power-delay and the Doppler-power spectral-density as well as the root-mean square delay-and Doppler-spread. This analysis shows, that our hybrid model is the first numerical simulation model that is able to model diffuse reflections inside a tunnel with correct non-stationary (i.e. time-variant) temporal correlation for a non-stationary V2V communication link.

IEEE Transactions on Antennas and Propagation, 2019

Second-order statistics of indoor directional channels are investigated using millimeter wave (mm... more Second-order statistics of indoor directional channels are investigated using millimeter wave (mmWave) band (30.4 to 37.1 GHz) ultra-wideband (UWB) channel measurements. Considering two main mmWave system assumptions (high bandwidth and high beamforming gain), this paper aims to investigate validity of the Rayleigh/Rice fading models for the cluster fading envelope. Results from the mmWave band study are compared to an already well studied lower frequency FCC band (3.4 to 10.1 GHz). During measurements, only selective objects (emulated multipath clusters in the propagation channel) are illuminated in a small lecture room. Experiments show that for both UWB channels, the complex received (Rx) signal is a circularly symmetric non-Gaussian random variable with highly correlated inphase (I) and quadrature (Q) components. These properties demonstrate that the intra-cluster multipath components (MPC) structure is sparse. Consequently, modeling the cluster fading envelope with Rayleigh/Rice distribution is not realistic. Therefore, sum-of-cisoids (SOC) principle is used for intra-cluster multipath modeling which inherently considers a correlation between I and Q components. It has been established that a reasonably good approximation of the cluster fading envelope can be obtained with N = 3-6 equal amplitude cisoids. However, we remark that Rayleigh/Rice models may become realistic cluster fading envelopes for narrowband mmWave systems.

IEEE Transactions on Antennas and Propagation, 2016

Ray-tracing tools allow for deterministic simulation of the channel impulse response. Studies sho... more Ray-tracing tools allow for deterministic simulation of the channel impulse response. Studies show that these tools work well when the impulse response consists only of a few distinct components. However, measurements of the channel impulse response in indoor environments reveal a diffuse tail. This diffuse tail is difficult to include in ray-tracing due to the computational complexity. We propose a hybrid model to include deterministic components and the diffuse tail by combining raytracing with a propagation graph. The recursive structure of the propagation graph allows for a computationally efficient calculation of the channel transfer function considering infinitely many components. We use ray-tracing and the theory of room electromagnetics to obtain the parameter settings for the propagation graph. Thus the proposed hybrid model does not require new or additional parameters in comparison to ray-tracing. Simulation results show good agreement with measurements with respect to the inclusion of the diffuse tail in both the delay power spectrum and the azimuth-delay power spectrum.

2016 10th European Conference on Antennas and Propagation (EuCAP), 2016

The vision of multi Gbit/s data rates in future mobile networks requires the change to millimeter... more The vision of multi Gbit/s data rates in future mobile networks requires the change to millimeter wave (mm-Wave) frequencies for increasing bandwidth. As a consequence, new technologies have to be deployed to tackle the drawbacks of higher frequency bands, e.g. increased path loss. Development and verification of those novel technologies required an understanding of the propagation effects at mm-Wave which enabled by channel sounding measurements and analysis. Due to the variety of considered frequency bands and the necessity of spatial resolved measurements for e.g. testing of beamforming approaches, measurement duration and comparability becomes problematic. This paper presents multi-band channel sounder architectures, usable to measure up to four frequency bands simultaneously. Furthermore, we present a measurement campaign, featuring full polarimetric and directional resolved dual-band measurements, which comprises the microwave band at 10 GHz and the mm-Wave band at 30 GHz. Preliminary analysis results are presented.

I E E E Antennas and Wireless Propagation Letters, 2015

2015 IEEE 81st Vehicular Technology Conference (VTC Spring), 2015

Sub-band divided ray tracing (SDRT) is one technique that has been extensively used to obtain the... more Sub-band divided ray tracing (SDRT) is one technique that has been extensively used to obtain the channel characteristics for ultra-wideband (UWB) radio wave propagation in realistic indoor environments. However, the computational complexity of SDRT scales directly with the number of sub-bands. Although we have proposed a low-complexity SDRT algorithm for one terminal position [1], the computational complexity is still extremely high when involving multiple mobile terminal positions. Moreover, some indoor positioning techniques require for high positioning accuracy data from measurements/simulations with a very fine spatial resolution. To cope with this, we propose an algorithm to reduce the computational complexity of SDRT for multiple mobile terminal positions. The algorithm uses a projection of all propagation paths on a subspace spanned by two-dimensional discrete prolate spheroidal (DPS) sequences at each sub-band. It is important to note that, since the geometrical information of the propagation paths is the same in all subbands, the subspace dimension and basis coefficients in frequency dimension do not need to be recalculated at different subbands. We justify the simplifications of the proposed method by numerical simulations. Furthermore, we evaluate the effect of antenna characteristics on the proposed algorithm. Our proposed algorithm reduces the computational complexity by more than one order of magnitude for indoor scenarios.

2013 IEEE International Conference on Communications Workshops (ICC), 2013

In this paper we present the results of real-life localization experiments performed in an unprec... more In this paper we present the results of real-life localization experiments performed in an unprecedented cooperative and heterogeneous wireless context. These measurements are based on ZigBee and orthogonal frequency division multiplexing (OFDM) devices, respectively endowed with received signal strength indicator (RSSI) and round trip delay (RTD) estimation capabilities. More particularly we emulate a multistandard terminal, moving in a typical indoor environment, while communicating with fixed OFDM-based femto-base stations (Femto-BSs) and with other mobiles or fixed anchor nodes (through peer-to-peer links) forming a wireless sensor network (WSN). We introduce the measurement functionalities and metrics, the scenario and setup , providing realistic connectivity and obstruction conditions. Out of the experimental data, preliminary positioning results based on cooperative and geometric algorithms are finally discussed, showing benefits through mobileto-mobile cooperation, selective hybrid data fusion and detection of unreliable nodes.

2008 IEEE Radar Conference, 2008

In this contribution, a low-complexity particle filter (PF) is proposed to track the parameters o... more In this contribution, a low-complexity particle filter (PF) is proposed to track the parameters of the signal reflected by a target illuminated with a digital-video-broadcast terrestrial (DVB-T) signal. The tracked parameters are the delay (time of arrival), the azimuth and elevation of arrival, the Doppler frequency, the complex amplitude of the target signal, as well as the rates of change of all but the last parameter. The proposed PF tracks these parameters based on samples of the target signal by assuming that the temporal behaviour of these parameters is governed by a multi-dimensional linear state-space model. The algorithm has an additional resampling step specifically designed to cope with the highly concentrated multi-dimensional posterior probability density function of the parameters. This step allows for tracking the parameters of the target signal with only a few particles, e.g. 50, leading to low computational complexity. Simulation results show that the PF outperforms the maximumlikelihood estimator applied to individual samples of the target signal in terms of higher accuracy and robustness. Under certain conditions usually met in reality the proposed PF can be used to track the parameters of the signals contributed by individual targets in multi-target scenarios.

2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS), 2014

We formulate a model for the outdoor-to-indoor radio channel in terms of a propagation graph. The... more We formulate a model for the outdoor-to-indoor radio channel in terms of a propagation graph. The model accounts for outdoor scattering and in-room reverberation. It is observed from the model how such a scenario results in channels with several room excitations leading to "clusters" in the simulated channel impulse responses. Simulation studies further indicate that the outdoor-to-indoor and inroom channels differ in terms of spatial envelope correlation.

2013 IEEE International Conference on Communications Workshops (ICC), 2013

This contribution introduces position estimation methods relying on observations of the received ... more This contribution introduces position estimation methods relying on observations of the received power and mean delay obtained in a wideband multi-link scenario. In particular, one-and two-step methods are introduced based on statistical models of the observed link parameters. The proposed methods are tested on data from a wideband measurement campaign. The results show that including observations of mean delay of the wideband links can notably improve positioning accuracy as compared to relying on observations of received power alone.

2008 Annual IEEE Student Paper Conference, 2008

An objective for future wireless communication systems is to increase capacity and transmission q... more An objective for future wireless communication systems is to increase capacity and transmission quality by exploiting the properties of the radio (propagation) channel. An important issue is to improve the knowledge of the temporal behavior of the radio channel through tracking and estimation algorithms. In this contribution the variation of the radio channel is described using a state-space model, where the state space consists of azimuth of arrival, delay, Doppler frequency, complex amplitude and the parameters' rate of change of propagation paths. Two nonlinear filtering algorithms are compared, i.e. a Particle Filter and an Extended Kalman Filter. Simulations are conducted to evaluate the performance of these algorithms in a single-scatterer environment. Experimental investigation using measurement data is presented.

For decades the terrestrial radio channel has been characterized andmodeled for communication pur... more For decades the terrestrial radio channel has been characterized andmodeled for communication purpose only, e.g. to design wireless systems and/or to assess their performance by means of Monte Carlo simulations. e recent emergence of localization capabilities in terrestrial wireless systems demand for novel channel models that, in addition, accurately emulate the locationdependent features of real channels. In this thesis we address and provide answers to the central questions of the cause, the ešect and the modeling of the dišuse component observed in delay power spectra measured in indoor environments. We show that this component carries a signicant portion of the total received power. us, the accurate modeling of it is of prime importance for both communication and positioning. To clarify the cause of the dišuse component we rst experimentally investigate the spread in delay and direction of multipath components in an indoor environment. e results indicate small per-path-compon...

12th European Conference on Antennas and Propagation (EuCAP 2018), 2018

The utilization of massive multiple-input multipleoutput (MIMO) antenna arrays at the base statio... more The utilization of massive multiple-input multipleoutput (MIMO) antenna arrays at the base station (BS) side has been identified as an enabling technique for 5G communication systems. To evaluate the true end-to-end performance of BS's, an over-the-air (OTA) radiated method is required. In this paper, we present a sectorized multi-probe anechoic chamber (MPAC) configuration equipped with a switch box for massive MIMO BS OTA testing. Simulations were performed for a BS equipped with an 8 × 8 planar array of half-wavelength element spacing at 3.5 GHz, where 1 m measurement range and 8 active OTA probes are considered. Due to the important role of beamforming techniques in 5G antenna arrays, the Bartlett beamforming power patterns under the channel models reproduced in the MPAC setups are utilized to quantify the channel emulation accuracy. Index Terms-antenna arrays, MIMO systems, performance testing, multi-probe anechoic chamber (MPAC). • an anechoic chamber, which is used to shield external unwanted interference and unintended reflections inside

IEEE Access, 2020

This paper analyzes the performance of well-known precoding schemes for massive multiple-input mu... more This paper analyzes the performance of well-known precoding schemes for massive multiple-input multiple-output (MMIMO) systems. The investigations are based on extensive measurements made with a sounding system capable of capturing the dynamic channels towards users moving in many different outdoor scenarios. Assuming ideal channel state information (CSI), results show that the mean sum-rate of the maximum ratio transmission (MRT) precoder varies considerably with the scenario, e.g., from 6.5 to 14.5 bit/s/Hz (10%-and 90%-percentiles) for a 64 element uniform linear array (ULA) at the base station (BS), while the zero-forcing (ZF) and signal to leakage and noise ratio (SLNR) precoders are more robust and higher performing with variation from 13.4 to 16.3 bit/s/Hz in the same conditions. However, when the CSI is non-ideal the performance drops. With the CSI delayed corresponding to movement of about 1/5 of a wavelength, the ZF and SLNR mean sum-rate is 60-92% of that achieved with ideal CSI (10%-and 90%-percentiles). More statistics for different massive array sizes with both delay and frequency offset CSI are given in the paper. INDEX TERMS Cellular communications, channel sounding, massive MIMO, multiuser , precoding, radio propagation measurements, sum-rate, time-varying channel.

2016 IEEE 27th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), 2016

We consider a ray-tracing tool, in particular the METIS map based model for deterministic simulat... more We consider a ray-tracing tool, in particular the METIS map based model for deterministic simulation of the channel impulse response. The ray-tracing tool is extended by adding a geometric stochastic propagation graph to model additional stochastic paths and the dense multipath components observed in measurements. The computational complexity of ray-tracing typically prohibits the inclusion of the dense multipath component or limits it to the early part of the impulse response. Due to computational reasons and for lack of detailed information is the description of the environment for ray-tracing often very simplistic, e.g. plain walls and thus neglecting the structures on the building facades, window frames, window sills, etc. Thus in measurements there are often additional components observed that are not captured by these simplistic ray-tracing implementations. In this contribution we introduce a flexible concept of a hybrid model that allows to simulate computationally efficient ...

IEEE Transactions on Antennas and Propagation, 2021

This article reports the comparison of multipath channels of outdoor small cells at 28 GHz simula... more This article reports the comparison of multipath channels of outdoor small cells at 28 GHz simulated by point-cloud-based ray tracer and those from measurements. The comparison shows that the ray tracer is capable of reproducing measured channels with reasonable accuracy, given proper permittivity values set for major building walls. The accuracy, however, depends on the types of point clouds we input to the ray tracer: 1) raw point cloud from laser scanning measurements of the cellular site; 2) flattened point cloud where structural details of the environments are all lost like what we find in publicly available digital maps; and 3) processed point cloud where missing sections are complemented, flat and rough sections of surfaces are identified and wedges are detected. For condensed parameters of channels such as path loss, delay, and angular spreads, ray tracing with the processed and raw point clouds shows equally good accuracy. In contrast, the ray tracing with the processed point cloud shows clear advantage of accuracy over that with the raw point cloud when simulating physical propagation paths. The raw point cloud produces many spurious paths that do not exist in measurements, whereas the processed point cloud reproduces multipath richness in form of many weak diffracted paths that are found in measurements and cannot be reproduced by diffuse scattering. Ray tracing with the flattened point cloud is in least agreement with measurements. Still, first-order specular reflections from large smooth walls are reproduced well by ray tracer with any of the tested point clouds. We thereby demonstrate the superiority of using the processed point cloud as inputs to ray tracer to obtain multipath channels with the highest fidelity to measurements.

2018 IEEE 29th Annual International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), 2018

This paper studies suitability of two polarimetric diffuse scattering models of electromagnetic f... more This paper studies suitability of two polarimetric diffuse scattering models of electromagnetic fields at 28 GHz from a facade of a modern shopping center. The models are integrated into our in-house ray-based wave propagation simulation tool. Parameter values of the scattering models are estimated in reference to polarimetric channel sounding at the same site. We found that Lambertian model represents the measured scattering better than SLD model as the facade elements are made of heterogeneous materials and non-uniformly oriented, leading to backscattering equally strong as forward scattering. The parameter values giving the best fit of the scattering models to measurements are in line with the previously reported values in the literature for below-6GHz RF.

IEEE Transactions on Antennas and Propagation, 2021

This paper presents a massive multiple-input multiple-output outdoor measurement campaign with bi... more This paper presents a massive multiple-input multiple-output outdoor measurement campaign with bidirectional angular discrimination. Two dynamic user arrays of eight elements each, are measured simultaneously. Multiuser consistency and spatial consistency is important for proper modelling and simulation of dynamic users in massive-MIMO channels. This paper will investigate the common scatterers between two moving users by considering the power contribution from physical objects to each user. Inter-user distance and user alignment in the direction of dominant scatterers are also considered. Paths are estimated from wideband dual directional beam-scanning. A method is developed to group the paths based on delay and angular development along the measured tracks. The estimated delay and angle of each path, along with ray tracing simulations, are used to map the interactions of each path to surrounding walls or objects. The power contributions from objects are compared to determine common scatterers between users, which can cause larger correlation and a reduced MIMO capacity.

IEEE Antennas and Wireless Propagation Letters, 2020

This paper analyses the impact of inter-user distance and angular separation on the channel corre... more This paper analyses the impact of inter-user distance and angular separation on the channel correlation and achievable sum-rate for a massive multiple-input multiple-output system in non line of sight conditions. The investigation is based on outdoor measurements on a channel sounding system capturing the dynamic channel of two user arrays. The paper analyses correlation and sum-rate with varying inter-user distance and angular separation of dominant beams towards the users. A large span of correlation and sum-rate values are found across the range of distances and angular separation. The investigation shows a moderate link between inter-user distance and correlation, but a strong impact on correlation is found only for low angular separation of the users. The results of this non line of sight (NLOS) scenario suggest that a distance based criteria alone is not sufficient to accurately model shared clusters and correlation.

IEEE Transactions on Vehicular Technology, 2018

Wave propagation in tunnels for vehicle-to-vehicle (V2V) communications scenarios is characterize... more Wave propagation in tunnels for vehicle-to-vehicle (V2V) communications scenarios is characterized by multiple diffuse reflections on tunnel surfaces as well as specular reflections on other objects inside the tunnel, leading to a non-stationary fading process. Such a fading process is difficult to model by ray tracing (RT), requiring a prohibitively high computational complexity due to the large number of diffuse reflections. In this work we propose two new ideas for modeling diffuse reflections in a non-stationary scenarios: (i) We partition the non-stationary fading process into multiple stationarity regions with a given extent in time and frequency for which approximate wide-sense stationarity can be assumed; (ii) we propose a hybrid model, tightly interlinking RT with a propagation graph, such that vertices for the propagation graph are obtained from interaction points calculated by RT for each stationarity region. We compare our hybrid model with measurement data in terms of the timevariant power-delay and the Doppler-power spectral-density as well as the root-mean square delay-and Doppler-spread. This analysis shows, that our hybrid model is the first numerical simulation model that is able to model diffuse reflections inside a tunnel with correct non-stationary (i.e. time-variant) temporal correlation for a non-stationary V2V communication link.

IEEE Transactions on Antennas and Propagation, 2019

Second-order statistics of indoor directional channels are investigated using millimeter wave (mm... more Second-order statistics of indoor directional channels are investigated using millimeter wave (mmWave) band (30.4 to 37.1 GHz) ultra-wideband (UWB) channel measurements. Considering two main mmWave system assumptions (high bandwidth and high beamforming gain), this paper aims to investigate validity of the Rayleigh/Rice fading models for the cluster fading envelope. Results from the mmWave band study are compared to an already well studied lower frequency FCC band (3.4 to 10.1 GHz). During measurements, only selective objects (emulated multipath clusters in the propagation channel) are illuminated in a small lecture room. Experiments show that for both UWB channels, the complex received (Rx) signal is a circularly symmetric non-Gaussian random variable with highly correlated inphase (I) and quadrature (Q) components. These properties demonstrate that the intra-cluster multipath components (MPC) structure is sparse. Consequently, modeling the cluster fading envelope with Rayleigh/Rice distribution is not realistic. Therefore, sum-of-cisoids (SOC) principle is used for intra-cluster multipath modeling which inherently considers a correlation between I and Q components. It has been established that a reasonably good approximation of the cluster fading envelope can be obtained with N = 3-6 equal amplitude cisoids. However, we remark that Rayleigh/Rice models may become realistic cluster fading envelopes for narrowband mmWave systems.

IEEE Transactions on Antennas and Propagation, 2016

Ray-tracing tools allow for deterministic simulation of the channel impulse response. Studies sho... more Ray-tracing tools allow for deterministic simulation of the channel impulse response. Studies show that these tools work well when the impulse response consists only of a few distinct components. However, measurements of the channel impulse response in indoor environments reveal a diffuse tail. This diffuse tail is difficult to include in ray-tracing due to the computational complexity. We propose a hybrid model to include deterministic components and the diffuse tail by combining raytracing with a propagation graph. The recursive structure of the propagation graph allows for a computationally efficient calculation of the channel transfer function considering infinitely many components. We use ray-tracing and the theory of room electromagnetics to obtain the parameter settings for the propagation graph. Thus the proposed hybrid model does not require new or additional parameters in comparison to ray-tracing. Simulation results show good agreement with measurements with respect to the inclusion of the diffuse tail in both the delay power spectrum and the azimuth-delay power spectrum.

2016 10th European Conference on Antennas and Propagation (EuCAP), 2016

The vision of multi Gbit/s data rates in future mobile networks requires the change to millimeter... more The vision of multi Gbit/s data rates in future mobile networks requires the change to millimeter wave (mm-Wave) frequencies for increasing bandwidth. As a consequence, new technologies have to be deployed to tackle the drawbacks of higher frequency bands, e.g. increased path loss. Development and verification of those novel technologies required an understanding of the propagation effects at mm-Wave which enabled by channel sounding measurements and analysis. Due to the variety of considered frequency bands and the necessity of spatial resolved measurements for e.g. testing of beamforming approaches, measurement duration and comparability becomes problematic. This paper presents multi-band channel sounder architectures, usable to measure up to four frequency bands simultaneously. Furthermore, we present a measurement campaign, featuring full polarimetric and directional resolved dual-band measurements, which comprises the microwave band at 10 GHz and the mm-Wave band at 30 GHz. Preliminary analysis results are presented.

I E E E Antennas and Wireless Propagation Letters, 2015

2015 IEEE 81st Vehicular Technology Conference (VTC Spring), 2015

Sub-band divided ray tracing (SDRT) is one technique that has been extensively used to obtain the... more Sub-band divided ray tracing (SDRT) is one technique that has been extensively used to obtain the channel characteristics for ultra-wideband (UWB) radio wave propagation in realistic indoor environments. However, the computational complexity of SDRT scales directly with the number of sub-bands. Although we have proposed a low-complexity SDRT algorithm for one terminal position [1], the computational complexity is still extremely high when involving multiple mobile terminal positions. Moreover, some indoor positioning techniques require for high positioning accuracy data from measurements/simulations with a very fine spatial resolution. To cope with this, we propose an algorithm to reduce the computational complexity of SDRT for multiple mobile terminal positions. The algorithm uses a projection of all propagation paths on a subspace spanned by two-dimensional discrete prolate spheroidal (DPS) sequences at each sub-band. It is important to note that, since the geometrical information of the propagation paths is the same in all subbands, the subspace dimension and basis coefficients in frequency dimension do not need to be recalculated at different subbands. We justify the simplifications of the proposed method by numerical simulations. Furthermore, we evaluate the effect of antenna characteristics on the proposed algorithm. Our proposed algorithm reduces the computational complexity by more than one order of magnitude for indoor scenarios.

2013 IEEE International Conference on Communications Workshops (ICC), 2013

In this paper we present the results of real-life localization experiments performed in an unprec... more In this paper we present the results of real-life localization experiments performed in an unprecedented cooperative and heterogeneous wireless context. These measurements are based on ZigBee and orthogonal frequency division multiplexing (OFDM) devices, respectively endowed with received signal strength indicator (RSSI) and round trip delay (RTD) estimation capabilities. More particularly we emulate a multistandard terminal, moving in a typical indoor environment, while communicating with fixed OFDM-based femto-base stations (Femto-BSs) and with other mobiles or fixed anchor nodes (through peer-to-peer links) forming a wireless sensor network (WSN). We introduce the measurement functionalities and metrics, the scenario and setup , providing realistic connectivity and obstruction conditions. Out of the experimental data, preliminary positioning results based on cooperative and geometric algorithms are finally discussed, showing benefits through mobileto-mobile cooperation, selective hybrid data fusion and detection of unreliable nodes.

2008 IEEE Radar Conference, 2008

In this contribution, a low-complexity particle filter (PF) is proposed to track the parameters o... more In this contribution, a low-complexity particle filter (PF) is proposed to track the parameters of the signal reflected by a target illuminated with a digital-video-broadcast terrestrial (DVB-T) signal. The tracked parameters are the delay (time of arrival), the azimuth and elevation of arrival, the Doppler frequency, the complex amplitude of the target signal, as well as the rates of change of all but the last parameter. The proposed PF tracks these parameters based on samples of the target signal by assuming that the temporal behaviour of these parameters is governed by a multi-dimensional linear state-space model. The algorithm has an additional resampling step specifically designed to cope with the highly concentrated multi-dimensional posterior probability density function of the parameters. This step allows for tracking the parameters of the target signal with only a few particles, e.g. 50, leading to low computational complexity. Simulation results show that the PF outperforms the maximumlikelihood estimator applied to individual samples of the target signal in terms of higher accuracy and robustness. Under certain conditions usually met in reality the proposed PF can be used to track the parameters of the signals contributed by individual targets in multi-target scenarios.

2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS), 2014

We formulate a model for the outdoor-to-indoor radio channel in terms of a propagation graph. The... more We formulate a model for the outdoor-to-indoor radio channel in terms of a propagation graph. The model accounts for outdoor scattering and in-room reverberation. It is observed from the model how such a scenario results in channels with several room excitations leading to "clusters" in the simulated channel impulse responses. Simulation studies further indicate that the outdoor-to-indoor and inroom channels differ in terms of spatial envelope correlation.

2013 IEEE International Conference on Communications Workshops (ICC), 2013

This contribution introduces position estimation methods relying on observations of the received ... more This contribution introduces position estimation methods relying on observations of the received power and mean delay obtained in a wideband multi-link scenario. In particular, one-and two-step methods are introduced based on statistical models of the observed link parameters. The proposed methods are tested on data from a wideband measurement campaign. The results show that including observations of mean delay of the wideband links can notably improve positioning accuracy as compared to relying on observations of received power alone.

2008 Annual IEEE Student Paper Conference, 2008

An objective for future wireless communication systems is to increase capacity and transmission q... more An objective for future wireless communication systems is to increase capacity and transmission quality by exploiting the properties of the radio (propagation) channel. An important issue is to improve the knowledge of the temporal behavior of the radio channel through tracking and estimation algorithms. In this contribution the variation of the radio channel is described using a state-space model, where the state space consists of azimuth of arrival, delay, Doppler frequency, complex amplitude and the parameters' rate of change of propagation paths. Two nonlinear filtering algorithms are compared, i.e. a Particle Filter and an Extended Kalman Filter. Simulations are conducted to evaluate the performance of these algorithms in a single-scatterer environment. Experimental investigation using measurement data is presented.