Troels Pedersen

• Associate Professor, PhD
• Professor (Associate) at Aalborg University

Stochastic radio channel models based on underlying point processes of multipath components have been studied intensively since the seminal papers of Turin and Saleh-Valenzuela. Despite of this, inference regarding parameters of these models has remained a major challenge. Current methods typically have a somewhat ad hoc flavor involving a multitud...

A polarimetric model for the power delay spectrum for inroom communication is proposed. The proposed model describes the gradual depolarization of the signal with delay. The model is based on the theory of room electromagnetics, specifically the mirror source approach, which is straightforwardly generalized to the polarimetric case. Compared to the...

Calibrating stochastic radio channel models to new measurement data is challenging when the likelihood function is intractable. The standard approach to this problem involves sophisticated algorithms for extraction and clustering of multipath components, following which, point estimates of the model parameters can be obtained using specialized esti...

We propose a multivariate log-normal distribution to jointly model received power, mean delay, and root mean square (rms) delay spread of wideband radio channels, referred to as the standardized temporal moments. The model is validated using experimental data collected from five different measurement campaigns (four indoor and one outdoor scenario)...

We propose Monte Carlo maximum likelihood estimation as a novel approach in the context of calibration and selection of stochastic channel models. First, considering a Turin channel model with inhomogeneous arrival rate as a prototypical example, we explain how the general statistical methodology is adapted and refined for the specific requirements...

Calibrating stochastic radio channel models to new measurement data is challenging when the likelihood function is intractable. The standard approach to this problem involves sophisticated algorithms for extraction and clustering of multipath components, following which, point estimates of the model parameters can be obtained using specialized esti...

We propose a multivariate log-normal distribution to jointly model received power, mean delay, and root mean square (rms) delay spread of wideband radio channels, referred to as the standardized temporal moments. The model is validated using experimental data collected from five different measurement campaigns (four indoor and one outdoor scenario)...

We propose a joint statistical model for the received power, mean delay, and rms delay spread, which are derived from the temporal moments of the radio channel responses. Indoor wideband measurements from two different data sets show that the temporal moments are strongly correlated random variables with skewed marginals. Based on the observations,...

Estimating parameters of stochastic radio channel models based on new measurement data is an arduous task usually involving multiple steps such as multipath extraction and clustering. We propose two different machine learning methods, one based on approximate Bayesian computation (ABC) and the other on deep learning, for fitting data to stochastic...

Estimating parameters of stochastic radio channel models based on new measurement data is an arduous task usually involving multiple steps such as multipath extraction and clustering. We propose two different machine learning methods, one based on approximate Bayesian computation (ABC) and the other on deep learning, for fitting data to stochastic...

This paper explores the feasibility of using the multiple-input multiple-output (MIMO) radio channel properties to passively detect and localize multiple humans in indoor environments. We propose to utilize the unique reverberation characteristics of indoor channels for the purpose of detecting, and the power angular delay profile (PADP) for locali...

This paper generalizes a propagation graph model to polarized indoor wireless channels. In the original contribution, the channel is modelled as a propagation graph in which vertices represent transmitters, receivers and scatterers while edges represents the propagation conditions between vertices. Each edge is characterized by an edge transfer fun...

This paper presents a reduced complexity method for computing the transfer matrix of wireless channels in complex indoor environments with a large number of rooms using propagation graphs. Multi-room indoor environments can be represented in a vector signal flow graph with rooms in the complex structure as nodes and propagation between rooms as bra...

We propose a stochastic multipath model for the received signal for the case, where the transmitter and receiver, both with directive antennas, are situated in the same rectangular room. This scenario is known to produce channel impulse responses with a gradual specular-to-diffuse transition in delay. Mirror source theory predicts the arrival rate...

This paper proposes a hybrid modeling approach for prediction of the room-to-room radio propagation channel. The model combines ray tracing with propagation graph. The propagation graph vertices are obtained at each room by ray tracing with the assumption that the receive antenna (or transmit antenna) virtually locates on the surface of the separat...

We propose a stochastic multipath model for the received signal for the case where the transmitter and receiver, both with directive antennas, are situated in the same rectangular room. This scenario is known to produce channel impulse responses with a gradual specular-to-diffused transition in delay. Mirror source theory predicts the arrival rate...

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 prohibitive...

A model for polarized wireless channels based on propagation graphs is presented in this talk with applications to dual polarized MIMO channels

Radio systems operating in time-varying propagation environments are exposed to rapid fading in the transfer function due to multi-path effects. In general propagation environments, where recursive scattering may occur, modeling and simulating the channel is challenging. In this contribution, we model the channel as a time-varying propagation graph...

Disruptive technologies proposed for 5G wireless systems and the IoT hold promise of providing unprecedented localization capabilities for a wide range of application scenarios and target environments. This whitepaper summarizes the expected features and resulting properties of upcoming localization systems exploiting 5G and IoT technologies. It al...

We analyze the path arrival rate for an inroom radio channel with directive antennas. The impulse response of this channel exhibits a transition from early separate components followed by a diffuse reverberation tail. Under the assumption that the transmitter's (or receiver's) position and orientation are picked uniformly at random we derive an exa...

The accuracy and availability of the users of satellite navigation (satnav) receivers is heavily influenced by the environment they are located in. Multipath propagation, signal shadowing, and blockage lower a satnav user's experience to a large extent especially in built-up areas. A precise description of the wave propagation mechanisms is hence c...

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 traci...

We propose a hybrid message passing method for distributed cooperative localization and tracking of mobile agents. Belief propagation (BP) and mean field (MF) message passing are employed for, respectively, the motion-related and measurement-related parts of the underlying factor graph. Using a Gaussian belief approximation, closed-form expressions...

We propose a hybrid message passing method for distributed cooperative localization and tracking of mobile agents. Belief propagation and mean field message passing are employed for, respectively, the motion-related and measurement-related part of the factor graph. Using a Gaussian belief approximation, only three real values per message passing it...

The delay power spectrum is widely used in both communication and localization communities for characterizing the temporal dispersion of the radio channel. Experimental investigations of in-room radio environments indicate that the delay power spectrum exhibits an exponentially decaying tail. This tail can be characterized with Sabine’s or Eyring’s...

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 fu...

We employ the theory of spatial point processes to revisit and reinterpret a particular class of time-variant stochastic radio channel models. Common for all models in this class is that individual multipath components are emerging and vanishing in a temporal birth-death like manner, with the underlying stochastic birth-death mechanism governed by...

OFDM ranging is becoming important for positioning using terrestrial wireless networks. Conventional ranging methods rely on a two-step approach: range related parameters, such as the time of arrival (TOA), the bias induced by non-line-of-sight (NLOS) propagations etc., are first estimated, based on which the range is then inferred. In multi-path c...

In this paper we study how the antenna radiation pattern is perturbed in the presence of a human phantom in terms of changes in the coefficients of the spherical harmonic antenna representation. The spherical harmonic basis allows for a compact representation of the antenna pattern which is attractive for simulation purposes. We propose a simple mod...

We address the problem of searching for the optimal pilot signal, i.e. pattern and signature, of an orthogonal frequency-division multiplexing (OFDM) system when the purpose is to estimate the delay and Doppler shift under the assumption of a single-path propagation channel. This problem is relevant for synchronization and for time-based localizati...

A model based on experimental observations of the delay power spectrum in closed rooms is proposed. The model includes the distance between the transmitter and the receiver as a parameter which makes it suitable for range based radio localization. The experimental observations motivate the proposed model of the delay power spectrum with a primary (...

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 cam...

We consider positioning in the scenario where only two reliable range estimates, and few less reliable power observations are available. Such situations are difficult to handle with numerical maximum likelihood methods which require a very accurate initialization to avoid being stuck into local maxima. We propose to first estimate the support regio...

We have conducted an indoor channel measurement campaign to characterize the propagation channel for the development of cooperative positioning algorithms. The campaign focused particularly on the characteristics of multi-link channels with applications to positioning. In this contribution we present the measurement campaign and preliminary results...

We investigate an extension to the probabilistic model of a wireless sensor network (WSN) in a recently proposed variational message passing (VMP) localization algorithm. This extension exploits network topology information to mitigate am-biguities in WSN localization schemes. We derive VMP schemes for direct (1-step) localization and 2-step locali...

We propose a novel algorithm for sensor self-localization in cooperative wireless networks where observations of relative sensor distances are available. The variational message passing (VMP) algorithm is used to implement a mean field solution to the estimation of the posterior probabilities of the sensor positions in an R 2 scenario. Extension to...

In measurements of in-room radio channel responses an avalanche effect can be observed: earliest signal components, which appear well separated in delay, are followed by an avalanche of components arriving with increasing rate of occurrence, gradually merging into a diffuse tail with exponentially decaying power. We model the channel as a propagati...

A general path loss model for in-room radio channels is proposed. The model is based on experimental observations of the behavior of the delay-power spectrum in closed rooms. In such a room, the early part of the spectrum observed at different positions typically consists of a dominant component (peak) that vanishes as the transmitter-receiver dist...

The analysis and design of low-density parity-check (LDPC) codes and their decoders is demonstrated by using extrinsic information transfer (EXIT) charts. Designs are performed for hard- and soft-decision detectors, and hard- and soft-decision message passing.

This paper proposes a stochastic wind power model based on an autoregressive integrated moving average (ARIMA) process. The model takes into account the nonstationarity and physical limits of stochastic wind power generation. The model is constructed based on wind power measurement of one year from the Nysted offshore wind farm in Denmark. The prop...

Binary message-passing decoders for low-density parity-check (LDPC) codes are studied by using extrinsic information transfer (EXIT) charts. The channel delivers hard or soft decisions and the variable node decoder performs all computations in the L-value domain. A hard decision channel results in the well-know Gallager B algorithm, and increasing...

This paper presents an overview on the performance of hybrid data fusion and tracking algorithms evaluated in the WHERE consortium. The focus is on small scale indoor scenarios with ultra wideband (UWB) complementing cellular communication systems, mid scale indoor scenarios with Wi-Fi aiding cellular communication systems, and large scale outdoor...

In this contribution, a particle filter (PF) is proposed for tracking a single target illuminated with a digital-video-broadcasting terrestrial (DVB-T) signal in a multistatic radar system. This algorithm utilizes a single-stage scheme, i.e. it estimates the target position trajectory in a Cartesian coordinate system directly from the signal reflec...

Positioning solutions in infrastructure-based wireless networks generally operate by exploiting the channel information of the links between the Wireless Devices and fixed networking Access Points. The major challenge of such solutions is the modeling of both the noise properties of the channel measurements and the user mobility patterns. One class...

High-resolution parameter estimation of the radio channel is of vital importance for defining param- eters of radio channel models. Typical estimators such as SAGE (Space Alternating Generalized Expectation- Maximization) are implemented in the way to minimize the L2-norm of the residual signal. This leads to a concentra- tion of parameter estimate...

In this paper, we investigate the impact of the spatiotemporal aperture of a channel sounding system equipped with antenna arrays at the transmitter and receiver on the accuracy of joint estimation of Doppler frequency and bidirection. The contribution of this paper is threefold. First, we state a spatiotemporal model that can describe parallel as...

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 t...

Due to the significantly reduced cost and effort for system calibration time-division multiplexing (TDM) is a commonly used technique to switch between the transmit and receive antennas in multiple-input multiple-output (MIMO) radio channel sounding. Nonetheless, Baum et al. (2004) have shown that phase noise of the transmitter and receiver local o...

In this contribution, a multi-variate probability density function (pdf) is derived and used to describe the normalized direction-(i.e. azimuth and elevation)-delay power spectral density of individual dispersed components in the response of the propagation channel. This pdf maximizes the entropy under the constraint that its first and second momen...

In this contribution a low-complexity particle filtering algorithm is proposed to track the parameters of time-variant propagation paths in multiple-input multiple-output (MIMO) radio channels. A state-space model is used to describe the path evolution in delay, azimuth of arrival, azimuth of departure, Doppler frequency and complex amplitude dimen...

Due to the significantly reduced cost and effort for system calibration time-division multiplexing (TDM) is a commonly used technique to switch between the transmit and receive antennas in multiple-input multiple-output (MIMO) radio channel sounding. Nonetheless, Baum et al. have shown that phase noise of the transmitter and receiver local oscillat...

In this contribution, the Fisher-Bingham-5 (FB5) probability density function (pdf) is used to model the shape of the direction power spectral density function (psdf) of individual path components in the radio channel. The FB5 distribution is selected because, among all direction distributions, it maximizes the entropy under the constraints that th...

Binary message-passing decoders for LDPC codes are analyzed using EXIT charts. For the analysis, the variable node decoder performs all computations in the L-value domain. For the special case of a hard decision channel, this leads to the well-know Gallager B algorithm, while the analysis can be extended to channels with larger output alphabets. By...

In this contribution the radio channel model proposed in [1] is extended to include multiple transmitters and receivers. The propagation environment is modelled using random graphs where vertices of a graph represent scatterers and edges model the wave propagation between scatterers. Furthermore, we develop a closed form analytical expression for t...

In this contribution, we derive a distribution that is suitable for characterizing biazimuth (azimuth of arrival and azimuth of departure) and delay dispersion of individual path components in the response of the radio channel. This distribution maximizes the entropy under the constraint that its first and second moments are specified. We propose t...

In this contribution, we derive a probability distribution suitable for characterizing bi-azimuth (azimuth of arrival and azimuth of departure) direction dispersion of individual path components in the response of the propagation channel. This distribution belongs to the family of generalized von-Mises-Fisher distributions. The elements in this fam...

In this paper, an azimuth spread estimator (ASE) for slightly distributed scatters (SDSs) is derived based on the generalized-array-manifold (GAM) approximation model (D. Asztely et al., 1997). To improve the performance of this estimator we propose an array size adaptation (ASA) technique that adjusts the array aperture selectively for each SDS by...

To save hardware and reduce the effort to calibrate the system, channel sounding with Tx and Rx antenna arrays is commonly performed in TDM mode where the array elements are successively switched. We refer to this technique as TDM-MIMO channel sounding. The ISI-SAGE algorithm (Fleury, B.H. et al., 2003; Yin, X. et al., 2003), applied in combination...

In this contribution we design a particle filtering approach to track the time-evolution of the parameters of propagation paths in radio channel. The time-evolution of the parameters is described using a dynamic state space model, where the state vector of a path contains the delay, direction of arrival, Doppler frequency, the rates of change in th...

The improved-search-and-initialization space-alternating generalized expectation-maximization (ISI-SAGE) algorithm is proposed in [1] and [2] for joint estimation of the relative delay, the direction (i.e. azimuth and co-elevation) of departure, the direction of arrival, the Doppler frequency (DF) as well as the complex weight of the propagation pa...