François Quitin

Distributed Localization of a RF Target in NLOS Environments

We propose a novel distributed expectation maximization (EM) method for non-cooperative RF target localization using a wireless sensor network. We consider the scenario where few or no sensors receive line-of-sight signals from the target. In the case of non-line-of-sight signals, the signal path consists of a single reflection between the transmitter and receiver. Each sensor is able to measure the time difference of arrival of the targets signal with respect to a reference sensor, as well as the angle of arrival of the targets signal. We derive a distributed EM algorithm where each node makes use of its local information to compute summary statistics, and then shares these statistics with its neighbors to improve its estimate of the target localization. We show that our distributed algorithm converges, and simulation results suggest that our method achieves an accuracy close to the centralized EM algorithm. We apply the distributed EM algorithm to a set of experimental measurements with a network of four nodes, which confirm that the algorithm is able to localize a RF target in a realistic non-line-of-sight scenario.

A time-variant statistical channel model for tri-polarized antenna systems

Polarized MIMO systems are an efficient solution for reducing inter-antenna correlation while maintaining compact terminal size. In this paper, a time-variant statistical channel model is proposed for tri-polarized antenna systems. The model is based on a coherent and a scattered component, where each component includes inter-channel correlation and cross-polar discriminations. The temporal variations of the channel are separated in slow and fast channel variations. A measurement campaign has been performed at 3.6 GHz to parameterize the model, in both static and mobile cases. A variant of the variogram technique has been adopted for extracting the slow-varying channel parameters. Experimental results are investigated and presented. The Doppler spectrum of the fast channel variations show fundamental differences between the static case and the mobile case. Finally, it is explained how the proposed model can be generated.

Radio Channel Modeling for 4G Networks

This chapter is dedicated to radio channel modeling for 4G networks. In addition to recent results in the area of 4G channel modeling at large, including complex environments such as aircrafts, COST 2100 has dealt with a number of specific topics which are presented in this chapter. Improved deterministic methods, including models of diffuse components are detailed in Sect. 3.2. The developed models namely propose new methods to account for macroscopic diffuse scattering in ray-tracing tools. The measurement-based modeling of the same diffuse or dense multipath components has represented one major research topic in COST 2100, especially regarding the extraction of such components from experimental data (Sect. 3.3). Another important topic of research has concerned the modeling of the polarization behavior of wireless channels (see Sect. 3.4), as multipolarized antenna arrays appear more and more as a realistic implementation of MIMO systems. The specific representation and modeling of multilink scenarios is dealt with in Sect. 3.5. Considering the correlations between multiple links is a significant requirement to design robust schemes in cooperative, relay or multihop networks. Finally, the COST 2100 model is presented in Sect. 3.6. Starting from a single-link implementation based on the COST 273 model (available online), it builds upon the work described in this chapter to propose an updated version of the COST 2100 model including enhancements such as diffuse and cross-polar components, as well as multi-link aspects.

UWB channel analysis within a moving car

Ultra-wideband communications inside a car are investigates in this paper. Measurements have been carried out in a typical sedan family car in two different environments. One of those was a one-way narrow street and measurement were taken while moving in the street. All the measurements were taken while varying the numbers of passengers. Based on those measurements, a channel model using reverberation chamber theory is proposed. Measurements results and channel model parameters are presented in this paper.

Extracting specular-diffuse clusters from MIMO channel measurements

In previous work, it has been observed that the specular and the diffuse component are linked in the angular domain. The idea of adding a diffuse component to each specular cluster has been proposed to model the specular-diffuse channel. In this paper, an approach is proposed to treat the specular and the diffuse measurement data simultaneously, with a clustering algorithm that is applied jointly on the specular and the diffuse component. The output of the clustering algorithm gives clusters that are characterized by their specular and their diffuse component. Measurement results are presented based on double-directional measurements, and parameter values are extracted using the proposed methodology.

Parameterization of a Polarimetric Diffuse Scattering Model in Indoor Environments

Diffuse or dense multipath components play an important role in determining the polarization behavior of wireless transmission channels. In this communication, we parametrize a polarimetric diffuse scattering model in two indoor environments. Our method relies on the empirical extraction of dense multipaths by means of a high resolution algorithm and on the investigation of the properties of this diffuse component. The analysis reveals that diffuse scattering significantly depolarizes the impinging wave in indoor scenarios, yielding cross-polar discrimination values close to 0 dB.

Multi-Polarized Channel Statistics for Outdoor-to-Indoor and Indoor-to-Indoor Channels

Compared to classical spatial MIMO wireless systems, cross-polarized MIMO systems are an interesting way to reduce equipment size while reducing the inter-antenna correlation. Cross-Polar Discrimination (XPD) and Co-Polar Ratio (CPR) are two important parameters describing multi-polarized channels. In this paper, the behavior of these parameters is investigated for different observation scales. A measurement campaign has been performed in both Outdoor-to-Indoor and Indoor-to-Indoor scenarios, at a frequency of 3.5GHz. Small-scale variations of XPD and CPR are analyzed in different spatial positions. The distance-related and large-scale variations of XPD and CPR are also investigated and a model is deduced.

Clustered channel characterization for indoor polarized MIMO systems

A cluster-based channel model is presented that includes polarization characteristics. Measurements have been carried out in an indoor environment at 3.6 GHz using a dual-polarized transmitter and a tri-polarized receiver. Individual propagation paths are extracted using the SAGE algorithm, and a cross-polar discrimination (XPD) per ray is defined. Clusters are identified in the co-elevation-azimuth-delay domain, with an automatic clustering algorithm. The cluster properties are investigated and polarization characteristics are identified on a per-cluster basis. Finally, the obtained model is simulated and extraction-independent parameters are compared with experimental parameters for validation.

Channel measurements and MB-OFDM performance inside a driving car

This paper investigates ultra-wideband intra-vehicular communications. Measurements have been carried out in a typical family car in two different environments. All the measurements were taken with different numbers of passengers. Based on those measurements, a channel model using reverberation chamber theory is proposed. Measurements results and performance of multi-band OFDM simulations are presented.

Joint Navigation and Synchronization Using SOOP in GPS-Denied Environments: Algorithm and Empirical Study

We consider the problem of tracking a receiver using signals of opportunity (SOOP) from beacons and a reference anchor with known positions and velocities, and where all devices have asynchronous local clocks or oscillators. Based on an extended Kalman filter, we propose a sequential estimator to jointly track the receiver location, velocity, and its clock parameters using time- difference-of-arrival and frequency-difference-of-arrival measurements obtained from the SOOP samples collected by the receiver and reference anchor. Field experiments are carried out using a software defined radio testbed, and Iridium satellites as the SOOP beacons. Experiment demonstrate that our measurement model has a good fit, and our proposed estimator can successfully track both the receiver location, velocity, and the relative clock offset and skew with respect to the reference anchor with good accuracy.