Vittorio Degli-Esposti

Survey of channel and radio propagation models for wireless MIMO systems

This paper provides an overview of the state-of-the-art radio propagation and channel models for wireless multiple-input multiple-output (MIMO) systems. We distinguish between physical models and analytical models and discuss popular examples from both model types. Physical models focus on the double-directional propagation mechanisms between the location of transmitter and receiver without taking the antenna configuration into account. Analytical models capture physical wave propagation and antenna configuration simultaneously by describing the impulse response (equivalently, the transfer function) between the antenna arrays at both link ends. We also review some MIMO models that are included in current standardization activities for the purpose of reproducible and comparable MIMO system evaluations. Finally, we describe a couple of key features of channels and radio propagation which are not sufficiently included in current MIMO models.

Measurement and Modelling of Scattering From Buildings

The results of a measurement campaign aimed at determining the far-field diffuse scattering pattern of typical building walls are shown in the paper. Such results are then used to determine and tune simple diffuse scattering models based on the effective roughness approach, to be embedded into ray tracing simulators. It is shown that by adopting an appropriate single-lobe scattering pattern the agreement between simulation and measurement is very good

Analysis of Multipath Propagation in Urban Environment Through Multidimensional Measurements and Advanced Ray Tracing Simulation

A multidimensional analysis of multipath propagation in urban micro- and macro-cellular environment has been carried out. Multidimensional measurement data, including path-loss, delay spread and direction-of-arrival are compared with simulations performed with a 3D ray tracing model which takes diffuse scattering into account. The results are analyzed highlighting the dominant propagation mechanisms in the different cases and model performance/shortcomings. In particular, the results show that diffuse scattering plays a key role in urban propagation, with an impact on both narrowband and wideband parameters in most cases. Also, the accuracy and the characteristics of environment representation can have a significant impact on prediction even in simple topologies.

Speed-Up Techniques for Ray Tracing Field Prediction Models

Despite their good performance, the widespread diffusion of ray tracing field-prediction models is still limited due to their high complexity and high computation time. In this paper, two different classes of methods for speeding up ray tracing urban field prediction are proposed, aimed at reducing the size of the input database and the number of rays to be handled by the algorithm. With the proposed techniques, a great computation time reduction can be achieved without sensibly affecting the accuracy of the prediction.

Analysis and Modeling on co- and Cross-Polarized Urban Radio Propagation for Dual-Polarized MIMO Wireless Systems

Cross-polarization coupling is an important radio propagation characteristic in dual-polarized multiple-input multiple output (MIMO) systems. Still, few studies analyze the polarimetric properties of the radio channel in relation to the actual propagation conditions and processes taking place in urban environment. The topic is studied in the present paper with the aid of dual-polarized MIMO measurements and ray tracing simulations. Several scenarios are considered, and the impact of the different propagation characteristics (LOS, NLOS, link-distance, presence of diffuse-scattering, angular distribution of the signal, etc.) on cross-polarization coupling is analyzed. Generally, a fairly high degree of coupling is observed due to multipath propagation and especially to diffuse scattering. Surprisingly, it does not appear to depend on link distance.

Ray-Tracing-Based mm-Wave Beamforming Assessment

The use of large-size antenna arrays to implement pencil-beam forming techniques is becoming a key asset to cope with the very high throughput density requirements and high path-loss of future millimeter-wave (mm-wave) gigabit-wireless applications. Suboptimal beamforming (BF) strategies based on search over discrete set of beams (steering vectors) are proposed and implemented in present standards and applications. The potential of fully adaptive advanced BF strategies that will become possible in the future, thanks to the availability of accurate localization and powerful distributed computing, is evaluated in this paper through system simulation. After validation and calibration against mm-wave directional indoor channel measurements, a 3-D ray tracing model is used as a propagation-prediction engine to evaluate performance in a number of simple, reference cases. Ray tracing itself, however, is proposed and evaluated as a real-time prediction tool to assist future BF techniques.

Polarimetric Properties of Diffuse Scattering From Building Walls: Experimental Parameterization of a Ray-Tracing Model

Dense multipath components may represent an important part of wireless transmission channels, yet little is known about their physical properties. For this reason, we parameterize an ad hoc diffuse scattering model, which can be easily included in ray-tracing tools. The work, focusing on the polarimetric properties of diffuse contributions scattered off building walls, relies on experimental data. By means of a joint post-processing of the data in conjunction with ray-tracing simulations, characteristic parameters of diffuse scattering are extracted. The analysis reveals that diffuse scattering represents an crucial part of the received power. Regarding depolarization caused by diffuse scattering, our work highlights that depolarization appears to be small for homogeneous brick walls, but is far from negligible for more complex wall structures.

Characterization of an Interleaved F-DAS MIMO indoor propagation channel

A key point in the deployment of new wireless services is the cost-effective extension and enhancement of the networks radio coverage in indoor environments. Distributed Antenna Systems using Fiber-optics distribution (F-DAS) represent a suitable method of extending multiple-operator radio coverage into indoor premises, tunnels, etc. Another key point is the adoption of MIMO (Multiple Input — Multiple Output) transmission techniques which can exploit the multipath nature of the radio link to ensure reliable, high-speed wireless communication in hostile environments. In this paper novel indoor deployment solutions based on Radio over Fiber (RoF) and distributed-antenna MIMO techniques are presented and discussed, highlighting their potential in different cases.

Analysis of Radio Propagation in Co- and Cross-Polarization in Urban Environment

The behaviour of radio propagation in co- and cross-polarization in urban environment is studied with the aid of both ray tracing simulation and MIMO measurements. A ray tracing (RT) model including diffuse scattering has been adopted, therefore allowing the tuning of the RT model and the analysis of the role of diffuse scattering in cross-polarization propagation. A high degree of cross-polarization coupling is observed, especially in NLOS cases, confirming the feasibility of efficient and compact MIMO schemes adopting dual polarized antennas.

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.