Yves Lostanlen

Three-Dimensional Urban EM Wave Propagation Model for Radio Network Planning and Optimization Over Large Areas

A new 3D urban electromagnetic wave propagation model is presented. It provides fast 3D deterministic predictions in urban radio configurations and over large areas. The various techniques to make it suitable to the network planning and optimization of large wireless networks are described. The resulting radio propagation maps exhibit seamless coverage between the various environments (dense urban, urban, and suburban). The model efficiently addresses all types of outdoor transmitter configurations (macrocells, minicells, microcells, and picocells) and all types of receiver locations (at ground level, over the rooftop, and at high building floors). It predicts the field strength as well as the dominant specular contributions of the impulse responses to build ray spectra (including delays and angles). Thus, the model may also be used to estimate the performances of new radio systems [diversity and multiple-input-multiple-output (MIMO)]. The narrowband power prediction of the model is evaluated by comparison with microcell measurements. The evaluation stresses the advantage of 3D modeling compared with the vertical-plane approach or 2D ray tracing. Finally, the ability of the model to simulate radio wideband characteristics in a complex environment is demonstrated by comparing delay-spread estimates to measurements collected from a high-macrocell transmitter in a hilly city and to arrival angles collected in a suburban macrocell area.

A deterministic ultra wideband channel modeling

We study the realisation of a deterministic channel modeling which allows the construction of a realistic received waveform from a wireless spread spectrum multiple-access (SSMA) using time hopping (TH) modulation. The goal is to reach the symbol decision from a simulated waveform. This paper explains how to use the uniform theory of diffraction (UTD) method combined with a ray tracing to obtain the received TH modulation waveform in indoor or outdoor environment.

Introduction of diffuse scattering to enhance ray-tracing methods for the analysis of deterministic indoor UWB radio channels (Invited Paper)

The paper presents a method to introduce the diffuse scattering into a deterministic 3D ultrawideband indoor simulator. The purpose it to enrich the wideband channel model with more phenomena inserted as pseudo-stochastic parameters. The model predicts the field strength as well as the specular contributions of the impulse responses, and then the diffuse scattering, which are all essential in the performance estimation of new radio systems (diversity, MIMO).

3D coverage analysis of LTE urban heterogeneous networks with dense femtocell deployments

Femtocell technology recently gained attention due to its potential benefits for mobile operators (significant capacity offload and extension of the coverage at low cost) but there are still hard technical challenges to be addressed (e.g., the optimization of the interference management). Furthermore, the deployment strategies are still in question, such as the femtocell access-mode (open or closed) and the spectrum usage to adopt. Consequently, reliable simulations are necessary in the perspective of massive femtocell deployments, in particular for characterization of the impact on the coverage quality. An original solution is introduced and exploited in this article. It offers two complementary approaches for two different applications: a synthetic model for realization of small-scale or illustrative case studies and a real model for realistic and large-scale heterogeneous network performance evaluation. It relies on a suite of simulation tools including the generation of random 3D femtocell deployments in synthetic or real environments; realistic pathloss predictions; and a 3D downlink coverage performance analysis (i.e., considering all floors) of long-term evolution heterogeneous networks. A first study shows not only a large improvement of coverage quality for femtocell users, but also a very significant degradation for non-subscribers in the vicinity of closed-access femtocells. The femtocells have a strong impact locally (gain or degradation depending on the access-mode and user type) and not only at their own floor. Therefore, a 3D evaluation is relevant. Then, a second study offers realistic and large-scale analyses of the coverage evolution after corporate femtocells have massively been deployed in urban macrocells. The results show a moderate impact on the average spectral efficiencies but a strong impact locally. In this study, closed-access femtocells cause dead zones for non-subscribers in 15% of indoor areas leading to non-uniform service coverage, whereas they increase the spectral efficiency of femtocell subscribers (by 1.5 bps/Hz in 20% of indoor areas). These are critical information for a mobile operator since the experience of its customers is much affected by the femtocell deployment and by the selected access mode.

Comparison of measurements and simulations in indoor environments for wireless local networks at 60 GHz

Indoor wireless local networks (WLAN) development in the millimetre band gives new perspectives, which are very promising in terms of announced data rate and offered services. Nevertheless strong free space attenuation as well as pieces of furniture and wall attenuations result in difficult propagation conditions. A French research project (RNRT COMMINDOR) has been set up to study and design new high data rate (155 Mbit/s) radiocommunication systems at 60 GHz in an indoor environment. SIRADEL takes part in this project by modelling the propagation phenomenon thanks to a ray-tracing tool associated to the Uniform Theory of Diffraction (UTD). Simulations are then compared to measurements realised within the framework of this project by the LCST Laboratory of INSA Rennes. The good behaviour of the propagation model is analysed for LOS and NLOS situations.

Performance evaluation of wireless multihop communications for an indoor environment

The effect of an arbitrary indoor infrastructure environment on the performance of a wireless multihop network is investigated. To this end, an accurate channel modeling tool based on 3D ray tracing is used first to evaluate the signal strength in different areas of the environment. Then, a discrete event simulator is applied to examine the performance of the network with two classes of routing protocols: traditional vs. opportunistic. It is shown that for an indoor environment, opportunistic routing performs better based on the obtained results, with respect to throughput, delay and delivery ratio.

Optimizing placements of backhaul hubs and orientations of antennas in small cell networks

While small cells (SCs) are an important feature of emerging network architectures, providing backhaul to SCs is a challenging problem. Non-line-of-sight (NLOS) wireless backhaul networks provide a cost effective approach in urban areas where providing a wired- or fiber-based backhaul is difficult. An important problem in designing such networks is to optimize the position of backhaul hubs in a way that all SCs are properly serviced. However, this is a NP-complete problem requiring suboptimal, but effective, solutions. In this work, we will propose a novel suboptimal algorithm, based on dynamic programming, to solve the NP-hard problem of hub placement in backhaul networks. We will further consider an extended problem of optimizing both the placement of hubs and the orientation of the hub antennas. Our design methodology is backed up with numerical examples using deterministic channel prediction tools which leads to a robust and smart design of the backhaul network.

Assessment of 3D network coverage performance from dense small-cell LTE

As wireless cellular networks are facing both a rapid growth of traffic demand and, in some countries, a higher public concern about field exposure, the wireless carriers are seriously considering radio network topology evolution. Deployment of small- or micro-cells, possibly as a complement to the macrocell layout, should offer high local capacity along with a reduced transmit power (at both the downlink and uplink). Network simulations assess the performance of such deployment scenarios, providing the required outcomes for elaboration of optimal strategies, engineering rules and business models. This paper presents an original suite of simulation tools based on advanced propagation models and 3-dimensional calculation of the signal-to-interference ratio (meaning calculation into the streets and into each building floor over the study area) for realistic analysis of heterogeneous macro and small-cell LTE networks in terms of coverage, spectral efficiency and total throughput. A dense urban scenario is analyzed, where the usual macro deployment scheme is completed with almost-uniformly distributed small-cells. The present study characterizes the promising improvements but also some challenging aspects of small-cell network deployments.

A new approach for radio propagation modeling in urban environment: knife-edge diffraction combined with 2D ray-tracing

The design of a deterministic radio propagation model adapted to built-up areas is a tedious problem when considering the needs of radio planners, i.e. great accuracy and reasonable processing time. In that perspective, an innovative model for micro-cells has been developed by the French company Siradel. It combines two usual modeling methods: the multiple knife-edge approximation to take into account the propagation above rooftops and 2D ray-tracing to predict lateral interactions. Radio grid coverage and comparisons with experimental data are presented to prove the pertinence of the model.

Indoor-to-outdoor path-loss models for femtocell predictions

Two different indoor-to-outdoor path-loss models are proposed in this paper: an analytical formula derived for link-level and system-level simulations in heterogeneous radio networks, and a ray-tracing based model providing deterministic path-loss predictions, helpful for precise radio analysis or radio-planning tasks. The models were elaborated from CW measurements collected around a large set of indoor transmitter situations at frequency 2.1GHz. They were elaborated for simulation of useful and interfering signals in the context of femtocell deployments.