Gaillot, Davy P

Joseph, Wout

Liénard, Martine

Martens, Luc

Tanghe, Emmeric

English

Ghent University Academic Bibliography

Room Electromagnetics in an Industrial WorkshopEmmeric Tanghe1, Davy P. Gaillot2, Martine Lie´nard2, Luc Martens1, and Wout Joseph11 INTEC, Ghent University/iMinds, Ghent, Belgium, emmeric.tanghe@intec.ugent.be2 IEMN, University of Lille 1, Lille, France, davy.gaillot@univ-lille1.frAbstract—This work validates the theory of Room Electro-magnetics (RE) for a small industrial workshop for shippingcontainer restoration. Radio channel sounding measurementswith a vector network analyzer and virtual antenna arrays werecarried out. The specular and dense multipath components wereestimated from channel sounding data by means of an iterativemaximum-likelihood algorithm (RiMAX). In agreement with RE,the dense multipath is well-described by a single exponentialdecay as function of delay with a reverberation time that isnearly constant across the room. The dense multipath is found tohave a longer reverberation time compared to office environmentsbecause of the highly reflective (metallic) nature of the industrialenvironment.Index Terms—room electromagnetics, dense multipath compo-nents, channel sounding, industrial environment.I. INTRODUCTIONThe Room Electromagnetics (RE) theory borrows from thescience of room acoustics and obtains an exponential decayfor the diffuse electromagnetic field under these assumptions:the field’s intensity does not depend on the direction (rich scat-tering environment) and its energy density is constant acrossthe whole room (valid for rooms that are small enough) [1].As with room acoustics, RE is a scalar theory and thereforedoes not account for more than one polarization at transmitterand receiver.This work presents a validation of the RE theory in anindustrial environment, specifically a workshop for shippingcontainer restoration. The validation is based on narrowbandchannel sounding around a 3 GHz center frequency. TheRiMAX framework is used to estimate the specular and densemultipath components from channel sounding data [2], [3].For the purpose of this paper we will equate the definitionsof dense multipath and diffuse multipath. Strictly speaking,the dense multipath estimated with RiMAX can, in additionto diffuse multipath, also contain low-SNR specular multipath.The idea is that these specular paths cannot be reliably detectedamong the diffuse multipath due to limitations of the estimatorand/or the measurement system’s aperture.II. CHANNEL SOUNDING MEASUREMENTSThe industrial environment under consideration is a work-shop for reparation of intermodal shipping containers, shownin Fig. 1. The workshop consists of a single room withdimensions 20.4 m (length) by 22.0 m (width) by 4.8 m(height). The building materials for the walls are a collectionof bricks, concrete slabs, steel plates, steel industrial doors, andglass windows. The floor and ceiling are made up of concreteslabs and corrugated steel panels, respectively. The workshop’sinventory consists largely of metal container parts, machinery,and small cranes.Fig. 1. Measurement environmentNarrowband frequency-domain channel sounding measure-ments were performed inside the workshop. A vector networkanalyzer was used to probe the radio channel in a 100 MHzbandwidth centered around 3 GHz (in 256 uniformly spacedfrequency points). At both link ends, a virtual antenna arraywas created by an automated positioning system. At both trans-mit and receive side, the virtual array was a planar horizontalUniform Circular Array (UCA) consisting of eight antennaelements. The inter-element spacing was 0.45 times the wave-length at the largest measurement frequency of 3.050 GHz.As transmitting (Tx) and receiving (Rx) antenna, broadbandomnidirectional discone antennas were used. Both antennaswere 1.50 m above ground level during measurements.In total, twelve Tx-Rx links were measured: the Tx re-mained at a fixed location while the Rx was moved to differentlocations between measurements. Measurements were donefor three different Tx-Rx link shadowing conditions: Line-of-Sight (LoS, three measurements), Obstructed Line-of-Sight(OLoS, four measurements), and Non-Line-of-Sight (NLoS,five measurements).III. MULTIPATH ESTIMATIONThe RiMAX maximum-likelihood multipath search algo-rithm is used to simultaneously estimate the Specular Mul-tipath Components (SMC) and the Dense Multipath Com-ponents (DMC) from the channel sounding data [2], [3].RiMAX’s data model assumes DMC that is spatially white attransmit and receive side. The DMC power ψ (τ) is modeledas an exponential decay as function of delay τ ,0 100 200 300 400 500 600 700 800 900 1000−110−100−90−80−70delay [ns]power [dB]  APDP measuredAPDP DMC + noiseSMCFig. 2. SMC and DMC + noise in the delay domain for the Tx-Rx1 linkψ (τ) = α1 exp[−τ − τdτr](τ > τd) . (1)In (1), α1, τd, and τr are the peak power, the onset time, andthe reverberation time of the DMC, respectively. Fig. 2 showsthe estimated multipath for an NLoS measurement. Shownare the measured Averaged Power Delay Profile (APDP), theestimated SMC, and the APDP of the DMC + measurementnoise obtained after subtracting the SMC from the measuredchannel response.IV. DISCUSSIONFirstly, Fig. 2 shows that the single exponential decay (1) fitsthe DMC process very well. Secondly, the DMC reverberationtime τr was found to vary between 64.6 and 84.5 ns across thetwelve Tx-Rx links. It was observed that τr does not changenoticeably between link shadowing categories and is evenfairly constant across all Tx-Rx links. The former observationwas backed by a Kruskal-Wallis analysis of variance test whichfound no difference in median τr between link shadowingcategories (p-value = 0.55) [4].The two observations made about DMC in the previousparagraph — a single exponential decay and a reverberationtime that is independent of Rx location — is entirely in linewith the theory of Room Electromagnetics (RE) [1]. The REtheory provides a simple relationship between the reverber-ation time τr, the room’s geometry and a single constantdescribing the room’s electromagnetic absorption qualities:τr =4VcηA(2)In (2), V and A are the room’s volume and area, re-spectively, c is the speed of light in vacuum, and η is thefraction of energy absorbed by the area A. Using the industrialworkshop’s dimensions, we obtain V = 2154.2 m3 andA = 1304.6 m2. The median τr across all Tx-Rx links equals75.8 ns. Using (2), we then obtain the median absorptioncoefficient η as 0.29. Formula (2) for the reverberation timeis also called Sabine’s model [1]. We chose Sabine’s modelover Eyring’s model, which replaces the factor 1/η in (2)with −1/ ln (1− η), because the former is preferred for smallvalues of η such as the one obtained in this study [5].The parameter η is particularly interesting to compare thereverberation properties of different rooms: unlike the τrparameter, η is independent of room geometry and solelydepends on the average electromagnetic absorption character-istics of the materials present. These materials in turn directlyrelate to the type of environment. For office environmentsand vertical polarization at both link ends [1], [6], and [5]found respectively η = 0.51, 0.45, and 0.47. In comparison,η = 0.29 in the industrial workshop for the same polarizationconditions reveals that the materials of the latter are 16 to 22%less absorbent. This is easily explained by the highly reflectivenature of the materials commonly found in an industrialenvironment.V. CONCLUSIONThis contribution presented a validation of the room elec-tromagnetics theory for a small industrial workshop. Thevalidation was based on channel sounding experiments withvirtual antenna arrays and the RiMAX algorithm was used toestimate the specular and dense multipath from the soundingdata.The dense multipath reverberation time is nearly constantand thus independent of transmitter/receiver location, whichis in line with room electromagnetics theory. Room electro-magnetics is further used to calculate the average absorptionof electromagnetic energy by the environment. The industrialworkshop is found to be 16 to 22% less absorbent compared tooffice environments in literature. This is due to the metallic andthus highly reflective nature of the materials in the workshop.ACKNOWLEDGMENTE. Tanghe is a Post-Doctoral Fellow of the FWO-V (Re-search Foundation - Flanders). This work was financiallysupported by the INTERREG IV project WiSE, and the RegionNord Pas-de-Calais and the French Ministry of Research aspart of the International Campus on Safety and Intermodalityin Transportation Systems (CISIT) project (France).REFERENCES[1] J. B. Andersen, J. O. Nielsen, G. F. Pedersen, G. Bauch, and M. Herdin,“Room Electromagnetics,” IEEE Antennas and Propagation Magazine,vol. 49, no. 2, pp. 27–33, April 2007.[2] A. Richter, “Estimation of Radio Channel Parameters: Models andAlgorithms,” Ph.D. dissertation, Technische Universita¨t Ilmenau, Fakulta¨tfu¨r Elektrotechnik und Informationstechnik, Ilmenau, DE, 2005.[3] E. Tanghe, D. P. Gaillot, W. Joseph, M. Lie´nard, P. Degauque, andL. Martens, “Robustness of high-resolution channel parameter estimatorsin the presence of dense multipath components,” IET Electronics Letters,vol. 48, no. 2, pp. 130–132, January 2012.[4] W. H. Kruskal and W. A. Wallis, “Use of ranks in one-criterion varianceanalysis,” Journal of the American Statistical Association, vol. 47, no.260, pp. 583–621, December 1952.[5] G. Steinbo¨ck, T. Pedersen, B. H. Fleury, W. Wang, and R. Raulefs,“Experimental validation of the reverberation effect in room electromag-netics,” in COST IC1004 8th Scientific Meeting, Ghent, BE, September2013, pp. 1–10.[6] A. Bamba, W. Joseph, E. Tanghe, G. Vermeeren, and L. Martens, “CircuitModel for Diffuse Multipath and Electromagnetic Absorption Predictionin Rooms,” IEEE Transactions on Antennas and Propagation, vol. 61,no. 6, pp. 3292–3301, June 2013.

Room electromagnetics in an industrial workshop

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Room electromagnetics in an industrial workshop

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