Method to match waves of ray-tracing simulations with 3- D high-resolution propagation measurements Guo, P.; van Dommele, A.R.; Herben, M.H.A.J.

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1 Method to match waves of ray-tracig simulatios with 3- D high-resolutio propagatio measuremets Guo, P.; va Dommele, A.R.; Herbe, M.H.A.J. Published i: Proceedigs of the 6th Europea Coferece o Ateas ad Propagatio (EUCAP202, March 202, Prague, Czech Republic Published: 0/0/202 Documet Versio Publisher s PDF, also kow as Versio of Record (icludes fial page, issue ad volume umbers Please check the documet versio of this publicatio: A submitted mauscript is the author's versio of the article upo submissio ad before peer-review. There ca be importat differeces betwee the submitted versio ad the official published versio of record. People iterested i the research are advised to cotact the author for the fial versio of the publicatio, or visit the DOI to the publisher's website. The fial author versio ad the galley proof are versios of the publicatio after peer review. The fial published versio features the fial layout of the paper icludig the volume, issue ad page umbers. Lik to publicatio Geeral rights Copyright ad moral rights for the publicatios made accessible i the public portal are retaied by the authors ad/or other copyright owers ad it is a coditio of accessig publicatios that users recogise ad abide by the legal requiremets associated with these rights. Users may dowload ad prit oe copy of ay publicatio from the public portal for the purpose of private study or research. You may ot further distribute the material or use it for ay profit-makig activity or commercial gai You may freely distribute the URL idetifyig the publicatio i the public portal? Take dow policy If you believe that this documet breaches copyright please cotact us providig details, ad we will remove access to the work immediately ad ivestigate your claim. Dowload date: 5. Jul. 208

2 Method to Match Waves of Ray-Tracig Simulatios with 3-D High-Resolutio Propagatio Measuremets Peg Guo, A. Raiier va Dommele, Matti H.A.J. Herbe Departmet of Electrical Egieerig Eidhove Uiversity of Techology Eidhove, the Netherlads Abstract High-resolutio propagatio measuremets were carried out to verify the agular ad delay dispersio predicted by ray-tracig models. To do the compariso betwee the measured ad simulated results, the correspodig waves should first be idetified. This paper itroduces a method to fid the correspodig relatioship of waves automatically. The results show that the algorithm ca successfully fid the matchig simulated ad measured waves. It also provides the iformatio to fid ad further ivestigate the most domiat propagatio mechaisms. Keywords- agular dispersio; agular spread; delay spread; agle of arrival; determiistic chael modellig I. INTRODUCTION For 4G wireless commuicatio systems, the covetioal semi-empirical or stochastic propagatio predictio models are isufficiet for etwork plaig []. Time dispersio ad agular dispersio i a radio chael are importat for the performace of the 4G etwork. Orthogoal-Frequecy Divisio Multiplexig (OFDM is applied for modulatio i the LTE system. The badwidth of sub-carriers of the OFDM system is determied by the kowledge of time dispersio i the radio chael. Moreover, smart ateas are used for the 4G etworks. These ateas are adaptive arrays or Multiple Iput Multiple Output (MIMO ateas. Agular dispersio due to multipath propagatio affects the spatial filter characteristics of the smart ateas. For adaptive atea arrays, agular dispersio degrades the performace of adaptive beam formig. While for MIMO a wide agular spread of the multipath waves produces a large de-correlatio of the spatial chaels ad hece icreases diversity performace. The iformatio of spread i agular domai ad time domai caot be predicted with the covetioal empirical propagatio models. Istead determiistic predictio models become more iterestig to predict the propagatio chaels for 4G etworks. The ray tracig (RT model is oe of the popular determiistic models owadays. It uses physical models of radio propagatio mechaisms, such as reflectio ad diffractio, ad detailed iformatio of the eviromet to provide deep isight ito the propagatio chaels [][2]. This RT model with a detailed buildig database results i excessive computatioal complexity, which limits the use by the mobile system operators. Most of the curret research i the area of determiistic propagatio modellig deals with reducig the computatioal complexity without losig the predictio accuracy. The accuracy of determiistic chael modellig is the object of debate ad there is still a wide margi for improvemets ad extesios. The commercially available RT-model has bee evaluated through compariso with measuremet results. I [3], the results of measuremets which were carried out i Rotterdam, the Netherlads are compared with the predictio results based o a RT-model with a maximum of two reflectios ad oe diffractio cotributio. The compariso results show that the agular spread ad delay spread are ot predicted accurate eough by the RT model. The mea error of agular spread predictio is 2 degrees, while the stadard deviatio of the error is aroud 6 degrees. I order to do a more detailed compariso of RT-predictios with measuremets, the correspodig propagatig electromagetic waves should be idetified firstly. This paper presets a method to fid the correspodig waves betwee measuremets ad simulatios. The compariso is achieved by usig the images of measuremet ad simulatio plots i time ad space domais, so that a matchig method ca be desiged based o patter recogitio as used i the image processig field. II. MEASUREMENTS AND SIMULATIONS The measuremet data used for compariso is obtaied from outdoor experimets performed with the 3-D high resolutio chael souder developed at TU/e [4]. This system is capable of characterizig the delay ad agular properties of mobile radio chaels with a resolutio better tha 5 degrees i both azimuth ad elevatio domai without ambiguities ad while movig through the eviromet at moderate urba speeds. The time resolutio is 20s with a uambiguous rage of 5.μs. The ray-tracig simulatio results i this paper are obtaied with the software package CRC-RayPredict [5]. A top-view of the measuremet sceario is show i Fig.. The dyamic measuremet ad simulatio results are plotted i the time ad agular domais as a fuctio of sapshot set show i Fig. 2 ad Fig. 3 respectively. The sapshot set umber is related to the time elapsed whe the vehicle is movig. The vertical oise bad i Fig. 2(a

3 betwee sapshot set k=3700 ad k=4000 is caused by the saturatio of the measuremet system. The most importat differece betwee the simulatio ad measuremet plots is the agular spread due to buildig surface roughess. I the simulatio, oly specular reflectio happes, resultig i clear lies i the plots alog the trajectory. I the measuremet, the rough surfaces of the buildigs itroduce scatterig, which cotributes to the agular dispersio aroud the specular reflectio waves alog the trajectory. (a Fig. Top-view of measuremet sceario at TU/e-campus ( Google Maps. (b (c (a (b Fig. 3 The simulated multipath compoets at the receiver i (a time domai (b elevatio domai (c azimuth domai alog the trajectory. III. DESCRIPTION OF THE COMPARISON METHOD The procedure to fid the correspodig waves betwee the simulatio ad measuremet results is based o patter recogitio [6]. This procedure cosists of the followig steps: clusterig, calibratio, feature geeratio, template matchig ad evaluatio, which are show i Fig. 4. (c Fig. 2 The measured multipath compoets at the receiver i (a time domai, (b elevatio domai (c azimuth domai alog the trajectory. Fig. 4 Procedure to fid the correspodig waves i the simulatio ad measuremet results.

4 A. Clusterig A hierarchical clusterig algorithm of the Nearest Neighbourhood is used to cluster the measuremet data. The purpose of clusterig is to group the measured waves with similar time delay ad Agle-of-Arrival (AoA together [4]. I this way, the specular reflectio ad the surroudig scattered rays, due to for istace surface roughess, are grouped together. The first 50 measuremet clusters with the largest average power are preseted i Fig. 5. Differet colours idicate differet clusters. Due to the limited umber of colours, some of them are used repeatedly. Clusterig the simulatio results ca either be doe with the same algorithm or by usig the iformatio of iteractio poits of the rays with the reflectig or diffractig objects from the simulator. The simulatio results with maximum two reflectios are clustered usig the same algorithm as that for the measuremet, which are show i Fig. 6. Fig. 5 The first 50 measuremet clusters with the largest average power plotted i time, elevatio ad azimuth domais. reflectio loss ad ca be idetified easily. The calibrated measured ad simulated delay profiles are show i Fig. 7. Fig. 7 Simulated delay profile (upper plot ad calibrated measured delay profile (lower plot. C. Feature Geeratio Features of each measured cluster are geerated afterwards to elimiate the scatterig effect due to surface roughess, so that further compariso is feasible. I this algorithm mea time delay, mea azimuth agle ad mea elevatio agle are chose as the features. The values of the features for each measuremet cluster at each sapshot set are calculated by Eq. [3]. τ i Pi τ = P i φ = jφ e i Pi Pi where represets the umber of Multipath Compoets (MPCs withi oe cluster at oe sapshot set. τ i, θ i, ϕ i ad P i represet the time delay, elevatio agle, azimuth agle ad received power of the ith MPC out of MPCs withi oe cluster at oe sapshot set. deotes takig the agle of the complex umber. The plots of the first 50 highest average power clusters with feature values i time ad agular domais are show i Fig. 8. It ca be see that the features of the measuremet clusters are represeted by lies that later o are compared with the lies of the simulatios. ( Fig. 6 Clustered simulatio results with maximum two reflectios plotted i time, elevatio ad azimuth domais. B. Calibratio Calibratio is ecessarily applied to elimiate for istace the time delay offset i the measuremets. The start poit of time delay i the measuremet is chose arbitrary, because the receiver does ot kow whe the waves depart from the trasmitter. The measured time delay is modified based o the theoretical time delay of Lie of Sight (LOS ray that has o Fig. 8 The mea time delay, mea elevatio agle ad mea azimuth agle, of the measuremet clusters show i Fig. 5.

5 D. Template Matchig The procedure of template matchig is show i Fig. 9 to fid which oe of the simulated clusters (template matches the measured cluster by usig feature values. Assume there are m clusters i the measuremet, clusters i the simulatio ad k sapshot sets alog the trajectory. First choose the objective measuremet cluster, e.g. m i. The the Euclidea distace is used to measure the differece betwee the selected measuremet cluster ad all simulatio clusters i time ad agular domais. The smaller the Euclidea distace is, the better the selected measuremet ad chose simulatio cluster match. The Euclidea distace value at each sapshot set is calculated by: 2 2 ( D j k = ( α j k + ( λ( τ j k (2 where (D j k is the Euclidea distace, (Δα j k is the agular differece ad (Δτ j k is the time delay differece betwee the feature value of measuremet cluster m i ad simulatio clusters at each sapshot set k. λ is chose as the ratio of maximum agle differece value 2π ad the maximum time delay differece value 5.μs to make the ifluece of them equal o the Euclidea distace. The agle differece (Δα j k betwee objective measuremet cluster m i ad idividual simulatio cluster j ca be calculated by Eq. 3 [7], usig the feature azimuth ad elevatio agle of objective measuremet cluster m i ad the agle values of the idividual cluster i the simulatio results. i = i + i = Choose measuremet cluster m i Geerate Euclidea distace (D j k i time ad agle domais at each sapshot set k betwee measuremet cluster m i ad simulatio clusters ( α j k cosφ ik cosθik cosφ jk cosθ jk (3 = cos siφik cosθik siφ jk cosθ jk siθik siθ jk After that, the Euclidea distace values are averaged over k sapshot sets to fid the differece i a dyamic situatio. I the ext step, the simulatio clusters, which are far from the objective measuremet cluster, are filtered out whe the agular ad time delay differece are larger tha a threshold that is based o the measuremet resolutio. Accordig to the measuremet system, the threshold of time delay differece Δτ equals 20s ad agle differece Δα equals 5º. I this way, the oise clusters i the measuremet (see Fig. 2(a ca be removed, because there are o simulatio clusters earby. Fially, the simulated cluster j with the smallest value of mea Euclidea distace is cosidered to match the objective measuremet cluster m i. The same procedure is repeated util all the measuremet clusters are examied. IV. MATCHING RESULTS Based o the method explaied i part III, the matchig results for this sceario are listed i Table I. TABLE I. MATCHING RESULTS INDICATED BY CLUSTER NUMBER Measuremet cluster umber Matchig simulatio cluster umber Iteractio poits provided by simulator LOS 2 2 Reflectio o Traverse buildig 98,59,03 3 Reflectio o IPO buildig 43,49,99,5, 88,90 4 First reflectio o IPO buildig Secod reflectio o Traverse buildig 22,28,57,25 5 First reflectio o Traverse buildig Secod reflectio o Sports Ceter buildig 33 9 First reflectio o Traverse buildig Secod reflectio o Sports Ceter buildig Geerate mea Euclidea distace D j over k sapshot sets betwee measuremet cluster m i ad simulatio clusters Filter out far-away simulatio clusters from measuremet cluster m i Fid correspodig simulatio cluster j with smallest mea Euclidea distace matchig with measuremet cluster m i Fig. 9 Procedure of template matchig by calculatig Euclidea distace. Accordig to the umber of matchig measuremet clusters, the results ca be divided ito three categories. First, oe measuremet cluster ca fid oly oe matchig simulatio cluster, e.g. measuremet cluster o. ad o. 2. From the iteractio poits provided by the simulator, it is idetified that measuremet cluster o. is the LOS wave ad cluster o. 2 is the wave with reflectio poit o the Traverse buildig. Fig. 0 ad Fig. show the plots of measuremet ad the correspodig simulatio clusters, demostratig the reliability of the matchig results. The secod category is that several measuremet clusters match with the same simulatio cluster. For example, there are six measuremet clusters that match with simulatio cluster o. 4, show i Fig. 2. This happes whe objects exist which are blockig the propagatio path for certai parts of the trajectory. Based o the cluster algorithm, the discoected measuremet clusters are regarded as differet clusters. Fig. 2 proves the matchig results for this situatio are also reliable. The last category is that some measuremet

6 clusters have o matchig simulatio cluster. By checkig the plots, it ca be foud that the oise clusters i the measuremet do ot match ay simulated cluster, as expected. It is also foud that some measuremet clusters with o matchig simulatio clusters are formed due to lamppost reflectios. For example, by checkig the AoA of MPCs superimposed o the video data, the reflectio iteractio poits are the lampposts poited by the red circles i Fig. 3. This ivestigatio idicates that lamppost reflectio plays a importat role i a real situatio. Therefore, the simulatio eviromet should iclude the positio of lampposts. Fig. 0 Feature values of measuremet cluster o. ad matchig simulatio cluster o.. Fig. Feature values of measuremet cluster o. 2 ad matchig simulatio cluster o. 2. Fig. 3 Agle-of-arrival of multipath compoets superimposed o omidirectioal video data showig lamppost reflectios. Fially, the matchig results for the strogest simulated MPCs usig the iteractio poits from Table I are verified with the correspodig video frames at various sapshot sets k. This is the evaluatio step of the matchig procedure (Fig. 4. V. CONCLUSIONS I this paper, the correspodig multipath waves betwee the simulatio ad measuremet results are successfully foud by the desiged algorithm which cosists of five steps: clusterig, calibratio, feature geeratio, template matchig ad evaluatio. The Nearest Neighbourhood clusterig algorithm ca successfully separate the multipath waves related to the physical iteractig objects i the measuremet. Based o the LOS wave, the time delay offset i measuremet results is removed i the calibratio step. By geeratig feature values of measuremet clusters, the agular dispersio due to surface roughess i measuremets ca be elimiated, so that the compariso betwee the simulatio ad measuremet results ca be coducted. The matchig plots ad the evaluatio results prove that the matchig results are reliable. It was foud that, i additio to LOS ad buildigs, lampposts play a importat role i a urba eviromet for the agular dispersio of radio waves. REFERENCES [] M.F. Iskader ad Z. Yu, Propagatio predictio models for wireless commuicatio system, IEEE Trasactios o Microwave Theory ad Techiques, Vol. 50, No. 3, Mar [2] L.M. Correia (ed., Mobile broadbad multimedia etworks: techiques, models ad tools for 4G, ISBN , May [3] O. Matel, A. Bokiye, A.R. va Dommele ad M.R.J.A.E. Kwakkeraat, Measuremet-based verificatio of delay ad agular spread ray-tracig predictios for use i urba mobile etwork plaig, COST 200 TD(09 94, Viea, Austria, Sept [4] M.R.J.A.E. Kwakkeraat, Agular dispersio of radio waves i mobile chaels, PhD thesis, Eidhove Uiversity of Techology, the Netherlads, 2008, [5] The software package CRC-RayPredict was developed by Y.L.C. de Jog at the Commuicatios Research Cetre Caada. [6] S. Theodoris ad K. Koutroumbas, Patter recogitio, Chapter 8, ISBN , [7] B. H. Fleury, First-ad secod-order characterizatio of directio dispersio ad space selectivity i the radio chael, IEEE Trasactios o iformatio Theory, Vol. 46, No. 6, Sept Fig. 2 Feature values of measuremet clusters o. 43, 49, 99,5,88,90 ad matchig simulatio cluster o. 4.