Comparing Radio Propagation Channels Between 28 and 140 GHz Bands in a Shopping Mall

S. L. H. Nguyen et al. , “Comparing Radio Propagation Channels Between 28 and 140 GHz Bands in a Shopping Mall, ” to be published in 2018 European Confer ence on Antennas and Propa gation (EuCAP) , London, UK, April 2018. Comparing Radio Propagation Channels Between 28 and 140 GHz Bands in a Shopping Mall Sinh L. H. Nguyen † , Jan J ¨ arvel ¨ ainen †‡ , Aki Karttunen † , Katsuyuki Haneda † , and Jyri Putkonen ∗ † Aalto University , School of Electrical and Engineering, Finland { sinh.nguyen, katsuyuki.haneda, aki.karttunen } @aalto.fi ‡ Premix Oy , Finland jan.jarvelainen@premixgroup.com ∗ Nokia Bell Labs, Finland jyri.putkonen@nokia-bell-labs.com Abstract —In this paper , we compar e the radio pr opagation channels characteristics between 28 and 140 GHz bands based on the wideband (several GHz) and directional channel sounding in a shopping mall en vironment. The measurements and data processing are conducted in such a way to meet requirements f or a fair comparison of large- and small- scale channel parameters between the two bands. Our results re veal that there is high spatial-temporal correlation between 28 and 140 GHz channels, similar numbers of strong multipath components, and only small variations in the large-scale parameters between the two bands. Furthermore, when including the weak paths there are higher total numbers of clusters and paths in 28 GHz as compared to those in 140 GHz bands. With these similarities, it would be very interesting to inv estigate the potentials of using 140 GHz band in the future mobile radio communications. Index T erms —5G, 28 GHz, 140 GHz, Channel modelling, D- band, Millimeter -wav e. I . I N T RO D U C T I O N Millimeter-w av e bands, referred as frequency bands from 30 GHz − 300 GHz, have been exploited for 5G radio com- munications in recent years [1], [2]. Howe ver , the majority of the propagation channel studies and experiments has been focused only to bands up to 100 GHz [3]–[7]. While abov e-100 GHz bands experience higher path loss, at the same time wider unused bandwidth chunks are av ailable in those bands, making them also possible candidates for future wireless systems. For example, in Finland a bandwidth of 7.5 GHz ( 141 − 148 . 5 GHz) in D-band is currently unused and could be exploited for future fixed and mobile radio communications [8]. Shopping mall is among the scenarios where mobile broad- band experiences are expected to be supported in 5G, i.e., “great service in a cro wd” [9]. Propagation channels in the shopping mall environment were studied in [10] at 28 GHz band, and in [11], [12] for 15, 28, 60, and 73 GHz bands. Literature on the channel measurements at above 100 GHz frequencies is in general very limited, and has not been found for the shopping mall en vironment in particular . Only one pre- vious work on very short range indoor pathloss measurement has been found in the literature, where line-of-sight (LOS) pathloss was measured as the antenna separation v aried from 20 to 180 cm [13]. In this paper , for the first time in the literature we report micr ocell directional channel measur ements at 140 GHz for a large indoor shopping mall environment. Furthermore, we compare the 140 GHz channel characteristics with its coun- terparts at 28 GHz using the data measured at the same links in the same manner . The wideband (4 GHz) and directional measurements and data processing were conducted in such a way allowing us to make a fair comparison of large- and small- scale channel parameters between the two bands. The similarity and difference in pathloss, and large- and small- scale parameters between the two bands are then analyzed to in vestig ate the possibility of using the 140 GHz frequencies for future mobile radio communications. I I . M E A S U R E M E N T S E T U P A N D E N V I R O N M E N T The wideband directional channel measurements were per- formed using the same approach reported in [11], [14], [15]. Specifically , two similar setup radio channel sounders were used to perform channel measurements in the 28 and 140 GHz frequency ranges, where the RF signals were generated using the Ka-band ( 26 . 5 − 40 GHz) and D-band ( 110 − 170 GHz) up- and down-con verters, respectively . The schematic diagram of the measurement system is sho wn in Fig. 1. The details of the channel sounder can be found in [11]. Rx horn antenna (19 dBi) Tx bicone antenna (2 dBi) Down converter Rotator Up converter Tripod V ector network analyzer Signal Generator LO signal Splitter IF signal RF signal 10 MHz sync Control PC W aveguide E/O O/E Optical fiber cable 200m 30 dB amp Fig. 1. Channel sounding system: Tx (Rx) includes a frequency multiplier (factor of 2 in 28-GHz and 12 in 140-GHz bands) and a mixer for up- con verting (down-con verting) the IF (RF) signal. The venue for the shopping mall measurements was the Sello shopping mall in Lepp ¨ avaara, Espoo, Finland, presented Tx19 Tx20 Tx18 Tx16 Tx13 Tx15 Tx21 Tx14 Tx12 Tx5 Tx4 Tx22 Tx2 Tx17 Tx23 Tx1 Tx24 Rx1 Tx7 50 40 Tx17 30 20 10 0 10 -10 Fig. 2. 3-D map of the Tx and Rx positions in the 3rd floor of the Sello shopping mall in the 140-GHz measurement, overlaid with the 3-D point cloud model of the environment. The green triangles present the Tx locations that were also measured at 28 GHz in the same day in November 2016; the yellow triangles present the Tx locations that were also measured at 28 GHz but in March 2015; the orange triangles present the Tx locations that were measured in 140 GHz band only . Fig. 3. Photo from the Sello shopping mall. T ABLE I S U MM A RY O F T H E M E AS U R E ME N T S . Parameter 28-GHz band 140-GHz band Center frequency 28 . 5 GHz 143 . 1 GHz Bandwidth 4 GHz 4 GHz T ransmit power 2 dBm − 7 dBm PDP dynamic range 123 dB 130 dB Tx / Rx height 1.9 /1.9 m Link distance range 3 − 65 m Rx antenna horn, 19 dBi, 10 ◦ az./ 40 ◦ el. HPBW Tx antenna bicone, 0 dBi, 60 ◦ el. HPBW in Fig. 3. The shopping mall is a modern, four-story building with a large open space in the middle and approximate dimensions of 120 × 70 m 2 . The floorplan of the channel measurements are sho wn in Fig. 2. In total, 18 Tx antenna locations were measured at 140 GHz, with antenna heights of 1 . 9 m and the Tx-Rx distance ranging from 3 to 65 m, approximately . The Tx were mov ed a long the corridor and around open space in the middle of the shopping mall. In three Tx locations, the LOS path was obstructed by the pillar or the escalator . The antenna locations were chosen such that human blockage could be av oided in order to maintain the repeatability of the measurements at both frequency bands. At each Tx location, the Rx horn antenna was rotated in the azimuth plane with 5 ◦ step, as similarly done in the directional measurements in [11], [14]. T o compare 140 GHz channels with its 28 GHz counterpart, 8 links (5 LOS and 3 obstructed LOS) that were measured in the same day are used for the comparison. As can be seen from T able II and Fig. 4, measurement specifications including bandwidth and antenna patterns were ensured to meet the requirements for comparability of channel’ s parameters across different frequencies, as defined in [6]. T ABLE II C O MPA R AB I L I TY B E T WE E N T W O F R E QU E N CY B A ND S . Requirement Comment Same environment 3 Same measurement time Approximately (in the same day) Same antenna locations 3 Comparable antenna patterns 3 Equal delay resolution 0 . 25 ns Equal spatial resolution 10 ◦ in azimuth, 40 ◦ in elev ation Same post processing method 3 Same power range 3 -20 0 20 -40 -30 -20 -10 0 Normalized gain (dB) Azimuth cut 28.5 GHz 143 GHz -20 -10 0 10 20 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 Normalized gain (dB) Elevation cut 28.5 GHz 143 GHz Fig. 4. Comparison of Rx radiation patterns in (left) azimuth plane and (right) elev ation plane between 28-GHz and 140-GHz bands. Link Tx17Rx1 -120dB -100dB -80dB 30 210 60 240 90 270 120 300 150 330 180 0 (a) Link Tx18Rx1 -120dB -110dB -100dB 30 210 60 240 90 270 120 300 150 330 180 0 (b) Link Tx19Rx1 -130dB -120dB -110dB -100dB -90dB 30 210 60 240 90 270 120 300 150 330 180 0 (c) Link Tx20Rx1 -130dB -120dB -110dB -100dB -90dB 30 210 60 240 90 270 120 300 150 330 180 0 (d) Link Tx21Rx1 -130dB -120dB -110dB -100dB -90dB 30 210 60 240 90 270 120 300 150 330 180 0 (e) Link Tx22Rx1 -130dB -120dB -110dB -100dB -90dB 30 210 60 240 90 270 120 300 150 330 180 0 (f) Link Tx23Rx1 -120dB -100dB -80dB 30 210 60 240 90 270 120 300 150 330 180 0 (g) Link Tx24Rx1 -120dB -100dB -80dB -60dB 30 210 60 240 90 270 120 300 150 330 180 0 (h) Fig. 5. Comparison of po wer -angular profiles between 28 GHz (dashed blue) and 140 GHz (solid red) for Tx positions from ((a) 17 to (h) 24. Tx positions 17, 19, 21, 23, 24 are in LOS and the rest are in obstructed LOS conditions. I I I . C O M P A R I S O N O F L A R G E - S C A L E P A R A M E T E R S (a) (b) Fig. 6. P ADPs of link Tx17-Rx1 and detected peaks (red dots) within 30-dB range in (a) 28 GHz and (b) 140 GHz measurements. From the measured po wer angular delay profiles (P ADPs), the multipath components (MPCs) in each measurement were e xtracted using the peak search algorithm in [14]. The peak detection algorithm is based on the assumption that the channel is deterministic for at least the strong M PCs, i.e., the arri ving signals from discrete specular reflectors are completely resolv- able either in delay or angular domain [16]. The assumption is justified by the v ery wide channel measurement bandwidth of 4 GHz and narro w azi muth beamwidth of 10 ◦ of the recei v e horn antennas at both measured fre q ue n c ies. The azimuth angle of arri v al (AoA) and amplitude of each MPC are calculated using the recei v e antenna pattern and subtracting the corresponding antenna g ain from the peak’ s amplitude [14]. 18 20 22 24 Tx positi on 0 20 40 60 80 100 N umbe r of MPCs 28 GHz 140 GHz (a) 18 20 22 24 Tx posi t i on 0 5 10 15 20 25 N umbe r of MPCs 28 GHz 140 GHz (b) Fig. 7. Number of detected specular paths within a) 30-dB threshold and b) 15-dB threshold in Sello shopping mall. The corresponding mean v alues plotted with horizontal dotted lines One e xample of the P ADPs and peak search is presented in Fig. 6, which sho ws the measured channel for the Tx position 17 (LOS). It can be noticed that m an y deterministic paths occur in both frequency bands. As depicted in Figs. 5 and 7, there are clearly more paths at 28 GHz than at 140 GHz when considering a 30-dB threshold seen from the strongest path amplitude. Howe ver , when 15-dB threshold is used, the number of (strong) paths is v ery similar between the two bands for all links, e xpect link Tx18-Rx1, which is OLOS. This similarity in the multipath richness between the two bands, especially in this indoor en vironment, can be explained by the fact that the environment consists of many surfaces considered smooth even at 140 GHz. From the detected MPCs, omni-direction pathloss, delay and angular spreads have been calculated for 28 and 140 GHz. Due to the low dynamic range at 140 GHz, a 30 dB threshold has been used. The results are presented in Figs. 8 and 9, and T able IV. It can be seen that the av erage delay spread is almost identical for the both frequency bands, and the azimuth spread is 10% higher at 28 GHz. The small difference between the bands can be explained by the fact that the most significant paths are found in both bands. When comparing link by link, noticeably higher DS and AS can be observed in 28 GHz in the obstructed LOS link Tx18-Rx1. 10 0 10 1 10 2 Link Distance [m] 70 80 90 100 110 Path Loss [dB] 28 GHz fspl 28 GHz meas. 140 GHz fspl 140 GHz meas. Fig. 8. Measured omni-direction pathloss at 28 GHz (dots) and 140 GHz (triangles) bands. The solid lines show the free-space pathloss (fspl) at corresponding frequencies. Fitting the measured omni-directional pathloss data of each of the two bands to the pathloss model equation P L ( d ) = 10 A log 10 ( d/ 1 m ) + B + N (0 , σ 2 ) , (1) we obtain the model parameters sho wn in T able III. It can be seen from Fig. 8 and T able III that except some additional fspl at 140 GHz, the slope and variations of the pathloss data of two bands are similar . T ABLE III P A T H LO S S M O D E L PAR A M E TE R S I N T H E S H OP P I N G M A LL I N 2 8 -G H Z A N D 1 4 0- G H Z B AN D S . Parameter 28 GHz 140 GHz A 2 . 10 2 . 22 B 59 . 16 70 . 77 σ 2.85 2.94 0 5 10 15 20 25 30 35 Link distance [m] 0 10 20 30 40 Delay spread [ns] 28 GHz 140 GHz (a) 0 5 10 15 20 25 30 35 Link distance [m] 10 20 30 40 50 Azimuth spread [ ° ] 28 GHz 140 GHz (b) Fig. 9. (a) Delay spread and (b) azimuth spread in the shopping mall. Mean values plotted with dotted lines. T ABLE IV M E AN O F D E L A Y A N D A Z I M UT H S P RE A D S OV E R A L L C O M MO N T X - R X L I NK S I N T H E S H O PP I N G M A L L A T 2 8 A N D 1 4 0 G H Z . Frequency Delay spread [ns] Azimuth spread [ ◦ ] 28 GHz 19 33 140 GHz 19 29 I V . C O M P A R I N G N U M B E R O F C L U S T E R S A N D I N T E R - C L U S T E R C H A R A C T E R I S T I C S T o obtain cluster parameters for each link of the two bands, a hierarchical clustering algorithm [14] was used with the detected MPCs. For the purpose of comparing cluster model parameters between the two bands, the same multipath component distance (MCD) threshold of 30 dB was used for both 28 and 140 GHz band. Denoting the number of clusters and the number of MPCs per cluster for a giv en link as N and M , respectiv ely , T able V presents the mean and standard deviation values of N and M in the 28 and 140 GHz measurements. It can be observed from the results that both the number of clusters and the number of paths per cluster are higher in the 28 GHz bands as expected from the higher total number of detected paths when higher threshold v alue is used. Comparing to the parameters adopted in 3GPP New Radio (NR) model TR 38.901 for abov e 6 GHz Indoor Office en vironment [4], that is, 15 clusters for LOS and 19for non- line-of-sight (NLOS) (each of them has 20 MPCs) scenarios, our results in both frequency bands appear to hav e smaller number of clusters and MPCs per cluster . As far as the relation between the cluster power and cluster propagation distance is concerned, Fig. 10 shows the empir- ical data obtained from the measurements and our clustering T ABLE V M E AN A N D S TAN D AR D D E VI ATI O N O F T H E N U MB E R O F C L US T E R S N A N D T H E N U M B ER O F M P C S P E R C L US T E R M F O R S H O PP I N G M A LL S C E NA R IO . Parameter 28-GHz band 140-GHz band N µ 7.9 5.9 σ 3.6 2.1 M µ 5.4 3.8 σ 6.0 2.5 process. Linear re gression fits well with the empirical data in both bands. The fitting model can be expressed as P c = A log 10 ( d c ) + B , (2) where P c and d c are the cluster power in dB and cluster prop- agation distance in m, respectiv ely . A simple liner regression provides that ( A, B ) is equal to ( − 30 . 5 , − 58 . 0) in the 28-GHz band and equal to ( − 24 . 8 , − 78 . 1) in the 140-GHz band. 0.6 0.8 1 1.2 1.4 1.6 1.8 log 1 0 (d) [m] -130 -120 -110 -100 -90 -80 -70 Power [dB] Powers vs. distance - 28GHz Linear t - 28GHz Powers vs. distance - 140GHz Linear t - 140GHz Fig. 10. Empirical cluster power [dB] versus cluster distance [ l og 10 (m)], and the linear fit at 28 and 140 GHz. T ABLE VI M O DE L PAR A M E TE R S A N D FI T T I NG E R RO R F O R T H E C O M P OS I T E P A S I N A Z IM U T H O F A L L C L U S TE R S . Model 28-GHz band 140-GHz band Gaussian σ [ ◦ ] 17.9 18.0 RMSE 0.011 0.005 V on Mises κ [ ◦ ] 8.2 8.2 RMSE 0.086 0.085 The generation of the cluster offset angle in 3GPP is based on the distribution of the composite po wer angular spectrum (P AS), and the AoAs can be determined via inv erse Gaussian [4] or in verse wrapped Gaussian functions. The latter can be closely approximated by V on Mises distrib ution that is mathematically simpler and more tractable. The fitting models for the normalized cluster power P n / max ( P n ) versus offset AoA φ n to both Gaussian and V on Mises distributions are P n max( P n ) = exp[ − ( φ n /σ ) 2 ] , (3) P n max( P n ) = e κ cos φ n 2 π I 0 ( κ ) , (4) respectiv ely , where I 0 ( κ ) is the modified Bessel function of order 0, 1 ≤ n ≤ N is the clustering index, N is the total number of clusters. The results in T able VI show that the model parameters are similar between 28 and 140 GHz bands. A C K N O W L E D G E M E N T The research leading to the results presented in this paper receiv ed funding from Nokia Bell Labs, Finland. R E F E R E N C E S [1] Nokia, “V erizon and Nokia conduct live 5G pre-commercial trial in Dallas-F ort W orth #MWC16, ” [Online] A vailable: http://www .company .nokia.com/en/news/press-releases/, Feb. 2016. 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