Azar, Y., Wong, G. N., Wang, K., Mayzus, R., Schulz, J. K., Zhao, H., Gutierrez, F., Hwang, D., Rappaport, T. S., 28 GHzPropagation Measurements for Outdoor Cellular Communications Using Steerable Beam Antennas in New York City, to

appear in the 2013 IEEE International Conference on Communications (ICC), June 9∼13, 2013.

28 GHz Propagation Measurements for OutdoorCellular Communications Using Steerable Beam

Antennas in New York CityYaniv Azar, George N. Wong, Kevin Wang, Rimma Mayzus, Jocelyn K. Schulz, Hang Zhao,

Felix Gutierrez, Jr., DuckDong Hwang, Theodore S. RappaportNYU WIRELESS

Polytechnic Institute of New York University, Brooklyn, NY 11201tsr@nyu.edu

Abstract—The millimeter wave frequency spectrum offers un-precedented bandwidths for future broadband cellular networks.This paper presents the world’s first empirical measurementsfor 28 GHz outdoor cellular propagation in New York City.Measurements were made in Manhattan for three different basestation locations and 75 receiver locations over distances up to500 meters. A 400 megachip-per-second channel sounder anddirectional horn antennas were used to measure propagationcharacteristics for future mm-wave cellular systems in urbanenvironments. This paper presents measured path loss as afunction of the transmitter - receiver separation distance, theangular distribution of received power using directional 24.5dBi antennas, and power delay profiles observed in New YorkCity. The measured data show that a large number of resolvablemultipath components exist in both non line of sight and lineof sight environments, with observed multipath excess delayspreads (20 dB) as great as 1388.4 ns and 753.5 ns, respectively.The widely diverse spatial channels observed at any particularlocation suggest that millimeter wave mobile communication sys-tems with electrically steerable antennas could exploit resolvablemultipath components to create viable links for cell sizes on theorder of 200 m.

Index Terms—28 GHz, millimeter wave cellular, multipath de-lay spread, path loss exponent, millimeter wave communications,RF channel, channel sounder, sliding correlator, 5G

I. INTRODUCTION

Cellular and wireless local area networks (WLAN) operatebetween 800 MHz and 5.8 GHz, and new 60 GHz WLANproducts are beginning to proliferate. The growing market forbroadband wireless services has led to a global bandwidthshortage for carriers [1][2][4]. Recent work suggests thatmobile cellular is possible at carrier frequencies of tens ofGHz, an order of magnitude greater than today’s cellular spec-trum bands, where high-gain miniaturized steerable antennascould be used to exploit the smaller wavelength [1][2][3][4],thus motivating researchers to develop new techniques for therarely-used millimeter wave (mm-wave) frequency bands. Atthe mm-wave bands of 28 GHz and 38 GHz, unlike at 60 GHzor 380 GHz, atmospheric absorption does not significantlycontribute to additional path loss, making it suitable foroutdoor mobile communications [1].

Advances in the semiconductor industry allow for low-costintegrated mm-wave electronics in CMOS, and cost-efficient

Fig. 1. Rain attenuation in dB/km across frequency and various rates ofrain fall. The rain attenuation at 28 GHz has an attenuation of 7 dB/km forvery heavy rainfall of 25 mm/hr. If cell sizes are about 200 m in radius, thisattenuation will reduce by 80%. The red ring donates the attenuation at 28GHz under very heavy rainfall [7].

small high-gain steerable antennas [1][2][3][4]. However, amyth in industry is that rain attenuation will challenge mm-wave cellular systems. Zhao et al studied the relationshipbetween rain attenuation as a function of rain rate and carrierfrequency [7], as shown in Fig. 1. The attenuation may bedivided by five for cell sizes with a radius of 200 m (i.e. simplyconvert 1 km to 200 m distance). Doing this conversion, Fig. 1shows that at a heavy rain rate of 7.6 mm/hour [6], the rainattenuation for a 200 m cell radius is only 0.6 dB at 28 GHzand 0.8 dB at 38 GHz. Even with very heavy rainfall of 25mm/hour, the rain attenuation is only 1.4 dB at 28 GHz and1.6 dB at 38 GHz. Thus, proper link design (with varying gainantennas, for example) could account for rain margin in futuremobile mm-wave cellular systems.

To study urban cellular propagation, it is customary toclassify the physical environment as being either line of sight(LOS) or non line of sight (NLOS) between a transmitter (TX)and receiver (RX). NLOS may be further divided into mod-erately and heavily obstructed environments, where moderateNLOS conditions have small obstructions, such as trees orbuilding edges that partially block the optical path betweenthe TX and RX, while heavily obstructed NLOS conditionshave large obstructions fully blocking the optical path.

Previous research in Austin, TX conducted rooftop-to-ground measurements at 38 GHz, and peer-to-peer channelsin an outdoor urban setting at both 38 GHz and 60 GHz forfuture generation cellular [4]. Previous measurements for 28GHz LMDS systems [8] showed that steerable antennas couldbe used for fixed point-to-multipoint links, whereas anotherstudy showed that NLOS links could be made using steerableantennas for cellular coverage up to 200 m [9]. This paperpresents the world’s first 28 GHz outdoor cellular propagationmeasurements in New York City for future fifth-generation(5G) mobile communications.

To describe radio propagation path loss (PL) as a functionof distance, the propagation path loss exponent (PLE) is aparameter that describes the attenuation of a signal as itpropagates in the channel. Path loss at a close-in referencedistance of d0 is calculated and measured to be free spaceloss by the equation [10]:

PLfs(d0) = 20log10(4πd0λ

) (1)

where λ is the wavelength of the carrier frequency. In ourmeasurements d0 = 5 m and λ = 10.71 mm at 28 GHz. Pathloss at a distance d, beyond d0 can be described by the pathloss exponent using the following equation:

PL(d)[dB] = PLfs(d0)[dB] + 10nlog10(d

d0) (2)

where PL(d) is the average path loss in dB for a givenTX-RX separation of d, and n is the average path lossexponent over distance and all pointing angles. LOS links withthe TX and RX antennas pointing towards each other (i.e.boresight) provide a path loss exponent of n = 2 with verysmall multipath delay spread [5], while the steerable antennasprovide different path loss exponents (and different multipathpower delay profiles (PDPs)) for different links made betweena TX and RX, depending on the orientation of antennas and thesurrounding LOS or NLOS environment. Path loss is importantfor determining coverage distances, system capacity, and linkbudgets for viable links in a cellular system. A higher PLEindicates greater attenuation of the propagating signal.

Angle of Departure (AOD) and Angle of Arrival (AOA)data at the TX and RX locations, respectively, are needed todetermine the angular spread and number of unique pointingangles of the mobile and base station antennas that yield viablelinks between TX and RX as given in [11]. While NLOSlinks may require equalization due to longer propagationdelay time, Signal-to-Noise Ratio (SNR) and power efficiency

are maximized by finding the optimal pointing angles at aparticular location.

II. 28 GHZ CHANNEL MEASUREMENT HARDWARE

A 400 megachip-per-second (Mcps) sliding correlator chan-nel sounder was used to conduct the propagation measure-ments. The probing signal consists of a pseudo-random noisesequence upconverted to 28 GHz with a maximum averageoutput power of +30 dBm before TX antenna. The slidingcorrelator allows a multipath time resolution of 2.3 ns and 178dB of total path loss (for the case of TX and RX using 24.5 dBiantennas). Note that the measured dynamic range of total pathloss likely meets or exceeds that of future 5G cellular systems,thus ensuring measured results are meaningful. We took greatcare to not record noisy PDPs in the case of insufficient SNR,and operated at a 10 dB SNR (i.e. 168 dB of total path loss).Two types of antennas were used: a 15 dBi horn antenna with30◦ beamwidth for both elevation and azimuth, and a 24.5dBi horn antenna with 10.9◦ beamwidth. The antennas werevertically polarized. We used the same hardware that was usedin previous measurement campaigns [9] with an intermediatefrequency (IF) of 5.4 GHz and a separately supplied localoscillator (LO) of 22.6 GHz.

III. 28 GHZ CHANNEL MEASUREMENT PROCEDURE

The 28 GHz channel propagation measurements were per-formed at the NYU campus in downtown Manhattan. Mea-surement sites included a wide range of urban environments,including parks, commercial districts, and general universityareas with high rise buildings and dense pedestrian and ve-hicular traffic. To emulate future cellular base stations withrelatively low heights, two TX sites were located on the ColesSports Center building rooftop (7 m above ground level, withthe TX located on the northwest and northeast corners ofthe roof), and one TX site was on the five-story balcony ofKaufman Business School (17 m above ground level) (seeFig. 2). All three TX sites used the same set of 25 RX sites,which were chosen randomly based on the availability of ACpower, thus yielding 75 unique TX-RX location combinations.

At each RX measurement location, the TX and RX direc-tional antennas were pointed in several different directions inelevation and the RX antenna was rotated exhausively overazimuth to find the strongest received power. The strongestlink was usually made when the TX and RX antennas weredirectly pointed at each other. The 0◦ azimuth angle of the TXwas set at the angle with the strongest link with 10◦ downtilt.Measurements were then taken for 3 different TX azimuthangles , -5◦, 0◦, and +5◦, and for 3 different RX elevations,-20◦, 0◦, and +20◦, with all possible combinations betweenthe two (i.e. 9 total TX-RX antenna configurations). For eachof the 9 TX-RX antenna configurations, the RX antenna wasrotated 360◦ in the azimuth plane and a power delay profilemeasurement was recorded at every 10◦ where a link was made(PL<168 dB). In all locations, both the TX and RX used 24.5dBi antennas with 10◦ 3 dB beamwidth.

Fig. 2. 28 GHz cellular measurement locations in Manhattan near the NYUcampus. Three base station locations (yellow stars on the two-story rooftopof Coles Recreational Center and five-story balcony of Kaufman BusinessSchool) were used to transmit to each of the 25 receiver locations within 20to 500 m. In total, 75 TX-RX location combinations were used for Manhattanmeasurements. Four RX locations on the west are not shown in the picture.Purple squares represent RX sites that are blocked by buildings. Signal couldonly be received at 26 of the 75 location combinations.

IV. 28 GHZ URBAN CHANNEL PROPAGATION ANALYSIS

Fig. 3 shows the path loss computed for each measurementacquired in New York City with the 24.5 dBi antennas. Thesmallest path loss is defined as the single best TX and RXantenna pointing combination at a given RX location, whichcorresponds to the strongest possible link created. The bestLOS PLE was n = 1.68 (due to groud reflection), with ashadowing factor (standard deviation of shadowing, or SF)of only 0.2 dB. The aggregated LOS PLE, considering allthe possible antenna configurations in a LOS environment,increased to 2.55 with a SF of 8.66 dB since antennas wereoften not optically aligned on boresight. In contrast, the NLOSPLE was 5.76, and reduced to 4.58 when only the best (i.e.strongest) NLOS link was considered at each RX location,yielding SFs of 9.02 dB and 8.83 dB, respectively. Theoverall PLE for all measurements, LOS and NLOS, was 5.73.The similarity of the overall PLE and NLOS PLE is dueto the NYC environment providing significantly more NLOSsituations, and very few LOS locations.

Fig. 4 is a polar plot that shows received power in dBm asa function of receiver azimuth angle in a NLOS environment.The three values at each azimuth angle in Fig. 4 indicatethe number of resolvable multipath components, path loss(relative to 5 m free space), and RMS delay spread. The plotshows for this RX location, 22 out of 36 possible azimuthangles in an urban NLOS environment are available. ReceivedPDPs were thresholded to ∼ 168 dB path loss floor, andmultipath components were detected by using a peak detectingalgorithm. Fig. 4 counters previous data that stated no morethan 5-10 links could be formed in a NLOS environment [5].Rich multipath will allow future beam steering technologiesto deduce algorithmically which azimuth angle would producethe greatest received power [12][13]. Angular analysis and raytracing of the measured PDPs allow reconstruction of the pathstaken by the RF signals for each AOA.

Figs. 5 and 6 show PDPs of the largest observed multipathdelay spread for a LOS and a NLOS environment. Fig. 5

Fig. 3. Measured path loss values relative to 5 m free space path loss for28 GHz outdoor cellular channels. These path loss values were measuredusing the 24.5 dBi narrow beam antennas. The RX antenna was rotated inthe azimuth plane in 10◦ steps. The values in the legend represent the PLEof each environment (LOS and NLOS).

shows a LOS PDP with a maximum excess delay (20 dB)of 753.5 ns transmitted from Kaufman balcony to a receiver52 m away. The transmitter was pointed -5◦ azimuth and -10◦ below horizon. The receiver was pointed away from theTX with 0◦ elevation. Fig. 6 shows the NLOS maximumexcess delay (20 dB) was 1388.4 ns, indicating that the farthestdistance the RF wave traveled was approximately 423 metersbeyond the propagation distance of the first arriving signal. Ahighly reflective environment with large radar cross sectionsfor distant reflectors is the most likely cause of such a highexcess delay. For most measurements, the RMS delay spread inLOS conditions did not exceed 100 to 200 ns over all locations(6 LOS TX-RX location combinations and 20 NLOS TX-RX

Fig. 4. Polar plot showing the received power at a NLOS location. This plotshows an AOA measurement at the RX on Greene and Broadway from theTX on the five-story Kaufman building (78 m TX-RX separation). The polarplot shows received power in dBm with varying receiver antenna azimuthangle. The perimeter of the plot shows for each azimuth angle three valuesthat correspond to the number of resolvable multipath components, path lossrelative to 5 m free space, and RMS delay spread.

Fig. 5. The largest observed multipath excess delay in a LOS urbanenvironment at 28 GHz. It was observed with the TX on the five-storyKaufman balcony and the RX located 52 m away from the TX. The referencepath loss, maximum excess delay (20 dB), RMS delay spread (στ ), and TXand RX azimuth and elevation angles are shown on the right of the PDP.

location combinations) and all beam configurations.Fig. 7 shows an AOA and AOD ray-tracing analysis for

the LOS case in Fig. 5. Fig. 8 shows the average number ofresolvable multipath components formed for various TX-RXdistances. Under LOS conditions, an average of 7.2 uniqueresolvable multipath components will exist for each TX-RXlink with a standard deviation of 2.2 paths between 35 mand 200 m. For NLOS conditions, an average of 6.8 uniqueresolvable multipath components will exist for each TX-RXlink with a standard deviation of 2.2 paths. For both LOS andNLOS, the average number of paths increased with distance(up to 100 m), after which the average number of paths tendedto slightly decrease with increasing distance beyond 100 m.

Fig. 9 shows an outage map for all Manhattan measure-ments. These RX outage sites correspond to no signal detectedfrom TX (i.e. PL >178 dB) at any angle. For path lossbetween 168 dB and 178 dB, signal could be detected but

Fig. 6. The largest observed multipath excess delay in a NLOS environmentat 28 GHz. It was observed with the TX on the two-story Coles buildingrooftop and the RX located (behind a building) 97 m away from the TX. Thereference path loss, maximum excess delay (20 dB), RMS delay spread (στ ),and TX and RX azimuth and elevation angles are shown on the right of thePDP.

Fig. 7. AOA measurements in outdoor downtown Manhattan for 28 GHz.The RX was located in front of WWH (Warren Weaver Hall) building andthe TX was located on the balcony of Kaufman. The plot shows a potentialpath obtained by manual ray tracing to achieve a 753.5 ns excess delay shownin Fig. 5 in a LOS environment. The green dot represents the RX and theyellow star represents the TX. White arrows represent the direction of the hornantenna. The cyan path simulates the route taken by the wave from the TXto the RX that resulted in the first received power. The purple path representsthe last received power 753.5 ns later.

was not strong enough to always be acquired. The map isdivided into different sectors which correspond to a TX site.The radii of these sectors are 200 m, which suggests that themaximum size of future mm-wave cellular networks in denseurban environments. It was found that an outage occurred in57% of all the receiver locations. Within 200 m, the outagedecreased to 16% as no signal could be acquired at four RXlocations shadowed by the Bobst building.

V. CONCLUSION

This article presented propagation measurements at 28 GHzin New York City. A total of 75 unique TX-RX combinationswere measured with two different antenna gains and 36pointing angles. The rate at which path loss increased as afunction of distance varied in different NLOS environments.The overall path loss exponent, n, was found to be 5.73;however, through the use of beam steering, the angles cor-responding to the lowest path loss can be found and exploited

Fig. 8. Average number of resolvable multipath components per TX-RXlink for different distances in 28 GHz using two 24.5 dBi horn antennas. Thedistribution increases up to 71 m and then decreases until 193 m. Averagenumber of resolvable multipath components was computed over all viablelinks made with all possible pointing angles at a particular T-R separation.

Fig. 9. Map showing all Manhattan coverage cells with radii of 200 m andtheir different sectors. Measurements were recorded for each of the 25 RXsites from each of the three TX sites (yellow stars).”Signal Acquired” meansthat signal was detected and acquired (PL<168 dB). ”Signal Detected” meansthat signal was detected, but low SNR prevented data acquisition (168 dB <PL<178 dB). ”No Signal Detected” occurred with PL >178 dB. To the westof Kaufman is the Bobst Library which blocked the signal from reaching the4 sites marked with crosses, which resulted in no signals being detected atthose locations.

to decrease the path loss exponent [12][13]. Considering, ateach location, only the best angle orientation with the highestreceived power, the path loss exponent dropped to 4.58 forNLOS and 4.47 over all locations. While performing 10◦

incremental azimuthal angular sweeps, PDPs were measuredwith less than 168 dB path loss typically at more than 20 outof 36 possible angles under dense urban NLOS conditions.For future development of a statistical channel model at 28GHz, we computed the average number of resolvable multipathcomponents, averaged over all pointing angles of the TX andRX, as a function of distance. Also, we found that 57% ofall receiver locations, which exceeded a TX-RX separationof 200 m, were outages, where no signal could be detected;however, the outage decreased to 16% for distances within 200m. We could find no links at distances greater than 200 m forManhattan with 178 dB PL. This maximal cell size means thatrain attenuation will not pose a significant problem due to therelatively shorter distances involved.

VI. ACKNOWLEDGMENT

This project was sponsored by Samsung DMC R&DCommunications Research Team (CRT) through SamsungTelecommunications America, LLC. The authors wish to thankShu Sun and Mathew Samimi of NYU WIRELESS for theircontributions to this paper, and Shadi Abu-Surra of Samsung,the NYU Administration, NYU Public Safety and NYPD fortheir support of our measurements. Measurements recordedunder U.S. FCC Experimental License 0040-EX-ML-2012.

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