Azar, Y., Wong, G. N., Wang, K., Mayzus, R., Schulz, J. K., Zhao, H., Gutierrez, F., Hwang, D., Rappaport, T. S., 28 GHz
Propagation 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 Outdoor
Cellular Communications Using Steerable Beam
Antennas in New York City
Yaniv Azar, George N. Wong, Kevin Wang, Rimma Mayzus, Jocelyn K. Schulz, Hang Zhao,
Felix Gutierrez, Jr., DuckDong Hwang, Theodore S. Rappaport
NYU WIRELESS
Polytechnic Institute of New York University, Brooklyn, NY 11201
[email protected]
Abstract—The millimeter wave frequency spectrum offers unprecedented bandwidths for future broadband cellular networks.
This paper presents the world’s first empirical measurements
for 28 GHz outdoor cellular propagation in New York City.
Measurements were made in Manhattan for three different base
station locations and 75 receiver locations over distances up to
500 meters. A 400 megachip-per-second channel sounder and
directional horn antennas were used to measure propagation
characteristics for future mm-wave cellular systems in urban
environments. This paper presents measured path loss as a
function of the transmitter - receiver separation distance, the
angular distribution of received power using directional 24.5
dBi antennas, and power delay profiles observed in New York
City. The measured data show that a large number of resolvable
multipath components exist in both non line of sight and line
of sight environments, with observed multipath excess delay
spreads (20 dB) as great as 1388.4 ns and 753.5 ns, respectively.
The widely diverse spatial channels observed at any particular
location suggest that millimeter wave mobile communication systems with electrically steerable antennas could exploit resolvable
multipath components to create viable links for cell sizes on the
order of 200 m.
Index Terms—28 GHz, millimeter wave cellular, multipath delay spread, path loss exponent, millimeter wave communications,
RF channel, channel sounder, sliding correlator, 5G
I. I NTRODUCTION
Cellular and wireless local area networks (WLAN) operate
between 800 MHz and 5.8 GHz, and new 60 GHz WLAN
products are beginning to proliferate. The growing market for
broadband wireless services has led to a global bandwidth
shortage for carriers [1][2][4]. Recent work suggests that
mobile cellular is possible at carrier frequencies of tens of
GHz, an order of magnitude greater than today’s cellular spectrum bands, where high-gain miniaturized steerable antennas
could be used to exploit the smaller wavelength [1][2][3][4],
thus motivating researchers to develop new techniques for the
rarely-used millimeter wave (mm-wave) frequency bands. At
the mm-wave bands of 28 GHz and 38 GHz, unlike at 60 GHz
or 380 GHz, atmospheric absorption does not significantly
contribute to additional path loss, making it suitable for
outdoor mobile communications [1].
Advances in the semiconductor industry allow for low-cost
integrated mm-wave electronics in CMOS, and cost-efficient
Fig. 1. Rain attenuation in dB/km across frequency and various rates of
rain fall. The rain attenuation at 28 GHz has an attenuation of 7 dB/km for
very heavy rainfall of 25 mm/hr. If cell sizes are about 200 m in radius, this
attenuation will reduce by 80%. The red ring donates the attenuation at 28
GHz under very heavy rainfall [7].
small high-gain steerable antennas [1][2][3][4]. However, a
myth in industry is that rain attenuation will challenge mmwave cellular systems. Zhao et al studied the relationship
between rain attenuation as a function of rain rate and carrier
frequency [7], as shown in Fig. 1. The attenuation may be
divided by five for cell sizes with a radius of 200 m (i.e. simply
convert 1 km to 200 m distance). Doing this conversion, Fig. 1
shows that at a heavy rain rate of 7.6 mm/hour [6], the rain
attenuation for a 200 m cell radius is only 0.6 dB at 28 GHz
and 0.8 dB at 38 GHz. Even with very heavy rainfall of 25
mm/hour, the rain attenuation is only 1.4 dB at 28 GHz and
1.6 dB at 38 GHz. Thus, proper link design (with varying gain
antennas, for example) could account for rain margin in future
mobile mm-wave cellular systems.
To study urban cellular propagation, it is customary to
classify 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 moderately and heavily obstructed environments, where moderate
NLOS conditions have small obstructions, such as trees or
building edges that partially block the optical path between
the TX and RX, while heavily obstructed NLOS conditions
have large obstructions fully blocking the optical path.
Previous research in Austin, TX conducted rooftop-toground measurements at 38 GHz, and peer-to-peer channels
in an outdoor urban setting at both 38 GHz and 60 GHz for
future generation cellular [4]. Previous measurements for 28
GHz LMDS systems [8] showed that steerable antennas could
be used for fixed point-to-multipoint links, whereas another
study showed that NLOS links could be made using steerable
antennas for cellular coverage up to 200 m [9]. This paper
presents the world’s first 28 GHz outdoor cellular propagation
measurements in New York City for future fifth-generation
(5G) mobile communications.
To describe radio propagation path loss (PL) as a function
of distance, the propagation path loss exponent (PLE) is a
parameter that describes the attenuation of a signal as it
propagates in the channel. Path loss at a close-in reference
distance of d0 is calculated and measured to be free space
loss by the equation [10]:
P Lf s (d0 ) = 20log10 (
4πd0
)
λ
(1)
where λ is the wavelength of the carrier frequency. In our
measurements d0 = 5 m and λ = 10.71 mm at 28 GHz. Path
loss at a distance d, beyond d0 can be described by the path
loss exponent using the following equation:
P L(d)[dB] = P Lf s (d0 )[dB] + 10nlog10 (
d
)
d0
(2)
where P L(d) is the average path loss in dB for a given
TX-RX separation of d, and n is the average path loss
exponent over distance and all pointing angles. LOS links with
the TX and RX antennas pointing towards each other (i.e.
boresight) provide a path loss exponent of n = 2 with very
small multipath delay spread [5], while the steerable antennas
provide different path loss exponents (and different multipath
power delay profiles (PDPs)) for different links made between
a TX and RX, depending on the orientation of antennas and the
surrounding LOS or NLOS environment. Path loss is important
for determining coverage distances, system capacity, and link
budgets for viable links in a cellular system. A higher PLE
indicates 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 to
determine the angular spread and number of unique pointing
angles of the mobile and base station antennas that yield viable
links between TX and RX as given in [11]. While NLOS
links may require equalization due to longer propagation
delay time, Signal-to-Noise Ratio (SNR) and power efficiency
are maximized by finding the optimal pointing angles at a
particular location.
II. 28 GH Z C HANNEL M EASUREMENT H ARDWARE
A 400 megachip-per-second (Mcps) sliding correlator channel sounder was used to conduct the propagation measurements. The probing signal consists of a pseudo-random noise
sequence upconverted to 28 GHz with a maximum average
output power of +30 dBm before TX antenna. The sliding
correlator allows a multipath time resolution of 2.3 ns and 178
dB of total path loss (for the case of TX and RX using 24.5 dBi
antennas). Note that the measured dynamic range of total path
loss likely meets or exceeds that of future 5G cellular systems,
thus ensuring measured results are meaningful. We took great
care 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 with
30◦ beamwidth for both elevation and azimuth, and a 24.5
dBi horn antenna with 10.9◦ beamwidth. The antennas were
vertically polarized. We used the same hardware that was used
in previous measurement campaigns [9] with an intermediate
frequency (IF) of 5.4 GHz and a separately supplied local
oscillator (LO) of 22.6 GHz.
III. 28 GH Z C HANNEL M EASUREMENT P ROCEDURE
The 28 GHz channel propagation measurements were performed at the NYU campus in downtown Manhattan. Measurement sites included a wide range of urban environments,
including parks, commercial districts, and general university
areas with high rise buildings and dense pedestrian and vehicular traffic. To emulate future cellular base stations with
relatively low heights, two TX sites were located on the Coles
Sports Center building rooftop (7 m above ground level, with
the TX located on the northwest and northeast corners of
the roof), and one TX site was on the five-story balcony of
Kaufman Business School (17 m above ground level) (see
Fig. 2). All three TX sites used the same set of 25 RX sites,
which were chosen randomly based on the availability of AC
power, thus yielding 75 unique TX-RX location combinations.
At each RX measurement location, the TX and RX directional antennas were pointed in several different directions in
elevation and the RX antenna was rotated exhausively over
azimuth to find the strongest received power. The strongest
link was usually made when the TX and RX antennas were
directly pointed at each other. The 0◦ azimuth angle of the TX
was set at the angle with the strongest link with 10◦ downtilt.
Measurements were then taken for 3 different TX azimuth
angles , -5◦ , 0◦ , and +5◦ , and for 3 different RX elevations,
-20◦ , 0◦ , and +20◦ , with all possible combinations between
the two (i.e. 9 total TX-RX antenna configurations). For each
of the 9 TX-RX antenna configurations, the RX antenna was
rotated 360◦ in the azimuth plane and a power delay profile
measurement was recorded at every 10◦ where a link was made
(PL<168 dB). In all locations, both the TX and RX used 24.5
dBi antennas with 10◦ 3 dB beamwidth.
Fig. 2. 28 GHz cellular measurement locations in Manhattan near the NYU
campus. Three base station locations (yellow stars on the two-story rooftop
of Coles Recreational Center and five-story balcony of Kaufman Business
School) were used to transmit to each of the 25 receiver locations within 20
to 500 m. In total, 75 TX-RX location combinations were used for Manhattan
measurements. Four RX locations on the west are not shown in the picture.
Purple squares represent RX sites that are blocked by buildings. Signal could
only be received at 26 of the 75 location combinations.
Fig. 3. Measured path loss values relative to 5 m free space path loss for
28 GHz outdoor cellular channels. These path loss values were measured
using the 24.5 dBi narrow beam antennas. The RX antenna was rotated in
the azimuth plane in 10◦ steps. The values in the legend represent the PLE
of each environment (LOS and NLOS).
IV. 28 GH Z U RBAN C HANNEL P ROPAGATION A NALYSIS
Fig. 3 shows the path loss computed for each measurement
acquired in New York City with the 24.5 dBi antennas. The
smallest path loss is defined as the single best TX and RX
antenna pointing combination at a given RX location, which
corresponds to the strongest possible link created. The best
LOS PLE was n = 1.68 (due to groud reflection), with a
shadowing factor (standard deviation of shadowing, or SF)
of only 0.2 dB. The aggregated LOS PLE, considering all
the possible antenna configurations in a LOS environment,
increased to 2.55 with a SF of 8.66 dB since antennas were
often not optically aligned on boresight. In contrast, the NLOS
PLE 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. The
overall PLE for all measurements, LOS and NLOS, was 5.73.
The similarity of the overall PLE and NLOS PLE is due
to the NYC environment providing significantly more NLOS
situations, and very few LOS locations.
Fig. 4 is a polar plot that shows received power in dBm as
a function of receiver azimuth angle in a NLOS environment.
The three values at each azimuth angle in Fig. 4 indicate
the number of resolvable multipath components, path loss
(relative to 5 m free space), and RMS delay spread. The plot
shows for this RX location, 22 out of 36 possible azimuth
angles in an urban NLOS environment are available. Received
PDPs were thresholded to ∼ 168 dB path loss floor, and
multipath components were detected by using a peak detecting
algorithm. Fig. 4 counters previous data that stated no more
than 5-10 links could be formed in a NLOS environment [5].
Rich multipath will allow future beam steering technologies
to deduce algorithmically which azimuth angle would produce
the greatest received power [12][13]. Angular analysis and ray
tracing of the measured PDPs allow reconstruction of the paths
taken by the RF signals for each AOA.
Figs. 5 and 6 show PDPs of the largest observed multipath
delay spread for a LOS and a NLOS environment. Fig. 5
shows a LOS PDP with a maximum excess delay (20 dB)
of 753.5 ns transmitted from Kaufman balcony to a receiver
52 m away. The transmitter was pointed -5◦ azimuth and 10◦ below horizon. The receiver was pointed away from the
TX with 0◦ elevation. Fig. 6 shows the NLOS maximum
excess delay (20 dB) was 1388.4 ns, indicating that the farthest
distance the RF wave traveled was approximately 423 meters
beyond the propagation distance of the first arriving signal. A
highly reflective environment with large radar cross sections
for distant reflectors is the most likely cause of such a high
excess delay. For most measurements, the RMS delay spread in
LOS 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 plot
shows an AOA measurement at the RX on Greene and Broadway from the
TX on the five-story Kaufman building (78 m TX-RX separation). The polar
plot shows received power in dBm with varying receiver antenna azimuth
angle. The perimeter of the plot shows for each azimuth angle three values
that correspond to the number of resolvable multipath components, path loss
relative to 5 m free space, and RMS delay spread.
Fig. 5.
The largest observed multipath excess delay in a LOS urban
environment at 28 GHz. It was observed with the TX on the five-story
Kaufman balcony and the RX located 52 m away from the TX. The reference
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 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 of
resolvable multipath components formed for various TX-RX
distances. Under LOS conditions, an average of 7.2 unique
resolvable multipath components will exist for each TX-RX
link with a standard deviation of 2.2 paths between 35 m
and 200 m. For NLOS conditions, an average of 6.8 unique
resolvable multipath components will exist for each TX-RX
link with a standard deviation of 2.2 paths. For both LOS and
NLOS, the average number of paths increased with distance
(up to 100 m), after which the average number of paths tended
to slightly decrease with increasing distance beyond 100 m.
Fig. 9 shows an outage map for all Manhattan measurements. These RX outage sites correspond to no signal detected
from TX (i.e. PL >178 dB) at any angle. For path loss
between 168 dB and 178 dB, signal could be detected but
Fig. 6. The largest observed multipath excess delay in a NLOS environment
at 28 GHz. It was observed with the TX on the two-story Coles building
rooftop and the RX located (behind a building) 97 m away from the TX. The
reference 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 the
PDP.
Fig. 7. AOA measurements in outdoor downtown Manhattan for 28 GHz.
The RX was located in front of WWH (Warren Weaver Hall) building and
the TX was located on the balcony of Kaufman. The plot shows a potential
path obtained by manual ray tracing to achieve a 753.5 ns excess delay shown
in Fig. 5 in a LOS environment. The green dot represents the RX and the
yellow star represents the TX. White arrows represent the direction of the horn
antenna. The cyan path simulates the route taken by the wave from the TX
to the RX that resulted in the first received power. The purple path represents
the last received power 753.5 ns later.
was not strong enough to always be acquired. The map is
divided into different sectors which correspond to a TX site.
The radii of these sectors are 200 m, which suggests that the
maximum size of future mm-wave cellular networks in dense
urban environments. It was found that an outage occurred in
57% of all the receiver locations. Within 200 m, the outage
decreased to 16% as no signal could be acquired at four RX
locations shadowed by the Bobst building.
V. C ONCLUSION
This article presented propagation measurements at 28 GHz
in New York City. A total of 75 unique TX-RX combinations
were measured with two different antenna gains and 36
pointing angles. The rate at which path loss increased as a
function 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 corresponding to the lowest path loss can be found and exploited
Fig. 8. Average number of resolvable multipath components per TX-RX
link for different distances in 28 GHz using two 24.5 dBi horn antennas. The
distribution increases up to 71 m and then decreases until 193 m. Average
number of resolvable multipath components was computed over all viable
links 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 and
their different sectors. Measurements were recorded for each of the 25 RX
sites from each of the three TX sites (yellow stars).”Signal Acquired” means
that signal was detected and acquired (PL<168 dB). ”Signal Detected” means
that signal was detected, but low SNR prevented data acquisition (168 dB <PL
<178 dB). ”No Signal Detected” occurred with PL >178 dB. To the west
of Kaufman is the Bobst Library which blocked the signal from reaching the
4 sites marked with crosses, which resulted in no signals being detected at
those locations.
to decrease the path loss exponent [12][13]. Considering, at
each location, only the best angle orientation with the highest
received power, the path loss exponent dropped to 4.58 for
NLOS and 4.47 over all locations. While performing 10◦
incremental azimuthal angular sweeps, PDPs were measured
with less than 168 dB path loss typically at more than 20 out
of 36 possible angles under dense urban NLOS conditions.
For future development of a statistical channel model at 28
GHz, we computed the average number of resolvable multipath
components, averaged over all pointing angles of the TX and
RX, as a function of distance. Also, we found that 57% of
all receiver locations, which exceeded a TX-RX separation
of 200 m, were outages, where no signal could be detected;
however, the outage decreased to 16% for distances within 200
m. We could find no links at distances greater than 200 m for
Manhattan with 178 dB PL. This maximal cell size means that
rain attenuation will not pose a significant problem due to the
relatively shorter distances involved.
VI. ACKNOWLEDGMENT
This project was sponsored by Samsung DMC R&D
Communications Research Team (CRT) through Samsung
Telecommunications America, LLC. The authors wish to thank
Shu Sun and Mathew Samimi of NYU WIRELESS for their
contributions to this paper, and Shadi Abu-Surra of Samsung,
the NYU Administration, NYU Public Safety and NYPD for
their support of our measurements. Measurements recorded
under U.S. FCC Experimental License 0040-EX-ML-2012.
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