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Received February 3, 2013, accepted April 8, 2013, date of publication May 10, 2013, date of current version May 29, 2013. Digital Object Identifier 10.1109/ACCESS.2013.
Millimeter Wave Mobile Communications for 5G
Cellular: It Will Work!
THEODORE S. RAPPAPORT^1 , SHU SUN^1 , RIMMA MAYZUS^1 , HANG ZHAO^1 , YANIV AZAR^1 ,
KEVIN WANG^1 , GEORGE N. WONG^1 , JOCELYN K. SCHULZ^1 , MATHEW SAMIMI^1 , AND
FELIX GUTIERREZ^1
(^1) NYU WIRELESS, Polytechnic Institute of New York University, New York, NY 11201, USA
Corresponding author: T. S. Rappaport ([email protected])
This work was supported by Samsung DMC R&D Communications Research Team and Samsung Telecommunications America, LLC.
ABSTRACT The global bandwidth shortage facing wireless carriers has motivated the exploration of the underutilized millimeter wave (mm-wave) frequency spectrum for future broadband cellular communication networks. There is, however, little knowledge about cellular mm-wave propagation in densely populated indoor and outdoor environments. Obtaining this information is vital for the design and operation of future fifth generation cellular networks that use the mm-wave spectrum. In this paper, we present the motivation for new mm-wave cellular systems, methodology, and hardware for measurements and offer a variety of measurement results that show 28 and 38 GHz frequencies can be used when employing steerable directional antennas at base stations and mobile devices.
INDEX TERMS 28GHz, 38GHz, millimeter wave propagation measurements, directional antennas, channel models, 5G, cellular, mobile communications, MIMO.
I. INTRODUCTION The rapid increase of mobile data growth and the use of smartphones are creating unprecedented challenges for wire- less service providers to overcome a global bandwidth short- age [1], [2]. As today’s cellular providers attempt to deliver high quality, low latency video and multimedia applications for wireless devices, they are limited to a carrier frequency spectrum ranging between 700 MHz and 2.6 GHz. As shown in Table 1, the global spectrum bandwidth allocation for all cellular technologies does not exceed 780 MHz, where each major wireless provider has approximately 200 MHz across all of the different cellular bands of spectrum available to them. Servicing legacy users with older inefficient cellphones as well as customers with newer smartphones requires simul- taneous management of multiple technologies in the same band-limited spectrum. Currently, allotted spectrum for oper- ators is dissected into disjoint frequency bands, each of which possesses different radio networks with different propagation characteristics and building penetration losses. This means that base station designs must service many different bands with different cell sites, where each site has multiple base stations (one for each frequency or technology usage e.g. third generation (3G), fourth generation (4G), and Long Term Evolution - Advanced (LTE-A)) [3], [4]. To procure new spectrum, it can take a decade of administration through reg-
ulatory bodies such as the International Telecommunication Union (ITU) and the U.S. Federal Communications Commis- sion (FCC). When spectrum is finally licensed, incumbent users must be moved off the spectrum, causing further delays and increasing costs.
TABLE 1. Current 2G, 3G, 4G, & LTE-A spectrum and bandwidth allocations [5].
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Mobile broadband networks need to support ever-growing consumer data rate demands and will need to tackle the exponential increase in the predicted traffic volumes. An effi- cient radio access technology combined with more spectrum availability is essential to achieve the ongoing demands faced by wireless carriers.
A. THE WIRELESS EVOLUTION To date, four generations of cellular communication systems have been adopted in the USA with each new mobile gener- ation emerging every 10 years or so since around 1980: first generation analog FM cellular systems in 1981; second gener- ation digital technology in 1992, 3G in 2001, and 4G LTE-A in 2011 [6]. The evolution from 1G to 4G is summarized in Table 2.
TABLE 2. Requirements and realities of 1G through 4G cellular systems [7].
First generation cellular networks were basic analog sys- tems designed for voice communications. A move to early data services and improved spectral efficiency was real- ized in 2G systems through the use of digital modula- tions and time division or code division multiple access. 3G introduced high-speed Internet access, highly improved video and audio streaming capabilities by using technolo- gies such as Wideband Code Division Multiple Access (W-CDMA) and High Speed Packet Access (HSPA). HSPA is an amalgamation of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), which extends and improves the performance of existing 3G mobile telecom- munication networks utilizing WCDMA protocols. An improved 3GPP (3rd^ Generation Partnership Project) stan- dard, Evolved HSPA (also known as HSPA+), was released in late 2008 with subsequent worldwide utilization beginning in 2010. HSPA has been deployed in over 150 countries by more than 350 communications service providers (CSP) on multiple frequency bands and is now the most extensively sold radio technology worldwide [8], although LTE is closing the gap rapidly. The International Mobile Telecommunications-Advanced (IMT-Advanced) standard is the next-generation of mobile communications technology defined by the ITU and
includes capabilities outstripping those of IMT-2000 (3G) mobile communication. ITU refers to IMT-Advanced as a 4G mobile communications technology, although it should be noted that there is no universally accepted definition of the term 4G. LTE radio access technol- ogy has been developed by the 3GPP to offer a fully 4G-capable mobile broadband platform [9]. LTE is an orthog- onal frequency-division multiplexing (OFDM)-based radio access technology that supports a scalable transmission band- width up to 20 MHz and advanced multi-antenna transmis- sion. As a key technology in supporting high data rates in 4G systems, Multiple-Input Multiple-Output (MIMO) enables multi-stream transmission for high spectrum effi- ciency, improved link quality, and adaptation of radiation patterns for signal gain and interference mitigation via adap- tive beamforming using antenna arrays [10]–[12]. The coa- lescence of HSPA and LTE will increase the peak mobile data rates of the two systems, with data rates exceeding 100 Mbps, and will also allow for optimal dynamic load balancing between the two technologies [8]. As the demand for capacity in mobile broadband commu- nications increases dramatically every year, wireless carriers must be prepared to support up to a thousand-fold increase in total mobile traffic by 2020, requiring researchers to seek greater capacity and to find new wireless spectrum beyond the 4G standard [13]. To improve the existing LTE network, the wireless technology roadmap now extends to IMT-Advanced with LTE-Advanced defined to meet IMT-Advanced require- ments, which will be theoretically capable of peak through- put rates that exceed 1 Gigabit per second (Gbps). LTE- Advanced supports heterogeneous networks with co-existing large macro, micro, and pico cells, and Wi-Fi access points. Low cost deployment will be realized by self-organizing features and repeaters/relays As fifth generation (5G) is developed and implemented, we believe the main differences compared to 4G will be the use of much greater spectrum allocations at untapped mm-wave frequency bands, highly directional beamforming antennas at both the mobile device and base station, longer battery life, lower outage probability, much higher bit rates in larger portions of the coverage area, lower infrastructure costs, and higher aggregate capacity for many simultaneous users in both licensed and unlicensed spectrum (e.g. the convergence of Wi-Fi and cellular). The backbone networks of 5G will move from copper and fiber to mm-wave wireless connec- tions, allowing rapid deployment and mesh-like connectivity with cooperation between base stations.
B. EARLY GLOBAL ACTIVITIES FOR Beyond 4G (B4G) AND 5G WIRELESS The evolution of wireless communication systems requires global collaboration, involving worldwide mobile commu- nication companies and governments. The Electronics and Telecommunication Research Institute (ETRI) in Korea has actively contributed to the development of 4G systems. In 2002, the Mobile Communication Research Laboratory
FIGURE 1. Rain attenuation in dB/km across frequency at various rainfall rates [26]. The rain attenuation at 28 GHz has an attenuation of 7 dB/km for a very heavy rainfall of 25 mm/hr (about 1 inch per hour). If cell coverage regions are 200 m in radius, the rain attenuation will reduce to 1.4 dB.
essential for flexibility, quick deployment, and reduced ongo- ing operating costs. Finally, as opposed to the disjointed spec- trum employed by many cellular operators today, where the coverage distances of cell sites vary widely over three octaves of frequency between 700 MHz and 2.6 GHz, the mm-wave spectrum will have spectral allocations that are relatively much closer together, making the propagation characteristics of different mm-wave bands much more comparable and ‘‘homogenous’’. The 28 GHz and 38 GHz bands are currently available with spectrum allocations of over 1 GHz of band- width. Originally intended for Local Multipoint Distribution Service (LMDS) use in the late 1990’s, these licensees could be used for mobile cellular as well as backhaul [25]. A common myth in the wireless engineering community is that rain and atmosphere make mm-wave spectrum useless for mobile communications. However, when one considers the fact that today’s cell sizes in urban environments are on the order of 200 m, it becomes clear that mm-wave cellular can overcome these issues. Fig. 1 and Fig. 2 show the rain attenuation and atmospheric absorption characteristics of mm-wave propagation. It can be seen that for cell sizes on the order of 200 m, atmospheric absorption does not create significant additional path loss for mm-waves, particularly at 28 GHz and 38 GHz. Only 7 dB/km of attenuation is expected due to heavy rainfall rates of 1 inch/hr for cellular propagation at 28 GHz, which translates to only 1.4 dB of attenuation over 200 m distance. Work by many researchers has confirmed that for small distances (less than 1 km), rain attenuation will present a minimal effect on the propagation of mm-waves at 28 GHz to 38 GHz for small cells [26].
FIGURE 2. Atmospheric absorption across mm-wave frequencies in dB/km [1]. The attenuation caused by atmospheric absorption is 0.012 dB over 200 m at 28 GHz and 0.016 dB over 200 m at 38 GHz. Frequencies from 70 to 100 GHz and 125 to 160 GHz also have small loss.
D. Mm-WAVE CELLULAR MEASUREMENTS: UNDERSTANDING THE CHANNEL Future wireless technologies must be validated in the most urban environments, such as New York City. In order to improve capacity and service quality, the cellular network architecture needs to support higher spatial reuse. Massive MIMO base stations and small-cell access points are two promising approaches for future cellular. Massive MIMO base stations allocate antenna arrays at existing macro base stations, which can accurately concentrate transmitted energy to the mobile users [24]. Small cells offload traffic from base stations by overlaying a layer of small cell access points, which actually decreases the average distance between transmitters and users, resulting in lower propagation losses and higher data rates and energy efficiency [24]. Both of these important trends are readily supported and, in fact, are enhanced by a move to mm-wave spectrum, since the tiny wavelengths allow for dozens to hundreds of antenna elements to be placed in an array on a relatively small physical platform at the base station, or access point, and the natural evolution to small cells ensures that mm-wave frequencies will overcome any attenuation due to rain. Understanding the radio channel is a fundamental require- ment to develop future mm-wave mobile systems as well as backhaul techniques. With a firm technical understanding of the channel, researchers and industry practitioners may then explore new methods for the air interface, multiple access, architectural approaches that include cooperation and inter- ference mitigation and other signal enhancement techniques. In order to create a statistical spatial channel model (SSCM) for mm-wave multipath channels, extensive measurements must be made in typical and worst-case operating conditions and environments. We have conducted extensive propagation measurements in urban environments in New York City and suburban environments in Austin, Texas in order to under- stand the mm-wave channel.
(b)
(a)
FIGURE 3. Block diagram of the (a) TX and (b) RX for the mm-wave propagation measurements at 28 GHz in New York City.
II. 28 GHZ BUILDING PENETRATION AND REFLECTION CAMPAIGN IN NEW YORK CITY
A. 28 GHZ BROADBAND CHANNEL SOUNDING HARDWARE Using a 400 Mcps sliding correlator channel sounder with 2.3 ns multipath resolution, we conducted extensive mm- wave propagation measurements at 28 GHz in New York City in 2012. The block diagram of the transmitter (TX) and
receiver (RX) is given in Fig. 3. A pseudo-random noise (PN) sequence sliding correlator was utilized as the probing signal, which was modulated to a 5.4 GHz intermediate fre- quency (IF) and upconverted to 28 GHz after mixing with a 22.6 GHz local oscillator (LO), in a manner similar to [27]. The transmitter power was +30 dBm (a typical value for lower power femtocells), fed to a steerable 10◦^ beamwidth 24.5 dBi horn antenna or a 30◦^ beamwidth 15 dBi horn antenna that was mechanically rotated. The receiver used the
FIGURE 4. Map of the penetration measurements through multiple obstructions in an office environment located at the 10th floor of 2 MetroTech Center in Brooklyn, New York. The TX location is represented by a yellow star, the RX locations where signals can be acquired are represented by green circles, and the RX locations where weak signals can be detected are in red triangles. The black cross denotes an outage [28].
same distance. Materials tested for penetration loss include: tinted glass, brick, clear non-tinted glass, and drywall. Table 3 summarizes the penetration loss results for these common building materials [28]. As shown in Table 3, tinted glass and brick pillars (typical exterior surfaces of urban buildings) have high penetration losses of 40.1 dB and 28.3 dB, respec- tively. This illustrates the fact that building penetration of mm-waves will be difficult for outdoor transmitters, thus pro- viding high isolation between outdoor and indoor networks. On the other hand, common indoor materials such as clear non-tinted glass and drywall only have 3.6 dB and 6.8 dB of losses, respectively, which are relatively low. In addition to penetration measurements for individual materials, penetration measurements were also made through multiple obstructions in typical office environments, to deter- mine overall average partition losses, as was done in [29] using ‘‘primary ray tracing’’ where a single ray is drawn between the TX and RX, and attenuations of obstructions are determined through measurements. As shown in Fig. 4, multiple indoor obstructions in an office building environ- ment were characterized using 8 RX locations, in which each RX location was selected to determine penetration through increasing layers of obstructions. Partition layers included multiple walls, doors, cubicles, and an elevator bank (RX 8) [28]. We used lower TX power which limited the maximum measurable path loss to about 169 dB. Table 4 presents a summary of the number and type of obstructions between the TX and RX, as well as the 28 GHz penetration loss results caused by multiple obstructions in a typical office environment. Note that the RX locations are ordered in increasing TX-RX separation distances. Data is grouped into three subsections: signal acquired (with val- ues listed), signal detected, and no signal detected. Signal acquired is defined as a location where the SNR is sufficiently high for accurate acquisition, i.e. penetration loss relative to
FIGURE 5. Images of the 28 GHz reflection measurement for outdoor tinted glass at ORH (top left), outdoor concrete wall at ORH (top right), penetration loss measurement for indoor clear non-tinted glass at MTC (bottom left) and tinted glass at ORH (bottom right) [28].
5 meters free space test is less than 64 dB. Signal detected is a location where the SNR is high enough to slightly distinguish a signal from noise but not strong enough to be acquired, i.e. penetration loss between 64 dB to 74 dB relative to a 5 m free space test. No signal detected denotes an outage, where the penetration loss is at least 74 dB greater than the 5 m free space test. As shown in Table 4, penetration loss does not greatly depend on the TX-RX separation distance, but mostly depends on the number and type of obstructions. The RX sites with TX-RX separation distances of 25.6 m and 11.4 m have virtually identical measured penetration losses of 45.1 dB; however, the site with 25.6 m separation distance has obstructions of four walls and two cubicles while the other site with 11.4 m separation distance has obstructions of three walls and one door. Note that one outage was found at the RX site with a separation distance of 35.8 m, a result of the large separation distance and the inability of RF waves to penetrate the metallic elevator bank. Table 5 summarizes and compares the reflection coeffi- cients for common indoor and outdoor building materials. As indicated in Table 5, the outdoor materials have larger reflection coefficients of 0.896 for tinted glass and 0. for concrete at a 10◦^ incident angle, as compared to clear non-tinted glass and drywall, which have lower reflection coefficients of 0.740 and 0.704, respectively. The results for outdoor tinted glass in ORH consistently show that a large portion of the signal (= 0 .896) is reflected and could not penetrate through the glass. In contrast, the clear non-tinted glass located inside the MTC building has a smaller reflection coefficient (= 0 .740) and causes only 3.9 dB of penetration loss compared to the 40.1 dB loss for the outdoor tinted glass in ORH. The high penetration loss through outdoor building materials and low attenuation through indoor materials sug- gest that RF energy can be contained in intended areas within
buildings which reduces interference, yet making outdoor- to-indoor building penetration more difficult. Fig. 5 presents photographs of the penetration and reflection measurements of common building materials at 28 GHz.
III. 28 GHz URBAN PROPAGATION CAMPAIGN IN NEW YORK CITY A. MEASUREMENT PROCEDURE The hardware system of Fig, 3 was used in the outdoor propa- gation measurement campaign in New York City. We selected one TX and 11 RX measurement locations at the NYU-Poly campus in downtown Brooklyn. The distance between the TX and RX ranged from 75 m to 125 m. At the NYU campus in Manhattan, 3 TX and 75 RX locations (with 25 RX sites for each TX site) were chosen with TX-RX separations varying from 19 m to 425 m to emulate future cellular base stations. At three of the measurement locations in Brooklyn, the RX was moved on an automated linear track of 10 wavelengths (107 mm) in half-wavelength (5.35mm) increments to study small scale signal level variations, i.e. small scale fading. At each track position, a 360◦^ azimuthal sweep was performed in steps of 10◦^ (if using the 10◦^ beamwidth 24.5 dBi narrow- beam horn antenna), or 30◦^ (if using the 30◦^ beamwidth 15 dBi wide-beam horn antenna). Large scale propagation char- acteristics were investigated in the remaining eight RX loca- tions in Brooklyn and all the Manhattan measurements using 24.5 dBi narrow beam antennas. At each TX and RX location, extensive measurements were conducted for three different TX azimuth angles, − 5 ◦^ , 0◦^ , and + 5 ◦^ from boresight to the receiver, and for three different RX elevation angles of − 20 ◦ , 0◦^ , and + 20 ◦^ creating nine possible antenna pointing com- binations between TX and RX. For each of the nine antenna pointing combinations, the RX antenna was swept 360◦^ in the azimuth plane in 10◦^ steps, and measurements were recorded if energy was received. Finally, cross polarization measure- ments were done at all Brooklyn RX sites where both vertical and horizontal electric polarization fields were measured. Propagation measurements were conducted in New York City around the NYU campuses in Manhattan and Brooklyn. Each location had the potential to collect 324 power delay profiles (PDPs) for all combinations (36 RX azimuth angles, 3 TX azimuth angles, and 3 RX elevation angles). Not all azimuth angles yielded a detectable signal.
B. PATH LOSS AND SIGNAL OUTAGE ANALYSIS Given the highly reflective outdoor environment, PDPs dis- played numerous multipath with large excess delay for both line-of sight (LOS) and non-line-of-sight (NLOS) environ- ments. The average number of resolvable multipath compo- nents in a LOS environment was 7.2 with a standard deviation of 2.2 for a TX-RX separation of less than 200 meters. NLOS measurements with TX-RX separation less than 100 meters showed that the number of average received multipath com- ponents is 6.8 with a standard deviation equal to that of a LOS case. With a 52 meter separation, in a LOS environment,
FIGURE 6. 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 a 24.5 dBi narrow beam antenna. The antennas were rotated in the azimuth plane, recording measurements at 10◦^ incremental steps. The values in the legend represent the PLE of each environment (LOS and NLOS) [31].
FIGURE 7. 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. Signal Detected means that signal was detected, but low SNR prevented data acquisition by the system [31].
a large 753.5 ns excess delay was observed, and a NLOS excess delay over 423 meters extended to 1388.4 ns. While these results were not commonly observed, these cases are evidence that enough signal strength can propagate through a highly reflective environment over a long distance to create a TX-RX link. When path loss was calculated for all locations, the best LOS path loss exponent (PLE) was n = 1.68 (here ‘‘best’’ means ‘‘smallest’’). The LOS PLE resulting from all the measurements acquired in New York City was n = 2. (which included many cases where the TX and RX had an optical LOS environment between them but the directional antennas were not precisely lined up on boresight). The aver- age PLE over all NLOS locations increased to n = 5.76, as
FIGURE 9. 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 T-R separation). The polar plot shows the received power in dBm, the number of resolvable multipath components, the path loss in dB with respect to the 5 m free space reference, and RMS delay spread with varying RX azimuth angles [31].
at 22 out of 36 RX azimuth angles. Furthermore, it is obvious that a wealth of multipath components exist at numerous different pointing angles, providing great diversity which can be utilized for beam combining and link improvement in future 5G systems. Small scale fading has also been explored by moving the RX at half-wavelength (5.35 mm) increments along a small scale linear track of 10 wavelengths (107 mm), while the TX was fixed at a certain location [32]. Fig. 10 shows the 3D power delay profiles of small scale fading for the TX-RX angle combination for the strongest received power. The maximum and minimum received signal pow- ers were −68 dBm/ns and −74 dBm/ns, respectively, yield- ing merely ± 3 dB fading variation. This outcome indi- cates that movements over the small scale track exert little influence on the AOA or the received power level of multipath signals.
IV. 38 GHz CELLULAR URBAN PROPAGATION CAMPAIGN IN AUSTIN A. 38 GHz BROADBAND CHANNEL SOUNDING HARDWARE AND MEASUREMENT PROCEDURE An 800 MHz null-to-null bandwidth spread spectrum sliding correlator channel sounder was employed in the 38 GHz prop- agation measurement campaign in Austin. The PN sequence was operating at 400 Mcps and 399.9Mcps at the TX and RX, respectively, to offer a slide factor of 8000 and adequate processing gain [33]. The PN sequence was modulated by a 5.4 GHz IF signal, which was input into the upconverter that contained LO frequency multipliers to generate a carrier fre- quency of 37.625 GHz with a +22 dBm output power before the TX antenna. A 25-dBi gain Ka-band vertically polarized
FIGURE 10. Power delay profiles measured over a 10-wavelength linear track at 28 GHz. The RX was 135 meters away from the TX. The TX and RX were pointed for maximum signal power. Track step size was half wavelength using 24.5 dBi horn antennas with beamwidths of 10.9◦^ on the TX and RX.
horn antenna with 7.8◦^ half-power beamwidth was utilized at the TX, and an identical antenna (and also a wider beam 13.3-dBi gain (49.4◦^ beamwidth) vertically polarized horn antenna) were used at the RX. The maximum measurable path loss was about 160 dB [23], [33]–[35]. 38 GHz cellular propagations measurements were con- ducted in Austin, Texas at the University of Texas main campus [33]. TX locations were placed on four rooftops with different heights, WRW-A (23 meters), ENS-A (36 meters), ENS-B (36 meters), and ECJ (8 meters). A total of 43 TX-RX combinations were measured with up to 12 various antenna configurations for each measurement location [33]. The RX was positioned in a number of LOS, partially obstructed LOS, and NLOS locations representative of an outdoor urban envi- ronment including foliage, high-rise buildings, and pedestrian and vehicular traffic. At each receiver location, measurements were acquired using a circular track with 8 equally spaced local area measurement points separated by 45◦^ increments. The radius of the circular track yielded a 10λ separation dis- tance between consecutive points along the circular track. For LOS links, the TX and RX were pointed directly at each other in both azimuth and elevation. The captured PDPs for each complete track measurement were then averaged and a new RX location was selected. NLOS conditions were taken over the circular track and a subsequent 360◦^ azimuth exhaustive signal search was conducted.
B. 38 GHz OUTDOOR MEASUREMENT RESULTS AOA measurements were shown to be most common when the RX azimuth angle was between − 20 ◦^ and + 20 ◦^ about the boresight of the TX azimuth angle [34]. After examining data for all RX locations for each corresponding TX, it was shown that a lower base station height is more likely to have more links with varying the TX azimuth angle. However, the site specific location of the RX impacts the observed AOA and multipath response. Designing for future base stations will require site specific deployment technologies.
FIGURE 11. Path loss scatter plot using 25dBi Rx antenna at 38 GHz. LOS and NLOS measurements have path loss exponents of 2.30 and 3.86, respectively, while the best NLOS links have a path loss exponent of 3.2 [35].
FIGURE 12. RMS delay spread as a function of arc length at 38 GHz. The delay spread decreases over longer arc lengths, which indicates that distance surmounts angle in determining delay spread. Nevertheless, a close-up of low arc lengths shows the angle playing a larger role in determining delay spread [35].
Path loss was determined for 38 GHz in Austin using 13.3 dBi and 25 dBi horn antennas [35]. For all TX locations, measurements at ECJ yielded the highest path loss using both antennas. The LOS PLE for the 25 dBi horn antennas was measured to be n = 2.30 and NLOS PLE was measured to be n = 3.86, as demonstrated in Fig. 11. Compared to measurements in Manhattan at 28 GHz, where the LOS PLE and NLOS PLE were 2.55 and 5.76 respectively, it is clear that PLE at 38 GHz in the light urban environment in Austin is considerably lower. Analysis of the RMS delay spread at 38 GHz showed sen- sitivity to antenna gains [23], [33]–[35]. While all cumulative distribution functions (CDF) for LOS and NLOS links are similar, a lower antenna gain was shown to have a higher RMS delay spread, whereas the 25 dBi antenna showed lower delays with greater TX-RX separation. Fig. 12 shows RMS delay spreads for the 25 dBi and 13.3 dBi steerable receiver antennas plotted as a function of arc length. By conducting an outage study in Austin, we were able to further establish that lower base station heights provide better close-in coverage. By comparing ENS and WRW, 36 and 18 meters in height respectively, we found that no
FIGURE 13. RMS delay spread as a function of TX-RX separation for all links using all possible pointing angles at 28 GHz in New York City. The green stars and blue circles denote the RMS delay spread in the NLOS and LOS measurement locations, respectively.
FIGURE 14. RMS delay spread as a function of TX-RX separation for all links using all possible pointing angles at 38 GHz in Austin, Texas. The green stars and blue circles denote the RMS delay spread in the NLOS and LOS environment, respectively.
FIGURE 15. Cumulative distribution function (CDF) of the RMS delay spread at 28 GHz measured for all links using all possible pointing angles in the dense urban environment in New York City. The CDFs for LOS and NLOS links over all TX-RX locations are distinguished by the extremely low delay spread in LOS, and extremely mutative spreads in NLOS.
outages occurred within a 200 m cell radius. However, beyond 200 m, 52.8% of locations were outages, 10% of those belong to WRW, and 27.3% to ENS. The coverage radius of 200 m is identical to that measured in New York City, thus suggesting that 200 m is a very achievable cell size for future 5G mm-wave cellular communications systems [23], [33]–[35].
the design of future mm-wave cellular systems. This work presents data collected in the urban environments around the University of Texas at Austin (38 GHz) and New York University (28 GHz). Outage studies conducted at 28 GHz and 38 GHz showed that consistent coverage can be achieved by having base stations with a cell-radius of 200 metres. Path loss was larger in New York City than in Austin, due to the nature of the denser urban environment. In New York City, reflection coefficients for outdoor materials were signif- icantly higher, for example, 0.896 for tinted glass, and 0. for clear non-tinted glass, compared with those of indoor building materials. Similarly, penetration losses were larger for outdoor materials in New York City. Since signals cannot readily propagate through outdoor building materials, indoor networks will be isolated from outdoor networks and this suggests that data showers, repeaters, and access points may need to be installed for handoffs at entrances of commercial and residential buildings. By observing the measured path loss and delay spread values from the heavy urban environment of New York City and the light urban environment of Austin, Texas, we found substantial differences in propagation parameters. Multipath delay spread is found to be much larger in New York City than in Austin, due to the highly reflective nature of the dense urban environment. Small scale fading, a key factor for the design of urban cellular, has been tested and shows little change in received power and impulse response when highly directional antennas and 400 Mcps signals are used. The data collected over the course of these measurement campaigns allows for development of statistical channel mod- els for urban environments, and are highly valuable for the development of 5G cellular communications at mm-wave bands in the coming decade.
ACKNOWLEDGMENT This work was sponsored by Samsung DMC R&D Communications Research Team (CRT), and by Sam- sung Telecommunications America, LLC. The authors thank George R. MacCartney, Shuai Nie, and Junhong Zhang for their contributions to this project, as well as researchers at Samsung, including W. Roh, D. Hwang, S. Abu-Surru, F. Kahn, and Z. Pi for their on-going interest and support of this work. Hughes Research Laboratory and National Instru- ments provided equipment used in this work. The authors also thank the NYU administration, NYU Public Safety, and the New York Police Department for their support of these measurements. Measurements were conducted under U.S. FCC experimental license 0040-EX-ML-2012.
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THEODORE S. RAPPAPORT (F’98) received the B.S., M.S., and Ph.D. degrees in electrical engi- neering from Purdue University, West Lafayette, IN, USA, in 1982, 1984, and 1987, respectively. He is an Outstanding Electrical and Computer Engineering Alumnus and Distinguished Engi- neering Alumnus from his alma mater. He holds the David Lee/Ernst Weber Chair in Electrical and Computer Engineering at Polytechnic Insti- tute, New York University (NYU-Poly), Brooklyn, NY, USA, and is a Professor of computer science and Professor of radiology at NYU. In 2012, he founded NYU WIRELESS, a multidisciplinary research center involving NYU’s engineering, computer science, and medical schools. Earlier in his career, he founded the Wireless Networking and Communica- tions Group (WNCG), University of Texas at Austin (UT), TX, USA. Prior to UT, he was on the electrical and computer engineering faculty of Virginia Polytechnic Institute and State University, Blacksburg, VA, USA, where he
founded the Mobile and Portable Radio Research Group (MPRG), one of the world’s first university research and teaching centers dedicated to the wireless communications field. In 1989, he founded TSR Technologies, Inc., Blacksburg, VA, USA, a cellular-radio/personal-communications-services software radio manufacturer that pioneered cellular E-911 and test equipment that he sold in 1993 to what is now CommScope, Inc. In 1995, he founded Wireless Valley Communications Inc., Austin, TX, USA, and a site-specific wireless network design and management firm that was sold in 2005 to Motorola, Inc. He has testified before the U.S. Congress, has served as an international consultant for the ITU, has consulted for more than 30 major telecommunications firms, and works on many national committees pertaining to communications research and technology policy. He is a highly sought-after consultant and technical expert, and serves on the Board of Directors of the Marconi Society. He has authored or co-authored more than 200 technical papers, over 100 U.S. and international patents, and several best-selling technical books. Dr. Rappaport was elected to the Board of Governors of the IEEE Com- munications Society (ComSoc) in 2006, and was elected to the Board of Governors of the IEEE Vehicular Technology Society (VTS) in 2008 and
SHU SUN (S’13) received the B.S. degree in applied physics from Shanghai Jiao Tong Univer- sity, Shanghai, China, in 2012. She is currently pursuing the Ph.D. degree in electrical engineering with the Polytechnic Institute, New York Univer- sity (NYU-Poly), Brooklyn, NY, USA. She joined NYU WIRELESS Research Cen- ter in August 2012. She has co-authored two conference publications, and is now working on millimeter-wave propagation measurements cam- paign for 5G cellular mm-wave communication systems.
RIMMA MAYZUS (S’13) is a sophomore in electrical engineering with Polytechnic Institute, New York University (NYU-Poly), Brooklyn, NY, USA. She has participated in the 28 GHz mm-wave propagation measurements campaign in 2012, and has co-authored three conference publications.
HANG ZHAO (S’13) is a second year undergrad- uate student in electrical engineering BS/MS pro- gram at Polytechnic Institute of New York Uni- versity (NYU-Poly), Brooklyn, NY, USA. She is currently an Undergraduate Researcher at NYU WIRELESS, and has a first-author conference publication and co-authored two conference pub- lications. Her current research interests include millimeter-wave propagation and semiconductor circuits.
