millimeter wave for 5g - university of texas at...

© Robert W. Heath Jr. (2015)

Millimeter Wave for 5GFeatures and implications (inspired by UT research)

Professor Robert W. Heath Jr.

Wireless Networking and Communications GroupDepartment of Electrical and Computer EngineeringThe University of Texas at Austin

www.profheath.org

Thanks to the National Science Foundation Grant No. NSF-CCF-1319556, NSF-CCF-1527079, NSF-CCF-1514275, the Intel / Verizon 5G program, the U.S. Department of Transportation through the Data-Supported Transportation Operations and Planning (D-STOP) Tier 1 University Transportation Center, the the Texas Department of Transportation under Project 0-6877, and gifts from Nokia, MERL, Huawei, and Toyota.


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Millimeter wave spectrum for 5G

* T. Rappaport et al., “Millimeter wave mobile communications for 5G cellular: It will work!” IEEE Access, 2013.** W. Roh et al., "Millimeter-wave beamforming as an enabling technology for 5G cellular communications: theoretical feasibility and prototype results,“, IEEE Commun. Mag.,, 2014*** A. Osseiran et al.,"Scenarios for 5G mobile and wireless communications: the vision of the METIS project," iIEEE Commun. Mag., May 2014

60 GHz7 GHz

Unlicensed6 GHz 100 GHz

E-band10 GHz total

28 GHz1.3 GHz

39 GHz1.4 GHz

37/42 GHz2.1 GHz

20 GHz x100 GHz<1 GHz

MmWave

2.4 GHz100 MHz

900 MHz2.6 MHz

5.2 GHz555 MHz

CmWave

More spectrum, in bands not previously used for cellular

Even more spectrum


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Implications of millimeter wave spectrum

Shared licensed access possible to reduce cost, give carriers access to

more spectrum*

Cognitive radio for shared spectrum with

satellite or radar*

Antennas are much smaller**Different propagation models**

* J. Andrews, F. Baccelli, and R. Heath “Fundamental Prop. of MmWave Networks: Signal, Intf., and Connectivity” NSF grant for $1M.** S. Rangan, T.S. Rappaport, E. Erkip, "Millimeter-Wave Cellular Wireless Networks: Potentials and Challenges,“, Proc. IEEE, 2014*** See UT’s response to FCC NOI comments here http://apps.fcc.gov/ecfs/comment/view?id=60001017585

carrier A

carrier B

satellitecommunications

cellular communications

surface movementradar (K, Ka bands)


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Higher data rates in 5G with mmWave

MmWave can provide high peak, average, and outage rates (if dense) ** T. Bai and R. W. Heath Jr., “Coverage and rate analysis for millimeter wave cellular networks”, IEEE Trans. Wireless Commun., Feb. 2015. ** T. Bai, A. Alkhateeb, and R. W. Heath, Jr., `Coverage and Capacity of Millimeter Wave Cellular Networks," IEEE Communications Magazine, Sept. 2014.

Upper cmWave 28 GHz:500 MHz, 64x4 SISO

mmWave 72 GHz:2 GHz, 400x25 SISO

0.0

20.0

40.0

60.0

80.0

100.0

120.0

28 sparse 28 dense 72 sparse 72 dense0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

28 sparse 28 dense 72 sparse 72 dense

5%

X c

apac

ity im

prov

emen

t Average

Baseline 2 GHz:50 MHz, 4x4 MIMO


Implications of mmWave on new 5G scenarios

5

VIRTUAL REALITY high data rateAUTONOMOUS

ROBOTSsmall sizeequipment

Vehicle driving cloud

V2X COMMUNICATIONSlow latency

mmWavebase station

AUTONOMOUS DRIVING high data rates

MmWave high data rates are required in different 5G scenarios


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Use of directional and adaptive antenna arrays

* Cudak, M. et. al., "Experimental mm wave 5G cellular system," in Globecom Workshops (GC Wkshps), 2014 ** W. Hong; K. Baek; Y. Lee; Y. Kim; S. Ko, "Study and prototyping of practically large-scale mmWave antenna systems for 5G cellular devices," in IEEE Commun. Mag., 2014*** W. Roh et al. "Millimeter-wave beamforming as an enabling technology for 5G cellular communications: theoretical feasibility and prototype results," in IEEE Commun. Mag., 2014**** G. M. Rebeiz et. al. “Millimeter-wave large-scale phased-arrays for 5G systems” Proc. IEEE MTT-S International Microwave Symposium, 2015.

IEEE Communications Magazine • February 2014 109

presented in [5], where link- and system-levelsimulation results are provided with variousnumbers of transmit/receive antennas and RFchains. Using a 500 MHz bandwidth at 28 GHz,[5] presents some notable results for the hybridbeamforming system including an 8 dB gain overthe conventional spatial multiplexing schemeand 8 Gb/s average sector throughput with 16antennas with 4 RF chains at the base stationand 8 antennas with a single RF chain at themobile station.

MMWAVE BEAMFORMINGPROTOTYPE

In this section, we present a detailed descriptionof the mmWave beamforming prototype devel-oped and tested at the DMC R&D Center, Sam-sung Electronics, Korea, including systemconfiguration, key parameters, and capabilities.The main purposes of the mmWave prototypeare to check the feasibility of mmWave bandsfor sufficiently large geographical coverage forcellular services and support for mobility even inNLoS environments. As a result, an mmWaveadaptive beamforming prototype was developedincluding RF units, array antennas, basebandmodems, and a diagnostic monitor (DM), asshown in Fig. 3.

Both transmit and receive array antennashave two channels and each comprises 32 anten-na elements arranged in the form of a uniformplanar array (UPA) with 8 horizontal and 4 ver-tical elements, confined within an area of 60 mm× 30 mm. This small footprint was made possi-ble by the short wavelength of the carrier fre-quency at 27.925 GHz. Two channels at thetransmit and receive array antennas are designedto support various multi-antenna schemes suchas MIMO and diversity. The array antenna isconnected to the RF unit, which contains a setof phase shifters, mixers, and related RF circuit-ry. The set of phase shifters control the phasesof the signals sent to the antennas to form adesired beam pattern. Therefore, by setting thephase shifter values to a particular set, transmitand receive array antennas are capable of form-ing a sharp beam pattern in the intended hori-zontal (azimuth) and vertical (elevation) angles.

In order to reduce the hardware complexity,a sub-array architecture was employed to group

8 antennas into a sub-array, thus requiring only4 RF units per channel instead of 32. The reduc-tion in the number of RF paths results in areduction of antenna gain at the desired angle(except antenna boresight), a reduction of beamscanning ranges, and an increase in side lobelevels, but still meets the overall beamformingrequirements. The resulting full width at halfmaximum (FWHM) of the beam at the antennaboresight is approximately 10° horizontally and20° vertically with an overall beamforming gainof 18 dBi. In addition, a set of beam patterns ispredefined to reduce the feedback overheadrequired for the adaptive beamforming opera-tion between the transmitter and the receiver,where the overlapped beam patterns cover theintended service area with a unique beam identi-fier (ID) for each beam. These beam IDs areused by the baseband modem to control thephase shifter weights and to feed back the pre-ferred transmission beam information to thetransmitter. Table 1 lists key system parametersof the implemented prototype.

The baseband modem shown in Fig. 3 wasdesigned and implemented for real-time opera-tion with commercial off-the-shelf signal pro-cessing units including Xilinx Virtex-6 fieldprogrammable gate arrays (FPGAs), and anADC and a DAC each with up to 1 Gs/s conver-

Figure 2. Block diagram of a hybrid beamforming architecture.

IFFT DACMixer

RF beamformer RF beamformer

MIMOchannel

H

...

P/S

MIM

O encoder

Baseband precoder

Transmitter ReceiverBaseband channel

IFFT FFT

RF chains

DACPA

LNA

ADC

Array ant.

Phase shiftersRF chains

... ...

......

......

P/S

S/P Baseband combiner

MIM

O decoder

Ntc

Nta Nr

aNr

c

FFTADC...S/P

Figure 3. Configuration of the mmWave beamforming prototype.

RF/antenna

Modem

Array antenna Diagnostic monitor

ROH_LAYOUT.qxp_Layout 1/30/14 1:20 PM Page 109

IEEE Communications Magazine • September 2014 67

The conformal topology further maximizes therange of the beamsteering scanning angles in theazimuth plane. Moreover, the slanted topologyconforms to the cellular device and enables thedesigned mmWave antenna array to appear asan extremely low profile metallic trace line thatencompasses the edges of the PCB. The width ofthe trace lines is less than 0.2 mm, which is evenless than the 1 mm spacing required from thePCB edges for conventional surface mount tech-nologies (SMTs). From the vantage point of thehardware layout, the inclusion of a total of 32mmWave antenna elements requires a negligibleantenna footprint. Based on this antenna solu-tion, a truly massive MIMO antenna system mayactually be realizable for mmWave 5G in thelong term.

The beam patterns of each set of phasedarray antennas are synthesized by the 28 GHzRF unit, composed of 32 6-bit phase shifters,power amplifiers, and low noise amplifiers forthe transmit and receive paths, respectfully.The phases of the 28 GHz RF signal are indi-vidually controlled to form a beam in theintended direction along the azimuth plane.Each mesh grid antenna element within the twosets of antenna arrays is connected with the 28GHz RF unit through K type coaxial connec-tors. The required RF signal phase informationrequired to steer the main lobe beam are storedand retrieved from the in-house designed base-band modem.

The modem analog front-end (AFE) is con-nected to the RF port of the RF unit to trans-mit and receive the complex analog basebandsignal. The analog beamforming algorithm usedin this work is designed to search for and identi-fy the strongest transmit and receive beamdirection within 45 ms. The current size of theRF unit and baseband modem prohibits fullimplementation inside the cellular phone proto-type in this research. We are exploring a num-ber of different approaches to completelyintegrate the mmWave antenna array, RF unit,and baseband modem in the foreseeable future.In the meantime, the mmWave cellular phoneprototype containing two sets of 16-elementmesh grid antenna arrays is tested and mea-sured in conjunction with a reference mmWavebase station prototype as illustrated in Fig. 4.The measurement scenario is confined to anLOS environment inside a laboratory located inthe headquarters of Samsung Electronics,Suwon, South Korea. The cellular phone proto-type is fixed at a distance of 6 m away from thebase station prototype. Afterward, both meshgrid antenna arrays are connected to the twoavailable downlink channels of the RF unit anddesignated as the device under test (DUT). A16-QAM signal with 528 Mb/s data rate is trans-mitted from the mmWave base station proto-type. Each of the antenna arrays are activatedalternately to separately measure the error vec-tor magnitude (EVM) for each discrete beamsteering angles and confirm 10–6 block errorrate (BLER). Based on this measurement, thenormalized radiation patterns of all the antennaarrays are retrieved. The identical procedure isrepeated for scenarios when the mesh gridantenna array is exposed to free space condi-

Figure 3. Photographs of the mmWave 5G antenna system prototype: a)standalone view of the antenna array with K type coaxial connectors; b)integrated inside a Samsung cellular phone and zoomed in views of themmWave antenna region.

<0.2 mm

16-element array 1

16-element array 2

(a)

(b)

Figure 4. Measurement configuration of the mmWave 5G cellular deviceprototype.

Carrier frequency

Bandwidth/duplexing

TX/RX configuration

Channel coding

Modulation

27.925 GHz

520 MHz / TDD

TX: base station (BS) ant.RX: mesh-grid array (MS)

LDPC

QPSK/16-QAM

256 elements (16 ×16) array(~24 dBi antenna gain)

MSBS

8 cm

8 cm

HONG_LAYOUT_Layout 8/28/14 4:45 PM 7

Prototype 64 element dielectric lens by Nokia*

Early mmWave devices will use simple adaptive beam steering

blocks are grouped together to form a TTI or slot. The payload burst is composed of 140 NSC-CP blocks containing 1 pilot block, 1 control block and 138 data blocks. 5 slots form a TDM frame and 40 frames form a TDM superframe. At a 1.536 GHz sampling rate, one slot period is exactly 100 us, one tenth of 4G and one superframe is 20 ms identical to 4G. Limitations on the available ADC rate have the system running at slightly slower sampling rate of 1.5 GHz. The numerology of the experimental system is captured in Table 1.

Figure 5 Frame Structure

The experimental system uses a standard LTE turbo decod-

er implementation for error correction. Multiple LTE physical resource blocks are mapped into three consecutive NCP-SC blocks and46 codewords occupy 138 NCP-SC blocks. As enumerated in Table 2, the experimental system has 4 modula-tion and coding levels providing data rates from 295 Mbps at cell edge to a peak of 2.3 Gbps for a single stream. For the commercial system it is envisioned that the system will support greater than 10 Gbps peak rate using 2x2 SU-MIMO by ex-ploiting polarization diversity of two RF antenna arrays.

Table 1 NCP-SC Frame & Slot Timing

Table 2 Modulation and Coding Levels

IV. EXPERIMENTAL SYSTEM

The experimental system was constructed using a dielectric lens antenna as a substitute for integrated mmWave panel as described in Section II. Much R&D is required to achieve the mmWave system vision and the lens acts as opportune proxy to prove many of the system concepts for access. A picture of the BS is shown in Figure 6.

Figure 6. Experimental mmWave BS

A dielectric lens focuses the mmWave energy like an opti-cal lens focuses light. The size and curvature of the lens de-termines the gain and beamwidth of the antenna. Figure 7 shows a block diagram of the dielectric lens system. In this case, the gain of the antenna is 28 dB and the corresponding half-power beamwidth (HPBW) is 3 degrees in both azimuth and elevation. The direction of the beam can be selected by moving the position of the focal point at the base of the lenses. This selection process is accomplished by using a 4 row by 16 column array of patch antennas to feed the lens. These 64 patch antennas are switched by 3 levels of SP4T switches that determine which one of the 64 elements is excited for trans-mission or selected for reception. The feeding array is de-signed such that the HPBWs slightly overlap, as seen in Figure 8, so that a gain within 3dB can be maintained over the steering range of the lens. The combination of the lens and feeder array may be steered +/- 4 degrees in elevation and +/- 17 degrees in azimuth. The 3-level switching matrix can be switched with 1 us settling time and driven by the baseband processing unit and switched in synchronization with the TDM slot structure.

Figure 7 The BS Dielectric Lens System

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Superframe 30000*TB

20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39

0 1 2 3 4

TDD Frame 750*TB

RESRVED

Payload Burst

TDM Slot 150*TB

0 1 237 38 39

�� ʅ^Ϳ �ʅ^Ϳ �ʅ^Ϳ ��

Modulation Coding Rate

Data Rate (Gbps)

BSPK 0.23 0.295QPSK 0.51 0.665

16 QAM 0.54 1.398 16 QAM 0.90 2.318

��

��

� ��

Globecom 2014 Workshop - Mobile Communications in Higher Frequency Bands

379

Prototype phased arrays by Samsung **, ***Antenna arrays provide

larger aperture

vs


7

Implications of adaptive arrays

Beam training is a source of overhead

Interference is bursty,SINR may be better*

Narrow beams reduce Doppler, require pointing**

stronger interference

weaker interference

MIMO is posible, but power consumption is an issue

* A. Thornburg, T. Bai, and R. W. Heath, Jr., "Interference Statistics in a Random mmWave Ad Hoc Network,” ICASSP 2015** Vutha Va, and Robert W. Heath, Jr, "Basic Relationship between Channel Coherence Time and Beamwidth in Vehicular Channels,'' IEEE VTC Fall, 2015


8

Blockage is a major channel impairment

Base station

HandsetBlocked by users’ body

XUser

self-body blocking

X

blockage due to people

hand blocking

blockage due to buildings

line-of-sight non-line-of-sight

Need models for blockage & system analysis including blockage* W. Roh et al. "Millimeter-wave beamforming as an enabling technology for 5G cellular communications: theoretical feasibility and prototype results," in IEEE

Commun. Mag., 2014.** M. Akdeniz, Y. Liu, S. Sun, S. Rangan, T. Rappaport, E. Erkip, “Millimeter Wave Channel Modeling and Cellular Capacity Evaluation, IEEE JSAC June 2014


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Implications of blockage

* T. Bai and R. W. Heath Jr., “Coverage and rate analysis for millimeter wave cellular networks”, IEEE Trans. Wireless Commun., Feb. 2015.* *T. Bai and R. W. Heath Jr., “Analysis of self-body blocking effects in millimeter wave cellular systems“, in Proc. of Asilomar Conf., Nov. 2014.

blockedinterferer

unblocked interferer used for macro diversity

upper array blocked with fingers

user with no coverage

lower array blocked by person

Handset diversity or user training

High BS density and multibaseconnective provide diversity

Indoor users not covered by outdoor infrastructure

Blockages reduce the impact of interference


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Power consumption may be high with mmWave

40mWBasebandPrecoding

Baseband processing

ADCRFChain

LNA

ADCRFChain

LNA

20mW200 mW -350 mW

Alternative mmWave MIMO architectures are needed

Power at 60 GHz1GHz BW

* R. Heath, N. Gonzalez-Prelcic, S. Rangan, A. Sayeed, W. Roh “Overview of signal processing techniques for millimeter wave MIMO systems”, under reviewIEEEE JSTSP 2015


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Implications of power consumption

* O. El Ayach, S. Rajagopal, S. Abu-Surra, Z. Pi, and R. Heath, “Spatially sparse precoding in millimeter wave MIMO systems,” IEEE Trans. Wireless Commun., 2014**A. Alkhateeb, J. Mo, N. G. Prelcic, and R. W. Heath Jr, “MIMO Precoding and Combining Solutions for Millimeter-Wave Systems,” IEEE Commun. Mag. 2014.*** Jianhua Mo and R. W. Heath, Jr., ̀ `Capacity Analysis of One-Bit Quantized MIMO Systems with Transmitter Channel State Information, '’ IEEE Trans. on Signal Processing, 2015

Design low poweranalog processing

network 1-bitADCADC

1-bitADCADC

BasebandCombining

Nr LrNs

RF combining

WBBWRF

RFChain

RFChain

Reduce resolution to operate with few bits **, ***

Adopt a hybrid architecture with many fewer RF chains

than antennas *

Non negligible power consumption at BB when

running at Gsa/s


12

Multiuser or massive MIMO at mmWave256 antennas or more @ BS

Large arrays @ MS

Large arrays are a natural application of massive MIMO techniques

* F Boccardi, RW Heath Jr, A Lozano, TL Marzetta, P Popovski , “Five Disruptive Technology Directions for 5G”, IEEE Communications Magazine, 2014

Less out of cell interference

Low channel dimensionality Incorporate blockage


13

Implications of using mmWave for massive MIMO

Choice of carriers depends on base station density

Number of users limited by RF configuration

MmWave massive MIMO needs dense BS

deployment

* T. Bai, R. Vaze, and R. W Heath, Jr., “ Analysis of Blockage Effects on Urban Cellular Networks”, IEEE Trans. Wireless, 2014.** T. Bai and R. W. Heath, Jr., “Uplink massive MIMO SIR analysis: how do antennas scale with users?” Proc. of Globecom 2015. Longer version on arXiv.*** T. Bai; R. Heath, "Asymptotic SINR for millimeter wave massive MIMO cellular networks," in Proc. of SPAWC, 2015

MmWave provides large gain in area throughput in small-cell regime

Hybrid precoding

Hybrid combining

Hybrid combining

Hybrid combining


The future is bright for mmWave


15

TRANSPORTATION

prototyping

joint radar and communication

WEARABLES

V2X communications

COMMUNICATION THEORY

stochastic geometric analysis

of mmWave cellular

overcomingblockage

mmWave massiveMIMO

MIMO SIGNAL PROCESSING

compressive channel estimation

multi stream beam training

SU and MU hybrid precoding

INFORMATION THEORY

capacity with low resolution ADCs

coverage and rate analysis

radar aided comm.

Cloud RAN

Cooperativenetworks

NETWORKS

www.profheath.org

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