Design and Performance of LTE Enabled Base Station

Antennas

Derek CampbellAltair Engineering, Inc.

Hampton, VA 23666

Antenna SystemsLas Vegas November 6 – 7, 2014

• Motivation

• Design Challenges

• Design Tools

• Base Station Antenna

• 3-Sector Antenna

• Conclusion

Overview

Motivation• LTE Experiencing Increased Popularity

– Tablet PC Comprises 50% of PC Market

– LTE Smartphone Market Increased 91% in 2014

• LTE Coverage Increasing

Commercial LTE ServiceCommercial LTE Network PlannedTrial LTE Service

http://en.wikipedia.org/wiki/LTE_%28telecommunication%29#mediaviewer/File:3GPP_Long_Term_Evolution_Country_Map.svg

Motivation

• Wireless Communication Divided into Cells

– Base Station Communicates with Mobile Units

– Finite Communication Links over Finite Distance

• Cells Sub-Divided into Sectors

– Typically 3 or 6 Sectors/Cell

– Mitigates Self-Interference

Motivation• Performance Limited by Self-Interference

– Typical Cell Radius: 1 – 5 kilometers– Typical Base Station Height: 30 meters– Distance to Horizon Larger than Inter-Site Distance

𝑫𝑫 = 𝟐𝟐 � 𝑹𝑹 � 𝒉𝒉 + 𝒉𝒉𝟐𝟐

Variable Value(s) Description

R 6,371 km Earth Radius

h 0 – 45 m Height

• Motivation

• Design Challenges

• Design Tools

• Base Station Antenna

• 3-Sector Antenna

• Conclusion

Overview

Design Challenges• Wireless Lagging Wired Technology

– Offers 1/10th Performance at a Given Time– 10 – 15 Years Behind a Given Performance Level

• Difficult to Simultaneously Achieve– Maximum Coverage, Capacity and Reliability– Minimize Cost and Consumed Power

• Antenna Design is an Economical Solution– Efficiently Transmits Energy– Directs Energy Toward Terrestrial Users

Ghosh, Arunabha, et al. Fundamentals of LTE. Pearson Education, 2010.

Frequency• Frequency Band Features

– Low Frequencies Offer Increased Coverage– High Frequencies Offer Increased Bandwidth

• Regional Frequency Allocations– North America: 700, 800, 1900 and 2100 MHz– Europe: 800, 900, 1800 and 2600 MHz– Asia: 1800 and 2600 MHz

• Frequency Selection– 1800 MHz Widely Used Throughout Europe and Asia– Offers Both Coverage and Bandwidth

Ghosh, Arunabha, et al. Fundamentals of LTE. Pearson Education, 2010.

Polarization• Vertical Polarization

– Primarily Used for Earth-to-Earth Communication• Widely Distributed Mobile Units

– Optimal for Omni-Directional Radiation– Optimal for Both Urban and Rural Environments

• Horizontal Polarization– Primarily Used for Broadcast Television– Minimizes Interference with Man Made Noise (V-Pol)

• Circular Polarization– Primarily Used for Satellite Communication– Counteracts Faraday Rotation in Ionosphere

Beamwidth• Maximize Capacity and Coverage

– Common Azimuth Beamwidths: 90º, 65º, and 33º• 75% of Wireless Communication

– Common Elevation Beamwidths: 13º, 10º, and 7º• Larger Beamwidths are More Robust

10º Ver. HPBW500 m Inter-Site Distance

70º Ver. HPBW1732 m Inter-Site Distance

Yilmaz, O., S. Hamalainen, and J. Hamalainen. "Analysis of antenna parameter optimization space for 3GPP LTE." Vehicular Technology Conference Fall (VTC

2009-Fall), 2009 IEEE 70th. IEEE, 2009.

• Motivation

• Design Challenges

• Design Tools

• Base Station Antenna

• 3-Sector Antenna

• Conclusion

Overview

FDTD

Numerical Methods

Full-waveMethods(Rigorous Solution)

UTD

ELEC

TRIC

AL

SIZ

E

COMPLEXITY OF MATERIALS

Asymptotic Methods(High-Frequency Approximation)

Hybridization to Solve Large and

Complex Problems

PO/GO

MLFMM

MOM

FEM

• Searchable Antenna Database– 255 Total Antennas

Antenna Magus

EM Analysis

Modify Geometry

Op

timizationFinal Geometry

ParametersFrequencyGainVSWR

Antenna Magus

• Motivation

• Design Challenges

• Design Tools

• Base Station Antenna

• 3-Sector Antenna

• Conclusion

Overview

Antenna Element• Bi-Quad Antenna Element

– Offers Primary Specifications• Design Using Antenna Magus

– Optimize Using FEKO

Specification ValueSize/Shape CompactPolarization VerticalFrequency 1800 MHzWire Diameter 1 mmInput Impedance 50ΩAzimuth Beamwidth 65º

MoM

Elevation

Azimuth

Base Station Antenna• Design Using Antenna Magus

– Optimize Using FEKO

Specification ValueNumber of Elements 10Stack Direction VerticalElevation Beamwidth 10ºFront/Back Ratio 20 dB

MLFMM

Antenna Down Tilt• Mechanical Down Tilt

– Physically Rotate Antenna– Experiences ‘Pattern Blooming’

• Electrical Down Tilt– Adjust Excitation with Phase Shifters– Prevents Pattern Blooming– Recommend for Interference Limited Systems– Remote (RET), Variable (VET) and Fixed Methods

• RET Facilitates Real-Time Adjustment (e.g. Rush Hour)

– Increases Capacity ~50%

Mechanical Down Tilt• Can Tilt ~40% of Elevation Beamwidth

Azimuth Elevation

Electrical Down Tilt• Does NOT Experience Pattern Blooming

θs

∆𝝋𝝋 =𝑵𝑵 � 𝟑𝟑𝟑𝟑𝟑𝟑 � 𝒅𝒅 � 𝒔𝒔𝒔𝒔𝒔𝒔𝜽𝜽𝒔𝒔

𝝀𝝀

𝒅𝒅 =𝝀𝝀𝟐𝟐

Azimuth Elevation

Base Station Antenna• Design Using Antenna Magus

– Optimize Using FEKO

Specification ValueNumber of Elements 10Stack Direction VerticalDown Tilt Method ElectricalDown Tilt Position 12ºElevation Beamwidth 10ºFront/Back Ratio 20 dB

MLFMM

• Motivation

• Design Challenges

• Design Tools

• Base Station Antenna

• 3-Sector Antenna

• Conclusion

Overview

Results• Base Station Antennas In Free Space

Intel Xeon E5-2650 2.0GHz 8-core 20MB cache2 CPUs (16 cores) 256 GB RAM

Method Unknowns Run Time MemoryMoM 25,491 8.226 min 10.315 GBDGFM 36,900 4.360 min 0.574 GB

Results• Base Station Antennas In Situ

Intel Xeon E5-2650 2.0GHz 8-core 20MB cache2 CPUs (16 cores) 256 GB RAM

Method Unknowns Run Time MemoryMoM 42,108 25.05 min 27.619 GBMoM/PO 16,617 0.049 min 0.339 GB

• Motivation

• Design Challenges

• Design Tools

• Base Station Antenna

• 3-Sector Antenna

• Conclusion

Overview

Future• LTE Supports SU-MIMO

– LTE Release 10

– Beamforming• Supports 1 User Equipment (UE)

• Benefits from Decorrelated Signals

• LTE Advanced Supports MU-MIMO– LTE Release 11

– Beamforming• Supports 8 User Equipment (UE)

• Benefits from Correlated Signals

>4λ

<1λ

Conclusions• LTE Popular Standard

– Wireless Communication

• Base Stations Relay Communication– Link Between User Equipment

• Several Technical Challenges– Achieve Higher SINR for Lower Cost

• CEM Analysis is a Critical Solution– FEKO: Leader for Electrically Large Base Stations

• Exciting New Technology in Development– LTE Advanced