LTE Outdoor Small Cell Antenna Considerations - ibtuf.com 2 Tuesday/1530 Ray Butler... · Technologies in LTE World Summit, Posted Online May 26, 2010: August 20, 2010 ... 3D calculations

LTE Outdoor Small Cell Antenna Considerations

Ray ButlerVice President Engineering

Copyright © 2014 CommScope, Inc. – All rights reserved.

2Copyright © 2014 CommScope, Inc. – All rights reserved.

Its ALL about Capacity!!!

Paul Rasmussen.O2’s Network In Meltdown From Smartphone Usage.FierceWireless Europe 11/18/2009

Did you know that watching a video on a smartphone uses the same capacity on a network as sending 500,000 text messages simultaneously?


Data Throughput Growth


Three Ways to Get More Capacity

Moray Rumney.Smart Cells and Wireless Capacity Growth. PowerPoint Presentation for Agilent Technologies in LTE World Summit, Posted Online May 26, 2010: August 20, 2010 http://3g4g.blogspot.com/2010/05/small-cells-and-wireless-capacity.html

10,000

1,000

100

10

0

20 25

2000

Growth factor

SpectralEfficiency

Spectrum Number ofCells/Sectors

Growth has historically

been dominated by the increase in the number of cells/sectors


eNodeB

Close to the radio users experience better data rates.The challenge is managing interference so users over the entire cell have a Great Experience

Claude Shannon

Shannon’s Law says…

…The capacity of any system is limited by the noise in the system

The highest achievable data rate requires…

• Widest RF bandwidth radios

• Highest performing RF equipment, especially BTS antennas

• Unlimited backhaul network

What Limits LTE?


Expanding LTE Capacity

Femtocells

ODAS

Metro Cells

Enterprise Cells

IDAS

Interference Management is Paramount!Interference Management is Paramount!

eNodeB

eNodeB


Quasi-Omni Half-Omni Back-to-Back Single Panel

360 deg. Omni or Sectored Coverage

Mounted on Building Façade with 180 deg.

Coverage

Street or Corridorwith Control over Front and Back Interference

Single Sector Front-facing Coverage

Emerging Metro Cell and ODASAntenna Options


Two Studies Confirm the Importance of Better RF Path Control

• University of Texas at Austin (UTA) Poisson distribution with 3D modeling in which the need at the time dictates the placement of both eNodeBs and metro cells (random distribution matches nature of population growth and distribution over time)1

– The information presented here was produced in a joint effort between UTA and CommScope

• Commissioned Telecom Technology Services design in which a underlayment of metro cells was inserted into Lower Manhattan and results were simulated using Forsk Atoll® model along with WinPropray tracing

1 White paper discussing Poisson distribution: J. G. Andrews, Senior Member, IEEE, F. Baccelli, and R. K. Ganti, Member, IEEE, “A Tractable Approach to Coverage and Rate in Cellular Networks,” IEEE Transactions on Communications, Vol. 59, No. 11, Nov. 2011


Main Objectives of UT-A Modeling

• Study 3D beamforming and its impact

• Determine impact of vertical directivity

• Determine impact of vertical antenna pattern, & tilt

Horizon

main beam

8°

42.69

6

Horizon

main beam

16°

20.92

6


Comparison of Methodologies

• Traditional Grid Model– BSs are not random, have hexagon

layout – BSs Density (BS Area, R, is cell radius):

– UE is located randomly in the network

• Poisson Point Processes (PPP )– BSs are random and modeled as PPP– BSs Density: λ BS/Area– UE is located at the origin point

22 9 3Rλ =


Poisson Point Distribution and Methodology Comparison

• Performance of fixed grid model is an upper bound• Performance of PPP model is a lower bound• Performance of fixed grid model is an upper bound• Performance of PPP model is a lower bound


Poisson Point Process Background and Improvement

• White Paper discussing PPP:– J. G. Andrews, Senior Member, IEEE, F. Baccelli, and R. K. Ganti,

Member, IEEE, “A Tractable Approach to Coverage and Rate in Cellular Networks,” IEEE Transactions on Communications, Vol. 59, No. 11, Nov. 2011

• University of Texas has developed their own propagation tool based on PPP in which a three dimensional topography is accounted for

– Incorporation of buildings of various heights as well as 3D RF patterns more closely simulates real world performance

• Result characterize the “lower bound” of predictions, or is “pessimistic”


The Combined UT-A/CommScopeNetwork Model

• Contains macro-cell BS and small-cell BS

• Base stations are modeled as PPP

• User located at the origin point

main beam

macro-cell BS

small-cell BS

�


Channel Model

( )( ) ( ) ( )dBi

,

, +

w

h v m

h SG Lh

G G G G

ϕ θ

ϕ θ ϕ θ

=

= +

Parameter Variables

Shadow fading parameter

Number of buildings across the direct path between transmitter and receiver K

Attenuation coefficient for each building, γ<1 γ

Normalized horizontal antenna gain Gh(�)

Normalized vertical antenna gain Gv(θ)

Maximum antenna gain Gm

Path loss L

Small-scale fading coefficient; Rayleigh fading hw

KS γ=


Macro Cell Antenna ModelHorizontal Gain

( )2

min 12 ,h hh

G FB

ϕϕ = −

Horizontal angle relative the main beam

Horizontal half power beam-width

Front back ratio

A sectored antenna with 65 degree horizontal HPBW and 25dB FBR

A sectored antenna with 65 degree horizontal HPBW and 25dB FBR

90

-20 dB

-10 dB

0 dB

30

210

60

240

270

120

300

150

330

180 0

Bh= 65, Fh=25dB


Macro Cell Antenna ModelVertical Gain

( )2

max 12 ,tiltv v

v

G FB

θ θθ − = −

HorizonOut-of-cell interference

main beam

�tilt�

Parameter Variables

Negative elevation angle relative to horizontal plane θ

Main beam down tilt angle θtilt

Vertical half-power beamwidth Bv

Side lobe level relative the max gain of main beam Fv

-15 dB

-10 dB

-5 dB

0 dB

-30

30

-60

60

-90

90

-60

60

-30

30

0 0

Bv= 7, Fv=18dB, θtilt=10


The Impact of Multiple Element Antennas at 1900MHz

-3db (HPBWv)

78º

-3db (HPBWv)

39º

• 1 element dipole• 2.15 dBi gain• 78º HPBWv

• 2 element dipole• 3 dBi gain• 39º HPBWv

• 4 element dipole• 6 dBi gain• 19.5º HPBWv

• Half power point moves out as vertical beamwidth is narrowed

• Increased reach yields increased interference

• Down tilt is used to control reach and interference

• Antenna height must be doubled at 700MHz due to wavelength to achieve same HPBWv

-3db (HPBWv)

19.5º

about 24” high


Small Cell Antenna ModelDipole Antennas

( ) ( )( ) ( )( ) ( )

2.7578 10

11.7339 10

47.6419.5 10

10log cos

10log cos

10log cos

v

v

v

v B tilt

v B tilt

v B tilt

G

G

G

θ θ θ

θ θ θ

θ θ θ

= °

= °

= °

= −

= −

= −( ) 0 dBhG ϕ =

• Length: 25 in. (635 mm)• Outer Diameter: 1.5 in. (38.1 mm)• Net Weight : 4 lb. (1.8 kg)• 20-25 deg. HPBWv

Theoretical Stacked Dipole Antennas of Varying Tilt

Theoretical Stacked Dipole Antennas of Varying Tilt

A Common Omni-Directional Antenna in Use Today

A Common Omni-Directional Antenna in Use Today

-30 dB

-20 dB

-10 dB

0 dB

-30

30

-60

60

-90

90

-60

60

-30

30

0 0

Bv= 78 deg.Bv= 39 deg.Bv= 19.5 deg.

θtilt= 8 deg. θtilt= 0 deg.

ASPP-2933E


Quasi-Omni Antenna ModelHorizontal Pattern

• Connects 3 sectored antennas to create one "quasi" omniantenna

( ) ( ) ( ) ( )( )

( )

10 1 1 2 1 3 1

2dBi

10log + +

min 12 ,

h

ii i h

h

G G G G

G FB

ϕ ϕ ϕ ϕ

ϕϕ

=

= −

Horizontal pattern of actual antennas(red and blue lines denote the +/- slants of the dual pol antenna)

Horizontal pattern of actual antennas(red and blue lines denote the +/- slants of the dual pol antenna)

-30 dB

-20 dB

-10 dB

0 dB

30

210

60

240

90

270

120

300

150

330

180 0

quasi omni


Quasi-Omni Antenna ModelVertical Patterns Assumed

( )2

max 12 ,tiltv v

v

G FB

θ θθ − = −

-15 dB

-10 dB

-5 dB

0 dB

-30

30

-60

60

-90

90

-60

60

-30

30

0 0


-15 dB

-10 dB

-5 dB

0 dB

-30

30

-60

60

-90

90

-60

60

-30

30

0 0



Path Loss Model

• Urban Macro to UE

• Outdoor Pico to UE

• R – BS-UE separation in kilometers

• Carrier frequency is 2GHz

( ) ( )dB10128.1 37.6 logL R R= +

( ) ( )dB10140.7 36.7 logL R R= +


UT PPP Simulation Settings (1/2)

Parameter Value

Power of macro cell BS 20 W

Macro cell BS density 2.05/km2

Height of macro cell BS 30 m

HPBWh of macro cell 65°

FBRh of macro cell 25 dB

Downtilt of macro cell 10°

HPBWv of macro cell 7°

SLLv of macro cell 18 dB

Gm of macro cell BS 18 dBi

Parameter Value

Power of small cell BS 2 W

Height of small cell BS 6 m

Gm of dipole small cell antenna with 78°HPBW

2.15 dBi

Gm of dipole small cell antenna with 39°HPBW

5.15 dBi

Gm of dipole small cell antenna with 19.5°HPBW

8.15 dBi

Gm of Real 2-elements dipole small cell antenna

5.15 dBi

Gm of quasi omni small cell antenna

10.2 dBi


UT PPP Simulation Settings (2/2)

Parameter Value

HPBWv of quasi omni small cell antenna 14°

SLLv of quasi omni small cell antenna 16 dB

Downtilt of small cell 8°and 16°

Attenuation coefficient γ -40 dB

Building density to macro-cell BS density ratio ρ 15

Average building height 15 m

Average building length 25 m


Simulation Results20W Macro / 2W Metro

Quasi-Omni Offers 8-40%

Improvement in Average Spectral

Efficiency over Typical Omni-

Directional Antenna

Quasi-Omni Offers 8-40%

Improvement in Average Spectral

Efficiency over Typical Omni-

Directional Antenna


Simulation Results60W Macro / 5W Metro

Little Appreciable ASE Difference Between High and Low Wattage Scenarios,

BUT, the Site Count Will Vary Significantly!

Little Appreciable ASE Difference Between High and Low Wattage Scenarios,

BUT, the Site Count Will Vary Significantly!


Atoll-Based Modeling

• CommScope commissioned study based on Telecom Technology Services design in which an underlayment of metro cells was inserted into Lower Manhattan and results simulated using Atoll

– 1.5 km in dense city area

– 1W and 5W metro cells

– Hot spot / Hot zone through more robust build out

– Bands of 700, 1900, 2600

– Tilt from zero to 16 degrees

– Various antenna patterns as well as antenna gain

– Design objective driven by RSRP or user throughput


Coverage and Key Performance Metrics

Use of 5W reduces site count ~30% (10 sites ~ $250, 000!)Use of Quasi-Omni reduces site count another ~25-30 %!

Use of Quasi-Omni improves average user DL throughp ut 23-40%

Use of 5W reduces site count ~30% (10 sites ~ $250, 000!)Use of Quasi-Omni reduces site count another ~25-30 %!

Use of Quasi-Omni improves average user DL throughp ut 23-40%


Summary

• Improved University of Texas model using Poisson distribution with 3D calculations and Atoll both confirm improvements of antenna tilt

• Impact of vertical beamwidth– Without down tilt, average spectral efficiency decreases as the vertical

beamwidth of small cell antenna decreases (beam reaches deeper into network, lowering SINR)

• Impact of antenna down tilt– Average spectral efficiency is improved approx. 40%– User throughput is improved 24-40%– Site count is reduced 25-30%

Control over Vertical Beamwidth and Down Tilt Matters!Control over Vertical Beamwidth and Down Tilt Matters!


Proposed Field Trial

• Commscope proposes a field trial to quantify benefits of antenna pattern improvements

– Horizontal and vertical patterns, including effects of tilt

• Trial could utilize macro-sites– Better availability and performance history than metro-sites

• Looking for an isolated cluster with 10 – 15 sites

• Trial duration would be ~8 weeks

• Specifics of trial on the following slides


Field TrialAzimuth Beam Parameters

• The angular span between the half-power (-3 dB) points measured on the cut of the antenna’s main lobe radiation pattern

• Actual beamwidths >65 deg. can be problematic to network performance

• Trend is to narrower beamwidths.

• The angular span between the half-power (-3 dB) points measured on the cut of the antenna’s main lobe radiation pattern

• Actual beamwidths >65 deg. can be problematic to network performance

• Trend is to narrower beamwidths.

• Smaller SPR indicates a higher performing antenna.

• It is a measure of how much energy is radiated outside of the sector.

• SPR is analytically determined from measured antenna range pattern data.

• Andrew recommends less than 2%

• Smaller SPR indicates a higher performing antenna.

• It is a measure of how much energy is radiated outside of the sector.

• SPR is analytically determined from measured antenna range pattern data.

• Andrew recommends less than 2%

Sector Power Ratio


Field TrialElevation Beam Parameters

• The trial would demonstrate the benefits of elevati on beamwidth and tilt • Also demonstrated would be the effects of mechanica l tilt on azimuth

beamwidth

• The trial would demonstrate the benefits of elevati on beamwidth and tilt • Also demonstrated would be the effects of mechanica l tilt on azimuth

beamwidth

With mechanical tilt of 8 degrees, antenna blooms to 93 degrees from no tilt beamwidth of 65 degrees


Trial –High Level Methodology

• Two week baseline period– Network based KPI’s baselined– UE based data performance

• Replace antennas– Optimize tilts, parameters

• Repeat two week test– Network and UE based

• Compile date, create report and conclusions

Thank you!


NH360QS-DG-F0M Measured Elevation Patterns

Overlay HB Elevation Patterns, T0, T8, T161710 MHz, 1940 MHz, and 2170 MHz

LB Elevation Patterns T0 698 MHz, 790 MHz, and 896 MHz


NH360QS-DG-F0M Measured Elevation Patterns

Overlay Measured HB Elevation Patterns, T0, T8, T161710 MHz, 1940 MHz, and 2170 MHz

T0GL -10 dB, +75º

Hor. Suppress 0 dB

T8GL -6 dB, +65º

Hor. Suppress 3 dB

T16GL -6 dB, +55°

Hor. Suppress 12 dB


NH65QS-DG-F0M Elevation Patterns

1710 MHzT0, T8, T16, T24, T32 T40

2170 MHzT0, T8, T16, T24, T32

• 5 Elements, 25” Antenna Length

• Overlay HB Elevation Patterns in Increments of 8°

• 2170 MHz: Grating lobes increases from 20 dB at tilt 0 to 0 dB (same level as main beam) for 32º Tilt. Suppression minimum at 13°tilt, T>13º su ppression determined by upper SLL levels.

• 1710 MHz: Grating lobes increases to 0 dB (same level as main beam) for 40º Tilt. Suppression minimum at 17°tilt, T>17°suppression determined by upper SLL levels

Grating Lobe T16Grating Lobe T16


NH65QS-DG-F0M Elevation Patterns – N5 vs N10

N=5 2170 MHzT0, T8, T16, T24, T32

• 5 Elements, 25” Antenna Length vs 10 Elements, 50” Antenna Length

• Main beam and GL are narrower for longer array, but at basically same levels and angles for longer array. Assume element pattern vertical BW 75º in simulation.

• Assume 1:N phase shifter for both (1:5 PS for 10 element has quantization lobes ignored here).

N=10 2170 MHzT0, T8, T16, T24, T32


The Impact of Down Tilt on Throughput and Site Count

Quasi-Omni with 12 deg. down tilt and 19.5 deg. HPV Wv

Typical Omni-directional with 0 deg. down tilt and 50 deg. HPVW v

eNodeB (baseline) with 40W and 10 deg. down tilt

2x5W LTE

1900MHz

2x5W LTE

1900MHz

Improved SINR Provides~25% Improvement in Average

Network Downlink Throughput

Improved RF Path Reduces Metro Cell Site Count ~25%

Avg. DL Rate (Mbps)

Site Count*

Omni 1.690 107

Quasi-Omni

2.090 77

* Based on on-street coverage of -95dBm RSRP


Another Option for Interference Control – eICIC and ABS

Metro Cells

Metro Cells

eNodeB

eNodeB

• Requires a compatible X2 interface between eNodeBs and metro cells (and among metro cells if in a contiguous application)

Metro Cells

Metro Cells

X2 Interface

eNodeB

Metro Cell

Almost Blank Sub-Frames


The Impact of eICIC Based on TTS Analysis

• Impact is only seen when there is pronounced cell overlap (raising noise floor)

Average Spectral Efficiency

Scenario Regular Omni Quasi 8 deg. Quasi 12 deg.

Without eICIC 144.0 157.3 169.2

With eICIC 145.2 157.7 172.0

Downlink Throughput - Mbps

Scenario Regular Omni Quasi 8 deg. Quasi 12 deg.

Without eICIC 1,040 1,136 1,222

With eICIC 1,048 1,139 1,242

1900MHz Quasi 12 deg. Down Tilt with Pronounced Coverage Overlap

Scenario DL Throughput (kbps) ASE

Without eICIC 525.29 72.75485

With eICIC 589.56 81.65651

Documents

LTE Outdoor Small Cell Antenna Considerations - ibtuf.com 2 Tuesday/1530 Ray Butler... · Technologies in LTE World Summit, Posted Online May 26, 2010: August 20, 2010 ... 3D calculations