LTE Outdoor Small Cell Antenna Considerations
IBTUF– January 13, 2014
Ray Butler
VP Engineering, Commscope
1
Its ALL about Capacity!!!
Did you know that watching a
video on a smartphone
uses the same capacity on a network as sending 500,000 text
messages simultaneously?
Paul Rasmussen.O2’s Network In Meltdown From Smartphone Usage.
FierceWireless Europe 11/18/2009
2
Data Throughput Growth
3
Three Ways to Get More Capacity!!
Growth factor
10,000
2000
1,000
100
20
25
Spectral
Efficiency
Spectrum
Growth has
historically
been
dominated by
the increase in
the number of
cells/sectors
10
0
Number of
Cells/Sectors
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
4
What Limits LTE
Shannon’s Law says…
…The Capacity of Any System is
limited by the noise in the system
Claude Shannon
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
The highest achievable data rate requires…
• Widest RF bandwidth radios
• Highest performing RF equipment, esp BSA
• Unlimited backhaul network
5
LTE Small Cell Considerations
The information presented here was gathered in
a joint effort by The University of Texas at Austin
and CommScope, Inc.
6
Main Objectives of Modeling
o Study 3D beamforming and its impact
• Determine impact of vertical directivity
• Determine impact of vertical antenna pattern
Horizon
8°
6𝑚
42.69 𝑚
main
beam
Horizon
16°
6𝑚
main
beam
20.92 𝑚
7
Comparison of Topology
• Traditional Grid Model
• BSs are not random, have hexagon layout
• BSs Density:
l  2 9 3R 2 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: l BS/Area
• UE is located at the origin point
8
Performance Comparison
o Performance of fixed grid model is an upper bound
o Performance of PPP model is a lower bound
Figure is from J. G. Andrews, F. Baccelli, and R. K. Ganti, “A tractable approach to coverage and rate
in networks,” IEEE Trans. Commun., vol. 59, no.11, pp. 3122-3134, Nov. 2011.
9
Poisson Point Process (PPP)
• 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
• Result defines the ‘lower’ bound of predictions or is ‘pessimistic’
10
Our System Model
• Contains macro-cell BS and small-cell BS
• Base stations are modeled as PPP
• User located at the origin point
𝜑
small-cell BS
main
beam
macro-cell BS
11
Channel Model
h  SG  ,   Lhw
G  ,  
dBi
 Gh    Gv   +Gm
• S
K
– Shadow fading parameter S  
• K
– number of buildings across the direct path between
transmitter and receiver
• γ
– Attenuation coefficient for each building, γ<1
• Gh(𝜑) – Normalized horizontal antenna gain
• Gv(θ) – Normalized vertical antenna gain
• Gm
– Maximum antenna gain
• L
– Path loss
• hw
– Small-scale fading coefficient, Rayleigh fading
12
Macro Cell Antenna Model
• Horizontal gain
90
0 dB
120
   2

Gh     min 12   , Fh 
  Bh 

60
Bh = 65, Fh = 25 dB
-10 dB
150
30
-20 dB
180
Horizontal angle
Front back ratio
relative the main
beam
Horizontal
half power
beam-width
0
210
330
240
300
270
•
We use sectored antenna
with 65 degree horizontal
HPBW and 25 dB FBR for
macro cell BSs.
13
Macro Cell Antenna Model
• Vertical gain
-90
Bv = 7, Fv = 18 dB, tilt = 10
0 dB
-60
-60
-5 dB
-10 dB
-30
-30
-15 dB
0
0
30
30
60
60
90
vertical pattern we use
vertical pattern from CommScope
14
Macro Cell Antenna Model
• Vertical gain
2


   tilt 
Gv    max  12 
 , Fv 


 Bv 
–θ
– Negative elevation angle relative to horizontal plane
– θtilt – Main beam down tilt angle
– Bv
– Vertical half-power beamwidth
– Fv
– Side lobe level relative the max gain of main beam
Out-of-cell
interference
Horizon
𝜃
𝜃 tilt
main
beam
15
Small Cell Antenna Model
• Dipole antennas:
Gh    0 dB
-3 dB
– 1 element
2.15 dBi
78°
-3 dB
– 2 elements
+3 dB
39°
-3 dB
– 4 elements
+6 dB
19.5°
-3 dB
16
Small Cell Antenna Model
• Dipole antennas:
Gv  
Bv  78
 10 log10 cos 2.75   tilt 
Gv  
Bv 39
 10 log10 cos11.73   tilt 
Gv  
-90
Bv 19.5
Bv = 78
0 dB
-60
-60
-90
Bv = 39
-20 dB
-60
-20 dB
-30
-30
-30
-30 dB
0
0
30
30
0
0
30
30
tilt = 16 degree
tilt = 8 degree
60
90
Bv = 39
Bv = 19.5
-10 dB
-30 dB
60
Bv = 78
0 dB
-60
Bv = 19.5
-10 dB
-30
 10 log10 cos 47.64   tilt 
60
60
90
17
Small Cell Antenna Model
• Real 2-elements dipole antenna:
– Vertical pattern:
Gh    0 dB
• Dimensions:
• Length: 635.0 mm | 25.0 in
• Outer Diameter: 38.1 mm | 1.5 in
• Net Weight : 1.8 kg | 4.0 lb
18
Small Cell Antenna Model
• Quasi-omni antenna
Connect 3 sectored antennas to create one "quasi" omni
antenna
– Horizontal pattern:
Gh    10 log10  G1 1  +G2 1  +G3 1  
Gi i 
dBi
   2

  min 12  i  , Fh 
  Bh 

19
Small Cell Antenna Model
– Horizontal pattern:
90
quasi omni
0 dB
120
60
-10 dB
-20 dB
150
30
-30 dB
180
0
210
330
240
300
270
Horizontal pattern used in analysis:
Generated using 3 sectored antenna with 73
degree horizontal HPBW and 25 dB FBR.
Horizontal pattern of actual antennas
(Red and Blue lines denote the +/slants of the dual pol antenna)
20
Small Cell Antenna Model
– Vertical pattern of quasi-omni antenna:
2


   tilt 
Gv    max  12 
 , Fv 


 Bv 
-90
Bv = 14, Fv = 16 dB, tilt = 16
Bv = 14, Fv = 16 dB, tilt = 8
-90
0 dB
-60
-60
-60
-5 dB
-5 dB
-10 dB
-30
-30
-10 dB
-30
-15 dB
0
30
30
60
90
-30
-15 dB
0
60
0 dB
-60
0
0
30
30
60
60
90
Vertical pattern we use: 14 degree vertical HPBW, 16 dB SLL
21
Path Loss Model
• Urban Macro to UE
LdB  R   128.1  37.6 log10  R 
• Outdoor Pico to UE
LdB  R   140.7  36.7 log10  R 
– R – BS-UE separation in kilometers
– Carrier frequency is 2 GHz
22
Small Cell Antenna Model
o Study focus
• Determine impact of vertical directivity
• Determine impact of vertical antenna pattern
Horizon
8°
6𝑚
42.69 𝑚
main
beam
Horizon
16°
6𝑚
main
beam
20.92 𝑚
23
Simulation Settings
Parameter
Value
Parameter
Value
Power of macro cell BS
20 W
Power of small cell BS
2W
Macro cell BS density
2.05/km2
Height of small cell BS
6m
Height of macro cell BS
30 m
Gm of dipole small cell
antenna with 78° HPBW
2.15 dBi
HPBWh of macro cell
65°
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
FBRh of macro cell
25 dB
Downtilt of macro cell
10°
HPBWv of macro cell
7°
SLLv of macro cell
Gm of macro cell BS
18 dB
18 dBi
24
Simulation Settings
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
25
Simulation Results
Comparison of coverage probability performance of different small cell
antenna pattern, θtilt = 8°, λ2 = 15 λ1
1
0.55
0.9
•
Coverage Probability
omni
0.5
0.8
0.7
0.45
0.6
0.4
0.5
Dipole omni, B v = 78
Dipole omni, B v = 39
0.4
Dipole omni, B v = 19.5
Quasi omni antenna
Real 2-elements dipole
Macro tier network
0.2
-10
-8
-6
antenna
performs
better.
tilt = 8 degree
0.3
With down tilt, the quasi
-4
-2
0
2
SIR threshold in dB
4
4
5
6
6
8
10
26
Simulation Results
Comparison of coverage probability performance of different small cell
antenna pattern, θtilt = 16°, λ2 = 15 λ1
1
0.9
•
omni antenna performs
0.8
Coverage Probability
With down tilt, the quasi
better.
tilt = 16 degree
0.7
•
Coverage
probability
increases
0.6
decrease
with
in
the
antenna
beam-width.
0.5
Dipole omni, B v = 78
Dipole omni, B v = 39
0.4
Dipole omni, B v = 19.5
Quasi omni antenna
Real 2-elements dipole
Macro tier network
0.3
0.2
-10
-8
-6
-4
-2
0
2
SIR threshold in dB
4
6
8
10
27
Simulation Results
Comparison of Area of Spectral Efficiency (ASE) of different small cell antenna
pattern with λ2 =15 λ1
Area spectral efficiency (bps/Hz/km2)
Cases
1-tier network contains only
macro tier BSs
Dipole
HPBWv = 78°
Dipole
HPBWv = 39°
2-tier
network
Real 2 elements
dipole
Dipole
HPBWv = 19.5°
Quasi-omni
HPBWv = 14°
No tilt
8° tilt
16° tilt
14.66
14.66
14.66
61.30
--
--
60.20
62.28
65.25
58.41
61.80
69.29
52.84
62.67
74.35
47.94
62.91
82.00
28
Simulation Results
Comparison of average area throughput with λ2 =15 λ1 and 20 MHz bandwidth
Average Area Throughput (Gbps/km2)
Cases
1-tier network contains only
macro tier BSs
Dipole
HPBWv = 78°
Dipole
HPBWv = 39°
2-tier
network
Real 2 elements
dipole
Dipole
HPBWv = 19.5°
Quasi-omni
HPBWv = 14°
No tilt
8° tilt
16° tilt
0.29
0.29
0.29
1.23
--
--
1.20
1.25
1.30
1.17
1.24
1.39
1.06
1.25
1.49
0.96
1.26
1.64
29
Simulation Results
Throughput gain over 2 elements no tilt dipole, λ2 =15 λ1
Throughput Gain
Cases
No tilt
8° tilt
16° tilt
Dipole
HPBWv = 78°
5.13%
Dipole
HPBWv = 39°
2.56%
6.84%
11.11%
Real 2 elements
dipole
0.00%
5.98%
18.80%
-9.40%
6.84%
27.35%
-17.95%
7.69%
40.17%
Dipole
HPBWv = 19.5°
Quasi-omni
HPBWv = 14°
30
Simulation Results of Part 3
Comparison of coverage probability performance of different small cell BS
power for quasi omni antenna, λ2 = 15 λ1
1
0.9
•
Quasi omni
Coverage
does
0.8
not
probability
increase
Coverage Probability
much as small cell BS
power increases from
0.7
0.6
down tilt is small.
Ps = 5W, tilt = 0 degree
Ps = 2W, tilt = 8 degree
0.5
Ps = 5W, tilt = 8 degree
Ps = 2W, tilt = 16 degree
0.4
Ps = 5W, tilt = 16 degree
Only macro tier network
0.3
0.2
-10
2W to 5W when the
Ps = 2W, tilt = 0 degree
-8
-6
-4
-2
0
2
SIR threshold in dB
4
6
8
10
31
Simulation Results RF Power
Comparison of ASE of different small cell antenna pattern and power with λ2 =15 λ1
Area spectral efficiency (bps/Hz/km2)
Cases
Dipole
HPBWv = 78°
Dipole
HPBWv = 39°
Real 2 elements
dipole
Dipole
HPBWv = 19.5°
Quasi-omni
HPBWv = 14°
No tilt
8° tilt
16° tilt
2W
5W
2W
5W
2W
5W
61.30
61.91
--
--
--
--
60.20
60.62
62.28
61.66
65.25
64.52
58.41
59.08
61.80
61.35
69.29
69.52
52.84
53.02
62.67
62.22
74.35
73.82
47.94
48.39
62.91
63.32
82.00
82.70
32
Simulation Results With 5W RF Power
Comparison of ASE of different small cell antenna pattern and power with λ2 =15 λ1
Area spectral efficiency (bps/Hz/km2)
Cases
No tilt
8° tilt
2W
5W
16° tilt
2W
5W
2W
5W
4.95%
4.75%
HPBWv = 39°
3.06%
2.57%
6.63% 4.33% 11.71%
Real 2 elements
dipole
0.00%
0.00%
5.80% 3.81% 18.63% 17.63%
-9.54% -10.29%
7.29% 5.28% 27.29% 24.91%
-17.93% -18.12%
7.70% 7.14% 40.39% 39.93%
Dipole
HPBWv = 78°
Dipole
9.17%
Dipole
HPBWv = 19.5°
Quasi-omni
HPBWv = 14°
33
Value Proposition
• Comparison of costs to add 40% more sties vs. adding a more
expensive antenna
35
Conventional Planning Tool Analysis
• Real 2-element dipole – HPBWv =
39°
• Quasi Omni – HPBWv = 7°
• 15 random BS
• Antenna Height = 7.62 m (25 ft.)
• 60 watt PA
• Each PA connected to 3 sectored
Quasi-Omni antenna
• Allows for each ‘sector’ to have
independent tilt
36
Conventional Planning Tool
Real 2-Element Dipole
– Single Fixed Tilt (0°)
Quasi-Omni –
Optimized Tilts
37
SIR Over Studied Area
100
90
80
Coverage Probability
70
60
Real 2 Element Dipole
50
Quasi-Omni 0 Tilt
40
Quasi-Omni Optimized Tilts
30
20
10
0
0~5
5 ~ 10 10 ~ 15 15 ~ 20 20 ~ 25 25 ~ 30 30 ~ 35 35 ~ 40 40 ~ 45 45 ~ 50 50 ~ 100
SIR (dB)
38
Tilt Settings of Planning Tool Optimization
Tilt Setting (degrees)
# of sectors at indicated tilt setting
0
34
1
9
2
6
3
7
4
6
5
7
6
17
7
11
8
12
9
17
10
13
• Shows significance of using a more sophisticated antenna
• By adjusting the tilts of the various ‘sectors’ of the quasi-omni,
compensation for variances in terrain, site placement, and other can
be made
• Emphasizes the importance of controlling the interference
experienced
• Using down tilt to limit out of cell coverage
• Narrower beamwidth antennas to better control where RF is transmitted
39
Validating the Value Proposition and Net
Pricing through RF Network Design
Omni, Patch, Panel, Tri-Panel/Sector, Quasi Omni
16º
6m (20’)
12º
8º
.25W to 20W
700MHz, 1900MHz, 2600MHz
22m (66’) to 43m (142’)
•
A cooperative study to determine how each of the following impacts networks and
subscribers (e.g., ASE, SINR and node count)
•
•
•
Power
Frequency
Antenna pattern
– Beam vertical directivity (tilt)
– Placement of null zones
– Site sectorization
40
Coverage and Key Performance Metrics
Quasi-Omni Achieves Best Performance in Hot-zone
PERCENTAGE OF COVERAGE AREAS EXPERIENCING GREATER THAN -105 dBm RSRP
LOCATION
TOTAL
COUNT
eNodeB
ALONE
1W OMNI
5W OMNI
1W QUASI
5W QUASI
On Street Locations
24,562
74.5%
76.0%
79.5%
78.7%
80.1%
In-Building Locations
30,226
31.4%
25.6%
30.9%
29.6%
31.6%
Courtyard Locations
2,980
27.2%
3.8%
10.3%
3.8%
6.0%
Site Count
--
36
149
107
113
77
Average Downlink
Throughput (kbps)
--
375
2,100
1,690
2,700
2,090
Improvement above
Macro Alone
--
--
460%
351%
620%
457%
•
Quasi-omni offers 28% reduction in site count over omni (backhaul and rental costs alone can
easily be about $350-400 per month per pole)
•
Quasi-omni offers 24% improvement in average user throughput
•
Detailed LTE Link Budget Analysis Complete
41
Summary
o Impact of down tilt
• Both coverage probability and ASE of the heterogeneous network are
improved with the introduction of small cell BS antenna down tilt.
• Both coverage probability and ASE increase when the down tilt of small
cell BS antennas increases.
o Impact of vertical beam-width
• With no small cell BS antenna down tilt, ASE decreases as the vertical
beam-width of small cell BS antenna decreases.
• With small cell BS antenna down tilt, both coverage probability and
ASE increase when the vertical beam-width of small cell BS antenna
decreases.
42
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
43
Field Trial – Azimuth Beam Parameters
Sector Power Ratio
•
•
•
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 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%
44
Field Trial – Elevation Beam Parameters
With mechanical tilt of 8 degrees, antenna blooms to
93 degrees from no tilt beamwidth of 65 degrees
•
The trial would demonstrate the benefits of EL Beamwidth and tilt
•
Demonstrate also the effects of mechanical tilt on AZ beamwidth
45
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
46
Thank you!
Q&A
47