White Paper
Twin Beam technology adds immediate
capacity without additional antennas
Philip Sorrells, V.P. Strategic Marketing – Wireless
May 15, 2013
Contents
Contents
Are snowballing capacity issues creating the perfect storm? 3
The quest for more capacity
3
Revisiting sectorization 4
Capacity performance makes six-sector attractive… in theory 5
The cost of better performance
6
Twin Beam technology makes six-sector implementation cost-effective and practical 6
Increasing capacity through pattern performance, signal strength and noise reduction 7
Reduced loading at the top of the tower
9
Success story: Twin Beam turns antenna competition into a solutions showcase
9
Improvements across the board
9
Making the complex simple
12
The bottom line is higher quality of service
12
References13
2
Are snowballing capacity issues creating the
perfect storm?
“Even as they build the next generation
of faster wireless networks… carriers
are discouraging heavy data users by
eliminating unlimited data plans and
enforcing monthly caps.”
Wireless carriers seek to ‘offload’ customers, Roger Yu,
USA Today, 5/23/2012
Today’s mobile subscribers have a voracious appetite for data. In 2012, the volume of global
mobile data traffic grew 70 percent, reaching 885 petabytes per month1. The growth is due
to multiple factors. The number of smartphones continues to increase, as does the amount of
data they consume. According to recent industry reports, 31 percent of all Internet users rely
exclusively on their mobile device for Internet connectivity. The average amount of traffic per
smartphone in 2012 was 342 MB per month, up from 189 MB per month in 2011 — an 81
percent rise1.
The deployment of 4G networks is also on the rise. At the end of 2012, there were 144 4G
networks worldwide. By the end of 2013, the number will swell to an estimated 230 2. In some
cases, wireless service providers (WSPs) are bypassing 3G altogether, opting to layer 4G
directly onto their current 2G systems.
The rapid adoption of 4G is placing further strain on capacity-strapped networks. In 2012,
a fourth-generation connection generated 19 times more traffic on average than a non-4G
connection1. Although 4G connections represent only 0.9 percent of mobile connections today,
they already account for 14 percent of mobile data traffic1.
The capacity crunch has become so critical that, as USA Today reported, “Even as they build
the next generation of faster wireless networks, carriers are discouraging heavy data users by
eliminating unlimited data plans and enforcing monthly caps.”
The quest for more capacity
In the quest for more capacity, WSPs are exploring a number of strategies — some old and some
new. Among the more traditional are cell densification and the purchase of additional spectrum.
Both strategies, however, present significant cost issues.
Increasing capacity
According to Shannon’s Law, increasing capacity in a given channel bandwidth
requires WSPs to improve the signal-to-noise ratio and/or increase frequency reuse.
Reducing noise
In 3G and 4G LTE networks, noise containment in the RF path is critical. External
noise from a variety of sources — including multi-path reflection, environmental noise
and interference from adjacent or nearby cells — can significantly decrease receiver
sensitivity at the base station. As noise within the sector increases, mobiles increase
their signal power levels, creating more uplink interference. Noise within the RF path
is also problematic, with thermal noise and passive intermodulation (PIM) being the
major culprits.
Increasing frequency reuse
Another strategy for growing capacity is to increase opportunities for frequency reuse
through higher order sectorization.
3
In the case of cell densification, adding new cells, the process of site acquisition and zoning
approval can take up to two years, resulting in lost revenue for the WSP. Once approved, a new
site can cost more than a quarter million dollars to build and commission.
Adding more spectrum, assuming it is available, can easily run into the billions of dollars. In January
2013, AT&T announced a deal to pay Verizon Wireless $1.9 billion for spectrum in the 700 MHz
band in 18 U.S. states3.
More recently, WSPs have experimented with offloading traffic to ancillary networks such as
localized Wi-Fi hot spots. This, too, is problematic. Creating a secure tunnel for the hand-off
typically requires a connection manager client running Internet Protocol Security (IPSec) suite. The
application must be downloaded and installed by the user and runs in the background where it can
significantly affect the battery life of the device4.
Small cell deployment is also being touted as an excellent way to add network capacity. According
to Joe Madden, Principal Strategist with Mobile Experts LLC., more than five million carrier-grade
small cells are expected to ship in 2017 5. But that does little to satisfy WSP’s immediate need for
more capacity.
Revisiting sectorization
In the last 50 years, wireless capacity has increased by a factor of about 1,000,000 6. This
growth has come from better spectral efficiency, more spectrum and more cells/sectors. Since
the 1990s, one of the most popular and effective strategies for increasing site and network
capacity has been sectorization. Figure 1 illustrates that sectorization and cell densification
have accounted for the majority of additional capacity over the last fifty years.
The first sectorized systems replaced standard 360-degree omni-directional antennas with
three separate directional antennas. The most commonly deployed configuration uses three
antennas, each with a nominal azimuth beamwidth of 65-degrees. While the antennas within a
sectorized cell share a common base transceiver station (BTS), each is managed and operated
independently with its own power level, frequencies and channels.
The use of three directional sector antennas versus one omni-directional antenna substantially
reduces co-channel cell interference and triples the opportunity for frequency reuse. As a result,
WSPs realize significant gains in capacity.
Figure 1
10,000
2,000
1,000
Growth Factor
“… more than five million carriergrade small cells are expected to
ship in 2017 5. But that still leaves
WSPs wondering how to resolve their
immediate capacity issues now.”
100
20
25
10
1
Spectral Efficiency
Spectrum
Number of Cells/Sectors
Smart Cells and Wireless Capacity Growth, Agilent Technologies, LTE World Summit, May 26, 2010
4
Capacity performance makes six-sector attractive…
in theory
Several years ago, WSPs began to experiment with higher order sectorization, splitting
traditional three-sector sites into six. The initial purpose was to generate additional capacity
in hot spots and spectrum-limited markets. A six-sector site application splits each of the
original 65-degree coverage areas into two sectors, each served by a separate narrowbeam
antenna with a nominal azimuth beamwidth of 33 to 38 degrees. Properly done, higher order
sectorization reduces the overlap interference, pilot pollution and soft hand-off areas — all of
which contribute to more efficient spectrum reuse.
In six-sector deployments, with rapid pattern roll-off and good sidelobe and backlobe
suppression, WSPs typically increase capacity by 70–80 percent 7. Because each antenna
is controlled separately, it provides tighter frequency and radiation control when it comes to
customizing the footprint of the cell site.
At the same time, six-sector antennas enable WSPs to take advantage of today’s more
sophisticated modulation schemes. Crossover points between sectors typically occur at
approximately –9dB, making them good candidates for use with 3G UMTS and CDMA
networks, as well as 4G LTE systems.
Higher order sectorization also enables WSPs to add capacity without adding sites. This is
especially important in high-density areas such as urban and suburban locations where WSPs
can respond quickly to changes in subscriber demographics by simply upgrading existing sites
from three- to six-sectors.
Figure 2 illustrates the significant reduction of inter-sector overlap in switching from a 65-degree
to a 33-degree antenna. Reducing the overlap decreases the soft handoff area and provides
additional capacity gains.
Figure 2
65° Sectors
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0
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According to a CDMA Development
Group study, six-sector sites can
improve voice capacity 70% to
100% and can increase data
throughput 50% to 70% above
current network baselines.
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5
The cost of better performance
Traditionally, cell splitting into six sectors has been limited due to the requirement to change
from one 65-degree antenna to two individual narrower beam antennas. The capacity and
performance enhancements gained by implementing higher order sectorization are often
undermined by the real cost of implementation. By definition, transitioning from a three- to a
six-sector design doubles the number of antennas that must be purchased and increases many
of the associated costs, including packaging, transportation and installation.
While the number of antennas required doubles, the net structural impact on the tower is even
higher. This is because, in order to generate a narrower beamwidth, a 33-degree antenna
must be physically larger than a 65-degree antenna. In many cases, the surface area of the
six-sector solution is more than double that of the three-sector solution. The larger surface area
creates significantly more wind loading. If mount arms are used to move the antenna away
from the tower, torque loads on the tower increase accordingly.
Larger antennas also add more weight to the top of the tower, which is becoming increasingly
crowded with other RF components such as filters, tower mounted amplifiers, multi-band
combiners, and remote radio heads. Nowadays, many tower manufacturers are switching to
lighter materials in order to save on manufacturing and customer shipping costs. As a result, the
heavily loaded, lighter towers are far more susceptible to increased twist and sway, which can
cause links to sporadically fail. In addition, tougher industry standards for tower loading, like
ANSI/TIA-222 Rev G, impose additional limitations on the tower’s structural capacity.
With six antennas instead of three, there is also increased potential for boresite alignment errors
during installation. The industry has benefitted from recently introduced installation aides such
as GPS assistance. Many installers, however, continue to align antennas using little more than
a compass, visible landmarks or even hand-drawn lines on the pavement below. In a UMTS
network, the antenna’s performance sensitivity to azimuth and tilt error increases as beamwidth
is reduced8.
When it comes to deploying a new site, zoning approval, especially in suburban
neighborhoods, is more difficult to obtain with a six-sector site as well. In 2009, the FCC
passed a regulation designed to shorten the time between the filing of the WSP zoning request
and the decision by the municipality — 90 days for a co-located site or 150 days for all other
applications. But the “shot clock”, as the law is known, has done little to speed the process.
For WSPs looking to deploy larger, more visible six-sector solutions, obtaining the necessary
approvals can take eight months or more.
For these reasons, the six-sector site design, despite its ability to increase capacity and
throughput, has not gained much traction in the market.
Twin Beam technology makes six-sector implementation
cost-effective and practical
Recently, however, CommScope
engineers have perfected a “sectorsculpting” multi-beam design that alters
the cost/benefit playing field for
six-sector deployment.
Recently, however, CommScope engineers have perfected a “sector-sculpting” multi-beam
antenna that alters the cost/benefit playing field for six-sector deployment. Introduced by
CommScope in 2013, sector sculpting enables WSPs to create a six-sector solution — with all
the expected capacity and pattern benefits — using just three Twin Beam antennas.
By enabling WSPs to achieve higher-order sectorization without additional antennas, the
technology effectively removes the major cost and time barriers associated with six-sector
deployment and provides a capacity-generating solution that WSPs can deploy immediately.
6
Figure 3
The Twin Beam design provides a theoretical doubling of sector capacity. Each antenna
produces two separate narrow azimuth beams whose positions are directed at +30-degrees
and –30-degrees of the antenna’s boresite. In extended trials, WSPs are realizing an estimated
80-percent gain in capacity, while reducing their antenna count by half and significantly
cutting CapEx and OpEx spending.
The architecture of the sector-sculpting Twin Beam antenna, shown in Figure 3, uses a Butler
matrix to split the input power and feed each of the four independently controlled column
arrays. Dielectrically loaded elements on the phase shifters, created by CommScope during
the development of the company’s patented remote electrical tilt (RET), enable WSPs to control
phase shifting on the elevation as well as the azimuth plane. The circuit power dividers are
standard off-the-shelf, solid-state 3 dB hybrid couplers.
Applications for the Twin Beam include single and multi-band for GSM, 3G and LTE.
High-band, low-band and dual-band models support all major mobile technologies in the
698–894 MHz, 824–960 MHz and 1710–2170 MHz bands, as well as 2 x 2 multiple-in
multiple-out (MIMO) technology.
Increasing capacity through pattern performance, signal
strength and noise reduction
Figure 4 illustrates the radiation pattern of a traditional 65-degree antenna, and the two
narrow beams generated by the Twin Beam antenna. Important characteristics to note include
the difference in sector overlap between the beams and the consistent position of the null fill at
approximately –9 dB.
Figure 4
Three-Sector 65°
Twin Beam 38°
Figure 5 shows the pattern of a single 65-degree antenna, in red, overlaid on the patterns
created by a Twin Beam antenna. As indicated by the patterns, the two narrow beams
produced by the Twin Beam antenna exhibit wider coverage at the sector edges, more rapid
pattern roll-off, and improved front-to-back ratio. This also enables providers of spectrum-limited
GSM systems to employ a more aggressive back-to-back reuse of their broadcast control
channel (BCCH).
7
Figure 5
Of particular note is the approximate 2–3 dB of increased gain at the boresite generated by
the Twin Beam compared to the 65-degree antenna. For WSPs using advanced modulation
schemes such as High-Speed Downlink Packet Access (HSDPA) and LTE, the increased gain
extends 16 and 64 QAM capacity further toward the sector edge. The improved throughput
yields higher quality of service for the customer. It also enables mobile devices to operate on
less power, further reducing interference levels.
The sector overlap, critical for increasing capacity, remains constant with the Twin Beam.
Both beams are generated from the same radome and precisely engineered to maintain
consistent overlap and null fill. In a traditional three-sector or six-sector site, each antenna must
be accurately aligned in order to achieve overlap consistency. As previously noted, alignment
issues due to human error are common in deploying any sectorized antenna solution.
PIM is also of particular concern in 3G and 4G LTE networks where noise suppression is
critical in order to reduce mobile power levels and associated uplink interference. It is important
to remember that PIM is a systems issue; two or more passive components are required in order
to create the disruptive intermodulation. Therefore, PIM must be controlled throughout the entire
RF path.
In the Twin Beam antenna system, CommScope achieves this through a rigorous and
proactive manufacturing program that includes extensive PIM testing on every component,
including the antenna. The program also provides PIM training and certification for customer
and third-party installers.
The ability of the Twin Beam sector-sculpting solution to effectively reduce PIM long term also
speaks to the importance of viewing the antenna as an entire RF system, including cabling,
connectors and any other passive components such as combiners and filters.
8
Reduced loading at the top of the tower
A single Twin Beam antenna has the same approximate physical dimensions as a single
33-degree antenna, for a given frequency range. At the top of the tower, the weight and wind
loading are essentially the same as well.
For capacity-strained sites, WSPs can simply replace the three existing 65-degree antennas
with three Twin Beam antennas and immediately realize dramatically improved capacity — on
the order of 70 to 80-percent. Because the antenna count remains the same, no new lease
requirements or lengthy zoning approvals are required.
Success story: Twin Beam turns antenna competition into
a solutions showcase
In late 2011, a major U.S. carrier was looking to add capacity within its core network in a
key metro market. Coverage was being provided by a cluster of high-profile, three-sector urban
sites operating in the 850 MHz and 1900 MHz bands. Nearly all of the sites were reaching
their UMTS capacity limits.
To generate added capacity at critical sites, the carrier was evaluating a variety of sectorsplitting solutions that would affect one sector at each site. The specific market represents a
high-revenue opportunity for the carrier, so time to market was also a key concern.
CommScope was one of three RF solutions providers asked to participate in the process.
Working with its design simulation partner, Telecom Technology Services, Inc. (TTS),
CommScope began by analyzing the carrier’s traffic patterns and capacity requirements. This
involved simulating network loads and conducting pre-implementation drive testing, not just at
the cell level, but at the cluster level as well.
Based on their preliminary assessment, CommScope and TTS developed a robust strategy
featuring the Twin Beam six-sector antenna solution. Beyond the advanced sector-splitting
technology, CommScope was also able to provide the necessary RF path components,
engineering design and project management for a turnkey solution.
“The selection process started out as an antenna-only comparison, but the ability to deliver
a turnkey capacity solution within the customer’s timeframe and budget soon became a key
driver,” said Mike Wolfe, CommScope Regional Sales Manager.
Improvements across the board
“Once we were able to show how
we could help improve performance
across the entire system, the
process became less of an antenna
comparison and more about who
could provide the best turnkey
solution.”
TTS ran simulations for the targeted sites in order to quantify the expected gains when switching
from the existing traditional three-sector configuration to the six-sector Twin Beam. Simulations
modeled 3G UMTS and 4G LTE environments.
Figures 6 and 7 illustrate the results of two UMTS simulations: Cell A, operating in the 1900
MHz frequency and Cell B, operating in the 850 MHz frequency. Figure 6 indicates the ability
of the Twin-Beam antenna to reduce the soft hand-off areas within a given sector. Once the
percentage of soft hand-off areas between the left and right beams are averaged, the total
sector shows a 3.69% decrease in sector overlap.
9
Figure 6: Percentage of soft hand-off areas1 (within sector)
Existing sector
Cell A
1900 MHz
Cell B
850 MHz
1
41.74
47.1
Split sector Twin Beam
40.29 (left beam)
35.81 (right beam)
38.41 (left beam)
43.73 (right beam)
Reduction in soft
hand-off area
–3.69
–6.03
The combined soft hand-off areas within a given sector, expressed as a percentage of the sector’s
total coverage area.
Figure 7: Radio Resource Efficiency1
Existing sector
Cell A
1900 MHz
Cell B
850 MHz
1
53.4
65.32
Split sector Twin Beam
54.33 (left beam)
76.11 (right beam)
56.35 (left beam)
69.52 (right beam)
Aggregate change
x2.44
x1.93
The percentage of a radio’s coverage area in which it is identified by mobile devices as the primary
or serving radio.
Figure 7 illustrates the expected gain in radio resource efficiency. Radio resource efficiency
is defined as the percentage of a radio’s coverage area in which it is identified, by mobile
devices within the coverage area, as the primary or serving radio. When the existing sectors
—Cell A and Cell B — are split, the radio resources available to handle traffic more than
doubles in Cell A and nearly doubles in Cell B.
Figure 8
10
The 4G LTE simulations indicated significant advantages in deploying a Twin Beam six-sector
solution in areas with high traffic loads. Figure 8 shows that, in a Twin Beam versus traditional
three-sector deployment, the difference in peak user throughput increases as the sector load
increases. This is primarily due to the Twin Beam’s ability to maintain a cleaner RF environment.
TTS also simulated the effect of the Twin Beam on pilot pollution, a key contributor of
interference. As shown in Figure 9, the results indicated a significant improvement in the ratio of
pilot pollution removed (green) versus pilot pollution added (red).
Another key benefit to note is that, as capacity and throughput increased at each individual
site, performance across the entire cluster improved. This was due in part to the ability of the
Twin Beam antennas to clean up inter-sector interference and reduce noise levels. As a result,
the cell clusters showed improvements in the dropped call rate (DCR), received signal strength
and system availability.
“Once we were able to show how we could help improve performance across the entire
system, the process became less of an antenna comparison and more about who could
provide the best turnkey solution,” Wolfe added.
Figure 9
Number of Bins Before
Number of Bins After
160
3.8
140
120
3.6
100
3.4
80
3.2
Percent
Number of Bins
Right Beam
4
60
3
40
2.8
20
Number of Pilot Polluters
Number of Bins Before
Number of Bins After
160
3.8
140
120
3.6
100
3.4
80
3.2
Percent
Number of Bins
Left Beam
4
60
3
40
2.8
20
Number of Pilot Polluters
11
Making the complex simple
Implementing a traditional six-sector solution involves greater complexity, such as additional
RF connections and the need for more accurate antenna alignment. As an end-to-end provider
who could design, engineer, install and support a turnkey solution, CommScope was able to
simplify an otherwise complex process.
In addition to demonstrating the capacity gains from the Twin Beam antennas, the CommScope
team created a validation package that included key performance indicator (KPI) reports and
post-installation drive testing in order to document the performance improvements. To further
improve system performance, they also recommended modifications to cells outside the scope
of the project and designed a construction plan with the assigned installation company. The
project was backed by the company’s comprehensive RF Path Warranty.
In the end, the implementation was successful, not only on the strength of the Twin Beam
antenna, but also because of CommScope’s ability to effectively address the project’s entire
ecosystem. “It really came down to close collaboration with the carrier to ensure their technical,
budgetary and scheduling goals were achieved.,” Wolfe said.
The bottom line is higher quality of service
Obviously, creating increased capacity and keeping ahead of the data tsunami are both
means to a greater end: increasing quality of service (QoS). In a July 2012 study by Comptel
Corp.9, more than one in five respondents said they had experienced poor QoS, such as
dropped calls, low bandwidth or slow loading of files at least once a week. Over two thirds
said they felt “neglected” by their WSP. About 40 percent said they planned to switch WSPs
within the next 24 months as a result.
On the positive side, customers have consistently voiced a willingness to pay more for better
QoS. A recent Comptel survey indicated that, worldwide, sixty percent of respondents would
pay more for better and faster service. In the U.S., studies suggest that customers would be
willing to pay as much as $10 a month more for more reliable connections, faster download
speeds and a more seamless user experience.
For WSPs, increasing the QoS means ramping up capacity — now. Increasing capacity using
traditional methods of cell densification and the addition of antennas is expensive and time
consuming. The Twin Beam sector-splitting solution is a fast and proven approach to quickly
add capacity at their most critical sites.
Twin Beam enables WSPs to significantly increase capacity without substantially increasing
costs. At the same time, it can improve throughput, allowing customers to take advantage
of faster data speeds throughout more of the network. The result is not only better, faster and
more consistent QoS, but lower churn and greater potential for attracting new revenue from
additional subscribers.
Ultimately, WSPs will succeed by continuing to increase their average revenue per user (ARPU).
Innovative strategies like CommScope’s sector-sculpting Twin Beam should be an important part
of the solutions mix.
12
References
Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update, 2012–2017,
Cisco, Feb. 2013
1
Global Mobile Broadband — The Fast Growth of LTE, Paul Budde Communication Pty Ltd,
March 12, 2013
2
AT&T to Buy Spectrum From Verizon for $1.9 Billion, Scott Moritz and Todd Shields,
Bloomberg, January 25, 2013
3
Managing Wireless Network Capacity, FierceWireless, May 2012
4
Madden: Small cells will carry more capacity than macros, Joe Madden, Fierce Broadband
Wireless, March 27, 2013
5
Smart Cells and Wireless Capacity Growth, Agilent Technologies, Moray Rumney,
May 26, 2010
6
CDMA Six Sector Cell Applications Handbook NBSS 7.0, Nortel, 1998
7
The Impacts of Antenna Azimuth and Tilt Installation Accuracy on UMTS Network Performance,
Esmael Dinan, Ph.D., Aleksey A. Kurochkin, Bechtel Telecommunications Technical Journal,
Vol. 4, No. 1 January 2006
8
Report: Want to Hold on to Subscribers? Show Them ‘More Love’, Andrew Burger,
Telecompetitor.com, 2/22/12
9
www.commscope.com
Visit our website or contact your local CommScope representative for more information.
© 2013 CommScope, Inc. All rights reserved.
All trademarks identified by ® or ™ are registered trademarks or trademarks, respectively, of CommScope, Inc.
This document is for planning purposes only and is not intended to modify or supplement any specifications or warranties relating to CommScope products or services.
WP-106683-EN (05/13)