1. Why Small is the Next
Big Thing: A Powerful
Toolbox of DAS and Small
Cell Power Solutions
GE
Critical Power
2. 2GE PowerfulToolbox | www.gecriticalpower.com
Abstract
Small cells, ranging from femtocells in
consumer applications, through pico,
metro and micro cells in enterprise, and
urban applications, are revolutionizing
the coverage, capacity and availability
of wireless data services.The insatiable
demand for more and faster data is
driving increasingly rapid deployment
of these small cells in defined high-
traffic, high-cell-use locations. If quality
of service is to be maintained, each
of these cells must be provided with
high quality uninterruptible power.
This paper outlines a diverse toolbox of
power solutions currently available for
these and other applications, including
local alternating current (AC) and direct
current (DC) uninterruptible power
supply (UPS) units and some innovative
remote powering options that provide
significant installation cost savings.
Introduction
The use of wireless data worldwide
is expected to exceed that of wired
data by 2015(1).The traditional macro
cell, installed throughout the United
States on the ubiquitous wireless
tower, is no longer able to support
the additional capacity and coverage
required at these data levels.The use
of small cells and distributed antenna
systems (DAS), which network smaller
communications nodes across a
defined area to fill in the gaps and add
additional capacity to existing high
user density areas, is growing rapidly.
In locations and venues such as
stadiums, resorts, malls, campuses etc.,
there’s a large demand for additional
data capacity and reliable coverage.
These applications are well served by
DAS and small cells, and are becoming
increasingly important as the majority
of wireless traffic is now generated
indoors. Small cells also create a new
level of demand visibility by enabling
location-based applications which can
sense both user presence and location to
customize information and applications.
DAS and Small
Cells Defined
There are many classifications of
small cells and DAS systems, with
varying definitions, but the following
(Figure One) outlines some of the
general classifications, performance
parameters and powering options.
DESCRIPTION # USERS COVERAGE RF POWER POWER OPTIONS
Wi Fi Wireless access point connected
to a wired LAN
<200 <100 ft 20-1,000 mW Small DC Battery Plant, Small AC UPS,
Line Power, Class 2 DC, Power over Ethernet (PoE)
DAS High power, multi frequency active
antenna system fed by a macro
base station
<1,800 1,000s of ft <10 W Small DC Battery Plant, Small AC UPS,
Line Power, Class 2 DC, PoE
Femtocell Cellular base station typically used for
a home or small business
4-6 <50 ft 10-100 mW Small DC Battery Plant, Small AC UPS,
Line Power, Class 2 DC, PoE
Picocell Cellular base station typically used for
an office building, airport or mall
32 10s of ft 100-250 mW Small DC Battery Plant, Small AC UPS,
Line Power, Class 2 DC, PoE
Metrocell High capacity, low power cellular
base station that fills coverage holes
within buildings
16-32 10s to 100s of ft 500mW-2 W Small DC Battery Plant, Small AC UPS,
Line Power, Class 2 DC
Microcell Short range base station for improving
indoor / outdoor coverage
32-200 100s of ft 5-10 W Small DC Battery Plant, Line Power,
Class 2 DC, AC UPS
Macrocell High power base station for coverage
areas from several city blocks to
several miles
<1,800 miles >10 W Medium - Large DC Battery Plant
Sources: AT&T 2011, Nokia Siemens Networks 2012
Figure 1 - Wireless Data Options
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Small Cells – The Next Big Thing
Small cells networks, ranging from femtocells in consumer applications, through pico, metro and micro cells (FiguresTwo and
Three) in enterprise and urban applications, are dramatically improving wireless data coverage, capacity and availability.
Figure 2 - DAS and Small Cell Network
Macrocell
Femtocell
Picocell
DAS System
Microcell
Carrier
Network
Internet
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Ericsson – The Dot Alcatel – Light Radio Metro Cell – Indoor AT&TFemtocell Alcatel Small Cell Metro Cell – Outdoor
Figure 3 - Small Cell Examples
(*) VDC = volts DC
Figure 4 - DAS and Small Cell Power
Powering Options
Telecommunications engineers can draw on a wide range of power options for small cell and
DAS networks, depending on theirfacilities and requirements (Figure Four).
DESCRIPTION POWER LEVEL ADVANTAGES DISADVANTAGES
AC UPS An uninterruptible AC power
source co-located with each
remote load
No practical
limit
Efficient, independent sizing
of reserve
High cost of equipment,
supplying utility power at
multiple locations
DC UPS
(DC Battery Plant)
An uninterruptible DC power source
co-located with each remote load
No practical
limit
Efficient, independent sizing
of reserve
High cost of equipment,
supplying utility power at
multiple locations
PoE Power over Ethernet – uses the
Category (Cat) 5 data cable to carry
powerfrom a central source to the
remote load
<25.5 W Inexpensive, easy installation,
centralized backup
Limited power, not helpful
with fiberfed data
Power Express
(Class 2 48 VDC*)
Limited power low voltage DC fed
to the remote load from a central
location
<100 W per
circuit
Can be installed without conduit,
low cost, centralized backup
Limited power
Power Express Plus
(Class 2 58 VDC)
Limited power low voltage DC fed
to the remote load from a central
location
<100 W per
circuit
Can be installed without conduit,
low cost, centralized backup
Limited power
Line Power
(±190 VDC)
Limited power, medium (±190 V)
voltage DC fed to the remote load
from a central location
<100 W per
circuit
Long reach, low cost,
centralized backup
Limited power, needs
downstream converter
RemotePowerfromaCentralLocationLocalPower
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Local Power
Powering a small radio set with uninterruptible power requires a battery backup to powerthe network during utility interruptions.
The remote radio heads typically used by DAS or small cell architectures can be AC, (110/240 volts), or DC,
(-48 volts), powered. Local power requires the provision of an AC outlet and a suitable uninterruptible power supply (UPS).
Small UPS
UPS systems (Figure Five), either AC or DC, can be provided at each remote location.
Remote Power from a Central UPS
Provisioning of a larger UPS to power many remote radios from a central location (Figure Six) offers many advantages including
reduced maintenance and replacement costs associated with multiple battery locations.This applies to AC or DC UPS systems.
Figure 5 - Local Power / Small UPS
Figure 6 - Remote Power / Larger AC and DC UPS
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Installation Costs
In the case of unprotected AC and DC wiring, local codes and the National Electric Code (NEC) require all power wiring to be
installed in conduit.This can be a labor intensive and costly process. NEC requirements also apply to local powering, where both
AC and DC UPS units require an AC power source at each remote location. In certain power-limited cases NEC installation
standards allow non-conduit deployments to be used.
Power Limited High Voltage DC Circuit
A power delivery infrastructure using high voltage DC (+/-190 volts) with a 100 volt-amperes (VA) power limit per circuit
(Figure Seven) can be installed using an appropriate cable, without the use of a protective conduit. As most remote radios do
not accept +/-190 volts DC directly, a down converter is used.The use of high voltage allows the delivery of power over greater
distances with smaller cables.
Parallel Circuits
To achieve a load power greaterthan 100 VA, multiple circuits also can be combined.The use of a power combiner can
be used to bundle circuits to provide adequate and NEC-compliance power (Figure Eight). Again, each circuit can use heavier gage
wire or multiple conductors to achieve a greater reach.
Figure 7 - Remote Power / Power Limited high voltage DC
Figure 8 - Parallel circuits – Multiple 100 VA limited high voltage DC circuits
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Reach Calculations
Each of these powering approaches offers its own set of performance attributes and distance capabilities for individual
communications nodes (Figure Nine).
Power Limited Low Voltage Circuit
A power delivery infrastructure using low voltage DC (-48 volts) with a 100 VA power limit per circuit also can be
installed using an appropriate cable, without the use of a protective conduit (Figure 10). Because many remote radios can accept
-48 volts DC directly, a down converter is not needed.This power delivery infrastructure is called a Class 2 power limited circuit for
National Electric Code.
100
90
80
70
60
50
40
30
20
10
0
0 .62 3.10 6.2 9.3 12.45
Distance (Miles)
Powerdeliveredtoloadper100Wconverter
3x22 AWG
2x22 AWG
20 AWG
22 AWG
24 AWG
26 AWG
Figure 10 - Remote Power – power limited low voltage DC
Figure 9 - Reach calculations for different wire gages
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100
90
80
70
60
50
40
30
20
10
0
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Distance (Feet)
Minimum Battery Voltage 42 V
Minimum Load Voltage 36 V
PowerdeliveredtoLoad(Watts)
12 AWG
14 AWG
16 AWG
18 AWG
20 AWG
Reach Calculations
All power delivery infrastructures using copper wire are subject to Ohm’s Law.The amount of power available to each circuit
is limited to 100 VA due to safety mandates. Losses in the cable will ensure that 100 VA or less always
reaches the far end (Figure 11).
If we can boost the voltage of the limiter input so that it is a constant higher voltage even during battery discharge, the reach
calculations can be performed at this higher voltage and the reach extended.This is easily done with a DC to DC converterthat can
operate at inputs down to 42 volts and provide a constant output voltage (Figure 12). The output voltage is typically chosen to be
57 volts DC, which gives a marked improvement in reach while still providing a margin of safety below the maximum SELV voltage
of 60 volts DC (Figures 13 and 14).
Figure 11 - Reach calculations – Power Limited low voltage DC
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Figure 12 - Single circuit – Power limited low voltage DC with DC boost converter
Figure 13 - Reach calculations – Power limited low voltage DC with boost converter
Forthe 12 American Wire Gage (AWG) wire with a 50 W (36 volts) load, the reach using 42 volt battery voltage is 1,263 feet.
Using the 57 V converter boosted voltage, the reach is 4,421 feet, an increase of 250 percent.
To compare the reach of a 12 AWG cable with and without the voltage booster, see Figure 14.
The results plotted in Figures 12 and 13 are calculated by the GE Power Express calculatortool available from the author(s) or your
local GE Critical Power sales representative.
100
90
80
70
60
50
40
30
20
10
0
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Distance (Feet)
Minimum Battery Voltage 57 V
Minimum Load Voltage 36 V
PowerdeliveredtoLoad(Watts)
12 AWG
14 AWG
16 AWG
18 AWG
20 AWG
10. 10GE PowerfulToolbox | www.gecriticalpower.com
100
90
80
70
60
50
40
30
20
10
0
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Distance (Feet)
PowerdeliveredtoLoad(Watts)
12 AWG
with voltage
booster
12 AWG
without voltage
booster
0 100 200 300 400 500 600 700 800 900 1000
Distance (Feet)
Minimum Battery Voltage 42 V
Minimum Load Voltage 36 V
1600
1400
1200
1000
800
600
400
200
0
PowerdeliveredtoLoad(Watts)
2 AWG
6 AWG
8 AWG
10 AWG
12 AWG
0 100 200 300 400 500 600 700 800 900 1000
Distance (Feet)
1600
1400
1200
1000
800
600
400
200
0
PowerdeliveredtoLoad(Watts)
2 AWG
6 AWG
8 AWG
10 AWG
12 AWG
Minimum Battery Voltage 57 V
Minimum Load Voltage 36 V
Figure 14 - Reach calculations – Power limited low voltage DC with and without boost converter
Figure 15 - Reach calculations / Secondary low voltage DC with various wire gages
Several DAS system manufacturers are now using remote radios that require more than 100 W of input power. These cannot be
used with Class 2 circuits because of the power limitation.
If we remove the power limiter, the low voltage circuit can be used to power larger loads or span longer distances. However, NEC
now mandates that the circuit must be protected by running it in a conduit.This increases installation costs, but may be needed if
the user must power larger loads and does not want to take the multi-circuit high voltage route.
Class 2 circuits are limited to 12 AWG cables by the NEC.This limitation does not apply to unlimited or Secondary circuits, so larger
wire gages are presented in the reach graph of Figure 15, which also compares the reach with and without the boost converter
option. The boost converter can be seen to more than double the reach of each circuit type at a given power level.
Larger Loads - Non-Power Limited Low Voltage Circuits
11. 11GE PowerfulToolbox | www.gecriticalpower.com
volts is recommended for traditional systems
v
volts is recommended for systems with a converter boost in the limiter
volts
volts
watts
gauge
volts amp limit
volts is recommended for traditional systems
volts is recommended for systems with converter boost in the limiter
volts
volts
watts
gauge
volts amp limit
amp
amp
volts
volts
watts
gauge
volts amp limit
amp
amp
Secondary Circuit Reach Calculator
Figure 16 - Reach Calculator / Power express plus Class 2 circuits
Figure 17 - Reach Calculator / Secondary circuits
(*) VDC = volts DC
Figure 18 -Typical remote DC power requirements
The following chart (Figure 18) details the input voltage range and input power ranges, and the reach for both Class 2 and
Secondary circuits.
INPUT VOLTAGE RANGE INPUT POWER REACH (CLASS 2) REACH (SECONDARY)
Low Power 1 38-60 VDC* 38-60 VDC* 1,071 ft. 12 AWG 2,455 ft. 12 AWG
Low Power 2 38-60 VDC 38-60 VDC 1,683 ft. 12 AWG 2,639 ft. 12 AWG
Med Power 1 36-75 VDC 36-75 VDC - 1,597 ft. 8 AWG
Med Power 2 36-75 VDC 36-75 VDC - 1,118 ft. 8 AWG
High Power 1 21-60 VDC 21-60 VDC - 508 ft. 8 AWG
High Power 2 21-60 VDC 21-60 VDC - 120 ft. 8 AWG
Tools – Reach Calculators
Below are screen shots (Figures 16 and 17) of the GE Reach Calculatortools for Class 2 and Secondary circuits for some
typical loads and applications. In both illustrations, the use of the voltage booster is assumed (57 volts minimum input).
12. 12GE PowerfulToolbox | www.gecriticalpower.com
Hybrid Fiber Cable
When the power circuit, such as a Class
2 circuit, does not need to be installed
in a conduit, as is the case when the
circuit is power limited (100 VA), this
opens the doorfor routing the power
cables in the same raceway as the fiber
cable. In fact, fiber optic cables are now
available with built-in power conductors,
referred to as hybrid fiber cable. This
means that both power and fiber
can be installed in a single operation,
connecting each remote to the central
communications and power location.
These cables can be used with high or
low voltage, power limited power circuits
and are available with differing fiber
types, counts and copper wire gages
as shown in the example data sheet in
Figure 19.
Copper/Fiber
Composite Cable
Rugged easy to use composite
cable consisting of flexible stranded
Copper conductors and integrating
communications links utilizing fiber
optic technologies.The breakout
design provides additional protection
from both the copper and fiber
channels by individually protecting
each with insulated jackets and
all-dielectric strength members.
For applications requiring remote
low-voltage power and high speed
communications, these designs
provide an efficient single-installation
option where space is of a premium
and devices are not easily accessed.
Applications
• Remote application of
low-voltage power
• Security networks
• IP enable appliances
• Wireless Access Points
Features
• Rugged riser rated constructions
• Water-blocked
• Flexible stranded Copper
(12 AWG, 14 AWG, 16 AWG,
18 AWG available)
• High-speed fiber optics
• UL 13, UL1666 rated
• NEC 725 classified
• CL2R-OF classified
Figure 19 - Example Hybrid Fiber Cable
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Cost Considerations
It is important to understand all the
factors that affect the cost of a remote
power installation. The initial cost of
equipment and installation are key
parts of this equation, but the cost
of operating and maintaining the
installation are equally important.
• Materials
-- In a centralized power scenario we
use a larger power plant and batteries
in place of many small plants. In this
case the larger power plant is typically
more cost effective. Some of this cost
advantage will be offset by the cost
of power limiters if these are used to
provide Class 2 protected circuits.
-- Materials used to connect the power
to the remotes will also vary. The cost
of conduit material can be eliminated
by the use of Class 2 power circuits.
• Installation
-- Installation costs are dramatically
affected by the specifics of a DAS
configuration. However, one of
the most significant parts of the
installation cost can be power.
Providing an AC drop (typically with
¾” conduit) to each remote location
can be very costly when there are
many remotes.
-- Typical job estimates show that the
cost of running power cable in conduit
can be three to four times the cost of
installing a Class 2 cable. With a DAS
system consisting of 50 remotes, each
requiring an average of 200 feet of
cabling, this difference is significant.
-- The remote will always require the
installation of a fiber optic cable for
data communications, so the use of a
hybrid fiber cable will not impact the
cost of installing that fiber if a Class 2
circuit protector is used. In this case,
power installation is “free” because
it costs no more to install the hybrid
fiber cable. The cost of a hybrid fiber
cable will be higher from a material
standpoint, but probably no more
than the combined cost of individual
fiber and copper cables.
• Operation
-- Operational costs of each powering
scenario are similar, since the power
used by the remote does not vary
significantly, whether it’s AC or DC.
• Maintenance
-- Maintenance costs are difficult to
quantify; each operator and situation
will require different maintenance.
However, maintenance of many
small battery installations will be
much more difficult and costly than
maintaining a single, large, centralized
battery system.
Summary
There are many ways to power DAS
and small cell equipment. The main
driverfor alternatives to a UPS for
each and every remote location is the
sheer number of systems required –
and the costs incurred in installation,
operation and maintenance. When
the required user experience dictates
the use of UPS unites, elimination
of the costs associated with battery
proliferation is a key consideration.
Each of the powering scenarios
discussed has advantages and
disadvantages, and the user must
decide which is most appropriate forthe
particular installation. See Figure 20 for
an abbreviated summary of these factors
for each of the scenarios discussed.
Conduit
Installation
50 x 200 ft.
= 10,000 ft.
Est.
$11 / ft.
Total
$110,000
Class 2 cable
installation
50 x 200 ft.
= 10,000 ft.
Est.
$3 / ft.
Total
$30,000
Clearly, Class 2 cable is significantly
less expensive to install.
BAT-
TERY
CON-
DUIT
REACH MAX PWR COST PROS CONS
Local Power
AC & DC UPS
Many AC N/A AC Circuit
Limited
5 Simple architecture, reserve
can be specific to remote unit
High cost, battery proliferation,
voltage drop for each remote
Line Power
(±190 VDC*)
Central 1 None Long
(miles)
100 VA /
cct.
4 Single battery location, low cost
cable and installation, combine
circuits for additional power
Converters at both ends
of span
Power Express
(Class 2, 48 VDC)
Central 1 None Medium
(Kft)
100 VA /
cct.
2 Single battery location, low cost
cable and installation, limiter
only at source, no converters
Limited reach, cannot
parallel circuits for
additional remote power
Power Express Plus
(Class 2, 57 VDC)
Central 1 DC Medium
(100’s ft)
Limited
by Ohm’s
Law
4 Single battery location, higher
power at remote, low cost
cable and installation, combine
circuits for additional power
Larger cables, conduit
installation cost
Low voltage Remote
(Secondary, 57 VDC)
Central 1 DC Medium
(100’s ft)
Limited
by Ohm’s
Law
4 Single battery location, Higher
Power at remote
Larger cables, conduit
installation cost
PoE Central 1 None Medium
(100’s ft)
25 W 2 Simple, plug and play, uses
existing Cat 5 cable
Low power only, limited reach
(*) VDC = volts DC
Figure 20 - Power scenario summary table
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Line Power – High voltage (±190 volts DC)
Power limited converters
Upstream
Downstream
• 16 Converter cards with 2 circuits
each totaling (32) circuits.
• Combined converter/limiter function
in one unit
• Dimensions are 3.5 in.
(H) x 12 in. (D) x 23 in. (W)
• Dimensions are 88.9mm
(H) x 305mm (D) x 584mm (W)
• Vertical Airflow
• No exposure of high voltage
• Optional Ethernet/TCP-IP from
CPS3200U with fan shelf
controller – QS941
• Twenty 100 VA input channels
• Wide operating temperature range
(-40 to +75 C)
• 1RU height, 10.63” width with
brackets for rack mounting
• Input current limit circuits prevents
overloading of upstream source
• Intuitive front panel power and alarm
status LEDs
• Two Form-C power alarm relays
• Fully modular with no wiring to
converter units
• Vertical airflow
• No exposure of high voltage
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Power Express – Low voltage power limiter
for Class 2 applications
• 19” rack mount shelf
• 1RU height
• 11.25” depth
• 32 circuits in 4 plug-in modules
• -40 C to +45 C operating
temperature range
• -40 VDC to -60 volts DC input
voltage range
• Shelf heat dissipation 227 BTU
max (56.75 BTU per module)
• Input Terminals
-- Two-hole lugs bulk dc power inputs
(left side of picture above)
-- 1/4 in. holes on 5/8 in. spacing
• Output Terminals
-- 32 spring cage connectors for quick
and easy installation
-- Will accommodate 12 AWG cables for
delivering Class 2 power circuits
• Alarm Terminals
-- Three wire connection
(NO, NC, Common)
-- Screw terminal
(no special connectors)
• Inter-Shelf Communications
-- RJ-45 connections for RS485
communications bus (upstream
controller interface for future use)
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CPL DC/DC Converters – Voltage booster for low
voltage remote application
• 19 in. Rack Mount Shelf
• 1RU Height
• 11.25 in. depth
• 8000 watts output per shelf
• -40 C to +75 C operating temperature
range
• -40 VDC to -72 volts DC input voltage
range
• - 44 VDC to -58 volts DC output
voltage range
• Shelf heat dissipation 3,032 BTU Max
(758 BTU per module)
Power Express Plus – Low voltage power
limiter for Class 2 applications with built in voltage booster
• 19 in. rack mount shelf
• 1RU Height
• 11.25 in. depth
• 32 circuits in 4 plug in modules
• -40 C to +45 C operating temperature
range
• -40 volts DC to -60 volts DC input
voltage range
• Shelf heat dissipation 227 BTU max
(56.75 BTU per module)
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• Input Terminals
-- Two-hole lugs bulk DC power inputs
(left side of picture above)
-- 1/4 in holes on 5/8 in spacing
• Output Terminals
-- 32 spring cage connectors for quick
and easy installation
-- Will accommodate 12 AWG cables for
delivering Class 2 power circuits
• Alarm terminals
-- Three wire connection
(NO, NC, Common)
-- Screw terminal
(no special connectors)
• Inter-Shelf Communications
-- RJ-45 connections for RS485
communications bus (upstream
controller interface for future use)
• Reach can be calculated based on
minimum voltage of 57.0 volts DC
Power Express Plus – Advantages
1. Modular (8 circuit) construction, reduces initial cost
2. Poke and place wire attachment – simplified installation
3. Boost converter included in module – 1RU total rack height
4. Dramatically extended reach (2-3X) because of 57 volts DC converter
5. Fixed limiter operation – not subject to installer error in fuse size.