Why Small is the Next Big Thing: A Powerful Toolbox of DAS and Small Cell Power...

Why Small is the Next Big Thing: A Powerful Toolbox of DAS and Small Cell Power Solutions

GECritical Power

2GE Powerful Toolbox | www.gecriticalpower.com

AbstractSmall 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.

IntroductionThe 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 DefinedThere 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


Small Cells – The Next Big ThingSmall cells networks, ranging from femtocells in consumer applications, through pico, metro and micro cells (Figures Two 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

MicrocellCarrier

Network

Internet


Ericsson – The Dot Alcatel – Light Radio Metro Cell – Indoor AT&T Femtocell Alcatel Small Cell Metro Cell – Outdoor

Figure 3 - Small Cell Examples

(*) VDC = volts DC Figure 4 - DAS and Small Cell Power

Powering OptionsTelecommunications engineers can draw on a wide range of power options for small cell and DAS networks, depending on their facilities 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 power from a central source to the remote load

<25.5 W Inexpensive, easy installation, centralized backup

Limited power, not helpful with fiber fed 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 converterRe

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Local PowerPowering a small radio set with uninterruptible power requires a battery backup to power the 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 UPSUPS systems (Figure Five), either AC or DC, can be provided at each remote location.

Remote Power from a Central UPSProvisioning 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


Installation CostsIn 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 CircuitA 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 CircuitsTo achieve a load power greater than 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


Reach CalculationsEach of these powering approaches offers its own set of performance attributes and distance capabilities for individual communications nodes (Figure Nine).

Power Limited Low Voltage CircuitA 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.

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Figure 10 - Remote Power – power limited low voltage DC

Figure 9 - Reach calculations for different wire gages


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Reach CalculationsAll 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 converter that 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


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

For the 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 calculator tool available from the author(s) or your local GE Critical Power sales representative.

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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


volts is recommended for traditional systems

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volts

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gauge

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volts is recommended for traditional systems

volts is recommended for systems with converter boost in the limiter

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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 CalculatorsBelow are screen shots (Figures 16 and 17) of the GE Reach Calculator tools 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).


Hybrid Fiber CableWhen 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 door for 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 CableRugged 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


Cost ConsiderationsIt 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.

SummaryThere are many ways to power DAS and small cell equipment. The main driver for 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 for the 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 PowerAC & 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


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


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)


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 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 volts DC 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)

• 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.

*Registered trademark of the General Electric Company.The GE brand, logo, and lumination are trademarks of the General Electric Company. © 2015 General Electric Company.Information provided is subject to change without notice. All values are design or typical values when measured under laboratory conditions.

DET-831, Rev. 05/2015

GE Critical Power 601 Shiloh Road Plano, TX 75074 +1 888 546 3243 www.gecriticalpower.com

ReferencesPaul Smith

Terrell Moorer

(1) Cisco Systems research report as reported by Gigaom – June 2011 http://gigaom.com/2011/06/01/cisco-wifi-vni-report/

Technical Marketing Manager GE Critical Power

Product Manager GE Critical Power

Why Small is the Next Big Thing: A Powerful Toolbox of DAS and Small Cell Power...

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