EBook: Powering Wireless Networks
Powering wireless networks
Contents123Elements of powerTo understand how wireless communication networks are powered, youneed to begin with the basics—which really haven’t changed all that45Introduction3Elements of power4Powering today’s macro site12PowerShift Macro16Powering small cell metro networks20PowerShift Metro24Conclusion28much since Thomas Edison lit up Manhattan’s Financial District (NYC) onSeptember 4, 1882. Sure, we’ve seen a lot of refinements, improvementsand safety measures since then, but the principles of power generation6and distribution still apply.If you want to prepare your networks to meet the power challenges oftomorrow, take a few minutes for this quick refresher on Power 101.Chapter 1: Introduction72
IntroductionPutting power in contextEvery year, our reliance on always-on technology grows. We expect to be ableWhat’s at stake from a business perspective? Plenty. A reliable power infrastructureto place a call or surf the internet with our cell phones at any time, under anyhas significant implications for both cost and revenue. Running power to thousandscircumstances. However, the electrical infrastructure that powers our wirelessof small cells will be expensive. Cutting cost by even a point or two can generatenetworks has not kept pace with the demand for more macro cells and small cells.major savings, as can reducing deployment times by a day or two. On the revenueThe challenge goes deeper than powering additional cell sites. The architectures ofcellular access are changing dramatically. Customer demand is pushing 5G rolloutswhich, in turn, require more RF equipment. Additional radios, more frequencies andside, we know the effect that network outages have on churn rates. With the vastmajority of cell sites relying on older power grids for primary power, the need forreliable backup power is more important than ever.increasing use of remote radio units, plus an entire small cell layer that still needs tobe built out are pushing outdated power systems to the brink.Welcome to the intersection of now and nextTo keep pace with the changes and, more importantly, to satisfy user expectationsof 24/7 availability, mobile operators need to re-evaluate all aspects of their powerinfrastructure. That means taking stock of where we are from a solution standpoint,where we need to be, and developing a cohesive, future-capable strategy to get usfrom here to there.That’s why CommScope has developed this ebook, to help keep you out in front.Here, you’ll find the “what,” “why” and “how” to help guide your power decisionsas you navigate what’s next. We’ve broken it down into easy-to-digest chapters andsections that walk you through the key issues of powering your macro and small cellnetworks. Along the way, we added the CommScope innovations designed to help yourealize the more efficient, future-ready power solutions needed to keep you and yournetworks moving forward.Chapter 1: Introduction3
Elements of powerTo understand how wireless communication networksare powered, you need to begin with the basics—which really haven’t changed all that much sinceThomas Edison lit up Manhattan’s Financial District(NYC) on September 4, 1882. Sure, we’ve seen a lotof refinements, improvements and safety measuressince then, but the principles of power generation anddistribution still apply.Chapter 2: Elements of powerThomas Edison’s Pearl Street Station was the first commercial central powerplant in the United States. It was located in the Financial District of Manhattan(New York City). Fired by coal and powered by six dynamos, it came on lineSeptember 4, 1882 and served an initial load of 400 lamps at 82 customers.4
Electricity generation,transmission and distributionSource: adapted from National EnergyTransformer steps upNeighborhood transformerTransformers on poles stepvoltage for transmissionsteps down voltagedown electricity before itEducation Development Projectenters houses(public domain)Power plantTransmission lines carryDistribution lines carrygenerates electricityelectricity long distanceselectricity to housesThe power generation and distribution chainWhether it’s your home, workplacecurrent (ac). Public power utilities usewhich is designed to handle onlyor wireless network, there’s more toa wide diversity of renewable and non-about 240 volts, the power needs toturning on the power (and keeping itrenewable power sources, includingbe stepped down using a transformer.on) than flipping a switch. A lot more!natural gas, coal, nuclear, solar, waterFinally, a management/control system isDID YOU KNOW?Delivering and maintaining just the rightand wind.needed to ensure the safe and efficientIn the late 1800s, Nikola Tesla was sureamount of electricity needed to powerthe myriad devices we rely on is asThe energy generated must then beavailability and use of power.he could transmit electricity wirelesslyover long distances—either via a series oftransported from the power source toTo take a deeper dive into the powerthe home. That’s where high-powergeneration and distribution chain andstrategically positioned towers (above) orFor example, consider the publictransmission lines (either overhead orsee how they’re being adapted for usesuspended balloons. He obviously failed,power grid that feeds most homesunderground) come in. The copperin outdoor wireless networks, read thebut that’s a story for another time.and businesses. It begins with a powerpower conductors in a high-voltageother chapters in this section.source that generates the raw electricalline carry about 800,000 volts of acpower in the form of alternatingcurrent. So, before it enters the home,complex as it is fascinating.Chapter 2: Elements of power5
Power sources for wireless networksLead-acid batteriesthe volume of a comparable VRLArated length of time. This configurationThese are commonly used as backupsbattery. Unlike VRLA batteries, whichalso provides a convenient means ofWhen the grid isn’t enoughfor telecom power systems. They areare composed of four 12 Vdc batteriesmaintaining the batteries. Often, thesecompact relative to their output and areper string, lithium-ion batteries arestrings will be installed with separateIt’s important to note that, in most cases, outdoor wireless networks use the publicsimilar to the kind you would find underpackaged in a single rack-mounteddisconnection breakers—making itpower grid as their primary source of electricity. Access to power drops is readilythe hood of your car. They are availablemodule that provides –48 Vdc output.easier to locate failures and isolateavailable and the cost per kilowatt is reasonable.in vented and valve-regulated forms.Should an individual module fail, theproblems that could otherwise crippleremaining modules will continue tothe entire system.provide backup power.GeneratorsThe challenge with the public power grid, however, is age and reliability. Each year,power outages affect every city in every country across the globe. When the gridis down, so is everything attached to it, including macro cell sites, small cells andDAS systems. Outages don’t affect just personal and business communications. Theycripple public safety and first responder providers and they affect smart city servicesand a host of other critical applications.Vented (also known as wet orflooded) batteriesVented batteries maintain a charge forup to 20 years or longer. However, theydemand a lot of costly maintenance suchas water treatment, spill containmentSo, while tapping the power grid for your primary source of power is usually fine, it isand forced-air ventilation. Thesenot enough. Provisioning your networks with a safe, reliable and cost-efficient powerdrawbacks make them less suited tobackup system is vital. The following overview highlights some of the most commonremote cell base stations.and emerging technologies for supplying backup power to wireless networks.Valve-regulated lead-acid batteries(VRLAs)VRLAs are recombinant batteries,and DAS networks, where tapping into the power gridmay not be the safest or most cost-effective solution. Wediscuss an alternative solution for those instances later on.Chapter 2: Elements of powerBatteries alone can maintain operationsThese are becoming popular asfor only a few hours. Longer ac servicebackups for telecom power systems.interruptions require a longer-termIn general, NiCad batteries have asolution. Unlike batteries, generatorslower temperature operating rangeprovide power by burning fuel, typicallyand have fewer (or no) battery coolingdiesel. Like batteries, there are differentrequirements, lighter weight andtypes and configurations available.longer life.Which one you install depends onBattery stringsfactors like space, cost and servicePower capacity is directly related to theexpectations.size of the battery; but, rather thanSince they operate outside the cellspending more on larger batteries, westation’s internal dc system, generatorscan achieve the same boost to capacityaren’t considered part of that system.by adding more battery strings inBecause they supply the dc system’sparallel, as opposed to adding themrectifiers with the ac power they need,in series. This safeguards against thehowever, they’re a vital link in assuringfailure of an individual battery, whichreliable operation. In the event theLithium-ion batterieswould remove its string from the systemstation must switch from external powerThese batteries are relatively new foraltogether. By connecting in parallel,to generator-supplied ac power, anwireless telecom applications. Theythe spare capacity is already online andelectrical device called a “transfer switch”are highly compact, about 50 percentready to maintain the current for itsshunts the load to the generator.which means oxygen and hydrogenThere are critical cases, especially with small cell networksNiCad batteriescan recombine to prevent water loss.Because they don’t need added water,they are easier to ship, maintain andinstall, making them the preferredchoice for cell site base station use.6
What about renewables?The international energy agency (IEA) in its latest global energy projection, theWorld Energy Outlook 2018 (WEO2018), has reported that global energy demand isexpected to grow by about 27 percent, or 3,743 million tons oil equivalent worldwidefrom 2017 to 2040.1 At the same time, the annual energy consumption by the mobileindustry has increased from 219 TWh in 2007 to 519 TWh in 2019, and it is speculatedthat the demand will rise at a yearly rate of 10 percent.2 Consequently, the electricitybill of telecom networks globally amounts to above US 10 billion per year.3The importance of estimating future energy requirements and their consequentcarbon emissions cannot be ignored when developing an effective energy policyCurrent statusFuture targetsNetwork operatorRenewable energyutilization (%)Reduction inemissions (%)Renewable energyutilization (%)Reduction inemissions (%)Target yearBaseline yearDeutsche Telecom52%2%100%90%2021 1 , 2030 ble40% 4Not stated50%20302017T-Mobile100%9%Already 100%Not statedN/aN/aVerizonN/a28% 550%50%20252016Virgin Media100%22%Already 100%Not stated20202014Vodafone15%3%Not stated50%202520173Source: Sustainability Journal; 9 Feb. 2021for the future.4 And, in fact, the industry is gradually moving toward the use ofrenewable sources such as wind, water and solar power. The table on the rightshows where the world’s major wireless providers are in their efforts to transition togreener energy and reduce their carbon footprints.To accommodate the shift toward renewables, wireless infrastructure partners havebegun to introduce solutions that enable service providers to integrate alternativeenergy sources into their overall power infrastructure. One such solution is a moreflexible rectifier, discussed in the next chapter.1World Energy Outlook 2018, Aug. 20202Sustainable power supply solutions for off-grid base stations, Energies, Sep. 20153Towards Energy Efficient Load Balancing for Sustainable Green WirelessNetworks Under Optimal Power Supply; IEEE Access, vol. 8, 20204Green energy solutions taking shapeTo meet their ambitious energy greenpeak shaving, MNOs run their macroartificial intelligence to power RRUs upgoals, the world’s cellular networksites via the grid when prices are lowand down based on traffic. This reducesoperators are getting creative in howand switch to battery power duringenergy consumption, thermal loadingthey power their systems.peak rate hours.and their associated costs.In some European countries, forOperators are also employing PIDTo learn more about minimizing powerexample, energy costs vary nsumption with PID controllers,the day depending on supply andcontrollers to boost energy efficiency.download CommScope’s white paper,demand for power. Using strategies likePIDs use special scripting, automation or“Potential energy savings using PID.”Analysis of Renewable Energy Usage by Mobile Data Network Operators; Sustainability Journal; 9 Feb. 2021Chapter 2: Elements of power7
Rectifiers: the ac-dc interfaceac power sourcing flexibilityNearly all modern communication networks (wired and wireless) run on directcurrent (dc) electricity. But, because homes and offices are powered by alternatingcurrent (ac), the electric grid is ac. Rectifiers are used to convert an ac power feed todc. In both macro sites and small cells, the rectifiers’ output is connected to the radioand its transmission equipment—the “load” for the current—as well as the backupWith ever-increasing utility costs, the ability to combine power from renewable sources with utility power is anotheraspect of power flexibility. To address this, some rectifiers can accept ac power from attached solar panels or windturbines just as easily as they can draw it from the utility’s transmission lines.Choosing the right rectifierThe first consideration in deciding which rectifier will best suit a given installation is the kind of ac power it will receive.battery equipment.The rectifier provides enough dc voltage level to maintain the charge in the backupbatteries. This level, called “float voltage,” supplies the equipment load as well as atrickle charge to the battery. In the event of an ac power interruption, the rectifiers goSwitchmode rectifiers are the preferred choice for cell and microwave sites since they can support multiple ac inputsand have a broader operating range—from single-phase to three-phase inputs. This flexibility means fewer rectifiers arerequired—saving money, space and maintenance.off-line and the batteries automatically kick in. When external ac power is restored,the rectifiers re-engage and the batteries return to their trickle-charging state.Multiple rectifier modules are usually required to supply power for the base station’sload. Modules are connected in parallel, enabling them to share an equal part ofthe load. This load sharing allows operators to design in a degree of redundancy toguard against individual rectifier module failures.Batteries– dcUtility gridR– terdcout dcA block diagram of a basic telecommunications power systemChapter 2: Elements of powerTomiscloads dcac 10ac 30LOADSdc fuel cellac or dc generatorPower source flexibility lets rectifiers draw from conventional or renewable sources8
Power distributionThe rectifier is merely the first stage in the power system.Once converted, the power must be distributed to themany component loads within the system. As mentionedabove, these loads include core elements like the radio,transmitter and battery backup, but they can also includesecondary systems like lighting, security networks andHVAC systems. In the most complex installations there maybe so many components that up to 80 circuit breakers arerequired to manage them.Bus bar conductorscorresponding negative lead of theFuses vs. circuit breakersprotection. Fuses are generally used forIn the macro layer, the cell site’sbattery. The battery return bus providesWhile both fuses and breakers providelower loads and offer the advantagesdistribution system is supported by thea common return point for the loadsovercurrent protection, they do it inof lower cost, greater flexibility and fastbus bar conductors, which physicallyconnected to the power system. Thisdifferent ways. Fuses are designed toaction. Circuit breakers are preferredconnect the rectifiers to the batteriescommon point is grounded to provide amelt under unsafe currents—physicallyfor larger loads and do not requireand dc loads. There are two bus barlow-impedance path for transients andbreaking the connection between thereplacement every time they are tripped.connectors: the charge bus and batterynoise and offers a ground reference topower source and the load. Circuitreturn bus.all connected equipment.breakers have internal switches thatSurge protectionThe charge bus is a current-carryingWithin the power distribution systempop to the “off” position under unsafeTypical variations in ac power are notconductor that connects the rectifier’sthere are a number of sub-systemsconditions—again providing a physicalthe only threat to a cell site. Electricaloutput to the battery string. Fordesigned to prevent overloads, over-break in the circuit.events like lightning can also produceinstance, in a –48 V system theheating and other unsafe conditions.Sensitive wireless equipment requiresnegative rectifier lead would terminateThese sub-systems include fuses and“fast blow” fuses or short delayon the charge bus along with thecircuit breakers and surge protectors.curve breakers to provide the neededChapter 2: Elements of powerthese surges on sensitive electronics.An SPD features a non-linear voltagecurrent characteristic that reduces unsafevoltages by increasing the conductedcurrent. In this case, a cell site’s SPDoperates on the same principle as asurge protector does in your home—safeguarding expensive electronics fromlightning-induced surges.excessive voltages and currents—events known as “electrical surges.”Surge protection devices (SPDs) areincorporated to reduce the effects of9
Power safety, maintenanceand managementModern telecommunication power plants are equippedwith electronic monitoring and control systems, generallycalled “controllers.” They keep track of system voltages,currents, temperatures and other key indicators. Theyalso allow operators to make adjustments from a centralmonitoring point—usually on the power plant itself, on thedistribution cabinet or in a rectifier slot.The following are some of the key functions and capabilities that controllers provide:Plant controlThis is useful for maintenance on VRLAin the backup batteries, the controllerthat allow easy disconnection forControl functions are extended frombatteries—equalizing cell voltagecan open additional contacts tomaintenance or replacement. Somethe supervisory panel to control otherwithin a battery string.equalize voltage and close themdisconnects incorporate safety measurespower system components. TheseHigh-voltage shutdown/again when levels equalize. Thissuch as overcurrent fusing or breakers.panels communicate directly withthe rectifiers and, in some cases, cancoordinate the sequenced restart ofovervoltage protection(HSVD/OVP)helps prevent damage to sensitiveelectronics and protect the batteryfrom over-discharging. LVDs alsoall rectifiers to prevent power surgesControllers can automatically shut downenable the operator to prioritize whichduring switchovers from external ac torectifiers when dc output overvoltagecomponents are disconnected, anda backup power source.conditions are detected—avoiding costlyin which order—preserving limitedManual equalizingdamage to load components.function when necessary.Low-voltage disconnect (LVD)Battery disconnectsThis allows a user to engage allrectifiers in equalize mode at once.Chapter 2: Elements of powerIf a low-voltage condition is detectedSwitches installed on a battery string10
Power conversiondc to dc power conversionSince a dc-dc converter system does notflexibility in adopting next-generationsecondary voltages, the need arisesSome wireless sites require multiplehave an associated battery connectedtechnology—offering new services whileto assign numbers to the distributiondc voltage outputs. Installing a secondto its output, it isn’t bound by a batterymaintaining older standards.positions of each voltage. A selectablerectifier plant is one solution, butsystem’s requirement for precise outputvoltage distribution panel makes thisrequires a second battery backup array.voltage. However, since it is necessarilyDisadvantages ofInstead, many operators use a dc-energized by the primary dc powerconverting voltagedc converter that changes a dc inputsystem, that demand must be figuredOn the downside, converting to a givenvoltage to a different dc output voltage.into the power system’s initial design.voltage is inherently less efficient thanThe solution consists of multiple dcAdvantages of converting voltageconverters arranged in parallel and maydrawing that voltage directly from therectifiers, so losses increase as more andfeature many of the same functions asModern dc-dc converters are essentiallymore dc power is converted away fromthe primary dc power system, such as“plug and play” devices designed tothe primary voltage.distribution. It also has dedicated fusesfit in the racks alongside rectifiers andother converters. This approach offersMapping the positionsor circuit breakers isolating it from therest of the system.communications providers the greatestChapter 2: Elements of powerorganization possible.Since a single power plant can generatevarying amounts of both primary and11
Powering today’smacro siteHow your macro site is powered has a lot to sayabout how profitable it is. Site architectures arequickly changing, with more active and passive RFcomponents being moved to the top of the tower.This shift is affecting tower loads and creatingadditional congestion at the top. At the same time,user expectations are increasing as everyoneassumes their mobile service will be available24/7, regardless of the weather or problems withthe local power grid. All of this has an immediateimpact on the network’s bottom line.In this section, we discuss some of the ways yourpower infrastructure can either help or harm yourefforts to improve site efficiency, availability, andyour OpEx and CapEx spend.Chapter 3: Powering Today’s Macro Site12
Power needs move to the topOne of the most significant architectural changes in cell sitedesign has been an explosion in the number of passive andactive RF components at the top of the tower. The maindrivers behind the change are the increasing number ofremote radio heads being deployed and the ramp-updc power plant remotedc inac in–48 Vdcdc outdc loaddc outTypical power feed for a remote radio headof 5G services.Remote radio heads (RRHs) have becometower isn’t feasible because of weatherone of the most important subsystemsrisks, so it must be housed in the shelter,of today’s distributed base stations.far away from the RRH. Therefore, aIn an RRH deployment, the basebandheavier gauge of power transmissionequipment remains on the ground whileline is needed to sustain the voltagethe remote radio head, containing therequired to operate the RRH. This addsbase station’s RF circuitry, analog/digitala significant weight onto the already-and up/down converters, is positionedoverloaded tower.on the tower. This frees up more spacein the base station shelter and reducescooling costs. At the top of the tower,the RRHs make MIMO operation easierand increase base station efficiency.Alternatively, you can convert the powerfeed, based on its voltage drop, to ahigher voltage at ground level to ensurethe correct voltage at the RRH.This wouldenable operators to deliver the rightIn addition to the optical fiberamount of power to the RRHs withoutconnecting it to the base station, the RRHhaving to substantially increase thealso requires a power feed. Herein liesconductor gauge and risk exceeding thethe challenge.tower’s loading capacities. This alternativeEach RRH needs a battery backup toensure operation in case of a powerfailure. Locating the battery on theChapter 3: Powering Today’s Macro Sitehas, in fact, been developed and is beingused successfully. For more, see the nextsection in this ebook on PowerShift.13
Saving space and cost in the shelterWhile relocating the RRH from the base station to the topof the tower saves space inside the shelter, the numberof additional radio units required for today’s advanced5G deployments threatens to outgrow the shelter.Additionally, it compounds the challenge of managing thethermal load inside.An integrated rectifier, dc distribution and controller power systemIn response, infrastructure providers such as CommScopehave developed new, more compact power solutions thatenable operators to save space and cooling costs insidethe shelter.-48 VdcIntegrated power systemssystem contains an integrated dc bus,generally used in cell site applications.To address these space limits,fuses or breakers and cabling tie-downsOnline inverters feature a dc inputCommScope produces integratedto distribute power to the load.and an ac output with an optional acpower systems with several componentsdc-ac invertersstandby line available.Some of the equipment operating atLike dc-dc converters, the input for aa cell site may require ac current fromdc-ac inverter is supplied by the primarybattery backup supplies. Since the entirepower plant. Like converters andsystem is built around DCD-A power, arectifiers, inverters are often installedA typical integrated cell site powerdc-ac inverter is needed to provide theand configured for redundancy. A staticsystem includes one or more shelvesnecessary ac voltage. There are twoswitch maintains equalized voltage toof rectifiers along with one or morebasic types of inverters.the load by switching automaticallybuilt into a single device and suited-48 erter-48 VimacvoltageoutTomiscloadsLOADReturnfor installation in a single rack. Thisapproach is increasingly common inmodern cell sites.shelves of dc-dc converters. Thisintegrates power conversion and powerdistribution functions, connecting themA dc-ac inverter system connected in series to a cell site’s power systemChapter 3: Powering Today’s Macro Sitewith bus conductors. The distributionOffline inverters feature an ac inputand an ac output with a standby dc lineconnection available. This is the typebetween external ac power and theinverter’s ac power. This switching isdone instantaneously—assuring nointerruption in operation.14
Right-sizing the power conductorNominal current discharge characteristic1.5at the cell site are approaching two kilowatts of demand.1.4A key question for network designers is: “How muchcopper is really needed to support the power needs ofVoltageAs wireless networks evolve, dc power consumption levelsthe site? There is no single standard for determining theFully charged voltage1.3Rule of thumbSize the conductors for a five-1.2volt drop when the cell site1.1is on battery (48 volts). WhenEnd of exponential zonethe battery powers the cellEnd of nominal zone0.90to tower-top electronics; so, to make a good selection,Nominal areaExponential area1right size of conductors to use when connecting dc powerDischarge curve12consider the following factors.34Time (hours)site, it will provide 48 volts, so56the tower-top electronics willinitially receive 43 volts andthe tower-top electronics willremain powered until it seesabout 38 volts (which means theVoltage dropbattery starts at 48 volts and will drainthe current for efficiency since theCostDue to the resistance of the cable itself,until the battery disconnect is triggeredrectifiers provide 54 Vdc power to theThe initial cost of the cable andRRUs when primary power is connected.volts). If the conductors are sizedtower-top electronics will always haveor the electronics reach their low-installation should be weighed againstbased on voltages supplied bya lower voltage than the power plantvoltage drop-out value.battery backup time, tower loading,the rectifiers while the primaryor the ground-mounted equipment.Battery backup timeElectrical codespermit costs, etc., in order to select thepower is connected, it is likelyoptimum conductor size.the tower-top electronics willeither drop out when theThe lower the input voltage the higherthe current needs to be to maintain theoutput power level. Voltage delivered atthe tower-top will depend on the powerplant voltage and the size and length ofthe conductors.Design caseThe critical factor when sizingconductors is knowing the voltage ofthe power source when the cell siteswitches to backup battery power. TheChapter 3: Powering Today’s Macro SiteAs the power requirements at the topbattery has drained down to 43Depending on the required cell siteof the tower have increased to 1600 reliability, the battery backup shouldwatts, electrical codes have become aFuture proofinglast until the technician can reachfactor since the amperages in conductorsConsider the site evolution over thethe site and ensure the generator hascan be exceeded. In the U.S., referencenext few years so an upgrade is notsuccessfully started. This can range fromthe latest NEC table 400.5(A)(1) andneeded soon after the cell site cabling isHere are some links to toolsone to eight hours.400.5(A)(3) if using SO type cablescompleted.that will help properly sizePower line lossesand Table 310.15(B)(16) and 310.15(B)Power loss is a function of the cable’sresistance multiplied by the square valueof the current. Use 54 volts to calculatebattery is engaged or there willbe little backup time.conductors.(3) (A). Outside the U.S., reference theapplicable standard for flexible cableampacity.FTTA Power Cal
Provisioning your networks with a safe, reliable and cost-efficient power backup system is vital. The following overview highlights some of the most common and emerging technologies for supplying backup power to wireless networks. There are critical cases, especially with small cell networks and DAS networks, where tapping into the power grid
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