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Reducing pullution costs in cellular networks (visit http://trends-in-telecoms.blogspot.com for more insights)

Reducing pullution costs in cellular networks (visit http://trends-in-telecoms.blogspot.com for more insights)






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    Reducing pullution costs in cellular networks (visit http://trends-in-telecoms.blogspot.com for more insights) Reducing pullution costs in cellular networks (visit http://trends-in-telecoms.blogspot.com for more insights) Document Transcript

    • C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® ENERGY EFFICIENCY IN COMMUNICATIONS Reducing Costs and Pollution in Cellular Networks Vincenzo Mancuso and Sara Alouf, INRIA Sophia Antipolis Méditerranée ABSTRACT diture. However, the availability of next genera- tion wideband and reliable cellular networks Cellular wireless networks are expected to (e.g., LTE and HSPA [1]) can help reduce the provide high-quality audio and video services GHG footprint by reducing the need for travel- while enabling fast and low-cost Internet access ing and printing documents, as emerged in a to mobile users. The need for green cost-efficient recent study by the Australian operator Telstra. networks is twofold: reduce the service price and To give an idea of the actual energy and pol- preserve the environment. In this work, we dis- lution cost induced by a base station, consider cuss the various strategies that help reduce infra- that most of the operating base stations continu- structure costs, power costs, and greenhouse gas ously consume at least 2 kW, mainly generated (GHG) emissions with no impairments on the by means of fossil fuels, and hence produce as quality of network services. These strategies much CO2 as a few automobiles in their average range over a wide area from enhancing the elec- utilization cycle. New generation base stations tronics, to developing new energy-aware radio reduce their consumption to typically 800 W for access protocols, to deploying enhanced base second-generation (2G) systems (GSM), and as stations with tunable capacity. To reduce both low as 430 W for 3G systems (UMTS). Manufac- capital and operational expenditures, and the turers are further targeting to halve the power GHG footprint, manufacturers propose new consumption of their base stations in two years, compact installation with lightweight antenna and to lower the environmental impact by allow- systems, very efficient power amplifiers, and effi- ing network operators to deploy cheaper multi- cient hardware and software. The resulting econ- technology sites. Manufacturers particularly omy can be up to 50 percent or more by reducing focus on new base station design, which would the electricity bill, sparing the use of air condi- reduce capital expenditures (CAPEX) and oper- tioning, and deploying compact sites that would ational expenditures (OPEX). To achieve this seldom require maintenance. Recent scientific goal, manufacturers and operators point at opti- publications confirm that a very high gain could mizing the architecture of the site and using be achieved by optimizing the use of base sta- renewable energies, improving the power effi- tions proactively, and huge additional improve- ciency of the hardware, and deploying smart ments could be obtained by optimizing power resource management tools that activate net- saving mechanisms by leveraging traffic statistics. work resources only when needed. Site design is fundamental for efficient usage INTRODUCTION of energy. For instance, flexible and lightweight sites could be better located to provide uniform Wireless communications are expected to be the coverage with no need for high transmission major worldwide cause of energy consumption power. Most important, site design is responsible within a few years, with a devastating impact in for minimizing ownership and management terms of pollution and energy waste. The high costs, and reducing the need for energy-hungry power needed for operating wireless devices air conditioning. Clearly, site design depends on causes huge greenhouse gas (GHG) emissions in the availability of more efficient, compact, and the atmosphere, while the portion of energy low-power-consuming electronic devices. A sub- actually traveling on the communication media is stantial reduction of the power needed to oper- one or two orders of magnitude smaller than the ate a base station also significantly helps the energy consumed by the overall system. Jointly deployment of sites totally or partially operated with the environmental impact of new wireless by means of renewable energies (e.g., solar pan- devices (e.g., new towers and base station sites), els, bio-fuels, and eolic turbines), as reported, the highly inefficient use of power might become for example, by Huawei and Ericsson. a serious menace for the environment. In partic- In terms of hardware improvements, manu- ular, base stations cause more than 80 percent of facturers are replacing existing power amplifiers the operator’s power consumption, which makes with new efficient devices using digital predistor- the design of base stations a key element for tion (DPD) or envelope tracking for wideband determining both the environmental impact of signals. Noticeably, using these efficient power wireless networking and the operational expen- amplifiers allow the deployment of new compact IEEE Communications Magazine • August 2011 0163-6804/11/$25.00 © 2011 IEEE 63C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND®
    • C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® sites, which can be operated with half the power and operation. We illustrate how green compo- A contribution to or less. nents have been introduced in the design of the Finally, operators are developing new man- core network and base station sites (possibly tar- green networking agement tools to reduce the amount of devices geting renewable power sources), in the adop- comes from the operating with low or zero load, which has been tion of efficient hardware, in the responsible use simplification of the shown to be almost as expensive as running at of packaging and energy, and in the introduction full capacity [2], say, by switching off unloaded of power saving features in resource manage- core network, base stations overnight, while avoiding coverage ment. and from the and capacity degradation. Operators like Huawai claim that using radio and computational CORE NETWORK RATIONALIZATION optimization of the resources efficiently might easily turn into a 40 A contribution to green networking comes from efficiency of percent drop in operational costs. the simplification of the core network, and from soft switches Recent scientific publications confirm that the optimization of the efficiency of soft switches power save and quality of service enhancements through which data streams are routed and con- through which data are not conflicting objectives for wireless network trolled. For instance, since 2007, the Australian streams are routed design. Power save modes and operational costs operator Telstra and Ericsson have been devel- optimization have been studied by means of ana- oping an efficient, compact, high-capacity mobile and controlled. lytical models and simulations. Sleep mode has soft switch server to simplify the mobile network. been proposed as an interesting solution for low The new soft switch comes with blade technology loaded transmitters, and it has been analytically (i.e., using electronic boards or blades), which is shown that optimal sleep periods can be selected highly modular and reduces the energy use of as a function of the statistical distribution of the the soft switch by up to 60 percent per sub- packet arrival over the wireless interface [3, 4]. scriber. This innovative mobile soft switch is suit- Optimization is carried out in terms of cost able for both GSM and UMTS networks, and reduction subject to quality of service constraints supports up to eight million subscribers with such as the average or maximum tolerable packet only two equipment shelves. Interestingly, not delivery time. The results of [3] can be used to only does the new technology allow the deploy- design the behavior of an on/off base station dur- ment of fewer soft switches (75 percent less) to ing time intervals in which the expected traffic is satisfy the traffic demand, but also each new stationary and data bursts can be modeled as mobile soft switch is easy to upgrade and exhibits memoryless arrivals. In case of more general traf- a GHG footprint as little as 10 percent that of fic patterns, dynamic programming has been used existing servers. Telstra is planning to replace by to characterize the optimal sleeping interval at 2010 the 18 current regional mobile soft switch each sleep mode activation epoch [4]. Joint radio servers spread across Australia by one mobile resource management strategies have been pro- soft switch server cluster using blade technology posed for the cooperation between GSM and (deployed at two sites for redundancy and UMTS systems on the same base station. The dependability issues). This rationalization should analytical study in [5] illustrates benefits offered reduce equipment floor space by 85 percent, cut by the cooperation of 2G and 3G systems. In par- energy use by 75 percent, and proportionately ticular, intertechnology handover (i.e., from 2G reduce the GHG footprint. Similarly, Huawei to 3G and vice versa) enables a substantial reduc- reports that its large-capacity mobile soft switch tion of the system blocking probability at no server uses a platform, named ATAE, that additional cost, with no need for increasing the enables a pool technique with results similar to capacity of the network. Furthermore, the deci- the Telstra case, and has brought an overall cost sion for a user to select one of the available radio reduction of 80 percent for the Sichuan mobile systems can be performed subject to congestion network in China. control and energy aware mechanisms, with the interesting conclusion that, under low load condi- GREEN BASE STATION SITES tions, the higher gain is obtained by letting all Here we show three different examples of site users use one technology only and putting in design, each targeting — for different environ- sleep mode the base station components operat- ments — low GHG footprint and low installa- ing on other technology. Also, standardization tion, operational, and maintenance costs. Then bodies like the Third Generation Partnership we discuss the utilization of renewable energy. Project (3GPP) have started to provide operators with suitable tools to implement power saving OPTIMIZED DESIGN mechanisms, such as continuous packet connec- The Tower Tube — The target of Ericsson’s tivity (CPC) for always on customers using high- introduction of a new radio base station site con- speed data connections [6]. cept, Tower Tube, is threefold: reducing pollu- The survey is organized as follows. We illus- tion causes, making the wireless network more trate the green strategies adopted by vendors cost efficient, and allowing the integration of the and operators. We introduce the architecture of site with the surrounding environment. Tower the newest base stations. We give insights on the Tube has a modern design for a 5-m-diameter, operational costs and energy consumption of a 40-m-high flexible concrete tower encapsulating base station. We conclude the survey. all radio base station equipment and antennas. The concrete itself has a lower environmental impact than traditional steel, producing 30 per- GREEN DEPLOYMENT STRATEGIES cent less CO2 emissions during production and In this section, we focus on the strategies that transportation. Unlike commonly adopted sites, aim at reducing operators’ costs and environ- the network equipment is installed at the bottom mental impact due to base station deployment of the site, and then rised by means of an elava- 64 IEEE Communications Magazine • August 2011C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND®
    • C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® tor to the top of the tower, next to the antennas. The advantages of this choice are particularly evident in the reduced loss in the feeder between Fixed input voltage the radio frequency (RF) unit and the antenna, OFDM signal and in the possibility to exploit the wind as a passive cooling system. Energy saving can be quantified in a 40 percent reduction of opera- tional costs. Additionally, since Tower Tube occupies 60–75 percent less space than conven- tional sites, site acquisition is cheaper, which means, lower capital expenditures are required. Even lower operational costs are possible with the wind-powered version of the Tower Tube, endowed with five-meter blades and a vertical rotor. Power dissipated as heat The Capsule Site — Finding new locations for radio base stations is challenging, especially in urban and suburban areas, where obtaining building permit for a base station might require Figure 1. 1024-subcarrier OFDM signal amplified with constant input voltage the design of an unobtrusive site, or also the supply. The power dissipated as heat is huge due to the difference between the integration of the site as a new landmark in the signal envelope and the voltage supply level. surroundings. The Ericsson Capsule Site is an example of base station site design for easy deployment in urban areas. The Capsule Site is In 2008, the GSM Association (GSMA), the an all-in-one solution encapsulating all necessary association gathering nearly 800 worldwide equipments. The site cover is made of compos- mobile operators, launched a plan for deploying ite, weighs 800 kg, and can be delivered and renewable energy sources for 118,000 new and installed in less than a day. existing base stations in developing countries by 2012. The expected green gain is to save 2.5 bil- The Flexi Base Station — An example of effi- lion liters of diesel and cut CO2 emission up to cient site design and management is the Flexi 6.3 million tons per year. Solar energy solutions base station by Nokia Siemens Networks. The have been proposed since 2000, at least to oper- benefits are as follows: ate in conjunction with diesel generators. Erics- • Reduce site energy costs up to 70 percent son and Alcatel-Lucent, among other companies, • Reduce size and weight of network equip- have proposed solar-powered base stations for ment by 80 percent macro-coverage and low capacity, useful for • Allow flexible location (i.e., indoor and out- rural or low-density areas. door) with no need for air conditioning Although the 100 percent-solar-powered solu- • Shorten antenna feeders tion is in the target, and operators like Orange • Make new sites ready for future radio tech- Guinea targeted at having more than one thou- nologies sand 100 percent-solar-powered base stations by The Flexi base station GHG footprint is further the end of 2009, many installations are still diminished by its software-based capacity and hybrid, using solar panels and batteries to capability upgrades. In fact, Flexi base stations replace only one out of the two diesel generators can be remotely managed, in terms of tuning the usually deployed. Nevertheless, the gain is high, running capacity (i.e., the number of GSM fre- since a typical site consumes approximately quencies in use), and also remotely upgraded, 20,000 liters of diesel per year, which can be canceling the need for site visits. The Flexi base effectively halved by means of solar panels and station is also ready for using renewable energy batteries. Further gain can be obtained by com- such as solar or wind power. bining multiple renewable power sources in the same site. By using solar and wind power, plus Renewable Power Sources — Considering an auxiliary diesel generator, African operator the demand for new base station installations in Zain has deployed a site in Dertu, a remote vil- many regions where an efficient power grid is lage in Kenya. The operational cost due to elec- not yet available (or where a power grid does tricity has been reduced by 80 percent for that not exist at all), the possibility to operate wire- site, compared with using diesel generators only. less base stations relies on the use of local power generators. In the past, power generators have ENERGY-EFFICIENT POWER AMPLIFIERS been using diesel engines, while the current Next generation cellular networks will make a trend is towards the replacement of diesel with large use of non-constant envelope signals. In bio-fuels, and traditional generators with solar- particular, the widely accepted adoption of or wind-powered generators. Unfortunately, a orthogonal frequency-division multiple access complete replacement is not possible in short (OFDMA) systems will challenge the manufac- terms, since many old installations require way turers to design more efficient and accurate too much energy to be reliably supplied by wideband orthogonal frequency-division multi- means of renewable sources. Hence, a consump- plexing (OFDM) modulators. In an N-subcarrier tion reduction strategy is strictly necessary to OFDM, the transmit power is evenly spread over enable the deployment of renewable energy- the subcarriers, and the peak-to-average power powered base stations. ratio (i.e., the ratio between the maximum IEEE Communications Magazine • August 2011 65C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND®
    • C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® ing in Class C, provides additional power when Variable input the carrier enters its nonlinear region. While several academic papers have quoted impressive- OFDM signal Voltage ly high efficiency capabilities for Doherty ampli- fiers [8], in practice, at the frequencies and with the high output power, which are used in cellular networks, the typical efficiency achieved is around 25 percent to 30 percent [10]. Doherty amplifiers have a limited bandwidth due to the complicated and essentially narrow-band match- ing required between the two internal amplifiers. However, the bandwidth available (few MHz) is adequate enough for cellular systems. Huawei, the Chinese telecom equipment provider, has launched a low-power base station adopting DPD and Doherty technologies. In Power dissipated as heat terms of energy, this base station can be run with as low as 500 W, thereby helping operators to save up to 5700 kWh/year, or, equivalently, Figure 2. Power amplifiers’ input voltage can be made variable when envelope reduce the CO2 emissions due to energy genera- tracking is used. The figure shows the case of OFDM signals with 1024 sub- tion by 1.7 tons of coal per year. Such low-power- carriers: very few power is wasted as heat as the difference between the signal demanding hardware can easily rely on renewable envelope and the voltage supply level is small. power supplies. Huawei’s solution has been uti- lized over 100,000 GSM base stations since 2007, so helping to save about 570 GWh/year, repre- instantaneous power and the average power) is senting a reduction of CO2 emissions equivalent equal to N [7]. Thereby, the maximum voltage — to burning 170,000 tons of coal. amplitude at the power amplifier is N times the average voltage amplitude, and it is not conve- Envelope Tracking Technology — Envelope nient to amplify the OFDM signal using a con- tracking was proposed by Bell Labs researchers stant input voltage, which would turn into in 1937, but it has been efficiently implemented constant power consumption even when the sig- only recently after very fast, low-noise power nal is very low (and the unused power is dissipat- transistors have became available (using ed as heat, Fig. 1). LDMOS, GaN, GaAs, etc.). The basic idea of In order to be power-efficient, the average envelope tracking is as follows: instead of chang- input power at the power amplifier has to be ing the signal to match the power amplifier char- kept as close as possible to the power needed for acteristics, dynamically try to adjust the supply transmitting the signal. Possible solutions consist voltage of the power amplifier to match the of either distorting the signal or dynamically envelope of the signal to be amplified. Thus, adapting the input voltage of the amplifiers. envelope tracking ensures that the output device remains in its most efficient operating region DPD and Doherty Power Amplifiers — Digi- (i.e., in saturation). Figure 1 shows the ineffi- tal predistortion (DPD) and Doherty techniques ciency of using power amplifiers with constant are used to adapt the signal to the amplifier’s input voltage supply. Without envelope tracking, characteristics and to boost the power emission the difference between the constant power fed when the signal level is above a fixed threshold, into the RF amplifier and the radio-frequency thus avoiding excessive signal clipping. output waveform is dissipated by the power tran- The DPD and linearization technique uses sistor as heat. With envelope tracking, as depict- pre-distortion of the signal to be transmitted and ed in Fig. 2, the supply voltage tracks the signal operates a compensation for nonlinearities in envelope, so the input power closely matches the the final RF output stage of the amplifier. In the RF output power. This matching turns into a process, it also improves adjacent channels inter- dramatic reduction of the energy dissipated as ference and reduces the error vector magnitude heat. Performing envelope tracking requires a (i.e., it improves the modulation accuracy) and CPU cost that can consume as much as a few allows some compensation for the distortion watts, which are negligible in comparison to the caused by nonlinearities near compression. This energy saved (tens or hundreds of watts) in the technology obtains the best result when DPD case of high-power amplifiers. and linearization are used as part of a feedback The first practical commercial implementa- system architecture incorporating active sam- tion of envelope tracking is very recent (Nujira, pling of the output signal. This way, in fact, the 2008), and can make a significant contribution to system fully compensates for changes in amplifi- the power efficiency of the power amplifiers, er characteristics with time, temperature, and improving this from the 15 percent of Class A/B signal characteristics [8]. power amplifiers to 45 percent nowadays, and, The Doherty power amplifier configuration according to vendors, the power efficiency will has been originally proposed in 1936 [9]; it uses soon reach 60 percent using the latest gallium two amplifying devices driven in parallel, with nitride power transistors for RF. Nujira intro- their outputs combined. One carrier amplifier, duced and patented High Accuracy Tracking operating in Class A/B, provides all the output (HAT), an ultra-high-efficiency wideband modu- power until the power required causes it to enter lator for radio-frequency with power amplifiers its nonlinear region. A peaking amplifier, operat- that make use of envelope tracking. It is, there- 66 IEEE Communications Magazine • August 2011C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND®
    • C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® by, suitable for a broad class of non-constant envelope modulators such as those required for Traditional Doherty Envelope tracking OFDM transmissions. HAT modulators for 3G technology technology (HAT) (code-division multiple access, CDMA), high- speed packet access (HSPA), digital video broad- Power ampl. effic. 15% 25% 45% cast (DVB), WiMAX, and Long Term Evoultion (LTE) provide the wireless manufacturer with Power consumption 51.7 MW 27.2 MW 16.1 MW the possibility to design smaller cost-effective base stations which also have a reduced environ- Power cost $54.3 M $28.6 M $17.0 M mental footprint: the first commercial HAT- based RF unit for WCDMA/HSPA/LTE CO2 emission 194,600 tons 102,400 tons 60,800 tons (February 2009) uses 50 percent less energy than traditional devices. By deploying base stations Table 1. Efficiency, costs and environmental impact of a 20,000-base-station using the HAT modulator, a cellular network network with different power amplifier technologies. with 20,000 base stations could save 35 MW, thus saving the operator each year $37 million in energy costs, which potentially reduces CO 2 • The traffic expectation for the next hour is emissions by 130,000 tons. Table 1 compares below the threshold. Class A/B, Doherty, and HAT power amplifiers • No relevant alarms and events are sched- in terms of per-amplifier efficiency and per-net- uled during the next hour. work costs. Doherty amplifiers’ performance is between that of traditional Class A/B and HAT. Smart Power Management — Another soft- ware for the dynamic activation of network ENERGY MANAGEMENT TOOLS equipment is Smart Power Management (SPM) Energy-efficient solutions should be able to cor- developed by Nortel. SPM software enables 2G relate energy consumption and traffic intensity. network operators to switch off the radio net- As a first step in this direction, wireless opera- work equipment when there is no traffic being tors have proposed the adoption of smart soft- processed by the system. Nortel estimates poten- ware features for enabling power saving at the tial power savings of up to 33 percent reduction base station. Here, we introduce some examples in base station power consumption. of such software. Dynamic Power Save — In February 2009, NectAct SQM — Energy conservation can be Alcatel-Lucent launched a new feature called obtained through traffic-load-driven capacity Dynamic Power Save, which promises power management at the base stations. Nokia Siemens consumption reduction up to 30 percent through Networks’ NetAct Service Quality Manager the possibility to turn off the power amplifiers in (SQM) is a software solution for managing avail- GSM transceivers on the basis of the traffic able capacity when traffic load is low. NetAct activity monitored by the base station. Interest- controls base station power consumption auto- ingly, the company says the software upgrade matically based on preconfigured settings; for can be installed on the (roughly) 500,000 Alca- example, NetAct’s power save function allows tel- Lucent base stations deployed over the past service providers to manage power consumption 10 years. during times of high and low traffic. Traffic pat- terns can be managed from the network down to Standby Mode — Standby operational modes the individual base station level. Software like have been launched since 2007 by Ericsson, NetAct SQM works for 2G and 3G systems, and whose power saving estimate is about 10 to 20 allows power to be saved by tuning the setting of percent, depending on the traffic pattern. the base station automatically. For instance, sys- tem capacity tuning is scheduled every few tens BEST PRACTICES FOR A of minutes, and the actual capacity is chosen as a LOW-CARBON ECONOMY function of the current traffic load, the history of the traffic load, and the estimate of the traffic Remarkable energy economy and GHG reduc- load during the next hour. Capacity adjustments tion can be obtained by adopting responsible consist of changing, say, the number of active practices for the setup and management of the frequencies for GSM access networks, which can network, beginning with the packaging. A clear also result in turning off all radios if the traffic example of such green practices can be observed during the next hour is expected to fall below a in the green action plan defined by China Mobile — minimum threshold. In particular, the commer- the Chinese cellular operator — for the manage- cial base station software NetAct SQM comes ment of packaging. This strategy is defined by with a strategy named base station power saving the following six R’s: Recovery & Recycle refer to at night, which allows the operator to set a time using recyclable packaging materials that require window during which the base station capacity low energy cost during their life-cycle. Right & can be reduced. The actual capacity decision is Reduce refer to using small and lightweight car- made in accordance with a traffic profile that is ton design, thereby reducing packaging and estimated over the hours of the week, and only transportation costs. Returnable & Reuse refer to after a series of preconditions is met: the use of efficient recycling systems in order to • Current traffic is below a tunable threshold. extend the life cycle of packaging materials. Fol- • Current traffic is within its expected profile lowing these directives, the Chinese manufactur- (so traffic estimates can be assumed to not er Huawei reported an annual cost reduction of exceed significantly the expected value). 12,000 m3 of lumber, 2,700,000 liters of oil, 0.75 IEEE Communications Magazine • August 2011 67C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND®
    • C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® Element Solution CAPEX saving OPEX saving Less CO2 Energy-efficient solutions should be Core network Compact soft switches 75% 90% 80–90% able to correlate Radio equipment next to the energy consumption Base station site > 50% 40–70% 30% antenna and traffic intensity. As a first Power amplifiers Envelope tracking — > 50% > 50% step in this direction, Software Site power save — Up to 40% Up to 40% wireless operators have proposed the Low-carbon practices Packaging, recycling, bio-fuels — > 40% > 50% adoption of smart Overall impact ~ 70% > 50% > 50% software features for Table 2. Impact of different strategies with respect to old-design base stations. enabling power saving at the base station. GWh of energy, and a cut of 6,172,000 tons in and multimode, Huawei, Alcatel-Lucent, and CO2 emissions. other manufacturers have proposed to locate The green strategies introduced so far repre- only the RF units on site, and to use the open sent the tools network operators can leverage to common public radio interfaces (CPRIs) to enable low-cost virtual infrastructure and ser- communicate with the baseband unit and other vices, contributing to reducing the need for trav- units like the remote control and transport eling and so to the rising of a low-carbon units. The base-band unit can be made as small economy. Since 2007, green technologies by as a 2U-unit (i.e., with a 19 ft × 3.5 ft front Ericsson, Nokia Siemens Networks, Alcatel- panel) and can be conveniently installed in Lucent, Huawei, Nujira, and other leading com- existing cabinets such as auxiliary power supply panies have been used worldwide to reduce cabinet, transmission equipment cabinet, or energy costs and correspondingly reduce GHG other remote equipment cabinets. The radio- emissions due to power generation. As an exam- frequency unit can be made light enough to be ple, in 2008, Ericsson set its first carbon foot- installed on a tower, a pole, or simply against a print target, aiming for a 40 percent reduction wall. Thereby, since the radio-frequency unit over five years, starting with a 10 percent reduc- installation is made easy, the conventional feed- tion in 2009. er is no longer used, which enables a closer Table 2 summarizes the impact of the differ- antenna interface and avoids a 3 dB power loss. ent strategies presented so far. Next, we focus on This base station can be used for both 2G and the site cost, illustrate the various cost compo- 3G radio access networks, as in the case of the nents incurred when operating a base station, Flexi base station. In particular, the control unit and the potential for reduction of each of these can be shared between 2G and 3G radio-fre- costs. quency units by simply loading the appropriate software. For example, the previously men- tioned Flexi base station was originally meant ARCHITECTURE OF A for GSM/EDGE networks, but it has been upgraded to support all 3GPP technologies GREEN BASE STATION from wideband CDMA (WCDMA)/HSPA to The analysis of expenditures on 3G network LTE, having them all running concurrently in a site construction shows that base station infra- single unit (Flexi Multiradio base station, on the structure costs make up 30 percent of the total market since early 2009). This upgrade has been cost. Other expenses such as the site acquisi- possible just by updating the base station soft- tion depend on the base station architecture. ware. Another multimode solution was recently Smaller size and more power-efficient base sta- proposed by the Chinese operator ZTE, whose tions imply reduced investments and opera- Unified Hardware Platform supports GSM, tional costs. In order to move further with cost CDMA, UMTS, time-division synchronous reduction, operators are asking for flexible CDMA (TD-SCDMA), and LTE. Other multi- base stations, where multiple technologies carrier RF units are available for CDMA, in could be run simultaneously, multiple carriers which one unit can support several carriers could be operated on demand, and easy (four to eight carriers in current implementa- upgrades could be performed by simply updat- tions), and multiple carriers can share the same ing software components. antenna system without the need of using a sig- From the operator’s perspective, running nal combiner. multiple radio technologies in a single base sta- Finally, it is worth mentioning that manufac- tion (multimode base station) means shared turers are developing new software defined radio CAPEX for the site and reduced management aimed at easily configuring the radio interface expenses. As detailed later, a base station main- and upgrading the transmission technology at ly consists of the baseband unit, the RF unit, zero cost. For example, in 2009 ZTE launched the transport unit, and a control unit, the other its software defined radio solution to be used for units being auxiliary to these networking units. GSM/CDMA/UMTS base stations, and also To make the installation simpler, more flexible, ready to evolve LTE. 68 IEEE Communications Magazine • August 2011C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND®
    • C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® 50 W Base station installa- Control unit tion and upgrade expenses include the acquisition of equip- 50 W 50 W 1000 W Network ment, the transport Transport Base-band Radio-frequency interface to the site, plus the costs for the site property (or rental) 60 W Air and for building the Antenna system interface 60 W site itself, including towers for the 150 W 500 W Power DC antenna system and Power supply Cooling system Data/signaling AC Control waterproof cases for the equipment. Figure 3. Modular composition of a high-power base station. A dual power supply, AC and DC, is usually needed to feed the cooling system and electronic devices, respectively. Only a minor fraction (e.g., 60 W) of the total power consumption (e.g., ~2 kW) is radiated on the air. BASE STATION sectors. Also, baseband units could be shared between multiple base stations, thus making it OPERATIONAL COST ANALYSIS possible to deploy simple base stations, which consist of RF unit, antenna system, and power In this section, we provide the reader with a supply only. detailed breakdown of the costs related to the Base station installation and upgrade expens- operation of a base station; in particular, we es include the acquisition of equipment, its analyze the operational costs due to power con- transport to the site, plus the costs of the site sumption. property (or rental) and building the site itself, including towers for the antenna system and OPERATIONAL COSTS waterproof cases for the equipment. These capi- A base station is a modular composition of sev- tal expenditures are strongly dependent on the eral units. The resulting base station building size and weight of the base station, and can blocks are depicted in Fig. 3 and introduced in range from a few thousand dollars to a few hun- what follows. dred thousand dollars. However, base station The antenna system includes one or more costs are dominated by the operational cost of antennas for one or more RF bands in use. The the energy needed to operate the site. For both baseband process unit is in charge of handling 2G and 3G base stations, vendors report typical the data and voice streams by operating digital consumption values on the order of several hun- signal processing, and generating and parsing dreds of watts (0.5 to more than 2 kW). In par- control signals. The RF unit is the RF modem ticular, baseband, control, and transport units that connects the baseband unit to the antenna operate with very low power, as they require system, and includes a digital processing board only a few tens of watts, resulting in as few as 5 and the power amplifiers necessary to drive the percent of the total power consumption. The RF antenna radiation. The control unit provides unit consumption is mainly due to the power configuration tools and management interfaces amplifiers that have to feed the antenna system. to the base station equipment, and handles This consumption is of the order of several hun- alarms and operational logs. The transport unit dreds of watts, with less than 100 W being radi- provides transport services for the data to be ated by the antenna. Noticeably, about half of exchanged between the base station and the core the power provided by the amplifiers is wasted network, including user generated data, voice by the antenna system on the feeder that con- and video streams, and control messages (e.g., nects the antenna to the RF unit (typical cable for handling handover procedures within the attenuation at 2 GHz is 0.1 to 0.5 dB/m, which radio access network). The cooling system is yields a typical 2 to 3 dB loss in traditional base responsible for control of the ambient tempera- station sites). ture so that electronic devices operate depend- Note that the power needed for digital pro- ably. The power supply unit has to provide the cessing, operated at both the baseband and RF base station equipment with continuous and sta- units, accumulates as little as 10 percent of the ble electrical power, and can include power gen- overall base station consumption. Furthermore, erators (e.g., solar panels and/or diesel according to Huawei’s data (which do not generators) and a voltage rectifier for AC/DC account for voltage rectifiers), 93 percent of the conversion. base station energy is spent on digital processing, Note that a base station might include one or transmission, and air conditioning, the remaining more RF units for different bands, for different 7 percent being spent on network devices and 2G/3G technologies, and for multiple coverage control units collocated at the base station site. IEEE Communications Magazine • August 2011 69C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND®
    • C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® Cost impact with traditional Relative saving estimate with Absolute saving estimate with base stations technological enhancements technological enhancements Control and transport 5% 60% 3% Digital processing (baseband 10% 50% 5% + RF) Power amplifiers (RF) 30–60% ~40% ~15% Antenna system 15–20% ~50% ~10% Air conditioning 10–25% 100% 10–25% AC/DC ~10% 100% ~10% Total 100% N/A 50–68% Table 3. Operational costs repartition for a traditional base station provided with a single radio board, a cooling system, and an AC/DC rectifier, plus control and transport devices. Original costs are compared with possible cost savings due to technology enhancements and usage of renewable energy. These data also confirm that digital processing, Table 3 summarizes the data on operational transport, and control operations consume a costs available on the manufacturers’ websites negligible amount of power in comparison with (e.g., published by Alcatel-Lucent, Ericsson, the power amplifiers stage within the RF unit. Huawei, Motorola, Nortel, Nokia Siemens Net- Overall, amplifiers’ consumption can represent works, SEI, Nujira, ZTE). The table shows that 60 percent of the total power, and, considering each base station component has a different electronic and transmission devices only (i.e., not impact on the overall operational costs. Control considering air conditioning), power amplifiers and transport units are considered together, are responsible for as much as 80 percent of since they are commonly deployed on a single base station consumption. physical device. Similarly, specific data about the Interestingly, a relevant fraction of the power standalone baseband unit are not available, consumption in a base station is due to the air while it is possible to obtain the overall con- conditioning system [2], and a non-negligible sumption of the transmission units (baseband, quote of energy (~10 percent) is wasted due to RF, and antennas), the cost due to the power AC/DC conversion needed to feed the electron- amplifiers, and data on the antenna system. ics present in the digital devices (i.e., the control, Hence, we split these cost in three parts: transport, baseband, and RF units) [2]. The • The cumulative consumption due to digital power wasted by auxiliary equipment, such as processing, which includes all baseband the air conditioning and voltage rectifier, can be costs plus the digital processing cost at the quantified in at least one forth of the overall RF unit base station power demand, but can grow up to • The remaining portion of RF consumption more than one third of the total power con- (i.e., the power amplifiers consumption), sumption. which is dissipated as heat In summary, the main causes of power con- • The consumption due to antennas sumption, and hence pollution, are the power The table also includes costs due to air condi- amplifiers in the RF unit and the air condition- tioning and voltage rectifiers (AC/DC). ing system. The former strongly affects the lat- Table 3 also enlightens how technological ter, since about half of the power used for improvements might dramatically reduce opera- control, transport, processing, and transmission tional costs up to nearly 70 percent. Power sav- is dissipated as heat by the power amplifiers. Air ings might be attained by making the electronic conditioning consumption also depends on the and network devices more efficient (more than 20 environmental conditions and the design of the percent of gain can be obtained by considering base station spaces, and it can be as power-hun- the first three rows in the table), shortening the gry as the power amplifiers. Remarkably, newly antenna feeder (another 10 percent reduction of proposed efficient power amplifiers might enable overall consumption), removing the need for the 20 percent economy over DPD power amplifiers air conditioning system by reducing the heat pro- and 40 percent over traditional amplifiers. Fur- duced by the power amplifiers (up to 25 percent thermore, these new power amplifiers eliminate less power), and eliminating the need for voltage the need for AC and allow the use of renewable rectifiers by using DC generators (e.g., renewable power sources, which do not require the pres- power supplies based on solar panels, which ence of power rectifiers, for a total potential might save an extra 10 percent). Note that effi- energy economy up to 50 percent and GHG cient electronics alone enable as much saving as emissions down to almost zero. Another 20 per- 50 percent or more of the overall consumption. In cent of economy can be obtained by optimizing fact, efficient electronics are necessary for design- the control and networking units of the base sta- ing small boards that can be located close to the tion. antenna and do not require air conditioning. 70 IEEE Communications Magazine • August 2011C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND®
    • C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND® MEASUREMENTS OF management tools have been coming into play, BASE STATION CONSUMPTION which try to enforce a sleep mode on the equip- A predominant por- ment expected to handle low or no traffic during There is quite a lot of data available in the sci- off-peak hours. tion of the base sta- entific literature about the power consumption Based on the data available on per device tion cost is incurred of each component of a base station, either for energy consumption, the survey strongly suggests as soon as the radio 2G base transceiver stations or 3G Node Bs, that high-efficiency electronics might dramatical- which is what 3G base stations are called. In ly reduce the consumption of next-generation devices are turned contrast, many base station vendors advertise the OFDMA-based systems. However, a predomi- on, and this does average power consumption of their equipment nant portion of the base station cost is incurred and usually provide aggregate data (i.e., per base as soon as the radio devices are turned on, and not depend on the station or even per network consumption data). this does not depend on the traffic flowing traffic flowing In [2], the authors report on a measurement through the devices. Therefore, smart and flexi- through the devices. study of a typical 2G/3G base station in the ble sleep mechanisms should be provided in Vodafone Portuguese mobile network. The order to make the energy consumption depend Therefore, smart and experimental study shows that for a common on the time-varying traffic load. flexible sleep outdoor base station, operating three RF units mechanisms should (one for GSM in the 900 MHz band, one for REFERENCES GSM in the 1800 MHz band, and one for [1] E. Dahlman et al., 3G Evolution: HSPA and LTE for be provided in order UMTS), about 76 percent of the power con- Mobile Broadband, Second Edition, Academic Press, to make the energy sumption is due to the electronics, while about Oxford, UK, 2008. 24 percent of the total power is consumed by the [2] F. Corriea Alegria and F. A. Martins Travassos, “Imple- consumption depend mentation Details of An Automatic Monitoring System cooling system. The same study shows that the Used on A Vodafone Radiocommunication Base Sta- on the time-varying cost of the GSM RF unit is roughly 30 percent tion,” IAENG Engineering Letters 16, vol. 4. higher than the cost of the UMTS RF unit. [3] S. Alouf, E. Altman, and A. P. Azad, “Analysis of an traffic load. Noticeably, for both technologies, the power M/G/1 Queue with Repeated Inhomogeneous Vacations with Application to IEEE 802.16e Power Saving Mecha- consumption only slightly fluctuates over time [2, nism,” Proc. QEST, Saint-Malo, France, 2008, pp. Fig. 22]. GSM consumption, in a time window of 27–36. 15 min, is reported to be 0.27 to 0.30 kWh; that [4] A. P. Azad et al., “Optimal Sampling for State Change is, it exhibits an average power consumption Detection With Application to the Control of Sleep Mode,” Proc. 48th IEEE Conf. Decision and Control ranging from 1.08 kW in off-peak hours to 1.20 (CDC), Shanghai, China, 2009. kW during peak hours. On the other hand, the [5] L. Saker, S.-E. Elayoubi, and H. O. Scheck, “Energy- UMTS consumption, in a time window of 15 Aware System Selection in Cooperative Networks,” min, ranges from 0.19 to 0.22 kWh, and corre- Proc. VTC Fall, 2009. [6] 3GPP TS 25.214, Physical Layer Procedures (FDD), spondingly the average drained power approxi- release 8. mately ranges from 0.76 kW to 0.88 kW during a [7] S. Shepherd, J. Orriss, and S. Barton, “Asymptotic Limits day. Note also that RF units are DCoperated. in Peak Envelope Power Reduction By Redundant Cod- With the efficiency of the AC/DC rectifier used ing in Orthogonal Frequency-Division Multiplex Modu- lation,” IEEE Trans. Commun., vol. 46, no. 1, 1998, pp. at the tested base station being about 92 per- 5–10. cent, the actual power consumption due to each [8] S.-C. Jung, O. Hammi, and F. M. G. Ghannouchi, RF unit is actually 8.7 percent higher than that “Design Optimization and DPD Linearization of GaN- discussed before (Section IV in [2]). based Unsymmetrical Doherty Power Amplifiers for 3G Multicarrier Applications,” IEEE Trans. Microwave Theo- The measurements reported in [2] suggest ry and Techniques, vol. 57, no. 9, 2009, pp. 2105–13. that the presence of traffic only slightly affects [9] W. H. Doherty, “A New High Efficiency Power Amplifier the power consumption at the base station. A for Modulated Wave,” Proc. IRE, vol. 24, 1936, pp. major reduction in the power consumption is 1163–82. [10] Y.-S. Lee et al., “Highly Linear and Efficient Asymmetri- then possible only by turning off the base station cal Doherty Power Amplifiers with Adaptively Biascon- radio(s). trolled Predistortion Drivers,” Proc. IEEE MTT-S Int’l. Microwave Symp. Digest, 2009, pp. 1393–96. CONCLUSIONS BIOGRAPHIES Throughout the article, we have surveyed the VINCENZO MANCUSO received his M.Sc. in electronics in 2001 strategies adopted by base station manufacturers and a Ph.D. in telecommunications in 2005 from the Uni- and operators on the road towards a low-cost versity of Palermo, Italy. He was with the University of and environment-friendly wireless networking. Roma “Tor Vergata” in Italy, then back to the University of Most of the current green best practices concern Palermo as a postdoc, and a visiting scholar at the ECE Department of Rice University, Houston, Texas. In June the rationalization of: 2009 he joined the MAESTRO team at INRIA Sophia Antipo- • Capital expenditures, by optimizing the base lis, Frence. Since September 2010 he has been with Insti- station site architecture and the distribution tute IMDEA Networks, Spain. of the sites over the targeted coverage area SARA ALOUF received an M.Sc. in computer networking and • Operational expenditures, by minimizing distributed systems in 1999 and a Ph.D. in computer sci- the energy consumption of electronic ence in 2002, both from the University of Nice Sophia devices and reducing the need for cooling Antipolis, France. During 2003–2004 she was a postdoctor- systems al fellow at the Free University at Amsterdam, and since March 2004 she has been with INRIA working as a full- In addition, since the majority of the operational time researcher in the MAESTRO project team. Her research expenditures are due to the electricity consump- interests include modeling and performance evaluation of tion of RF transceivers, new software-based communication networks. IEEE Communications Magazine • August 2011 71C qM IEEE M ommunications q qM Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page MqM q Qmags THE WORLD’S NEWSSTAND®