ericsson White paper Uen 284 23-3262 | February 2015 RADIO SITE TRANSFORMATION Time to rethink high-capacity radio site design More than ever, operators are being pressured by capacity demands, driven by unprecedented consumer use of smartphones and tablets. Multi-standard networks (2G to 4G and later 5G) that use multiple bands and layers (small cells and Wi-Fi) are being deployed in order to meet these demands. However, to meet the requirements of multiple standards, bands and layers, operators need a new approach to radio site design and building practice. Efficiency in the extreme As operators strive to deliver excellent mobile broadband performance in the busiest parts of their networks – city centers, business parks, transport hubs, public venues and hub sites – they will need to deploy extreme capacity sites to efficiently serve the growing volumes of 2G, 3G, 4G, and future 5G, mobile traffic. Ericsson measurements from live networks show that a relatively small number of sites carry the vast majority of traffic, as illustrated in Figure 1. The performance of such sites is therefore key to operator revenue generation and protection. Capacity demand Number of installed RBSs Urban (downtown) Suburban (residential and industry) Rural (roads, villages) Open (roads, villages) Figure 1: The majority of mobile traffic, and therefore revenue, is concentrated in a minority of cell sites. To stay competitive, operators need to pay special attention to these revenue-critical sites, as current site designs are unlikely to be able to deliver the required performance efficiently enough. A systematic approach to radio site design is required: one that encompasses physical building practice; the relative merits of distributed, centralized and coordinated radio architecture; fronthaul and backhaul transport needs; as well as power requirements and energy efficiency. RADIO SITE TRANSFORMATION • Efficiency in the extreme 2 Differentiating where it counts Most operators today offer excellent coverage for voice and accessing internet-based services, but with growing levels of mobile broadband traffic (especially video traffic), speed and latency are becoming the key issues, especially in high-density areas like city centers. As people increasingly expect good connectivity and high data speeds wherever they go – even to the extent of replacing their fixed home broadband services with mobile ones – low latency and high throughput are becoming the key markers for differentiation. Traffic growth hotspots Mobile data traffic from smartphones, tablets and laptops is expected to grow at a compound annual rate of 40 percent between 2014 and 2020 (as illustrated in Figure 2), resulting in an eightfold increase in traffic by the end of 2020. Monthly traffic per active mobile subscription is expected to grow from 900MB in 2014 to 3.5GB in 2020 [1]. 30 Data: mobile PCs, tablets and mobile routers Data: mobile phones 25 Voice 20 15 10 5 0 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 Figure 2: Global monthly mobile traffic (exabytes). Much of this traffic growth is coming from cities, where there is the twin challenge of rising mobile broadband adoption and use in parallel with rapid population growth. According to the United Nations, more than half the world’s population already lives in cities, and this proportion is expected to rise to two-thirds by 2050 [2]. People in cities are not only used to getting excellent mobile coverage, they also expect instantaneous connectivity and rising data speeds. At many city center sites, Ericsson field measurements show that capacity needs are doubling roughly every 18 months. In areas like city centers, therefore, data-handling capacity is the main driver for radio network development; maximizing peak rates and minimizing latency are key to differentiation and user satisfaction. In response, operators are rolling out new high-capacity radio technologies – including highspeed 3G, 4G and small cells – in a growing number of frequencies, as part of multilayered networks. In very high traffic locations, where obtaining new radio sites is typically costly, difficult and time-consuming, there is extreme pressure on existing radio sites to deliver more capacity, more efficiently, in the same footprint. Backhaul throughput must also increase in line with radio access capacities. Busier sites may require multi-gigabit capacities in the backhaul, which can be provided with fiber or microwave. New generations of cellular technology appear in shorter and shorter cycles, but it is not feasible for operators to completely replace hardware each time a new technology comes along. Existing investments need to be protected and reused, while new technologies are integrated smoothly and efficiently. RADIO SITE TRANSFORMATION • Differentiating where it counts 3 Radio site trends Multiband, multi-standard sites with as many as 10 separate frequency bands are becoming more commonplace, driven by capacity demand and the need to reduce capex and opex. This – in parallel with growing performance requirements, which include rising demand for network sharing, better coverage and higher throughput – is increasing configuration complexity. The main impact of rising traffic demand on radio sites is an increase in the amount of equipment needed: more radios to handle the air interface; more baseband units to deliver radio features for improved capacity, coverage and latency performance; more capable transmission units to provide RAN connectivity (backhaul); more power backup systems to ensure continuous operation during power outages; more site routers to handle connectivity within the site (fronthaul); and more splitter units to make cabling more manageable. All this equipment must be economically justified, engineered and installed in tight spaces. At the same time, there is a growing focus on energy-efficiency, driven by cost pressure and regulatory requirements. Deployment flexibility is increasingly important as more and more equipment is needed on site: floor space is limited and wall space is often needed to install equipment. Moving to main-remote The proportion of main-remote deployments, with radios placed outside the cabinet nearer to the antenna, as well as antenna-integrated radios is steadily increasing, driven by performance advantages, lower energy consumption and deployment flexibility. A basic principle of cell site design is that higher output power offers greater options for delivering better network performance in terms of coverage, capacity and latency. There will always be some power loss in the feeders between antennas and radios, meaning longer feeders are detrimental to network performance: it is better to place the radio as close as possible to the antenna. This makes main-remote radios that can be placed outdoors better than a cabinet radio, since they can be placed very close to the antenna (which a cabinet radio usually cannot). The lower power losses of these main-remote designs also reduce power consumption for the same network performance. Another reason for the popularity of main-remote designs is a practical one. Cabinet radios need to be installed on the floor. In space-limited sites, there may not be enough floor space to accommodate a cabinet with all the radio units needed to match current and future traffic demand. In such locations, it is essential to use all available space, including wall space, which can be done with main-remote designs. One other practical aspect is that some site equipment is better centralized (such as transmission and power backup), while other equipment is better distributed (such as radios close to antennas). This means that using cabinet radios also increases equipment costs if radios need to be located close to the antenna for a three-sector site (because this requires three cabinets instead of one). These effects are then multiplied in multiband and multilayer sites. In addition, radio features like carrier aggregation and multiple-input, multiple-output (MIMO) further add to the need for cabling between radios and baseband units. Building extreme capacity sites that support multiple frequency bands cost-efficiently presents significant challenges. Site acquisition has always been an issue in areas like city centers, and is becoming more difficult and costly. This means that developing extreme capacity solutions within existing sites is likely to be the favored option for most operators. Operators need to plan and map out their next steps for these revenue-critical sites. RADIO SITE TRANSFORMATION • Differentiating where it counts 4 Delivering efficient growth One way in which operators are meeting mobile broadband capacity needs in high-density areas where site acquisition options are limited is through the deployment of additional bandwidth in the form of new radio technologies or additional frequency bands, or both. By 2020, it will not be uncommon to see radio sites with as many as 10 frequency bands across different technologies. Meeting the needs of multiple radio bands across multiple radio technologies – 2G, 3G, 4G and later 5G – within the existing site footprint will call for solutions that incorporate a much higher number of radios, baseband and transmission units than before. However, today’s hardware is simply too large and insufficiently systematized to enable extreme capacity sites to be built efficiently in existing locations. Balancing site design It is important to balance the dimensioning between the four main types of equipment on a site: radio, baseband, transmission and power. The capacity and latency delivered are only as good as the weakest link in the radio-baseband-transmission chain. The power solution, including backup, must take into consideration the other three equipment types. When defining and dimensioning the transmission part, it is important to consider the backhaul capacity needed and the latency of the fiber or microwave connection used. With centralized baseband, it may be better to use wavelength division multiplexing (WDM) fiber for fronthaul since it simplifies practical transmission aspects when using radio features like carrier aggregation and coordination. In some scenarios, wireless fronthaul can be used when fiber is not viable. Planning the power solution with respect to power consumption and power losses is extremely important in high-capacity sites, where any interruption in operation could have a significant impact on revenue and reputation. Here, the choice between AC and DC solutions could be crucial: AC exhibits less power loss but comes with bigger safety risks. Intelligent power consumption algorithms for traffic handling during power outages and battery charging can make a big difference to overall power consumption. Common building practice As the trend continues toward placing (smaller) radio units outside cabinets, closer to the antennas (to minimize losses and latency), with a growing number of frequencies and sectors per site, more and more (fronthaul) transmission branches are needed to connect the growing number of radios efficiently to a growing number of baseband units and maximize the overall performance and reliability of the cell. In addition, access to the power supply is needed not just at the cabinet, but also for the radios. This is leading to a massive increase in the amount and complexity of cabling. A new approach to designing and building site solutions is needed that offers systematic characteristics – in terms of ease of construction, ease of expansion, power-efficiency and safety – that deliver the desired network performance at the right lifetime cost. Revenue-critical sites will demand highly efficient modular systems that are easy to install, configure, expand and adapt to new mobile broadband demands. More equipment on site requires a common building practice in order to optimize site cost and network performance. Form factor becomes critical: size (volume) and weight must be minimized in order to enhance installation flexibility (such as wall mounting), and make equipment easier to handle. Traditional main-remote radios have occupied 20-40 liters and weighed roughly 20-40 kg. With high-capacity sites most likely needing to support as many as 10 frequency bands, there may be 30 radios on a three-sector site. When baseband units, transmission units, site routers and cabling are also included, it is easy to see the practical importance of form factor. A common form factor for the different equipment types is important to make installation as flexible as possible. It is also important that connectors are placed in such a way that the units can be easily installed in different ways to increase installation flexibility. To reduce the number of cables needed between radios and baseband units, for example, Common RADIO SITE TRANSFORMATION • Delivering efficient growth 5 Public Radio Interface (CPRI) splitter units can be used. These also have the advantage of reducing the number of ports needed in the baseband unit (as shown in Figure 3). Radio Baseband Baseband Radio Radio CPRI splitter Radio Radio Radio Common Radio Radio Radio Radio CPRI cable/port reduction Figure 3: CPRI splitters reduce both the amount of cabling and the number of ports needed in the baseband unit at radio sites. Enhancing overall efficiency New performance-enhancing radio techniques – such as carrier aggregation, MIMO and increasing antenna element arrays – are driving a rapid increase in demand for digital signal processing power needed to handle radio signaling. This in turn is driving the need for more energy-efficient site solutions, especially as the radio network represents the dominant proportion of overall mobile network energy use. The processing needs at radio sites will only become greater as traffic volumes rise and new radio technologies, including 5G, are rolled out. To reduce overall energy costs, operators could introduce energy management schemes that adapt power usage to traffic levels. For example, features for dynamically reconfiguring three-sector sites to omni-operation, reconfiguring antennas from MIMO to single-input, multiple-output (SIMO) mode, and discontinuous transmission are all based on traffic load. As a result, the radio system makes a shift from being ‘always on’ to ‘always available.’ At multi-standard, multiband sites, it is possible to shut down certain bands during low-traffic periods to reduce energy use. Transmission equipment can be handled in a similar way. Distributed, centralized or virtualized One important aspect of improving overall efficiency is how to handle the increasing baseband processing requirements. At a strategic level, operators need to decide where the switching, routing and ‘intelligence’ to handle the growing volumes of internet traffic in their networks will reside. The basic choice is to make such functionality, including baseband hardware, centralized, distributed or even virtualized. As the number of radios per site increases, and the variety of advanced techniques for deriving extra capacity and throughput from each channel grows, the need for baseband processing increases. Essentially, this is driving the need for more baseband units, with progressively more digital signal processing power over time. The performance of baseband units has increased dramatically in recent years, with the availability of Many Core Architecture processors that enable several thousand active users to be simultaneously handled by a single board, for example. Traditionally, baseband units are placed near the radio units to minimize latency. Where WDM fiber is available, operators have the option of deploying locally centralized ‘baseband hotels’ to coordinate processing power between clusters of cell sites. The coordination gains are initially significant, but tail off as the size of the coordination clusters grows (as shown in Figure 4), while the maximum distance between the coordinated baseband resources and the radios is limited by acceptable levels of delay, latency and jitter. The location of cluster borders and the availability of suitable power supplies also need to be considered carefully when adopting a centralized approach. There are practical limitations to the deployment of such baseband hotels, because the CPRI interface they require has significantly higher data rate and latency requirements than the Iub, X2 and S1 interfaces typically used between baseband units and the core nodes Evolved Packet Core (EPC) and radio network controller (RNC). The dark fiber or WDM connections needed are not widely available. Virtualizing baseband digital signal processing – essentially, putting processing resources in the cloud – presents significant risks to overall performance. Furthermore, it is unlikely that the commercial, off-theshelf hardware used in virtualized solutions will be viable from a performance or energy-efficiency perspective. RADIO SITE TRANSFORMATION • Delivering efficient growth 6 As operators deploy a mix of macro cells, small cells and Wi-Fi to meet rising capacity needs, RAN architecture will evolve to incorporate a mix of distributed and centralized RAN approaches. Techniques like Coordinated Multi-Point (CoMP), in which users are served by multiple cell sites to maximize throughput performance, will be key to delivering spectral efficiency and lower total cost of ownership. Capacity increase 100 80 60 40 20 0 1 2 3 4 5 6 Size of coordination clusters 3 1 3 1 2 7 8 9 3 1 2 2 Figure 4: Incremental capacity gains diminish as the number of cells included in a coordination cluster increases. Figure 5: Uncoordinated network cluster size 1. Figure 6: Coordinated network cluster size 3. RADIO SITE TRANSFORMATION • Delivering efficient growth 7 Advanced radio integrated transport Whether they employ distributed or centralized baseband, extreme capacity solutions will require tight radio and backhaul transport integration to ensure superior user experience and maximum efficiency. They will need fronthaul, access routers and backhaul that can support the new capacity levels and strict timing requirements, as well as provide more efficient provisioning and maintenance. To keep operating costs down and increase agility, fronthaul and backhaul network provisioning needs to be fully integrated with rest of the RAN. The solutions will also need a very resilient backhaul transport solution because of their critical value, where no single point of failure should determine their continuous operation. Meeting the strict latency requirements of centralized and coordinated RAN architecture will require a fronthaul network that can deliver very high capacity with minimal latency, over CPRI connections. Low-latency (sub-100 microseconds) transport of CPRI enables the coordination of various radio sites for maximum capacity (through CoMP). Operators need to invest in transport hardware that can enable them to skip an upgrade cycle or two by seamlessly keeping pace with traffic growth in ever-shortening capex cycles. In extreme cases, traffic in backhaul links at baseband hotels is already reaching multi-Gigabit Ethernet (GE) levels and could well reach 100GE interfaces within a few years. At the cell sites, keeping up with traffic growth will require multiple 10GE interfaces within five years. Operators can break frequent and expensive capex cycles by adopting a 7-10 year view, perhaps with solutions that enable ‘pay-as-you-grow’ capacity licenses. Managing backhaul latency and packet loss is critical in ensuring the QoE for users in a mobile network. Advanced integration between backhaul network and RAN enables key information exchange across each domain in order to enable more intelligent and automatic mitigations. This way, the network can automatically heal a congested connection when possible by using softwaredefined networking and traffic engineering capabilities. For example, users may be load-balanced to different eNodeBs that have a backhaul connection that is healthier. If this fails, then in extreme scenarios such as a stadium event, admission control may be used by the RAN instead. In addition, making the backhaul more aware of each individual subscriber in a radio network enables more granularity in how traffic is engineered and load balanced, further improving utilization of the network and improving QoE. Greater granularity also enables Network Functions Virtualization and orchestration to be introduced more easily for mobility anchor points such as an Evolved Packet Gateway. Subscriber-aware backhaul enables individual users or even individual user applications, such as video, to be handled in a way that goes far beyond simple QoS mechanisms. Advanced, radio-integrated transport plays a pivotal role in handling performance at these revenue-critical sites. RADIO SITE TRANSFORMATION • Delivering efficient growth 8 Conclusion Operators need to meet growing traffic capacity demands, especially in busy, densely populated areas, with their current mobile network as the starting point. Existing site solutions and strategies are unlikely to be able to address the coming site challenges. A radio site transformation is needed for high-capacity radio site design. With operators deploying a mix of distributed, centralized and coordinated radio architecture, there will also be a significant impact on the transport network. The transport solution will need to be fully integrated with the rest of the site in order to make installation and operation as simple and seamless as possible. Any system is only as good as its weakest link, so all site equipment – including the antenna system, cabling, fronthaul and backhaul – needs to be carefully chosen and dimensioned. Operators will benefit from deploying site solutions that are compact, systematic and modular in design, in order to take care of radio functionality, baseband processing, transmission, power and battery backup as efficiently as possible. RADIO SITE TRANSFORMATION • conclusion 9 GLOSSARY CoMP CPRI GE MIMO SIMO WDM Coordinated Multi-Point Common Public Radio Interface Gigabit Ethernet multiple-input, multiple-output single-input, multiple-output wavelength division multiplexing RADIO SITE TRANSFORMATION • glossary 10 References 1. Ericsson, November 2014, Ericsson Mobility Report, available at: http://www.ericsson.com/res/docs/2014/ericsson-mobility-report-november-2014.pdf 2. United Nations, accessed February 2015, Global Issues – Human Settlement, available at: http://www.un.org/en/globalissues/humansettlements/ RADIO SITE TRANSFORMATION • REFERENCES 11
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