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Advanced mobile services such as LTE are forcing mobile operators to re-evaluate macro-focused network architecture. Even 3G service coverage maps are believed to be optimistic in many cases, and subscribers don’t like it when they think they should be able to zip around the Web and find out that they can’t. Imagine how much more disappointment there can be with LTE, when users expect multiple megabits per second.
Why small cells are needed
Service providers have already been looking for new ways to roll out new services. The 3G rollout showed that the large macro cells initially deployed for 2G services weren’t up to the task of delivering higher-speed data. For years, service providers have been splitting cells and using distributed antenna systems to provide effective 3G services (especially for dense user populations). This trend will accelerate as LTE services are being deployed. Small cell architecture offers the opportunity for carriers to provide truly eye-popping service quality on a build-as-you-grow basis.
Another reason why small cells play a role in LTE network rollouts is that macro base stations have virtually saturated most markets, and there is rising community resistance to more big towers in cities and suburbs. With municipalities (especially in residential neighborhoods) now blocking and delaying cellular construction, mobile operators in many cases can’t add more macro towers even if they want to, and small cells will fill the gaps.
Small cells deliver coverage and capacity improvements for a better user experience
Coverage: The higher frequencies often used for LTE are not as effective at penetrating buildings from the external, macro networks now operated by cellular providers. Comparatively, while fully penetrating a building with an 850 MHz or 900 MHz signal is relatively easy, it is much harder to drive a signal farther than a few feet inside a building when the signal transmits at 2.1 GHz or higher. Without nearby macro towers, even outdoor areas need coverage supplemented by DAS or distributed radios to meet service needs. Strong signals will be required to achieve the data rates required for 3G and LTE services. (700 MHz services will be an exception to this problem, but they will still need higher capacity, as described below.)
Capacity: Our experience with the iPhone, Android, BlackBerry and other mobile application platforms shows that data usage can increase tenfold or more as users adopt these devices, placing a real strain on the network. Data usage has been doubling for the past three years to an average of 5 gigabytes per month per user today, and Cisco projects that data usage will be 18 times what it is today by 2016. With a promise of ten or more times as much throughput as 3G, LTE services increase the capacity squeeze: 3G services provided 800 to 1,200 kilobits per second of data service, while LTE services provide 10 to 14 megabits per second of service. Small cell solutions can increase capacity by delivering it over a smaller area to fewer users. Since the capacity is divided among fewer users, the capacity per user increases. Further, using a DAS architecture that uses a centralized base station hotel to simulcast services throughout a market creates a more spectrum- and backhaul-efficient network.
Small cell options
The marketplace offers two types of solutions to enable small cell architecture:
–Small base stations such as micro, pico and femto cells, which provide coverage and capacity for a specific frequency to a specific area; and DAS, which precisely extends multiple base stations’ signals to targeted areas through dozens or hundreds of antenna points.
One big difference between pico/micro cells and DAS is that pico/micro cells deliver a specific service, so they must be supplemented or replaced as new services come online. LTE is only the first of several high-speed variants we will see in the marketplace over the next few years. Already, service providers are planning ahead to LTE-Advanced and other more advanced versions of LTE and HSPA. As a result, service providers using pico, micro or femto cells will have to replace or supplement them with additional small cells as new services come online. DAS, on the other hand, delivers whatever service the service provider desires, subject to which base station is providing a signal to the DAS network. In this case, the carrier wouldn’t have to change the DAS to support new services, only the base station that feeds the DAS network. This simplifies the network upgrade path and minimizes operation and maintenance costs. Adding service to a small cell DAS network is approximately half the cost of adding additional services by overlaying picocells or microcells. The savings largely come from leveraging existing infrastructure; DAS requires less fiber, service adds fit in the existing cabinet- saving real estate rental and by utilizing the existing power plant.
Small cells also open up the market to more competition. Unlike macro base stations, which are proprietary technology manufactured only by a few large vendors, a dozen or more competitors offer pico/micro cells and DAS. This gives service providers a wider choice of solutions to meet a variety of deployment needs, and it tends to hold down prices of the systems due to higher competition.
Pico/micro cell and DAS products offer the chance for service providers to not only deliver LTE service, but to do so with higher quality of service by placing the cell signal as close to the user as possible. By using smaller cells and the right products, service providers can deliver high-quality service throughout a coverage area without the dead zones so common in macro networks. The challenge will be to choose the right mix of products to provide the best level of service while meeting each service provider’s business needs. Fortunately, small cell products offer opportunities to actually improve the business case.
Small cell advantages
Capital expenditures: Small cell products are quicker to deploy, scalable and incrementally cost far less than macro cells, so service providers can deploy them with a “build as you grow” strategy. For example, a service provider can start out by covering portions of an urban core where the concentration of early
LTE adopters will be higher, and then move out from there as demand grows. Service providers are also exploring the use of femtocells to boost service quality in residences or offices. With a DAS architecture, the network can be designed with the future in mind. The simulcast feature allows the service to be migrated to add capacity as-needed. The site development costs are accounted for up front and fewer radios will be required as the simulcast ratio can be modified to adjust for service-level adoption. Future upgrades to the DAS network will be minimal to add or move capacity.
Operating expenses: It costs plenty to maintain current macro cells, and the vision of having thousands of small base stations to look after can strike fear into the heart of any network manager. Technicians will be required to visit each cell site location for service changes. Other recurring costs include: fiber to each cell site location, power and real estate (pole attachments for picocells and microcells). For a typical operator, the fiber and lease opex can be approximately three times greater when deploying distributed base stations versus DAS due to the fact that the base stations are typically dedicated systems requiring separate infrastructure and physical space. To reduce field service time and cost, service providers can also use DAS to extend signals out from centrally located base station hotels. This minimizes real estate needs and costs and provides the service provider one place to make network changes and manage maintenance versus disperse sites throughout a market. A change in service on the same frequency can be managed by a DAS through changes only at the BTS hotel versus truck-rolls to each cell site and facing the possibility of needing new permits, zoning, etc., saving a minimum of $2,000 per cell site or radio head location and no additional time lost, bringing service to market in days rather than months or years.
Frequency management: Spectrum is limited, and small cells make it much more critical to re-use frequency efficiently. DAS can help by expanding the size of one base station’s coverage area and by enabling digital simulcast and extending the station’s capacity to multiple antenna points, directing the capacity where it is needed most. And as those capacity needs change over time, the network adjustments can be made to the simulcast configuration without physical hardware changes in the network.
Flexibility: While macro cell coverage is an all-or-nothing proposition for a given area, small cell solutions allows service providers to be very precise in choosing which services to offer where. DAS can deliver any frequency (and most DAS can deliver multiple frequencies) to specific areas so service providers can more easily choose where to implement LTE services.
Scalability: Small cell solutions also make it easier to scale services. If the service provider uses base station hotels, it is even easier to add more base station capacity and drive it through a DAS. This way, the mobile service is not tied to a fixed physical location. The DAS nodes cast a coverage area net that capacity and new services can be pushed to through service changes at the base station hotel. Typically, a change to the simulcast ratio in a DAS network to add capacity can be done within hours.
Backhaul: Small cells will require far more backhaul connections than current macro networks. While a macro base station requires just one backhaul link, each of hundreds or thousands of small cells will require a backhaul connection. In offices and residences, the subscriber’s own broadband connection can provide this link, but service providers will need to plan how to provide backhaul to urban core base stations mounted in street furniture or on building walls. Utilizing DAS may offer more options to network infrastructure by utilizing incumbent FTTX connectivity and centralized radios in a BTS hotel.
Small cell architecture is playing an important role in LTE network deployments by filling in coverage and capacity holes in the macro network. With the right mix of DAS and small cell solutions, mobile operators can deploy LTE and give customers the service they expect.
