Finding the right small-cell architecture for 4G

Advanced mobile services such as WiMax, high-speed packet access, long-term evolution and UMTS are forcing mobile operators to re-evaluate macro-focused network architecture. Even today’s 3G service coverage maps are 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 will be when 4G arrives and users expect a few megabits per second. But it doesn’t have to be this way. Small-cell architecture offers the opportunity for carriers to provide truly eye-popping service quality on a build-as-you-grow basis.

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, carriers have been splitting cells and using in-building distributed antenna systems (DASs) to provide effective 3G services (especially for dense user populations). This trend will accelerate as 4G services arrive. The issues are coverage and capacity.     

Coverage: The higher frequencies often used for 4G are not as effective at penetrating buildings as the external, macro networks now operated by cellular providers. 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. 

Capacity: Our experience with the iPhone, Blackberry and other mobile application platforms shows that data usage can increase 10-fold or more as users adopt these devices, placing a real strain on the network. With a promise of 10 or more times as much throughput as 3G, 4G services will increase the capacity squeeze.

But the advent of 4G doesn’t mean that carriers must walk away from billions of dollars in macro-cell architecture investments. These investments will continue to provide broad voice and lower-speed data services for years, but for 4G they will have to be supplemented with small-cell topologies and associated equipment.

The marketplace offers two new types of solutions to enable small-cell architecture:

• Small base stations such as micro-, pico- and femtocells, which provide coverage and capacity over limited areas.
• DASs, which precisely extend a base station’s signal to targeted areas.

These products offer the chance for carriers to not only deliver 4G services, but to do so with higher quality. By using smaller cells and the right products, carriers 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 carrier’s business needs. Fortunately, small-cell products offer opportunities to actually improve the business case. Here are some of the issues:

Capex: Small-cell products cost far less than macro-cells and they can be deployed in a matter of days or weeks, so carriers can deploy them with a build-as-you-grow strategy. For example, a carrier can start out by covering portions of an urban core where the concentration of early 4G adopters will be higher and then move out from there as demand grows. Carriers are also exploring the use of femtocells to boost service quality in residences or small offices.

Opex: 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. However, small base stations don’t require the expensive real estate of macro-cells, they use far less power, and those deployed indoors will require very little maintenance. To reduce travel time for service technicians, carriers can also use DAS technology to extend signals out from centrally located base station hotels.

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.

Flexibility: While macro-cell coverage is an all-or-nothing proposition for a given area, micro-cell equipment allows carriers to be very precise in choosing which services to offer where. Any small base station or DAS can deliver any frequency (and most DASs can deliver multiple frequencies), so carriers can more easily choose where to supplement 2G/3G service and when to migrate to 4G service.

Scalability: Small-cell gear also makes it easier to scale services. It’s easier to deploy small base stations, so it’s easy to add more of them as capacity demands warrant. If the carrier uses base station hotels, it is even easier to add more base station capacity and drive it through an existing DAS.

Backhaul: Small cells will require far more backhaul connections than current macro networks. In offices and residences, the subscriber’s own broadband connection can provide this link, but carriers will need to plan how to provide backhaul to urban core base stations mounted in street furniture or on building walls.

The move from 2G to 3G services was characterized by hype and subscriber disappointment, as carriers struggled to deliver what they promised. Small-cell architecture makes it possible to roll out 4G services that work as advertised and improve the carrier business case.