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Dealing with Density: The Big Move to Smaller Cells

Cellular networks have a big problem: too many people want to use them for too many new things. Conceived and designed for voice traffic — not photos, videos, music downloads or other high-bandwidth fun — traditional wireless networks are struggling to keep up.

You can’t find a report that doesn’t show that global mobile data traffic has tripled each year for the past three years. And there’s more to come. This traffic is expected to grow by more than 25x in the next four years.

Massive growth in data traffic has profound implications for network infrastructure. In response, carriers are looking at several techniques and technologies to catch up with rapid growth in bandwidth demand, but there is no silver bullet. Operators will use a combination of tools to manage this data explosion: acquiring new spectrum, deploying more efficient wireless technologies like LTE, putting smarter Wi-Fi everywhere, adding femtocells and getting more aggressive about cell splitting. Other techniques include more use of tiered mobile data pricing plans and traffic flow optimization.

FIGURE 1: Where Capacity will be Added

As a result radio access network (RAN) infrastructure will change dramatically. Operators will begin deploying large numbers of small form factor RAN devices to accommodate bandwidth growth, and combination Wi-Fi/Pico LTE nodes will also become an important part of the solution.

While operators continue to rely on their macro cellular networks to provide wide-area coverage for voice, they’re hurrying to find complementary alternatives that will ease the increasing pressure, especially in areas where 3G/4G subscriber density and usage is high, like urban centers, airports and transit stations, and stadiums and convention centers. And each operator wants to find the right technologies and deployment strategy before their competitors figure it out and take their subscribers with them.

To address all this, mobile operators are looking at anything and everything including:

  • Upgrading the 3G HSPA network — this makes technical and financial sense but doesn’t provide the increase in capacity that is required in high-traffic areas.

  • Building a Wi-Fi underlay network — for mobile data offload to address the immediate need for additional capacity.

  • Purchasing more RF spectrum — as operators move to macro LTE to establish coverage, promote device adoption and maintain access for high-mobility users.

  • Rolling out a small-cell LTE underlay network — to provide additional capacity where needed, once LTE device adoption takes off. The small-cell LTE network complements the Wi-Fi network (and to a large extent it is expected to cover the same high-traffic areas) and the LTE macro network (mostly deployed for coverage and high-mobility access) to provide an additional capacity boost.

  • Using 5GHz Wi-Fi for NLOS backhaul — as the sheer number of smaller cells makes it nearly impossible to run expensive fiber or fixed broadband connections everywhere they're required.

Operators need a roadmap for a long-term and multi-step strategy to increase RAN capacity density (i.e., capacity per square kilometer) in high-traffic areas to meet the subscriber demand for data services. Wi-Fi for mobile data offload is one of the most efficient and economical means by which operators can immediately realize a steep increase in capacity — getting access to most desirable locations in high-traffic areas.

FIGURE 2: Total RAN Capacity Density

Wi-Fi, long regarded the ugly step-child in the RAN family because of its inherent unreliability and unpredictability, has grown up to be considered now one of the best solutions to traffic congestion in high-density locations — not only because of improvements to the technology like 802.11n with adaptive antenna arrays, but also because nearly all smartphones, tablets and laptops support Wi-Fi connectivity. Operators are also exploring additional options, such as small cell underlays, to provide high capacity density, while complementing and strengthening their Wi‑Fi and macro cell deployments.

Content caching, tiered pricing and policy enforcement are other approaches available to mobile operators that can further improve their network utilization and allow them to actively manage the traffic beyond the RAN within the core. While these solutions do not increase capacity, they make data transmission more efficient and allow operators to pack more content within the same infrastructure.

De-congesting Networks Calls for a New Approach

The conventional approach to addressing demands on 3G networks has been to increase cellular capacity by boosting cell density. This worked fine for a while, until the iPhone came along. Now, with bandwidth demands accelerating at an exponential rate, adding more capacity with the conventional approach is no longer workable. Because most high-traffic areas are in urban centers, deploying and operating equipment is more expensive, and space becomes difficult to obtain. And as the density of macro cells increases, self-interference becomes more prevalent and more difficult to manage, resulting in a decline in per-sector throughput as incremental returns to further cell splitting diminish.

A different approach is needed to increase capacity sufficiently (see Figure 2). Such an approach is based on lower-power, shorter-range equipment such as smart Wi-Fi access points (APs) or 4G small cells installed closer to subscribers, in dense deployments. By limiting the transmitting range, the impact of interference is reduced while capacity density is increased relative to macro sites with much larger coverage areas.

LTE and Wi-Fi: A Peaceful Co Existence

LTE small-cell deployments are a popular long-term strategy in the works for mobile operators because they promise to provide the capacity boost needed along with the flexibility and compact form factor needed for highly localized deployments in high-traffic environments. Shipments of low power pico cell devices are anticipated to see strong growth over the next 5 years (see Figure 3).

FIGURE 3: Low Power Pico Cell Shipment

Meanwhile, subscribers are demanding more Wi-Fi connectivity for the convenience and free access it provides. Worldwide hotspot venues are projected to increase to over 1.2 million venues in 2015 from under 421,000 in 2010. Usage will show similar growth, increasing from four billion connects in 2010 to 120 billion by 2015.

Yet for operators building disparate hotspots isn’t the answer. The key is the integration of Wi-Fi hotspots within their overall mobile infrastructure — making Wi-Fi a seamless extension to the operators’ mobile infrastructure. This lets them retain visibility and control over subscribers, simplify the authentication process, and deliver value-added services wherever their customers roam — thereby reducing churn.

Given these scenarios, mobile operators have an opportunity to combine Wi-Fi offload and LTE small cells to their advantage. Not only can Wi-Fi and LTE operate side by side, but they complement each other in an integrated deployment strategy, delivering the highest capacity increase afforded by next-generation radio technology and spectrum availability, combined with the lowest total cost of ownership. Each can play an important role within a multi-technology, multi-layer cellular network — spanning from macro base stations at one end to residential femtocells at the other.

Additionally, by putting a Wi-Fi offload infrastructure in place first, the operator takes care of most of the hard work to roll out LTE small cells, by securing a network of permitted Wi-Fi access points and small cell sites with power, backhaul and lease agreements, ahead of its competitors without Wi-Fi offload. Access to appropriate mounting real estate is make-or-break for small-cell strategies and in most dense urban environments is tightly constrained, turning the siting race into a winner-takes-all event.

The initial deployment of an IEEE 802.11n Wi-Fi offload solution provides mobile operators with an immediate capacity increase, available to most data-centric devices already in the hands of their subscribers. But, equally important, the Wi-Fi infrastructure provides the foundation on which mobile operators can realize their longer-term data strategy, by establishing a network of sites that can be shared by Wi-Fi and LTE small cells. Once they decide to roll out LTE small cells, operators can simply add an LTE small module or upgrade to their Wi-Fi access points — sharing permitting, lease costs and backhaul capacity.

New Wi-Fi offload systems with adaptive antenna arrays for more reliable radio performance, carrier-level scalability for aggregating and processing Wi-Fi traffic for the evolved packet core, and flexible management options will give service providers powerful new tools to integrate Wi-Fi and LTE underlays with the macro core.

This will help to optimize the use of network resources while giving their subscriber a smooth, seamless access to their multi-technology, multi-layer network. And it couldn’t come soon enough as Apple’s iPhone and its imitators continue to overwhelm mobile internet networks.

By Arnaud Le Hung, EMEA Marketing Director