Delivering consistent indoor coverage for cellular devices continues to be a top priority for mobile operators. Regardless of the pervasiveness of cellular towers in any given region, our study shows that more than 50 percent of mobile subscribers continue to experience poor quality signal, dropped calls, or dead zones for a variety of reasons, from construction materials to local topography. Remote regions present an even bigger challenge as distances between towers increase.

A challenge in addressing the last mile of coverage is that the cost of infrastructure development is significant. By way of an anecdotal example, let’s say there is a specific cost to provide service to 90 percent of customers 90 percent of the time in 90 percent of all covered areas. However, increasing those numbers to 100 percent could easily cost 10 times the initial network investment, which means consumers would be paying $1,000 a month per service versus $100. Simply put, it’s too expensive to achieve perfect cellular service through infrastructure investments alone.

With 80 percent of mobile traffic consumed indoors, according to Cisco, that last mile is critical. As cell phone capabilities and consumer demands grow, that number will continue to increase. As such, inconsistent coverage will become a deal breaker for many consumers and businesses, rather than simply an inconvenience.

A promising trend has been advancements in complementary indoor coverage solutions, ranging from small cells and Wi-Fi calling to signal boosters. Each has its place in the solution spectrum; and in many cases, more than one technology will be integrated to address any gaps in coverage. Some require broadband connectivity; others rely strictly on cellular signals. Some are more costly and complicated to install and configure; others are simple plug-and-play systems.

Let’s look at the available options and the role they will play in improving indoor coverage.

Fixed Backhaul Solutions

Small cells are, in essence, cellular base stations that generate their own signal rather than boosting an existing one. Generally speaking, residential small cells haven’t lived up to their original promise, whereas enterprise small cells hold great capacity promise, but can still come up short in terms of coverage. Both residential femtocells and small cells necessitate registration and configuration, creating adoption and deployment hurdles in residential applications. Enterprise-grade small cell deployments can be a costly and somewhat complex endeavor since they require RF design, cabling, and configuration by engineers and technicians.

Wi-Fi Calling is gaining popularity as an option among operators and consumers alike. As with small cells, Wi-Fi calling requires a backhaul to the core network. Operators use it as a way to offload traffic onto Wi-Fi and more efficiently use their cellular networks. Consumers like Wi-Fi calling because it can help them to reduce their phone bills. However, not every mobile operator offers this service, and only newer smartphones with native Wi-Fi calling capabilities – like the iPhone (News - Alert) 6 – can support all of the features. Wi-Fi calling requires a connection to a broadband network, tends to have a limited coverage footprint, and frequently has issues with the handover of calls between indoor and outdoor settings.

Wireless Backhaul Solutions

Cellular-based solutions have proven to be an extremely valuable resource as either a primary or backup solution, particularly in areas without broadband or where signal interference is high. These can work in two different ways.

The first is known as an outside-in solution, in which users receive a mobile signal from an outdoor cellular network such as a macrocell (base station) that is outside the building. The second category is inside-in or in-building solutions that are designed to boost and deliver signals from a signal source inside a building. The most popular choices are boosters directly coupled to small cells and distributed antenna systems. In many cases, they are used in tandem to cover larger spaces (e.g. parking arcades) or very remote sites.

When it comes to signal boosters, there is however a distinct division within this category that is important to consider. Traditional repeaters (often referred to as bi-directional amplifiers or BDAs) have historically not been supported by mobile network operators because they can cause interference on the cellular network. They can also have labor-intensive installation requirements, including the need for external antennas, cables, ladders, and drilling.

On the other hand, carrier-specific signal boosters eliminate any interference issues and as a result are approved by the FCC (News - Alert) to deliver a much higher gain and a larger coverage footprint (up to 13,000 square feet). These boosters are specifically authorized by mobile operators for use on their networks, and are unconditionally network safe. These plug-and-play systems amplify a wireless signal coming from the macro network or small cell, and do not require cabling, registration, or configuration. Depending on the project, they can be used as a standalone solution or as a complementary technology to other indoor coverage solutions for much larger scale implementations. The intelligence built into the chips that power signal boosters enables them to survey their surroundings and constantly adjust to ensure optimum performance levels within the coverage bubble, without the risk of interference with the macro network or any other wireless solutions.

In areas that demand a larger footprint (more square feet of coverage), DAS may be a good alternative. A DAS is a collection of connected indoor antennas that is backhauled to a central service hub. This service hub can either be connected directly to the cellular network or, in some cases, it can collect and repeat signals off air from the macro network. DAS is a flexible and effective alternative that can be configured to receive signals from a variety of technologies including small cells and direct connection to the network core. The major caveat with DAS is that the cost per square foot covered is high and the systems are often complex to install. Therefore, DAS  tends to be used primarily in larger facilities

Where the real innovation is to be found is in hybrid solutions. Dan Connelly, president of Atlantic Technology Group in Rockville, Md., says he turns to a range of solutions to address specific indoor coverage challenges.

“Typically when somebody calls about coverage problems the first question they ask is: What are my options?” he explains. “At that point we ask what carrier they are using. If it’s AT&T or T-Mobile (News - Alert), a signal booster is a nice, easy, and quick implementation. If they’re a multi-carrier establishment, we move to wideband amplifiers or install an antenna to amplify everyone’s signal.”

A second driving factor in choice is the square footage of the area in question. “If a customer needs to cover a smaller area, signal boosters can do the job. In fact, you can deploy multiple smart signal boosters on different floors if it makes economic sense. But when talking 50,000 square feet or more, at that point DAS moves up the list considerably as an option. It also moves up significantly in price, as in many cases multiple antennas are required.” An extreme example for Connelly was a first responders’ facility that required eight different antennas on the roof to meet public safety coverage requirements.

Connelly often combines DAS with signal boosters to extend indoor coverage at a lower cost. “In many cases, approval for DAS can take a long time, so we often deploy signal boosters as an interim solution. Alternatively, we use them in buildings where there might be a couple of problem spots to augment the overall DAS solution.”

Connelly notes that the FCC’s rulings have provided stronger guidelines around approvals for wideband boosters and carrier-specific signal boosters. “In the case of wideband, they have made manufacturers tone down the gain, whereas carrier-specific signal boosters are approved to deliver significantly higher gain,” he explains. “One other distinction is that wideband amplifiers are in essence a point solution with heavy cabling requirements and can’t be expanded. With carrier-specific signal boosters, DAS can become much more expandable, because they are wireless and simple to deploy, so they don’t have an expensive installation component.”

As with any technology choice, not all indoor solutions will fit all scenarios. The key to finding the right technology – or combination thereof – is understanding what makes the most sense when based on a customer’s location, available services, coverage needs, and budget.

George Lamb is vice president of operations and support at Nextivity (www.nextivityinc.com).