July 25, 2017 —
The problem for in-building wireless communications coverage, as Mike Collado explained it, is that the macro wireless network was never designed or engineered to support in-building wireless for today’s connected world. Collado serves as Corning’s director of wireless applications marketing, and he spoke earlier this year at the Network Infrastructure Forum, a part of the International Wireless Communications Expo. Collado said that among those with an interest in having in-building wireless coverage are wireless service users, mobile network operators, building owners and public safety agencies.
Mobile network operators focus their efforts on developing and sustaining their macro networks, Collado said. They pay attention to quality of service and the cost per bit of delivering service. He said buildings that lack good, reliable wireless coverage and capacity cost their owners revenue. Moreover, owners could face legal liabilities and public relations failures for not having wireless coverage and capacity in their buildings if something bad happens. He said social media readily spreads the word when coverage in a building is poor, and that’s not good for property owners.
Public safety agencies want in-building coverage so their increasingly complex wireless devices, which now include more functions than two-way radio, work properly indoors to help with their tasks and to help their first-responders do their jobs safely, Collado said. “And I would argue that users rely upon their smartphones in order to stay safe,” he said. “You don’t think about pulling a fire alarm because remember we were taught in elementary school, ‘Don’t touch the fire alarm.’ You call 911.”
Among developments spurring the need for in-building wireless systems are energy efficiency and commercial building codes. Building owners’ desire to obtain Leadership in Energy and Environmental Design (LEED) green-building certification motivates them to install energy-efficient reflective glass. Collado said the glass wreaks havoc on RF. “It creates either a dark building or a shadow building,” he said. “A LEED building can block the macro network from reaching another building.”
Commercial building codes increasingly are requiring owners to enable their buildings for indoor public safety wireless communications. “There are new stakeholder roles in order to make this work with wireless operators retreating from playing a starring role in funding and owning and operating these networks,” Collado said. “Others are going to step up and play new and different roles. All of those roles are going to have to align and intertwine to develop and deliver the desired results and outcomes.”
What’s in the Toolkit
Three categories of tools in what Collado called the in-building wireless toolkit can be used to construct indoor systems: legacy, current and emerging tools (see Figure 1). Various tools help to achieve desired outcomes based on the type of building and the needs and requirements of users, operators, owners and public safety agencies.
Legacy tools include signal boosters, such as bidirectional amplifiers, which Collado said are sold for broadband communications. Another legacy tool, repeaters, uses digital signal processing and channelization. And a third legacy tool is passive distributed antenna system (DAS) networks, one type of which is consists of leaky coaxial cable.
Passive DAS uses signal amplification at one end of a length of leaky coaxial cable through which the signal radiates. As a result, Collado said, the greater the distance from the amplifier, the more the signal strength diminishes. A more sophisticated passive DAS uses amplification at the headend, and coaxial cable feeds a series of antennas throughout the structure.
Current tools include active analog DAS, which needs a signal source. The signal can be taken off the air, although Collado said it often works better if the wireless carrier places a base station at the headend to supply the signal. He said an analog DAS converts RF to light, sends the light through fiber-optic cable for the risers, and then converts the light back to RF for the horizontal runs.
Another current tool is small cells, which Collado classifies into two types: picocells and microcells, and e-femtocells that use the internet as backhaul to the carrier core. Other small cells, such as Ericsson Radio Dot and SpiderCloud, have direct connections with the carrier core.
A third current tool is voice over Wi-Fi. Collado said whether voice over Wi-Fi provides satisfactory wireless telephone calls depends on the quality of the building’s Wi-Fi connection.
Among what Collado calls emerging tools are some that reimagine existing tools and others that represent innovations. One is active digital DAS. “With active digital DAS, as opposed to looking at it from an RF perspective, it’s IP,” he said. “It’s a more intelligent DAS system. You’re able to fine-tune what is distributed to each antenna.”
Because the key to DAS is a signal source and distribution, Collado said a pragmatic approach uses small cells as the signal source, followed by active analog DAS or active digital DAS to distribute the signal throughout a building.
Collado said centralized DAS involves collocating the headend equipment. It places the large base stations and other space-consuming gear in another location, perhaps a less expensive real-estate location separate from the building to be served or, if there are space constraints, it puts the base station where it’s possible to deploy it. The collocated headend gear then uses a fiber path to distribute the signal into the building.
With cloud DAS — sometimes called virtualized DAS — essentially the signal source is in the cloud, which refers to computer servers in a data center linked via the internet.
Other emerging tools that use unlicensed spectrum operate at 5 GHz. “Using unlicensed spectrum offers a way to enable LTE in a building to help augment the capacity of the wireless network to provide the desired quality of service or quality of experience in the building,” Collado said.
The Citizens Broadband Radio Service (CBRS) offers the use of shared spectrum that Collado said holds the promise of enabling third parties, neutral hosts and building owners to own and operate wireless networks somewhat independently of the wireless network operator. “CBRS is a new initiative that is gaining traction and momentum,” Collado said. “It may take years for it to become real because the chipsets in smartphones have to enable and support CBRS.”
Generally, the enterprise needs to step up and own or fund part, if not all, of the infrastructure for enabling the in-building coverage, Collado said. He said that measured as a cost per square foot, certain technologies lend themselves better than others that could be deployed in small, medium-size and large buildings or venues.
Collado described a case study for what he called the middleprise, or a building from 100,000 square feet to 500,000 square feet in size (see Figure 2). “They’re hotels. They’re office buildings. They’re residential buildings. In this case, we’re going to look at new construction for a hotel with 350,000 square feet.” Collado said certain things need to happen.
“First of all, you will have a public safety communications requirement for a new building,” he said. “That could depend on the location or municipality and what signals must be delivered to support public safety operations in that jurisdiction. You could use signal boosters to support multiple public safety signals and frequencies cost effectively. Or, potentially, you may need to use a public safety DAS, which is more expensive, depending on how many public safety frequencies it must carry.”
Guests expect Wi-Fi service, so the hotel will have to have to be fitted with Wi-Fi access points. Collado said it’s impossible to control which wireless carriers guests will be using with their phones, so the Wi-Fi service has to support multiple network operators.
Ways to Enable Coverage
A hybrid solution could be used with a middleprise installation, such as the hotel in this example. Collado said a small cell could provide the signal source, and a DAS could distribute the signal in the building. “Cloud DAS is a more virtualized signal source and very much an emerging technology in the toolkit,” he said. “That could be a potential way. Using unlicensed and shared spectrum could be a couple of years down the road, but those are all ways to enable in-building coverage and capacity in this middleprise type of scenario.”
Collado said the emerging tools in the kit require not only developing innovative technologies, but also new business models that align the needs the user, the building owner, the carrier and public safety agencies. “What a great time to be in the wireless industry to solve some of these new and deep challenges,” he said.