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Three enterprise cellular options

When building a more complex WLAN for mobile devices is not a viable choice, there are a few enterprise cellular options that can extend coverage.

As employees increasingly rely on mobile devices, enterprises must provide seamless wireless coverage inside buildings. Some companies do this by extending their wireless LANs, but others find they must extend and optimize enterprise cellular coverage inside their buildings as part of the solution.

Deciding whether to focus on extending wireless LAN (WLAN) or cellular coverage will require considering the number of users that must be served, as well as the kinds of apps that must be supported and the amount of money available for buildout. In cases where just a few employees need mobile device support, for example, the cost of building a complex 802.11 wireless LAN may not be justified.  In other scenarios, enterprises may be housed in structures that prevent Wi-Fi buildout.

Enterprises will also have to consider the following questions in choosing a wireless technology:

  • Are there just a few areas within the building without sufficient signal strength and bandwidth, or are problem areas widespread?
  • Are there structural issues limiting signal strength?
  • How much bandwidth will be required? Will just a few employees use mobile devices in the building or is heavy usage expected? Will the traffic be just low-bandwidth voice or will employees view video on tablets or smartphones?

Combining enterprise cellular and Wi-Fi

Most current phones and tablets can communicate on both 802.11 (Wi-Fi) and cellular service, and they are capable of switching seamlessly between the two. However, enabling the seamless transition between the two means adding a fixed-mobile controller.

Fixed-mobile controllers reside on the building’s wired network and either replace or work in conjunction with the PBX. Calls within the enterprise are routed between target phones but outside calls and Internet access are routed through the enterprise broadband connection.

Beyond adding a controller, involving the 802.11 infrastructure for voice traffic adds additional complexity and cost. Additional access points (APs) may be required to handle the load, and it may also be necessary to replace existing APs with those that have prioritization features that limit latency on voice traffic. Network delays and short-term disruptions that can be tolerated when the network carries just email and Web access are not acceptable for voice calls. What's more, enterprises must train help desk staff and implement wireless LAN diagnostic tools designed for voice. Wireless LANs must also be prioritized for video.

Read more about prioritizing wireless LAN for voice.
Read more about prioritizing wireless LAN for video.

Extending enterprise cellular coverage with cellular repeaters

Enterprises that choose to extend cell coverage often have to contend with thick concrete walls, foil-backed insulation or blocked cell towers that reduce signal strength. In cases where there is a strong enough outside signal, enterprises can turn to cellular repeaters to extend in-building cellular coverage.

The solution consists of an antenna mounted outside the building, an amplifier and a second antenna inside the building. The outside antenna picks up the signal, which is then amplified and rebroadcast inside the building.

Low-cost repeaters designed to support a home or small office may be the right solution if there is a single low-signal area within a building. Repeaters that cover larger areas require professional installation to avoid problems such as interference between the two antennas.

Repeaters are limited to specific radio frequency bands, so it’s necessary to choose a solution that supports all of the bands used within your organization. Remember also that repeaters are regulated by the FCC. Make sure the solution you choose is approved, or check with your service provider to learn how to gain approval.

The only cost of this solution is the equipment and installation cost. Cellular providers do not add charges when repeaters are used. For small facilities -- or where just a small area of a building must be covered -- repeaters can be the simplest and lowest cost solution.

Read more about distributed antenna system technology.

Femtocells for extended enterprise cellular

Femtocells generate and transmit cellular signals within a building. Unlike cellular repeaters, femtocells receive and transmit calls back to the service provider through the Internet via a wired broadband connection. As a result, in addition to providing a strong signal, femtocells reduce cellular charges. Traffic to the service provider via the Internet is not charged at cellular rates. However, load on the broadband connection will increase, possibly requiring an upgrade to increased bandwidth and additional Quality of Service facilities to guarantee low latency for voice calls.

Femtocells generate a signal, rather than simply amplifying or retransmitting. As a result, units are specific to individual service providers and are normally sold or leased by the service provider. If employees use more than one provider, multiple femtocells will be required in each part of the building. Professional installation will usually be required. Each unit will provide coverage for a limited area, so in many cases multiple units must be installed and care must be taken when placing the units to avoid interference among them. Enterprises must avoid transmitting signal outside the building, and they must configure access control on the unit, or they risk providing cell service for the immediate neighborhood. 

Because femtocells are supported by the network service provider, they don't require additional support staff or diagnostic tools.

About the author: David B. Jacobs of The Jacobs Group has more than 20 years of networking industry experience. He has managed leading-edge software development projects and consulted to Fortune 500 companies as well as software startups.

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This was last published in October 2011

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