Primer: short-range communication technologies

Many companies are looking to short-range communications to improved in-building coverage. This is a brief explanation of the options available to them. 

Short-range wireless communication is used to extend wireless communication facilities into areas that would otherwise be out of range. These can include remote spots without good cellular coverage, along with underground areas, such as mining environments, transportation tunnels, and even shopping malls. They are often, but not always, connected to a wired backhaul, which then provides the necessary connection to the core network.

Short-range wireless communication devices fall into three broad categories: femto cells, cellular repeaters, and satellite phone repeaters. Each of them offers different characteristics that will suit specific operational environments.

A femto cell is a small communications base station with a range of around 50 metres, designed for use in the home or office. It eliminates the need for dual mode (3G and WiFi devices) by providing 3G connectivity, connecting to the cellular network via a wired backhaul. In an underground environment, that backhaul could consist of an Ethernet to fibre connection, tying into a fibre-optic cable connecting the femto cell with the surface. At the surface, a fibre-to-Ethernet connection would then link to a DSL modem, possibly via a series of meshed WiFi connections. This DSL modem could then connect to the cellular and/or plain old telephone system (POTS) networks.

Companies can also take advantage of WiMax-enabled femto cells, which provide much longer-range coverage than 3G femto cells. WiMax femto cells can extend a network by tens of kilometres, but they need to have a line of sight connection with the mobile devices that they are serving. The drawback to WiMax photocells devices is that they cannot be used with a device unless it is WiMax enabled, and there are very few of those.

Unlike a femto cell, a cellular repeater doesn't require an end-to-end wired backhaul connection. Instead, it uses two antennae - one outside a building, and a second antenna inside the building connected to a base unit. Between them, these two antennae extend the coverage of a local macro cell. The outside antenna acts as a bidirectional relay with the cellular tower, and connects to the base unit antenna inside the building via a coaxial cable. The base unit antenna relays signals between mobile devices in the building and the outside antenna, which then passes them on to the cellular tower.

The cellular repeater can be used to cover a wider area than a 3G femtocell, and so can be useful in larger environments located in places with little or no existing mobile coverage. It can also be useful in situations where customers may not have direct wired access to the mobile network, but are instead simply connecting wirelessly to the macro network.

The satellite phone repeater is used in situations where no cellular tower may be available at all. A company operating in a very remote mining environment where there is no local mobile coverage in the region, for example, might use a satellite repeater to connect 3G-enabled mobile devices with the cellular network via a satellite link. In an underground environment, satellite phone repeaters might be used to connect to a satellite base station, which would then be linked via a wired connection to a satellite ground station on the surface. This ground station would then act as a relay between the satellite base station and the cellular and POTS networks.

By using short-range wireless communications, companies can bring five-bar coverage to areas that previously suffered from little or no cellular signal. That will not only make voice communications possible, but will also open up possibilities for data communications that could in turn be used for process automation.