Mobile phone operator Orange plans to offer a business version next year of the mobile-over-DSL technology it already offers consumers.

The Onsite Coverage service will enable businesses to improve mobile phone coverage at sites in remote or densely-built areas by installing a PicoBTS, or small mobile base station, on or near their premises.

Orange, a subsidiary of France Télécom, has tested the service with customers in Switzerland and plans to introduce it there at the start of next year, extending the service to its mobile networks in France, Poland, Spain and the UK later in the year, it said Friday.

Over the last year, Orange and other GSM operators have launched services allowing consumers to connect Wi-Fi base stations to their home broadband connections, and to place calls through them using mobile phones compatible with a technology called UMA (Unlicensed Mobile Access).

UMA uses the GSM SIM (Subscriber Identity Module) to authenticate the caller in order to determine who to bill and which calling number to present. The goal of UMA services is to improve indoor coverage, and to allow the customers to make cheaper calls when using the Wi-Fi broadband connection, thus capturing additional revenue that might go to other fixed-line operators.

BT was one of the first to offer a consumer UMA service, branding it Fusion.

Orange has launched a service in France, the UK and elsewhere, known variously as Unik or Unique, while in June, T-Mobile announced the rollout across the US of a service it had tested in Seattle.

Orange already offers to install mobile repeaters to provide additional coverage or capacity in sites such as business parks, but these use expensive leased lines to haul traffic back to the mobile network backbone. The advantage of Onsite Coverage is that it can use cheaper DSL connections wherever the fixed line network is accessible.

There are other ways of extending GSM coverage to remote areas on the cheap. In rural France and in parts of the Scottish Highlands, with the support of local government, competing network operators share base stations, enabling them to cover large areas with a single transmitter where otherwise they would have been forced to install three or four.

This technique works fine in sparsely populated areas, but does not have the capacity to support businesses needing to make many simultaneous calls from a single site.

The PicoBTS transmitters Orange will use for Onsite Coverage have a range of 50 metres. They can handle voice calls, text messages and GPRS data connections for email and so on for up to 50 users, the company said. If more range or more capacity is needed, they can install another transmitter.

In contrast to Orange's Unik consumer service, which offers preferential tariffs for calls made through the home base station, calls made through Onsite Coverage transmitters will be charged just like other mobile calls, because the base station is treated as part of the Orange network.

However, businesses wanting additional in-building coverage on their own premises may be asked to pay an additional monthly rental fee for the transmitters, the company said.