We are now roaming at 30,000 feet...

Soon, even a window seat above the Atlantic will no longer be beyond the reach of the chirping mobile phone. What's the tech behind that change and just how welcome is it, asks Anthony Plewes.

Over the past few months, a host of airlines have announced trials or full launches of on-board mobile telephony systems. Although use of the mobile will still be prohibited during takeoff and landing, those who really cannot afford to switch off for more than 10 minutes will be able to make and take calls during the flight.

All calls will be routed through the plane's on-board GSM network and charged to the customer on their monthly bill as a standard international roaming call.

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In Europe, Air France started its trial with technology partner OnAir at the end of 2007. The first phase provided simple data services such as email and SMS to passengers on their mobile phones.

When the aircraft reaches 10,000 feet, passengers are alerted by a new cockpit light that they can switch on their phones. Some 80 per cent of passengers using the service gave it their approval, according to Air France. The airline has started the next phase of the trial that will allow passengers to use their phone for voice calls.

Other airlines are moving faster. Dubai-based Emirates launched its first full production mobile service in March this year on an Airbus 340, and it is deploying the system from technology partner AeroMobile on a number of its aircraft.

Emirates has been a keen provider of aircraft telephony for some time. Its back-of-the-seat phones incorporated in the entertainment system reportedly carry 7,000 calls per month.

Emirates chose to deploy in-flight mobile phone technology because its passengers wanted to use their own phones. "It is a logical extension of using your mobile on the ground. It is not a revolutionary service - people just want to use their own phone in flight," says David Coiley, VP strategy and external relationships at independent GSM operator AeroMobile.

All these early trials and launches are powered by solutions provided by either OnAir or AeroMobile. These companies have created the in-flight system and have set up relationships with network owners for roaming agreements.

They are in effect acting as airborne mobile virtual network operators and typically have a revenue-sharing agreement with the airline.

Airborne base stations

The key technology in allowing mobile phone use on planes is the picocell. These miniature base stations are the size of an A4 notebook and effectively create a cell for the aircraft.

"Because the phones are closer to the picocell they use less power, which both conserves battery life and doesn't interfere with the aircraft instruments," according to an OnAir spokesman. He adds that they also run a leaky cable along the aircraft ceiling to bring the radio signals even closer to the passenger.

Picocells are not new technology but, according to Chris Cox of picocell manufacturer ip.access, the technology needs to be adapted for use in aircraft. "The biggest difference is that it is a high-vibration environment, so the equipment needs to be much more resilient," he says.

In addition, the picocell needs to be able to stop mobile phones on the airplane attempting to connect with external base stations. It does this by generating RF noise and this is switched on above a certain altitude.

Cabin crew are able to turn the picocells on and off at the appropriate time and only activate voice or data as the airline demands. Australian airline Quantas, for example, reportedly only has plans to offer data and will leave voice switched off permanently.

Once connected to the picocell, the calls are then routed over the aircraft's existing satellite gateway to the solution provider's terrestrial network. OnAir, for example, works with Monaco Telecom which will have the roaming agreements with the passenger's home network, and the call will thus be charged as an international roaming call.

Typically these calls are expected to cost between $3 and $4 per minute, with SMS received at no charge and sent for about $1 per message.

In some cases the aircraft's satellite connection will be the connectivity bottleneck. So although 14 calls can connect to the picocell, only six simultaneous calls can be taken over the satellite connection.

This volume will be cut further with additional data usage. If the system supports email attachments through GPRS connections, it will need to use an upgraded satellite network.

Inmarsat provides most of the satellite connections for the aviation industry. According to an Inmarsat spokesman the market moves very slowly and many aircraft have not yet upgraded to the company's SwiftBroadband network, which provides two channels of 432Kbps connectivity.

OnAir has incorporated SwiftBroadband into its solution, while AeroMobile also uses older lower-bandwidth satellite connections.

Clearing regulatory hurdles

The technology is only half the story. In Europe alone, there are numerous regulatory hurdles. First, the technical solution needs to be approved by the European Aviation Safety Agency (Easa) to ensure it does not interfere with aircraft navigation.

According to an Easa spokesman, it has approved OnAir's technical solution installed in Air France's A318, and it is also working on approval for a number of other systems. Next, the communication system will have to be approved by the local telecoms regulator. In the UK, Ofcom has given the concept the green light.

Finally, the mobile telephony system will have to be approved by the national regulator of the airline. The UK's regulator, the Civil Aviation Authority (CAA) says any UK airline that wants to install an in-flight mobile telephony system will have to demonstrate how they will police passengers and how they will prevent them from using their phones during takeoff and landing.

No UK airline has approached the CAA to approve a mobile phone system, according to a spokesman.

Dissenting voices

News that passengers will be able to use mobile phones on flights has hardly been greeted with universal acclaim. In fact, many people seem to picture themselves sitting next to an inconsiderate oaf bellowing into his phone.

This resistance to mobile telephony on planes has even prompted airlines, such as Emirates' local competitor Qatar Airways, to publicly announce they will not be allowing people to make voice calls on board.

Is this what phone use on planes will be like in practice? Early reports from airlines that are using the technology are positive.

According to Emirates' technology partner AeroMobile, people typically keep their calls short, at about two minutes. This is in fact very similar to the length of calls it experienced with its legacy back-of-seat telephones.

The limitation of air-to-ground connectivity also means that only a limited number of people can call at the same time. What's more, the noisy environment within the cabin means that only people directly next to the caller will be disturbed by the conversation.

It does, however, seem inevitable that some people will abuse the facility and dealing with them will be left to the flight crew. Despite this, bringing mobile telephony to the skies is a positive development for business travellers wanting connectivity on the move.