Nikkei Electronics Asia --September 2010
Feature
Mitsubishi Electric's Onboard Aircraft Internet

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Aug 31, 2010 23:46 Tetsuo Nozawa

Using Millimeter Waves to Hit 100Mbit/s within 20km

Millimeter wave base station for aircraft service

Mitsubishi Electric Corp. of Japan has developed a system using millimeter waves to implement communication between base stations and aircraft in flight, with a peak data transfer rate of 100Mbit/s. Essentially the same system can also be used for communication between aircraft, making it possible provide broadband onboard Internet connection even for aircraft over the Pacific Ocean, for example.

The frequency used will probably be about 45GHz, because the atmosphere is highly transparent to millimeter waves in this band. The 60GHz waveband, in contrast, suffers high attenuation when passing through atmosphere. A source at Mitsubishi Electric says that a range of about 100km is relatively easy to achieve with 45GHz, although the effective data rate does drop with distance. The data rate at up to 20km is 100 Mbit/s, but degrades to 1Mbit/s at 100km.

Recent improvements to the technology concentrate on acquiring and tracking aircraft, which move linearly at high speed. Concretely, a phased array antenna system (Fig.1) has been developed for use with the transceiver mounted on the aircraft's belly, changing gain under phase control. In addition to the millimeter waves used for communication, a beacon signal is also output to notify base stations of aircraft position. Base stations mechanically aim reflectors according to beacon signals, tracking the aircraft.

Fig.1 Aircraft Antenna and Transceiver
Prototypes of the array antenna mounted on the plane's undercarriage (a), and the millimeter-wave transceiver module (b). The array antenna is made of plastic, with 16 rows of 16 elements each. The transceiver module includes mixer, phaser, and amp implemented as GaAs MMICs, along with bandpass and lowpass filters.

According to a source at the company the system is not intended only for use between base stations and aircraft, but between aircraft in flight as well: "Aircraft are in flight between Japan and the United States, over the Pacific Ocean, at intervals of 50km to 100km. If these aircraft are used as relays it should be possible to provide onboard Internet service without having to use satellite links."

Onboard Internet service has been provided in the past by Boeing Co. of the US on international flights using Mitsubishi Electric microwave antennas and satellite links, but in addition to the high cost of satellite circuits, users were only able to achieve throughputs of 150kbit/s to 200kbit/s. The service was launched in 2004, but terminated less than three years later, in 2006 Note 1). The new system offers lower service provision cost and simple bandwidth expansion, and is therefore unlikely to suffer the same fate as its predecessor.

Note 1) At present, onboard Internet service is available in the United States and nearby regions, with a maximum data transfer rate of 3.1Mbit/s between a CDMA2000 1x EV-DO Rev. A base station and the aircraft.