Fujitsu has developed what it claims is the world's first impulse radio-based high-capacity wireless transmission equipment using 70-100GHz millimetre-band transmissions, resulting in over 10Gbit/s throughput.
The technology is proposed as an alternative to fibre-optic trunk lines where such lines would be difficult to lay, and also for ultra-fast wireless LANs.
"For wireless transmissions at speeds exceeding 10Gbit/s, it is best to use the 70-100GHz millimetre band, as it is relatively easy to secure wide swaths of bandwidth and is thus suitable for long-distance transmissions," said Fujitsu.
"However, equipment that operates at these high frequencies requires the use of multiple, single-purpose electronic components, resulting in a high parts count, and there has been minimal progress on miniaturising the equipment and reducing its cost. Impulse radio obviates the need for bulky oscillators and other components, resulting in compact and inexpensive hardware."
In an impulse radio transceiver (see the diagram), the RF transmitter has three components: a short-pulse modulator, a filter, and a power amplifier.
The receiver consisting of a low-noise amplifier, detector, and limiting amplifier.
Impulse radio has issues that conventional radio does not have.
"On the receiving side, waveform distortions - introduced into the signal by the wiring path from the antenna to the amplifier - need to be reduced, and the minute millimetre-band signals need to be faithfully amplified," said Fujitsu. "On the sending side, the millimetre-band pulse signal sent from the transmitter has a propensity towards time variations. At the receiving end, this can lead to slippage on the determination of a millimetre-band pulse as being a 0 or 1, resulting in faulty reception. Therefore, the time variation needs to be minimised."
To address these issues, the firm developed technologies based on its indium-phosphide HEMTs (high electron mobility transistors) which are faster and less noisy that GaAs HEMTs.
A broadband, high-gain, low-noise amplifier was developed, connected to the receiving antenna by a path that has the reverse transmission characteristics of the low-noise amplifier "so that waveform distortions introduced by the interconnect cancel each other out, resulting in a signal waveform that is close to the form it was received as", said Fujitsu.
In the transmitter, Fujitsu Laboratories created a circuit for the InP HEMT short-pulse generator, that generates a pulse based on a 10GHz clock "which has minimal jitter compared to the 10Gbit/s data signal, while referencing the 10Gbit/s data signal", said Fujitsu.
The receiver had a sensitivity of 0.25uW - suitable for km-class transmissions, said the firm (see eye diagram)
Jitter on the transmitter was 0.3ps.
The company aims to develop commercial systems by around 2012.