YOKOSUKA-In what they say is the first ever demonstration of its kind, researchers at the Radio Communi cations Research Center of the Com muni cation Research Laboratory (CRL; Ministry of Post and Telecommuni cations) have transmitted gigahertz-band multiple-radio-frequency media over a single optical fiber.
Optical fiber usually transmits digital signals, but can transmit radio-frequency signals if they first are converted to light. Because the circuitry for analog conversion is so simple, this technique could be used to transmit radio-frequency media in areas where radio waves cannot be sent through free space, such as in tunnels. The method developed by the researchers allows multiple services to be provided through one line so that communications infrastructure can be greatly simplified (see figure).
The research group is especially interested in applying the method to intelligent transportation systems (ITS) such as electric toll collection. Cars do not stop at electric toll-collection stations. Instead, the stations rely on radio communication between roadside devices and cars to collect tolls.
In the experiment, electric toll-collection systems were integrated with the Personal Handy System (PHS: a common Japanese cell phone system). Although the electric toll-collection system uses a frequency of 5.8 GHz and the PHS uses 1.9 GHz, only a single antenna was necessary because the PHS signal was converted to 5.8 GHz. The different signals are separated at the receiver. For the PHS to function on highways, relatively simple details such as the switchover between stations remain to be ironed out. The researchers currently are investigating ways to create a similar system that can transmit sound and moving images, as well.
Courtesy of O plus E magazine, Tokyo
