Abstract

The European ACTS CRABS¹ (Cellular Radio Access for Broadband Services) project has investigated the possibility of bypassing the problem of last-mile re-cabling for broadband access through the use of an LMDS (Local Multipoint Distribution System)² cellular radio approach at 40 GHz. Digital TV would be carried using the standard DVB-S frequency allocation, translated on a 40 GHz carrier. Interactivity would be supported in a dedicated downlink band and a suitable uplink (return) band, both translated to 40 GHz too. Next to the users’ antenna, proper transponders would down-convert video to the DVB-S 950–2150 MHz band, so that it can be received using standard satellite receiver “set-top boxes”, and downlink interactive data down to the first GHz. Another transponder would up-convert the collected user interactive data to 40 GHz for relay to the cell center. A quite important problem to be solved in the CRABS project was the distribution/collection of these bi-directional signals inside an apartment building, or block of houses, from/to a single shared rooftop or block Master Antenna. In fact due to the costs and other obvious practical reasons, it is not possible to install antenna and transponders for each single user. At these frequencies, up to 2150 MHz, the traditional copper-based approach would require thick and expensive coaxial cables, which would have, nonetheless, very severe attenuation problems. Furthermore, their bi-directional use for interactivity would be very difficult from a technical point of view. Our goal was to find a solution based on optical fiber, with no active components except at the terminals. The specifications were to be able to serve as many users as possible within at least 200 m from the antenna. We had to carry it out over a single fiber, which meant a bi-directional light propagation. Finally, cost had to be as low as possible, especially for those components that scaled as the number of users, like the end-user opto-electrical transceivers. The cost constraint made the task technically challenging. We called our project MAPON (Master Antenna Passive Optical Network).

© 2002 Optical Society of America