We are conducting research into a wireless transmission system to be used in mobile outside broadcasts of events that take place over a wide area such as road races. The use of this MIMO※ reception system makes it less likely for transmitted images to "drop out" by enabling signals received from a number of base stations installed around the event area to be composited.
- Coverage of reception areas of up to 16 base stations by one receiver
- Radio waves in the gigahertz bands (such as the 1.2-GHz band, 2.3-GHz band, or 6 to 7 GHz bands) have larger propagation losses from the environment they pass through in comparison with radio waves in the 800-MHz band that are used for conventional mobile outside broadcasts. This makes it difficult to provide stable mobile outside broadcasts that do not cause outage. We have prototyped a receiver that enables dramatic improvements in wireless link reliability by collecting the received signals of up to 16 base stations into optical fibers and selectively combining them.
- Selecting and combining of the best four branches and compensating for path length differences of up to 160 km
- The optical fibers that collect together the received signals from base stations (branches) to the receiver have a wide range of lengths. In addition, the wireless propagation path lengths also change constantly as the transmitter moves. Since the reception performance after combination of branch signals with greatly different path lengths would deteriorate, the receiver compensates for delay time differences corresponding to path length differences, selects the best four branches, and combines them.
- Prototypes compact radio-frequency (RF) down-converter and IF-band five-optical-wavelength multiplex transmitter
- We have prototyped a compact radio-frequency (RF) down-converter, which has the same level of performance as the one of conventional FPUs, and an IF-band five optical wavelength multiplex transmitter, which can transmit up to five IF signals on one optical fiber. This enables an increase in reception points at low cost, without having to install new optical fiber links.
In the works
We will conduct field experiments using gigahertz-band radio waves and evaluate the effects of the improved wireless link reliability due to this MIMO reception system.
- ※MIMO:Multiple-Input Multiple-Output
MIMO reception mechanism