Autonomous driving technologies will require increasingly faster and larger-capacity wireless communications. To this end, efforts are under way to make effective use of the millimetre wave band, and even higher frequency bands for mobile communications.

In high-speed mobile environments, rapid changes in communication conditions occur due to both the movement of the vehicle itself and surrounding high-speed vehicles.

To boost millimetre-wave transmissions, high-frequency distributed MIMO systems can be deployed in which a single base station uses a large number of antennas distributed among various locations for transmission to each mobile terminal.

For high-frequency distributed MIMO transmission, it is necessary to detect the optimal combination of distributed antennas and beams in response to changes in the radio communication environment for each mobile terminal.

NTT and DOCOMO have developed a beam-search technology that can rapidly detect the optimum combination of distributed antennas and beams using the same beam identification signal.

Billed as a successful demonstration of future high frequency 6G communications in cars and trains, the demonstration was conducted in a simulated high-speed mobile environment, driving a mobile-terminal vehicle at 100 km/h, with three distributed antennas at 150m intervals installed on one side of the road.

The technology selects the most appropriate antennas and beams at high speed and uses frequency and timing-compensation technology to prevent significant changes in reception frequency and timing on the mobile-terminal side, even if the terminals are moving at high speed or are shielded by other vehicles moving at high speed.

According to the three partner companies, the demonstration verified the potential of mmWave distributed MIMO to achieve stable, high-capacity wireless communications in high-speed moving environments, such as automobiles and trains, for purposes such as providing large-volume content to many passengers and collecting massive sensing data for automated driving.

"Throughput drop during antenna switching was suppressed to maintain throughput at about 100Mbps," the partner companies said.

"The result was stable high-capacity communication using millimetre waves even during high-speed travel."

The three companies say they will proceed with verifications of actual services on roads and railways, aiming to eventually implement high-frequency distributed MIMO in high-speed mobile environments.