In order to achieve 5G communication rates, research is centred on hybrid beamforming that uses millimetre waveband and multiple antenna elements to transmit signals simultaneously as beams to individual devices.
However, with this method, interference occurs when sending signals to multiple devices, leading to reduced transmission rates. For example, in a system with 128 antenna elements, and 8 multiplexed beams, the number of D/A circuits with hybrid beamforming can be reduced to one sixteenth that of digital beamforming, but because the multiplexed beams interfere with each other, the transmission rate falls to just one eighth that of digital.
Fujitsu has found that with an interleaved structure, which is a type of hybrid beamforming, it is possible to cancel out interference between beams.
With an interleaved-type device, there is increased spacing between antenna elements within a subarray (which is a collection of antenna elements connected to one D/A circuit), increasing the subarray's area.
When an antenna's range is spread out, its beam becomes narrower, and as the antenna elements are spread out, an undesired emission, called a grating lobe, can occur. If the elements for different subarrays are placed alternately, then the signals from both subarrays, A and B, will both be sent as radio waves in both directions the arrays are transmitting.
Signal A, however, will be sent in the same phase in both directions, while, due to the positional relationship between antenna elements, the radio wave phase will change for signal B, depending on the direction. Using this characteristic, by coding the signal appropriately between subarrays, the interference can be cancelled out and the beam can be multiplexed.
Fujitsu says it should be possible for multiple users in busy areas to simultaneously, and with stability, communicate at high rates – even when doing data-intensive activities such as uploading videos.
