There are 3 types of beamforming used in 5G :
- Analog beamforming uses the same signal is fed to each antenna and then analog phase-shifters are used to steer the signal emitted by the array so beams are controlled by a series of phase-shifters to send the same signal from multiple antennas but with different phases
So it is low cost but support only single stream transmission one of the main limitation and main problem here is that this approach does not allow different beamforming weights to be applied for different users and so only single beam is generated at a time it means that Beamforming and mimo will loose benefit of spatial multiplexing
- Digital beamforming designs different signals for each antennas in the digital baseband. There is RF CHAIN for each antenna This makes digital beamforming particularly desirable for spatial multiplexing, where we want to transmit a superposition of signals, each with a separate directivity.
- Hybrid beamforming combines the digital beamforming and analog beamforming, it means part of the beamforming is done by digital processing in the baseband, and part of the beamforming by analog RF beamformers. The number of TRXs and RF Chains in the beamforming antenna are in general lower than the number of antennas.
The motivation for hybrid beamforming is to minimize the number of RF chains, which will reduce energy consumption and design complexity, making it more generally cost-effective. This is the solution used in mmwave bands (FR2 bands)