We can now cancel interference at the receiver's second antenna or antenna element using digital pre-coding techniques by canceling h12, h32, and so on. We can only use the singular value decomposition technique (SVD) and other operations at the digital pre-coding matrix to get h11, h22, and other data streams for independent data streams.
Similarly, in a MIMO system, we can consider the aforementioned for multi-user digital beamforming. Assume that there are N users connected to a base station (BS). So, we know that between the transmitter (here, BS) and the receivers, there will be a channel matrix (say, H) (here, users). We've already established that the received signal is designated as in the preceding paragraph.
y = √pHDs + n
Now, for multiuser MIMO, digital pre-coding matrix, D, can be expressed as,
D = [D1,D2,D3, … ,DN]
Where DN denotes the user N's digital pre-coder. We now delete the interference at user N by canceling all other users' links at user N with (Hu)DN = 0, where N u. Simply put, 'u' stands for user u, and all values of link contribution from other users at user u are set to zero during signal processing for user u. At the user u's signal processing, we only accept (Hu)Du; other terms such as HuD1, HuD2, and so on should be zero if a proper signal processing method is applied at the receiver side of user u.
Digital beam forming is a frequently used pre-coding technique for canceling interference between MIMO antennas at both the transmitter and receiver. It can also be used to cancel the interface between multi-user MIMO. In MIMO, we need a total number of RF chains equal to the entire number of antenna components for digital pre-coding. In a MIMO system, each RF is capable of providing a single data stream. This is acceptable for digital beam forming in lower dimensions. However, when it comes to huge MIMO transmission, point-to-point MIMO isn't actually scalable. However, as the number of antenna elements increases, the signal correlation at the receiver improves.
Analog vs Digital Beamforming:
In analog beamforming, a single data stream is transmitted using just one RF chain.
It is used to control the phases of the original signals.
For the largest antenna, more array gain is achievable.
SNR effective
Both the Phases and amplitudes are controlled using digital beamforming to eliminate interferences beforehand.
BS employs Nt antennas to simultaneously transmit Nr data streams to a user with Nr antennas (Nr < Nt)
Number of antennas at the receiver = Number of simultaneously available data streams
Using its Nt number of RF chains, the BS applies an Nt X Nr digital precoder D.
RF chain for each antenna element
# mimo beamforming # analog beamforming