Hybrid Beamforming:
Hybrid beam formation was developed to address some of the limitations of digital pre-coding approaches. Every antenna element is connected to an RF chain in digital pre-coding (beam forming) method. We also know that each RF chain is in charge of providing a separate data stream between the transmitter and the receiver. We know that a larger number of independent data streams leads to higher data rates. It has a spatial multiplexing feature for MIMO. As a result, we may assume that switching from MIMO to massive MIMO will benefit us more in terms of spatial multiplexing in massive MIMO, where each antenna is coupled to a single RF chain. We'll proceed with a definition of hybrid beam forming.
Overview of hybrid beam forming with example:
Unlike digital beam forming, more than one antenna element is connected to a single RF chain in hybrid pre-coder (beam forming). Let me give you an example to help you understand. Let's assume there are 64 antenna elements in a MIMO system and we're only using four RF chains. A single RF chain is used to connect 16 antenna elements. The hybrid pre coder can be divided into two parts at this point. Because 16 antennas are joined to a single RF chain, the signal is sent by all 16 antenna elements. As a result, it can produce a beam and maximize SNR at the receiver. We may, on the other hand, guide the beam in a variety of ways. This is a characteristic of analog pre-coders (beam forming).
Fig: Hybrid Beamforming
Similarly, we can use a digital pre-coding technique to cancel interference across four existing RF networks. As a result, we can define hybrid pre-coding as a strategy that combines a lower-dimensional digital pre-coder with a big array size. The huge array is utilized to boost correlation gain at the receiver side and to remove interference between simultaneous data streams using a digital pre-coder.
Why hybrid beam forming is suitable for massive MIMO system?
Now we'll talk about why we're switching from MIMO to huge MIMO technology and why we're employing hybrid pre-coding. The first reason is that if each antenna element continues to use a single RF chain, signal processing on the reception side will become extremely complex.
Massive MIMO uses hundreds of antenna elements that are put very close together. As a result, there's a danger that antenna elements will be burned. Second, for smaller dimensional MIMO, such as 2 X 2, 3 X 3 MIMO, digital pre-coding is fine. This is also useful for MIMO point-to-point transmission.
However, if the size of MIMO grows larger, such as beyond 8 x 8 MIMO, point-to-point communication becomes less scalable. In the context of signal processing at the receiver, it becomes more complicated. On the other hand, increasing the antenna array size results in better signal correlation at the receiver side, which helps to battle high path-loss, particularly when employing a very high frequency band, such as the millimeter wave band.
Signals in the higher frequency spectrum are reflected and refracted several times. As a result, receiving LOS (Line of Sight) between transmitter and receiver is extremely challenging. Point-to-point communication is not a smart concept in this situation. As a result, we adopt a hybrid pre-coding technique with fewer RF chains and a big array antenna (in the analogue pre-coder component) to boost gain even further. As a result, the hybrid pre-coding technique is both cost-effective and simple. We attain the same degree of performance in hybrid pre-coding as we do in digital pre-coding.
MATLAB is a powerful mathematical tool that assists students, engineers, and scientists in implementing mathematics in complicated systems and producing understandable graphs and graphics. Now, using MATLAB, we will compare different types of beamforming, such as analogue beamforming, digital beamforming, and hybrid beamforming.
Assume you have a MIMO system with 64 antenna elements on the transmitter and 16 antenna elements on the receiver.
MATLAB Script: