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What is the process of beamforming in MIMO / Massive MIMO systems?



Beamforming is a technology that has been around for years. Beamforming is a technique for focusing a signal in a specific direction to be received at maximum gain at the receiver side. Because signal transmission from the transmitter to the receiver is directional, the receiver receives a greater signal in this process. When we send a signal from the transmitter to the receiver, the transmitter antenna spreads the signal out in an omnidirectional pattern. It'll be much easier if you've observed an antenna's radiation pattern. Using a directional beam, you can think of beamforming as directional communication between a transmitter and receiver.

More than one antenna element is required to form a beam. They will, of course, be closely spaced for proper beam forming. The resultant phase of the signals will be fixed when we send signals from multiple nearby antennas. Simply put, directional communication is possible because the signal transmission on one side is stronger than on the other, as opposed to omnidirectional transmission.


1. Beamforming in MIMO:

We can use a MIMO system or a Massive MIMO system for better beam formation. Antennas (antenna elements) are close together here. Antenna elements are typically spaced at half-wavelength intervals. When we transmit the same signal from several antennas in a multiple input multiple output (MIMO) system, it generates a beam to the receiver in a specific direction, allowing the receiver to receive a stronger signal. It also boosts the signal-to-noise ratio (SNR) at the receiver end.
On the other hand, spatial multiplexing is one of the most essential characteristics of MIMO systems. As a result, we can send multiple data streams to the transmitter and receiver at the same time. As a result, we will be able to reach higher data rates. It will be easier to understand if you use an example. Assume there is only one transmitter and receiver antenna, and they communicate at a data rate of 150 kbps. There are numerous simultaneous data streams between the transmitter and receiver if there are multiple antennas on the transmitter and receiver sides or if MIMO antennas are available. There are two data streams available at the same time between the transmitter and the receiver. Then the communication speed between them will be two times faster than before. Then it'll be around 300 kbps.

When more antenna elements are close together, we can produce a more powerful narrow beam. There are hundreds of antenna elements in large MIMO. As a result, we can use massive MIMO to create a narrower beam. Conversely, if we broadcast signal bits at higher frequencies, we can also obtain a smaller beam. For example, in the case of 60 GHz communication rather than 28 GHz extremely high frequency (EHF) communication, we can produce a narrower beam utilizing the same size MIMO antenna.


Figure: A hybrid beamforming example using a 64 x 16 MIMO system and 4 RF chains functioning at both TX and RX at 28 GHz


2. Various Types of Beamforming in MIMO:

During the beamforming process, some issues may develop. Internal interference between multiple data streams transmitted from many antennas in a MIMO system between transmitter and receiver can be a big issue. As a result, we'll need to use a pre-coding strategy to eliminate interference between many data streams. There are various techniques for pre-coding. We'll talk about it later.

Analog, digital, and hybrid beamforming are the main examples of beamforming techniques. Beam steering is used for analog beam forming. Digital beam forming can regulate a signal's amplitude and phase, whereas analog beam forming can only adjust the phase. Hybrid beam formation is comparable to digital beamforming. However, it is less complicated. As a result, in the case of massive MIMO communication, it is a cost-effective and widely accepted technology.

# mimo beamforming  # analog beamforming

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