
Grid of Beams (GoB) precoding is a codebookbased precoding technique used in 5G systems.

GoB precoding works by dividing the space into a grid of beams.

The gNB selects a subset of beams to transmit data to the user equipment (UE) based on the likelihood of reception by the UE.

The number of beams in the grid is determined by the number of antennas in the gNB antenna array.

In 5G, antenna arrays are defined by: N1: the number of columns and N2: the number of rows. for example N1=2 and N2=2 is shown in the figure.

The number of total beams that can be formed in the grid is equal to: (N1×O1)×(N2×O2).

The oversampling factors (O1 and O2) helps to maximizes precoding gain by spanning for more directions that can precisely locate the UE.

The beams are formed by combining signals from different subsets of the antennas in the gNB antenna array.

The signals are combined using a precoding matrix, which adjusts amplitude and phase of the signals.

The precoding matrix is designed to maximize the signaltonoise ratio (SNR) at the UE. A higher SNR results in a betterquality signal.

A Discrete Fourier Transform (DFT) based GoB is a precoding technique that contains a fixed number of precoders.

Unlike other techniques such as MRT or ZF, which estimate beamforming weights from the channel matrix to precisely optimize the received power, GoB has a definite, predefined number of beamforming weights.

The beamforming weights in GoB are determined based on a Discrete Fourier Transform DFT.

Each beamforming weight in the DFTbased GoB corresponds to a specific direction in space.

The DFTbased GoB is a simple and efficient way to implement beamforming in mobile communication systems.

The use of a fixed number of beamforming weights in the DFTbased GoB simplifies the hardware and reduces the computational complexity of the system.
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