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Beamforming

Beamforming is a MIMO technique that uses multiple antennas at both the transmitter and receiver to form directional beams that focus the energy toward the intended receiver, rather than scattering it in all directions. To enhance the performance of wireless systems, beamforming exploits the spatial dimension, adding to the traditional time and frequency dimensions used in communication links. Various methods include transmit beamforming, receive beamforming, adaptive beamforming, hybrid beamforming, and massive MIMO beamforming.

Hybrid Beamforming

Hybrid beamforming involves digital precoding of transmission signals and analog beamforming that spatially separates the data streams when they are transmitted. After the signals propagate through the channel, the receiver can recover the spatially separated and precoded streams without interference from other streams. The precoder maps the input data streams to the output transmit data chains (see Precoding). Each transmit chain is transmitted by a physical radio unit. The number of transmit antennas, NT, must be greater than the number of transmit chains, NTxchains, and the number of transmit chains, NTxchains, must be greater than or equal to the number of input streams, NStreams.

The signal paths form transmit chains through a hybrid beamformer.

For an example that demonstrate hybrid MIMO beamforming, see MIMO-OFDM Precoding with Phased Arrays. This example models the radiating elements that comprise a transmitter and the front-end receiver components, for a MIMO-OFDM communications system.

Massive MIMO Beamforming

Massive MIMO beamforming refers to beamforming a few transmit chains onto a large number of antennas (nominally greater than 64).

For an example that demonstrate massive MIMO beamforming, see Massive MIMO Hybrid Beamforming. This example uses hybrid beamforming at the transmit end of a massive MIMO communications system, using multi-user and single-user system techniques. The example determines the channel state information at the transmitter by using full channel sounding.

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