Beamforming technology focuses radio signals towards wireless stations (STAs) in specific directions, thereby comprehensively improving the received signal strength indicators (RSSIs) of STAs and also increasing STA throughput. This technology is introduced to the Wi-Fi (also known as WiFi) field in Wi-Fi 4 (802.11n).
Why Is Beamforming Necessary for Wi-Fi?
Wi-Fi standards have been dedicated to increasing transmission rates. Since Wi-Fi 4 (802.11n) introduced multiple-input multiple-output (MIMO) and beamforming technologies, the maximum transmission rate has surged to hundreds of megabits per second and even higher.
MIMO technology multiplies transmission rates by adopting multi-antenna transmission. STAs in practice, however, usually have only one or two antennas each. This causes gain differences between the transmit and receive signals on the STAs. That is, when a STA sends signals to an AP, the AP can use its multi-antenna system to enhance the receive gain and achieve higher signal strength. It is not the case for reverse transmission. When an AP sends signals to a STA, if only antennas of the same number as those on the STA are used, the multi-antenna gain is not utilized. To address this issue, beamforming technology is introduced. It enables APs and STAs to negotiate higher transmission rates by increasing the RSSIs of STAs.
To ensure the AP's multi-antenna resources are fully utilized, Wi-Fi 5 (802.11ac) introduces multi-user MIMO (MU-MIMO) technology so that an AP can send signals to multiple STAs at the same time, improving wireless transmission efficiency. MU-MIMO is dependent on beamforming. Beamforming technology superimposes signals from multiple antennas of an AP so that each STA can receive only its own signals during MU-MIMO communication, preventing signal interference between the STAs. On top of that, the latest-generation Wi-Fi 6 (802.11ax) standard further increases the number of MU-MIMO users, which is also made possible by the use of beamforming.
How Does Beamforming Work?
How does beamforming form the shape of a beam? Signal beams are similar to light beams. The shape of a light beam produced by a flashlight is fixed. If another flashlight produces a light beam in the same direction, the two light beams are superimposed, thereby increasing the beam brightness and changing the beam shape. If more flashlights are used, the brightness and shape of the superposed beam both continue to change. In the case of multiple flashlights, turning on/off the flashlights or adjusting the light intensity also affects the beam shape.
Likewise, in wireless communication, an antenna emits radio beams like a flashlight. With multiple antennas, the radio beam shape can be adjusted by controlling radio signals transmitted by each antenna.
In a multi-antenna system, when signals transmitted by different antennas arrive at a location, a spatial hole may occur if two beams have equal attenuation but opposite phases. Beamforming technology enables two beams to be superimposed with the best effect by pre-compensating the phases of transmit antennas.
Beamforming implementation
For more information, see Beamforming
