Beamforming is a method of concentrating radio frequency (RF) energy in order to improve the signal to noise ratio (SNR) at the receiver, thereby improving network performance and predictability. Enterprise WLAN vendors are now integrating beamforming technology into their access points (APs) so it is important to understand the types of beamforming and the benefits that beamforming can provide.
Beamforming is not new. At the most basic level, beamforming affects the radiation pattern of a wireless signal. The radiation pattern refers to the way in which the electromagnetic waves propagate outward from the antenna element. For example, the most commonly deployed antenna is the omnidirectional antenna. The radiation pattern for the omnidirectional antenna is in the shape of a doughnut (see Figure 1). This type of antenna is a good choice for hotspots or any environment where the intent is to propagate the WLAN signal in a broadly dispersed pattern.
Figure 1: OMNI radiation pattern (source: Cisco Systems)
WLAN venders currently offer three types of beamforming. Each type affects radiation patterns in different ways.
Static beamforming involves the use of internal or external antennas that have a fixed radiation pattern (such as a YAGI antenna) that emits a directional radiation pattern (see Figure 2). A directional pattern is a good choice in environments where the intent is to propagate the WLAN signal in a particular direction, such as down a hallway or toward the interior of a building.
Figure 2: Directional radiation pattern (source: Cisco Systems)
Transmit beamforming propagates two or more phase-shifted copies of a signal on a frame-by-frame basis, so that they will be in-phase at particular points in space where the transmitter believes the receiver to be, thereby increasing SNR.
Dynamic beamforming changes the antenna radiation pattern on a frame-by-frame basis using a central processing unit (CPU) controlled antenna array in order to increase the SNR at the receiver.
In subsequent posts we will look at each of the beamforming types. Next time, we will look at static beamforming.
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