Beamforming : Revolutionary Technology in Wi-Fi

Beamforming is an important companion to 4×4 Multiple Input Multiple Output (MIMO) technology for Full-11n™ Wi-Fi wireless networking. When it is included, it enables dramatic improvement in Wi-Fi 802.11n performance, reliability, range and coverage. It is a non-proprietary wireless technology that can be integrated across a range of devices, from access points to laptops to smartphones. It greatly improves wireless performance, providing a 2X-3X improvement over previous wireless solutions.

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There are two ways to define Beamforming technology, one is technical and other is non-technical:

Beamforming is a technique implemented in digital signal processing (DSP) logic to improve range and data rate for a given client, or device. In a basic system (single stream), Beamforming works on the principle that signals sent on separate antennas can be coordinated to combine constructively at the receive antenna. Specifically, the phases of the transmit signals are manipulated to improve directivity. Beamforming is specified in the IEEE 802.11n specification and takes advantage of the multiple transmit antennas available in a multiple input, multiple output (MIMO) system.

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Consider previous generations, wireless like a light bulb, with a hotspot or access point “radiating” wireless indiscriminately in a set area. Beamforming is like a laser — the hub recognizes the device that needs wireless and focuses the wireless directly where it’s needed — whether it’s one device or 20.

How it works:Beamforming is a signal processing technique used to control the directionality of the transmission and reception of radio signals. The most effective type of beamforming is dynamic digital beamforming. This type of beamforming uses an advanced, on-chip digital signal processing (DSP) algorithm to gain complete control over Wi-Fi signals. By creating several independent signal paths to optimally focus radio energy to and from client devices on a per-packet basis, performance is dramatically improved. In the case of a two-stream configuration, this makes it possible to steer the energy of the antenna array in the independent spatial directions associated with both data streams, while simultaneously avoiding interference.

beamforming[3]

When combined with 4×4 MIMO, dynamic digital beamforming is particularly powerful. This is because a 4×4 MIMO system supports two data streams and provides two extra transmit antennas that may be used for beamforming, to allow significant focusing of the energy in two directions while reducing interference with coexisting systems. This type of combined solution can deliver from 12 to 25 dB of system gains relative to 802.11n wireless LAN systems without dynamic digital transmit beamforming.

In contrast, a 3×3 system transmitting two data streams has significantly lower reliability since there is only one extra antenna to focus energy in the two required directions. A 2×2 system gets very little benefit from transmit beamforming since has only the minimum required antennas. While dynamic digital beamforming works with any number of receive antennas, it is most powerful in a 4×4 MIMO configuration.

Users can identify that beamforming is supported by their product if the vendor touts the technology as a differentiating feature. For example, Cisco brands beamforming as ClientLink/ClientLink2.0 on its enterprise access point products. As part of the 11ac wireless specification, beamforming is expected to become standard on wireless device beginning in 2013. Enterprises, however, can begin to take advantage of the technology now to improve performance while ensuring their technology investments will not be nullified with the next generation of wireless solutions.

Applications of Beamforming Technology:

Beamforming Application

Beamformers vs. Omnidirectional Antennas :

1) Beamformers have much higher Gain than omnidirectional antennas: Increase coverage and reduce number of antennas!

2) Beamformers can reject interference while omnidirectional antennas can’t: Improve SNR and system capacity!

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3) Beamformers directionally send down link information to the users while omnidirectional antennas can’t: save energy!

4) Beamformers provide N-fold diversity Gain of omnidirectional antennas: increase system capacity(SDMA)

5) Beamformers suppress delay spread:improve signal quality.

 

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Limitations : Standards based beamforming adds a feedback overhead in the system. Also, since CSI is changing from time to time, especially with motion of either AP or client, the steering matrix needs frequent updating. Additionally, it operates on a per-client basis. Since broadcast signals cannot be optimized, which would include beacons, the overall maximum range of the AP cannot be increased using only beamforming. 2×2 systems get only a modest benefit from beamforming since they only have the minimum required antennas. However, 4×4 systems are becoming the defacto configurations in APs, thus making the 2×2 limitation non-existent. For systems that do implement 2×2 APs, it is only a marginal design change to the system with potential to provide better gain than if it were implemented without. Additionally, since most enterprise APs and hotspots already deploy MIMO systems, which are now emerging in home APs as well, it is more beneficial to implement beamforming than not. Finally, referring to the aforementioned use case scenario, where the AP and a client such as a TV are relatively fixed, per-client improvement is highly desirable.

Sources :Quantenna, Marvell

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Rahul Mishra
A Post Graduate in Network Technology from Amity University and Founder of TechniCafe. He is Extensively experienced in Cisco core networking, VoIP technology and RSA Data Loss and Prevention.
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