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May 28, 2012

Transmit Beamforming Comes with a Big BUT...

Glapaby Steven Glapa
Senior Director of Product Marketing

Sumo-Wrestler 


Rapidly rising performance requirements on enterprise and carrier Wi-Fi networks dictate squeezing every available Mbps out of infrastructure gear — naturally driving increased interest in using any and all advances in RF technology. 

One in particular, so-called transmit beamforming (commonly abbreviated as TxBF), is getting much more attention these days.  While this is a potentially useful tool, be careful not to be fooled by vendor claims.  As always, the devil is in the details.

Wp-image.jpgSince discussing RF technologies with precision can get complicated, a careful, step-by-step search for the devil behind TxBF really requires the bandwidth of a proper whitepaper rather than a simple blog entry.  For those interested in the technical hows and whys, we’ve published the step-by-step story in just such a beefy whitepaper.  For the less patient, we’ll summarize the key findings here.

RF BUILDING BLOCKS

Many of the tech Chart-2nologies available to help improve radio performance come from the broad category known as “smart antennas.” There are many variations on the theme, but the idea common to them all is using more than one antenna on one or both ends of the link to send and/or receive radio signals in a more controlled manner, to increase signal quality and throughput.

There’s now a whole family of multi-antenna techniques that can be employed to achieve RF performance gains in Wi-Fi.  In a properly designed Wi-Fi system, all of these tools can be used in combination to maximize results. Click on the chart for more detail

Note that both AA and TxBF are often referred to loosely as “beamforming,” since many in the industry consider the term to mean generically “shaping radio energy in space to focus on the target recipient.”  There are fundamental differences in how these two technologies operate; however, yielding very significant differences in the performance improvements they can deliver in the real world.

 

ASSESSING TRANSMIT BEAMFORMING

Transmit beamforming allows an access point to concentrate energy in the direction of a particular client using signal processing techniques (phasing or timing the signals differently) at the baseband chipset.  Explicit client feedback is required for APs to determine the correct phasing for each client.

While a promising potential addition to the RF toolkit, in reality, TxBF is subject to a number of constraints and disadvantages:

Txbf-supportNo Client Support.  There’s simply no way around it. Today this is a complete show-stopper. To achieve any real performance gains with TxBF in Wi-Fi, clients must support the optional feature in the 802.11n standard that provides explicit feedback to the AP about how to do beamforming effectively for each client. 

As we show in the figure (right), this feature has zero support in the market today and none on the way in the foreseeable future.

Incompatibility with Spatial Multiplexing.  The explanation for this one is definitely best left to our beefy whitepaper, since it requires looking under the hood of how spatial multiplexing in 802.11n really works. The bottom line is that with any commercially practical number of radio chains, it’s impossible to achieve the higher data rates in 802.11n and use TxBF at the same time.

Lots of Self-Interference.  With only 3 or even 4 radio chains to work with, TxBF makes very symmetric beam patterns, generally sending as much energy away from the client of interest as it does toward it. This increases self-interference in the multi-AP networks that are critical to success in today’s high-demand-density venues, reducing spectrum re-use and overall system capacity.

Incompatibility with Polarization Diversity.  There’s a technical subtlety at work here, too (have we mentioned that we have a beefy whitepaper to cover these things?).  The net is that TxBF will fail frequently when used with today’s mobile clients with arbitrary orientation.

Modest Gains at Best.  Even when it works, the Wi-Fi chipset engineering community predicts that performance gains in practice will be modest, on the order of 2–3 dB.

ASSESSING ADAPTIVE ANTENNAS

Adaptive antennas — the basis for Ruckus BeamFlex technology — involve manipulating the inherent directionality and polarization of the physical antenna structure itself.  This is achieved by electronically switching a subset of a large number of small antenna elements into use with each radio chain for each packet sent.  Element selection is optimized client by client, based on achieved throughput, relying on the ACK packet that all clients send as a 100% standard part of the Wi-Fi protocol.

As a result of this unique “layer zero” role in the system, adaptive antennas have none of the operational limitations of TxBF.  Specifically, adaptive antennas:

  • require no special client behavior beyond mandatory elements in the 802.11 standards (for b, g, or n);
  • can be used simultaneously with spatial multiplexing and polarization diversity;
  • mitigate interference through highly asymmetric beam patterns; and
  • deliver 2 to 3x the performance improvement of TxBF, through better leverage of multipath and statistical optimization techniques.

WHAT'S IT ALL MEAN?

TxBF-AA-comparisonIn short, while vendors are now marketing TxBF as THE solution to the RF performance problem all by itself, it’s not going to do much if any good any time soon (click on figure left).

There are circumstances when TxBF will be useful when client support emerges and in combination to adaptive antenna switching.  Since it’s available in the next generation of Wi-Fi chipsets TxBF in combination with BeamFlex adaptive antennas, in a form of “BeamFlex 2.0”, offers a best-of-both-worlds solution that yields higher SINR gain with less interference than TxBF alone.  

Chart

So don’t return to the old omni-antenna reference-design implementations that continue to pollute both the enterprise and carrier network landscape with such mediocre Wi-Fi performance. 

Ultimately combining TxBF with adaptive antenna technology will simply deliver the best of both worlds yielding what no other Wi-Fi supplier can provide and every customer wants: PERVASIVE PERFORMANCE.

 

 

 

May 04, 2012

A PUBLIC APOLOGY

Chick-with-foil-hatIt’s not often when an equipment supplier has to stand up and apologize in public. 

This is one of those times. And we are one of those companies willing to do so. So consider this our mea culpa.

We recently received this actual correspondance (click on email below) from a concerned party about a new promotional video that we developed (view the video below).  It was meant to be a tongue and cheek piece about how religious we are about Wi-Fi. But it backfired.

For years, wireless vendors of all variety have been preaching the benefits of their technologies.  We’ve all seen the ads…happy, attractive, young professionals using their laptop, smartphone or tablet to access the Internet wirelessly from unusually remote locations.  Email

We’re led to believe that being able to view cute kitten videos while perched on a bluff above a sunset drenched beach will greatly enrich our lives and give us an LOL feeling that will never go away.  It’s a digital utopia brought to you by your chosen Wi-Fi, cellular, 3G/4G vendor, through the magical portal of that cool little device you carry in your pocket.

But it’s all a lie.

Some believe that the brilliant [yet sinister] marketing minds in the industry have manufactured this New World Vision simply to cover up the real reason our companies are pushing for pervasive wireless coverage:  spiritual domination. But this is NOT our goal or plan at Ruckus Wireless.

As the thinking goes, it’s all part of a massive, highly-organized plan to take over the souls of the world’s unsuspecting population.  The idea is elegantly simple at its core…if we can control every individual on the planet, we control everything.  We can control the labor force, we can control commerce, we can eliminate territorial boundaries, we can deem individual governments obsolete, we can end war...and we will profit handsomely.

Well, we would have profited handsomely, if not for the work of one incredibly brave whistleblower.  This individual somehow uncovered our plans, and as a result, Ruckus is ready to come clean.  Here's the "wireless commercial" to which the email refers.

We are willing to stand up for the human race and pledge to do no evil [for reals].  We have seen the light…and our focus now is to relentlessly pursue justice for the common man, and utilize all of our resources to expose the plot for World Wide Wireless (WWW).

This is our commitment to mankind – for the record.

It's nice to know the Internet
can still blow our mind on occasion.