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Just finished watching a very informative video given by Gene Hill on beam forming.

Over the last few years there have been a lot of very clever technologies employed in Wi-Fi such as Single Channel Architecture. However there has been very little on the RF side that has shown much interest to me. The Ruckus Adapative Beam Forming system looks very impressive. [ I have zero affiliation with any manufacturer ]. For those not familiar with this system, and for folks who don???¡é?¡é?????¡é???¡ét have an RF background, I hope the following notes will help:

Imagine a radio transmitter attached to an omnidirectional antenna [ one that can radiate signal equally in all directions ???¡é?¡é?????¡é?€?? it can???¡é?¡é?????¡é???¡ét quite do this in paractice, but nearly so ]. Let???¡é?¡é?????¡é???¡és imagine that we were transmitting 1 W of power out of the transmitter, straight into the antenna [ the FCC wouldn???¡é?¡é?????¡é???¡ét be too happy !! ]. That one watt of power would be radiated equally all over. Now imagine that we have a special instrument that measures signal power. It has an antenna that has one square foot of area. We measure the power received fifty feet away from the antenna where out AP is going to be. Lets say it was ???¡é?¡é?????¡é?€?? 70 dBm [ just a made up number ]. We could say that the amount of power per square foot is -70 dBm per square foot [ square meters are normally used ]. We call this the Power Flux Density or PFD. This is a very imporatnt factor in radio link engineering.

Now we replace the omnidirectional antenna with a Yagi [ semi-directional ] antenna. We again measure the PFD. This time we see the PFD value much higher than previously. This is because the same transmit power [ 1W ] has been ???¡é?¡é?????¡­?¡°concentrated???¡é?¡é???????? by the beam into a narrow ???¡é?¡é?????¡­?¡°tunnel???¡é?¡é???????? [ the antenna transmit beamwidth ]. If we can increase our PFD [ provided that the noise environment has not changed ] then we can increase our signal to noise ratio. This enables us to have/do more ???¡é?¡é?????¡­?¡°good things???¡é?¡é????????. We could increase our data rate for example. An antenna has a receive beamwidth [ Rx B/W ] as well. Unfortunately this Rx B/W acts as a funnel to pick up noise and interference. However, the narrower the funnel is, the more immune the system is to picking up interference [ except when the interfering source is directly in line with the ???¡é?¡é?????¡­?¡°funnel???¡é?¡é????????.

But the problem here [ in e.g an indoor environment ] is that you may need to have more coverage than the single semi-directional antenna can provide, which means more AP???¡é?¡é?????¡é???¡és etc. This is where the planning phase comes in, with compromises being made and balancing cost, coverage etc.

The same thing can happen with a flashlight like the Maglite. This device has a bulb which produces a fixed amount of light. When you spread out the beam and point it towards someone???¡é?¡é?????¡é???¡és face, they might blink a little because the light PFD is fairly small [ lumens per square meter ]. However if you play with the focus and narrow that beam way down and then shine it, that could actually hurt someone???¡é?¡é?????¡é???¡és eyes, because the light PFD is so high.

Imagine a dark room with a lot of people in it. You could shine the narrow beam on each one by mechanically rotating the beam.

The Ruckus system basically does this electronically by pumping all the [ legal now !! ] power into a narrow beam directly at each client in turn. It???¡é?¡é?????¡é???¡és like having undivided attention to each person in turn. High values of PFD will be achieved. Ruckus have claimed antenna gain increases of up to 9dB and I can see no reason to dispute this.

The ground work for this came from NASA. Satellites use many different types of beams: global [ covering about one third of the earth as viewed from the satellite, hemi-beams covering say the Americas and zonal beams covering say the Eastern seaboard ]. One other type of beam is called a spot beam and is a very narrow focused beam. Covering say Florida.
http://www.iabg.de/infokom/teleport/images/intelsat-905-3355-1.jpg
http://www.satsig.net/africa/linksat/intelsat-905-east-hemi-beam.gif
http://www.satsig.net/skyway/is601-west-hemi-and-zone.jpg
http://www.frosat.net/images/sat/beam/3592/1002-359S1.jpg




You trade off coverage [ global gives more than spot ] with PFD [ higher PFD and hence smaller antenna or higher throughput than global with same antenna ]. The problem was how to change the spot beams to different locations ? In the old days, this was done via mechanically moving the satellite antenna, This is a scary thing, as motors and materials do not behave as on earth [ there is no gravity, so lubricants do not adhere to the surfaces well ???¡é?¡é?????¡é?€?? metal on metal in space can can actually cause the surfaces to fuse together ]. You could end up with a fused motor causing a spot beam to end up pointing in the middle of the ocean. Later phased array systems allowed beams to move without mechanically moving the antenna. NASA developed the ACTS satellite which ???¡é?¡é?????¡­?¡°scanned???¡é?¡é???????? using small spot beam across the United States in a raster pattern. Each station tooks turns in transmitting [ by knowing when the beam was due ???¡é?¡é?????¡­?¡°overhead???¡é?¡é???????? ]. By narrowing down the beamwidth, you can increase the PFD and reduce the antenna size [ for a satellite system ]. An experimental wrist watch satellite communications unit [ a la Dick Tracey ] was developed utilizing a very small spot beam.

http://acts.grc.nasa.gov/
http://www.nasa.gov/centers/glenn/images/content/83575main_fs013fig5.gif

Ruckus have really hit the mark by adapting this system for use in Wi-Fi. It is very clever and kudos to the engineers for working out the many complex issues in getting it to work.

Dave

Dave,

Thanks for the great write up and the great question you posted today during the webinar. Your mastery of RF is a true asset to the Wi-Fi and CWNP community. I'd like to sit down with you and your favorite beverage and pick your brain. I wonder what the over/under would be in how long I could actually keep up. :)

GT

Sincerely, GT, I won't mind joining you. I'm wondering if its the recovery process that heightens your depth of insight into RF (pun intended)!...dave are you related to Professor Charles Xavier (X-Men) :D ? Are you planning on visiting Nigeria again ? Please do let me know if perhaps, maybe somehow, there's a slim possibility of such a probability ;-)
You rock!

Dave,

Very good info, I wanted to know if Ruckus have got a patent for this Adaptive array BeamForming technology. If not , is there any other vendor which uses this?

GT,
I have seen all your video's on CWNP.com, www.youtube.com/GTHillWiFi and Webinar [Ruckus Roadshow]. Very informative.
The CWNA Study Digest on GTHill.com is really good resource for ones who are taking the CWNA.
If videos were added to the GThill.com website it would be even better.

Thanks, :)

Hi Nagaraj

I think GT might be able to tell you that.

In the following, you can see some of the beam patters formed in the military systems. Usually when you see a six-sided flat object on a modern naval vessel, it is a phased-array [ beamforming ] radar. The last picture shows a massive military early warning system in Alaska.

http://defense-update.com/images_new/mf-star_scenario.jpg

http://www.globalsecurity.org/military/systems/ship/systems/images/spy-1-variants.jpg

http://www.missiledefenseadvocacy.org/data/images/radar%20pictures/cobra-dane2sm.jpg

Over-the ???¡é?¡é?????¡é?€??horizon radar uses an interesting RF propagation phenomenon:

http://en.wikipedia.org/wiki/Over-the-horizon_radar

Regular radar systems [ many working in the Wi-Fi range !! ???¡é?¡é?????¡é?€?? one of the reasons parts of 802.11h were ???¡é?¡é?????¡­?¡°developed???¡é?¡é???????? DFS, TPC etc ] are pretty much line-of-sight.

Dave

Nagaraj,

Thank you for the kind words. There will be videos available on my website within the next 30 days if all goes well.

Ruckus has indeed patented their antenna array along with quite a few other innovative patents. If to go to www.uspto.gov and search for Ruckus or Ruckus Wireless, you will find quite a few.

It cost me a few dollars, but I downloaded all of Ruckus's patents so I could try to better understand their technology. It is very complicated to read, but still some information can be had from reading the patents.

I'll be sending a newsletter out to all that are registered at GTHill.com with some exciting announcements. Stay tuned!

GT

Thanks Dave,GT

Looking forward for a well framed whitepaper on RF by Dave and more updates on GTHill.com :D

If Dave writes the paper, I'll post it on www.gthill.com and send him a cool GTHill Polo or something. :)

GT

A quick introduction. I have been a working RF/electronicis technician since 1969. I am studying the CWNP materials to possibly start a second career.

Ron Schmitt's book [quote]Electromagnetics Explained[/quote] is an excellent general book for a deeper intuitive understanding of RF. I do not recommend it for the beginner, but for GTHill and other CWNE's it may fill a desire to learn more. It should never become obsolete.

Jerry Hubbard

Dave, just saw this--outstanding review and commentary! However, I did not see the link to the video--can you repost? I did not see it listed on Ruckus site or YouTube.

Also, I think we still have a pending lunch next time you are over St. Pete way (I might beat GT to the invitation). I too would like to pick your brain on this and other RF topics (maybe my amateur radio/engineering background can keep up....)