Ruckus And On-Antenna Phased Arrays

Fortunately, an omnidirectional antenna is not the only way to obtain 360 degrees of wireless coverage. If you had enough directional antennas with overlapping cones of coverage, you could effectively cover 360 degrees. But the beauty of this sort of setup is that you don’t have to run all of those antennas all of the time. Once you get a fix on the direction of the client, you simply have to determine which set of antennas (two or more) will create an optimal beam to the desired point.

Keep in mind that this isn’t always a straight line. The client could be around a corner, and the better signal might be had by bouncing the stream off of a couple of walls rather than trying to punch straight through the obstructions. Or conditions may change. Doors can open and close. People move around. Someone might turn on a microwave oven and spew interference all over the spectrum. All of these things can alter signal paths and hamper traffic.

Traditionally, the only way an access point had to deal with dropped packets or CRC errors (corruption) was to drop transmit speeds. The PHY rate might ratchet down from 54 Mbps to 48, then 36, and so on until the client started acknowledging packet receipts. The slower the speed, though, the longer the radio stays on for a given data burst, and the longer the radio is on, the more susceptible it is to interference. So when conditions turn bad, you can get into this negative feedback loop that just slaughters performance. An intelligent antenna system will both dynamically change the beam orientation to a more optimal direction as well as forestall reducing the PHY rate until absolutely necessary.

Communication between the AP and client helps with these improvements, but it’s not strictly essential. The bulk of optimization gets done by the access point. In the tests that follow, we did not use a Ruckus client adapter for two reasons. First, Ruckus told us that 75% of the performance improvement seen above standard 802.11n comes from the access point, so adding in a proprietary client would only yield a small benefit. Second, relatively few real-life scenarios can dictate the client. It’s not like you can say, “Feel free to use my wireless LAN, but just make sure you use an XYZ adapter.”

Ruckus uses “on-antenna” beamforming, a technology developed and patented by Ruckus under the brand name “BeamFlex.” Essentially, BeamFlex uses an array of antennas and analyzes every packet to assess signal performance. Depending on the configuration, a BeamFlex access point can configure into any of thousands of possible antenna signal combinations. The access point monitors connections in real-time and modifies beams on the fly to fit dynamic conditions. Keeping with the MRC legacy, antennas that need signal boosting get boosted while those that don’t are attenuated. This results in up to a 10 dB signal gain along the target beam as well as a -17 dB interference rejection in the direction of backlobes.