The Client That Could Be
Ever since the days when 802.11a/g grew a second antenna, we’ve had “transmit/receive diversity,” which sends the same data stream out over multiple antennas and simply lets the access point select whichever antenna is receiving the best signal. Applied to 802.11n, transmit diversity used multiple antennas to help increase range and better deal with difficult locations. This is why 11n does a generally better job than 11a/g at eliminating dead spots.
However, 802.11n equipment got another jump in intelligence with the addition of maximal ratio combining (MRC). This technology combines multiple antenna signals in such a way that strong signals are multiplied while weak signals are attenuated. The signals you want get boosted, while those you don’t have their power cut. MRC is built into all 802.11n chips.
Now, as you might expect, the receiving end can play an important role in optimizing chip-based beamforming. With 802.11a/g, access points could listen to the client and use rudimentary MRC analysis to boost power along the best-suited beam, providing a gain of roughly 1 to 2 dB. The catch here is that the access point was doing all the work. There was no active feedback coming from the 802.11a/g clients.
With “implicit beamforming,” wherein an 802.11n AP is communicating with 802.11n clients, you can have some feedback. Rather than having the access point perform all of the signal analysis, it can query the client and see if it agrees that this or that particular beam orientation is optimal. Having this limited two-way communication yields a maximum of 3 dB additional gain, but the bad news is that there are currently no products on today’s market supporting implicit beamforming.
With “explicit beamforming,” feedback between the AP and client happens much more frequently. This way, if a client moves or an antenna gets adjusted or anything happens to alter the dynamics of the signal strengths, the system is able to adapt almost instantaneously to a new, optimized configuration. Again, having the client involved in this way can yield up to a 3 dB benefit with two radios, but there are no products available today offering this capability. Hopefully this will change.
- beamforming ,
- wifi ,
- ruckus
first post?!?!?!
No, REAL first, dipshit.
I don't think it's a problem that this is really only enterprise-class hardware. The very fact that there's an tenna sensitivity that can cripple the entire system shows that for Joe Apefist this is too much trouble for its own worth.
But, the tech shows amazing potential and given some tweaking time, I'm sure it will become more robust and more economical and will rapidly see adoption at home.
Personally I can't wait!
As a crude guide if you want 10dB gain over omnidirectional (10x the power in some direction) then you need to have 10 antenae to cover all directions. It works but with an obvious price in money and size, and a more subtle one in intereference for/from other transmitters unlucky enough to be in the chosen direction.
Personally I'd prefer multiple omni basestations and just focus on minimising distance. Inverse square law is your friend.
Personally I'd prefer multiple omni basestations and just focus on minimising distance. Inverse square law is your friend.
:-)
Yeh totally why punch through 4 walls when you can punch through 2. Plus you can site access points/ repeaters in free space away from mwave reflective objects.
Also note that much more important to enterprise wireless LANs is NOT the raw AP to single client thoughput that so many of these gearhead tests do. We are constantly faced with offering stable and usable wifi for dozens to hundreds of concurrent users in crowded areas (conference centers, auditoriums....) Like any shared medium, Wifi suffers from co-channel interference and overly RF loud clients.
One BIG advantage that you will see enterprise vendors work towards is NOT how much speed to any one client you can get, but how much Reduced interference beamforming will allow to neighboring wireless APs in the same ESS. The net result is that all users see benefit of solid and stable wireless connectivity.