New technologies in 802.11n
Published: 24 Jun 2008
Smart antennas and beamforming
We can now tackle smart antenna technology. The term smart antenna in reality is a misnomer, as all of the intelligent signal conditioning takes place before the RF signal gets to the appropriate set of antennas. Beamforming is the technology that does all the hard work. The following definition is from a University of Washington web site and is the best explanation of beamforming we've come across. The site even has interactive models to help explain the technology.
"Beamforming is a general signal processing technique used to control the directionality of the reception or transmission of a signal on a transducer array.
Using beamforming you can direct the majority of signal energy you transmit from a group of transducers (like audio speakers or radio antennae) in a chosen angular direction. Or you can calibrate your group of transducers when receiving signals such that you predominantly receive from a chosen angular direction."
Beamforming isn't new, being a key component of both radar and sonar systems for many years. Recently, telco and Wi-Fi researchers have become interested in beamforming and the ability to steer signals to where they do the most good. Ruckus Wireless is one such company and has a great deal of research expertise in beamforming. Ruckus Wireless also has been instrumental in introducing products into the Wi-Fi market that have beamforming capabilities. BeamFlex is its interpretation of beamforming, and the following description comes from one of the company's technical articles:
"Central to BeamFlex is an agile antenna system with multiple antenna elements that can be combined in real time to offer an exponential increase in diversity order. With N number of high-gain, directional antenna elements, a BeamFlex antenna array provides 2N-1 unique radiating patterns to maximize range and coverage in a home.
A Diversity Combiner composed of low cost, software-controlled circuitry allows the BeamFlex software to manage antenna combining in real time. The core of the BeamFlex software is an expert system that constantly learns the environment — the RF conditions, communicating devices, network performance and application flows.
A Path Control module selects optimum antenna combinations on a per packet basis to ensure a quality signal path to each receiving device.
The Transmission Control module sets the transmission policies including data rate and queuing strategy based on application and station knowledge. The BeamFlex software interfaces to the 802.11 MAC layer and is compatible with standard 802.11 chipsets. Residing in the host processor, it adds minimal incremental CPU load and memory utilization."
In my research on smart antenna systems and beamforming, the Ruckus Wireless approach has surfaced as a very elegant design. It has the potential to alleviate concerns about the inability of MIMO and spatial multiplexing to be reliable enough. The individual advantages are as follows:
* BleamFlex antenna arrays can rapidly present many different antenna configurations. This translates into significantly different RF signal patterns that will afford spatial multiplexing technology the best opportunity of success.
* BeamFlex antenna arrays use both horizontal and vertical polarised antenna elements, once again, to create RF signal patterns with increased diversity and ensure recognition by the 802.11n receiver using spatial multiplexing.
* BeamFlex architecture uses application-level performance parameters when making decisions on how to optimise the signal quality rather than information from the PHY and MAC layer that doesn't take into account QoS or application networking requirements.
The following diagram depicts current equipment from Ruckus Wireless, which includes all of the above-mentioned features.
I'm more interested in a symbiotic relationship between the BeamFlex antenna and 802.11n technology so as to have the best of both worlds. Ruckus is continuing work on this front as shown in the following diagram.
Final thoughts
I remain very optimistic about 802.11n being a disruptive technology that will alter everyone's perception of data networks. 802.11n's antenna diversity and spatial multiplexing are vast improvements over what's been available in previous standards. I'm just concerned that the required reliability will not be there until additional RF signal conditioning like that offered by Ruckus Wireless is used to combat environmental variables.
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- Wi-Fi: The next generation
- 802.11-ngratitude
- Ruckus mixes meshing with 802.11n
- Ten tips for preparing a Wi-Fi rollout
- Securing the wireless frontier
- The role of Wi-Fi in unified communications
- 802.11n: Morphing to meet new demands
- Colubris Wireless MultiService Controller review
- New technologies in 802.11n
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