Smart antennas should improve spectral efficiency

The last newsletter introduced the concept of Multiple Input Multiple Output, or MIMO, smart antenna technology. Through the use of multiple transmit and receive antennas, MIMO allows an access point to grab multiple different radio-frequency streams and choose the best one for better performance on a given communications path.

In addition, MIMO uses the additional paths to carry more information, resulting in stronger coverage overall.

MIMO also generally supports beam forming – the ability to direct an RF transmission to its destination rather than broadcasting it everywhere. It does this by choosing the best base antenna and output power on the transmitting antenna for forwarding packets to a particular client.

By carefully directing a transmission, MIMO’s beam-forming capability should make it more difficult for someone to snoop on a conversation.

There are a number of vendors at work on MIMO, which is aimed at increasing spectral efficiency, and MIMO technology is being developed for the 2.4 GHz and 5 GHz WLAN bands. Last time, I mentioned MIMO-enhanced 802.11a/b/g access points from Airespace, due out in the third quarter. In addition, Airgo Networks makes MIMO chip sets, and Intel, Atheros and Broadcom are either investigating or building MIMO chips.

Other non-MIMO smart antenna technologies are also in production by companies such as Vivato Networks and Motia.

Because smart antenna technology such as MIMO is said to bring “RF switching” to access points, one question you might wish to ask WLAN switch vendors using the technology is whether you still need, well, their wireless switches. Likely, you will hear that, yes, of course, you need them for centralized security, RF management and so forth.

This likely is true, but be sure to press your vendor on the specifics of why, if the spectral efficiency becomes so strong that the APs, in effect, become switches themselves, you still require this capability in yet another device.