Silex Unwired

Missions for Wireless LAN (3)

Posted by Y. S. on April 26, 2012

To Be Faster – 3:  Using Millimeter Wave

Since laws hinder the use of the 2.4GHz and 5GHz bands, we may come up with the idea to use a totally different frequency.  It is a 60GHz band and is called Millimeter Wave.  Consecutive bands more than 10GHz have been made available on an unlicensed basis in some countries.  The IEEE802.11ad standard has been now researched and developed as the Wireless LAN in the 60GHz band.  An organization called WiGig is also promoting to standardize this frequency band at the same time.

The millimeter wave can get a broad range of band and is less affected by interference.  The millimeter wave is attenuated because of a resonance of the oxygen molecule, so it shortens the communication distance in the air and doesn't go through objects including walls and glass windows.  The millimeter wave has a directional characteristic like a laser beam (see note below). The radio wave hardly ever goes to the direction except the antenna's radiation patterns.  In regard to the radio wave in 2.4GHz that freely goes to neighborhoods within a few meters radius, there is no chance for the radio wave in 60GHz to go through the next room separated by a couple inches of a wall.  It means that the radio rarely causes interference and is hardly ever tapped.

(Note) The millimeter wave technology has been developed for military operations, such as for missile guidance, because of its sharp directional characteristic.

on the other hand, the strong directional characteristic can be an obstacle when it is used as Wireless LAN.  If the angle of antenna placement is moved a little bit, it may cause a communication error.  Even for the fixed devices, it is difficult to use the millimeter wave. Furthermore, if the antennas try to send the millimeter wave to many devices, antennas have to move side to side and up and down to lock on to a target. How can we solve this problem?  I can tell you that there is a technology to do it.  It is named phased array antennas.  The phased array antennas control a directional characteristic by electrically adjusting antenna phases with many small antennas placed on a flat surface (see note below). The operation using this structure is called "Beam Steering".

(Note) It used to be a military technology. Some people may know it as "hexagonal boards placed on the bridge of the Aegis".

SiBeam in the U.S. took the initiative of Beam Steering with array antennas. It is used for WiHD (Wireless HDMI) specifications in the 60GHz band.  However, it still needs a larger area to be installed, and hasn't been suitable for a smaller portable devices.

Summary

The millimeter wave technology has a new chance for high-speed wireless communication. It will be able to exceed the speed of 1Gbps . But it uses extremely high frequency as compared to existing Wireless LAN, so it needs some breakthroughs including Beam Steering to be put into practical use. The first generation products with WiHD have come out to the market.  It still needs more time to become popular and small enough for terminals.

Through my first article, I have introduced trends of Wireless LAN technology to get faster and their pros and cons. You understand there are no right solutions compatible for many applications.  It is hard to predict which technology will lead the market.  All of them may be used depending on applications or market demands. A totally new technology could enter the field and solve all issues. Nobody knows yet, but I personally think this is an interesting topic.

There are other high speed technologies including the Shannon theory and UWB.  But I would like to move on and introduce the "near future of Wireless LAN".

Tags: Qualcomm Atheros, AR6003, Wireless Module, Wi-Fi, Silex