How many antennas are enough?

Massive MIMO promises to push the envelope of Wireless Broadband further….


Consider this…You have just received a link to the latest HD video on unusual sightings in the wild, and you race to stream the video to your smartphone. As luck would have it, your wireless signal fades and you are not the first one to watch the unusual video! You curse the phone and the service provider but to no avail. It is the last mile that is the problem here. Your wireless signal faded unexpectedly, right when you needed it the most.

What if, you had, not one antenna on your phone, but an array of antennas, that could mitigate the well known problem of multipath fading. Massive MIMO (Multiple Input Multiple Output) addresses exactly this challenge.

MIMO is a technology used in 4G Wireless Broadband. It provides multiple communication paths between the transmitters and the receivers. This is made possible by deploying multiple antennas on the transmitting as well as receiving side. Whereas it is comparatively easier to deploy multiple antennas on the cell towers, it is much more challenging to deploy multiple antennas on the smartphones.

This is because of the limits imposed by basic physics. The multiple antennas on a device must be separated by a distance of half wavelength to avoid mutual coupling between the antennas. For example, for a carrier frequency of 1800 MHz, half wavelength distance is about 8 cm. Antenna separation of this magnitude is difficult to achieve within the form factor of a smartphone.

Welcome Millimeter Wave carrier frequencies! If we push up the carrier frequency to, let us say, 60 GHz, the required minimum separation between multiple antennas is pushed down to only 2.5 mm. Well, that implies that we could easily fabricate 16 antenna elements within a square of 1 cm.

In other words, with Massive MIMO, we have the ability to squeeze an array of 16 antennas or more, within the form factor of a smartphone. Infact, the next generation Wireless Broadband standard called WiGig (IEEE 802.11ad) aims to achieve a robust data rate of upto 7 Gbps by using 60 GHz unlicensed carrier and Massive MIMO techniques.

Isn’t it great to dream of freedom from multipath fades?
What do you think?

Places to go from here:

Wireless Gigabit Alliance


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