MIMO (say: my-moh)

July 19th, 2018

No, MIMO is NOT the latest animated Disney character or fancy new bathroom sink.

In the case of WiFi 802.11n, MIMO is an acronym for ‘multi-in/multi-out’, a new way to say there is more than one unique data stream sent over-air to increase your overall data speed.

To accomplish this, Access Points seem to be springing evermore antennas. I guess if two antennas were better than one, then, six or nine antennas must be truly awesome? In reality that extra data speed may be difficult to benefit from with any degree of reliability due to the limited improvements of receiver sensitivity, only about 1 to 2dB. Things are no better in the other direction where transmission gains are 0dB.

There are two modes to MIMO. Where you increase your bandwidth, or attempt to, with different RF signals this is known as MIMO mode B. This describes the bulk of the outdoor MIMO equipment marketed these days, including WIFI 802.11n.

When moving away from the IEEE802.11n standard, and in this case its limitations, one can experience the true joy that only MIMO mode A can provide. Unlike mode B which divides the data into different streams, mode A sends the same data on all streams on the same RF channel. The net benefit of doing this in the case of Redline’s www.rdlcom.comRDL3000 radio is 4dB improvement on the receiver and on the transmitter an even better 5dB.

For those who missed out on logarithms in grade eight, 4dB+5dB = 9dB which represents an EIGHT TIMES improvement in signal. It gets better. In the case of the RDL3000, it is intelligent enough to know when the conditions exist to seamlessly switch from mode A to mode B to take advantage of improved wireless conditions where, in its case, the benefits are realized in both directions.

WiMAX systems employ MIMO-A also. However in the drive to keep subscriber radio costs down there are no CPEs with MIMO-A on transmit. Although there is still benefit in the downlink direction, which admittedly works well for residential customers, it doesn’t fit as well into up and coming industrial applications where bandwidth demands are much more symmetrical, and often more demanding from a propagation perspective.

In summary, with broadband wireless, as with many things in life, the devil is always in the details so do your homework to make sure you’re getting the best bang for your dollar (or peso, euro, real, dinar, franc, ringgit etc.)