BY Chris DeMartino | Sep 05, 2017

Multiple-input, multiple-output (MIMO) technology is currently receiving a great deal of attention. Specifically, massive MIMO is something that is often discussed with regard to 5G communications, and is the subject of Keysight Technologies’ new white paper, “Massive MIMO: Answering Some Common Questions.”

The white paper provides a brief history of MIMO technology, explaining how its roots can be traced back many years. Several people involved with the technology’s early work are mentioned. Moreover, MIMO technology has been associated with the IEEE 802.11 wireless-local-area-networking (WLAN) standard since IEEE 802.11n, as well as cellular mobile radio since 2007.

After explaining what MIMO technology is, the author describes three different use cases. For one, MIMO technology allows for the use of more than one path to decrease the error rate of a single set of data. It can also allow for the use of more than one path for different sets of data. Lastly, MIMO technology can manipulate the inherent nature of multipath interference to either cancel or augment the signal at any physical location in the radio channel.

Several MIMO terms are then defined. The first one is single-user MIMO (SU-MIMO), which involves using multiple radio paths to improve communications with a single user. The other terms defined are multi-user MIMO (MU-MIMO), full-dimension MIMO (FD-MIMO), and the aforementioned massive MIMO.

The white paper then answers some oft-asked questions concerning MIMO technology. The first question is simply whether or not MIMO is the same as beamforming. The author states they are not the same, proven in part by the fact that beamforming is utilized in many non-MIMO applications. Another question is with regard to just how many antennas are associated with massive MIMO. The white paper also discusses the feasibility of massive MIMO based on frequency-division-duplex (FDD) communications. The last question concerns whether or not massive MIMO is only usable at millimeter-wave frequencies.