Now that we have had a good understanding of what 5G millimeter wave is, let's turn our attention to another fundamental technique that we earlier learned that would provide significant benefits to 5G performance, and that is Massive MIMO. Although we have seen some of the initial fundamentals of Massive MIMO in Module 3, let's now try to take a deeper look. We'll learn about what Massive MIMO is, and what are some of its immediate benefits. We will first look at the conceptual angle of those benefits. Then as always, we'll try to give you some practical examples of what kind of benefits we can expect from realistic 5G deployments that can carefully leverage Massive MIMO. As we already know, Massive MIMO is MIMO that is deployed on a massive scale. That makes it an integral part of both 5G millimeter wave as well as Sub-6 deployments, although two slightly different degrees. Massive MIMO, also known as M-MIMO, in short-time, has essentially two sides of the same point in that there are certain prerequisites to Massive MIMO. If you deploy and implement those correctly, you'll get to reap certain enormous benefits of Massive MIMO. Let's first look at the prerequisites. Prerequisites, if you read the name carefully, Massive MIMO, may be somewhat understandable to you. That is, an antenna array is a fundamental prerequisite, and Massive MIMO, because it entails many more antenna, would require a panel with many individual antenna elements. That panel of multiple antenna elements, or simply called antennas, is quite an antenna array. Now, for 5G, Sub-6, or millimeter wave, each of those individual antennas is very small and that is because something we have seen earlier. The physical size of the antenna is roughly inversely proportional to the frequency of operation. High frequency of 5G operation makes those antennas smaller than those for legacy technologies. This is where the difference between Sub-6 and millimeter wave that I earlier alluded to also comes into picture in that because millimeter wave or frequencies of operation are significantly higher than those for Sub-6. Stands to reason that 5G millimeter wave antennas will be substantially smaller than the antennas that would be needed for 5G Sub-6. To summarize, an antenna array is a rectangular panel in most cases that fits many more antennas. For Sub-6, it might be on the order of, let's say, 10, 30, or 60 antennas, whereas, for millimeter wave, it could be easily on the order of 100, 250, or 500 antennas.