When the channel matrix is sparse, why will we use massive MIMO?
It's used for beamforming purposes. We'll be able to build a directional beam toward the users/receivers via massive MIMO. On the other hand, we'll be able to use the spatial multiplexing property to enable simultaneous data streams from BSs or APs (access points) to numerous receivers. Let me offer you a simple example. Assume that the BS has 16 MIMO antennas and that four users want to connect to it. Now, to enable proper beamforming (on the BS side), we can use each of the four antenna elements to construct a beam that is supposed to be targeted at a specific user. Then we may utilize three more beams in the same way to link the rest three users. This is a case of spatial multiplexing in action. Obviously, need to deploy a precoding method to cancel interferences between different simultaneous paths.
Why are we going to use mm-Wave even if it experiences a high path loss?
The main reason for choosing mm-Wave is because of its huge bandwidth capacity. In electronics, communication bandwidth is measured by a range of frequencies within a band. Here, one thing is clear: we can't increase the range of frequencies beyond transmitting or operating frequencies. For example, a 10% bandwidth at 100 KHz is only 10 KHz while a 10% bandwidth of 1 GHz is 100 MHz. Hope you got the point.
Because the coverage area of 5G is less than that of 4G, we'll be placing billions of APs (access points) everywhere, such as on the tops of street poles or on buildings. So, how can 5G maintain its ultra-low latency when there are a large number of APs and APs are connected to BSs? I hope you understood the question. Because there are many APs, the link speed may be reduced owing to a lot of processing before reaching the core network, and the same is true for the reverse connection path.
For 5G communication, many countries are still using the sub-6 GHz spectrum. As a result, the latency will always be lower than that of the current 4G technology. However, the aforementioned issue may arise when we use the millimeter wave band for 5G connectivity. In those cases, however, APs can be connected to BSs via fiber wires. It will have the ability to behave as a simple bridge.
Backhaul, on the other hand, can be used in the future to connect BSs to BSs. Because the millimeter wave spectrum has such a great potential for a high data transfer rate, it has a lot of potentials. Backhauls may be positioned at high altitudes. As a result, they will communicate with one another in the manner of free space communication. There will be no obstacle between the two backhauls.
