What's 5G Vol.5. Let us explain about the features of 5G millimeter wave
5G bands, especially millimeter waves, are difficult to handle. The higher the wavelength of electromagnetic waves,
the shorter the wavelength and the greater the straightness.
The microwave and millimeter wave bands are used for radar because straightness is convenient for capturing reflected waves.
On the other hand, it has the disadvantage that even if the wavelength is short and it propagates the same distance, the wave number is large
and it is attenuated and does not propagate to a far place.
The reason why the radar antenna of the weather and air traffic control tower is large is to catch weak reflected waves.
5G / millimeter-wave communication that uses such a band brings about a different situation than before.
First of all, since it does not propagate to a far place, it is difficult for one base station to cover a radius of several hundred meters to
several kilometers as before. Inevitably, the number of base stations should be increased and the base stations should be installed closer to the users.
According to my estimation, in order to develop the same service as the current one in millimeter waves,
100 to 1,000 times as many base stations as the current one will be required.
It is estimated that the number of base stations in the future will be 10 times that of the population, so many base stations will be needed.
However, there is no place where a large number of tower-type base stations can be installed as it is now,
so we expect small and inexpensive small cells to enter our lives. Also, if there are base stations around us,
it is not correct to say that communication is possible. In the case of millimeter waves, the straightness is high and the wraparound (diffraction)
of electromagnetic waves is weak, so the shadow of radio waves is formed. In other words,
communication is not possible in places where the antenna cannot be seen (NLOS: Non Line Of Sight).
The base station must be visible to all users. The surest thing is to place a base station (small cell) on the ceiling of each room in the building.
However, the coverage area does not expand in buildings with low ceilings. Since the terminal (smartphone, etc.) is used at the height of the line of sight
(0.8m to 1.5m), the height to the ceiling is 0.7 to 2.2m. Then, it is easy to think that a wide area can be covered by
"pouring" radio waves from a tall building (for example, Sky Tree) like a shower,
but millimeter waves that do not propagate to a far place will be attenuated by the height difference and the radio waves will be weakened.
At the same time, there are many shadows. After all, it is most reliable to place a base station (small cell) close to the user.
In addition, short wavelength millimeter waves are disturbed by everything. Rain and snow, water droplets and ice on the antenna cover,
and even the hands and fingers holding the terminal (smartphone) can be obstacles. Please refer to the separate section(
Let us explain about the characteristics of electro-magnetic wave of millimeter band from the technical viewpoint
of this column for the reason.
There are many challenges to the spread of 5G. So what are the uses to drive local 5G demand?
The biggest merit of using a mobile network is that you can get information from all over the world with a terminal (smartphone) anytime and anywhere,
and you can talk with your favorite people and send emails, but If you put up with it "anywhere", you can do it on your home or work PC.
In order to utilize the potential of 5G as well as local 5G, at least one of the following conditions should be met.
○ The user moves around, or the user does not stay in a specific place (office, etc.)
○ A small number of users need a large amount of data, or a large number of users use the data at the same time.
○ Real-time performance is important
○ Work in dangerous places or perform dangerous work
For example, FTTH (Fiber To The Home) is sufficient for a specific place such as an office or home, and there is no need to make a huge investment to make it wireless.
Wi-Fi can also be one of the solutions if real-time performance is not required.