Conventional communication has seen a paradigm shift right from a simple circular-dialled and wired phone to a recent handy, stylish cell phone with 4G and 5G connectivity. What is this shift? Well, we do not try to understand history. But we will try to know the recent technology, using simple puzzles and short stories. And as usual, we will connect all the dots at the end of this blog.
1. Imagine that there is a huge storm and wind is blowing like crazy. You are out on the road and you are standing very near a tall building; versus, you are standing on the road which is plain (like a highway). Where, do you think, you will be hit more by the storm?
2. Imagine that you are lost in a forest and you are trying desperately to find the way out. There are your 50-odd friends and relatives who are also out to find you. None of you have electronic communication equipment. Will it be easy for you to track them by giving our loud calls to help them reach you? Or it would be easier for all those 50 people to make a chaos and try to find you?
3. Imagine that in the same storm mentioned above, there are pieces of small paper chits and loads of tin sheets, both subjected to blowing winds. Which of these would be able to scatter faster to larger distances?
The answers to all these puzzle questions are simple. You would be hit more by the storm if you are standing on the highway road. You would be able to find the way out if “You” call out. Smaller pieces would be able to go in any nook-and-corner of the surroundings, as compared to the larger tin sheets.
These intuitive answers were quite non-intuitive in conventional communication electronics, unless someone started thinking out-of-the-box.
Conventionally, we have antenna in the cellular networks which take care of limited number of subscribers in their own region. Normally there are lesser antennas and more subscribers in a given region and the signals flow in all directions and try to catch your phone and offer connectivity. They face problems to reach people behind huge buildings and behind small hills. They travel with limited range, trying to manage the concept of cellular networks. In handling connectivity, they give rise to complicated antenna structures, higher bandwidths and more repeaters in between. Expensive components are required to handle these systems.
Welcome to 4G and 5G Technology and welcome to Massive MIMO / Adaptive Beam forming / SDMA technology. In this, small, cheap, low-power antenna units are used in array forms. Imagine a stack of 8 such structures arranged vertically. They all send out signals with a small delay (phase difference) with-respect-to each other. The idea is to use very small packet of information (like those tiny pieces of paper) and transmit it in air. They would reach the receiver, rather quickly, and a beam formation will happen, (like a constructive interference) to make the beam more focused at the receiver cellphone. The signal will hit the person on the highway much faster and with higher impact (just as the person hit by a storm on the highway). However, if the user is standing behind a building, even though the small bits will make the signal reach to his cellphone, the signal may be weak (just the way in which he will be less-hit by the storm). In that case, instead to one vertical array of antenna, researchers and technologists have devised an array of antennas like 64 elements with 64 trans-receivers, which create a 3-Dimensional beam of signal, which will be able to reach every nook-and-corner of the space around, including the place behind tall buildings. Hence the signal reaches everywhere; which is the beauty of new M-MIMO (Massive – Multiple input multiple output) technology.
Let us say that you enter a new network, say because your travel from one city to another. How would you be recognised? Conventionally, the antenna in that cellular region will trace you by sending signals which are called as “pilot” signals. But in the MIMO technology, your phone will send pilot signal and get identified in the network (just like the person lost in the forest). The technology is just reverse.
This is just opposite to the earlier approach towards communication technology. Earlier complicated electronic equipments, especially trans-receivers were used for far-reaching signals. Now cheaper, low-power electronic components are used in array form to get more directed energy using 3D beam formation technology. Smaller regions in space are used (through higher frequency) and polarization and time-delay techniques are used for better and stronger coverage.
Sprint Massive MIMO and Erricson are good examples of companies implementing 5G and above, using the frequency in the range of 24.5 GHz to 52.6 GHz, bipolar antenna arrays with base stations kept about 100 m apart in urban setups. Cisco estimates that by end of 2020 – as 5G rolls out to a mainstream audience – there will be 5.5 billion mobile users around the world, each consuming 20GB of data per month.
Following points are interesting in this new technology:
1. Number of antennas are much higher than number of users!
2. The technology uses cheaper and low-power antennas as compared to earlier ones.
3. Your cell phone sends signal to get introduced in the network (and not vice-versa), which is opposite to roaming technology earlier.
4. Space division is achieved using beam formation, which is an excellent solution after consuming Time-Division and Frequency-Division.
Where there is a will, there is a way..!! And nature does this all the time..!! Simplest example is photosynthesis using small leaves which work as solar cells. They are much cheaper, easily replaceable and are in abundance. Our antennas are doing the same..!!
We have tried to mimic nature… but we had to go through a large energy-intensive cycle of communication evolution before we “realized” how nature does it, just naturally..!!