Next up is advanced channel coding. This may also be unfamiliar to many of you, so let me take a minute to explain technically what that is. In module 1, we saw that there are several impediments that a wireless signal faces, for example, pathloss, noise, interference. A principle effect of those impediments is that they change the nature of the wireless signal so that by the time the signal reaches the receiver, it looks slightly or sometimes substantially different from the intended wireless signal sent by the transmitter and at such, it becomes somewhat or significantly difficult for the receiver to decode that wireless signal and demodulate or extract the intended data from the carrier wave. Is there a way to limit the effect of such impediments on the outgoing wireless signal? Indeed there is. That protection mechanism, so to speak, is called channel coding, or in communication parlance, it is also known as error control coding or forward error correction code just so you know. Channel coding at a high level is about taking your intended data that the transmitter has in mind and wrapping it up, so to speak, in additional metadata. That way, even if some of that data gets corrupted because of noise interference and pathloss, by looking at the metadata and the original data together, the receiver can make some educated guess about what the original data might have been. If the channel coding algorithms are designed and implemented correctly, it is possible that in most cases the receivers educated guess will be correct and the receiver will be able to decode and demodulate the data even in presence of noise and interference. As always, there is an easier way to understand this. Imagine that you have a precious glass, an ancient artifact that you have to send from one point to another. At the simplest end, what you can do is just put that glass in a box and send that box across. If the postal carrier handles that box carefully, sure the glass will safely reach your destination. But what if and the postal carrier happens to drop that box by mistake, or what if the road on the way is bumpy so that the artifact gets damaged a little? To avoid that, what you would naturally do is that you would probably wrap that glass in bubble wrap. You would pack it with packing foam, then fit that neatly in a tight box. Maybe write a note on that box saying fragile, handle with care. That way you're postal carrier will precisely know that this box needs to be handled very carefully. Even for example, the road is bumpy and the box happens to shake a little bit, your glass will be very protected because it is surrounded by bubble wrap and packing foam. Just like packing foam and bubble wrap help your precious glass artifact reach one point from another, even in presence of bumpy roads, etc, such channel coding metadata helps your intended transmission reach the other end even in presence of impediments such as pathloss, noise, and interference. A significant effect of channel coding is that it improves efficiency of communication overall. Imagine this. Let's say that a transmitter sends a certain piece of data to the receiver without any channel coding. Let's say that there are errors in transmission and because the receiver may not be able to correctly decode that data, the transmitter would have to retransmit the same data or transmit it again. If the second transmission once again encounters errors, the transmitter will have to send it a third time, and it would have to keep repeating it until the receiver correctly receives the data, and this without any channel coding or metadata. Because there was no protection to the data, the data had to be sent multiple times. But if you added sufficient protection to the data, it is possible that the data with that perfection can reach the other end in one or maybe two tries. Because you had to make maybe just one or two tries instead of 5, 6 or even more tries without coding, you can see that you have made your communication more efficient. You are able to send your intended data to the other end in fewer tries and that is what makes your communication more efficient. This is how channel coding improves overall efficiency of your communication system. Coming back to our regular transportation analogies, what is one straightforward way to understand the effects of channel coding? Well, it is in terms of two cars, one of which has a modern, efficient and well-maintained engine, whereas the other car has a slightly older or not so well maintained and hence inefficient engine. Goes without saying that the car with efficient engine will be able to travel faster and farther as the top car does, while at the same time potentially consuming fewer energy or fuel resources. Because the top car had an advanced, more efficient engine, it was able to go faster and farther and more efficiently, whereas the lower car lagged on all three counts. That is the effective practical difference between a system with and without channel coding, so to speak. The effect of channel coding or advanced channel coding in 5G is that it allows efficient delivery of significantly high data rates such as multiple Gbps. Keep in mind, the car not only was faster, but it could also go farther, and that is the equivalent of multi-Gbps data rates that 5G systems will be able to achieve on account of the efficiency imparted by the channel coding mechanisms.
