From the course: 5G Architecture, Design, Protocols, Evolution, and Deployment

5G resource grid

From the course: 5G Architecture, Design, Protocols, Evolution, and Deployment

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5G resource grid

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(bright music) - [Instructor] Let's visualize the allocation of resources in time and frequency domain with an example here. So the resource block is the basic unit of frequency allocation. It always consists of 12 consecutive subcarriers in the frequency domain. For example, at 15 kilohertz subcarrier spacing, one resource block occupies 180 kilohertz. And we have a time domain where we have a 10 millisecond, where we have one complete radio frame. So one radio frame here in this case, if you are just converting into a slot of 0.5 millisecond, in that case we have certain OFDM symbols in time domain zero to six, so total seven OFDM symbols in 0.5 millisecond, total 40 OFDM symbols in one millisecond sub. On the frequency side, if you see we have certain kind of subcarriers, which is ranging from one to 12 in this case. And now we have total small boxes here. If you see, these are the resource elements. Now, within a one millisecond, if you see we have around 12 subcarriers into 40 OFDM symbols, which is 168 resource elements per slot here of one millisecond. But as we changing the slot size, we'll keep on changing the number of resource elements accordingly, but numerology has an impact here where we talked about the numerology, we have a different subcarrier spacing, which will keep on changing the resource block bandwidth and accordingly the OFDM symbol duration. So if the spacing, subcarrier spacing is 15 kilohertz, the resource block bandwidth, of course it is 12 into 15, which is 180 kilohertz. We have the OFDM symbol duration in time domain is around 66.7 microseconds. The total 14 OFDM symbols in that case would make one millisecond. Similarly, as we keep on changing the subcarrier spacing from 15 to 30, the resource block bandwidth in that case would be increasing from 180 to 360 kilohertz. But in this case, the OFDM symbol duration would be decreased accordingly. For the overall slot, the duration will come down from one millisecond to 0.5 millisecond. As we go beyond 30 kilohertz towards 60 kilohertz in numerology, in that case, the resource block bandwidth would increase to 720 kilohertz. The OFDM symbol duration will further decrease down to half of that of 30 kilohertz, and in that case, the slot duration will also decrease from 0.5 millisecond to 0.25 millisecond. Now, if you see this is the different kind of flexibility we have. Now, taking an example of the change in the subcarrier spacing and the time domain OFDM symbols in this case, if you see the duration will also change. So visualizing it with one example, say for example, there is a 15 kilohertz where the resource block in this case is narrower in frequency, but the time is one millisecond in this case. If we compare it with the higher numerology, where we have the 30 kilohertz of spacing here, if you see the frequency bandwidth, in this case, the subcarrier spacing has increased. Similarly, the time domain where the OFDM symbol size, the duration has decreased by half. So this is a kind of more flexible way of allocating the resources. If we have different use cases, we want to send the traffic quickly. We can go for maybe in that case, the subcarrier spacing of 30 kilohertz because that can be sent in 0.5 millisecond. Whereas on the other side, if we have just to broadband services, we can use subcarrier spacing of 15 kilohertz. So we have that kind of flexibility in 5G with the introduction of numerology. So here the source blocks always consists of 12 subcarriers. Numerology changes the subcarrier spacing and symbol duration. Increase in subcarrier spacing reduces the symbol and slot duration, which enables faster data transmission. And this dynamic adaptation is one key feature that makes 5G more flexible than previous generations.

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