The necessity of null subcarrier in OFDM?

1. What is null subcarrier?
2. Why is subcarrier needed?
3. What happens if number of subcarrier is increased?
4. How does OFDM subcarrier work?

What is null subcarrier?

The null subcarrier at DC is used to allow the use of simple (again, cheaper) direct-conversion (zero-IF) RF receivers. One disadvantage of zero-IF receivers is that they typically encounter a strong interfering signal at DC.

Why is subcarrier needed?

Each subcarrier is used to carry additional information. The use of subcarriers allows the separate signals to all be received together as one transmission and then separated out by the receiver. It also allows for isolating the signals so only certain equipment receives specific channels.

What happens if number of subcarrier is increased?

8.1.

The more subcarriers are used, the longer their symbol rate is, which means that the overall rate of information remains the same, but a longer symbol rate is useful for multipath mitigation (recall conditions when equalizers are required).

How does OFDM subcarrier work?

Both OFDM and OFDMA divided a channel into subcarriers through a mathematical function known as an inverse fast Fourier transform (IFFT). The spacing of the subcarriers is orthogonal, so they will not interfere with one another despite the lack of guard bands between them.