Orthogonal frequency division multiplexing (OFDM) has been adopted in 4th generation (4G) networks. With an appropriate cyclic prefix (CP) OFDM is able to combat the delay spread of wireless channels with simple detection methods, which makes it a popular solution for current broadband transmission.
However traditional OFDM is unable to meet many new demands required for 5G networks.
To address the new challenges in 5G networks, various types of modulation have been proposed as shown below.
In the classification above not only Orthogonal and Non-Orthogonal Multiplex schemes schemes are shown but also different schemes are classified according to their basic principles.
Comparisons of Non-Orthogonal multiple access (NOMA) schemes
In the table above, several typical Non-Orthogonal multiple access (NOMA) schemes based on various multiplexing techniques is shown. With different multiplexing techniques, the features of these NOMA schemes are different as shown below.
The key techniques and features of the above mentioned Non-Orthogonal Multiple Access Schemes are Summarized above.
For more details take a look at the reference below.
Y. Cai, Z. Qin, F. Cui, G. Y. Li and J. A. McCann, "Modulation and Multiple Access for 5G Networks," in IEEE Communications Surveys & Tutorials, vol. 20, no. 1, pp. 629-646, Firstquarter 2018.