- 6.1 Introduction
- 6.2 Basic Principles and Features of Non-orthogonal Multi-user Access
- 6.3 Downlink Non-orthogonal Multi-user Transmission
- 6.4 Uplink Non-orthogonal Multi-user Access
- 6.5 Summary and Future Work
Multiple access technologies have been a key way to distinguish different wireless systems from the first generation (1G) to the current fourth generation (4G). For example, frequency division multiple access (FDMA) is used for 1G, time division multiple access (TDMA) mostly for 2G, code division multiple access (CDMA) for 3G, and orthogonal frequency division multiple access (OFDMA) for 4G. Most of these are orthogonal multiple-access (OMA) schemes, especially for the downlink transmission; in other words different users are allocated with orthogonal resources, either in time, frequency or code domain, in order to alleviate cross-user interference. In this way, multiplexing gain is achieved with reasonable complexity.
The fast growth of mobile Internet has propelled the 1000-fold data-traffic increase that is expected for 2020. Spectral efficiency therefore becomes one of the key challenges ...