Multi-Symbol Rate NOMA for Improving Connectivity in 6G Communications Networks

In non-orthogonal multiple access (NOMA), user pairing, power allocation, and performance evaluation are typically performed assuming all users have equal symbol rates. However, such an assumption can significantly limit the design flexibility of NOMA and devalue its potential. Therefore, this article considers a generalized scenario in which the user-paring process may include users with different symbol rates. Hence, the proposed configuration is denoted multi-symbol rate NOMA (MR-NOMA). In MR-NOMA, the relationship between symbol rate and energy is exploited to add a new degree of freedom when assigning power to paired users. That is, the fact that the symbol energy is proportional to the symbol duration extends the range of power values that can be allocated to high symbol rate users while satisfying the quality-of-service requirements for all users. Consequently, the number of users served can be increased, or such a feature can be used to increase the link throughput. The results obtained for the two-user scenario show that with optimal power selection, users of high and low symbol rates can achieve lower bit error rates (BERs), which in turn increases system throughput as a result of improved transmission reliability.