On the performance of non-orthogonal multiple access considering backward compatibility

This paper evaluates the performance of a non-orthogonal multiple access (NOMA) system considering backward compatibility issue. This issue is considered by assuming that backward/legacy devices are incapable to perform successive interference cancellation (SIC), which is the baseline for NOMA systems. In a normal NOMA two-user pair between a cell center user (CCU) and a cell edge user (CEU), the CCU needs to perform SIC for data recovery, whereas the CEU does not need to perform SIC. Considering this, for the cell edge legacy devices, they can get paired in the conventional NOMA user pairing fashion, as they do not need to perform SIC being CEUs. But for the cell center legacy devices, they cannot get paired, as they are unable to perform SIC. In these scenarios, we evaluate the performance of a NOMA system, and investigate user pairing strategies to improve the system performance. Detailed mathematical analysis is provided to investigate the sum capacity of the NOMA system, followed by validation using simulations. It is shown through results that performance of the NOMA system in the presence of legacy devices can be improved through efficient user pairing strategies.