Radio-Frequency Front-End Impairments: Performance Degradation in Nonorthogonal Multiple Access Communication Systems

The explosive growth of connected devices poses key challenges on the effective design and deployment of future wireless systems and networks. Nonorthogonal multiple access (NOMA) has been recently proposed as a viable solution to such related challenges because it has been shown to be capable of enabling increased spectral efficiency, massive connectivity, and low latency. NOMA allows multiple users to share the same frequency bands and time slots through power-domain or code-domain multiplexing, while successive interference cancelation (SIC) eliminates the resulting multiuser interference. However, transceiver architectures inevitably suffer from radio-frequency (RF) front-end-associated impairments, such as in-phase (I)/quadrature-phase (Q) imbalances, dc offsets, and power amplifier (PA) nonlinearities. This article addresses the main RF impairments that degrade the performance of communication systems in the context of NOMA-based communication scenarios. In addition, it provides useful insights into the potential opportunities and challenges that are envisioned to enable efficient design and implementation of NOMA in future wireless networks. Extensive computer simulations assuming such impairments reveal that NOMA communication systems experience significant performance degradation compared to conventional orthogonal multiple access (OMA) schemes. Furthermore, the different users in NOMA inevitably experience different levels of degradation, which highlights the importance for accurate modeling and dynamic compensation of the incurred impairments to ensure successful deployment of NOMA in critical applications, such as vehicle-to-vehicle communications.