The orthogonal frequency division multiplexing (OFDM) and the non-orthogonal multiple access (NOMA) scheme are presented as promising techniques to meet the requirement of fifth-generation (5G) communication systems. Although much attention has recently been devoted to study these techniques, some scenarios have still been less explored. Considering that a fundamental part of any communication system is the use of power amplifiers, this paper presents an analytical evaluation of the bit error rate (BER) of NOMA-OFDM systems in the presence of a high power amplifier (HPA) with memory. Considering that the non-linear distortions generated by the HPA can be modeled using a polynomial model with memory, new theoretical expressions are developed to obtain the BER of the system. Specifically, exact BER expressions for a downlink NOMA-OFDM system with two users are presented and verified by Monte Carlo simulation results. The obtained numerical results demonstrate that the performance degradation of both users is highly dependent on the non-linear distortions, even when the successive interference cancellation (SIC) technique is performed perfectly.INDEX TERMS 5G, bit error rate, high power amplifier, non-linearity, non-orthogonal multiple access, orthogonal frequency division multiplexing.
The fifth generation (5G) of mobile communications systems plans to support different types of applications, where each of these applications may have different requirements. For this reason, the main characteristic of 5G mobile communications systems is the flexibility of their architecture. An interesting proposal that can meet the requirements of these applications is the multi-carrier waveform Generalized Frequency Division Multiplexing (GFDM). However, due to its multi-carrier nature, this new waveform is highly sensitive to non-linear distortions arising mainly from high-power amplifiers (HPA). In addition, the wideband characteristics of multi-carrier signals result in frequency-dependent distortions, typically know as memory effects. This paper presents the development of closed-form analytical expressions that could be used to evaluate the impact of the distortions induced by non-linearities with memory in the outof-band emissions and the bit error rate performance of GFDM-based systems. The resulting analytical expressions are general enough to obtain numerical results for different parameters of the GFDM-based system.
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